HK1163140A - Fluorosulfonates - Google Patents

Description

Fluorosulfonate salt

Technical Field

The present invention relates to a process for the dispersion polymerization of fluorinated monomers in an aqueous polymerization medium in the presence of fluorosulfonate surfactants.

Background

Dispersion processes for polymerizing fluoroolefin monomers in aqueous media are well known. Such processes use surfactants to provide stability to the resulting aqueous dispersion of fluoropolymer particles. Due to the effect of surfactants on reaction rate, dispersed fluoropolymer particle size, dispersion stability, color, etc., different surfactants are selected for use in the dispersion polymerization reaction.

In WO2005/121290 Kappler and Lina disclose a process for preparing fluoropolymers by polymerizing an aqueous dispersion of vinylidene fluoride, the dispersion comprising a fluorosurfactant selected from one or more of the following: r_f(CH₂CF₂)m-₁-(CH₂)_nCO₂M[1]R_f(CH₂CF₂)mSO₂M[2]R_f(CH₂CF₂)m(CH₂)_nSO₂M[3]Wherein R is_fIs a linear or branched perfluoroalkyl group containing 1 to 5 carbon atoms, M is an integer from 2 to 6, n is an integer from 0 to 2, and M is a hydrogen atom or an alkali metal atom or an ammonium group containing at least one lower alkyl substituent.

Polymerization of other monomers, such as tetrafluoroethylene with hexafluoropropylene or perfluoro (methyl vinyl ether), is very sensitive to chain transfer during polymerization. As proposed in WO2005/121290, vinylidene fluoride is less sensitive to such chain transfer. It would be desirable to have a polymerization process that uses surfactants containing low levels of fluorine that can be used with these more sensitive monomers.

It is also known that fluorocarbon "tails" present in the hydrophobic segment of surfactants provide extremely low surface energies. Such fluorinated surfactants are more surface active than their hydrocarbon counterparts. For surfactants with fluorochemical chains, the longer the perfluoroalkyl chain, the higher the percentage of fluorine contained, and the better the performance provided generally, at a given concentration. However, fluorinated materials derived from longer perfluoroalkyl chains are relatively expensive. Therefore, it is desirable to reduce the fluorine content while delivering the same or better performance.

The present invention provides a polymerization process using a surfactant containing a small amount of fluorine, which is effective for monomers sensitive to chain transfer.

Summary of The Invention

The invention comprises a process comprising polymerizing in an aqueous medium at least one fluorinated olefin monomer other than vinylidene fluoride in the presence of a compound of formula (1):

R_f(CH₂CF₂)_m-(CH₂)_nSO₃M (1)

wherein

Rf is C₁To C₄A linear or branched perfluoroalkyl group,

m is an integer of 1 to 6,

n is a number from 0 to 4,

m is H, NH₄Li, Na or K.

The invention also comprises a method of modifying the surface behaviour of a liquid, which method comprises adding to the liquid a composition of a compound of formula (1) as defined above.

Detailed Description

The process according to the present invention comprises polymerizing at least one fluorinated olefin monomer other than vinylidene fluoride in an aqueous medium comprising an initiator and a polymerization agent comprising a compound of formula (1):

R_f(CH₂CF₂)_m-(CH₂)_nSO₃M (1)

wherein

Rf is C₁To C₄A linear or branched perfluoroalkyl group,

m is an integer of 1 to 6,

n is a number from 0 to 4,

m is H, NH₄Li, Na or K.

One advantage of using fluorosulfonate surfactants of formula (1) in dispersion polymerization processes is that with reduced concentrations of fluorinated surfactants and reduced levels of fluorine, more stable dispersions and faster polymerization rates are obtained, and "fluorine efficiency" is improved. As used herein, the term "fluorine efficiency" refers to the ability to obtain the desired polymer dispersion using a minimum amount of fluorosurfactant and using a lower level of fluorine. It has been found in the present invention that surfactants of formula (1) where m is 1 are more stable in aqueous media than the corresponding compounds where m is 2 or higher. Without being bound by theory, when M is 1, M is a less acidic hydrogen than when M is 2 or higher. Another advantage of the process of the present invention is that monomers sensitive to chain transfer can be polymerized to obtain stable fluoropolymers.

The fluorosulfonate surfactant of formula (1) used in the method of the present invention can be prepared according to the following reaction scheme 1.

Scheme 1

R_f(CH₂CF₂)_m(CH₂)_nI+KSCN→KI+R_f(CH₂CF₂)_m(CH₂)_nSCN (III)

Telomerization of vinylidene fluoride (VDF) with linear or branched perfluoroalkyl iodides is well known, see, for example, Balague et al, "Synthesis of fluorinated polymers, Part 1, Telomerization of vinylidine fluoride with perfluorinated ethylene oxide" (J.Fluor. chem., 1995, 70(2), 215-23). The particular telomer iodides can be isolated by fractional distillation. The telomer iodides R obtained are treated with ethylene by the process described in U.S. Pat. No. 3,979,469_f(CH₂CF₂)_mI, obtaining telomer ethylene iodides R_f(CH₂CF₂)_m(CH₂)_nI(II)。R_f(CH₂CF₂)_m(CH₂)_nI reacts with potassium thiocyanate and methyl trioctyl ammonium chloride in water to obtain telomer ethylene thiocyanate R_f(CH₂CF₂)_m(CH₂)_nSCN (III). Chlorine gas was then added to the mixture of telomeric ethylene thiocyanate and acetic acid. The product obtained is Rf (CH)₂CF₂)_m(CH₂)_nSO₂Cl (IV), which is subsequently treated with methanol to give the product R_f(CH₂CF₂)_m(CH₂)_nSO₃H(V)。

According to the present invention, the surfactant of formula (1) is preferably sufficiently dispersed in an aqueous medium to be effectively used as a polymerization agent. As used herein, "dispersed" refers to dissolution in the case where the surfactant is soluble in the aqueous medium, or dispersion in the case where the surfactant is not completely dissolved and is present in the aqueous medium in the form of very small particles (e.g., about 1nm to about 1 micron particle size distribution). Similarly, "disperse" as used herein refers to dissolving or dispersing the surfactant such that it is dispersed as defined above. The surfactant is preferably sufficiently dispersed such that the polymerization medium containing the surfactant appears colorless and transparent or nearly colorless and transparent.

The total amount of polymeric agent used in the preferred processes according to the present invention is preferably from about 5 to about 10,000 micrograms/gram by weight of water in the aqueous medium, more preferably from about 5 to about 3000 micrograms/gram by weight of water in the aqueous medium. The total amount of polymerization agent used is even more preferably from about 0.01% to about 10% by weight based on the weight of water in the aqueous medium, still more preferably from about 0.05% to about 3% by weight, more preferably from about 0.05% to about 3% by weight based on the weight of water in the aqueous medium.

It is preferred that at least a portion of the polymerization agent is added to the polymerization reaction before the polymerization reaction begins. If added subsequently, a variety of modes of polymerization agent addition may be employed; including continuous addition throughout the polymerization, or metered or intermittent addition at a predetermined time during the polymerization. According to one embodiment of the present invention, substantially all of the polymerization agent is added to the aqueous medium prior to the start of the polymerization reaction, preferably prior to the addition of the initiator.

According to a preferred embodiment of the present invention, the polymerization agent used in the practice of the present invention is preferably substantially free of perfluoropolyether oils (i.e., perfluoropolyethers having neutral nonionic (preferably fluorine or hydrogen) end groups). By substantially free of perfluoropolyether oils, it is meant that the aqueous polymerization medium contains no more than about 10 micrograms per gram of such oil on a water basis. Thus, the fluoropolymer dispersions preferably produced are of high purity and preferably substantially free of perfluoropolyether oils. Further, in a preferred process, the polymerization medium is substantially free of fluoropolymer seed at the start of polymerization (the start point). In this preferred form of the invention, no fluoropolymer seed, i.e., small particles of separately polymerized fluoropolymer in dispersion form, is added prior to the start of the polymerization reaction.

It has been found that the polymerization agent of formula (1) used in the present invention can produce fluoropolymers and provide low levels of undispersed polymer (known as coagulum) substantially comparable to those produced using typical perfluoroalkane carboxylic acid surfactants and at high dispersed solids concentrations.

The polymerization process may be carried out as a batch, semi-batch, or continuous process in a pressurized reactor. In a batch process, all the ingredients are added to the polymerization reactor at the beginning of the reaction and allowed to react to completion before being discharged from the vessel. In a semi-batch process, one or more ingredients (e.g., monomers, initiators, surfactants, etc.) are added to the vessel during the reaction after the initial charge to the reactor. At the end of the semi-batch process, the contents were discharged from the vessel. In a continuous process, a reactor is precharged with a specified composition, then monomers, surfactant, initiator and water are continuously added to the reactor while an equal volume of reaction product is continuously removed from the reactor, and a controlled volume of reaction product is obtained within the reactor. After this initial step, the continuous process can be carried out indefinitely as long as the feed is continuously metered into the reactor and the product is removed. When a stop is desired, the feed to the reactor is stopped and the reactor is vented.

In a preferred embodiment of the present invention, the polymerization process is carried out as a batch process in a pressurized reactor. Suitable vertical or horizontal reactors for carrying out the process according to the invention are equipped with stirrers for the aqueous medium. The reactor provides for sufficient contact of gas phase monomers, such as Tetrafluoroethylene (TFE), to achieve the desired reaction rate and uniform incorporation of comonomer, if used. The reactor preferably includes a cooling jacket surrounding the reactor so that the reaction temperature can be conveniently regulated by circulation of a temperature-controlled heat exchange medium.

In a typical process, deionized and degassed water of the polymerization medium is first added to the reactor, and then the surfactant of formula (1) in acid or salt form is dispersed into the medium. The surfactant is dispersed as described above. Preferably, at least a portion of the polymerization agent (surfactant) is added to the polymerization reaction, preferably before the polymerization reaction begins. If added subsequently, various modes of polymerization agent addition may be used, including continuous addition throughout the polymerization reaction, or metered or intermittent addition at predetermined times during the polymerization reaction.

In the case of Polytetrafluoroethylene (PTFE) homopolymers and modified Polytetrafluoroethylene (PTFE), paraffin wax is usually added as a stabilizer. Suitable methods for Polytetrafluoroethylene (PTFE) homopolymers and modified Polytetrafluoroethylene (PTFE) include first pressurizing the reactor with Tetrafluoroethylene (TFE). If used, comonomers such as Hexafluoropropylene (HFP) or perfluoro (alkyl vinyl ether) (PAVE) are then added. A free radical initiator solution, such as ammonium persulfate solution, is then added. In the case of Polytetrafluoroethylene (PTFE) homopolymers and modified Polytetrafluoroethylene (PTFE), a second initiator, which is a succinic acid source such as disuccinyl peroxide, may be present in the initiator solution to reduce coagulum. Alternatively, redox initiator systems such as potassium permanganate/oxalic acid may be used. The temperature is raised and, as soon as the polymerization begins, additional Tetrafluoroethylene (TFE) is added to maintain the pressure. The start of the polymerization reaction is referred to as the onset point and is defined as the time at which a significant drop in gaseous monomer feed pressure, for example, of about 10psi (about 70kPa) is observed. Comonomers and/or chain transfer agents may also be added as the polymerization proceeds. For certain polymerizations, additional monomers, initiators, and/or polymerization agents may be added during the polymerization.

After the batch dispersion polymerization reaction is complete (typically several hours), when the desired amount of polymer or solids content has been obtained, the feeds are stopped, the reactor is vented and purged with nitrogen, and the raw dispersion in the vessel is transferred to a cooling vessel.

The solids content of the dispersion at the completion of the polymerization reaction may vary depending on the intended use of the dispersion. For example, the process of the present invention can be used to prepare "seed" dispersions having a low solids content, e.g., less than 10% by weight, which can be used as "seeds" for subsequent polymerization processes to obtain higher solids content. In other processes, the fluoropolymer dispersion produced by the process of the present invention preferably has a solids content of at least about 10 weight percent. More preferably, the fluoropolymer solids content is at least about 20 wt%. The solids content of the fluoropolymer produced by the process preferably ranges from about 14 wt.% to about 65 wt.%, even more preferably from about 20 wt.% to about 55 wt.%, and most preferably from about 35 wt.% to about 55 wt.%.

In a preferred process of the present invention, the polymerization reaction produces less than about 10 weight percent undispersed fluoropolymer (coagulum), more preferably less than 3 weight percent, even more preferably less than 1 weight percent, and most preferably less than about 0.5 weight percent, based on the total weight of fluoropolymer produced.

The polymeric dispersions may be stabilized with anionic, cationic or nonionic surfactants for certain uses. Typically, however, the virgin polymer dispersion is transferred to a dispersion concentration operation which produces a concentrated dispersion that is typically stabilized with a nonionic surfactant by known methods. The solids content of the concentrated dispersion is typically from about 35 to about 70 weight percent. Certain grades of Polytetrafluoroethylene (PTFE) dispersions may be prepared for use in producing fine powders. For this purpose, the dispersion is coagulated, the aqueous medium is removed and Polytetrafluoroethylene (PTFE) is dried to produce a fine powder.

The dispersion polymerization of melt-processible copolymers is similar except that a significant amount of comonomer is added to the batch initially and/or incorporated during polymerization. Chain transfer agents are typically used in significant amounts to reduce molecular weight to increase melt flow rate. The same dispersion upconcentration operation can be used to produce a stable upconcentrated dispersion. Alternatively, for melt-processible fluoropolymers that can be used as molding resins, the dispersion is coagulated and the aqueous medium is removed. The fluoropolymer is dried and then processed into a convenient form such as flakes, chips or pellets for use in subsequent melt processing operations.

The process of the present invention may also be carried out as a semi-batch or continuous process in a pressurized reactor. These processes are particularly useful for preparing fluorocarbon elastomers. In the semi-batch emulsion polymerization process of the present invention, a gaseous monomer mixture (initial monomer feed) of the desired composition is fed into a reactor containing an aqueous medium pre-load. Other ingredients such as initiators, chain transfer agents, buffers, bases and surfactants may be added to the preload along with the water and may also be added during the polymerization reaction. During the polymerization reaction, other monomers are added at a rate necessary to maintain the system pressure in concentrations commensurate with the desired final polymer composition. Polymerization times in the range of about 2 to about 30 hours are typically employed in semi-batch polymerization processes. In a continuous process, the reactor is completely filled with an aqueous medium so that no vapor space exists. A solution of gaseous monomers and other ingredients such as water soluble monomers, chain transfer agents, buffers, bases, polymerization initiators, surfactants, etc. are fed into the reactor in separate streams at constant rates. The feed rate is controlled so that the average polymer residence time in the reactor is generally between 0.2 to about 4 hours, depending on the monomer reactivity. The polymerization temperature is maintained in the range of about 25 deg.C to about 130 deg.C for both types of processes, preferably in the range of about 50 deg.C to about 100 deg.C for semi-batch operation, and preferably in the range of about 70 deg.C to about 120 deg.C for continuous operation. The polymerization pressure is controlled in the range of about 0.5 to about 10MPa, preferably about 1 to about 6.2 MPa. The amount of fluoropolymer formed is approximately equal to the incremental feed amount added and is in the range of about 10 to about 30 parts by weight fluoropolymer per 100 parts by weight of the aqueous emulsion, preferably in the range of about 20 to about 30 parts by weight fluoropolymer.

According to the present invention, the polymerization reaction uses a radical initiator capable of generating radicals under polymerization conditions. The initiator used in the present invention is selected according to the type of fluoropolymer and the desired characteristics to be obtained, such as end group type, molecular weight, etc., as is well known in the art. For certain fluoropolymers, such as melt-processible Tetrafluoroethylene (TFE) copolymers, water-soluble salts of inorganic peracids are used that produce anionic end groups in the polymer. Such preferred initiators have a long half-life, preferably persulfate salts, such as ammonium persulfate or potassium persulfate. To shorten the half-life of persulfate initiators, reducing agents such as ammonium bisulfite or sodium metabisulfite, whether or not metal catalyst salts such as Fe are present, can be used. Preferred persulfate initiators are substantially free of metal ions and most preferred are ammonium salts.

To prepare Polytetrafluoroethylene (PTFE) or modified Polytetrafluoroethylene (PTFE) dispersions for dispersion end uses, it is preferred to add small amounts of short chain dicarboxylic acids such as succinic acid or initiators that generate succinic acid such as disuccinic acid peroxide (DSP) in addition to the relatively long half-life initiators such as persulfate salts. Such short chain dicarboxylic acids are generally beneficial for reducing undispersed polymer (coagulum). To prepare Polytetrafluoroethylene (PTFE) dispersions for the production of fine powders, redox initiator systems, such as potassium permanganate/oxalic acid, are generally used.

Sufficient initiator is added to the aqueous polymerization medium to initiate the polymerization and maintain the desired reaction rate for the polymerization. At the beginning of the polymerization reaction, it is preferred to add at least a portion of the initiator. Various modes of addition may be used, including continuous addition throughout the polymerization, or metered or intermittent addition at predetermined times during the polymerization. A particularly preferred mode of operation is to pre-charge the initiator to the reactor and to continuously add additional initiator to the reactor as the polymerization proceeds. The total amount of ammonium persulfate and/or potassium persulfate used during the polymerization reaction is preferably from about 25 micrograms/gram to about 250 micrograms/gram, based on the weight of the aqueous medium. Other types of initiators, such as potassium permanganate/oxalic acid initiators, can be used in amounts and according to methods known in the art.

For the polymerization of certain types of polymers, such as melt-processible Tetrafluoroethylene (TFE) copolymers, chain transfer agents can be used in the process according to the present invention to reduce the molecular weight for the purpose of adjusting melt viscosity. Chain transfer agents useful for this purpose are those known to be useful in the polymerization of fluorinated monomers. Preferred chain transfer agents include hydrogen, aliphatic hydrocarbons having 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, halogenated hydrocarbons containing hydrogen, or alcohols. Representative examples of such chain transfer agents are alkanes such as ethane, chloroform, 1, 4-diiodoperfluorobutane and methanol.

The amount of chain transfer agent and mode of addition depends on the activity of the particular chain transfer agent and the desired molecular weight of the polymer product. Various modes of addition may be used, including a single addition before the start of the polymerization reaction, a continuous addition throughout the polymerization reaction, or a metered or intermittent addition at a predetermined time during the polymerization reaction. The amount of chain transfer agent added to the polymerization reactor is preferably from about 0.005 to about 5 weight percent, more preferably from about 0.01 to about 2 weight percent, based on the weight of the resulting fluoropolymer.

According to the present invention, there is provided as one embodiment of the invention a process comprising polymerizing an olefin fluoromonomer in an aqueous medium comprising a surfactant of formula (1). The surfactant of formula (1) is used in a process for the aqueous dispersion polymerization of olefin fluoromonomers. Water soluble initiators are generally used in amounts of about 2 to about 500 micrograms/gram by weight of water present. Examples of such initiators include ammonium persulfate, potassium persulfate, permanganate/oxalic acid, and disuccinic peroxide. The polymerization is carried out by adding water, surfactant, olefin fluoromonomer, and optionally chain transfer agent to the polymerization reactor, stirring the contents of the reactor, and heating the reactor to the desired polymerization temperature, e.g., from about 25 ℃ to about 110 ℃.

The amount of the above-mentioned surfactant of formula (1) used in the process of the present invention is within a known range, for example, from about 0.01% to about 10% by weight, preferably from about 0.05 to about 3% by weight, more preferably from about 0.05 to about 1.0% by weight, based on the water used in the polymerization reaction. The surfactant concentration useful in the polymerization process of the present invention may be above or below the critical micelle concentration (c.m.c.) of the surfactant.

As a result of the above-described aqueous dispersion polymerization of olefinic fluoromonomers, the process of the present invention provides fluoropolymer dispersions.

The fluoropolymer dispersions formed by the present invention are comprised of fluoropolymer particles made from at least one fluorinated monomer, i.e., wherein at least one monomer comprises fluorine, preferably an olefinic monomer having at least one fluorine, or a perfluoroalkyl group attached to a doubly-bonded carbon. The fluorinated monomers used in the process of the present invention are preferably independently selected from the group consisting of: tetrafluoroethylene (TFE), Hexafluoropropylene (HFP), Chlorotrifluoroethylene (CTFE), trifluoroethylene, hexafluoroisobutylene, perfluoroalkylethylene, fluorovinyl ether, Vinyl Fluoride (VF), vinylidene fluoride (VF2), perfluoro-2, 2-dimethyl-1, 3-dioxole (PDD), perfluoro-2-methylene-4-methyl-1, 3-dioxolane (PMD), perfluoro (allyl vinyl ether), and perfluoro (butenyl vinyl ether). A preferred perfluoroalkyl ethylene monomer is perfluorobutyl ethylene (PFBE). Preferred fluorovinyl ethers include perfluoro (alkyl vinyl ether) monomers (PAVE) such as perfluoro (propyl vinyl ether) (PPVE), perfluoro (ethyl vinyl ether) (PEVE), and perfluoro (methyl vinyl ether) (PMVE). Non-fluorinated olefinic comonomers such as ethylene and propylene can be copolymerized with fluorinated monomers.

Fluorovinyl ethers also include those useful for introducing functional groups into fluoropolymers. These include CF₂＝CF-(O-CF₂CFR_f)_a-O-CF₂CFR′_fSO₂F, wherein R_fAnd R'_fIndependently selected from F, Cl or a perfluorinated alkyl group having 1 to 10 carbon atoms, a ═ 0, 1, or 2. Such polymers are disclosed in U.S. Pat. No. 3,282,875 (CF)₂＝CF-O-CF₂CF(CF₃)-O-CF₂CF₂SO₂F, perfluoro (3, 6-dioxa-4-methyl-7-octenesulfonyl fluoride)) and U.S. Pat. Nos. 4,358,545 and 4,940,525 (CF)₂＝CF-O-CF₂CF₂SO₂F) In (1). Another example is perfluoro (4, 7-dioxa-5-methyl-8-nonenoic acid methyl ester) CF disclosed in U.S. Pat. No. 4,552,631₂＝CF-O-CF₂-CF(CF₃)-O-CF₂CF₂CO₂CH₃. Similar fluorovinyl ethers having nitrile, cyanate, carbamate, and phosphonate functional groups are disclosed in U.S. Pat. Nos. 5,637,748, 6,300,445, and 6,177,196.

The invention is particularly useful when preparing Polytetrafluoroethylene (PTFE) dispersions including modified polytetrafluoroethylene (modified PTFE). PTFE and modified PTFE typically have a particle size of at least about 1X 10⁸Pa · s, and at this high melt viscosity, the polymer does not flow significantly in the molten state and is therefore not a melt-processable polymer.

Polytetrafluoroethylene (PTFE) refers to self-polymerized tetrafluoroethylene in the absence of any significant comonomer. Modified PTFE refers to copolymers of Tetrafluoroethylene (TFE) with a low concentration of comonomer such that the melting point of the resulting polymer is not significantly lower than that of PTFE. The concentration of such comonomers is preferably less than 1 wt%, more preferably less than 0.5 wt%. For significant efficacy, a minimum amount of at least about 0.05 wt.% is preferably used. The modified PTFE contains a small amount of comonomer modifier which can improve film forming capability during baking (fusing), such as perfluoroolefin, notably Hexafluoropropylene (HFP) or perfluoro (alkyl vinyl ether) (PAVE), where the alkyl group contains 1 to 5 carbon atoms, with perfluoro (ethyl vinyl ether) (PEVE) and perfluoro (propyl vinyl ether) (PPVE) being preferred. Also included are Chlorotrifluoroethylene (CTFE), perfluorobutyl ethylene (PFBE), or other monomers that introduce bulky side groups into the molecule.

The present invention is particularly useful when preparing melt-processible fluoropolymer dispersions. By melt-processible, it is meant that the polymer can be processed in the molten state (i.e., fabricated from the melt into shaped articles such as films, fibers, and tubes, etc., that exhibit sufficient strength and toughness to be useful for their intended use) using conventional processing equipment such as extruders and injection molders. Examples of such melt-processible fluoropolymers include homopolymers such as polychlorotrifluoroethylene, or copolymers of Tetrafluoroethylene (TFE) and at least one copolymerizable fluorinated monomer (comonomer) typically present in the polymer in an amount sufficient to reduce the melting point of the copolymer significantly below that of the Tetrafluoroethylene (TFE) homopolymer Polytetrafluoroethylene (PTFE), for example to a melting temperature of no more than 315 ℃.

Melt-processible Tetrafluoroethylene (TFE) copolymers typically incorporate an amount of comonomer into the copolymer to provide a copolymer having a Melt Flow Rate (MFR) of about 1-100g/10min, as determined according to ASTM D-1238 at the temperature standard for the particular copolymer. The melt viscosity is preferably at least about 10 as measured at 372 deg.C by ASTM D-1238 modified as described in U.S. Pat. No. 4,380,618²Pa · s, more preferably at about 10²Pa s to about 10⁶Pa s range, most preferably about 10³To about 10⁵Pa · s. Other melt-processible fluoropolymers are copolymers of ethylene (E) or propylene (P) with Tetrafluoroethylene (TFE) or Chlorotrifluoroethylene (CTFE), in particular Ethylene Tetrafluoroethylene (ETFE), Ethylene Chlorotrifluoroethylene (ECTFE) and Propylene Chlorotrifluoroethylene (PCTFE). Preferred melt-processible copolymers useful in the practice of the present invention comprise at least about 40 to 98 mole percent tetrafluoroethylene units and about 2 to 60 mole percent of at least one other monomer. Preferred comonomers with Tetrafluoroethylene (TFE) are perfluoroolefins having 3 to 8 carbon atoms, such as Hexafluoropropylene (HFP) and/or perfluoro (alkyl vinyl ether) (PAVE), wherein the linear or branched alkyl group contains 1 to 5 carbon atoms. Preferred PAVE monomers are those in which the alkyl group contains 1, 2, 3 or 4 carbon atoms, and the copolymer can be made using several PAVE monomers.

Preferred Tetrafluoroethylene (TFE) copolymers include 1) tetrafluoroethylene/hexafluoropropylene (TFE/HFP) copolymers; 2) tetrafluoroethylene/perfluoro (alkyl vinyl ether) (TFE/PAVE) copolymer; 3) tetrafluoroethylene/hexafluoropropylene/perfluoro (alkyl vinyl ether) (TFE/HFP/PAVE) copolymer, wherein the perfluoro (alkyl vinyl ether) is perfluoro (ethyl vinyl ether) or perfluoro (propyl vinyl ether); 4) melt-processible tetrafluoroethylene/perfluoro (methyl vinyl ether)/perfluoro (alkyl vinyl ether) (TFE/PMVE/PAVE) copolymer wherein the alkyl group of perfluoro (alkyl vinyl ether) (PAVE) has at least two carbon atoms; and 5) tetrafluoroethylene/hexafluoropropylene/vinylidene fluoride copolymer (TFE/HFP/VF 2).

Also useful polymers are film-forming polymers of polyvinylidene fluoride (PVDF), and copolymers of vinylidene fluoride and polyvinyl fluoride (PVF), and copolymers of vinyl fluoride.

The invention is also useful when preparing dispersions of fluorocarbon elastomers. These elastomers typically have a glass transition temperature below 25 ℃ and exhibit little or no crystallinity at room temperature. The fluorocarbon elastomeric copolymers produced by the process of the present invention typically comprise 25 to 70 weight percent copolymerized units of a first fluorinated monomer, which may be vinylidene fluoride (VF2) or Tetrafluoroethylene (TFE), based on the total weight of the fluorocarbon elastomer. The residual units in the fluorocarbon elastomer may be comprised of one or more other comonomers different from the first monomer, selected from the group consisting of: fluorinated monomers, alkyl olefins, and mixtures thereof. The fluorocarbon elastomers made by the process of the present invention may also optionally comprise one or more cure site monomer units. The copolymerized cure site monomer, if present, is typically present at a level of from 0.05 to 7 weight percent based on the total weight of the fluorocarbon elastomer. Examples of suitable cure site monomers include: i) a fluorinated olefin or fluorinated vinyl ether comprising bromine-, iodine-, or chlorine-; ii) a nitrile group-containing fluorinated olefin or fluorinated vinyl ether; iii) perfluoro (2-phenoxypropyl vinyl ether); and iv) a non-conjugated diene.

Preferred fluorocarbon elastomeric copolymers based on Tetrafluoroethylene (TFE) include tetrafluoroethylene/perfluoro (methyl vinyl ether) (TFE/PMVE); tetrafluoroethylene/perfluoro (methyl vinyl ether)/ethylene (TFE/PMVE/E); tetrafluoroethylene/propylene (TFE/P); and tetrafluoroethylene/propylene/vinylidene fluoride (TFE/P/VF 2). Preferred fluorocarbon elastomeric copolymers based on vinylidene fluoride (VF2) include vinylidene fluoride/hexafluoropropylene (VF 2/HFP); vinylidene fluoride/hexafluoropropylene/tetrafluoroethylene (VF 2/HFP/TFE); and vinylidene fluoride/perfluoro (methyl vinyl ether)/tetrafluoroethylene (VF 2/PMVE/TFE). Any of these elastomeric copolymers may further comprise cure site monomer units.

The present invention also provides a method of reducing the surface tension of a medium (typically a liquid), said method comprising adding to said medium a compound of formula (1) as described above. The standard surface tension of deionized water was 72 dynes/cm. The compound of formula (1) above is a fluorinated sulfonate surfactant that reduces surface tension at a specified rate. Generally, the higher the concentration of surfactant in water, the better the performance obtained. This surface tension value in the medium (typically a liquid) is less than about 25 millinewtons per meter, preferably less than about 20 millinewtons per meter at a concentration of surfactant in the medium of less than about 1 wt%.

The compounds of formula (1) above contain at least one hydrophobic moiety comprising R_fA fluoroalkyl group. Therefore, the compound is capable of reducing the surface tension at an extremely low concentration. Having R_fThe fluoroalkyl group is a hydrophobic moiety, and the compound of the present invention represented by formula (1) exhibits hydrophobic and oleophobic properties. The compound represented by formula (1) further comprises a hydrophilic moiety comprising a sulfonic acid or a salt of the acid. The hydrophilic moiety can provide effective solubility in aqueous media, and thus the compounds of the present invention represented by formula (1) exhibit surfactant properties. The compound represented by formula (1) is a fluorinated sulfonate surfactant.

Thus, the compounds of formula (1) are useful as antistatic agents in films. The compounds are distinguished by their excellent chemical stability in corrosive media, especially very acidic solutions. The compounds are also very low foaming agents. Such surfactants impart other properties. Said compounds can be used in formulations based on aggressive (highly acidic, oxidizing or reducing) media, such as in chrome plating baths. For example, such fluorosulfonate surfactants useful in the present invention can be used as special additives to improve the performance of backup valve-regulated lead acid batteries. Polyfluoroalkyl sulfonic acid was used as an electrolyte additive to improve the performance of a back-up VRLA battery as described by Torcheux in "Effect of a specific additive on the performance of a standard by value-regulated lead acid batteries" ("Journal of Power Source", Vol.78, pp.147-155 (1999)). The surfactant with high stability in sulfuric acid even at high potential used in the present invention can effectively reduce electrochemical activity at the electrode and limit corrosion and drying-out; thereby remarkably improving the performance of the battery.

The compounds of formula (1) above are suitable for providing improved surface effects to a medium to which a surfactant is added. Improved surface effects include blocking resistance, enhanced hiding (leveling), spreadability, wettability, permeability, foam inhibition, and dispersibility. The improved surface effects provided by the compounds of the present invention are suitable for many industrial applications, including aqueous coatings such as inks, paints, varnishes, and the like. For example, the fluorosulfonate surfactant of formula (1) provides surface wetting to the components to be treated and promotes the formation of a layer of foam on the surface of the chromium plating bath, preventing the generation of hazardous fuming chromic acid. In metal processing, fluorosulfonate surfactants of formula (1) are useful for cleaning, descaling, and pickling.

In particular, the surfactants of formula (1) can be used to provide excellent chemical stability in aggressive or corrosive media, especially very acidic solutions. Thus, the surfactant of formula (1) confers properties that prove useful in formulations based on highly acidic, oxidizing or reducing media. The use of shorter perfluoroalkyl groups simultaneously provides this stability, thereby providing fluorine efficiency.

Materials and test methods

Material

Tetrafluoroethylene is available from E.I.du Pont DE Nemours and Company (Wilmington, DE). Olefins are commercial grade materials and can be used as such from e.i. du Pont DE Nemours and Company (Wilmington, DE). Vinylidene fluoride is available from Solvay Solexus, Inc (West Deptford, NJ). Other reagents are commercially available, for example from Aldrich Chemical Co. (Milwaukee, Wis.). Initiator ammonium persulfate was purchased from Sigma-Aldrich Corporation (st. louis, MO).

Compound 1

Ethylene (25g, 0.53 mol) was added to the charged C₄F₉CH₂CF₂I (217g, 0.87 mol) and d- (+) -limonene (1g) in an autoclave, then the reactor was heated at 240 ℃ for 12 hours. The product C was obtained by vacuum distillation at about 81 to 91 ℃ and 19 to 24mmHg (2533 to 3200Pa)₄F₇CH₂CF₂CH₂CH₂I, yield 62%. C is to be₄F₇CH₂CF₂CH₂CH₂I (140g, 0.33 mol) was added to a mixture of ethanol (165mL) and water (165 mL). Sodium sulfite (83g, 0.66 mol) was added followed by 8g of copper. The reaction mixture was stirred vigorously under reflux for one week. 500mL of water was added and filtered at 75 ℃. The filtrate was cooled and product C was collected by filtration as a white solid₄F₇CH₂CF₂CH₂CH₂SO₃Na(112g，84％)。

¹H NMR(CDCl₃，400MHz)δ3.22～3.05(4H，m)，2.59～2.46(2H，m)

¹⁹F NMR(CDCl₃，373Hz)δ-81.44(3F，t-t，J₁＝9.7Hz，J₂＝4.1Hz)，-95.39(2F，t-t，J₁＝30.0Hz，J₂＝15.0Hz)，-112.90～-113.13(2F，m)，-124.98～-125.00(2F，m)，-126.16～-126.27(2F，m)。

Compound 2

Ethylene (25g, 0.53 mol) was added to the charged C₄F₉CH₂CF₂I (217g, 0.87 mol) and d- (+) -limonene (1g) in an autoclave, then the reactor was heated at 240 ℃ for 12 hours. The product C was obtained by vacuum distillation at about 81 to 91 ℃ and 19 to 24mmHg (2533 to 3200Pa)₄F₇CH₂CF₂CH₂CH₂I, yield 62%. Potassium thiocyanate (21.34g, 0.22 mol) was added to C₄F₇CH₂CF₂CH₂CH₂I (50g, 0.11 mol) in 50g of aqueous solution of a mixture of methyltrioctylammonium chloride (0.2222 g). The reaction was heated at 90 ℃ overnight. After phase separation, the product C is distilled off as a colorless liquid₄F₇CH₂CF₂CH₂CH₂SCN (38g, 95%). b.p.84-85 ℃/0.7 torr

¹H NMR(CDCl3，400MHz)δ3.09(2H，t，J＝8.0Hz)，2.78～2.62(2H，m)，2.50(2H，t-t，J1＝16.7Hz，J2＝6.0Hz)

¹⁹F NMR(CDCl3，373Hz)δ-81.49(3F，t-t，J1＝10Hz，J2＝3Hz)，-92.76～93.91(2F，m)，-113.09(2F，m)，-124.68～124.78(2F，m)，-126.16～126.77(2F，m)

MS：370(M⁺+1)

Chlorine (118g, 1.66 mol) and water (40g, 2.22 mol) were added to C in an autoclave at 45-50 ℃ over 10 hours₄F₇CH₂CF₂CH₂CH₂SCN (205g, 0.56 mole) and acetic acid (109g, 1.82 mole). The product from the reactor was heated in a 70 ℃ flask equipped with a stir bar and hot water (70 ℃) was added. The organic layer was separated and toluene (216.25g) was added. The product was washed twice with 3.5% saline solution in toluene at 70 ℃. After the second wash, a dean-stark trap was installed to remove water. The final product was 70 wt% C₄F₇CH₂CF₂CH₂CH₂SO₂Cl (228g, 39%) in toluene. At 70 ℃ C₄F₇CH₂CF₂CH₂CH₂SO₂Cl (7g, 0.0171 mol, 70.3% in toluene) was added dropwise to methanol (10g, 0.313 mol). After refluxing the reaction mixture overnight, methanol and toluene were distilled off. Using 70 DEG CDilution of the end product C with deionized water₄F₇CH₂CF₂CH₂CH₂SO₃H (5.2g, 77.7%) until it is 30% active.

¹H NMR(D₂O，400MHz)δ3.22～2.99(2H，m)，2.59～2.42(2H，m)

¹⁹F NMR(D₂O，377MHz)δ-81.52～81.53(2F，m)，-95.24～95.54(2F，m)，-12.88～113.30(2F，m)，-124.93～125.11(3F，m)，-126.16～126.31(2F，m)

Test method

Test method 1 surface tension measurement

The surface tension was measured using a Kruess tensiometer (model K112.501) according to the instructions of the equipment. The Wilhelmy plate method was used. A vertical plate of known perimeter was attached to the balance and the force due to wetting was measured. Ten replicates were performed for each dilution and were set up using the following instrument: the method comprises the following steps: the plate method SFT; spacing: 1.0 s; wet growth: 40.2 mm; minimum reading: 10; minimum standard deviation: 2 dynes/cm; acceleration of gravity (gr.acc): 9.80665m/s 2

Examples

Example 1

Distilled water (450mL), C was added to a 1L stainless steel reactor₄F₉CH₂CF₂CH₂CH₂SO₃Na (3.0g), disodium hydrogenphosphate (0.4g) and ammonium persulfate (0.4g), followed by Tetrafluoroethylene (TFE) (40g) and Hexafluoropropylene (HFP) (140g) were added. The reactor was heated at 70 ℃ for eight hours with stirring. With saturated MgSO₄The aqueous solution coagulates the polymer emulsion that has been unloaded from the reactor. The polymer precipitate was collected by filtration and washed several times with warm water (70 ℃). Vacuum furnace at 100 DEG CAfter drying in (100mmHg, 13300Pa) for 24 hours, 34g of a white polymer was obtained. Tm: 249.08 deg.C; composition of¹⁹F NMR (mol%): HFP/TFE (12.8/87.2)

Example 2

29.6g C₄F₉CH₂CF₂CH₂CH₂SO₃A solution of Na, 18.5g of disodium phosphate heptahydrate and 24,900g of deionized deoxygenated water was charged to a 40 liter reactor. The solution was heated to 80 ℃. After removing traces of oxygen, the reactor was pressurized with 2441 grams of a mixture of 4.2 weight percent vinylidene fluoride (VF2), 85.8 weight percent Hexafluoropropylene (HFP), and 10.0 weight percent Tetrafluoroethylene (TFE). At the end of the pressurization, the reactor pressure was 2.0 MPa. To the reactor was added 50.0mL of an initiator solution containing 1% ammonium persulfate and 5% disodium phosphate heptahydrate to initiate polymerization. As the reactor pressure was decreased, a mixture of 35.0 wt% vinylidene fluoride, 37.0 wt% hexafluoropropylene, and 28.0 wt% tetrafluoroethylene was added to the reactor to maintain a pressure of 2.0 MPa. After 45g of this monomer mixture had been charged, 26.0g of a mixture comprising 37.29 mol% of 1, 4-diiodoperfluorobutane, 46.38 mol% of 1, 6-diiodoperfluorohexane, 11.98 mol% of 1, 8-diiodoperfluorooctane and 3.76 mol% of 1, 10-diiodoperfluorodecane was charged into the reactor. Additional initiator solution was added to maintain the polymerization rate. After 3700 grams of the monomer mixture had been charged, 5.0 grams of 4-iodo-3, 3, 4, 4-tetrafluoro-1-butene (ITFB) was added to the reactor at a feed rate per 1000 grams of monomer. After a total of 8333g of main monomer had been added incrementally (corresponding to a total of 127mL of initiator solution, 20.4g of ITFB and 15.5 hours), the monomer and initiator feeds were stopped. The reactor was cooled and the pressure inside the reactor was reduced to atmospheric pressure. The resulting fluoroelastomer latex had a solids content of 24.7 wt.% solids, a pH of 4.0, and an average particle diameter of 312nm as measured by a BI-9000 particle sizer (Brookhaven Instruments Corporation) and the latex was coagulated with an aluminum sulfate solution, washed with deionized water and dried. The fluoroelastomer had an intrinsic viscosity of 0.43dl/g, a Mooney viscosity ML (1+10) of 64, and contained 34.3% by weight of VF2,36.9 wt.% HFP, 28.5 wt.% TFE, and 0.22 wt.% I.

Example 3

Compound 2, prepared by the above method, was used in surface tension measurements as described in test method 1. The results are shown in Table 1.

Comparative example A

The procedure used in example 3 above was followed, but using a catalyst having the formula F (CF)₂)₆CH₂CH₂Perfluoroalkyl ethyl alcohol of OH as the fluorine-containing compound. The product was added to water and the surface tension was determined using test method 1. The results are shown in Table 1.

Table 1: surface tension measurement

^*The examples were added to DI water by weight of additive solids; standard deviation < 1 dyne/cm; the temperature was 23 ℃.

The standard surface tension of deionized water was 72 dynes/cm.

The data in table 1 show that the surface tension of each aqueous solution is significantly reduced when the fluorosulfonic acid surfactant described above is added at the specified rate. Example 3 shows a comparable surface tension reduction to comparative example a. The surfactant of example 3 worked as effectively as comparative example a, but had a lower fluorine content and therefore a greater fluorine efficiency.

Example 4

Distilled water (450mL), C was added to a 1L stainless steel reactor₄F₉CH₂CF₂CH₂CH₂SO₃Na(4.0g), disodium hydrogen phosphate (0.4g) and ammonium persulfate (0.4g), followed by Tetrafluoroethylene (TFE) (46g) and perfluoro (methyl vinyl ether) (PMVE) (39 g). The reactor was heated at 70 ℃ for eight hours with stirring. The polymer emulsion was discharged from the reactor and saturated MgSO₄And (4) washing with an aqueous solution. The polymer precipitate was collected by filtration and washed several times with warm water (70 ℃). After drying in a vacuum oven (13300Pa) at 100 ℃ for 24 hours, 56g of a white polymer were obtained. Tg: -7.3 ℃; composition of¹⁹F NMR (mol%): PMVE/TFE (25.3/74.7).

Claims (10)

1. A process comprising polymerizing at least one fluorinated olefin monomer other than vinylidene fluoride in an aqueous medium in the presence of a compound of formula (1) to obtain an aqueous dispersion of a fluoropolymer:

R_f(CH₂CF₂)_m-(CH₂)_nSO₃M (1)

wherein

Rf is C₁To C₄A linear or branched perfluoroalkyl group,

m is an integer of 1 to 6,

n is a number from 0 to 4,

m is H, NH₄Li, Na or K.

2. The method of claim 1, wherein the compound of formula (1) is present in the aqueous medium in an amount of from about 0.01% to about 10% based on the weight of water in the aqueous medium.

3. The process of claim 1 wherein said aqueous dispersion of fluoropolymer formed has a fluoropolymer solids content of at least about 10% by weight.

4. The process of claim 1 wherein said aqueous medium is substantially free of perfluoropolyether oils and wherein said aqueous medium is substantially free of fluoropolymer seeds at the point of polymerization initiation.

5. The process of claim 1 wherein said polymerization produces less than about 10 weight percent undispersed fluoropolymer based on the total weight of fluoropolymer produced.

6. The process of claim 1 wherein said fluorinated olefin monomer is selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and perfluoro (alkyl vinyl ether).

7. The method of claim 1 wherein the fluoropolymer is an elastomer.

8. A method of modifying the surface behaviour of a liquid, the method comprising adding to the liquid a composition of a compound of formula (1):

R_f(CH₂CF₂)_m-(CH₂)_nSO₃M (1)

wherein

Rf is C₁To C₄A linear or branched perfluoroalkyl group,

m is an integer of 1 to 6,

n is a number from 0 to 4,

m is H, NH₄Li, Na or K.

9. The method of claim 8, wherein the surface behavior is selected from the group consisting of wetting, antistatic, defoaming, penetrating, spreading, leveling, flowing, emulsifying, dispersing, repelling, peeling, lubricating, etching, adhering, and stabilizing, and wherein the liquid is a coating composition, a battery composition, a fire extinguishing agent, a latex, a polymer, a floor finish, an ink, an emulsifier, a foaming agent, a peeling agent, a repelling agent, a flow modifier, a film evaporation inhibitor, a wetting agent, a penetrating agent, a cleaning agent, an abrasive, a plating agent, a corrosion inhibitor, an etchant solution, a welding agent, a dispersion aid, a microbial agent, a pulping aid, a rinse aid, a polishing agent, a personal care composition, a drying agent, an antistatic agent, a floor finish, or an adhesive.

10. The method of claim 8, wherein the liquid is a highly acidic, oxidizing or reducing medium.