Method for producing a polymer by nitroxyl-controlled polymerisation, and polymer

Abstract

The invention relates to a method for producing a polymer by means of nitroxyl-controlled polymerisation. According to the invention, a mixture is initiated which contains at least one radically polymerisable monomer and additionally contains at least one initiator, at least one reactive agent that converts at least one portion of the alkoxyamine end groups produced during the radical polymerisation into a non-polymerisable group, and at least one additive that accelerates the hydroxyl-controlled polymerisation and/or the conversion of the alkoxyamine end groups into a non-polymerisable group.

Claims

1. A process for preparing a polymer by nitroxyl-controlled polymerization, comprising the following steps: a) providing a mixture susceptible to radical polymerization, comprising: i) at least one monomer A1 polymerizable by radical polymerization, or a monomer mixture comprising the at least one monomer A1 and also at least one further monomer A2, capable of radical polymerization and different from the monomer A1, and ii) at least one initiator B selected from the group consisting of an alkoxyamine B1 which initiates the radical polymerization by cleaving into an alkyl radical and a nitroxyl radical and an initiator B2 which comprises at least one radical initiator and at least one nitroxyl radical, b) initiating the radical polymerization and maintaining the polymerization over a time period which allows polymerization to a conversion of 10 to 100%, c) adding at least one reactive agent C after a polymerization conversion of between 10% and 100%, in an amount which converts at least a portion or the entirety of the alkoxyamine end groups of the polymer generated in the nitroxyl-controlled radical polymerization into a non-polymerizable group, wherein the at least one reactive agent C is selected from the group consisting of substituted phenols, hydroxyquinone, and isobutyl vinyl ether, and d) adding, to at least step c), at least one additive D which accelerates the nitroxyl-controlled polymerization reaction and/or the conversion of the alkoxyamine end groups of the polymer into a non-polymerizable group, wherein the at least one additive D is selected from the group consisting of carboxylic acid derivatives, ketones and combinations thereof, wherein steps a) to d) are performed in a one-pot reaction.

2. The process of claim 1, wherein the at least one monomer A1 is selected from hydroxystyrene monomers whose hydroxyl group is protected with a protecting group which is inert under the conditions of the radical polymerization, and/or the monomer mixture comprises at least one hydroxystyrene monomer A1 and at least one further monomer A2 which is capable of radical polymerization and is different from the hydroxystyrene monomer A1.

3. The process of claim 2, wherein the one or more hydroxystyrene monomers are selected from the group consisting of alkoxy-, aryloxy-, acyloxy-, silyloxy-, carbamyloxy- and sulfonyloxy-substituted hydroxystyrenes.

4. The process of claim 2, wherein the one or more hydroxystyrene monomers are selected from the group consisting of 4-acetoxystyrene, 4-tert-butoxystyrene, 4-trimethylsilyloxystyrene, 4-tert-butyldimethylsilyloxystyrene, 4-triethylsilyloxystyrene, 4-triisopropylsilyloxystyrene, 4-methoxystyrene, 4-methoxymethoxystyrene, 4-benzoxystyrene, 4-p-methoxybenzoxystyrene, 4-benzyloxymethoxystyrene, 4-tert-butyloxycarbonyloxystyrene, 4-triphenylmethyloxystyrene, 4-pivaloyloxystyrene, 4-benzoyloxystyrene, 4-p-toluenesulfonyloxystyrene, and 4-methylsulfonyloxystyrene, and combinations thereof.

5. The process of claim 1, wherein the carboxylic acid derivatives are selected from the group consisting of carboxylic anhydrides, carboxylic esters and carbonitriles, and the ketone is acetylacetone.

6. The process of claim 1, wherein the at least one additive D is used in an amount of 5 to 600 mol % based on the amount of initiator B.

7. The process of claim 1, wherein the at least one further monomer A2 is selected from the group consisting of styrenes, isoprene, butadiene, and acrylates.

8. The process of claim 7, wherein the acrylates are of the formula: ##STR00007## where, in each case independently of one another, R.sup.1 is hydrogen or an alkyl group, and R.sup.2 is a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, t-amyl, benzyl, cyclohexyl, 9-anthracenyl, 2-hydroxyethyl, 3-phenyl-2-propenyl, adamantyl, methyladamantyl, ethyladamantyl, isobornyl, 2-ethoxyethyl, n-heptyl, n-hexyl, 2-hydroxypropyl, 2-ethylbutyl, 2-methoxypropyl, 2-(2-methoxyethoxy), 2-naphthyl, 2-phenylethyl, phenyl, lauryl, myristyl, cetyl, stearyl, ceryl, isodecyl, 2-ethylhexyl, ethyltriglycol segment, tetrahydrofurfuryl, butyldiglycol, 2-dimethylaminoethyl, polyethylene glycol segment, methylpolyethylene glycol segment, or glycidyl.

9. The process of claim 1, wherein the molar fraction of the at least one hydroxystyrene monomer A1, based on the entirety of the at least one hydroxystyrene monomer A1 and the at least one further monomer A2 in the monomer mixture, is from 0.1 to 99.9 mol %.

10. The process of claim 1, wherein the at least one alkoxyamine B1 is selected from compounds having the following general formula ##STR00008## where, in each case independently of one another, R.sup.3 is a group having at least one carbon atom which is in a position to enter into homolytic cleavage of the bond between oxygen atom and residue R.sup.3 and to form a radical .R.sup.3, the residue R.sup.3 being selected from the group consisting of 1-phenylethyl, tert-butyl, cyanoisopropyl, phenyl, and methyl, R.sup.4, R.sup.5, R.sup.7 and R.sup.8 are identical or different and are selected from the group consisting of linear, branched or cyclic and/or unsubstituted or substituted alkyl residues, the residues R.sup.4, R.sup.5, R.sup.7 and R.sup.8 being identical or different and being selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, neopentyl, benzyl, and cyclohexyl, or the moieties R.sup.4—C—R.sup.5 and R.sup.7—C—R.sup.8, via the radicals R.sup.4 and R.sup.5 and/or R.sup.7 and R.sup.8, form a cyclic structure which in turn may be substituted or unsubstituted, R.sup.6 and R.sup.9 are identical or different and are selected from the group consisting of linear, branched or cyclic and unsubstituted or substituted alkyl residues, or the moiety R.sup.6—C—N—C—R.sup.9, via residues R.sup.6 and R.sup.9, forms a cyclic structure which in turn is substituted or unsubstituted and/or fused to an aliphatic or aromatic ring system, the cyclic structure having one of the following general formulae ##STR00009## where, in each case independently of one another at each occurrence, R.sup.10 and R.sup.11 are identical or different and are selected from the group consisting of linear or branched and/or unsubstituted or substituted alkyl residues, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, neopentyl, benzyl, cyclohexyl, and hydrogen.

11. The process of claim 1, wherein the at least one initiator B2 comprises at least one radical initiator selected from the group consisting of peroxides, azo compounds, dibenzoyl peroxide, cumene hydroperoxide, dicumyl peroxide, 1,1-di(tert-butylperoxy)cyclohexane, tert-amyl peroxyacetate, diisopropyl peroxydicarbonate, peroxodisulfates, azobis(isobutyronitrile); redox systems, and photoinitiators, and at least one nitroxyl radical selected from the group consisting of nitroxyl radicals having the following general formula ##STR00010## where, in each case independently of one another, R.sup.4, R.sup.5, R.sup.7 and R.sup.8 are identical or different and are selected from the group consisting of linear, branched or cyclic and unsubstituted or substituted alkyl residues, the residues R.sup.4, R.sup.5, R.sup.7 and R.sup.8 being identical or different and being selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, neopentyl, benzyl, and cyclohexyl, or the moieties R.sup.4—C—R.sup.5 and/or R.sup.7—C—R.sup.8, via the radicals R.sup.4 and R.sup.5 and/or R.sup.7 and R.sup.8, form a cyclic structure which in turn is substituted or unsubstituted, R.sup.6 and R.sup.9 are identical or different and are selected from the group consisting of linear, branched or cyclic and unsubstituted or substituted alkyl residues, or the moiety R.sup.6—C—N—C—R.sup.9, via the residues R.sup.6 and R.sup.9, forms a cyclic structure which in turn is substituted or unsubstituted and/or fused to an aliphatic or aromatic ring system, the cyclic structure being selected from structures having the following general formulae ##STR00011## where in each case independently of one another at each occurrence; and R.sup.10 and R.sup.11 are identical or different and are selected from the group consisting of linear or branched and/or unsubstituted or substituted alkyl residues, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, neopentyl, benzyl, cyclohexyl, and hydrogen.

12. The process of claim 1, wherein, based on the total amount of substance of monomers A1, or A1 and A2, the initiator B is used in an amount of 0.1 to 20 mol %.

13. The process of claim 1, wherein the at least one reactive agent C is selected from the group consisting of 2,6-di-tert-butyl-p-cresol, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 2,6-di-tert-butylphenol.

14. The process of claim 1, wherein the at least one reactive agent C is used in an amount of 10 to 1000 mol %, based on the concentration of initiator B.

15. The process of claim 1, wherein the mixture susceptible to radical polymerization comprises a solvent, the solvent being selected from the group consisting of PGMEA, ethyl acetate, toluene, xylene, ethylbenzene, anisole, acetone, 2-butanone, acetonitrile, dimethyl sulfoxide, tetrahydrofuran, dioxane, diethyl ether, tert-butyl methyl ether, pentane, hexane, heptane, cyclopentane, cyclohexane, methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monobutyl ether, and combinations thereof.

16. The process of claim 1, wherein the polymerization reaction is initiated thermally or actinically, and/or wherein the temperature for the initiation and/or polymerization reaction is adjusted to 60 to 180° C.

17. The process of claim 1, wherein after the conclusion of step c), the protecting group of the hydroxystyrene monomer A1 bonded in the polymer is eliminated.

18. The polymer prepared by the process of claim 1, wherein the molecular weight of said polymer remains unchanged by heating to a temperature between 100° C. and 130° C. over a time period of between 15 and 180 minutes.

Description

COMPARATIVE EXAMPLE 1. POLYMERIZATION WITHOUT END GROUP SUBSTITUTION AND SUBSEQUENT HYDROLYSIS

(1) In this comparative example, 4-acetoxystyrene was copolymerized with styrene by NMP and the resultant polymer was hydrolysed to poly(4-hydroxystrene-co-styrene) without prior substitution of the end groups capable of polymerization. The polymerization reaction for this purpose was discontinued by lowering of the temperature to room temperature. The determination of the molecular weights and their distributions before and after the hydrolysis demonstrates that the hydrolysis increased the breadth of the molecular weight distribution.

(2) a) Polymerization

(3) A 2 L jacketed reactor with stirrer, dropping funnel and nitrogen feed line is charged with 750 mL (4.36 mol) of destabilized 4-acetoxystyrene and 166 mL (1.45 mol) of styrene. 72.4 g (0.28 mol) of EBTEMPO, 100 mL of methoxy-2-propyl acetate (PGMEA) and 79 mL (0.83 mol) of acetic anhydride are dissolved in 100 mL of the monomer mixture, degassed by introduction of nitrogen and introduced into the dropping funnel. The rest of the monomer mixture is likewise degassed by introduction of nitrogen. After heating of the monomer mixture to 130° C., the initiator mixture is placed into the reactor and stirring takes at 130° C. for 6 hours. In the course of cooling to room temperature, the mixture is diluted with 1 L of toluene and, when room temperature is reached, the polymer is precipitated from 12 L of a mixture of methanol and water (5:1). The polymer is filtered and dried to constant weight under reduced pressure at 60° C.

(4) b) Hydrolysis

(5) 15 g of poly(4-acetoxystyrene-co-styrene) from a) are dispersed in 150 mL of methanol and degassed by introduction of nitrogen. The mixture is admixed with 1.05 mL of methanesulfonic acid and stirred at room temperature and under nitrogen overnight, the polymer going into solution in the course of the reaction. The product is subsequently precipitated from water and isolated by filtration. The residue is dissolved in ethyl acetate and extracted twice with water. A final precipitation from hexane isolates the polymer.

(6) c) Characterization

(7) The molecular weight distributions of the copolymers prepared in a) and b) were investigated by size exclusion chromatography (GPC) (Tab. 1).

(8) TABLE-US-00001 TABLE 1 Number-average and weight-average molecular weights and polydispersities of the polymers prepared in comparative example 1a) and 1b), measured by GPC (polystyrene calibration). Mw Polymer Mn [kDa] [kDa] PDI before hydrolysis (poly(4-acetoxystyrene-co- 1.99 2.54 1.28 styrene) from comparative example 1a)) after hydrolysis (poly(4-hydroxystyrene-co- 1.68 2.43 1.45 styrene) from comparative example 1b))

(9) From Tab. 1 it is apparent that the average molecular weights after the hydrolysis are lower than before. This is because the molar mass becomes lower as a result of elimination of the acetate groups. It is additionally evident in Tab. 1 that after the hydrolysis, the breadth of the molecular weight distribution increases significantly (polydispersity index before hydrolysis=1.28; after hydrolysis=1.45), this being attributable to the fact that during the hydrolysis, the alkoxyamine end groups enter into secondary reactions which lead to products of coupling of the polymer chains with one another, with a higher molecular weight, this being undesirable for possible use as binders in photoresists.

INVENTIVE EXAMPLE 1: ACCELERATED END GROUP SUBSTITUTION AND SUBSEQUENT HYDROLYSIS

(10) In a first inventive example, the alkoxyamine end groups capable of polymerization from the poly(4-acetoxystyrene-co-styrene) prepared in comparative example 1a) were replaced by a hydrogen atom in the presence of a polymerization-accelerating additive. The end group-substituted polymer was subsequently hydrolysed to poly(4-hydroxystrene-co-styrene). The determination of the molecular weights and their distributions before and after the hydrolysis demonstrates that the breadth of the molecular weight distribution was not altered by the hydrolysis.

(11) a) End Group Substitution

(12) 20 g of the polymer prepared in comparative example 1a) are dissolved in 40 mL of PGMEA with 2.6 g (0.016 mol) of BHT and 2.27 g (0.022 mol) of acetic anhydride. The solution is degassed by introduction of nitrogen. The reaction mixture is stirred at 130° C. for 2 hours, during which the solution takes on an orange-red coloration indicating the release of the TEMPO. After cooling to room temperature, the polymer is precipitated from hexane and isolated by filtration.

(13) b) Hydrolysis

(14) 15 g of poly(4-acetoxystyrene-co-styrene) from inventive example a) are dispersed in 150 mL of methanol and degassed by introduction of nitrogen. The mixture is admixed with 1.05 mL of methanesulfonic acid and stirred at room temperature and under nitrogen overnight, the polymer going into solution in the course of the reaction. The product is subsequently precipitated from water and isolated by filtration. The residue is dissolved in ethyl acetate and extracted twice with water. A final precipitation from hexane isolates the polymer.

(15) c) Characterization

(16) The molecular weight distributions of the copolymers prepared in a) and b) were investigated by size exclusion chromatography (GPC) (Tab. 2).

(17) TABLE-US-00002 TABLE 2 Number-average and weight-average molecular weights and polydispersities of the polymers prepared in inventive example 1a) and 1b), measured by GPC (polystyrene calibration). Mw Polymer Mn [kDa] [kDa] PDI before hydrolysis (poly(4-acetoxystyrene-co- 2.11 2.62 1.24 styrene) from inventive example 1a)) after hydrolysis (poly(4-hydroxystyrene-co- 1.77 2.21 1.25 styrene) from inventive example 1b))

(18) From Tab. 2 it is apparent that—as already observed in comparative example 1—the average molecular weights after the hydrolysis are lower than before. In contrast to comparative example 1, the broadening of the distribution observed after the hydrolysis is no more than negligible, within the range of measurement inaccuracy.

COMPARATIVE EXAMPLE 2. UNACCELERATED END GROUP SUBSTITUTION

(19) In a second comparative example, 4-acetoxystyrene and styrene were again copolymerized by NMP. To remove the accelerator present in the polymerization, the polymer was isolated by precipitation. Subsequently, in a downstream step, the alkoxyamine end groups capable of polymerization were substituted by a hydrogen atom. In contrast to inventive example 1, no polymerization-accelerating additive was added to the substitution reaction in this comparative example. The progress of the substitution reaction was determined by NMR spectroscopy.

(20) a) Polymerization

(21) A 2 L jacketed reactor with stirrer, dropping funnel and nitrogen feed line is charged with 750 mL (4.36 mol) of destabilized 4-acetoxystyrene and 125 mL (1.09 mol) of styrene. 71.27 g (0.27 mol) of EBTEMPO, 100 mL of methoxy-2-propyl acetate (PGMEA) and 77 mL (0.82 mol) of acetic anhydride are dissolved in 100 mL of the monomer mixture, degassed by introduction of nitrogen and introduced into the dropping funnel. The rest of the monomer mixture is likewise degassed by introduction of nitrogen. After heating of the monomer mixture to 130° C., the initiator mixture is placed into the reactor and stirring takes at 130° C. for 6 hours. In the course of cooling to room temperature, the mixture is diluted with 1 L of toluene and, when room temperature is reached, the polymer is precipitated from 12 L of a mixture of methanol and water (5:1). The polymer is filtered and dried to constant weight under reduced pressure at 60° C.

(22) b) End Group Substitution

(23) 5 g of the polymer obtained in a) are dissolved in 10 mL of PGMEA. 2 equivalents of BHT are added and the reaction mixture is degassed by introduction of nitrogen. The reaction mixture is subsequently heated with stirring at 130° C. for 6 hours. An orange-red coloration of the reaction mixture here indicates the release of the persistent TEMPO radical. After 2 hours, a sample of the mixture is taken for determining the fraction of alkoxyamine end groups that have remained. The polymer is isolated by precipitation from hexane.

(24) c) Characterization

(25) The substitution of the alkoxyamine group is investigated by .sup.1H NMR spectroscopy. The percentage fractions of end groups determined, based on the number of polymer chains, are listed in Tab. 3.

(26) TABLE-US-00003 TABLE 3 Percentage fractions of alkoxyamine end groups (based on number of polymer chains) of the polymer resulting from comparative example 2: during end group substitution with and without acceleration after 2 h and 6 h reaction time after 2 h after 6 h reaction reaction time time Percentage fractions of alkoxyamine end groups in 47% 2% the polymer in the case of end group substitution without acceleration (comparative example 2)

(27) From Tab. 3 it is apparent that the end groups in the case of the unaccelerated substitution reaction are still 47% after 2 hours, and even after 6 hours of reaction time there are still 2% of the alkoxyamine end groups remaining in the polymer. Moreover, in the .sup.1H NMR spectrum of the polymer, there were signals evident in the range between 1.3 and 1.5 ppm which were not assignable to the desired polymer (otherwise unidentifiable impurities).

INVENTIVE EXAMPLE 2. DEMONSTRATION OF ACCELERATED END GROUP SUBSTITUTION

(28) In a second inventive example it is demonstrated that the addition of an accelerator accelerates not only the polymerization but also the end group substitution. Additionally it is demonstrated that through the acceleration of the end group substitution it is possible to reduce the formation of secondary reactions. In order to visualize this effect, the 4-acetoxystyrene from comparative example 2a) was used as starting material. The alkoxyamine end groups capable of polymerization in this material were substituted by a hydrogen atom in a downstream step. To accelerate the substitution reaction, acetic anhydride was added. The progress of the substitution reaction was determined by NMR spectroscopy.

(29) a) End Group Substitution

(30) 5 g of the polymer obtained in comparative example 2a) are dissolved in 10 mL of PGMEA. 2 equivalents of BHT and also 3 equivalents of acetic anhydride, based on the initiator concentration, are added and the reaction mixture is degassed by introduction of nitrogen. The reaction mixture is subsequently heated with stirring at 130° C. After 2 hours the reaction mixture is cooled to room temperature. An orange-red coloration of the reaction mixture here indicates the release of the persistent TEMPO radical. The polymer is isolated by precipitation from hexane.

(31) b) Characterization

(32) The substitution of the alkoxyamine group is investigated by .sup.1H NMR spectroscopy. The percentage fractions of end groups determined, based on the number of polymer chains, are listed in Tab. 4.

(33) TABLE-US-00004 TABLE 4 Percentage fractions of alkoxyamine end groups (based on number of polymer chains) of the polymer resulting from inventive example 2a) after 2 h and 6 h reaction time after 2 h after 6 h reaction reaction time time Percentage fractions of alkoxyamine end groups 0% — in the polymer in the case of end group substitution with acceleration (inventive example 2)

(34) From Tab. 4 it is apparent that the end groups in the case of the accelerated substitution were removed quantitatively after just 2 hours. Moreover, in the .sup.1H NMR spectrum of the polymer, there were no signals apparent in the range between 1.3 and 1.5 ppm that could not be assigned to the desired polymer

INVENTIVE EXAMPLE 3: DEMONSTRATION OF THE IMPROVED TEMPERATURE STABILITY WITH END GROUP SUBSTITUTION AS ONE-POT REACTION

(35) A second inventive example illustrates the advantageous nature of carrying out the end group substitution in a one-pot reaction. For this purpose, a further polymer was prepared by the same process as in the examples described above, with the difference that here the end group substitution was carried out as a one-pot reaction, with the polymerization-accelerating agent still being present during the end group substitution as well. This polymer too was hydrolysed as described in comparative example 1b) and inventive example 1b). As a further characterization step, a temperature stability test was added here.

(36) a) Polymerization and End Group Substitution

(37) A 2 L jacketed reactor with stirrer, dropping funnel and nitrogen feed line is charged with 750 mL (4.36 mol) of destabilized 4-acetoxystyrene and 166 mL (1.45 mol) of styrene. 72.4 g (0.28 mol) of EBTEMPO, 100 mL of methoxy-2-propyl acetate (PGMEA) and 79 mL (0.83 mol) of acetic anhydride are dissolved in 100 mL of the monomer mixture, degassed by introduction of nitrogen and introduced into the dropping funnel. The rest of the monomer mixture is likewise degassed by introduction of nitrogen. After heating of the monomer mixture to 130° C., the initiator mixture is placed into the reactor and stirring takes at 130° C. for 6 hours. After 6 hours, the reaction mixture is admixed with 102 g (0.46 mol) of BHT in solution in 100 mL of PGMEA. After a further 2 hours of stirring at 130° C., cooling takes place to room temperature. In the course of cooling to room temperature, the mixture is diluted with 1 L of toluene and, when room temperature is reached, the polymer is precipitated from 12 L of a mixture of methanol and water (5:1). The polymer is filtered and dried to constant weight under reduced pressure at 60° C.

(38) b) Hydrolysis

(39) 15 g of the poly(4-acetoxystyrene-co-styrene) prepared in a) are dispersed in 150 mL of methanol and degassed by introduction of nitrogen. The mixture is admixed with 1.05 mL of methanesulfonic acid and stirred at room temperature and under nitrogen overnight, the polymer going into solution in the course of the reaction. The product is subsequently precipitated from water and isolated by filtration. The residue is dissolved in ethyl acetate and extracted twice with water.

(40) A final precipitation from hexane isolates the polymer.

(41) c) Temperature Stability Test

(42) Investigated comparatively in this test are the polymer from b) and also the polymer from inventive example 1b) after separate end group substitution. For this test, the polymers in solid form are heated in an oven at 130° C. under an air atmosphere for 3 hours. After cooling to room temperature, both samples have their molecular weight distributions determined by GPC and compared with those before the temperature stability test.

(43) TABLE-US-00005 TABLE 5 Change in the molecular weight distribution of 4-hydroxystyrene-styrene copolymers by heating at 130° C. for 3 h, measured by GPC (polystyrene calibration) as a function of the method of end group substitution. Method of end group Molecular weight distribution after heating at substitution 130° C. for 3 hours subsequently substituted shoulder in the region between 4000 g/mol and (inventive example 1b)) 9000 g/mol substituted in situ no change (inventive example 3b))

(44) From Tab. 5 it is apparent that in the case of the sample wherein the end groups were substituted in an operating step downstream of the polymerization, the subsequent heating at 130° C. for 3 hours to test the temperature stability produces a high molecular mass fraction which is distinct as a shoulder between 4000 g/mol and 9000 g/mol. In the case of the sample for which the end group substitution was carried out as a one-pot reaction, this shoulder is not in evidence. This means that apparently before or during the end group substitution as a downstream operation, secondary reactions occur to form species which give rise to a molecular weight broadening only in a subsequent temperature stability test. These secondary reactions may occur, for example, during the cooling of the polymerization mixture, if radicals are still formed intermediately by dissociation of the alkoxyamine end groups, but these radicals find no monomer to react with.

INVENTIVE EXAMPLE 4: DEMONSTRATION OF THE ACCELERATED END GROUP SUBSTITUTION AND OF THE RESULTANT IMPROVED TEMPERATURE STABILITY IN A ONE-POT REACTION

(45) In the fourth inventive example it is shown that in a one-pot reaction as well, the substitution of the end groups capable of polymerization proceeds more quickly in the presence of a polymerization-accelerating additive than in its absence. Additionally it is demonstrated that the resultant end products have an improved temperature stability relative to those whose end groups have been substituted without acceleration in a one-pot reaction. In order to be able to carry out unaccelerated end group substitution, it was necessary to carry out the polymerization itself without an accelerating additive, and hence in this example the polymerization time was longer than in the examples shown above. For this purpose, a copolymerization of 4-hydroxystyrene and styrene was carried out without addition of an accelerator, and the reaction mixture was divided into two fractions following complete conversion of the monomers. Added to the first fraction at reaction temperature was an accelerating additive and also an additive which replaces the polymerizable end groups by hydrogen atoms. Added to the second fraction was only the additive that replaces the polymerizable end groups by hydrogen atoms. Both fractions were subsequently hydrolysed to the poly-4-hydroxystrene copolymers and subjected lastly to a temperature stability test.

(46) a) Polymerization

(47) A 50 mL round-bottomed flask with magnetic stirring rod, septum and nitrogen feed line is charged with 15 mL (98.1 mmol) of destabilized 4-acetoxystyrene and 2.2 mL (19.2 mmol) of styrene, 1.209 g (4.69 mmol) of EBTEMPO and 2 mL of methoxy-2-propyl acetate (PGMEA), and this initial charge is degassed by introduction of nitrogen. The flask is placed in an oil bath preheated to 130° C. and the mixture is stirred at 130° C. until monomers are no longer detectable in the .sup.1H NMR spectrum of the mixture (after 48 hours). After this time, half of the reaction mixture is removed and is placed under nitrogen into a second round-bottomed flask preheated to 130° C., where it is admixed with 3.2 g of Irganox 1076 (fraction II). The mixture in the original flask (fraction I) is admixed with 1.2 mL (12.7 mmol) of acetic anhydride and also 3.2 g of Irganox 1076. Both reaction mixtures are stirred at 130° C. until reactive end groups are no longer identifiable in the .sup.1H NMR spectrum (Tab. 6).

(48) TABLE-US-00006 TABLE 6 Percentage fractions of alkoxyamine end groups (based on number of polymer chains) of the polymers originating from inventive example 4a): during end group substitution with and without acceleration after reaction times of 2 h and 7 h after 2 h after 7 h reaction reaction time time Percentage fractions of alkoxyamine end groups 0% — in the polymer with end group substitution with acceleration (fraction I) Percentage fractions of alkoxyamine end groups 45% 0% in the polymer with end group substitution without acceleration (fraction II)

(49) In accordance with the results in Tab. 6, fraction I is cooled to room temperature after 2 hours and fraction II after 7 hours. Both reaction mixtures are diluted with 10 mL each of ethyl acetate and precipitated from n-heptane. The polymers are filtered and dried to constant weight under reduced pressure at 60° C.

(50) a) Hydrolysis

(51) 5 g each of the poly(4-acetoxystyrene-co-styrenes) prepared in a) are dispersed in 50 mL of methanol and degassed by introduction of nitrogen. The mixtures are admixed with 0.35 mL of methanesulfonic acid and stirred at room temperature under nitrogen overnight, the polymer going into solution in the course of the reaction. The products are subsequently precipitated from water and isolated by filtration. The residues are dissolved in ethyl acetate and extracted twice with water.

(52) A concluding precipitation from hexane isolates the polymers.

(53) b) Temperature Stability Test

(54) The hydrolysed polymers of fraction I and fraction II are heated as solids in an oven at 130° C. under an air atmosphere for 3 hours. After cooling to room temperature, the number-average molecular weights of both samples are determined by GPC and compared with those before the temperature stability test (Tab. 7).

(55) TABLE-US-00007 TABLE 7 Number-average molecular weights of the polymers prepared in inventive example 4 before and after the temperature stability test, measured by GPC (polystyrene calibration). Mn Polymer [kDa] Increase End groups substituted with acceleration before heating 1.89 (Fraction I from inventive example 4 after heating at 2.01 6.4% after hydrolysis) 130° C. for 3 h End groups substituted without before heating 2.27 acceleration (Fraction II from inventive after heating at 2.70 18.9% example 4 after hydrolysis) 130° C. for 3 h

(56) From Table 6 it is evident that even in a one-pot reaction, the substitution of the end groups capable of polymerization proceeds more quickly in the presence of a polymerization-accelerating additive than in its absence. In fraction I, which contains an accelerating additive, all of the end groups are substituted after just 2 hours, whereas in fraction II without accelerator this is the case only after 7 hours.

(57) It is additionally evident from Tab. 7 that the end products originating from the accelerated end group substitution have an improved temperature resistance relative to those whose end groups were substituted without acceleration. The number-average molecular weight of the polymer originating from fraction I (with accelerator) increases by only 6% as a result of the temperature stability test, whereas the polymer originating from fraction II (without accelerator) records a molecular weight increase of almost 19% as a result of heating at 130° C. for 3 hours.

INVENTIVE EXAMPLE 5: DEMONSTRATION OF THE IMPROVED TEMPERATURE STABILITY WITH ACCELERATED END GROUP SUBSTITUTION IN A ONE-POT REACTION, IN DIRECT COMPARISON TO AN ACCELERATED AND AN UNACCELERATED END GROUP SUBSTITUTION AFTER PRIOR ISOLATION OF THE POLYMER

(58) In a fifth inventive example it is demonstrated that the conversion of the alkoxyamine end groups into non-polymerizable groups in the presence of a polymerization-accelerating additive, which hence also accelerates the end group substitution, without isolation of the polymer between polymerization and end group substitution, leads to a polymer having improved temperature stability.

(59) For this purpose a copolymerization of 4-hydroxystyrene and styrene was carried out in the presence of an accelerator and the reaction mixture, after complete conversion of the monomers, was divided into three fractions. The first fraction was admixed at reaction temperature with an additive which replaces the polymerizable end groups by hydrogen atoms.

(60) The two other fractions were isolated by precipitation and the end group substitution was carried out in a subsequent step both with and without addition of an accelerator. All three fractions were subsequently hydrolysed to the poly-4-hydroxystrene copolymers and subjected lastly to a temperature stability test.

(61) a) Polymerization

(62) A 50 mL round-bottomed flask with magnet stirring rod, septum and nitrogen feed line is charged with 15 mL (98.1 mmol) of destabilized 4-acetoxystyrene, 2.2 mL (19.2 mmol) of styrene, 1.209 g (4.69 mmol) of EBTEMPO, 1.32 mL (14.0 mmol) of acetic anhydride and 2 mL of methoxy-2-propyl acetate (PGMEA) and this initial charge is degassed by introduction of nitrogen. The flask is placed in an oil bath preheated to 130° C. and the mixture is stirred at 130° C. for 2 hours. After this time, ⅓ of the reaction mixture is removed twice and cooled to room temperature, subjected to precipitation from heptane, filtered and dried (fraction II and fraction III). The fraction in the original flask (fraction I) is admixed with 1.6 g of Irganox 1076 at reaction temperature. After stirring for a further 2 hours at this temperature, the mixture is cooled to room temperature.

(63) The polymers from fraction II and fraction III are each dissolved in 3 mL each of methoxy-2-propyl acetate (PGMEA) in a 50 mL round-bottomed flask with magnetic stirring rod, septum and nitrogen feed line, and 1.6 g of Irganox 1076 is added in each case. Fraction II is additionally admixed with 0.4 mL (4.24 mmol) of acetic anhydride. The dissolved fractions II and III are degassed by introduction of nitrogen, placed in an oil bath preheated to 130° C., and stirred at this temperature until reactive end groups are no longer identifiable in the .sup.1H NMR spectrum. Fraction II is cooled accordingly after 2 hours and fraction III after 7 hours to room temperature.

(64) All three reaction mixtures (fraction I, II and III) are diluted each with 10 mL of ethyl acetate and precipitated from n-heptane. The polymers are isolated by filtration and dried to constant weight under reduced pressure at 60° C.

(65) a) Hydrolysis

(66) 5 g each of the poly(4-acetoxystyrene-co-styrenes) prepared in a) are dispersed in 50 mL of methanol and degassed by introduction of nitrogen. The mixtures are admixed with 0.35 mL of methanesulfonic acid and stirred at room temperature under nitrogen overnight, the polymer going into solution in the course of the reaction. The products are subsequently precipitated from water and isolated by filtration. The residues are dissolved in ethyl acetate and extracted twice with water.

(67) A concluding precipitation from hexane isolates the polymers.

(68) b) Temperature Stability Test

(69) The hydrolysed polymers of fractions I, II and III are heated as solids in an oven at 130° C. under an air atmosphere for 3 hours. After cooling to room temperature, the molecular weight distributions of all samples are determined by GPC and compared with those before the temperature stability test (Tab. 8).

(70) TABLE-US-00008 TABLE 8 Polydispersity indices of the polymers prepared in inventive example 5 before and after the temperature stability test, measured by GPC (polystyrene calibration). PDI Polymer (Mw/Mn) Increase End groups substituted with before heating 1.31 acceleration in a one-pot reaction after heating at 1.34 2.3% (Fraction I from inventive 130° C. for 3 h example 5 after hydrolysis) End groups substituted with before heating 1.34 acceleration after prior after heating at 1.44 7.5% isolation (Fraction II from 130° C. for 3 h inventive example 5 after hydrolysis) End groups substituted without before heating 1.29 acceleration after prior isolation after heating at 1.40 8.5% (Fraction III from inventive 130° C. for 3 h example 5 after hydrolysis)

(71) From table 8 it is apparent that the method of end group substitution has a critical influence on the temperature resistance of the hydrolysed polymers. The breadth of the molecular weight distribution of fraction I, in other words of the polymer whose end groups underwent accelerated substitution in a one-pot reaction, increases by only 2.3% after heating at 130° C. for 3 hours. The breadth of the molecular weight distribution of fraction II, in other words of the polymer whose end groups were subjected to accelerated substitution after prior isolation, increases by 7.5% already after heating at 130° C. for 3 hours. The breadth of the molecular weight distribution of fraction III, in other words of the polymer whose end groups were subjected to unaccelerated substitution after prior isolation, increases indeed by 8.5% after heating at 130° C. for 3 hours. From this it can be inferred that the accelerated end group substitution in a one-pot reaction yields products having the best temperature resistance, but also that the acceleration of end group substitution after prior isolation of the polymers still has a stabilizing effect on the temperature resistance of the polymers.