TWI900587B - Electrochemically debondable adhesive composition - Google Patents

Abstract

The present invention is directed to a curable and electrochemically debondable adhesive composition comprising, based on the weight of the composition: from 40 to 99 wt.% of a) at least one ethylenically unsaturated non-ionic monomer; from 0.9 to 50 wt.% of b) at least one polymerizable ionic compound, wherein said polymerizable ionic compound comprises: b1) at least one compound in accordance with general formula IV; and / or b2) at least one compound in accordance with general formula V; and, from 0.1 to 10 wt.% of c) at least one free radical initiator.

Description

Electrochemically debondable adhesive composition

The present invention relates to a curable adhesive composition that can be debonded from a specific substrate to which it is applied. More particularly, the present invention relates to a curable and electrochemically debondable adhesive composition comprising a polymerizable electrolyte.

Adhesive bonding and polymeric coatings are commonly used in the assembly and surface treatment of manufactured products. They replace mechanical fasteners such as screws, bolts, and rivets, providing bonding with reduced machining costs and greater flexibility in the manufacturing process. Adhesive bonding evenly distributes stress, reduces fatigue, and seals joints, making them impervious to corrosive species.

While adhesive bonding offers many advantages over mechanical fasteners, disassembly of adhesive-bonded objects is often difficult in practical applications, such as recycling the bonding primary material. Mechanical adhesive removal via processes such as sandblasting or wire brushing is often excluded, in part because the adhesive is located between the substrates and is therefore inaccessible or difficult to remove without damaging the substrate surface. Debonding via the application of chemicals and/or high temperatures, as disclosed in, for example, U.S. Patent No. 4,171,240 (Wong) and U.S. Patent No. 4,729,797 (Linde et al.), can be effective but can be time-consuming and complex to perform; furthermore, the aggressive chemicals and/or harsh conditions required can damage the substrate being separated, rendering it unsuitable for subsequent applications.

With these issues in mind, some authors have sought to develop electrochemically debondable adhesive compositions, where an electric current is passed through the cured composition to break the bond at the adhesive-substrate interface.

US 2007/0269659 (Gilbert) describes an adhesive composition capable of debonding at two interfaces, the composition: (i) comprising a polymer and an electrolyte; (ii) promoting bonding of the two surfaces; and (iii) debonding from both the anode and cathode surfaces in response to application of a voltage across the two surfaces to form an anode interface and a cathode interface.

US 2008/0196828 (Gilbert) describes a hot melt adhesive composition comprising: a thermoplastic component; and an electrolyte, wherein the electrolyte provides sufficient ionic conductivity to the composition to enable a faradaic reaction at a bond formed between the composition and a conductive surface and to debond the composition from the surface.

WO2007/142600 (Stora Enso AB) describes an electrochemically weakenable adhesive composition that provides adhesive adhesion to conductive surfaces and sufficient ionically conductive properties to enable the adhesive adhesion to be weakened when a voltage is applied to the adhesive composition, wherein the composition comprises an effective amount of at least one ionic compound to impart the ionically conductive properties, and wherein the ionic compound has a melting point of no more than 120°C.

EP 3363875 A (Nitto Denko Corporation) provides an electrolytically strippable adhesive composition that forms an adhesive layer with high adhesion and is easily stripped after a short application of a voltage. The electrolytically strippable adhesive composition of the present invention comprises a polymer and 0.5 to 30 wt.% of an ionic liquid, based on the weight of the polymer, wherein the anion of the ionic liquid is a bis(fluorosulfonyl)imide anion.

WO2013/135677 (Henkel AG & Co. KgaA) describes a hot-melt adhesive comprising: 20 to 90 wt% of at least one polyamide having a molecular weight (Mw) of 10,000 to 250,000 g/mol; 1 to 25 wt% of at least one organic or inorganic salt; and 0 to 60 wt% of other additives, wherein the adhesive has a softening point of 100°C to 220°C.

WO2016/135341 (Henkel) describes a reactive hot-melt adhesive composition that at least partially loses its adhesive strength upon application of a voltage, thereby debonding substrates bonded thereto. More specifically, the reactive hot-melt adhesive composition comprises: a) at least one isocyanate-functional polyurethane polymer; and b) at least one organic or inorganic salt.

WO2017/133864 (Henkel) describes a method for reversibly bonding a first substrate and a second substrate, wherein at least the first substrate is a non-conductive substrate. The method comprises: a) coating a surface of the non-conductive substrate(s) with a conductive ink; b) applying an electrically debondable hot-melt adhesive composition to the conductive ink-coated surface of the first substrate and/or the second substrate; c) contacting the first and second substrates such that the electrically debondable hot-melt adhesive composition is interposed between the two substrates; d) forming an adhesive bond between the two substrates to provide a bonded substrate; and e) applying a voltage to the bonded substrates to substantially weaken the adhesion at at least one interface between the electrically debondable hot-melt adhesive composition and the substrate surface.

When an ionic liquid or electrolyte is included in the adhesive composition, compatibility of the electrolyte with the polymer matrix can be difficult to achieve. In the prior art, electrolyte leakage and phase separation from the curing polymer matrix have been identified as drawbacks in the application of electrically debondable adhesives.

There remains a need in the art for an adhesive composition that can be conveniently applied to the surfaces of substrates to be bonded, provides effective bonding within composite structures containing the substrates upon curing, and can be effectively debonded from the substrates by conveniently applying an electric potential across the cured adhesive. Furthermore, the cured adhesive should provide a stable polymer matrix that minimizes component leakage and prevents phase separation.

According to a first aspect of the present invention, a curable and electrochemically debondable adhesive composition is provided, comprising, based on the weight of the composition: 40 to 99 wt.%, preferably 45 to 90 wt.%, of a) at least one ethylenically unsaturated and nonionic monomer; and 0.9 to 50 wt.%, preferably 5 to 30 wt.%, of b) at least one polymerizable ionic compound, wherein the polymerizable ionic compound comprises: b1) at least one compound according to formula IV: and/or b2) at least one compound according to formula V: wherein: R ⁷ is selected from: C ₁ -C ₃₀ alkyl; C ₂ -C ₈ alkenyl; C _{1 -C 30} heteroalkyl; C ₃ -C ₃₀ cycloalkyl; C ₆ -C ₁₈ aryl; C ₁ -C ₉ heteroaryl; C _{7 -C 18} alkaryl; C _{2 -C 5} heterocycloalkyl; or -R ^a -C(=O)-R ^b , wherein R ^a is C ₁ -C ₆ alkylene and R ^b is C ₁ -C ₆ alkyl; each R ⁸ is independently selected from H, C ₁ -C ₁₈ alkyl, C ₁ -C ₁₈ heteroalkyl, C ₃ -C ₁₈ cycloalkyl, C ₆ -C ₁₈ aryl, C ₁ -C ₉ heteroaryl, C _{7 -C 18} alkaryl, or C ₂ -C R ₉ is H or C ₁ -C ₄ alkyl; each R ¹⁰ is ^{independently} selected from: C ₁ -C ₃₀ alkyl; C ₁ -C ₃₀ heteroalkyl; C _{3 -C 30} cycloalkyl; C ₆ -C ₁₈ aryl; C ₁ -C ₉ heteroaryl; C _{7 -C 18} alkaryl; C _{2 -C 5} heterocycloalkyl; or -Ra- ^C (=O) ^-Rb , wherein ^Ra is C ₁ -C ₆ alkylene and R ^b is C ₁ -C ₆ alkyl; A is a non-polymerizable anion; T is an olefinically unsaturated anion; d and m are each an integer having a value of at least 1; e and n have values such that the compound is electrically neutral; and, is a covalent bond, a C ₁ -C ₂ alkylene group, -CH ₂ OC(=O)-, -CH ₂ CH ₂ OC(=O)-, p-benzyl or p-tolyl; and 0.1 to 10 wt.%, preferably 0.1 to 5 wt.% of c) at least one free radical initiator.

The adhesive composition can be formulated as a one-component (1K), two-component (2K) or multi-component composition. A preference can be noted for part b), which consists of the compounds according to part b1) and/or part b2).

In one embodiment of the composition, part a) comprises 40 to 95 wt.%, preferably 45 to 90 wt.%, of a1) at least one (meth)acrylate monomer represented by formula I, based on the weight of the composition: H ₂ C═CGCO ₂ R ¹ (I) wherein: G is hydrogen, halogen or C ₁ -C ₄ alkyl; and R ¹ is selected from C ₁ -C ₃₀ alkyl, C ₂ -C ₃₀ heteroalkyl, C ₃ -C ₃₀ cycloalkyl, C ₂ -C ₈ heterocycloalkyl, C ₂ -C ₂₀ alkenyl and C ₂ -C ₁₂ alkynyl.

Part a) of the composition may be further characterized by comprising 0 to 30 wt.%, e.g., 0 to 15 wt.%, of a2) at least one (meth)acrylate monomer represented by formula II: H ₂ C═CQCO ₂ R ² (II) wherein: Q may be hydrogen, halogen, or C ₁ -C ₄ alkyl; and, R ² may be selected from C ₆ -C ₁₈ aryl, C ₁ -C ₉ heteroaryl, C ₇ -C ₁₈ alkylaryl, and C ₇ -C ₁₈ aralkyl.

In another embodiment of the composition, which is not intended to be mutually exclusive of those given above, part a) thereof comprises 0 to 50 wt.%, preferably 5 to 25 wt.%, of a3) at least one (meth)acrylate functional oligomer, based on the weight of the composition.

Regarding the electrolyte b) of the curable and electrochemically debondable composition, the ionic compounds according to Formulae IV and V, as defined above and described in detail below, contain functional groups reactive toward free radical polymerization, preferably vinyl, allyl, or propenyl groups. The polymerizable electrolyte should thus polymerize with any of the aforementioned monomers a).

In the case of compounds of formula IV (b1), the cations are based on the imidazolium ring and, after completion of the selected curing profile, become covalently bonded to the adhesive matrix; the counteranions (A) are free to move within the polymer matrix. In contrast, in the case of compounds of formula V (b2), the anions of the polymerizable electrolyte become covalently bonded to the adhesive matrix after curing, while the cations based on the imidazolium ring are free to move within the matrix.

Preferred compounds b1) may exist alone or in combination and include, but are not limited to: 3-vinyl-1-methyl-1H-imidazolium iodide; 3-vinyl-1-methyl-1H-imidazolium chloride; 3-vinyl-1-methyl-1H-imidazolium bromide; 3-vinyl-1-methyl-1H-imidazolium methanesulfonate; 3-vinyl-1-methyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-vinyl-1-ethyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-vinyl-1-methyl-1H-imidazolium hexafluorophosphate; 3-vinyl 1-Methyl-1H-imidazolium 4-methylbenzenesulfonate; 3-vinyl-1-methyl-1H-imidazolium tetrafluoroborate; 3-vinyl-1-ethyl-1H-imidazolium iodide; 3-vinyl-1-ethyl-1H-imidazolium bromide; 3-vinyl-1-ethyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-vinyl-1-ethyl-1H-imidazolium hexafluorophosphate; 3-vinyl-1-ethyl-1H-imidazolium tetrafluoroborate; 3-vinyl-1-(1-methylethyl)-1H-imidazolium bromide; 3-(1,1-dimethylethyl)-1-vinyl-1H-imidazolium bromide imidazolium bromide; 3-vinyl-1-propyl-1H-imidazolium bromide; 3-vinyl-1-(phenylmethyl)-1H-imidazolium bromide; 1-vinyl-3-(4-methylphenyl)-1H-imidazolium chloride; 3-vinyl-1-(1-methylpropyl)-1H-imidazolium chloride; 1-butyl-3-vinyl-1H-imidazolium bromide; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium iodide; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium chloride; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl) [(trifluoromethyl)sulfonyl]methanesulfonamide; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium hexafluorophosphate; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium tetrafluoroborate; 3-[(4-vinylphenyl)methyl]-1-ethyl-1H-imidazolium chloride; 1-[(4-vinylphenyl)methyl]-3-ethyl-1H-imidazolium salt with 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 1-(3-aminopropyl)-3-[(4-vinylphenyl)methyl]-1H-imidazolium chloride; 1-butyl-3-[(4-vinylphenyl)methyl]-1H-imidazolium chloride.

Preferred compounds b2) may exist alone or in combination and include, but are not limited to: 1-methyl-3-hexyl-1H-imidazolium 4-vinylbenzenesulfonate; 1-dodecyl-3-vinyl-1H-imidazolium 4-vinylbenzenesulfonate; 1-methyl-3-propyl-1H-imidazolium 4-vinylbenzenesulfonate; and 3-ethyl-1-methyl-1H-imidazolium 4-(1-methylvinyl)benzenesulfonate.

In particular, good results are obtained when part b) of the composition comprises or consists of at least one compound selected from the group consisting of 3-methyl-1-hexyl-1H-imidazolium 4-vinylbenzenesulfonate; 3-vinyl-1-ethyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; and 3-methyl-1-butyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide.

According to a second aspect of the present invention, a bonding structure is provided, comprising: a first material layer having a conductive surface; and a second material layer having a conductive surface, wherein a cured electrochemically debondable adhesive composition as defined above and in the appended claims is disposed between the first material layer and the second material layer.

According to a third aspect of the present invention, a method for debonding a bonded structure as defined above and in the appended claims is provided, the method comprising the steps of: i) applying a voltage to two surfaces to form an anode interface and a cathode interface; and ii) debonding the surfaces.

Step i) of this method is preferably characterized by at least one of the following: a) applying a voltage of 1 to 100 V; and b) applying the voltage for a duration of 1 second to 180 minutes.

By applying an electric potential across the bonding layer between the composition and the conductive surface, the adhesive properties of the composition are disrupted. Without intending to be bound by theory, it is believed that Faradaic reactions occurring at the interface between the adhesive composition and the conductive surface disrupt the interaction between the adhesive and the substrate, thereby weakening the bond therebetween. This interfacial disruption can be the result of one or more processing steps, such as chemical degradation of the debondable material, outgassing at the interface, and/or embrittlement of the material through changes in the crosslink density of the adhesive composition.

Definitions As used herein, the singular forms " a ,""an," and " the " include plural referents unless the context clearly dictates otherwise.

As used herein, the terms " comprising /comprises/comprised of" are synonymous with " including /includes " or " containing /contains " and are inclusive or open-ended and do not exclude additional unlisted members, elements or method steps.

As used herein, the term " consisting of " excludes any elements , ingredients , members or method steps not specified.

When amounts, concentrations, sizes and other parameters are expressed in the form of ranges, preferred ranges, upper limits, lower limits or upper and lower limits, it should be understood that any range obtained by combining any upper limit or preferred value with any lower limit or preferred value is also specifically disclosed, regardless of whether the obtained range is explicitly mentioned in the context.

Furthermore, according to standard understanding, a weight range expressed as " 0 to x " specifically includes 0 wt. %: the ingredient defined by the range may be absent from the composition or may be present in the composition in an amount of up to x wt. %.

The words " preferred ,"" preferably ,"" suitable ," and " particularly " are frequently used herein to refer to embodiments of the present invention that may provide particular benefits under certain circumstances. However, the recitation of one or more preferred, desirable, or specific embodiments does not imply that other embodiments are not applicable and is not intended to exclude such other embodiments from the scope of the present invention.

As used throughout this application, the word “ may ” is used in a permissive sense, meaning it is possible, rather than a mandatory sense.

As used herein, room temperature is 23°C ± 2°C. As used herein, " ambient conditions " means the temperature and pressure of the environment in which the composition is located or the environment in which the coating or the substrate on which the coating is located.

In the context of the present invention, a " two-component ( 2K ) composition " is understood to be a composition in which the first component (1) and the second component (2) must be stored in separate containers due to their (high) reactivity. The two components are mixed only shortly before coating and subsequently react, usually without further activation, to form bonds and thus a polymeric network. In this context, higher temperatures can be applied in order to promote the crosslinking reaction.

As used herein, the term " electrochemically debondable " means that after the adhesive cures, the bond strength can be weakened by at least 50% after applying a 50 V potential for 60 minutes. The cured adhesive is applied between two substrates that are bonded via the adhesive such that an electric current flows through the adhesive bond layer. Bond strength is measured by a tensile lap-shear (TLS) test performed at room temperature and based on ASTM D3163-01 ( Standard Test Method for Determining Strength of Adhesively Bonded Rigid Plastic Lap - Shear Joints in Shear by Tension Loading ). The bond overlap is 2.5 cm x 1.0 cm (1" x 0.4"), and the bond thickness is 0.1 cm (40 mil).

The term " electrolyte " is used herein according to its standard meaning in the art to refer to a substance containing free ions that can conduct electricity by displacement of charged carrier species. The term is intended to encompass molten electrolytes, liquid electrolytes, semi-solid electrolytes, and solid electrolytes in which at least one of the cationic or anionic components of the electrolyte structure is essentially free to displace, thereby acting as charge carriers.

The curable adhesive composition of the present invention and the cured adhesive obtained therefrom have " electrolyte functionality " because the adhesive material allows ion conduction, whether anionic, cationic, or both.

Electrolyte functionality is understood to be derived from the ability of the composition and cured adhesive to dissolve ions of at least one polarity.

The term " Faraday reaction " refers to an electrochemical reaction in which a substance is oxidized or reduced.

As used herein, the term " monomer " refers to a substance that can undergo polymerization to provide a building block to the chemical structure of a polymer. As used herein, the term " monofunctional " refers to a substance having one polymerizable moiety. As used herein, the term " polyfunctional " refers to a substance having more than one polymerizable moiety.

As used herein, the term " ethylenically unsaturated monomer " refers to any monomer containing a terminal double bond that is capable of polymerization under normal conditions of free radical addition polymerization.

As used herein, the term " equivalent " ( eq . ) relates to the relative number of reactive groups present in a reaction, as is common in chemical notation.

As used herein, " ( meth ) acryl " is a shorthand term for " acryl " and/or " methacryl ." Thus, the term " ( meth ) acrylate " refers collectively to both acrylate and methacrylate.

As used herein, a " _C1 - _Cn alkyl " group refers to a monovalent group containing 1 to n carbon atoms, which is a radical of an alkane, and includes both straight-chain and branched-chain organic groups. Thus, a " _C1 - _C30 alkyl " group refers to a monovalent group containing 1 to 30 carbon atoms, which is a radical of an alkane, and includes both straight-chain and branched-chain organic groups. Examples of alkyl groups include, but are not limited to, methyl; ethyl; propyl; isopropyl; n-butyl; isobutyl; dibutyl; tertiary butyl; n-pentyl; n-hexyl; n-heptyl; and 2-ethylhexyl. In the present invention, such alkyl groups may be unsubstituted or substituted with one or more substituents selected from halogen, hydroxyl, nitrile (-CN), amide, and amino ( _-NH2 ). Where applicable, preferred substituents will be indicated in this specification. However, in general, it should be noted that alkyl groups containing 1 to 18 carbon atoms (C ₁ -C ₁₈ alkyl), such as alkyl groups containing 1 to 12 carbon atoms (C ₁ -C ₁₂ alkyl) or alkyl groups containing 1 to 6 carbon atoms (C ₁ -C ₆ alkyl) are preferred.

As used herein, the term " C ₁ -C ₁₈ hydroxyalkyl " refers to a HO-(alkyl) group having 1 to 18 carbon atoms, wherein the point of attachment of the substituent is through the oxygen atom and alkyl is as defined above.

" Alkoxy " refers to a monovalent group represented by -OA, where A is an alkyl group; non-limiting examples are methoxy, ethoxy, and isopropoxy.

As used herein, the term " C ₁ -C ₆ alkylene " is defined as a saturated divalent hydrocarbon group having a linear, branched, or cyclic portion, or a combination thereof, and having 1 to 6 carbon atoms.

The term " _C3 - _C30 cycloalkyl " is understood to mean an optionally substituted, saturated monocyclic, bicyclic, or tricyclic alkyl group having 3 to 30 carbon atoms. Generally, cycloalkyl groups containing 3 to 18 carbon atoms ( _C3 - _C18 cycloalkyl) are preferred. Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, adamantane, and norethane. In the present invention, such cycloalkyl groups may be unsubstituted or substituted with one or more substituents selected from halogen, _C1 - _C6 alkyl, and _C1 - _C6 alkoxy.

As used herein, " _C6 - _C18 aryl ," used alone or as part of a larger group (e.g., in " aralkyl "), refers to optionally substituted monocyclic, bicyclic, and tricyclic ring systems, wherein the monocyclic system is aromatic or at least one ring in the bicyclic or tricyclic system is aromatic. Bicyclic and tricyclic ring systems include benzo-fused 2-3 membered carbon rings. In the present invention, such aryl groups may be unsubstituted or substituted with one or more substituents selected from halogen, _C1 - _C6 alkyl, and _C1 - _C6 alkoxy. Exemplary aryl groups include phenyl, (C ₁ -C ₄ )alkylphenyl, such as tolyl and ethylphenyl, indenyl, naphthyl, tetrahydronaphthyl, tetrahydroindenyl, tetrahydroanthracenyl, and anthracenyl. It is noted that phenyl is preferred.

As used herein, " _C2 - _C20 alkenyl " refers to a alkyl group having 2 to 20 carbon atoms and at least one olefinically unsaturated unit. Alkenyl groups may be linear, branched, or cyclic and may be optionally substituted. As generally understood by those skilled in the art, the term " alkenyl " also encompasses groups having " cis " and " trans " configurations, or alternatively, " E " and " Z " configurations. However, in general, it should be noted that unsubstituted alkenyl groups containing 2 to 10 ( _C2-10 ) or 2 to 8 ( _C2-8 ) carbon atoms are preferred. Examples of such _C2 - _C12alkenyl groups _include , but are not limited to: _-CH═CH2 ; -CH═CHCH3; _-CH2CH═CH2 ; -C( _{═CH2 )} ( _CH3 ); -CH═CHCH2CH3; _{-CH2CH═CHCH3} ; -CH2CH2CH═CH2 _; -CH═C( _CH3 ) ₂ ; _{-CH2C ( ═CH2 ) ( CH3 ) ; -C ( ═CH2} ) _{CH2CH3 ; -C} ( _{CH3 ) ═CHCH3 ; -C} ( _CH3 ) _{CH═CH2 ; -CH═CHCH2CH2CH3 ; -CH2CH═CHCH2CH3 ; -CH2CH2CH═CHCH3 ; -CH2CH2CH2CH═CH2} ; -C(═CH ₂ )CH ₂ CH ₂ CH ₃ ; -C(CH ₃ )═CHCH ₂ CH ₃ ; -CH(CH ₃ )CH═CHCH _; -CH(CH ₃ )CH ₂ CH═CH ₂ ; -CH ₂ CH═C(CH ₃ ) ₂ ; 1-cyclopent-1-enyl; 1-cyclopent-2-enyl; 1-cyclopent-3-enyl; 1-cyclohex-1-enyl; 1-cyclohex-2-enyl; and 1-cyclohexyl-3-enyl.

As used herein, " alkaryl " refers to an aryl group substituted with an alkyl group, and " substituted alkaryl " refers to an alkaryl group further carrying one or more substituents as described above. In addition, as used herein, " aralkyl " means an alkyl group substituted with an aryl group as defined above.

As used herein, the term " hetero " refers to a group or moiety containing one or more heteroatoms selected from N, O, Si, P, and S. Thus, for example, " heterocyclo " refers to a cyclo group having N, O, Si, P, or S as part of the ring structure. " Heteroalkyl ,"" heterocycloalkyl ," and " heteroaryl " moieties are alkyl, cycloalkyl, and aryl groups, respectively, as defined above, containing N, O, Si, P, or S as part of their structure.

For the sake of completeness, the term " _C2 - _C30 heteroalkyl " refers to an "alkyl" group in which at least one carbon atom is replaced by a heteroatom , the group having a total of 2 to 30 carbon atoms. A specific example of such a heteroalkyl group is a " _C2 - _C18 alkoxyalkyl " group, which herein refers to an alkyl group having an alkoxy substituent as defined above and wherein the moiety ( alkyl - O - alkyl ) contains a total of 1 to ₁₈ carbon atoms: such groups include methoxymethyl ( _-CH2OCH3 ), 2 _{- methoxyethyl (-CH2CH2OCH3 ) and 2} - _ethoxyethyl ( _{-CH2CH2OCH2CH3} ). Another example of a heteroalkyl group is a " _C2 - _C30 aminoalkyl group ," which refers herein to an alkyl group substituted with at least one group selected from -NH(R'), -N(R')(R''), or N ⁺ (R')(R'')(R'''): wherein R', R'', and R''' are _C1 - _C6 alkyl groups, with the proviso that the groups contain a total of 2 to 30 carbon atoms: such groups include 2-(dimethylamino)ethyl, 2-(diethylamino)ethyl, and 2-(trimethylamino)ethyl.

The term " _C1 - _C9 heteroaryl " refers to an aryl group having 1 to 9 carbon atoms and 1 to 4 heteroatoms, which may be attached via a heteroatom (if applicable) or a carbon atom. The heteroaryl ring may be fused or otherwise attached to one or more heteroaryl rings, aromatic or non-aromatic hydrocarbon rings, or heterocycloalkyl rings. Examples of heteroaryl groups include, but are not limited to, pyridine; furan; thiophene; 5,6,7,8-tetrahydroisoquinoline; pyrimidine; thienyl; benzothienyl; pyridyl; quinolinyl; pyrrolyl; pyrimidinyl; imidazolyl; benzimidazolyl; furanyl; benzofuranyl; thiazolyl; benzothiazolyl; isoxazolyl; oxadiazolyl; isothiazolyl; benzoisothiazolyl; triazolyl; tetrazolyl; pyrrolyl; indolyl; pyrazolyl; and benzopyrazolyl.

The term " _C2 - _C8 heterocycloalkyl " refers to a saturated cycloalkyl group having 2 to 8 carbon atoms and 1 to 4 heteroatoms, which may be attached via a heteroatom (if applicable) or a carbon atom. The heterocycloalkyl ring may be fused or otherwise attached to other heterocycloalkyl rings and/or non-aromatic hydrocarbon rings, as appropriate. Preferred heterocycloalkyl groups have 3 to 7 ring atoms. Examples of heterocycloalkyl groups include, but are not limited to, piperidine; morpholine; piperidine; tetrahydrofuran; pyrrolidine; pyrazole; piperidinyl; piperidine; morpholine; and pyrrolidinyl.

As used herein, the term " aliphatic " includes saturated and unsaturated, non-aromatic, straight chain, branched chain, acyclic or cyclic hydrocarbons, which may be substituted with one or more functional groups, provided that the substitution results in a stable moiety. As will be understood by those skilled in the art, " aliphatic " is intended to encompass alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, and cycloalkynyl moieties.

As used herein, " aromatic " refers to a broad class of unsaturated cyclic hydrocarbons containing one or more rings. Such cyclic hydrocarbons may contain carbon (C), nitrogen (N), oxygen (O), sulfur (S), boron (B), or any combination thereof. At least some carbon is also included. Aromatics include both aryl and heteroaryl rings. Aryl or heteroaryl rings may be further substituted with additional aliphatic, aromatic, or other groups, provided that the substitution results in a stable moiety.

As used herein, the term " free radical initiator " refers to any chemical species that, upon exposure to sufficient energy (in the form of radiation, heat, or the like), decomposes into two uncharged components, each possessing at least one unpaired electron. For the sake of completeness, the term " free radical initiator " encompasses thermal free radical initiators and free radical photoinitiators, which can be activated upon exposure to an energetic activating beam (e.g., electromagnetic radiation): thermal free radical initiators are preferred herein.

The molecular weights of the macromolecular, oligomeric, and polymeric components of the curable compositions described herein may be measured by gel permeation chromatography (GPC), for example, according to ASTM 3536, using polystyrene calibration standards.

Unless otherwise specified, the viscosity of the coating compositions described herein was measured using a Brookfield Viscometer under standard conditions of 20°C and 50% relative humidity (RH). The calibration method, spindle type, and rotation speed of the Brookfield Viscometer were selected according to the manufacturer's instructions to suit the composition being measured.

a) Nonionic Matrix Monomer The compositions of the present invention comprise at least one ethylenically unsaturated and nonionic monomer, the (co)polymerization of which produces the matrix of the releasable adhesive. Monomer a) can, in principle, be any ethylenically unsaturated and nonionic monomer. However, the present invention is particularly applicable to compositions in which the (meth)acrylic monomer comprises at least 50 mol%, preferably at least 75 mol%, of the total molar amount of the ethylenically unsaturated and nonionic monomers present.

a1) Aliphatic and cycloaliphatic (meth)acrylate monomers In an important embodiment of the present invention, the composition of the present invention comprises 40 to 95 wt.%, preferably 45 to 90 wt.%, based on the weight of the composition, of a1) at least one (meth)acrylate monomer represented by formula I: _H2C = _CGCO2R1 (I ⁾ wherein: G is hydrogen, halogen or _C1 - _C4 alkyl; and, ^R1 is selected from: _C1 - _C30 alkyl; _C2 - _C30 heteroalkyl; _C3 - _C30 cycloalkyl; _C2 - _C8 heterocycloalkyl; _C2 - _C20 alkenyl; and _C2 - _C12 alkynyl.

For example, R ¹ can be selected from C ₁ -C ₁₈ alkyl, C ₂ -C ₁₈ heteroalkyl, C ₃ -C ₁₈ cycloalkyl, C ₂ -C ₈ heterocycloalkyl, C ₂ -C ₈ alkenyl, and C ₂ -C ₈ alkynyl.

The monomer a1) is preferably characterized in that R ¹ is selected from C ₁ -C ₁₈ alkyl and C ₃ -C ₁₈ cycloalkyl. This preference is expressly intended to include the embodiment in which R ¹ is C ₁ -C ₆ hydroxyalkyl.

Examples of the (meth)acrylate monomer a1) according to formula (I) include, but are not limited to: methyl (meth)acrylate; ethyl (meth)acrylate; butyl (meth)acrylate; hexyl (meth)acrylate; 2-ethylhexyl (meth)acrylate; dodecyl (meth)acrylate; lauryl (meth)acrylate; cyclohexyl (meth)acrylate; isobutyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate (HEMA); 2-hydroxypropyl (meth)acrylate; ethylene glycol monomethyl ether (meth)acrylate; ethylene glycol monoethyl ether (meth)acrylate; ethylene glycol monododecyl ether (meth)acrylate; diethylene glycol monomethyl ether (meth)acrylate; trifluoroethyl (meth)acrylate; and perfluorooctyl (meth)acrylate.

a2) Aromatic (meth)acrylate monomer: The composition of the present invention may further comprise 0 to 30 wt.%, e.g., 0.1 to 30 wt.%, 0.1 to 25 wt.%, or 0.1 to 15 wt.%, based on the weight of the composition, of a2) at least one (meth)acrylate monomer represented by formula II: H ₂ C═CQCO ₂ R ² (II) wherein: Q may be hydrogen, a halogen, or a C ₁ -C ₄ alkyl group; and, R ² may be selected from a C ₆ -C ₁₈ aryl group, a C ₁ -C ₉ heteroaryl group, a C ₇ -C ₁₈ alkylaryl group, and a C ₇ -C ₁₈ aralkyl group.

Exemplary (meth)acrylate monomers a2) according to formula (II) that can be used alone or in combination include, but are not limited to: benzyl (meth)acrylate; phenoxyethyl (meth)acrylate; phenoxydiethylene glycol (meth)acrylate; phenoxypropyl (meth)acrylate; and phenoxydipropylene glycol (meth)acrylate.

a3) (Meth)acrylate-Functionalized Oligomer In an important embodiment of the present invention, not intended to be mutually exclusive with the inclusion of aliphatic and cycloaliphatic monomers (a1) and aromatic monomers (a2), the compositions of the present invention include 0 to 50 wt.%, preferably 5 to 25 wt.%, of a3) at least one (meth)acrylate-functionalized oligomer, based on the weight of the composition. These oligomers may have one or more acrylate and/or methacrylate groups attached to the oligomeric backbone. These (meth)acrylate functional groups may be terminal on the oligomer and/or distributed along the oligomeric backbone.

Preferably, the at least one (meth)acrylate functional oligomer: i) has two or more (meth)acrylate functional groups per molecule; and/or ii) has a weight average molecular weight (Mw) of 300 to 1000 Daltons.

Examples of such oligomers that can be used alone or in combination include, but are not limited to: (meth)acrylate-functional urethane oligomers, such as (meth)acrylate-functional polyester urethanes and (meth)acrylate-functional polyether urethanes; (meth)acrylate-functional polyepoxy resins; (meth)acrylate-functional polybutadiene; (meth)acrylate polyol (meth)acrylates; polyester (meth)acrylate oligomers; polyamide (meth)acrylate oligomers; and polyether (meth)acrylate oligomers. Such (meth)acrylate functionalized oligomers and methods for their preparation are disclosed in, inter alia, U.S. Patent Nos. 4,574,138, 4,439,600, 4,380,613, 4,309,526, 4,295,909, 4,018,851, 3,676, and 4,676,613. ,398; U.S. Patent No. 3,770,602; U.S. Patent No. 4,072,529; U.S. Patent No. 4,511,732; U.S. Patent No. 3,700,643; U.S. Patent No. 4,133,723; U.S. Patent No. 4,188,455; U.S. Patent No. 4,206,025; U.S. Patent No. 5,002,976. Among the aforementioned polyether (meth)acrylate oligomers, specific examples include, but are not limited to: PEG 200 DMA (n≈4); PEG 400 DMA (n≈9); PEG 600 DMA (n≈14); and PEG 800 DMA (n≈19), where the designated number (e.g., 400) represents the weight average molecular weight of the diol portion of the molecule.

The present invention does not exclude the presence of other ethylenically unsaturated and nonionic monomers that do not meet the definitions of a1), a2), and a3). However, the addition of such other monomers should be subject to the following conditions: the total amount of ethylenically unsaturated and nonionic monomers should not exceed 95 wt.%, based on the total weight of the composition. The total amount of ethylenically unsaturated and nonionic monomers should preferably not exceed 90 wt.%, based on the total weight of the composition.

Without intending to limit the present invention, such other ethylenically unsaturated and nonionic monomers may include: polysiloxane (meth)acrylate monomers such as those taught and claimed in U.S. Patent No. 5,605,999 (Chu); α,β-ethylenically unsaturated monocarboxylic acids containing 3 to 5 carbon atoms such as acrylic acid, methacrylic acid, crotonic acid; C ₁ -C ₁₈ alkyl crotonic acid esters; α,β-ethylenically unsaturated dicarboxylic acids containing 4 to 6 carbon atoms and anhydrides, monoesters and diesters of such acids; vinyl esters such as vinyl acetate, vinyl propionate and VEOVA available from Shell Chemical Company. ^TM series monomers; vinyl halides and vinylidene halides; vinyl ethers, such as vinyl ethyl ether; vinyl ketones, including alkyl vinyl ketones, cycloalkyl vinyl ketones, aryl vinyl ketones, arylalkyl vinyl ketones, and arylcycloalkyl vinyl ketones; aromatic or heterocyclic aliphatic vinyl compounds; poly(meth)acrylates of alkane polyols, such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate, trihydroxymethylpropane tri(meth)acrylate. esters, glycerol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate; poly(meth)acrylates of alkylene glycols, such as diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dibutylene glycol di(meth)acrylate, and di(1,5-pentanediol) dimethacrylate; polyethylene glycol di(meth)acrylate; and bisphenol A di(meth)acrylates, such as ethoxylated bisphenol A (meth)acrylate ("EBIPMA").

Representative examples of other ethylenically unsaturated polymerizable nonionic monomers include, but are not limited to, ethylene glycol dimethacrylate (EGDMA); fumaric anhydride, maleic anhydride, and itaconic anhydride; and monoesters and diesters with _C1 - _C4 alcohols, such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, and tertiary butanol. Representative examples of vinyl monomers include, but are not limited to, the following compounds: vinyl acetate; vinyl propionate; vinyl ethers, such as vinyl ethyl ether; and vinyl ethyl ketone. Representative examples of aromatic or heterocyclic aliphatic vinyl compounds include, but are not limited to, styrene, α-methylstyrene, vinyltoluene, tertiary butylstyrene, 2-vinylpyrrolidone, 5-ethylidene-2-northene, and 1-vinylcyclohexene, 3-vinylcyclohexene, and 4-vinylcyclohexene.

b) Electrolyte The composition of the present invention comprises 0.9 to 50 wt.%, for example 5 to 50 wt.% or 10 to 45 wt.% of b) at least one polymerizable ionic compound, wherein the polymerizable ionic compound comprises: b1) at least one compound according to formula IV: and/or b2) at least one compound according to formula V: wherein: R ⁷ is selected from: C ₁ -C ₃₀ alkyl; C ₂ -C ₈ alkenyl; C _{1 -C 30} heteroalkyl; C ₃ -C ₃₀ cycloalkyl; C ₆ -C ₁₈ aryl; C ₁ -C ₉ heteroaryl; C _{7 -C 18} alkaryl; C _{2 -C 5} heterocycloalkyl; or -R ^a -C(=O)-R ^b , wherein R ^a is C ₁ -C ₆ alkylene and R ^b is C ₁ -C ₆ alkyl; each R ⁸ is independently selected from H, C ₁ -C ₁₈ alkyl, C ₁ -C ₁₈ heteroalkyl, C ₃ -C ₁₈ cycloalkyl, C ₆ -C ₁₈ aryl, C ₁ -C ₉ heteroaryl, C _{7 -C 18} alkaryl, or C ₂ -C R ₉ is H or C ₁ -C ₄ alkyl; each R ¹⁰ is ^{independently} selected from: C ₁ -C ₃₀ alkyl; C ₁ -C ₃₀ heteroalkyl; C _{3 -C 30} cycloalkyl; C ₆ -C ₁₈ aryl; C ₁ -C ₉ heteroaryl; C _{7 -C 18} alkaryl; C _{2 -C 5} heterocycloalkyl; or -Ra- ^C (=O) ^-Rb , wherein ^Ra is C ₁ -C ₆ alkylene and R ^b is C ₁ -C ₆ alkyl; A is a non-polymerizable anion; T is an olefinically unsaturated anion; d and m are each an integer having a value of at least 1; e and n have values such that the compound is electrically neutral; and, It is a covalent bond, a C ₁ -C ₂ alkylene group, -CH ₂ OC(=O)-, -CH ₂ CH ₂ OC(=O)-, p-benzyl or p-tolyl.

In the above formula, ^R7 is preferably selected from: _C1 - _C12 alkyl; _C2 - _C6 alkenyl; _C1 - _C12 heteroalkyl; _{C3 - C18} cycloalkyl; C6-C18 aryl; C1- _C9 heteroaryl; _{C7 - C18} alkaryl; _{C2 - C5 heterocycloalkyl} ; or -Ra ^- C(=O) ^-Rb , wherein ^Ra is _{C1 - C6} alkylene and _Rb ^is _C1 - _C6 alkyl. More specifically, ^R is selected from: _C1 - _C8 alkyl; _C2 - _C4 alkenyl; _C1 - _C8 heteroalkyl; _{C3 - C12} cycloalkyl; _C6 - _C18 aryl; C1-C9 heteroaryl; _C7 - _C18 alkaryl _{; C2 - C5} heterocycloalkyl; or _-Ra - ^C (=O) ^-R , wherein ^Ra is _{C1 - C4} alkylene and ^R is _C1 - _C4 alkyl. Given that ^R can be alkenyl, it should be noted that the imidazolium moiety can have more than one ethylenically unsaturated group: exemplary moieties in this regard include 1,3-divinyl- 1H -imidazolium and 3-vinyl-1-(2-propen-1-yl) -1H -imidazolium.

Each R ⁸ is preferably independently selected from H or C ₁ -C ₆ alkyl, and more specifically, independently selected from H or C ₁ -C ₂ alkyl. It is noted that at least one R ⁸ is preferably H. R ⁹ is preferably H or C ₁ -C ₂ alkyl, and more specifically, H or methyl.

Each R ¹⁰ is preferably independently selected from: C ₁ -C ₁₂ alkyl; C ₁ -C ₁₂ heteroalkyl; C _{3 -C 18} cycloalkyl; C ₆ -C ₁₈ aryl; C ₁ -C ₉ heteroaryl; C ₇ -C ₁₈ alkaryl; C _{2 -C 5} heterocycloalkyl; or -R ^a -C(═O)-R ^b , wherein R ^a is C ₁ -C ₆ alkylene and R ^b is _{C 1} -C ₆ alkyl. More specifically, R ¹⁰ is selected from: C ₁ -C ₈ alkyl; C ₁ -C ₈ heteroalkyl; _{C 3 -C 12} cycloalkyl; C ₆ -C ₁₈ aryl; C ₁ -C ₉ heteroaryl; C 7 -C ₁₈ alkaryl; C _{2 -C 5} heterocycloalkyl; or -R ^a -C(═O)-R ^b , wherein R ^a is C ₁ -C ₄ alkylene and R ^b is _{C 1} -C ₄ alkyl.

With respect to the compound of formula IV, the anion A is typically selected from the group consisting of fluoride, chloride, bromide, iodide, perchlorate, nitrate, nitrite, phosphate, sulfate, sulfite, carbonate, hydrogen carbonate, hydrogen phosphate, hydrogen sulfate, hydrogen sulfite, dihydrogen phosphate, trifluorophosphate, hexafluorophosphate, methylsulfate, ethylsulfate, methylcarbonate, methylsulfonate, ethylsulfonate, 4-methylbenzenesulfonate, diethylphosphate, formate, acetate, propionate, tartrate, octanoate, bis(2,4,4-trimethylpentyl)phosphinate, bis(malonato)borate, bis(oxalato)borate; Bis(pentafluoroethyl)phosphinate; tetracyanoborate; tetrafluoroborate; bis(phthalato)borate; bis(salicylate)borate; bis(trifluoromethylsulfonyl)methane; bis(trifluoromethyl)imidate; tetrakis(hydrosulfato)borate; tetrakis(methylsulfonato)borate; trifluoromethylsulfonate; tris(heptafluoropropyl)trifluorophosphate; tris(nonafluorobutyl)trifluorophosphate; tris(pentafluoroethyl)trifluorophosphate; tris(pentafluoroethylsulfonyl)trifluorophosphate; trichlorozincinate; trifluoroacetate; bromoaluminate; chloroaluminate; dichlorocopperate; thiocyanate; toluenesulfonate; and dicyanamide.

The anion A is preferably selected from the group consisting of fluoride, chloride, bromide, iodide, perchlorate, nitrate, formate, acetate, octanoate, tetrafluoroborate, trifluorophosphate, hexafluorophosphate, methylsulfate, ethylsulfate, methylcarbonate, methylsulfonate, 4-methylbenzenesulfonate, trifluoromethylsulfonate, bis(trifluoromethylsulfonic acid)imide, trifluorophosphate, and trifluoroacetate; and tris(perfluoroethyl)trifluorophosphate. More specifically, the anion A is selected from the group consisting of fluoride, chloride, bromide, iodide, tetrafluoroborate, hexafluorophosphate, methylsulfate, ethylsulfonate, 4-methylbenzenesulfonate, and bis(trifluoromethylsulfonic acid)imide.

The anion T may be selected from: ethylenically unsaturated carboxylate anions (R-COO-); ethylenically unsaturated sulfonate anions (R-SO ₃ ^- ); ethylenically unsaturated phosphonate anions (R-PO ₃ ^{2 -} ); ethylenically unsaturated phosphinate anions (RP(H)O ₂ ^- ); and ethylenically unsaturated phosphate anions (RO-PO ₃ ^{2 -} ), wherein R is an organic group containing ethylenic unsaturation, which is polymerized under normal conditions and is preferably derived from (meth)acrylic acid, vinyl acid or allyl acid.

Representative anions T include (meth)acrylate; itaconate; maleate; crotonate; isocrotonate; vinylbenzoate; 2-acrylamido-2-methylpropanesulfonate; sulfoethyl (meth)acrylate; sulfopropyl (meth)acrylate; sulfomethylated acrylamide; allylsulfonate; vinylsulfonate; 4-vinylbenzenesulfonate (4-styrenesulfonate); 4-isopropenylbenzenesulfonate (4-methylstyrenesulfonate); allylphosphonate; and monoacryloxyethylphosphate.

Exemplary compounds b1) according to Formula IV include, but are not limited to: 3-vinyl-1-methyl-1H-imidazolium iodide; 3-vinyl-1-methyl-1H-imidazolium chloride; 3-vinyl-1-methyl-1H-imidazolium bromide; 3-vinyl-1-methyl-1H-imidazolium methanesulfonate; 3-vinyl-1-ethyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-vinyl-1-methyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-vinyl-1-methyl-1H-imidazolium hexafluorophosphate; 3-vinyl-1-methyl-1H-imidazolium 4-methylbenzenesulfonate; 3-vinyl-1-ethyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 1-Methyl-1H-imidazolium tetrafluoroborate; 3-Vinyl-1-ethyl-1H-imidazolium iodide; 3-Vinyl-1-ethyl-1H-imidazolium bromide; 3-Vinyl-1-ethyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-Vinyl-1-ethyl-1H-imidazolium hexafluoro Phosphate; 3-vinyl-1-ethyl-1H-imidazolium tetrafluoroborate; 1,3-divinyl-1H-imidazolium chloride; 1,3-divinyl-1H-imidazolium tetrafluoroborate; 1,3-divinyl-1H-imidazolium hexafluorophosphate; 3-vinyl-1-ethyl-2-methyl-1H-imidazolium iodide; 3-vinyl-1,2- Dimethyl-1H-imidazolium iodide; 3-vinyl-1,2-dimethyl-1H-imidazolium chloride; 3-vinyl-2-ethyl-1-methyl-1H-imidazolium iodide; 3-(aminomethyl)-1-vinyl-1H-imidazolium bromide; 3-vinyl-1-(1-methylethyl)-1H-imidazolium bromide; 3-(1,1-dimethylethyl)-1-vinyl-1H-imidazolium bromide; 3-vinyl-1-propyl-1H-imidazolium bromide; 1-(2-aminoethyl)-3-vinyl-1H-imidazolium chloride; 1-(cyanomethyl)-3-vinyl-1H-imidazolium bromide; 1-[2-(diethylamino)ethyl]-3-vinyl-1H-imidazolium chloride; 3-Vinyl-1-(2-propen-1-yl)-1H-imidazolium chloride; 3-Vinyl-1-(2-propen-1-yl)-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-Vinyl-1-(2-propen-1-yl)-1H-imidazolium bromide; 3-Vinyl-1-(phenylmethyl)-1H-imidazolium bromide; 1-Vinyl-3-(4-methylphenyl)-1H-imidazolium chloride; 3-Vinyl-1-(2-hydroxyethyl)-1H-imidazolium chloride; 3-Vinyl-1-(1-methylpropyl)-1H-imidazolium chloride; 1-Butyl-3-vinyl-1H-imidazolium bromide; 3-Vinyl-1-(2-ethoxy)-1H-imidazolium 1-Methyl-3-(2-propen-1-yl)-1H-imidazolium bromide; 1-Methyl-3-(2-propen-1-yl)-1H-imidazolium iodide; 1-Methyl-3-(2-propen-1-yl)-1H-imidazolium chloride; 1-Methyl-3-(2-propen-1-yl)-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 1- Methyl-3-(2-propen-1-yl)-1H-imidazolium hexafluorophosphate; 1-methyl-3-(2-propen-1-yl)-1H-imidazolium tetrafluoroborate; 1-ethyl-3-(2-propen-1-yl)-1H-imidazolium iodide; 2-methyl-3-(2-propen-1-yl)-1-propyl-1H-imidazolium bromide; 3-(2- 1-Propylene-1-yl)-1-propyl-1H-imidazolium bromide; 3-(2-hydroxyethyl)-1-(2-propen-1-yl)-1H-imidazolium bromide; 1-butyl-3-(2-propen-1-yl)-1H-imidazolium bromide; 1,3-di-2-propen-1-yl-1H-imidazolium bromide; 1,3-di-2-propen-1-yl- 1H-Imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 1,3-di-2-propen-1-yl-1H-imidazolium tetrafluoroborate; 3-(2-hydroxyethyl)-1-(2-propen-1-yl)-1H-imidazolium bromide; 1-(2-cyanoethyl)-3-(2-propen-1-yl)-1H-imidazolium bromide compound; 1-methyl-3-(2-oxopropyl)-1H-imidazolium tetrafluoroborate; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium iodide; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium chloride; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium hexafluorophosphate; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium tetrafluoroborate; 3-[(4-vinylphenyl)methyl]-1-ethyl-1H-imidazolium chloride; 1- [(4-vinylphenyl)methyl]-3-ethyl-1H-imidazolium salt with 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 1-(3-aminopropyl)-3-[(4-vinylphenyl)methyl]-1H-imidazolium chloride; 1-butyl-3-[(4-vinylphenyl)methyl]-1H-imidazolium chloride; 1-methyl-3-[[(1-oxopropen-1-yl)oxy]methyl]-1H-imidazolium bromide; 1-ethyl-3-[[(1-oxopropen-1-yl)oxy]methyl]-1H-imidazolium iodide; and 1-butyl-3-[[(1-oxopropen-1-yl)oxy]methyl]-1H-imidazolium iodide. For the sake of completeness, these compounds may be present in the composition of the present invention alone or in combination of two or more.

Without intending to limit the present invention, representative compounds according to Formula IV include:

For the sake of completeness, NTf2- in the above description represents the bis(trifluoromethanesulfonyl)imidate anion.

Exemplary compounds b2) according to formula V include, but are not limited to: 3-(3-cyanopropyl)-1-methyl-1H-imidazolium 2-acrylate; 3-hexyl-1-methyl-1H-imidazolium 2-acrylate; 3-hexadecyl-1-methyl-1H-imidazolium 2-acrylate; 3-ethyl-1-methyl-1H-imidazolium 2-methyl-2-acrylate; 1-methyl-3-(phenylmethyl)-1H-imidazolium 2-methyl-2-acrylate; 3-ethyl-1-methyl-1H-imidazolium 1-[2-[(1-oxo-2-propen-1-yl)oxy]ethyl]1,2-phthalate; 3-ethyl-1-methyl-1H-imidazolium 2-methyl-2-[(1-oxo- [0014] The following are the salts of: 1-methyl-3-hexyl-1H-imidazolium 4-vinylbenzenesulfonate; 1-dodecyl-3-vinyl-1H-imidazolium 4-vinylbenzenesulfonate; 3-vinyl-1-hexadecyl-1H-imidazolium 4-vinylbenzenesulfonate; 1-methyl-3-propyl-1H-imidazolium 4-vinylbenzenesulfonate; and 3-ethyl-1-methyl-1H-imidazolium 4-(1-methylvinyl)benzenesulfonate. For the sake of completeness, these compounds may be present in the composition of the present invention alone or in combination of two or more.

Without intending to limit the present invention, representative compounds according to Formula V include:

It should be noted that the electrically debondable adhesive formulation may, in certain embodiments, contain both: b1) one or more compounds according to Formula IV; and b2) one or more compounds according to Formula V. When both are present, the preferred ratio of b1) to b2) is 5:1 to 1:1, for example 4:1 to 2:1.

c) Free Radical Initiator The compositions of the present invention include c) at least one free radical initiator. Based on the total weight of the composition, the composition typically contains 0.1 to 10 wt.%, e.g., 0.1 to 5 wt.%, or 0.1 to 2.5 wt.%, of c) the at least one free radical initiator.

Without intending to limit the present invention, one class of exemplary free radical initiators suitable for use herein is an organic peroxide selected from, for example, cyclic peroxides; diacyl peroxides; dialkyl peroxides; hydroperoxides; peroxycarbonates; peroxydicarbonates; peroxyesters; and peroxyketals.

Although certain peroxides, such as dialkyl peroxides, have been particularly disclosed as suitable initiators in U.S. Patent No. 3,419,512 (Lees) and U.S. Patent No. 3,479,246 (Stapleton) and may indeed be useful herein, hydroperoxides represent the preferred class of initiators for the present invention. Furthermore, although hydrogen peroxide itself may be used, the most desirable polymerization initiators are organic hydroperoxides. For the sake of completeness, the definition of hydroperoxide includes substances such as organic peroxides or organic peroxyesters that decompose or hydrolyze in situ to form organic hydroperoxides: examples of such peroxides and peroxyesters are cyclohexyl and hydroxycyclohexyl peroxides and tributyl perbenzoate, respectively.

In one embodiment of the present invention, the free radical initiator comprises or consists of at least one hydroperoxide compound represented by the following formula: ^RpOOH wherein: ^Rp is an aliphatic or aromatic group containing up to 18 carbon atoms, and preferably wherein: ^Rp is _C1 - _C12 alkyl, _C6 - _C18 aryl or _C7 - _C18 aralkyl.

As exemplary peroxide initiators that can be used alone or in combination, there can be mentioned: cumyl hydroperoxide (CHP); p-menthane hydroperoxide; tert-butyl hydroperoxide (TBH); tert-butyl perbenzoate; tert-butyl peroxypivalate; di-tert-butyl peroxide; tert-butyl peroxyacetate; tert-butyl peroxy-2-hexanoate; tert-amyl hydroperoxide; 1,2,3,4-tetramethylbutyl hydroperoxide; benzoyl peroxide; dibenzoyl peroxide; Acyl; 1,3-bis(tertiary butylperoxyisopropyl)benzene; diacetyl peroxide; butyl 4,4-bis(tertiary butylperoxy)valerate; p-chlorobenzyl peroxide; tertiary butyl isopropyl peroxide; di-tertiary butyl peroxide; diisopropyl benzene peroxide; 2,5-dimethyl-2,5-di-tertiary butylperoxyhexane; 2,5-dimethyl-2,5-di-tertiary butyl-peroxyhex-3-yne; and 4-methyl-2,2-di-tertiary butylperoxypentane.

Without intending to limit the present invention, another exemplary class of free radical initiators suitable for use herein is an azo polymerization initiator selected from, for example, azonitriles; azoesters; azoamides; azoamidines; azoimidazolines; and macroazo initiators.

As representative examples of suitable azo polymerization initiators, there may be mentioned: 2,2'-azobis(2-methylbutyronitrile); 2,2'-azobis(isobutyronitrile); 2,2'-azobis(2,4-dimethylvaleronitrile); 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile); 1,1'-azobis(cyclohexane-1-carbonitrile); 4,4'-azobis(4-cyanovaleric acid); 2,2'-azobis(2-methylpropionic acid) dimethyl ester; 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]; 2, 2'-Azobis(N-butyl-2-methylpropionamide); 2,2'-Azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride; 2,2'-Azobis[2-(2-imidazolin-2-yl)propane]; 2,2'-Azobis(2-methylpropionamidine) dihydrochloride; 2,2'-Azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate; 4,4-Azobis(4-cyanovaleric acid), polymer with α,ω-bis(3-aminopropyl)polydimethylsiloxane (VPS-1001, available from Wako Pure Chemical Industries, Inc.); and 4,4'-azobis(4-cyanovaleric acid)·polyethylene glycol polymer (VPE-0201, available from Wako Pure Chemical Industries, Inc.).

It is not excluded that the compositions of the present invention may include at least one free radical photoinitiator compound which, upon irradiation with actinic radiation, initiates polymerization or hardening of the composition.

Generally, free radical photoinitiators are divided into "Norrish I" photoinitiators, which form free radicals by cleavage, and "Norrish II" photoinitiators, which form free radicals by hydrogen abstraction. These Norrish II photoinitiators require a hydrogen donor to serve as a free radical source. Because initiation is based on a bimolecular reaction, Norrrish II photoinitiators are generally slower than Norrrish I photoinitiators, which are based on the unimolecular formation of free radicals. On the other hand, Norrish II photoinitiators have better light absorption characteristics in the near-UV spectral region. Those skilled in the art should be able to select the appropriate free radical photoinitiator based on the actinic radiation used in curing and the sensitivity of the photoinitiator to that wavelength.

Preferred free radical photoinitiators are those selected from the group consisting of benzoylphosphine oxide; aryl ketones; benzophenones; hydroxyketones; 1-hydroxyphenyl ketones; ketal; and metallocenes. For the sake of completeness, combinations of two or more of these photoinitiators are not excluded in the present invention.

Particularly preferred free radical photoinitiators are those selected from the group consisting of: benzoin dimethyl ether; 1-hydroxycyclohexyl phenyl ketone; benzophenone; 4-chlorobenzophenone; 4-methyldiphenyl ketone; 4-phenylbenzophenone; 4,4'-bis(diethylamino)benzophenone;4,4'-bis(N,N'-dimethylamino)benzophenone(Michler'sketone); isopropyl 9-oxysulfonium; ; 2-hydroxy-2-methylpropiophenone (Daracur 1173); 2-methyl-4-(methylthio)-2-(N-morpholinyl)propiophenone; methylphenylglyoxylic acid; methyl 2-benzoylbenzoate; 2-ethylhexyl 4-(dimethylamino)benzoate; ethyl 4-(N,N-dimethylamino)benzoate; phenylbis(2,4,6-trimethylbenzyl)phosphine oxide; diphenyl(2,4,6-trimethylbenzyl)phosphine oxide; and ethyl phenyl(2,4,6-trimethylbenzyl)phosphinate. Furthermore, for assurance, combinations of two or more of these photoinitiators are not excluded from the present invention.

When the compositions of the present invention include a free radical photoinitiator, irradiation of the curable compositions generates active species from the photoinitiator, initiating the curing reaction. Once these species are generated, the curing chemistry follows the same thermodynamic rules as any chemical reaction: the reaction rate can be accelerated by heat. The practice of using thermal treatment to enhance the actinic radiation cure of monomers is generally known in the art.

As those skilled in the art will recognize, a photosensitizer can be incorporated into the composition to improve the efficiency with which the energy delivered by the photoinitiator c) is used. The term " photosensitizer ," as used in its standard meaning, refers to any substance that increases the rate of photoinitiated polymerization or shifts the wavelength at which polymerization occurs. The photosensitizer should be used in an amount of 0 to 25 wt.%, based on the weight of the free radical photoinitiator.

The use of free radical (photo)initiators may generate residual compounds in the final cured product from (photo)chemical reactions. These residues can be detected by conventional analytical techniques, such as infrared, ultraviolet, and NMR spectroscopy; gas or liquid chromatography; and mass spectrometry. Thus, the present invention may include a cured matrix (co)polymer and detectable residues from the free radical (photo)initiator. These residues are present in small amounts and generally do not interfere with the desired physicochemical properties of the final cured product.

d) Solubilizer The compositions of the present invention may optionally contain a solubilizer. For example, the composition may contain 0.1 to 10 wt.% or 0.1 to 5 wt.% of the solubilizer, based on the weight of the composition. The solubilizer functions to promote the miscibility of electrolyte b) in the adhesive composition. The solubilizer may or may not form part of the polymer matrix formed after the adhesive composition cures, but it does help promote ion transfer therein. Therefore, the solubilizer is preferably a polar compound and preferably liquid at room temperature.

Classes of suitable solubilizers include: polyphosphazenes; polymethylene sulfides; polyoxyalkylene glycols; polyethyleneimines; polysilicone surfactants, such as polyalkylsiloxanes and polyoxyalkylene-modified polydimethylsiloxanes, including but not limited to poly(C2-C3)oxyalkylene-modified polydimethylsiloxanes; copolymers of functionalized polyalkylsiloxanes and epoxies, such as polydimethylsiloxane ( PDMS ); polyols; and sugars. For the sake of completeness, fluorinated polysilicone surfactants, such as fluorinated polysilanes, are intended to be included within the term polysilicone surfactant.

Polyols and sugars, such as ethylene glycol, 1,3-propylene glycol, cyclohexanediol, hydroquinone, catechol, resorcinol, phloroglucinol, pyrogallol, hydroxyhydroquinone, tris(hydroxymethyl)benzene, tris(hydroxymethyl)benzene having three methyl or ethyl substituents bonded to the remaining benzene carbon atoms, isosorbide, isomannide, isoidide, glycerol, cyclohexane-1,2,4-triol, 1,3,5-cyclohexanetriol, pentane- 1,2,3-triol, hexane-1,3,5-triol, erythritol, 1,2,4,5-tetrahydroxybenzene, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, inositol, fructose, glucose, mannose, lactose, 1,1,1-tris(hydroxymethyl)propane, 1,1,1-tris(hydroxymethyl)ethane, di(trihydroxymethylpropane), trihydroxymethylpropane ethoxylate, 2-hydroxymethyl-1,3-propanediol, pentaerythritol allyl ether, and pentaerythritol.

Among the polyoxyalkylene glycols, it is particularly preferred to use polyoxy(C ₂ -C ₃ )alkylene glycols having a weight-average molecular weight of 200 to 10,000 g/mol, for example 200 to 2,000 g/mol.

Additive and Adjuvant Ingredients The compositions obtained in the present invention will typically further comprise adjuvants and additives that can impart improved properties to the compositions. For example, such adjuvants and additives can impart one or more of the following properties: improved elastic properties; improved elasticity recovery; longer open-process time; faster cure time; and lower residual viscosity. Such adjuvants and additives include: non-polymerizable electrolytes; toughening agents; conductive particles; non-conductive fillers; catalysts; plasticizers; stabilizers, including UV stabilizers; antioxidants; reactive diluents; desiccants; adhesion promoters; fungicides; flame retardants; rheological adjuvants; colorants or pastes; and/or, to a lesser extent, non-reactive diluents as appropriate.

Such adjuvants and additives may be used in desired combinations and proportions, provided that they do not adversely affect the properties and essential characteristics of the composition. Although exceptions may exist in some cases, the total amount of such adjuvants and additives should not exceed 20 wt.% of the total composition and preferably should not exceed 10 wt.% of the composition.

The presence of non-polymerizable electrolytes in the compositions of the present invention is not excluded. Exemplary electrolytes include non-polymerizable salts of cations selected from the group consisting of ammonium; pyridinium; phosphonium; imidazolium; oxazolium; guanidinium; and thiazolium. Although the anions of such non-polymerizable salts are not particularly limited, preferred anions are selected from the group consisting of halide ions; PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₃ ) ₂ N ⁻ , CF ₃ CO ₂ ^{− ,} and CCl ₃ CO ₂ ^- pseudohalides and halogen-containing compounds; carboxylic acid anions, in particular formate, acetate, propionate, butyrate and lactate; hydroxycarboxylic acid anions; pyridinate and pyrimidinate; carboxylic acid imides; bis(sulfonyl)imides and sulfonimides; sulfates, in particular methylsulfate and ethylsulfate; sulfites; sulfonates, in particular methanesulfonate; and phosphates, in particular dimethyl-phosphate, diethyl-phosphate and di-(2-ethylhexyl)-phosphate.

When included in the composition, the non-polymerizable electrolyte should be present in an amount less than 10 wt. % of the total weight of the polymerizable ionic compound (part b).

The presence of a toughening agent in the compositions of the present invention can facilitate debonding of cured adhesives. Without intending to be bound by theory, the toughening agent facilitates phase separation in the cured adhesive under an applied electric potential. Specifically, good debonding results were achieved when the compositions of the present invention comprised at least one toughening agent selected from epoxy-elastomer adducts and a toughening rubber dispersed in a matrix polymer in the form of core-shell particles.

The elastomer-containing adduct may be used alone or in combination of two or more specific adducts. Furthermore, each adduct may be independently selected from a solid adduct or a liquid adduct at a temperature of 23°C. Typically, suitable adducts are characterized by a weight ratio of epoxy to elastomer of 1:5 to 5:1, for example, 1:3 to 3:1. A guiding reference for suitable epoxy/elastomer adducts is U.S. Patent Publication 2004/0204551. Exemplary commercial epoxy/elastomer adducts useful herein include, but are not limited to, HYPDX RK8-4, available from CVC Chemical, and B-Tough A3, available from Croda Europe Limited.

The term " core-shell rubber " or CSR is used in accordance with its standard meaning in this art to refer to a rubber particle core formed from a polymer comprising an elastic or rubbery polymer as a primary component and a shell formed from a polymer graft-polymerized onto the core. The shell partially or completely covers the surface of the rubber particle core during the graft polymerization process. By weight, the core should comprise at least 50 wt.% of the core-shell rubber particle.

The core polymer material should have a glass transition temperature ( _Tg ) of no more than 0°C, and preferably a glass transition temperature ( _Tg ) of -20°C or lower, more preferably -40°C or lower, and even more preferably -60°C or lower. The shell polymer is a non-elastic, thermoplastic, or thermosetting polymer having a glass transition temperature ( _Tg ) above room temperature, preferably above 30°C, and more preferably above 50°C.

Without intending to limit the present invention, the core may comprise: diene homopolymers, such as homopolymers of butadiene or isoprene; diene copolymers, such as copolymers of butadiene or isoprene with one or more ethylenically unsaturated monomers, such as vinyl aromatic monomers, (meth)acrylonitrile, or (meth)acrylates; polymers based on (meth)acrylate monomers, such as polybutyl acrylate; and polysiloxane elastomers, such as polydimethylsiloxane and crosslinked polydimethylsiloxane.

Likewise, without intending to limit the present invention, the shell may comprise a polymer or copolymer of one or more monomers selected from the group consisting of (meth)acrylates, such as methyl methacrylate; vinyl aromatic monomers, such as styrene; vinyl cyanides, such as acrylonitrile; unsaturated acids and anhydrides, such as acrylic acid; and (meth)acrylamide. The polymer or copolymer used in the shell may have acid groups ionically crosslinked via metal carboxylates, particularly via salts that form divalent metal cations. The shell polymer or copolymer may also be covalently crosslinked via monomers having two or more double bonds per molecule.

Preferably, any included core-shell rubber particles have an average particle size (d50) of 10 nm to 300 nm, for example, 50 nm to 250 nm: particle size refers to the diameter or maximum dimension of a particle in a particle distribution and is measured by dynamic light scattering. For the sake of completeness, this application does not exclude the presence of two or more types of core-shell rubber (CSR) particles with different particle size distributions in the composition to provide a balance of key properties of the resulting cured product, including shear strength, peel strength, and resin fracture toughness.

The core-shell rubber can be selected from commercially available products, examples of which include: Paraloid EXL 2650A, EXL 2655, and EXL 2691 A available from Dow Chemical; Clearstrength® XT100 available from Arkema; Kane Ace® MX series available from Kaneka, and particularly MX 120, MX 125, MX 130, MX 136, MX 551, MX553; and METABLEN SX-006 available from Mitsubishi Rayon.

The composition of the present invention may contain conductive particles. For example, the composition may contain 0 to 10 wt.% or 0.1 to 5 wt.% of conductive particles, based on the weight of the composition.

Broadly speaking, there is no particular intention to limit the shape of the particles used as conductive fillers: acicular, spherical, elliptical, cylindrical, beaded, cubic, or flake-shaped particles may be used alone or in combination. Furthermore, it is contemplated that agglomerates of more than one particle type may be used. Similarly, there is no particular intention to limit the size of the particles used as conductive fillers. However, such conductive fillers will typically have an average volume particle size of 0.1 to 1500 μm, e.g., 1 to 1250 μm, as measured by laser diffraction/scattering methods.

Exemplary conductive particulate fillers include, but are not limited to, silver; copper; gold; palladium; platinum; nickel; gold- or silver-plated nickel; carbon black; carbon fiber; graphite; aluminum; indium tin oxide; silver-plated copper; silver-plated aluminum; metal-coated glass spheres; metal-coated fillers; metal-coated polymers; silver-coated fibers; silver-coated spheres; antimony-doped tin oxide; conductive nanospheres; silver nanospheres; aluminum nanospheres; aluminum nanospheres; copper nanospheres; nickel nanospheres; carbon nanotubes; and mixtures thereof. Particulate silver and/or carbon black are preferably used as the conductive filler.

The composition of the present invention may optionally contain a non-conductive filler. For example, the composition may contain 0 to 10 wt.% or 0.1 to 5 wt.% of non-conductive particles, based on the weight of the composition.

Broadly speaking, there is no particular intention to limit the shape of particles used as non-conductive fillers: acicular, spherical, elliptical, cylindrical, beaded, cubic, or flake-shaped particles may be used alone or in combination. Furthermore, it is contemplated that agglomerates of more than one particle type may be used. Similarly, there is no particular intention to limit the size of particles used as non-conductive fillers. However, such non-conductive fillers will typically have an average volume particle size of 0.1 to 1500 μm, e.g., 1 to 1250 μm, as measured by laser diffraction/scattering methods.

Exemplary non-conductive fillers include, but are not limited to, calcium carbonate, calcium oxide, calcium hydroxide (lime powder), precipitated and/or pyrogenic silicic acid, zeolite, bentonite, wollastonite, magnesium carbonate, diatomaceous earth, barium sulfate, aluminum oxide, clay, talc, titanium oxide, iron oxide, zinc oxide, sand, quartz, flint, mica, glass beads, glass powder, and other abrasive minerals. Organic fillers may also be used, particularly wood fiber, wood flour, sawdust, cellulose, cotton, wood pulp, sawdust, chopped grass straw, chopped hay, ground walnut shells, and other chopped fibers. Short fibers such as glass fiber, glass filament, polyacrylonitrile, carbon fiber, Kevlar fiber, or polyethylene fiber may also be added.

The pyrogenic and/or precipitated silicic acid preferably has a BET surface area of 10 to 90 m ² /g. When used, it does not cause any additional increase in the viscosity of the composition according to the invention, but does help to strengthen the cured composition.

It is also conceivable to use pyrogenic and/or precipitated silicic acids with a relatively high BET surface area, preferably 100 to 250 m ² /g, as fillers: due to the larger BET surface area, a smaller weight fraction of silicic acid is required to achieve the desired effect of strengthening the cured composition.

Hollow spheres with a mineral or plastic shell are also suitable as non-conductive fillers. For example, these spheres can be hollow glass spheres commercially available under the trademark Glass Bubbles®. Plastic hollow spheres, such as Expancel® or Dualite®, can also be used and are described in EP 0 520 426 B1: they are made of inorganic or organic materials and each have a diameter of 1 mm or less, preferably 500 µm or less.

Non-conductive fillers that impart variability to the composition may be preferred for many applications: such fillers are also described as rheological adjuvants, for example hydrogenated castor oil, fatty acid amides or expandable plastics such as PVC.

The desired viscosity of the resulting curable composition can determine the amount of filler used. With regard to the latter consideration, the total amount of filler (conductive and non-conductive) present in the composition should not prevent the composition from being readily suitable for coating the composition onto a substrate by the selected method. For example, a curable composition intended to be extrudable from a suitable dispensing device, such as a tube, should have a viscosity of 1000 to 150,000, preferably 10,000 to 100,000 mPas.

For the purposes of the present invention, a " plasticizer " is a substance that reduces the viscosity of a composition and thereby facilitates its processability. The plasticizer herein may constitute up to 10 wt.% or up to 5 wt.%, based on the total weight of the composition and is preferably selected from the group consisting of diurethanes; ethers of monofunctional, linear or branched C4-C16 alcohols, such as Cetiol OE (available from Cognis Deutschland GmbH, Düsseldorf); esters of abietic acid, butyric acid, thiobutyric acid, acetic acid, propionic acid and citric acid; esters based on nitrocellulose and polyvinyl acetate; fatty acid esters; dicarboxylic acid esters; esters of OH-carrying or epoxidized fatty acids; glycolates; benzoates; phosphates; sulfonates; trimellitic acid esters; polyether plasticizers, such as blocked polyethylene glycol or polypropylene glycol; polystyrene; hydrocarbon plasticizers; chlorinated paraffin; and mixtures thereof. It should be noted that, in principle, phthalates could be used as plasticizers, but these are not preferred due to their toxicological potential.

For the purposes of the present invention, " stabilizer " is understood to mean an antioxidant, UV stabilizer, thermal stabilizer, or hydrolysis stabilizer. The total amount of stabilizers herein may be up to 10 wt.%, or up to 5 wt.%, based on the total weight of the composition. Standard commercial examples of suitable stabilizers for use herein include: hindered phenols; thioethers; benzotriazoles; benzophenones; benzoates; cyanoacrylates; acrylates; amines of the hindered amine light stabilizer (HALS) type; phosphorus; sulfur; and mixtures thereof.

It should be noted that compounds with metal chelating properties can be used in the compositions of the present invention to help enhance adhesion of the cured adhesive to the substrate surface. Furthermore, an acetoacetate-functionalized modified resin sold by King Industries under the trademark K-FLEX XM-B301 is also suitable as an adhesion promoter.

To further increase shelf life, it is often desirable to further stabilize the compositions of the present invention with respect to moisture permeation through the use of a desiccant. It is also sometimes desirable to reduce the viscosity of the adhesive compositions of the present invention for specific applications by using a reactive diluent. The total amount of reactive diluent present will typically be 0 to 10 wt.%, e.g., 0.1 to 5 wt.%, based on the total weight of the composition.

Where the presence of solvents and non-reactive diluents is effective in adjusting the viscosity of the compositions of the present invention, their presence is not excluded. For example, but for illustration only, the compositions may contain one or more of the following: xylene; 2-methoxyethanol; dimethoxyethanol; 2-ethoxyethanol; 2-propoxyethanol; 2-isopropoxyethanol; 2-butoxyethanol; 2-phenoxyethanol; 2-benzyloxyethanol; benzyl alcohol; ethylene glycol; ethylene glycol dimethyl ether; ethylene glycol diethyl ether; ethylene glycol dibutyl ether; ethylene glycol diphenyl ether; diethylene glycol; diethylene glycol monomethyl ether; diethylene glycol monoethyl ether; diethylene glycol mono-n-butyl ether; diethylene glycol dimethyl ether; diethylene glycol diethyl ether; diethyl ether; diethylene glycol di-n-butyl ether; propylene glycol butyl ether; Propylene glycol phenyl ether; dipropylene glycol; dipropylene glycol monomethyl ether; dipropylene glycol dimethyl ether; dipropylene glycol di-n-butyl ether; N-methylpyrrolidone; diphenylmethane; diisopropylnaphthalene; petroleum distillates, such as Solvesso® products (available from Exxon); alkylphenols, such as tertiary butylphenol, nonylphenol, dodecylphenol, and 8,11,14-pentadecatrienylphenol; styrenated phenol; bisphenols; aromatic hydrocarbon resins, especially those containing phenolic groups, such as ethoxylated or propoxylated phenols; adipates; sebacates; phthalates; benzoates; organic phosphates or sulfonates; and sulfonamides.

In addition to the above, the non-reactive diluents preferably account for less than 10 wt.%, especially less than 5 wt.% or less than 2 wt.%, based on the total weight of the composition.

Methods and Applications To form the composition, the aforementioned components are combined and mixed. Importantly, this mixing results in a uniform distribution of the polymerizable electrolyte, compound b1) and/or b2) throughout the adhesive composition: This thorough and effective mixing ensures a homogeneous distribution of charged species in the resulting polymer matrix after curing, thereby providing sufficient ionic conductivity to support electrochemical reactions at the interface with the conductive substrate.

As is known in the art, to form a one-component (1K) curable composition, the components of the composition are combined and homogeneously mixed under conditions that inhibit or prevent the reaction of the reactive components: such conditions will be readily understood by those skilled in the art. Therefore, it is generally preferred that the curing agent components are not mixed manually, but rather are mixed by a machine (static or dynamic mixer), for example, in a water-free environment without intentional exposure to light, in predetermined amounts.

For two-component (2K) compositions, the reactive components are brought together and mixed in a manner that causes them to harden. For one-component (1K) and two-component (2K) compositions, the reactive compounds should be mixed under sufficient shear to obtain a homogeneous mixture. This is believed to be achievable without special conditions or special equipment. That is, suitable mixing devices may include: static mixing devices; magnetic stir bar devices; wire whisk devices; screw augers; batch mixers; planetary mixers; C.W. Brabender or Banburry® type mixers; and high shear mixers, such as blade type blenders and rotary impellers.

For small lining applications, typically with volumes of less than 2 litres, the preferred packaging for two-component (2K) compositions would be a side-by-side twin or coaxial barrel, in which two tubular chambers are arranged side by side or inside each other and sealed with pistons: actuation of these pistons causes the components to be extruded from the barrel, preferably via a tightly mounted static or dynamic mixer. For larger volume applications, the two components of the composition may be advantageously stored in drums or barrels: in this case, they are extruded by a hydraulic press, in particular with the aid of a follower plate, and supplied via pipes to a mixing device that ensures a fine and highly homogeneous mixing of the hardener and binder components. In any case, for any package, it is important that the adhesive components are disposed of in an air-tight and moisture-tight manner to allow the two components to be stored for an extended period of time, ideally 12 months or more.

Non-limiting examples of two-component dispensing apparatus and methods that may be suitable for use with the present invention include those described in U.S. Patent No. 6,129,244 and U.S. Patent No. 8,313,006.

Where applicable, two-component (2K) compositions should generally be formulated to exhibit an initial viscosity (measured immediately after mixing, e.g., up to two minutes after mixing) that does not hinder the method of applying the composition to a substrate. In addition, two-component (2K) compositions should further be formulated to exhibit a pot life of at least 30 minutes and typically at least 60 or 120 minutes, where the " pot life " is the time required for the viscosity of the curable composition to reach a value that is twice the viscosity of the freshly mixed curable composition at 20°C and 50% relative humidity.

According to the broadest process aspect of the present invention, the composition described above is applied to a substrate and then cured in situ. Before applying the compositions, it is usually advisable to pre-treat the relevant surface to remove foreign matter therefrom: if applicable, this step can help the composition to adhere thereto subsequently. Such treatments are known in the art and can be carried out in a single or multi-stage manner, consisting, for example, of one or more of the following: etching with an acid appropriate to the substrate and, if appropriate, an oxidizing agent; sonication; plasma treatment, including chemical plasma treatment, corona treatment, atmospheric plasma treatment, and flame plasma treatment; immersion in a water-based alkaline degreasing bath; treatment with an aqueous cleaning emulsion; treatment with a cleaning solvent, such as carbon tetrachloride or trichloroethylene; and water rinsing, preferably with deionized or demineralized water. In those cases where a water-based alkaline degreasing bath is used, any degreasing agent remaining on the surface should be removed by rinsing the substrate surface with deionized or demineralized water.

In some embodiments, adhesion of the coating composition of the present invention to a preferably pre-treated substrate can be enhanced by applying a primer thereto. While one skilled in the art will be able to select a suitable primer, references for guidance in selecting a primer include, but are not limited to, U.S. Patent Nos. 3,671,483, 4,681,636, 4,749,741, 4,147,685, and 6,231,990.

The composition is then applied to the preferably pretreated, optionally primed, substrate surface by conventional coating methods, such as brush coating; roller coating, for example, using a 4-coat roll apparatus in the case of solvent-free compositions or a 2-coat roll apparatus for solvent-containing compositions; doctor blade coating; printing; and spraying methods, including but not limited to air atomizing spraying, air-assisted spraying, airless spraying, and high volume low pressure spraying.

As noted above, the present invention provides a bonded structure comprising: a first material layer having a conductive surface; and a second material layer having a conductive surface, wherein a cured electrochemically debondable adhesive composition, as defined above and in the appended claims, is disposed between the first and second material layers. To produce such a structure, the adhesive composition may be applied to at least one inner surface of the first and/or second material layers, and the two layers are then optionally brought into contact under applied pressure, such that the electrically debondable adhesive composition is interposed between the two layers.

It is recommended that the composition be applied to the surface at a wet film thickness of 10 to 5000 μm, for example 50 to 2500 μm. Applying thinner layers within this range is more economical and offers the potential to reduce harmful thicker cured areas. However, strict control must be exercised when applying thinner layers to avoid the formation of discontinuous cured films and short contacts.

The curing of the coating composition of the present invention is generally carried out at a temperature in the range of 40°C to 200°C, preferably 50°C to 190°C and in particular 60°C to 180°C. The suitable temperature depends on the specific compounds present and the desired curing rate and can be determined in individual cases by a person skilled in the art, if necessary using simple preliminary tests. Of course, curing at lower temperatures within the aforementioned range is advantageous because it does not require significant heating or cooling of the mixture from the ambient temperature that usually prevails. However, where applicable, the temperature of the mixture formed from the individual components of the composition can be raised to above the mixing temperature and/or coating temperature using known means including microwave induction.

The present invention will be described with reference to the accompanying drawings, in which: Figure 1a depicts a bonded structure according to a first embodiment of the present invention. Figure 1b depicts a bonded structure according to a second embodiment of the present invention. Figure 2a depicts initial debonding of the structure of the first embodiment after a voltage is applied to the structure. Figure 2b depicts initial debonding of the structure of the second embodiment after a voltage is applied to the structure.

As shown in the accompanying Figure 1a, a bonded structure is provided in which a layer of cured adhesive (10) is disposed between two conductive substrates (11). A layer of non-conductive material (12) may be disposed on the conductive substrates (11) to form a more complex bonded structure as depicted in Figure 1b. The layers of the conductive substrates (11) are in electrical contact with a power source (13), which may be a battery or an AC driven direct current (DC) power source. The positive and negative terminals of the power source (13) are shown in a fixed position, but those skilled in the art will recognize that the polarity of the system can be reversed.

The two conductive substrates (11) are shown in the form of layers that can be composed, inter alia, of: a metal film; a metal grid or lattice; deposited metal particles; a resin material that exhibits conductivity by means of conductive elements disposed therein; or a conductive oxide layer. Exemplary conductive elements include silver filaments, single-walled carbon nanotubes, and multi-walled carbon nanotubes. Exemplary conductive oxides include doped indium oxides, such as indium tin oxide (ITO); doped zinc oxide; antimony tin oxide; cadmium succinate; and zinc succinate. In addition to the selection of conductive materials, those skilled in the art will recognize that the effectiveness of the debonding operation may be diminished where the conductive substrate (11) is in the form of a grid or mesh that provides limited contact with the cured adhesive layer (10).

When a voltage is applied between the conductive substrates (11), a current is supplied to the adhesive composition (10) disposed therebetween. This induces electrochemical reactions at the interfaces of the substrates (11) and the adhesive composition, which are understood to be oxidation at the positively charged or anodic interface and reduction at the negatively charged or cathodic interface. These reactions are believed to weaken the adhesive bond between the substrates, allowing the debondable composition to be easily removed from the substrates.

For illustrative purposes only, as depicted in Figures 2a and 2b, debonding occurs at the positive interface, i.e., the interface between the adhesive composition (10) and the conductive surface (11) in electrical contact with the positive electrode. By reversing the direction of the current flow before separating the substrates, the adhesive bond at the interface between the two substrates can be weakened.

However, it should be noted that the composition of the adhesive layer (10) can be adjusted so that debonding occurs at the positive interface or the negative interface or both. For some embodiments, applying a voltage across the two surfaces to form an anode interface and a cathode interface will cause debonding to occur simultaneously at both the anode and cathode adhesive/substrate interfaces. In an alternative embodiment, if the composition does not respond to direct current at both interfaces, opposite polarities can be used to debond both substrate/adhesive interfaces simultaneously. The current can be applied in any suitable waveform, with the limitation that the total time allowed for debonding to proceed at each polarity is sufficient. In this regard, sinusoidal, rectangular, and triangular waveforms may be suitable and may be applied by a controlled voltage or controlled current source.

Without intending to limit the present invention, it is believed that the debonding operation can be effectively performed when at least one, and preferably both, of the following conditions are activated: a) applying a voltage of 1 to 100 V, such as 20 to 50 V; and b) applying the voltage for a duration of 1 second to 180 minutes, such as 1 second to 30 minutes. In cases where the self-curing adhesive peeling of the conductive substrate is promoted by applying a force, such as a weight or a spring, the potential may only need to be applied for a few seconds.

The following examples illustrate the present invention and are not intended to limit the scope of the invention in any way.

EXAMPLES The following substances and their abbreviations were used in the examples: MMA: methyl methacrylate MAA: methacrylate EGDMA: ethylene glycol dimethacrylate PEG-MEA: polyethylene glycol methyl ether acrylate BENZYL MA: benzyl methacrylate HEMA: (hydroxyethyl) methacrylate IBOA: isobutyl acrylate AIBN: azobisisobutyronitrile, purchased from Sigma Aldrich BPO: benzoyl peroxide, purchased from PanReac AppliChem HEXMIM StSO3: 3-methyl-1-hexyl-1H-imidazolium 4-vinylbenzenesulfonate EMIM acrylate: 1-ethyl-3-methyl-1H-imidazolium acrylate ViEIM NTf2: 3-vinyl-1-ethyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide BMIM NTf2: 3-methyl-1-butyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide PEG400: polyethylene glycol available from Sigma Aldrich. CN966H90: An aliphatic polyester urethane diacrylate oligomer blended with 10% 2(2-ethoxyethoxy)ethyl acrylate, available from Sartomer SR9054: An acid acrylate adhesion promoter available from Sartomer Preparation of the first set of formulations: Formulations EDA1 to EDA14 described in Tables 1a and 1b below plus controls 1, 2, and 3 were formed by mixing. Table 1a Element Control 1 (g) EDA1 (g) EDA2 (g) EDA3 (g) EDA4 (g) EDA5 (g) EDA6 (g) EDA7 (g) EDA8 (g) MMA 0.780 0.780 0.780 0.780 0.780 0.780 0.780 0.780 0.780 MAA 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 EGDMA 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 PEG-MEA 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 AIBN 0.061 0.073 0.073 0.077 0.069 0.065 0.069 0.069 0.061 HEXMIM StSO3 0.623 (1.78 mmol) 0.208 (0.59 mmol) 0.104 (0.30 mmol) 0.052 (0.15 mmol) 0.208 (0.59 mmol) 0.312 (0.89 mmol) ViEIM NTf2 0.717 (1.78 mmol) 0.717 (1.78 mmol) 0.359 (0.89 mmol) 0.180 (0.44 mmol) 0.240 (0.59 mmol) 0.120 (0.30 mmol) Copolymer PE 0.463 (1.16 mmol) Table 1b Element EDA9 (g) EDA10 (g) EDA11 (g) EDA12 (g) Control 2 (g) EDA13 (g) Control 3 (g) EDA14 (g) MMA 0.780 0.780 0.780 0.780 0.630 0.630 MAA 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 EGDMA 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 PEG-MEA 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 BENZYL MA 0.780 0.780 0.150 0.150 AIBN 0.061 0.061 0.061 0.073 0.039 0.047 0.057 0.065 HEXMIM StSO3 0.052 (0.15 mmol) 0.052 (0.15 mmol) 0.052 (0.15 mmol) 0.105 0.105 ViEIM NTf2 0.179 (0.44 mmol) 0.179 (0.44 mmol) 0.179 (0.44 mmol) 0.359 0.359 BMIM NTf2 0.012 0.20 carbon black 0.012 PEG-400 0.012

The parenthesized amounts of polymerizable electrolytes given in Table 1a and Table 1b are in millimoles (mmol).

Comparatives 1, 2, and 3 consist of non-ionic matrix monomers that form adhesives and do not contain any ionic species. Formulations EDA1 to EDA7, EDA9 to EDA11, and EDA13 to EDA14 are based on the copolymerization of non-ionic matrix monomers and polymerizable ionic compounds.

EDA8 is a blend of a nonionic matrix monomer and a curable polymerizable electrolyte (PE) copolymer and is obtained as follows: First, ViEIM NTf2 (0.359 g) and HexMIM StSO3 (0.104 g) are mixed with azobis(2-isobutyronitrile) (0.008 g) at 3600 rpm for 1 minute; the mixture is then cured at 80°C for 15 minutes; then the mixture is cured at 120°C for 2 hours; and finally, the cured material is mixed with the nonionic matrix monomer and azobis(2-isobutyronitrile).

EDA12 forms the reference and is based on a mixture of a non-ionic matrix monomer and a non-polymerizable ionic compound (BMIM NTf2).

The coating compositions for formulations EDA1 to EDA14 and the control were applied to 1.25 mm thick aluminum (AA6016) substrates using glass beads with diameters ranging from 100 to 200 μm as spacers. The substrates were cut into 2.5 cm × 10 cm specimens for tensile testing. Tensile lap-shear ( TLS ) testing was performed at room temperature according to ISO 4587 ( Adhesives - Determination of tensile lap - shear strength of rigid - to - rigid bonded assemblies ) (International Organization for Standardization, 2003 ). The bonding overlap area of each substrate was 2.5 cm x 1.0 cm, and the bonding thickness was 0.1 cm (40 mil). An INSTRON 3366 with a 10 kN load cell was used.

The applied adhesive composition was cured at the overlapping area by applying a temperature of 80°C for 15 minutes and 120°C for 120 minutes. The bonded structure was then stored at room temperature for 24 hours before initial tensile testing.

Example 1 After the 24-hour storage period, the tensile lap shear strength was studied before and after applying a constant potential of 50 V to the adhesive layer for 30 minutes. The results are reported in Table 2 below. Table 2 Adhesive Initial bond strength (MPa) 50 V , bonding strength after 30 minutes ( MPa ) Control 1 2.03 (± 0.59) 2.11 (± 0.28) EDA1 3.67 (± 0.56) 3.15 (± 0.06) EDA2 2.18 (± 0.36) 1.48 (± 0.20) EDA3 3.44 (± 0.31) 0 EDA4 3.07 (± 0.58) 0.71 (± 0.62) EDA5 2.63 (± 0.51) 1.10 (± 0.23) EDA6 2.66 (± 0.34) 1.71 (± 0.12) EDA7 3.85 (± 0.71) 2.80 (± 0.63) EDA8 2.09 (± 0.13) 2.08 (± 0.33) EDA9 2.61 (± 0.09) 0.97 (± 0.09) EDA10 1.98 (± 0.41) 0 EDA11 2.35 (± 0.11) 0 EDA12 (reference) 1.60 (± 0.60) 0 Control 2 1.76 (± 0.77) 1.17 (± 0.61) EDA13 2.60 (± 0.54) 1.54 (± 0.12) Control 3 1.53 (± 0.63) 2.32 (± 0.45) EDA14 2.67 (± 0.86) 0

Formulations containing polymerizable ionic compounds increase initial adhesion strength. Formulations based on copolymerization of polymerizable ionic compounds with non-ionic matrix monomers show a decrease in adhesion strength after voltage application.

Example 2 This example investigates the electrical delamination behavior of the adhesive formulation EDA5 after the 24-hour storage period by measuring the tensile lap shear strength before and after applying different constant potentials on the adhesive layer for 30 minutes. The results are reported in Table 3 below. Table 3 Adhesive Initial bond strength (MPa) 20 V , bonding strength after 30 minutes ( MPa ) 50 V , bonding strength after 30 minutes ( MPa ) 80 V , bonding strength after 30 minutes ( MPa ) control 2.03 (± 0.59) 2.11 (± 0.28) EDA5 2.63 (± 0.51) 1.59 (± 0.22) 1.10 (± 0.23) 0

Example 3 This example studies the electrical delamination behavior of the adhesive by measuring the tensile lap shear strength before and after applying a constant potential of 50 V for 30 minutes to the adhesive layer after the 24-hour storage period and after the 2-month storage period. The results are reported in Table 4 below. Table 4 Adhesive Initial bond strength (MPa) 50 V , bonding strength after 30 minutes ( MPa ) Bond strength after aging for 2 months ( MPa ) Bond strength after aging for 2 months , 50 V , 30 minutes ( MPa ) control 2.03 (± 0.59) 2.11 (± 0.28) EDA5 2.63 (± 0.51) 1.10 (± 0.23) 2.34 (± 0.03) 0.97 (± 0.42) EDA11 2.35 (± 0.11) 0 2.30 (± 0.26) 0 EDA12 (reference) 1.60 (± 0.60) 0 0 0

Formulations based on copolymerization of non-ionic matrix monomers with polymerizable ionic compounds maintained initial bond strength after two months and still showed a decrease in bond strength after application of voltage.

Preparation of the second set of formulations: The formulations EDA15 to EDA19 described in Table 5 below plus control 4 were formed under mixing. Table 5 Element Control 4 (g) EDA15 (g) EDA16 (g) EDA17 (g) EDA18 (g) Reference EDA19 (g) CN966H90 0.600 0.600 0.600 0.600 0.600 0.600 HEMA 0.340 0.340 0.340 0.340 0.340 IBOA 0.340 SR9054 0.060 0.060 0.060 0.060 0.060 0.060 BPO 0.040 0.040 0.040 0.040 0.040 0.040 HEXMIM StSO3 0.208 0.208 0.312 EMIM Acrylate 0.108 ViEIM NTf2 0.717 0.717 0.717 ViEIM MMS 0.760 BMIM NTf2 0.231

The control 4 is composed of a non-ionic matrix monomer that forms an adhesive and does not contain any ionic species. Formulations EDA15 to EDA18 are based on the copolymerization of a non-ionic matrix monomer and a polymerizable ionic compound.

EDA19 forms the reference and is based on a mixture of a non-ionic matrix monomer and a non-polymerizable ionic compound (BMIM NTf2).

The coating compositions for formulations EDA15 to EDA19 and control 4 were applied to 1.25 mm thick aluminum (AA6016) and 1.5 mm thick stainless steel (1.4301). Glass beads with diameters of 100 to 200 μm were used as spacers. The substrates were cut into specimens measuring 2.5 cm × 10 cm (1" × 4") for tensile testing. Tensile lap shear (TLS) testing was performed at room temperature according to ISO 4587 ( Adhesives - Determination of tensile lap shear strength of rigid-to-rigid bonds ) (ISO, 2003). The bonding overlap area of each substrate was 2.5 cm × 1.0 cm, and the bonding thickness was 0.1 cm (40 mil). A Zwick Z020 with a 20 kN load cell was used.

The applied adhesive composition was cured at the overlapping area by applying a temperature of 80°C for 15 minutes and 120°C for 30 minutes. The bonded structure was then stored at room temperature for 24 hours before initial tensile testing.

Example 4 The tensile lap shear strength was studied after the 24-hour storage period before and after applying a constant potential of 50 V to the adhesive layer for 30 minutes. The results are reported in Table 6 below. Table 6 Adhesive aluminum stainless steel Initial bond strength (MPa) 50 V , bonding strength after 30 minutes ( MPa ) Initial bond strength (MPa) 50 V , bonding strength after 30 minutes ( MPa ) Control 4 11.02 (± 0.39) 11.19 (± 0.46) 11.05 (± 0.54) 10.58 (± 0.10) EDA15 12.38 (± 0.64) 0 9.19 (± 1.03) 0 EDA16 9.76 (± 0.17) 4.39 (± 0.12) Not measured Not measured EDA17 5.82 (± 0.14) 0 Not measured Not measured EDA18 10.54 (± 0.04) 2.86 (± 0.03) Not measured Not measured EDA19 6.03 (± 0.39) 0 6.46 (± 0.62) 0

Formulations EDA15 and EDA18, which contain polymerizable ionic compounds, maintained their initial bond strength, while the initial strength of formulation EDA17 decreased. Formulation EDA19, which contains a non-polymerizable ionic liquid, experienced a 50% decrease in initial strength. Formulations based on copolymerization of polymerizable ionic compounds with non-ionic matrix monomers exhibited reduced bond strength after voltage application.

Example 5 This example investigates the electrical delamination behavior of some of the above adhesives (EDA15 versus EDA19) by measuring the tensile lap shear strength before and after applying a constant potential of 50 V for 30 minutes to the adhesive layer after the 24-hour storage period and after 1 week, 1 month, 2 months, and 3 months of storage. The air-conditioned chamber used was set to 23°C and 50% relative humidity. The results are reported in Tables 7 and 8 below. Table 7 aluminum Storage time EDA15 EDA19 Initial bond strength (MPa) 50 V , bonding strength after 30 minutes ( MPa ) Bond strength after aging for 2 months ( MPa ) Bond strength after aging for 2 months , 50 V , 30 minutes ( MPa ) initial 12.38 (± 0.64) 0 6.03 (± 0.39) 0 1 week 12.45 (± 0.56) 0 5.83 (± 0.38) 0 1 month 10.00 (± 0.88) 0 4.48 (± 0.95) 0 2 months 10.94 (± 0.20) 0 4.18 (± 0.16) 0 3 months 11.03 (± 1.43) 0 Not measured Not measured Table 8 stainless steel Storage time EDA15 EDA19 Initial bond strength (MPa) 50 V , bonding strength after 30 minutes ( MPa ) Bond strength after aging for 2 months ( MPa Aging , 2 months 50 V , bond strength after 30 minutes ( MPa ) initial 9.19 (± 1.03) 0 6.46 (± 0.62) 0 1 week 9.38 (± 0.69) 0 5.46 (± 0.33) 0 1 month 9.09 (± 1.75) 0 4.25 (± 0.30) 0 2 months 8.51 (± 0.51) 0 4.58 (± 0.21) 0 3 months 8.13 (± 0.28) 0 Not measured Not measured

Formulation EDA15, based on a copolymer of a non-ionic matrix monomer and a polymerizable ionic compound, showed a slight decrease in bond strength (12%) after three months. Formulations based on a mixture of a non-polymerizable ionic liquid and a non-ionic matrix monomer exhibited a larger decrease in bond strength of 30% to both aluminum and stainless steel after two months. All formulations showed a decrease in bond strength after voltage application.

In view of the foregoing description and examples, it will be obvious to those skilled in the art that equivalent modifications can be made without departing from the scope of the claimed patent.

10: Cured adhesive layer/adhesive composition 11: Conductive substrate/conductive surface 12: Non-conductive material layer 13: Power supply

The present invention will be described with reference to the accompanying drawings, in which: Figure 1a depicts a bonded structure according to a first embodiment of the present invention. Figure 1b depicts a bonded structure according to a second embodiment of the present invention. Figure 2a depicts initial debonding of the structure of the first embodiment after a voltage is applied to the structure. Figure 2b depicts initial debonding of the structure of the second embodiment after a voltage is applied to the structure.

Claims (17)

A curable and electrochemically debondable adhesive composition comprising, based on the weight of the composition, 40 to 99 wt.% of a) at least one ethylenically unsaturated and nonionic monomer; and 0.9 to 50 wt.% of b) at least one polymerizable ionic compound, wherein the polymerizable ionic compound comprises: b1) at least one compound according to formula IV: and/or b2) at least one compound according to formula V: wherein: R ⁷ is selected from: C ₁ -C ₃₀ alkyl; C ₂ -C ₈ alkenyl; C _{1 -C 30} heteroalkyl; C ₃ -C ₃₀ cycloalkyl; C ₆ -C ₁₈ aryl; C ₁ -C ₉ heteroaryl; C _{7 -C 18} alkaryl; C _{2 -C 5} heterocycloalkyl; or -R ^a -C(=O)-R ^b , wherein R ^a is C ₁ -C ₆ alkylene and R ^b is C ₁ -C ₆ alkyl; each R ⁸ is independently selected from H, C ₁ -C ₁₈ alkyl, C ₁ -C ₁₈ heteroalkyl, C ₃ -C ₁₈ cycloalkyl, C ₆ -C ₁₈ aryl, C ₁ -C ₉ heteroaryl, C _{7 -C 18} alkaryl or C ₂ -C R ₉ is H or C ₁ -C ₄ alkyl; each R ¹⁰ is ^{independently} selected from: C ₁ -C ₃₀ alkyl; C ₁ -C ₃₀ heteroalkyl; C _{3 -} C ₃₀ cycloalkyl; C ₆ -C ₁₈ aryl; C ₁ -C ₉ heteroaryl; C _{7 -} C ₁₈ alkaryl; C _{2 -} C ₅ heterocycloalkyl; or -R ^a -C(=O)-R ^b , wherein R ^a is C ₁ -C ₆ alkylene and R ^b is C ₁ -C ₆ alkyl; A is a non-polymerizable anion; T is an ethylenically unsaturated anion selected from itaconate; maleate; crotonate; isocrotonate; vinylbenzoate; 2-acrylamido-2-methylpropanesulfonate; sulfoethyl(meth)acrylate; sulfopropyl(meth)acrylate; sulfomethylated acrylamide; allylsulfonate; vinylsulfonate; 4-vinylbenzenesulfonate; 4-isopropenylbenzenesulfonate; allylphosphonate; and monoacryloxyethylphosphate; d and m are each an integer having a value of at least 1; e and n have values such that the compound is electrically neutral; and, is a covalent bond, a C ₁ -C ₂ alkylene group, -CH ₂ OC(=O)-, -CH ₂ CH ₂ OC(=O)-, p-benzyl or p-tolyl; and 0.1 to 10 wt.% of c) at least one free radical initiator. The adhesive composition of claim 1, comprising: 45 to 95 wt.% of a) the at least one ethylenically unsaturated and nonionic monomer; 5 to 30 wt.% of b) the at least one polymerizable ionic compound; 0.1 to 5 wt.% of c) the at least one free radical initiator; and 0 to 10 wt.% of d) a solubilizer. The adhesive composition of claim 1 or 2, wherein part a) comprises 40 to 95 wt.% of a1) at least one (meth)acrylate monomer represented by formula I: _H2C = _CGCO2R1 (I ⁾ wherein: G is hydrogen, halogen or _C1 - _C4 alkyl; and ^R1 is selected from: _C1 - _C30 alkyl; _C2 - _C30 heteroalkyl _; C3- _C30 cycloalkyl; C2- _C8 heterocycloalkyl; _{C2 - C20} alkenyl; and _C2 - _C12 alkynyl. The adhesive composition of claim 1 or 2, wherein part a) comprises up to 50 wt.% of a3) at least one (meth)acrylate-functional oligomer, based on the weight of the composition. The adhesive composition of claim 4, wherein part a) comprises 5 to 25 wt.% of a3) at least one (meth)acrylate functional oligomer, based on the weight of the composition. The adhesive composition of claim 1 or 2, wherein part a) comprises at least one α,β-ethylenically unsaturated monocarboxylic acid having 3 to 5 carbon atoms. The adhesive composition of claim 1 or 2, wherein in part b): R ⁷ is selected from: C ₁ -C ₈ alkyl; C ₂ -C ₄ alkenyl; C ₁ -C 8 _heteroalkyl ; C _{3 -C 12} cycloalkyl; C ₆ -C ₁₈ aryl; C ₁ -C ₉ heteroaryl; C _{7 -C 18} alkaryl; C _{2 -C 5} heterocycloalkyl; or -R ^a -C(=O)-R ^b , wherein R ^a is C ₁ -C ₄ alkylene and R ^b is C ₁ -C ₄ alkyl; each R ⁸ is independently selected from H or C ₁ -C ₂ alkyl; R ⁹ is H or methyl; and R ¹⁰ is selected from C ₁ -C ₈ alkyl; C ₁ -C ₈ heteroalkyl; C _{3 -C 12} cycloalkyl; C ₆ -C C ₁ -C ₉ heteroaryl; C _{7 -C 18} alkaryl; C _{2 -C 5} heterocycloalkyl; or -R ^a -C(═O)-R ^b , wherein R _a is C ₁ ^-C ₄ alkylene and R ^b is C ₁ -C ₄ alkyl. The adhesive composition of claim 1 or 2, wherein part b) comprises: b1) at least one compound selected from the group consisting of: 3-vinyl-1-methyl-1H-imidazolium iodide; 3-vinyl-1-methyl-1H-imidazolium chloride; 3-vinyl-1-methyl-1H-imidazolium bromide; 3-vinyl-1-methyl-1H-imidazolium methanesulfonate; 3-vinyl-1-methyl-1H-imidazolium methanesulfonate; 3-vinyl-1-methyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-vinyl-1-methyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-vinyl-1-methyl-1H-imidazolium hexafluorophosphate; 3-vinyl-1-methyl-1H-imidazolium 4-methylbenzenesulfonate; 3-vinyl-1-methyl-1H-imidazolium tetrafluoroborate; 3-vinyl-1-ethyl-1H-imidazolium iodide; 3-vinyl-1-ethyl-1H-imidazolium bromide; 3-vinyl-1-ethyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-vinyl-1-ethyl-1H-imidazolium hexafluorophosphate; 3-ethyl Vinyl-1-ethyl-1H-imidazolium tetrafluoroborate; 3-vinyl-1-(1-methylethyl)-1H-imidazolium bromide; 3-(1,1-dimethylethyl)-1-vinyl-1H-imidazolium bromide; 3-vinyl-1-propyl-1H-imidazolium bromide; 3-vinyl-1-(phenylmethyl)-1H-imidazolium bromide; 1-vinyl-3-(4-methyl)-1H-imidazolium bromide phenyl)-1H-imidazolium chloride; 3-vinyl-1-(1-methylpropyl)-1H-imidazolium chloride; 1-butyl-3-vinyl-1H-imidazolium bromide; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium iodide; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium chloride; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium chloride 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium hexafluorophosphate; 3-[(4-vinylphenyl)methyl]-1-methyl-1H-imidazolium tetrafluoroborate; 3-[(4-vinylphenyl)methyl]-1-ethyl-1H-imidazolium azolium chloride; the salt of 1-[(4-vinylphenyl)methyl]-3-ethyl-1H-imidazolium and 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; 1-(3-aminopropyl)-3-[(4-vinylphenyl)methyl]-1H-imidazolium chloride; 1-butyl-3-[(4-vinylphenyl)methyl]-1H-imidazolium chloride; and/or b 2) at least one compound selected from the group consisting of: 1-methyl-3-hexyl-1H-imidazolium 4-vinylbenzenesulfonate; 1-dodecyl-3-vinyl-1H-imidazolium 4-vinylbenzenesulfonate; 1-methyl-3-propyl-1H-imidazolium 4-vinylbenzenesulfonate; and 3-ethyl-1-methyl-1H-imidazolium 4-(1-methylvinyl)benzenesulfonate. The adhesive composition of claim 1 or 2, wherein part b) comprises at least one compound selected from the group consisting of: 3-methyl-1-hexyl-1H-imidazolium 4-vinylbenzenesulfonate; 3-vinyl-1-ethyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide; and 3-methyl-1-butyl-1H-imidazolium 1,1,1-trifluoro-N-[(trifluoromethyl)sulfonyl]methanesulfonamide. The adhesive composition of claim 1 or 2, wherein part c) comprises at least one azo radical initiator selected from the group consisting of azo nitrile; azo ester; azo amide; azo amidine; azo imidazoline; and a macromolecular azo initiator. The adhesive composition of claim 1 or 2, wherein the composition comprises d) a solubilizer in an amount of up to 10 wt.% based on the weight of the composition, and the solubilizer is selected from the group consisting of: polyoxyalkylene glycol; polysilicone surfactant; polyol; and sugar. The adhesive composition of claim 1 or 2, wherein the composition comprises conductive particles in an amount of up to 10 wt.% based on the weight of the composition. The adhesive composition of claim 12, wherein the conductive particles are selected from the group consisting of silver, carbon black, and mixtures thereof. A bonding structure comprising a first material layer having a conductive surface; and a second material layer having a conductive surface; wherein the curable and electrochemically debondable adhesive composition of any one of claims 1 to 13 is disposed between the first material layer and the second material layer. A method for debonding a bonded structure as claimed in claim 14, the method comprising the steps of: 1) applying a voltage to two surfaces to form an anode interface and a cathode interface; and 2) debonding the surfaces. The method of claim 15, wherein the voltage applied in step 1 is 0.5 to 200 V. The method of claim 16, wherein the voltage is applied continuously for 1 second to 30 minutes.