DE19858103A1 - Process for living free radical polymerization - Google Patents

Abstract

The invention relates to a method for the living free-radical polymerization of one or more ethylenically unsaturated monomers by means of a free-radical polymerization initiator and in the presence of a stable N-oxyl radical. As free-radical polymerization initiator a combination of at least two different initiators having different dissociation constants kD is used.

Description

The invention relates to a method for living free radical polymers on of ethylenically unsaturated monomers in the presence of a stable N-oxyl radicals.

Radically initiated polymerizations of monomers having at least one ethylenically unsaturated group have the disadvantage that the molecular weight of the polymer chains does not normally increase with the polymerization conversion and that the polymer chains of the resulting polymer generally do not have a uniform molecular weight. This means that the available polymer is usually not monodisperse with regard to the molecular weight property, but usually has a related polydispersity index PDI of ≧ 2 (PDI = M _w / M _n , with M _w = weight-average molecular weight and M _n = number-average molecular weight ). This is presumably due in particular to termination reactions due to an irreversible combination of growing free radical polymer chain chain ends, as well as chain transfer reactions, disproportionation and elimination.

Another disadvantage of classic radical-initiated polymerization is in that a change made during polymerisation to polymeri monomers usually do not form segmented copolymers (block polymers) leads. For example, changing the monomers in the Emulsion polymerization into core / shell polymer particles, the core of which consists of one and the shell of which is composed of the other type of monomer, the core and  Basically not chemically, but only physically are bound. The phase connection of the shell to the core is therefore at classical radical polymerization is insufficient in some cases.

It is known from the prior art that the implementation of radical init ized polymerizations at temperatures above 100 ° C in the presence of a stable (essentially non-initiating) N-oxyl radical Control of the free radical initiated polymerization. For example in the prior application DE-A-198 03 098 radically initiated, aqueous Emulsion polymerizations using stable N-oxyl radicals fenbart.

The underlying mechanism of action is probably due to the fact that stable N-oxyl radicals reactive radical ends of a growing polymer Do not terminate the sat chain irreversibly at elevated temperatures, but only temporarily block. This results in a reduction in the stationary con concentration of free radical polymer chain ends, which increases the poss possibility of irreversible termination of chain growth by combination two growing polymer chain ends reduced. This leads to on average the polymerisation conversion (ideally linear) growing polymer chains. The latter causes a growth with the polymerization conversion (ideally linear) the average molecular weight of the polymer formed with an ideal with 1 lying polydispersity index PDI. At the same time, however, results from Ver Reduction of the stationary concentration of growing free radical polymers tion chain ends a very low polymerization rate.

The object of the present invention is therefore the polymerization rate to increase density without the polydispersity of the resulting polymer essential Lich increase.  

This task is accomplished by a process for living free radical polymers sation of one or more ethylenically unsaturated monomers using a radical polymerization initiator and in the presence of a stable N-oxyl radicals solved. The method according to the invention is then known is characterized by the fact that an initiator combination is the radical polymerization initiator at least two different initiators is used, in which the used Initiators have different dissociation constants.

The availability of a simple, quick, control would be radically initiated polymerization for the production of polymers advantageous in that it allows a controlled adjustment of the molecular weight of the Polymer would allow in reasonable reaction times. Furthermore it opens up direct access to block copolymers because the free radi Kalischen polymer chain ends not destroyed by combination, but single reversibly blocked. That is, after the consumption of a first monome The type can continue the polymerization with the addition of further types of monomers will.

Furthermore, by increasing the rate of polymerization at the same time taking advantage of stable N-oxyl radicals the long polyme reduced periods of risk. It is thus an economically viable application ches procedure provided.

According to the invention, the polymerization is carried out by a combination of radicals polymerization initiators initiated, the different dissociation con have a constant.

Initiators are preferably used whose dissociation constants k _D differ by a factor of 10 ² to 10 ³ . Particularly preferably, a first initiator has a dissociation constant k _D of 10 ^-2 to 10 ^-3 s ^-1 at 115 ° C and a second initiator has a dissociation constant of about 10 ^-5 s ^-1 at 115 ° C. It is very particularly preferred to use benzoyl peroxide (BPO) or 2,2'-azobisisobutyronitrile (AIBN) as the first initiator and dicumyl peroxide (DCPO) as the second initiator. The total amount of initiator is usually (1st + 2nd initiator) 0.05 to 4, preferably 0.1 to 2 and particularly preferably 0.15 to 0.8 part by weight, based on the amount of the monomers.

Usually the initiators are immediately before the start of the polymerization admitted. However, it is also possible to use the initiator continuously or in portions to add during the polymerization.

Suitable stable N-oxyl radicals according to the invention are all those Consideration mentioned in the earlier priority application DE-A-198 03 098.

Such suitable, derived from a secondary amine, stable N-oxyl radicals are, for. B. Compounds of general formula I.

therein R ¹ , R ² , R ⁵ and R ⁶ = the same or different straight or ver branched, optionally substituted alkyl groups, or
R ¹ and R ² and / or R ⁵ and R ⁶ = part of a ring system, and
R ³ and R ⁴ = the same or different straight or branched chain, optionally substituted alkyl groups or R ³ CNCR ⁴ = part of a cyclic structure with an optionally fused other saturated or aromatic ring, the cyclic structure or the aromatic ring optionally sub are established.

Examples of these are stable N-oxyl radicals of the general formula I in which R ¹ , R ² , R ⁵ and R ^{6 are} (identical or different) methyl, ethyl, n-propyl, isopropyl, n Butyl, iso-butyl, tert-butyl, linear or branched pentyl, phenyl or substituted groups thereof and R ³ and R ⁴ for (same or different) methyl, ethyl, n-propyl , iso-propyl, n-butyl, iso-butyl, tert-butyl, linear or branched pentyl, substituted groups thereof or - if R ³ CNCR ⁴ forms part of a cyclic structure - the cyclic structure

in which n = an integer from 1 to 10, preferably 1 to 6, including substi such cyclic groups. As exemplary representatives 2,2,6,6-tetramethyl-1-oxyl-piperidine, 2,2,5,5-tetramethyl-1-oxyl-pyrrolidine, 4- Hydroxy-2,2,6,6-tetramethyl-1-oxyl-piperidine and 4-oxo-2,2,6,6-tetramethyl-1-oxyl called piperidine.

The stable N-oxyl radicals can be derived from the corresponding secondary amines NEN by oxidation, e.g. B. with hydrogen peroxide. As a rule, they are can be represented as pure substance.

N-Oxyl radicals from the group of the piperidine or pyrrolidine N-oxyls and di-N-oxyls of the following general formulas II to IX are preferably used:

With
m = 2 to 10,
R ⁷ , R ⁸ , R ⁹ = independently of one another

M ^⊕ = hydrogen or an alkali metal ion (in particular K ^⊕ or Na ^⊕ ),
q = an integer from 1 to 10,
R ^{1 '} , R ^2' , R ^{5 '} , R ^6' = independently of one another and independently of R ¹ , R ² , R ⁵ , R ^{6 the} same groups as R ¹ ,
R ¹⁰ = C ₁ to C ₄ alkyl, -CH = CH ₂ , -C∼CH, -CN,

-COO ^⊖ M ^⊕ , -COOCH ₃ or -COOC ₂ H ₅ ,
R ¹¹ = an organic radical which has at least one primary, secondary (e.g. -NR ¹ ) or tertiary amino group (e.g. -NR ¹ R ² ) or at least one ammonium group -N ^⊕ R ¹³ R ¹⁴ R ^{15 has} X ^⊖ , with X ^⊖ = F ^⊖ , Cl ^⊖ , Br ^⊖ , HSO ₄ ^⊖ , SO ₄ ^{2 ⊖} , H ₂ PO ₄ ^⊖ , HPO ₄ ^{2 ⊖} or PO ₄ ^{3 ⊖} and R ¹³ , R ¹⁴ , R ¹⁵ independent organic radicals (e.g. independently of one another the same groups as R ¹ ),
R ¹² = independently of R ^{11, the} same groups as R ¹¹ or -H, -OH, C ₁ - to C ₄ -alkyl, -COO ^⊖ M ^⊕ , -C∼CH,

or hydroxy substituted C ₁ to C ₄ alkyl (e.g. hydroxyethyl or hydroxypropyl) and
R ¹³ = -H, -CH ₃ or

Preferably R ¹ = R ² = R ⁵ = R ⁶ = R ^{1 '} = R ^2' = R ^{5 '} = R ^6' = -CH ₃ .

Other stable N-oxyl radicals suitable in the process according to the invention are described in the earlier priority application DE-A-198 03 098.

A compound of the general formulas I or II is particularly preferred as stable N-oxyl radical used. The stable ones are very particularly preferred N-oxyl radicals 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), 4-hydroxy- 2,2,6,6-tetramethyl-1-piperidinyloxy (HO-TEMPO), di-tert-butyl-nitroxide (DTEN) used.

Mixtures of stable N-oxyl radicals can also be used according to the invention be set.

The molar ratio between stable N-oxyl radicals and radical Po The polymerization initiator is übli in the process according to the invention Usually 0.5 to 5, preferably 0.8 to 4.

Suitable monomers are all ethylenically unsaturated monomers that are free radical are polymerisable, ie polymerisie in the presence of so-called "free radicals" ren.

As at least one ethylenically unsaturated group having monomers come z. B. into consideration: olefins such as ethylene or propylene, vinyl aromatic monomers such as styrene, divinylbenzene, 2-vinylnaphthalene and 9-vinylanthracene, substituted vinyl aromatic monomers such as p-methylstyrene, α-methylstyrene, o-chlorostyrene, p-chlorostyrene, 2, 4-dimethylstyrene, 4-vinylbiphenyl and vinyltoluene, esters from vinyl alcohol and monocarboxylic acids containing 1 to 18 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and vinyl stearate, esters from 3 to 6 carbon atoms containing α, β- monoethylenically unsaturated mono- and dicarboxylic acids, such as in particular acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid, with Al in general having 1 to 20, preferably 1 to 12, particularly preferably 1 to 8 and very particularly preferably 1 to 4 carbon atoms kanols such as, in particular, acrylic acid and methacrylic acid, methyl, ethyl, n-butyl, isobutyl, tert-butyl and -2-ethylhexyl ester, dimethyl maleate or n-butyl maleate, the nitriles of the aforementioned nten α, β-monoethylenically unsaturated carboxylic acids such as acrylonitrile and methacrylonitrile as well as C _4-8 conjugated dienes such as 1,3-butadiene and isoprene.

Suitable styrene compounds are those of the general formula XI:

in which R 'and R "independently of one another are H or C ₁ -C ₈ -alkyl and N is 0, 1, 2 or 3.

Accordingly, ethylenically unsaturated monomers are preferably selected from in the process according to the invention

• Styrene compounds of the general formula XI,
• C ₁ to C ₂₀ alkyl esters of acrylic acid or methacrylic acid,
• - serve with conjugated double bonds,
• - Ethylenically unsaturated dicarboxylic acids and their derivatives, and
• - Used ethylenically unsaturated nitrile compounds.

Particularly preferred in the process according to the invention are the monomers styrene, α-methylstyrene, divinylbenzene, vinyltoluene, C ₁ - to C ₈ -alkyl (meth) acrylates, in particular n-butyl acrylate, 2-ethylhexyl acrylate or methyl methacrylate and butadiene, and also acrylonitrile and Monomer mixtures which are composed of at least 85% by weight of the aforementioned monomers or mixtures of the aforementioned monomers are used.

Furthermore, one can crosslink, for example, in the production of polymers use monomers. Crosslinking monomers are bifunctional or polyfunctional nelle comonomers with at least 2 olefinic double bonds, for example Butadiene and isoprene, divinyl esters of dicarboxylic acids such as succinic acid and Adipic acid, diallyl and divinyl ethers, bifunctional alcohols such as ethylene glycol and butane-1,4-diol, the esters of acrylic acid and methacrylic acid with the above bifunctional alcohols, 1,4-divinylbenzene and triallyl cyanurate. Especially be preferred are the acrylic acid ester of tricyclodecenyl alcohol, which is sold under the name Dihydrodicyclopentadienyl acrylate is known, as well as the allyl esters of acrylic acid and methacrylic acid.

The inventive method is suitable for all known methods of free radical polymerization. The method according to the invention is preferred as Mass (= bulk), solution, suspension, microsuspension, emulsion or mini Emulsion polymerization carried out. The polymerizations can be continuous or be carried out discontinuously. The used for the polymerization Equipment depends on the corresponding polymerization process.

Depending on the polymerization process, other suitable additives can be used be added. Can in a microsuspension polymerization process protective colloids suitable for stabilizing the emulsion, for example be. Such protective colloids are water-soluble polymers that form the monomers droplets and envelop the polymer particles formed from them and onto them Protect way from coagulation. Suitable protective colloids are a priority older application called DE-A-198 03 098. In an emulsion polymerization process Ren are also suitable emulsifiers for stabilizing the emulsion  admitted. These are soap-like auxiliaries that surround the monomer droplets len and thus protect against convergence.

Furthermore, additives can be added that determine the polymers Give properties. Examples of such additives are polymers, paints substances and pigments and ferromagnetic pigments.

The proportion of additives is generally at least 0.1% by weight, preferably at least 0.5 wt .-%, based on the total mass of the mixture. That invented Process according to the invention is carried out at temperatures from 0 to 200 ° C., preferably 70 to 160 ° C, particularly preferably 80 to 150 ° C. The balance between free polymer chain ends and reversibly blocked by N-oxyl radicals Chain ends are temperature dependent. At higher temperatures there is a bigger problem number of free polymer chain ends.

The polymers obtainable by the process according to the invention are available Lich the property of molecular weight almost monodisperse. The polydispersity dex PDI is generally 1.0 to 1.8, preferably 1.0 to 1.7, especially preferably at 1.0 to 1.5.

As the following examples show, the use of the invention makes one Initiator combination in the process according to the invention an increase in the polymer speed with almost constant polydispersity compared to one Process achieved in which only one initiator at the beginning of the polymerization reaction is added.

The following examples further illustrate the invention.  

example 1

0.8 g (5.13 mmol) HO-TEMPO are placed in 120 g (1.15 mol) degassed styrene Stirring dissolved. After the reaction mixture is warmed to 115 ° C a total of 0.7 g (4.27 mmol) of AIBN and DCPO (AIBN + 7.5 mol% DCPO) under Nitrogen added to start the polymerization. According to various The following diagrams for the reaction times to be taken are samples the reaction mixture is extracted and quenched in liquid nitrogen to obtain the Re stop action.

Example 2

The reaction conditions correspond to those in Example 1, with the difference that that the initiator mixture is composed of AIBN + 15 mol% DCPO.

Comparative Example 3

The reaction conditions correspond to those in Example 1, with the difference that no initiator combination but AIBN alone is used as the initiator. The sales regulations are carried out with a NETZSCH TG 209 device. For this purpose, the samples are heated in nitrogen at a rate of 20 km ^-1 from 25 to 510 ° C. The weight loss at over 275 ° C results in the polymer content or the monomer conversion.

The molecular weights are determined by means of gel permeation chromatography (GPC) on samples which are taken directly from the reaction mixture, with THF as solvent, with 1 ml min ^-1 through three Waters Ultrastyragel columns HR4, HR3 and HR1 in series and a Waters 410 R1 detector . Polystyrene is used as a standard.

The effect of using an initiator combination according to the invention on the kinetics, the molecular weight and the polydispersity of the resulting re polyme is shown in FIG. 1 and FIG. 2.

Show it:

Fig. 1 Increase in the molecular weight of the polymer with increasing conversion (the initiator ratios are molar ratios; the lines have been inserted for a better overview).

The molecular weight is Mn on the ordinate axis and on the Ab The sales (%) are given.

Fig. 2 change in the polydispersity of the resulting polymer with increasing conversion (the initiator ratios are molar ratios; the lines have been inserted for a better overview).

The polydispersity is on the ordinate axis and on the abscissa the turnover (U) specified.

Fig. 1 and 2 show that the rate of polymerization can be increased by using an initiator combination, without the polydispersity of the polymers to increase entste Henden.

Claims (10)

1. A process for living free radical polymerization of one or more ethylenically unsaturated monomers using a radical polymerization initiator and in the presence of a stable N-oxyl radical, characterized in that an initiator combination of at least two different initiators is used as the radical polymerization initiator , in which the initiators used have different dissociation constants k _D. 2. The method according to claim 1, characterized in that the dissociation constants k _D at least two of the initiators used differ by a factor of 10 ² to 10 ³ . 3. The method according to claim 2, characterized in that a first initiator has a dissociation constant k _D of 10 ^-2 to 10 ^-3 s ^-1 at 115 ° C and a second initiator a dissociation constant k _D of about 10 ^-5 s ^-1 115 ° C. 4. The method according to claim 3, characterized in that as the first initiator Benzoyl peroxide (BPO) or 2,2'-azobisisobutyronitrile (AIBN) and as second initiator dicumyl peroxide (DCPO) is used.   5. The method according to any one of claims 1 to 4, characterized in that the stable N-oxyl radical is a compound of general formula I.
With
R ¹ , R ² , R ⁵ , R ⁶ = the same or different straight or branched chain, optionally substituted alkyl groups or
R ¹ and R ² and / or R ⁵ and R ⁶ = part of a ring system, and
R ³ , R ⁴ = the same or different straight or branched chain, optionally substituted alkyl groups or R ³ CNCR ⁴ = a part of a cyclic structure with an optionally fused other saturated or aromatic ring, the cyclic structure or the aromatic ring optionally being substituted are used. 6. The method according to claim 5, characterized in that a compound of the following general formulas II to IX is used as the stable N-oxyl radical:
With
m = 2 to 10,
R ⁷ , R ⁸ , R ⁹ = independently of one another
M ^⊕ = hydrogen or an alkali metal ion (in particular K ^⊕ or Na ^⊕ ),
q = an integer from 1 to 10,
R ^{1 '} , R ^2' , R ^{5 '} , R ^6' = independently of one another and independently of R ¹ , R ² , R ⁵ , R ^{6 the} same groups as R ¹ ,
R ¹⁰ = C ₁ to C ₄ alkyl, -CH = CH ₂ , -C∼CH, -CN,
-COO ^⊖ M ^⊕ , -COOCH ₃ or -COOC ₂ H ₅ ,
R ¹¹ = an organic radical which has at least one primary, secondary (e.g. -NR ¹ ) or tertiary amino group (e.g. -NR ¹ R ² ) or at least one ammonium group -N ^⊕ R ¹³ R ¹⁴ R ^{15 has} X ^⊖ , with X ^⊖ = F ^⊖ , Cl ^⊖ , Br ^⊖ , HSO ₄ ^⊖ , SO ₄ ^{2 ⊖} , H ₂ PO ₄ ^⊖ , HPO ₄ ^{2 ⊖} or PO ₄ ^{3 ⊖} and R ¹³ , R ¹⁴ , R ¹⁵ independent organic radicals (e.g. independently of one another the same groups as R ¹ ),
R ¹² = independently of R ^{11 the} same groups as R ¹¹ or -H, -OH, C ₁ - to C ₄ -alkyl, -COO ^⊖ M ^⊕ , -C∼CH,
or hydroxy substituted C ₁ to C ₄ alkyl (e.g. hydroxyethyl or hydroxypropyl) and
R ¹³ = -H, -CH ₃ or
7. The method according to claim 6, characterized in that 2,2,6,6- Tetramethyl-1-piperidinyloxy (TEMPO), 4-hydroxy-2, 2,6, 6-tetramethyl-1- piperidinyloxy (HO-TEMPO) or di-tert-butyl-nitroxide (DTBN) as a stable N-oxyl radical is used. 8. The method according to any one of claims 1 to 7, characterized in that the ethylenically unsaturated monomer is selected from styrene compounds of the general formula XI
(in which R 'and R "independently of one another are H or C ₁ -C ₂ alkyl and n is 0, 1, 2 or 3,
C ₁ -C ₂₀ alkyl esters of acrylic acid or methacrylic acid, dienes with conjugated double bonds, ethylenically unsaturated dicarboxylic acids and their derivatives, and ethylenically unsaturated nitrile compounds. 9. The method according to claim 8, characterized in that as styrene compounds of the general formula XI divinylbenzene, vinyl toluene or C ₁ -C ₈ alkyl (meth) acrylates are used. 10. The method according to any one of claims 1 to 9, characterized in that the polymerization as mass (= bulk), solution, suspension, microsus pension, emulsion or mini-emulsion polymerization is carried out.