EP1658318A1

EP1658318A1 - Method for the synthesis of copolymers for producing polymethacrylimides

Info

Publication number: EP1658318A1
Application number: EP04764449A
Authority: EP
Inventors: Jonas Scherble; Peter Stein; Iulian Corneliu Alupei; Helmut Ritter; Sabine Schwarz-Barac
Original assignee: Roehm GmbH Darmstadt
Current assignee: Roehm GmbH Darmstadt
Priority date: 2003-08-29
Filing date: 2004-08-25
Publication date: 2006-05-24
Also published as: DE10340330A1; WO2005023883A1; US20070142588A1; CA2529610A1; JP2007504289A; CN1823101A; TW200514794A; KR20060110861A

Abstract

The invention relates to a method for producing polymethacrylimides in two steps: 1) radical copolymerization of (meth)acrylamides (A, (Me,H)HC=CHCONHR2) and alkyl(meth)acrylic esters (B) and optionally further ethylenically unsaturated monomers in the presence of an aqueous solvent. The monomers (A) include, in addition to acrylamide and methacrylamide, (meth)acrylamides that are substituted on their nitrogen group (R2 <> H). The monomers (B) are the (meth)acrylic esters of secondary or tertiary alcohols, preferably tert. butylmethacrylate. 2) Thermal or catalytic reaction of the copolymers produced in 1) to polymethacrylimide or for R2 <> H to N-substituted polymethacrylimides while alkenes are separated.

Description

Process for the synthesis of copolymers for the production of polymethacrylimides

Technical field of the invention

The invention relates to copolymers based on (meth) acrylamides and (meth) acrylic esters, which are prepared by radical polymerization in a water-containing diluent. These copolymers can be used as a molding composition for the production of polymethacrylimide foams or molding compositions.

State of the art

Polymethacrylimides are used on an industrial scale in two forms of derivatization. On the one hand, the poly-N-methyl methacrylimide (PMMI) is to be mentioned, which is available under the trade name PLEXIMID ⁰ . PMMI is a highly heat-resistant, transparent plastic with high UV stability. PMMI is used as an injection moldable molding compound, for example in the automotive sector. PMMI molding compound is produced by a polymer-analogous reaction of polymethyl methacrylate molding compound with methylamine in an extruder.

The second type of polymethacrylimide available on an industrial scale is the unsubstituted variant, ie there is no N-alkylation. This is therefore simply referred to as polymethacrylimide (PMI). The production takes place in the casting process, which is why PMI, in contrast to PMMI, has high degrees of polymerization and is no longer meltable. As a highly heat-resistant, creep-resistant foam, PMI is widely used in sandwich constructions and is available under the trade name ROHACELL ^® . PMI foam is produced using the casting process (DE 3346060). Here, the monomers methacrylic acid and methacrylonitrile are mixed with initiators, blowing agents and optionally other monomers or additives and filled into a chamber made of glass and / or metal plates, which are kept at a certain distance with a sealing cord. This chamber is immersed in a water bath at a defined temperature and the copolymer obtained is converted into a polymethacrylimide and simultaneously foamed in a second step by heating to temperatures between 150 ° C. and 250 ° C. The problem here is that the rate of polymerization of methacrylic acid is significantly higher than that of methacrylonitrile, which is why the methacrylic acid reacts first during the polymerization, so that a mixture of copolymers with significantly different compositions is obtained. It is also difficult to remove the heat of polymerization in the casting process. Particularly with increasing polymer thickness (> 20 mm), inadequate heat dissipation or too high a polymerization temperature can lead to uncontrolled polymerization, which can destroy the material and possibly its immediate surroundings. The selected polymerization temperatures and thus speeds must therefore be set so low in the chamber process that the polymerization time can be more than a week depending on the thickness.

JP 04170408 and EP532023 describe the production of PMI foams. First, a copolymer is prepared from tert-butyl methacrylate, methacrylic acid and methacrylonitrile by bulk polymerization. The use of tert-butyl methacrylate, which releases isobutene when heated, means that additional blowing agents can be dispensed with. This process also has two disadvantages: First, as above, it is a casting process, which brings with it the problems with heat dissipation that have already been discussed. Second, the claimed methacrylonitrile-based compositions do not allow substitution of the imide hydrogen atom by other functional groups. Another known process which has already been able to solve some of the problems mentioned above is the preparation of N-substituted polymethacrylimides described in WO03 / 033556 in a water-containing diluent in the presence of cyclodextrins. However, the process described there has the disadvantage that the cyclodextrins required for the polymerization there have to be used in relatively high concentrations of 150 mol% based on 100 mol% monomers and more and then have to be separated from the polymer in a complex manner. In addition, unsubstituted methacrylamide cannot be used because this monomer is too polar to form an inclusion compound with the cyclodextrins.

task

It is therefore the task to develop a process for the production of a molding compound which can be further processed into a PMI foam by heating. The process is intended to ensure sufficient heat dissipation and thus make it possible to produce large quantities in a short time. Furthermore, the method should make it possible to substitute the imide hydrogen atom of polymethacrylimide in order to specifically influence the foam properties through the choice of the side chains. Last but not least, monomers are to be reacted in the process which, in contrast to the comonomer pair methacrylic acid / methacrylonitrile, have a comparable reactivity.

In the context of the present invention, therefore, monomers are preferably used which ideally provide statistical copolymers (n 1, r ₂ 1, ri and r ₂ are the copolymerization parameters) or even tend to alternate copolymers (r 1, r ₂ 0). In order to avoid complex cleaning steps of the polymer, the use of cyclodextrins should also be avoided. solution

The above objects can be achieved by precipitation or suspension polymerization of the monomers in the presence of an aqueous diluent.

By carrying out the polymerization in the presence of an aqueous phase, excellent heat dissipation is ensured because of the high heat capacity of the water, in particular in comparison to the cast polymerization mentioned.

In a method according to the invention

(Meth) acrylamides H ₂ C = CR1CONHR2 (A)

and alkyl (meth) acrylic ester H ₂ C = CR ¹ COOR ⁵ (B)

copolymerized in the presence of a diluent (C).

The group of (meth) acrylamides (A) (R ¹ = H, CH ₃ ) includes, in addition to the water-soluble methacrylamide, also N-substituted (meth) acrylamides (R2 <> H). R2 can be an alkyl or aryl radical with up to 36 carbon atoms, which additionally contains oxygen, nitrogen, sulfur and phosphorus atoms in the form of typical organic functionalities, such as ether, alcohol, acid, ester, , Amide, imide, phosphonic acid, phosphonic acid esters, phosphoric acid esters, phosphoric acid, phosphinic acid esters, sulfonic acid, sulfonic acid ester, sulfinic acid, sulfinic acid ester functions, silicon, aluminum and boron atoms or also halogens such as fluorine, chlorine, bromine or iodine can. Examples of R2 include, but are not limited to: methyl, ethyl, propyl, 2-propyl, butyl, tert-butyl, hexyl, ethylhexyl, octyl, dodecyl, octadecyl, -R3-PO (OR4) 2, where R3 is an alkyl radical with up to 12 C atoms and R4 is an alkyl with up to 4 C atoms, Methylene dimethyl phosphonate, methylene diethyl phosphonate, methylene diisopropyl phosphonate. Mixtures of different methacrylamides can also be used.

As branched alkyl methacrylates (B) in addition to tert-butyl methacrylate (R5 = tert-butyl) e.g. iso-propyl methacrylate (R5 = iso-propyl), sec-butyl methacrylate (R5 = iso-butyl) or methacrylic ester of longer-chain secondary or tertiary alcohols (R5 = alkyl) can also be used. The corresponding alkyl ester acrylates (R1 = H) or mixtures of the monomers mentioned can also be used. The chemical and physical properties of the polymers can be varied by copolymerization with one or more further ethylenically unsaturated monomers.

The monomers (A) and (B) are polymerized in the manner of a precipitation or suspension polymerization in an aqueous medium (C), preferably in water. In the present context, the term aqueous medium is to be understood as meaning mixtures of water and thus miscible organic liquids. Such organic liquids are, for example, glycols such as ethylene glycol, propylene glycol, block copolymers of ethylene oxide and propylene oxide, alkoxylated C ₁ -C ₂ -alcohols, furthermore methanol, ethanol, isopropanol and butanol, acetone, tetrahydrofuran, dimethylformamide, N-methylpyrrolidone or else mixtures. If the polymerization is carried out in mixtures of water and water-miscible solvents, the proportion of water-miscible solvents in the mixture is up to 45% by weight. However, the polymerization is preferably carried out in water.

The precipitation or suspension polymerization of the monomers is usually carried out with the exclusion of oxygen at temperatures of 10 to 200 ° C., preferably 20 to 140 ° C. The polymerization can be carried out batchwise or continuously. Preferably, at least some of the monomers, initiators and optionally regulators are metered uniformly into the polymer during the polymerization Reaction vessel, wherein the components can also be mixed continuously or batchwise outside the reaction vessel. However, in the case of smaller batches, the monomers and the polymerization initiator can be placed in the reactor and polymerized, where appropriate cooling must be used to ensure that the heat of polymerization is dissipated sufficiently quickly.

Possible polymerization initiators are the compounds which are customarily used in radical polymerizations and which give free radicals under the polymerization conditions, such as, for example, peroxides, hydroperoxides, peroxodisulfates, percarbonates, peroxiesters, hydrogen peroxide and azo compounds. Examples of initiators are hydrogen peroxide, dibenzoyl peroxide, dicyclohexylperoxodicarbonate, dilauryl peroxide, methyl ethyl ketone peroxide, acetylacetone peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, tert-butyl perneodecanoate, tert-amyl perpivalate, tert-butyl butyl perodobutyl peroxobutyl peroxobutyl peroxobutyl peroxyl benzoate, ammonium nitrate, sodium, potassium peroxyl benzene, , 2,2'-azo-bis (2-amidinopropane) dihydrochloride, 2- (carbamoylazo) isobutyronitrile and 4,4'-azobis (cyanovaleric acid). The initiators are usually used in amounts of up to 15, preferably 0.02 to 10% by weight, based on the monomers to be polymerized. The use of the known redox initiators, in which the reducing component is used in molar deficiency, is also suitable. Known redox initiators are, for example, salts of transition metals such as iron-II-sulfate, copper-I-chloride, manganese-II-acetate, vanadium-III-acetate. Redox initiators which can furthermore be used are reducing sulfur compounds, such as sulfites, bisulfites, thiosulfates, dithionites and tetrathionates of alkali metals and ammonium compounds, or reducing phosphorus compounds in which the phosphorus has an oxidation number of 1 to 4, such as sodium hypophosphite, phosphorous acid and phosphites. Mixtures of the initiators or initiator systems mentioned can also be used. In order to control the molecular weight of the polymers, the polymerization can optionally be carried out in the presence of regulators. Suitable regulators include, for example, aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde and isobutyraldehyde, formic acid, ammonium formate, hydroxylammonium sulfate and hydroxylammonium phosphate. Furthermore, regulators can be used which contain sulfur in organically bound form, such as SH compounds containing organic compounds such as thioglycol acetic acid, mercaptopropionic acid, mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptohexanol, dodecyl mercaptan and tert-dodecyl mercaptan. Salts of hydrazine such as hydrazinium sulfate can also be used as regulators. The amounts of regulator, based on the monomers to be polymerized, are 0 to 20, preferably 0.5 to 15% by weight.

By heating the copolymer to 100-300 ° C., optionally under a nitrogen atmosphere or in vacuo, isobutene or other volatile elimination products from the alkyl ester units are obtained by thermal syn-elimination from the tert-butyl ester units (I). The resulting acid groups partially react further with neighboring amide groups and a copolymer of imide, anhydride, amide and remaining alkyl ester units (II) results.

II R = -H, -alkyl

Thermal syn elimination is favored over depolymerization in poly (tert-butyl methacrylate). The formation of methacrylic acid and / or methacrylic anhydride units prevents depolymerization and thus degradation to the respective monomers (G.Scott, Polymer Degradation and Stabilization, 1. Polymers and Polymerization, University Press, Cambridge, GB, 1985). The release of isobutene can also be catalyzed by deprotection of the carboxylic acid by photogenerated acid PAG, cf. Chem. Mater. 1996, 8, 2282-2290. Elimination can also be carried out by acid hydrolysis (K. Matsumoto et al., J. Polym. Sei. Part A Polym. Chem. 2001, Vol. 39, 86-92).

The alkenes released by thermal elimination act as blowing agents. If the reaction is carried out in a thin layer, the blowing agent diffuses and bubble-free, colorless films are obtained, cf. Angew. Makromol. Chem., II, 1970, 119, 91-108. Foaming can be achieved by extracting from the polymer e.g. produces a block by pressing or by melting the polymer under pressure so that the resulting propellant gas remains dissolved in the polymer. The latter can be achieved, for example, by extrusion or by foam injection molding.

The polymerization of copolymers of (meth) acrylic esters and (meth) acrylic amides in the presence of an aqueous diluent described in the context of the present invention has the following advantages over the prior art:

The polymerization in the diluent water or in aqueous solvent mixtures ensures good dissipation of the heat of reaction at all times, so that the polymerization temperature can be maintained within a narrow range even at high reaction rates.

The polymerization can be carried out inexpensively under normal pressure, but if necessary also under elevated pressure or in vacuo.

The extensive elimination of organic solvents is economical and has ecological advantages through the conservation of resources. There are also advantages under the aspect of occupational safety, since water is perfect as a solvent is harmless and organic solvents in a mixture with water experience a significant reduction in vapor pressure, so that both the pollution of the room air and the risk of fire and explosion are reduced.

Since the resulting copolymers are water-insoluble in the diluent and coolant, the polymer can be separated off in a technically simple and inexpensive manner, for example by filtration or by centrifugation. Since the use of cyclodextrins can be dispensed with, further purification steps of the polymer are omitted.

When the copolymers are heated, the secondary or tertiary alcohol esters are thermally syn-eliminated. The resulting alkenes act as foaming agents. Foaming therefore takes place without the additional use of blowing agents. However, additional blowing agents such as azodicarbonamide or urea can be used to regulate the foam density. The amount of blowing agent added is usually 0-20% by weight, but can also be higher.

The use of (meth) acrylamides as comonomers to the (meth) acrylic esters offers the advantage over the copolymerization of methacrylonitrile and (meth) acrylic esters that N-substituted imides are accessible by substituting a hydrogen atom on the nitrogen of the (meth) acrylamide.

Polymers produced according to the invention are suitable for the production of foams or PMI molding compositions, including N-substituted ones. EXAMPLES

Synthesis of Polv (tet-butyl methacrylate-co-N-methacrylamide)

Example 1 :

A 4 L three-necked flask equipped with a KPG stirrer and a nitrogen supply was evacuated three times and aerated with argon. 3400 mL of distilled water degassed in the ultrasonic bath were introduced into the flask. Argon was bubbled through the solution for 10 hours using an injection needle. 24.03 g (0.282 mol) of methacrylamide and 45.83 mL (0.282 mol) of teAt-butyl methacrylate were then added under counter-argon flow. The reaction mixture was again degassed several times with vigorous stirring and aerated with argon. After stirring for 1 h, the reaction mixture was heated to 40 ° C. Now 1 mL of the initiator solutions (redox initiators K ₂ S ₂ θ8 and NaaSaOs) were pipetted into the reaction solution so that the initiator concentration based on the monomers was 1 mol%. The copolymerization was terminated after 4 hours by cooling in an ice bath and by injecting air. The precipitated copolymer was filtered off, washed with 3 × 100 ml of water and then dried under high vacuum. The copolymer was obtained in a yield of 80%. According to NMR, the amide was incorporated in a proportion of 0.57. The weight average molecular weight was 774 400 g / mol, the number average molecular weight 383 500 g / mol and the polydispersity 2.0. The glass transition temperature of the copolymer is 125 ° C. Example 2:

The preparation and polymerization were carried out analogously to Example 1. However, only 0.41 g (4.8 mmol) of methacrylamide and 0.68 g (4.8 mmol) of tert-butyl methacrylate were used. The reaction was carried out in a 250 mL three-necked flask at a temperature of 50 ° C. The polymerization was stopped after 4 h. The copolymer was obtained in a yield of 30%. According to NMR, the amide was incorporated in a proportion of 0.53. The weight average molecular weight was 233 100 g / mol, the number average molecular weight 107 900 g / mol and the polydispersity 2.2. The glass transition temperature of the copolymer is 122 ° C.

Example 3:

A 100 mL three-necked flask equipped with a nitrogen supply was evacuated three times and aerated with nitrogen. The initiator solutions (redox initiators 0.215 g K ₂ S ₂ O ₈ (0.8 mmol) and 0.15 g Na ₂ S ₂ O ₅ in 23 mL water) were then introduced into the three-necked flask. The reaction mixture was stirred under a nitrogen atmosphere and heated to the respective reaction temperature (Table 1). 2.84 g (20 mmol) tert-butyl methacrylate and 1.7 g (20 mmol) methacrylamide were dissolved in 7 mL methanol. This mixture was added dropwise to the initiator solution over 15 minutes while passing a gentle stream of nitrogen through the solution. The copolymerization was terminated after the respective reaction time (Table 1) by adding 0.1 g of methylhydroquinone as an inhibitor. The precipitated copolymer was filtered off, washed with 200 ml of methanol, filtered off, washed again with 3 × 50 ml of methanol and then dried and analyzed under high vacuum. Table 1: Reaction conditions for copolymerizations carried out in a water-methanol mixture

Example 4:

A 100 mL three-necked flask equipped with a nitrogen supply was evacuated three times and aerated with nitrogen. 2.55 g (20 mmol) methacrylamide were dissolved in 30 mL degassed, distilled water. 2.84 g (30 mmol) of terf-butyl methacrylate were then added with stirring and in countercurrent nitrogen. The emulsion was stirred for 10 min under a nitrogen atmosphere and then heated to the respective reaction temperature. The copolymerization was initiated by adding the initiators (0.27 g (1 mmol) K ₂ S ₂ θ8 and 0.19 g (1 mmol) Na ₂ S ₂ O ₅ ). The copolymerization was terminated after the respective reaction time (Table 2) by adding 0.1 g of methylhydroquinone as an inhibitor. The precipitated copolymer was filtered off, washed with 200 ml of methanol, filtered off, washed again with 3 × 50 ml of methanol and then dried and analyzed under high vacuum. Table 2: Reaction conditions for copolymerizations carried out in water

From N-Ge old (elementary analysis), infrared spectroscopy

Thermolysis of the copolymers to poly (methacrylimides)

Examples 5-9: Foaming the copolymer from Example 1

The copolymer from Example 1 was finely pulverized and processed into tablets with a diameter of 12.5 mm (Examples 5, 8, 9) and 40 mm (Examples 6, 7). The tablets were foamed by heating under the conditions shown in Table 3. The composition of the copolymer foam was determined by NMR and the glass transition temperatures by DSC. Table 3: Foaming of the copolymer from Example 1

Examples 10-12: Foaming of the copolymer from Example 2

The copolymer from Example 2 was finely pulverized and processed into tablets with a diameter of 12.5 mm. The tablets were foamed by heating under the conditions shown in Table 4. The composition of the copolymer foam was determined by NMR, the molecular weights by volume exclusion chromatography based on PS standards and the glass transition temperatures by DSC.

Table 4: Foaming of the copolymer from Example 2

Comparative Example 1:

330 g of isopropanol and 100 g of formamide were added as blowing agents to a mixture of 5700 g of methacrylic acid, 4380 g of methacrylonitrile and 31 g of allyl methacrylate. Furthermore, the mixture was mixed with 4 g of tert-butyl perpivalate, 3.2 g of tert-butyl per-2-ethyl-hexanoate, 10 g of tert-butyl perbenzoate, 10.3 g of cumyl perneodecanoate, 22 g of magnesium oxide, 15 g of release agent (PAT 1037a) and 0.07 g of hydroquinone added.

This mixture was polymerized for 68 hours at 40 ° C. and in a chamber formed from two glass plates measuring 50 × 50 cm and an 18.5 mm thick edge seal. The polymer was then subjected to an annealing program ranging from 32 ° C. to 115 ° C. for 32 hours. The subsequent foaming took place at 205 ° C. for 2 h 25 min. The foam thus obtained had a density of 235 kg / m ³ .

Comparative Example 2:

A foam with a density of 71 kg / m ³ was produced in accordance with DE 33 46 060, 10 parts by weight of DMMP being used as the flame retardant. For this purpose, 140 g of formamide and 135 g of water were added as a blowing agent to a mixture of equal molar parts of 5620 g of methacrylic acid and 4380 g of methacrylonitrile. Furthermore, 10.0 g of tert-butyl perbenzoate, 4.0 g of tert-butyl perpivalate, 3.0 g of tert-butyl per-2-ethylhexanoate and 10.0 g of cumyl perneodecanoate were added as initiators to the mixture. In addition, 1000 g of dimethyl methane phosphonate (DMMP) were added to the mixture as a flame retardant. Finally, the mixture contained 20g release agent (MoldWiz) and 70g ZnO and 0.07g hydroquinone. This mixture was polymerized for 92 hours at 40 ° C. in a chamber formed from two glass plates of size 50 * 50 cm and a 2.2 cm thick edge seal. The polymer was then subjected to a tempering program ranging from 40 ° C. to 115 ° C. for 17.25 hours. The subsequent foaming took place at 215 ° C. for 2 hours. The foam thus obtained had a density of 71 kg / m ³ .

Comparative Example 3

For this purpose, a mixture of 5700 g methacrylic acid and 4300 g methacrylonitrile, 140 g formamide and 135 g water were added as blowing agents. Furthermore, 10.0 g of tert-butyl perbenzoate, 4.0 g of tert-butyl perpivalate, 3.0 g of tert-butyl per-2-ethylhexanoate and 10 g of cumyl perneodecanoate were added to the mixture as initiators. In addition, 1000 g of dimethyl methane phosphonate (DMMP) _t were added to the mixture as a flame retardant. Finally, the mixture contained 15 g of release agent (PAT) and 70 g of ZnO and 0.07 g of hydroquinone.

This mixture was polymerized for 92 hours at 40 ° C. in a chamber formed from two glass plates of size 50 * 50 cm and a 2.2 cm thick edge seal. The polymer was then subjected to a tempering program ranging from 40 ° C. to 115 ° C. for 17.25 hours. The subsequent foaming took place at 220 ° C. for 2 hours. The foam thus obtained had a density of 51 kg / m ³ .

Comparative example 4

The procedure was essentially the same as in Comparative Example 2, except that the foaming was carried out at 210 ° C. and the density of the foam obtained was then 110 kg / m ³ .

Claims

PATENT CLAIMS

1. Process for the preparation of copolymers from A) (meth)acrylamides (A) of the formula I

H ₂ C=CR ¹ CONHR ² where:

R ¹ =H or CH ₃ ,

R ² is an alkyl or aryl radical with up to 36 carbon atoms, which additionally contains oxygen, nitrogen, sulfur and phosphorus atoms in the form of typical organic functionalities such as ether, alcohol, acid, ester and amide - may contain imide, phosphonic acid, phosphonic acid esters, phosphoric acid esters, phosphinic acid, phosphinic acid esters, sulfonic acid, sulfonic acid ester, sulfinic acid, sulfinic acid ester functions, silicon, aluminum and boron atoms or halogens such as fluorine, chlorine, bromine or iodine, can be methyl, ethyl, propyl, 2-propyl, butyl, tert-butyl, hexyl, ethylhexyl, octyl, dodecyl, octadecyl, or -R3-PO(OR4)2; whereR3 is an alkyl radical with up to 12 carbon atoms and R4 is an alkyl with up to 4 carbon atoms, methylene dimethyl phosphonate, methylene diethyl phosphonate.

B) Alkyl(meth)acrylic ester H2C=CR1COOR5 where: R ¹ has the meanings given above. R ⁵ can have the meanings isopropyl or tert-butyl or isobutyl; furthermore, R ⁵ can also be a longer-chain secondary or a longer-chain tertiary alcohol. C) a water-containing diluent and optionally further monomers copolymerizable with A) or B), characterized in that the monomers A) and B) are used in a molar ratio of 1:10 to 10:1.

2. The method according to claim 1, characterized in that the monomers A) and B) are used in a molar ratio of 1:5 and 5:1.

3. The method according to claim 1, characterized in that the monomers A) and B) are used in a molar ratio of 1:2 to 2:1.

4. The method according to claim 1, characterized in that a mixture of methanol, water and possibly other organic solvents is used as diluent C).

5. The method according to claim 1, characterized in that the diluent C) consists of more than 50% by weight of water.

6. The method according to claim 1, characterized in that the diluent C) consists of more than 80% by weight of water.

7. The method according to claim 1, characterized in that tert-butyl methacrylate is used as monomer (B).

8. The method according to claim 1, characterized in that the copolymer is converted into a polymethacrylimide by heating with the elimination of gaseous reaction products.

9. The method according to claim 1, characterized in that the alkyl esters of the copolymer are first cleaved by catalysis and the reaction product is converted in a second step by heating to form a polymethacrylimide.

10. Composition containing copolymer according to one of the above claims and additional blowing agents.

11.Composition according to claim 10, characterized in that the blowing agent is an alcohol with 3-8 carbon atoms, urea, N-monomethyl and/or N,N'-dimethyl urea, formic acid, formamide and/or water.

12. A process for producing foam, characterized in that copolymer or a composition according to one of claims 1 to 11 is pressed into a shaped body and then foamed by heating.

13. Use of the copolymers obtainable according to one of claims 1 to 11 as a general molding compound.

1 . Use of the molding compound according to claim 13 for producing foams.

15. A process for producing foam bodies, characterized in that molding material according to claim 13 is processed by foam extrusion or foam injection molding.

16. Use of the copolymers obtainable according to claims 1 to 9 for the use or production of coating agents.

17. Use of the copolymers obtainable according to claims 1 to 9 for the use or production of membrane materials.

18. Use of the foams mentioned in claims 12, 14 and 15 in sandwich constructions.

19. Use of the foams or sandwich constructions that can be produced according to one of the preceding claims in space, air, water or land vehicles.