CA2657206C

CA2657206C - Anhydrized copolymer

Info

Publication number: CA2657206C
Application number: CA2657206A
Authority: CA
Inventors: Herbert Leder; Juan Carlos Ruggieri
Original assignee: BellandTechnology AG
Current assignee: BellandTechnology AG
Priority date: 2006-07-07
Filing date: 2007-06-27
Publication date: 2015-04-07
Anticipated expiration: 2027-06-27
Also published as: CN101490109A; EP2041192A1; EP2041192B1; PL2041192T3; DE102006032225A1; ES2656397T3; WO2008003421A1; CN101490109B; CA2657206A1

Abstract

The invention relates to a copolymer comprising monomer units carrying carboxyl groups, particularly for the production of articles of daily use, wherein the carboxyl groups are present along a carbon chain of the copolymer and are each at least partially linked to a side group of a monomer unit adjacent within the carbon chain while forming intramolecular anhydride structures. The invention also relates to a method for producing copolymers and the use of the method in the production of articles of daily use.

Description

Description Anhydrized copolymer [0001] The invention relates to an anhydrized copolymer, a process for its preparation and the use of the copolymer according to the invention for the production of articles of daily use.

[0002] Polymers, such as copolymers, in particular terpolymers, based on a,(3-unsaturated monocarboxylic acids and neutral unsaturated vinyl monomers, are important starting materials for the production of a multiplicity of articles of daily use. The properties, for example the hardness, of the polymers and in particular the properties of the articles of daily use which are produced therefrom can be influenced in a targeted manner by the choice of starting monomers.

[0003] What is decisive for the production of polymeric articles of daily use is the thermal stability of the polymers at their processing temperatures. An example of a readily processable polymer combination comprising a polymer based on a,(3-unsaturated monocarboxylic acids is disclosed in EP 0 928 316 B1. However, at their processing temperatures, polymers frequently give rise to considerable problems, which in some cases can be avoided only by additional and in particular expensive operations. Thus, particularly the processing of the polymers based on methacrylic acid frequently leads to considerable evolution of smoke and gas, with the result that, for example, the exposure to harmful substances at the work place is increased. In principle, processing problems in the case of polymers make it more difficult to maintain quality standards in the case of the products to be produced therefrom.

[0004] It is therefore the object of the invention to provide a copolymer which avoids the disadvantages mentioned in the prior art and can be handled and processed without difficulties, particularly at its processing temperature.

[0005] This object is achieved by a copolymer comprising monomer units carrying carboxyl groups, in particular for the production of articles of daily use, the carboxyl groups being present along a carbon chain of copolymer and being at least partly linked in each case to a side group of a neighboring monomer unit within the carbon chain, with the formation of intramolecular anhydride structures.
The linkage between the carboxyl groups and the side groups in the copolymer is preferably based exclusively on the formation of intramolecular anhydride structures.

[0006] The invention provides a copolymer which in particular is thermally stable at its processing temperature and can be processed without difficulties to give the desired articles of daily use. This is achieved, according to the invention, by the presence of intramolecular anhydride structures in the copolymer, with the result that the reacted carboxyl groups of the copolymer can no longer undergo undesired secondary reactions. The other carboxyl groups are present either in isolation or with steric shielding within the carbon chain of the copolymer. They are therefore likewise not available for secondary reactions. In this way, uncomplicateci and in particular low-risk processing of the copolymer according to the invention is possible.

[0007] The presence of intramolecular anhydride structures in the copolymer according to the invention was verified by the inventors in particular using measured IR(infrared) spectra (figures 1 and 2).
Furthermore, the presence of intramolecular anhydride structures could be confirmed on the basis of the measurement of the torque by the so-called Brabender long-term experiment, according to which the torque did not increase in the case of mixtures of anhydrized copolymer and reactive components and besides the copolymer remained soluble. In contrast, the torque increases through the development of intermolecular crosslinking reactions between non-anhydrized copolymer and reactive components owing to the formation of larger copolymer molecules. Consequently, the solubility of the crosslinked copolymer also decreases to an increasing extent.

[0008] In the context of the present invention, a copolymer is to be understood as meaning a polymer that comprises at least two different monomer units. In the context of the present invention, a copolymer is also to be understood as meaning in particular a terpolymer.

[0009] In the context of the present invention, anhydrizing is to be understood as meaning the reversible formation of intramolecular anhydride structures in the copolymer.

[0010] In the context of the present invention, monomer units carrying carboxyl groups are to be understood as meaning monomer units within the copolymer which have in each case a carboxyl group or carboxylate group or a masked carboxyl group, in particular an ester group, outside the carbon chain of the polymer.

[0011] In the context of the present invention, a neighboring monomer unit is to be understood as meaning a monomer unit whose side group is reactive toward carboxyl groups. The neighboring monomer units are preferably the monomer units introduced in the preceding section and carrying carboxyl groups.

[0012] In the context of the present invention, a neutral vinyl monomer is to be understood as meaning a vinyl monomer which carries neither acidic nor basic groups, in particular no carboxyl groups.

[0013] In one embodiment, the side group of the neighboring monomer unit within the copolymer chain is a carboxyl group. Thus, the intramolecular anhydride structuresof the copolymer form in each case by a condensation reaction between two carboxyl groups.
Water is formed as a low molecular weight condensation product and can be removed from the reaction batch without technical effort. In this way, the reaction can advantageously be shifted in favor of the intramolecular anhydride structures in the copolymer.

[0014] In a preferred embodiment, the side group of the neighboring monomer unit within the copolymer chain is a masked carboxyl group, i.e. a group derived from the carboxyl group. The masked carboxyl group is preferably an ester group. Ester groups are particularly preferred as neighboring side groups for the formation of intramolecular anhydride structures in the copolymer. The alcohols forming by condensation reaction are in principle good leaving groups in organic reactions. Furthermore, low molecular weight alcohols, in particular n-butanol, can be easily removed from the reaction batch, for example by thermal reaction procedure. Thus, the formation of the intramolecular anhydride structures in the copolymer can be promoted in a particularly advantageous manner.

[0015] Furthermore, the masked carboxyl groups can be transferred to unmasked, i.e. free, carboxyl groups of neighboring monomer units by so-called neighboring group effects. This is effected, for example, by a nucleophilic attack of an unmasked carboxyl group on a masked carboxyl group, with the result that the attacking carboxyl group is itself masked. On the other hand, an unmasked carboxyl group arises from the originally masked carboxyl group. In this way, migration of carboxyl groups along the copolymer chain is possible before the carboxyl groups are consumed by formation of intramolecular anhydride structures. It is also possible that the carboxyl groups, after their migration along the carbon chain of the copolymer, are sterically shielded or isolated and in particular are no longer available for further reactions.

[0016] In a further embodiment of the copolymer according to the invention, the anhydride structures are present in the form of rings, preferably in the form of six-membered rings. The anhydride structures of the copolymer according to the invention are preferably glutaric anhydride structures.

[0017] In a particularly preferred embodiment, the intramolecular anhydride structures are formed in each case by reaction between the carboxyl group of a methacrylic acid unit and the ester group of an alkyl acrylate unit, in particular of an n-alkyl acrylate unit, preferably of an n-butyl acrylate unit.

[0018] According to the invention, it is intended in particular that the copolymer be free of covalent crosslinkages, in particular with impact-resistant components and/or stabilizers. This facilitates the recoverability of the copolymer according to the invention in a particularly advantageous manner.

[0019] In a further embodiment of the copolymer according to the invention, the proportion by weight of free carboxyl groups (carboxyl content) in the anhydrized copolymer is at least 13% by weight.
Particularly preferably, the proportion by weight of free carboxyl groups in the anhydrized copolymer is from 13 to 50% by weight, in particular from 13 to 25%
by weight, preferably from 13 to 20% by weight. The reacted carboxyl groups are deactivated by the anhydride formation. The other carboxyl groups are deactivated in particular owing to their steric shielding or isolation.

[0020] The copolymer according to the invention is in particular amorphous, preferably completely amorphous.

[0021] In a further embodiment, the copolymer according to the invention has a different glass transition temperature (Tg), preferably a lower glass transition temperature (Tg), compared with before the formation of the intramolecular anhydride structures.
The copolymer according to the invention preferably has a glass transition temperature (Tg) in the range from 85 C to 155 C, in particular in the range from 90 C to 150 C.

[0022] In a preferred embodiment of the invention, the copolymer is free of exothermic changes on heating to temperatures above the glass transition temperature (Tg), in particular on heating to its processing temperature. This is due particularly advantageously -as already mentioned several times - to the fact that the carboxyl groups on the one hand are consumed by the formation of intramolecular anhydride structures and on the other hand are no longer reactive in particular due to stearic shielding or isolation. In this way, the copolymer according to the invention is extremely thermally stable, with the result that substantially improved handling and in particular processing of the copolymer is possible.

[0023] In a further embodiment, the monomer units carrying carboxyl groups within the copolymer chain are a,(3-unsaturated monocarboxylic acid units, preferably methacrylic acid and acrylic acid units.

[0024] In a preferred embodiment, the copolymer is formed on the basis of at least two monomers from the group consisting of an acrylic acid, an alkyl acrylate and a neutral vinyl monomer. The acrylic acid is preferably acrylic acid itself, i.e. propenoic acid, and/or methacrylic acid. Preferably, the alkyl acrylate is an n-alkyl acrylate, preferably n-butyl acrylate.
According to the invention,it is furthermore intended that the neutral vinyl monomer be styrene or derivatives thereof, preferably styrene. The copolymer according to the invention is in particular a terpolymer, preferably based on methacrylic acid, n-butyl acrylate and styrene.

[0025] In a further embodiment, the copolymer has a proportion by weight of methacrylic acid in the copolymer of from 20 to 80% by weight, in particular from 25% to 70% by weight, preferably of about 40% by weight. Preferably, the copolymer according to the invention has a proportion by weight of n-butyl acrylate in the copolymer of from 15 to 70% by weight, preferably from 20 to 65% by weight, in particular from 20 to 40% by weight. Furthermore, the copolymer according to the invention has in particular a proportion by weight of neutral vinyl monomer in the copolymer of from 5 to 60% by weight, preferably from 10% by weight to 40% by weight.

[0026] The copolymer according to the invention can be compounded with numerous additives, for example with polymers, such as polymethyl methacrylate, plasticizers and fillers.

[0027] The copolymer according to the invention is particularly advantageously compounded with at least one impact-resistant component and/or at least one stabilizer. In this way, the properties of the copolymer can be controlled or influenced in a targeted manner according to the type of articles to be produced, in particular articles of daily use. The impact-resistant components are preferably polymeric compounds, in particular so-called core-shell structures. The shell and in particular the core of the core-shell structures may consist of polymers, in particular of copolymers. Thus, the shell may consist of a copolymer based on methacrylate and styrene. The core may be formed in particular from polybutadiene or a copolymer based on butadiene, in particular based on butadiene and styrene. The impact-resistant components are preferably only physically crosslinked with the copolymer according to the invention. Impact-resistant components which may be used are also those which have epoxy groups, for example a terpolymer of ethylene, butyl acrylate and glycidyl methacrylate.

[0028] The copolymer according to the invention, which is preferably transparent and colorless, may be in particular a suspension or solution polymer, the solution polymer being preferred for industrial production. Furthermore, the copolymer according to the invention may be a mass polymer. According to the invention, it is also possible for the copolymer to be a dispersion polymer.

[0029] The copolymer according to the invention can be dissolved in particular in an alkali medium, preferably an aqueous alkali. The solubility of the copolymer is based substantially on the opening of the intramolecular anhydride structures with salt formation of the copolymer. Preferably, the original number of carboxyl groups in the copolymer, i.e. the number of carboxyl groups prior to the anhydrizing of the copolymer, is retained as a result of the opening of the anhydride structures.

[0030] Furthermore, the copolymer, in particular a salt of the copolymer, can be precipitated. Preferably, the copolymer according to the invention can be precipitated in an acidic medium, in particular in a mineral acid, which is preferably dilute. The precipitation of the copolymer is based substantially on the protonation of the carboxylate groups forming during the salt formation of the copolymer to give carboxyl groups.- As a result of the formation of the carboxyl groups, the copolymer loses its salt character and hence in particular its water solubility. The copolymer is precipitated.

[0031] In a particularly preferred embodiment, the copolymer according to the invention can be regenerated (recovered or recycled) by further anhydrizing after opening of the anhydride structures and conversion of the carboxylate groups into carboxyl groups. The recoverability of the copolymer according to the invention is based substantially on the reversibility of the anhydrizing of the copolymer. The number of intramolecular anhydride structures in the regenerated copolymer corresponds in particular to the number of intramolecular anhydride structures in the copolymer in the original anhydrized state.

[0032] The present invention furthermore relates to a copolymer comprising monomer units carrying carboxyl groups, in particular for the production of articles of daily use, the copolymer being compounded by at least one impact-resistant component and/or at least one stabilizer, preferably by at least one impact-resistant component, and the carboxyl groups being present along a carbon chain of the copolymer and being linked at least partly in each case with a side group of a neighboring monomer unit within the carbon chain by formation of intramolecular, preferably exclusively intramolecular, anhydride structures. Regarding further features in this context, reference is made to the present description in its entirety.

[0033] The present invention also relates to a process for the preparation of a copolymer having anhydride groups on a carbon chain of the copolymer, carboxyl groups along the carbon chain of a thermoplastic copolymer undergoing ah intramolecular reaction, preferably exclusively intramolecular reaction, at least partly in each case with a side group of a neighboring monomer unit within the carbon chain, the side group being a carboxyl group or a group derived therefrom, by dry heating to give the anhydride structures. The side group derived from the carboxyl group is preferably an ester group.

[0034] In a particularly preferred embodiment of the process according to the invention, the conversion of the carboxyl groups into the intramolecular anhydride structures is carried out in an extruder, preferably in a twin-screw extruder. The conversion of the carboxyl groups into the anhydride structures can be carried out in particular directly after the copolymerization.

[0035] In a further embodiment of the process according to the invention, the copolymer is heated at a temperature between 180 C and 280 C, in particular between 220 C and 280 C, preferably between 260 C and 275 C, in particular at a temperature of about 270 C.
Particularly advantageously, the copolymer is heated for a short period.

[0036] The reaction of the carboxyl groups is carried out, for example, in an oven, preferably for up to 120 minutes, in particular for from 60 to 120 minutes.
In the extruder, the anhydrizing takes place substantially more rapidly, for example within a few minutes, since rapid and gentle heating and circulation take place here.

[0037] In a further embodiment, the copolymer can be shaped after the anhydrizing, immediately or preferably after prior compounding, to give the corresponding articles, for example to give sheets, extrudates and profiles, which can be further processed in particular by thermoforming and welding. It is also possible according to the invention first to prepare the copolymer in granular form or in powder form and optionally later to further process it in the desired manner, in particular thermoplastically, for example by injection molding or sheet production.

[0038] The copolymer is preferably compounded after the anhydrizing, in particular by addition of at least one impact-resistant component and/or at least one stabilizer.

[0039] In a particularly preferred embodiment of the process according to the invention, the copolymer is recovered with removal of compounding agents, the recovery comprising the following steps:

- preparation of a solution of the copolymer in an alkali medium with opening of the intramolecular anhydride structures and salt formation of the copolymer, - separation of the dissolved copolymer from the undissolved compounding agents and from impurities, - reduction of the pH of the solution with precipitation of the copolymer, - dry heating of the precipitated copolymer with re-formation of the intramolecular anhydride structures.

[0040] Products produced from the copolymer can be comminuted for recycling the polymer prior to the preparation of the copolymer solution, and in particular milled or shredded. In this way, the preparation of the copolymer solution can be accelerated.

[0041] The solution of the copolymer is prepared in particular in aqueous alkali, preferably in aqueous sodium hydroxide solution. The compounding agents, in particular the impact-resistant components, are present in alkali media advantageously in disperse, in particular in finely disperse, form.

[0042] The separation of the dissolved copolymer from the undissolved compounding agents and the impurities can be carried out, for example, by filtration.

[0043] The pH of the copolymer solution separated from the undissolved compounding agents and impurities is preferably reduced by addition of an acid, in particular a medium-strength acid. The acid is advantageously a mineral acid, preferably phosphoric acid. For the precipitation of the copolymer, a pH of < 6, in particular < 4.5, preferably of about 2.5, can be established. The precipitated copolymer can be further purified by additional washing steps, for example for removing salt residues, with the use of wash liquids, for example deionized water.

[0044] Regarding further details on the recovery process of the copolymer, reference is made in each case to the disclosure content of EP 0 468 375 Bi and EP 0 553 683 Bl.

[0045] The invention finally relates to the use of the copolymer for the production of articles of daily use, in particular of containers, crockery, for example dishes, or other articles of daily use. The articles of daily use may be in particular catering products, for example catering cups. Furthermore, the copolymer according to the invention is suitable for the production of sheets, in particular for packaging purposes (packaging sheets).

[0046] The copolymer according to the invention is distinguished in an advantageous manner by its thermal stability, in particular at its processing temperature.
Thus, uncomplicated and in particular low-risk processing of the copolymer according to the invention to give the desired articles of daily use is possible.
For example, no additional operations or safety precautions, for example owing to possible evolution of smoke or development of odor during heating of the copolymer according to the invention to its processing temperature, are required. Furthermore, no undesired crosslinking reactions with added additives, in particular with impact-resistant components, occur in the case of the copolymer according to the invention.
In this way, nozzle deposits in the processing machines, for example extruders, and in particular additional cleaning steps can be avoided.

[0047] Further features and details of the invention are evident from the following description of a preferred embodiment in the form of an example in combination with the figures and subclaims. Here, the individual features can be realized in each case by themselves or as a plurality in combination with one another in an embodiment.

The figures show the following:

figure 1: infrared spectrum of a non-anhydrized copolymer, figure 2: infrared spectrum of an anhydrized copolymer, figure 3: DSC recording (differential scanning calorimetry recording) of a non-anhydrized copolymer, figure 4: DSC recording (differential scanning calorimetry recording) of an anhydrized copolymer, figure 5: behavior of the torque during the processing of a compound of anhydrized copolymer on the one hand and non-anhydrized copolymer on the other hand, figure 6: behavior of the torque during processing of a compound of anhydrized copolymer on the one hand and non-anhydrized copolymer on the other hand, the copolymer having been recovered (recycled) beforehand in each case.

Description of figures

[0048] Figure 1 shows the IR spectrum of a non-anhydrized copolymer based on methacrylic acid, n-butyl acrylate and styrene. The spectrum shows a substantial band at about 1693 cm-1, which is the vibration band of the acyl group of the carboxyl groups present in the copolymer.

[0049] Figure 2 shows the IR spectrum of an anhydrized copolymer based on methacrylic acid, n-butyl acrylate and styrene. In addition to a vibration band at about 1695 cm-l, which is attributable to acyl groups of the carboxyl groups still present in the copolymer, the spectrum shows substantial bands at about 1726 cm-1, 1755 cm-1 and 1799 cm-1, which indicate the presence of intramolecular anhydride structures in the copolymer.

[0050] Figure 3 shows the DSC curve of a non-anhydrized copolymer based on methacrylic acid, n-butyl acrylate and styrene. The DSC recording shows two exothermic changes during the entire measuring time.
The first exothermic change takes place in a temperature range of between about 127 C and 137 C and corresponds to the glass transition temperature range of the copolymer. With the aid of the so-called tangential method, a glass transition temperature (Tg) of about 133 C can be determined. The second exothermic change takes place in a temperature range between about 225 C and 245 C and is attributable to the formation of the intramolecular anhydride structures in the copolymer.

[0051] Figure 4 shows the DSC recording of an anhydrized copolymer based on methacrylic acid, n-butyl acrylate and styrene. The DSC recording shows only one exothermic change, namely in the temperature range between about 107 C and 117 C. The exothermic change recorded in this temperature range corresponds to the glass transition temperature range of the copolymer.
With the aid of the tangential method, a glass transition temperature of about 115 C can be determined.

[0052] Figure 5 graphically reproduces the behavior of the torque during processing of compounded copolymers based on methacrylic acid, n-butyl acrylate and styrene. The compounding agent used was an impact-resistant component which was capable of reacting with free carboxyl groups. The copolymer was used firstly in the anhydrized form and secondly in the non-anhydrized form. The graph shows that the torque of the anhydrized copolymer remains substantially constant. This means that the anhydrized copolymer undergoes no reaction with the reactive compounding agent. Otherwise, the torque would have to increase owing to the formation of larger copolymer molecules (because of intermolecular crosslinkages). In the case of non-anhydrized polymer, on the other hand, the increase in the torque indicates a crosslinking reaction with the compounding agent.

[0053] Figure 6 graphically reproduces the behavior of the torque during the processing of the compound described in figure 5 and comprising anhydrized copolymer on the one hand and non-anhydrized copolymer on the other hand, the copolymer having been recovered or recycled beforehand in each case. The graph clearly shows that the curve characteristic described in figure 5 for the behavior of the torque also applies to the case where the compound arises from a recovered copolymer. Regarding further details, reference is therefore made in particular to the description of figure 5.

Example 1: Preparation of terpolymer based on 50% by weight of methacrylic acid, 40% by weight of n-butyl acrylate and 10% by weight of styrene

[0054] The polymerization of the monomers is carried out as a batch in a stirred tank reactor using ethanol as a solvent (weight ratio of ethanol/monomers 50/50) and in the presence of a peroxide initiator at a reaction temperature of about 80 C. The resulting heat of polymerization is removed via reflux cooling of the condensed solvent. After the end of the polymerization (about 7 hours), the polymer solution is pumped into an intermediate container and transferred from this to a twin-screw extruder. In the first part of the extruder, from 70% to 95% of the solvent are evaporated off under ambient conditions. The copolymer is then heated to about 270 C in the extruder. The copolymer passes through this temperature stage in the course of a few minutes (from 1 to 2 minutes), during which it is anhydrized. The remaining solvent is removed with the eliminated reaction products, in particular butanol and water, and with residual monomers and initiator residues in a downstream vacuum station or in two downstream vacuum stations. The final and anhydrized terpolymer can then be compounded, for example with a stabilizer and an impact-resistant component, and then granulated. The compounding can also be carried out in the first or in a second extruder.

[0055] A terpolymer based on 40% by weight of methacrylic acid, 25% by weight of n-butyl acrylate and 35% by weight of styrene can be prepared according to example 1, a weight ratio of ethanol/monomers of 40/60 being used for the preparation of the terpolymer. A
copolymer based on 40% by weight of n-butyl acrylate and 60% by weight of methacrylic acid can likewise be prepared. In the latter case, a weight ratio of ethanol/monomers of 50/50 is used for the preparation of the copolymer.

Example 2: Properties of copolymers before and after their anhydrizing Copolymer I: terpolymer based on 50% by weight of methacrylic acid, 40% by weight of n-butyl acrylate and 10% by weight of styrene Copolymer II: terpolymer based on 40% by weight of methacrylic acid, 25% by weight of n-butyl acrylate and 35% by weight of styrene Copolymer III: copolymer based on 40% by weight of n-butyl acrylate and 60% by weight of methacrylic acid Copolyme Carboxyl Carboxyl' T. (non- Tg r content content anhydrized (anhydrized (non- (anhydrized ) [ C] ) [ C]
anhydrized ) [% by ) [% by weight]
weight]
I 23.8 13.8 137 100

[0056] The values in percent by weight [% by weight]
stated in examples 1 and 2 for the monomers and the carboxyl content are based in each case on the total weight of the respective copolymer.

Claims

claims

1. A copolymer comprising monomer units carrying carboxyl groups, wherein the carboxyl groups are present along a carbon chain of the copolymer and a part of the carboxyl groups in each case are linked with a side group of a neighboring monomer unit within the carbon chain with formation of intramolecular anhydride structures, characterized in that the copolymer is a terpolymer based on methacrylic acid, n-butyl acrylate and styrene.

2. The copolymer as defined in claim 1, characterized in that the anhydride structures are in each case a glutaric anhydride structure.

3. The copolymer as defined in claim 1 or 2, characterized in that the anhydride structures are formed in each case by reaction between the carboxyl group of a methacrylic acid unit and the ester group of an n-butyl acrylate unit.

4. The copolymer as defined in any one of claims 1 to 3, characterized in that the proportion by weight of free carboxyl groups in the anhydrized copolymer (carboxyl content) is from 13 to 50% by weight.

5. The copolymer as defined in any one of claims 1 to 4, characterized in that the copolymer has a different glass transition temperature (T g) compared with before the formation of the intramolecular anhydride structures.

6. The copolymer as defined in any one of claims 1 to 5, characterized in that the copolymer has a glass transition temperature (T g) in the range from 85°C
to 155°C.

7. The copolymer as defined in any one of claims 1 to 6, characterized in that the copolymer has a proportion by weight of methacrylic acid in the copolymer of from 20 to 80% by weight.

8. The copolymer as defined in any one of claims 1 to 7, characterized in that the copolymer has a proportion by weight of n-butyl acrylate in the copolymer of from 15 to 70% by weight.

9. The copolymer as defined in any one of claims 1 to 8, characterized in that the copolymer has a proportion by weight of styrene in the copolymer of from 5 to 60% by weight.

10. The copolymer as defined in any one of claims 1 to 9, characterized in that the copolymer can be regenerated (recycled) after opening of the anhydride structures.

11. A composition comprising a copolymer as defined in any one of claims 1 to 10, characterized in that the copolymer is compounded with at least one impact-resistant component and/or at least one stabilizer.

12. A process for the preparation of the copolymer as defined in any one of claims 1 to 10, comprising subjecting a part of carboxyl groups in each case along the carbon chain of a thermoplastic copolymer to an intramolecular reaction with a side group of a neighboring monomer unit within the carbon chain, the side group being a carboxyl group or a group derived therefrom, by dry heating to give the anhydride structures.

13. The process as defined in claim 12, characterized in that the reaction is carried out in an extruder.

14. The process as defined in claim 12 or 13, characterized in that the copolymer is heated at a temperature between 180°C and 280°C.

15. A process for the production of the composition as defined in claim 11, comprising compounding said copolymer and at least one impact-resistant component and/or at least one stabilizer.

16. A process for recovery of a copolymer as defined in any one of claims 1 to 10, characterized in that the copolymer is recovered with removal of compounding agents, the recovery comprising the following steps:
- preparation of a solution of the copolymer and an alkali medium with opening of the intramolecular anhydride structures and salt formation of the copolymer, - separation of the dissolved copolymer from the undissolved compounding agents and impurities, - reduction of the pH of the solution with precipitation of the copolymer, and - dry heating of the precipitated copolymer with re-formation of the intramolecular anhydride structures.

17. The process as defined in claim 16, characterized in that the pH is reduced by addition of an acid.

18. The use of a copolymer as defined in any one of claims 1 to 10 or of the composition as defined in claim 11 for the production of containers, crockery, catering products, sheets, extrudates or profiles.