NO153594B - PROCEDURE FOR THE PREPARATION OF A PREPARATION BASED ON PSYLLIUM SEEDS AND LATE FRUITS. - Google Patents

Description

Copolymer of vinyl chloride and N-arylmaleimide.

This invention relates to new polymeric products, particularly those prepared by polymerizing N-substituted maleimides with vinyl chloride.

According to the invention, there is provided a new class of thermoplastic materials which are polymeric products containing from 99 to 60 weight percent vinyl chloride units, from 1 to 40 weight percent N-aryl maleimide units and from 0 to 20 weight percent units derived from at least one other copolymerizable, ethylenically unsaturated compound .

These products are thermoplastic, strong and unaffected by water, and are often more stable against degradation at elevated temperatures than homopolymers of vinyl chloride. The products which are copolymers of vinyl chloride with N-aryl maleimides alone or with a third monomer whose homopolymer has a softening point at least as high as a polyvinyl chloride of similar molecular weight have most of the properties usually associated with vinyl chloride plasters, but in addition have the appropriately increased softening points, often of an order of magnitude sufficient to permit continuous contact with boiling water without severe deformation. This improvement is further achieved without any significant increase in water sensitivity and little or no reduction in thermal stability.

It should be noted that the nature of the product will be at least partially determined by the relative proportions of the monomers, and that a number of different new thermoplastic materials can be obtained. In order for the polymeric product to be castable or otherwise moldable approximately like polyvinyl chloride, the amount of vinyl chloride must not be below 60 percent by weight. On the other hand, in order to achieve a useful increase in the softening point, at least 1 percent by weight of N-arylmaleimide must be copolymerized with the vinyl chloride.

It has been found as a general rule that as the N-aryl maleimide content is increased, the tensile yield strength is increased, but the castability is reduced. In order to obtain the best combination of good casting properties and high tensile strength, products containing from 70 to 90 weight percent of vinyl chloride residues, 10 to 30 weight percent of N-aryl maleimide residues and 0 to 20 weight percent of residues derived from other monomers that are copolymerizable with both vinyl chloride and N-aryl maleimide, a total of 100 per cent.

Here, an N-aryl maleimide is to be understood as a compound which is conceptually derived by replacing the hydrogen atom which is linked to the imide nitrogen atom in maleimide, with a monovalent aromatic radical. The monovalent aromatic radical may be derived from a fully aromatic hydrocarbon which is unsubstituted, e.g. benzene, diphenyl or naphthalene, or having one or more of the hydrogen atoms replaced by other monovalent atoms or groups; e.g. halogen atoms (such as chlorine, bromine, fluorine), hydroxyl groups, nitro groups, alkyl, aralkyl and cycloalkyl groups (especially containing up to 4 aliphatic carbon atoms), and groups of the structure -NH2, -NHR, -NRR', -OR, - CN,

-MOR, -SR, -COOR,"-COOH, -OCOR, -NHCOR

and -CONHR where M is a divalent aliphatic hydrocarbon radical, e.g. alkylene, and R and R' are each monovalent hydrocarbon radicals such as e.g. alkyl, cycloalkyl, aryl, alkaryl or aralkyl, preferably containing no more than eight carbon atoms, or halogenated (e.g. brominated, chlorinated or fluorinated) derivatives thereof. Two of the hydrogen atoms in the aromatic hydrocarbon can be replaced by a divalent radical so that, for example, get compounds such as indene or coumarone. It is preferred that the substituent does not contain any active hydrogen atoms as these can take part in reactions that are harmful to the polymerization reaction. Examples of such substituents are -OH, -NH, and

-COOH groups. N-maryl maleimides which have been found to be particularly suitable for use according to the invention are N-phenyl maleimides and substituted derivatives thereof in which at least one of the aromatically bonded hydrogen atoms is substituted with a halogen atom, a nitro group, a nitrile group or an alkyl or alkoxy group containing from 1 to 4 carbon atoms. . Examples of preferred aromatic and substituted aromatic radicals are phenyl, p-diphenyl, a-naphthyl, |3-naphthyl, o-, m- and p-tolyl, 2, 3, and 4-chlorophenyl, 4-bromophenyl, 2, 3 and 4-nitrophenyl 2,4,5-trichlorophenyl, 2,4,6-tribromophenyl, 2,3 and 4-t-butylphenyl, 2,4-dinitrophenyl, 4-benzylphenyl, 2 and •3-methoxyphenyl, 4-ethoxyphenyl, 4 -phenoxyphenyl, 2-chloro-4-phenoxy-methylphenyl, 4-cyanophenyl and 2-methyl-4-chlorophenyl.

It is further preferred that the substituent is not such that it increases the basic character of the imido nitrogen atom, as the products obtained by polymerizing these monomers with vinyl chloride may have reduced heat stability. Examples of such substituents is halo-

gene atoms and alkoxy groups. In some cases, however, it is desirable to use N-(halogen-substituted aryl)-maleimides because they generally give products with a good color. In these cases, it is preferred to use the bromine- or chlorine-substituted derivatives due to their availability.

When N-(substituted phenyl)-maleimides are used, those having a substituent in the 2-position on the phenyl radical are preferred, as the use of such compounds generally leads to polymeric products with less color than is obtained with other substituted N-phenyl maleimides.'

Examples of monomers which may constitute units forming up to 49% by weight of the copolymer are ethylenically unsaturated hydrocarbons (eg alkenes, dienes and aralkenes) and their halogenated derivatives; ethylenically unsaturated esters, e.g. esters of saturated alcohols and ethylenically unsaturated carboxylic acids and esters of ethylenically unsaturated alcohols and saturated carboxylic acids, ethylenically unsaturated ethers and anhydrides of ethylenically unsaturated acids. Specific examples include styrene, halogen-substituted styrenes, α-alkyl (e.g. α-methyl) styrene, unsaturated (e.g. vinyl or allyl) esters of fatty acids (especially acetic acid), alkyl esters of acrylic acid (e.g. methyl- , ethyl, n-butyl, 2-ethylhexyl and octadecyl acrylate), alkyl esters of methacrylic acid (e.g. methyl methacrylate, butyl methacrylate, 2-ethylhexyl and octadecyl methacrylate), alkenyl ethers such as vinyl ethers of alcohols containing up to 4 carbon atoms, acrylonitrile, methacrylonitrile, vinylidene chloride, dialkyl esters of monoethylenically unsaturated dicarboxylic acids such as diethyl fumarate and dimethyl maleate, maleic anhydride, dienes such as butadiene, isoprene and divinylbenzene, or other polyethylenically unsaturated compounds such as glycol dimethacrylate. The monomer is preferably one which has no detrimental effect on the properties of the copolymer.

Normally, such a third copolymerizable component is introduced to modify the properties in a desired way, e.g. to improve the flow properties under the conditions of manufacture, or to reduce residual . color in the copolymer, or to introduce unsaturated groups for later crosslinking. The addition of some of these monomers may, however, reduce or destroy the improvement in softening point achieved by introducing the N-arylmaleimide. When it is desired to retain the improvement in terms of softening point, suitable comonomers are those whose homopolymers have at least as high a softening point as a polyvinyl chloride of the same molecular weight. The softening points of the homopolymer and the polyvinyl chloride can be compared by any suitable test, such as e.g. 1/10 Vicat softening point or heat deformation temperature. Examples of such monomers are vinylidene chloride, acrylonitrile, methyl methacrylate, styrene, α-methylstyrene, o-chlorostyrene and maleic anhydride. In other cases where it is desired to increase the softening point, it is generally not preferred to use a third monomer.

The product can be produced by any of the well-known polymerization processes used for vinyl chloride, i.e. in bulk, in solution, in aqueous emulsion or in aqueous suspension (e.g. by what is usually referred to as a granular process in vinyl chloride poly -merization technique). When using a solvent process, the organic compound used as a solvent should not react with any of the monomers, and should preferably have little or no chain transfer effect on the polymerization reaction. Suitable solvents are hydrocarbons such as hexane, heptane, octane, benzene or toluene, alcohols such as methanol or ethanol, ethers such as diethyl ether, or ketones such as acetone. Chlorinated hydrocarbons can also be used, but these tend to have a chain transfer effect on the polymerization. Examples are 1,1-dichloroethane, tetrachloroethane, methyl dichloride, chloroform and carbon tetrachloride.

The polymerization can be initiated by means of any suitable source of free radicals, but is preferably produced. in the presence of a free-radical-releasing catalyst which is active at the polymerization temperature.

Polymerization is preferably carried out in an aqueous medium as this provides good dispersion of the polymerization heat, and the use of expensive equipment for solvent recovery is avoided. Emulsion polymerization in an aqueous medium is carried out by reacting the reacting components dispersed in water in the presence of a water-soluble free-radical catalyst, generally in the presence of a surface-active agent. The surfactant may be anionic (e.g. a salt of a long-chain alkylsulfonic acid), non-ionic (e.g. a water-soluble polymer such as polyethylene oxide) or cationic (e.g. a quaternary ammonium salt), and can be selected from those which were generally known for the polymerization of vinyl chloride. In granular polymerization, a dispersant (e.g. a protective colloid such as methylcellulose or hydrolyzed polyvinyl acetate) and a monomer-soluble catalyst are used. Temperatures that are usually used for the production of polyvinyl chloride (ie from 25 to 80°C) can be used for polymerisation, and a very suitable temperature range is from 25 to 65°C, although higher or lower temperatures can possibly be used.

Suitable catalysts are selected from those commonly used for the homopolymerization of vinyl chloride. For granular polymerization, e.g. azo nitriles such as α α'-azodiisobutyronitrile, and monomer soluble peroxides such as lauroyl peroxide, benzoyl peroxide and other organic compounds containing the peroxide O-O link. When it comes to emulsion polymerization, hydrogen peroxide or water-soluble salts of peroxyacids are generally used. An example is ammonium persulfate. It has been found that the presence of the N-aryl maleimide can increase the reaction time and also decrease the molecular weight of the product. The former effect can be reduced by choosing a more active catalyst, and the latter effect can be avoided to a certain extent by lowering the polymerization temperature. If a further increase in reaction time is to be avoided, it may also be desirable in this case to compensate for this by weighing a more active catalyst. The amount of catalyst required to give the desired results is usually between 0.01 and 2 percent based on the weight of the polymerizable monomers.

In the preferred process, the water, catalyst, surfactant (ie emulsifier or dispersant) and N-aryl-maleimide are added to a reaction vessel from which water is then removed, e.g. when flushing with an inert gas, e.g. nitrogen, or by evacuation or both. The vinyl chloride is then introduced into the vessel, and the reacting substances are brought to the reaction temperature to initiate polymerisation. This process can occasionally produce a non-homogeneous product, and to improve the homogeneity it may be desirable to add the desired amount of N-arylmaleimide continuously or discontinuously during the reaction. In such a case, the compound is suitably added as a solution in a suitable solvent or as a dispersion in water.

As the amount of N-aryl-maleimide found in the polymer is usually higher than one would expect after the monomer addition, it may be necessary to add the N-aryl-maleimide to the polymerization in a quantity ratio slightly below that desired for the polymeric product . A reduction of up to approx. 5 or 10 percent by weight is usually sufficient, although a higher reduction may be necessary in some cases.

After the polymerisation, the polymeric product can be separated from the reaction liquid in any suitable way such as e.g. by filtration or centrifugation, by heat or by a combination of these methods. The product can then be cleaned, e.g. by washing with a suitable selective solvent such as water, an ether or an alcohol. Finally, it can be dried, e.g. in a fluidized bed or by spray drying or by drying in an oven.

Less important components can be added to the product, and examples of such components include fillers (e.g. fiberglass), pigments, heat and light stabilizers, plasticizers, lubricants and mold release agents. The copolymers can also be mixed with other polymeric material, e.g. thermoplastic materials such as polyvinyl chloride or synthetic rubbers such as those derived from butadiene.

As the products according to the invention generally possess most of the properties that are generally associated with polyvinyl chloride, they can be used with good effect for applications where a polyvinyl chloride would be used. The preferred products according to the invention can also be used for many purposes where polyvinyl chloride cannot be used due to its poor dimensional stability at high temperatures. The present materials are thus particularly suitable for the production of rigid castings using any of the manufacturing processes used for thermoplastic materials, such as profile injection, injection molding, compression molding or trans-compression molding. The polymers which have reduced viscosities (measured for a solution of 0.5 g of polymer in 100 ml of dimethylformamide at 25°C) of at least 0.3 are particularly suitable for such purposes.

The shaped articles made from many of the polymeric products can be subjected to high temperatures that are generally above the softening points of homopolymers of vinyl chloride. Applications include pipes and joints for use in hot water pipes. Other applications will be obvious to a polymer manufacturer.

The invention shall be illustrated by the following examples where all parts are parts by weight. In all examples, the reduced viscosities were measured in solutions of 0.5 g of polymer in 100 ml of dimethylformamide at 25°C, unless otherwise stated.

Example 1.

One hundred parts of vinyl chloride was dispersed in 200 parts of water using 0.5 part of partially hydrolyzed polyvinyl acetate as dispersant. One part of lauroyl peroxide was added as a catalyst, and the dispersion was stirred under an atmosphere of nitrogen at 7-14 kg/cm 2 and at a temperature of 45°C for 66 hours. The resulting slurry of polymer 1 water was centrifuged to separate the solid product which was then washed thoroughly with water and dried in vacuo. The yield was 98 parts polyvinyl chloride with a reduced viscosity of 1.2 and 1/10 and 10/10 Vicat softening points of 76 and 103°C measured on a sample stabilized with 2% by weight of a commercially available organotin stabilizer and extruded from the polymer without prior processing.

The polymerization was repeated using 90 parts of vinyl chloride and 10 parts of N-phenylmaleimide. The yield of the product after 66 hours of reaction at 45 °C, followed by separation, purification and drying, was approx. 100 percent of the theoretical. It was in the form of whitish granules and had a reduced viscosity of 0.94. The product was mixed with 2% by weight of a commercially available organotin stabilizer by adding a solution of the stabilizer and evaporating the solvent, and cast at 170°C to give light brown sheets with a 1/10 Vicat softening point measured under the same conditions as for the homopolymer of vinyl chloride, at 79.5°C, 3.5°C higher than for polyvinyl chloride. 10/10 Vicat softening point was 113°C.

Analysis of the copolymer according to the chlorine content showed that it contained 89 weight percent vinyl chloride units and 11 weight percent N-phenyl-maleimide units.

Example 2.

The procedure according to example 1 was repeated using 80 parts of vinyl chloride and 20 parts of N-phenyl-maleimide, and after 46 hours of polymerization and subsequent separation, purification and drying, 95.2 parts of polymeric product were obtained in the form of whitish grains with a reduced viscosity of 0.80.

After admixture with 2% by weight of a commercially available organotin stabilizer in the same manner as described in Example 1, the product was cast at 170°C to give light brown plates with 1/10 and 10/10 Vicat softening points, measured as in " example 1, at 103°C (27°C higher than for polyvinyl chloride) and 121.5°C.

Analysis of the product by chlorine content showed that it contained 78.5 weight percent vinyl chloride units and 21.5 weight percent N-phenyl-maleimide units.

As a comparison, the process was repeated using 20 parts of N-benzyl maleimide, 80 parts of vinyl chloride, 285 parts of water, one part of lauroyl peroxide and 0.7 part of partially hydrolyzed polyvinyl acetate. The polymerization was carried out at 45°C for 29 hours, and the product was filtered, washed with water and carefully dried to give 45.5 parts of polymeric material containing 26.2% by weight of N-benzyl maleimide, as shown by nitrogen analysis. The product was mixed with a stabilizer as in Example 1 and compression molded to give sheets with a 1/10 Vicat softening point of only 73°C (lower than polyvinyl chloride), and was also insoluble in all common solvents.

As a further comparative experiment, 80 parts of vinyl chloride were polymerized with 20 parts of maleimide in 200 parts of water and in the presence of one part of lauroyl peroxide and 0.5 part of partially hydrolyzed polyvinyl acetate. The polymerization was carried out for 17 hours at 45°C, and the product was filtered, washed and dried to give 56.2 parts of polymeric material having a reduced viscosity of 0.7 and containing 44.7 weight percent maleimide. Die-cast sheets of the stabilized polymer had a 1/10 Vicat softening point of only 61.8°C and were noticeably unstable. After a few days, the container in which the samples were stored showed signs of corrosion by hydrogen chloride. After immersion in water at 55-60 °C, the product was further found to be considerably more sensitive to water than polyvinyl chloride. This is shown in the following table.

The weight reduction after the initial increase indicates that the vinyl chloride/maleimide polymerization product is dissolving.

Example 3.

The procedure. according to example 1 was repeated using 30 parts of N-phenyl-maleimide, 70 parts of vinyl chloride and a temperature of 40°C so that 68 parts of pale yellow grains with a reduced viscosity of 0.87 were obtained. The product was mixed with 2% by weight of a commercially available organotin stabilizer and extruded at 170°C to give brown, opaque plates with 1/10 and 10/10 Vicat softening points of 130 and 147°C. Analysis showed that the product contained 63 weight percent vinyl chloride and 37 weight percent N-phenyl-maleimide. A comparison between the product according to this example and the products according to examples 1 and 2 is shown in the following table.

It should be noted that the Vicat softening points show a steady increase with increasing N-aryl maleimide content, while the molecular weights (as shown by reduced viscosity) decrease. This reduction is to some extent offset in example 3 by the dense polymerization temperature.

Example 4.

A series of granular polymerizations of vinyl chloride and N-phenyl-maleimide were carried out at 50 °C in a stirred autoclave containing 4000 parts of water with eight parts of lauroyl peroxide as catalyst and 10 parts of partially hydrolyzed polyvinyl acetate as dispersant. In each case, all components except the vinyl chloride were added to the vessel which was then slowly evacuated, flushed twice with nitrogen and then evacuated again before introducing the vinyl chloride. Monomers were used in amounts totaling 2000 parts in each case.

After separation, washing and drying, the products were ground with 1% by weight divalent lead stearate on a two roll mill and then compression molded at 215°C into test pieces whose Vicat softening points were measured. The Fikentscher K value for each product was noted to give an indication of the molecular weight. The K-value was calculated from viscosity measurements of solutions of 0.25 g of polymer in 50 ml of ethylene dichloride at 25°C. For some of the test pieces, the Macklow-Smith yield pressure was obtained, which indicates the castability of the products. An increase in flow pressure indicates a reduction in castability.

The general decrease in molecular weight and increase in Macklow-Smith yield pressure with increase in N-aryl maleimide content should be noted. The apparent reduction of 1/10 Vicat softening point is believed to be due to the milling conditions used before extrusion. The figures do not represent a real value for the temperature at which the product becomes plastic, as it was noticed during production that with increasing N-aryl-maleimide content the product became more difficult to gel under the conditions normally used for polyvinyl chloride . For trial E, the grinding temperature even had to be raised to 170°C before a satisfactory crimp could be obtained. This suggests that the true softening point of the product actually increases with increasing N-aryl maleimide content.

Example 5.

A further series of granular polymerizations of vinyl chloride with N-phenyl-maleimide was carried out at 60 °C using lauroyl peroxide as catalyst and partially hydrolysed polyvinyl acetate as dispersant. In most cases, the monomer addition amounted to 2000 parts and 4000 parts of water were used. In example F, however, the water addition was 2000 parts and the monomer addition 1000 parts.

During painting, the product was mixed with 1% by weight divalent lead stearate, and for the Vicat tests, test pieces were pressure-molded at 215°C.

While the increase in 1/10 Vicat softening point is very small as the N-aryl maleimide content increases, the increasing difficulty in painting the material suggests that the temperature at which the material becomes plastic was increased considerably. This was particularly noticeable for the material which contained 33.3% by weight. N-phenyl-maleimide.

Example 6.

A further series of granular polymerizations of vinyl chloride and N-phenyl-maleimide was carried out at 70°C using 4000 parts water, a total of 2000 parts monomer, 2 parts lauroyl peroxide and 5 parts dispersant. Test conditions and results are indicated in the following table:

Example 7.

To an autoclave were added 3500 parts of distilled water, 8 parts of lauroyl peroxide, 10 parts of partially hydrolyzed polyvinyl acetate and 200 parts of N-phenylmaleimide as a solution with a strength of 40 g/100 ml of ethylene dichloride. The vessel was then evacuated, flushed twice with nitrogen, evacuated again and 1800 parts of vinyl chloride was added and polymerization was carried out at 60°C to give 1728 parts of whitish product.

Example 8.

To an autoclave were added 200 parts of water, 6 parts of ammonium persulfate, 3.33 parts of a salt

of an organic sulfonate as an anionic emulsifier and 400 parts of N-phenylmaleimide. After evacuation and flushing, 1,600 parts of vinyl chloride were added to the vessel, and the temperature was raised to 50°C. After 8 hours the polymerization was complete, and after separation, purification and drying, 1610 parts of a whitish product were obtained.

Example 9.

The procedure according to Example 5K was repeated using 8 parts lauroyl peroxide, 10 parts dispersant and N.-. chlorophenylmaleimide instead of N-phenylmaleimide. 1655 parts of a white product with a Fikentscher K value of 49.6 were obtained. After milling at 150°C for 10 minutes, it was extruded to give a specimen with a 1/10 Vicat softening point of 83°C.

Example 10.

To a vessel was added 200 parts of water containing 1 part of lauroyl peroxide, 0.5 part of partially hydrolyzed polyvinyl acetate and 20 parts of N-o-chlorophenylmaleimide. The vessel was then pressurized with N2 and vented 3 times to remove any dissolved air. 80 parts vinyl chloride was then added and the pressure was raised to 8.5 kg/cm 2 with nitrogen. The mixture was shaken at 45°C for 24 hours. The product was filtered off, washed well with hot water followed by ethanol and then dried in vacuo at 70-75°C to give 67 parts with a reduced viscosity of 1.08. The product contained 22.3% by weight of N-o-chlorophenyl-maleimide based on nitrogen analysis. After mixing with 2% by weight stabilizer in the same way as described in example 1, it could be press-molded into sheets with 1/10 and 10/10 Vicat softening points of 89 and 136.6°C respectively.

Example 11.

The procedure of Example 10 was repeated using N-o-tolylmaleimide instead of N-o-chlorophenylmaleimide, and the polymerization was carried out at 45°C for 23 hours. The product was processed as described in Example 10 to give 55.3 parts of polymeric material having a reduced viscosity of 1.02 and containing 62.5 weight percent vinyl chloride based on chlorine analysis. In this and all of the following examples, the polymer was mixed with 2 percent by weight of an organotin stabilizer in the same manner as described in Example 1, and plates were compression molded from the mixture. The die-cast plates in this case had 1/10 and 10/10 Vicat softening points of 73.4 and 153.2°C.

Example 12.

The procedure of Example 10 was carried out using 20 parts of N-phenylmaleimide, 70 parts of vinyl chloride and 10 parts of vinyl ether. Polymerization was carried out at 55°C for 19 hours. The polymer was processed as described above to give 76.4 parts of product with a reduced viscosity of 0.64. Die cast castings had 1/10 and 10/10 Vicat softening points of 75.8 and 118.2°C. The product contained 37% by weight of chlorine, indicating the presence of 65.3% by weight of vinyl chloride. Nitrogen analysis (2.1 weight percent) indicated the presence of 26 weight percent N-phenyl-maleimide.

Example 13.

160 parts of methanol, 10 parts of N-phenylmaleimide and 1 part of lauroyl peroxide were added to a vessel. The vessel was then pressurized to 7.0 kg/cm<2> with nitrogen and vented 3 times, and 90 parts of vinyl chloride was added. The mixture was shaken at 50°C and 9.5 kg/cm^ for 3 days, after which the product was filtered off, washed well with methanol and dried in vacuo at 60°C to give 73.8 parts of polymeric material with a reduced viscosity of 0.38 and containing 85% vinyl chloride by weight. Die cast castings exhibited 1/10 and 10/10 Vicat softening points of 70.8 and 100°C. It was assumed that these low readings were due to the product's low molecular weight.

Example 14.

The procedure according to example 13 was repeated with 10 parts of N-phenylmaleimide, 90 parts of vinyl chloride, 240 parts of methanol and 1 part of acetyl-cyclohexyl-sulphonyl peroxide. The mixture was shaken at 25°C for 3 days and the solids were isolated to give 73 parts of polymeric product having a reduced viscosity of 0.4 and containing 86.8 weight percent vinyl chloride based on chlorine analysis.

Example 15.

The procedure according to example 2 was repeated, but in this case the N-phenylmaleimide was added in 8 portions at half-hour intervals during the polymerization in the form of a dispersion in water. The yield was 48.5 parts of a product with a reduced viscosity of 0.78. A portion was mixed with 2% by weight of an organotin stabilizer and compression molded at 200°C to give brown, opaque specimens with 1/10 and 10/10 Vicat softening points of 114— 120°C and 139— 143°C. Chlorine analysis indicated a vinyl chlorine content of 60% by weight.

Claims (5)

1. Copolymer, characterized in that it contains 99 to 60 percent by weight vinyl chloride copolymerized with 1 to 40 percent by weight of at least one N-arylmaleimide and optionally up to 20 percent by weight of at least one other ethyl-enunsaturated compound that is copolymerizable with both vinyl chloride and N-arylmaleimide. 2. Copolymer as stated in claim 1, characterized in that it contains 90 to 70 weight percent vinyl chloride and 10 to 30 weight percent N-arylmaleimide, and if desired up to 20 weight percent of at least one other copolymerizable monomer. 3. Copolymer as stated in claims 1 to 2, characterized in that the N-arylmaleimide is N-phenylmaleimide or a substituted derivative thereof, in which at least one of the aromatically bonded hydrogen atoms is replaced by a halogen atom, a nitro group, a nitrile group or an alkyl or alkoxy group with from 1 to 4 carbon atoms. 4. Copolymer according to one of claims 1 to 3, characterized in that the N-arylmaleimide is an N-(2-substituted phenyl)-maleimide. 5. Process for producing a copolymer according to one of claims 1 to 4, characterized in that said substances are copolymerized in the presence of a free-radical initiator.