CA1069644A

CA1069644A - Acrylonitrile polymers stabilized against thermal discoloration with mono and di-isocyanates

Info

Publication number: CA1069644A
Application number: CA243,759A
Authority: CA
Inventors: Manfred Krieg; Armin Meyer
Original assignee: Roehm GmbH Darmstadt
Current assignee: Roehm GmbH Darmstadt
Priority date: 1976-01-19
Filing date: 1976-01-19
Publication date: 1980-01-08

Abstract

ABSTRACT OF THE DISCLOSURE
The Specification describes polymer materials comprising (a) a homopolymer of acrylonitrile or a copolymer of acrylonitrile and at least one further copolymerisable monomer, the copolymer containing at least 20% by weight of units of acrylonitrile; and (b) at least one alkyl, cycloalkyl or aryl isocyanate in an amount sufficient to inhibit or prevent thermal discoloration. The anti-discoloration additive can be incorporated into a monomer composition from which the homopolymer or copolymer is formed or can be admixed with the formed polymer.

Description

106~t~44 ! The present invention relates to polymer materials having an increased resistance to thermal discoloration.
Homopolymers and copolymers of acrylonitrile have an advantageous combination of strength and toughness, which renders them useful for numerous industrial applications.
These polymers have the disadvantage, however, that they tend to turn yellow or even brown when heated to tempera-tures above 80, particularly above 120C. Temperatures of this order are often unavoidable in the processing or use of the polymers and therefore numerous attempts have been made to avoid such thermal discolo~ation. As a consequenee, a number of compounds have bee~ found which suppress dis-coloration to such an extent that it is no longer trongly apparent in the case of fibres or thin films. However, in moulded articles with wall thicknesses of up to several centimetres, the polymers treated wqth the previously proposed additives still tend to have a yellow to dark brown appearance. The cause of discolo~ation was recognised from the investigations carried out by Kirby, Brandrup et al (Macromolecules, vol. 1, No. 1 (1~68)p. 53-86~, to be the polymerisation of the nitrile groups to form structures of the formula . . , ~
, . . .

- :. . : . , -.. . . . .
,, , ! 1 0~9 6 ~
~ , ''' CH2 / CH2 ~ / 2~ f H2 ' . ¦ CH ~H ~H CH

,,, ~ N N N / 151 ,,, . '.
.

Such structures may ~e formed even if acrylonitrile forms a proportion of for example only 20% of a copolymer, since this monomer has the tendency to form longer cohesive sequences, owing to its copolymerisation behaviour.
The reaction sequence which precedes the polymerisation of the nitrile groups has also been researched extensively.
A key role in this reaction sequence is played by an enolic structure of formula

2~H/CH2 ~CH2 -~-ZC~ \ OH
CN
. ~' .

This enolic structure initiates the polymerisation of the nitrile groups. Various mechanisms can be postulated for

- 3 - -,, .
. .", '.

. ... . . , - . . .
. . . . . . .. .. . . . . .
. . . .. .

~C~69 ~ 4'~

the formation of structures of this kind, but hitherto no-one has succeeded in preventing the formation and further reaction of the enols.
The present invention is bas~d on the discovery that isocyanates of the type specified below prevent or inhibit the thermal discoloration of homo- and copolymers of acrylonitrile although the precise mechanism by which such compounds inhibit discoloration has not yet been elucidated.
According to one feature of the present invention we provide polymer materials comprising ~a) a homopolymer of acrylonitrile or a copolymer of acrylonitrile and at least one further copolymerisable mon~,mer, the copolymer containing at least 20% by weight of units of acrylonitrile; and (b) at least one alkyl, cycloalkyl or aryl isocyanate in an amount sufficient to inhibit or prevent thermal discoloration of the said materials.
It should be noted that the isocyanates which may be employed in accordance with the present invention are not limited to mono-isocyanatesbut include compounds having more than one isocyanate group, as exemplified below.
The isocyanate employed in the above-defined polymer .
n'aterials according to the invention may be an alkyl iso-cyanate such as iso~utyl iso~:yanate, octyl isocyanate or ,, : - , . .
. . . . .... - :

3.069644 hexamethylene di-isocyanate; a cycloalkyl isocyanate such as isophorcne di-isocyanate;or an aryl isocyanate such as phenyl isoc-yanate or toluene di-isocyanate.
The polymer material according to the invention can be S prepared in various ways, provided that the resulting ma~erial c~,ntains an effective amount of the isocyanate when it is heated to a temperature at which discoloration would occur in the absence of the additive.
The discoloration reactions, like most reactions in 10 organic chemistry, proceed at a terminal velocity which is . .
; dependent on temperature. It is therefore possible for the polymer materials according to the invention to be prepared before conditions which promote discoloration have resulted in disadvantageous discoloration of the materials.
The pol,vmer materials according to the invention are homogeneous in the sense that they contain at least an effec-tive quantity of the added compound to inhibit or prevent therrnal discoloration at every point, even if there are still variations in concentration. The simplest and fastest ; way of determining whether such homogeneity has been achieved in individual cases is by heating a sample and testing it for disadvantageous discoloration. Conditions which result in premature decomposition of the additives must be avoided., .
. ` , ' "'~
' ' . , , , .:

~069~

The amounts in which the isocyanate are added to the polymer materials depend on various factors and should be determined separately in individual cases. The proportion of acrylonitrile in the composition of the polymer, the maximum possible temperature and duration of heating and the degree of discoloration acceptable in practice are usually the most important factors in the determination.
Taking into account these factors, the effective amoun;~
of isocvanate generally ranges from 0.05 to 5%-'and preferably 0.1 to 2%, based on the weight of polymer material. As a rule, the above amounts can be exceeded without disadvantage.
According to a further feat~re of the present invention , we provide a process for the preparation of polymer materials as hereinbefore defined which comprises incorporating an effective amount (as herein defined) of at least one alkyl, cycloalkyl or aryl isocyanate in a monomer composition comprising acrylonitrile and, if desired, at ]east one further copolymerisable monomer, (or in a partially polymerised comp-osition derived therefrom), the monomer composition containing at least 20% by weight of acrylonitrile; and polymerising the said composition.
The term "effective amount" is ~sed herein in relation . ' 1069644 ;

to the above-defined process according to the ir.vention to denote an amount of the said isocyanate which is at least sufficient to inhibit or prevent thermal discoloration o~
the polymer materials produced by the process.
The polymer material according to the invention is ; preferably prepared by bulk polymerisation wherein the isocyanate may be dissolved in acrylonitrile or in an appropriate acrylonitrile-containing monomer mixture, if desired after partial polymerisation, and the polymerisa-tion carried out in conventional manner. The polymerisa-tion may be carried out for example in a chamber consisting of two glass plates and an intermediate gasket around the edge thereof.
The polymer material according to the invention can alternatively be prepared by bead polymerisation. For the preparation of the polymer materials in this way, the isocyanate may be dissolved in acrylonitrile or in an appropriate acrylonitrile-containing monomer mixture, if desired after partial polymerisation, and the polymerisation .. . . .
~ ~ 20 carried out in conventional manner in the aqueous phase.
; Another possibilit!y is the polymerisation of the acrylo-nitrile in solution, for example i~ dimethylformamide or dimethylacetamide. The isocyanates can then be added to :~ :~ .
: ~ the monomer solution although it sh uld be checked that they ~ ;

:, : ;'`' ~ r ., : . ... . .

are not separated from the polymer when the solution is further processed. This precaution must also be observed with other polymerisation processes, e.g. precipitation or emulsion polymerisation.

The monomer~which may be copolymerised with acrylo-nitrile are generally unsaturated radically polymerisable compounds, particularly preferred monomers including styrene, ~-me~hylstyrene, butadiene, isoprene, acry'ic and methacrylic acid esters and methacrylonitrile. Vinyl esters, unsaturated ketones, vinylalkyl ethers, vinyl chloride and vinylidene chloride can also be employed as comonomers. In addition, cross-linking monomers, such as divinylbenzene, triallyl cyanurate or glycol dimethacrylate, can also be used.
Although the preferred embodiment s the addition of the isocyanate to the monomers, with subsequent polymerisation, I the isocyanate can alternatively be mixed with the finished ¦ polymer which is not yet discoloured~ For example, the ¦ isocyanate may be added to a solution of the polymer and fibres or films may be produced from this solution in conventional manner.
If the polymer is present in a finely divided form, e.g. as a precipitation polymer powder or a bead polymer, :1 - 8 .

.

`

10696'~
the isocyanate may be allowed to penetrate the polymer particles by diffu-sion. For this purpose, the polymer particles may be brought into direct contact with the isocyanates which are generally present as liquids, or with their vapours, solutions or emulsions. If solutions or emulsions are used, the carrier liquid should not be a solvent for the polymer. The time taken for the isocyanate to be homogeneously distributed in the polymer particles by diffusion may be from several hours to several days.
The present invention also provides a process for the preparation of polymer materials as referred to above which comprises admixing at least one alkyl, cycloalkyl or aryl isocyanate with a homopolymer of acrylonitrile or a copolymer of acrylonitrile and at least one further copolymerisable monomer, the copolymer containing at least 20% by weight of units of acrylonitrile; the isocyanate being employed in an amount sufficient to inhibit or prevent thermal disc~loration of the resulting materials.
According to this latter possibility the finely divided polymer can be mechanically mixed with the isocyanate and the mixture then homogenised by co-melting. For this purpose an extruder, for example, one with one or preferably several screws may be used. The melting temperature required depends on the softening temperature of the polymer and is generally from 180 to 220C.
As indicated above, polymers or copolymers of acrylonitrile, in the absence of the compounds to be added according to the invention, are ` formed as clear products which are yel~owish to dark brownish-yellow in colour when the layers are several millimetres to several centimetres thick.

~ .
. ~

_ g _ , ~
.

10694~

When the layers are thicker, i.e~ from about half a millimetre upwards, the discoloration is a considerable problem, particularly if the product is heated to even higher temperatures, e.g. 150-180C, for moulding. By means of the present invention, we have succeeded in reducing this discoloration to a slight yellow tinge (at a thLckness of 3 - 5 mm), and, in the most successful cases, to colourlessness.
The activity of the isocyanatescan be further increas-ed by co-use of aliphatic th~ioethers (e.g. bis-(2-methoxy-carbonylethyl)-sulphide or -propyl-sulphide) and/or nitro-alkanes(preferably containing l to 8 carbon atoms) which are therefore advantageou~y incorporated into the polymer materials according to the present invention.
The invention is with advantage applicable to the production of polymers from which moulded articles with wall thicknesses of at least O.S mm can be made, i.e. bulk polymers and moulding ccmpounds. These are generally copolymers in which the proportion of acrylonitrile units is between 20 and 85%, particula~ly between 50 and 85~/o~ and which are produced by bulk or bead polymerisat~on. In such cases, : ~ :
15-80%, preferably 15-50%, of the weight of the copolymers is made up of units of styrene, a-methylstyrene, butadiene , ~

:: , .

~06g~

¦ or alkyl esters of acrylic or methacr~lic acid, and at most minor amounts of other monomers. If desired, an emulsion polymer containing acrylonitrile may be initially prepared and then converted into a bead-like product in a second step, by graft polymerisation.
Moulded articles produced from the polymer materials according to the invention have been formed to retain their pale colour even in use. When they are weathered (in a Xenotest apparatus) only a slight increase in the yellowing factor has been found if a conventional W protector is added to the plastic. We have tested polymer materials according to the invention by heating them several times, ;
or a long time after manufacture, to temperatures which would normally result in discoloration, and have found that - 15 the stabilising effect is unchanged and the products retain their light colour. It should be appreciated that the stabilising effect of the isocyanates relates only to temperatures to which the products are conventionally sub-jected in practice. If these temperatures are exceeded substantially, discoloration may occur although to a lesser extent than might have otherwise been the case. Other con-ventional additives, such as dyes, pigments, stabilisers, plasticisers and the like may if desired, be employed in the polymer materials.
.
. . . ...

: ,.,'~~'' ' ' :.

` -10~9644 The following Examples illustrate the present invention.
In the Examples the yellowing factor G is calculated, using the following formula, from the transmission values for light ~ -of the wavelengths 420, 560 and 620 nm, using the transmission 5 values for pure polymethyl methacrylate (PMMA) as a compari-son standard.
G = (420, A - 420, B) - (620, A 620, B) .100 560, A

420, A = transmission value for PMMA at 420 nm (analogously 620, A and 560, A for 6~.0 and 560 nm, respectively.
420, B = transmission value for, the sample tested, at 420 nm (analogously 620, B for 620 nm) Gloo relates to materials which were heated to 100C for 2 hours and G150 to material which were additionally heated to 150C for 30 mins.
Example A mixture of 70 parts of acrylonitrile, 30 parts of methyl methacrylate, 0.3 parts of ethyleneglycol dimethyl-acrylate, 0.2 parts~of cyclohexyl isocyanate and 0.15 parts of tert. butyl perpivalate was placed in a chamber consist-ing of two glass sheets with an elastic sealing cord placed ~ . ~.
. ~ .

: : '' :.
, . - , , - : .. . . ~ .
.. .. . . . . . : ~ . .. :

1069644 ~ ~

therebetween and was polymerised in a water bath at 45C ~ -for 20 hours. Subsequently, polymerisation was completed for 2 hours at 100C. Compared with a sheet without the additive according to the invention, the sheet had a sub-stantially lighter colour which remained essentially unchanged even under thermal stress (30 minutes at 150C). -Example 2 A light-coloured thermostable polymer sheet was produced analogously to Example 1, using a mixture of 0.4 parts of isophorone diisocyanate and 0.1 parts of bis-(2-methoxycarbonylethyl)-sulphide as thermostabiliser, instead of 0.2 parts of cyclohexyl isocyanate.
.~ .
Example 3 A mixture of 65 parts of acrylonitrile, 30 parts of methyl methacrylate, 5 parts of styrene, 0.3 parts of divinyl benzene, 0.3 parts of 2,4-diisocyanatotoluene, 0.2 parts of divinyl sulphone and 0.2 parts of dilauroyl per-oxide was polymerised, analogously to Example 7, to form a light-coloured thermostable sheet.

Example 4 !
A mixture of 50 parts of acrylonitrile, 50 parts of styrene, 0.4 parts of cyclohexyl isocyanate and 0.1 parts of azobisisobutyronitrile was polymerised between glass plates ' ' :
~"

; ~

.

'J ~f~L'~

analogously to Example 7 to form a sheet 5 mm thick.
The sheet was yellowish; on being heated to 150 for 30 mins. the coloration deepened somewhat. A comparison sheet without the additive according to the invention was distinctly yellow after the end of polymerisation and became deep yellow on being heated to 150 for 30 mins.
Example 5 30 parts of a monomer mixture of 80 parts of acryl-onitrile and 20 parts of methyl methacrylate were polymerised at 45C in 70 parts of dimethyl acetamide after the addition of 0.2 parts of ter. butyl perpivalate.
The highly viscous polymer solution was mixed with 0.7 parts of cyclohexyl isocyan,ate and 0.2 parts of bis-(2-methoxycarbonylethyl)-sulphide. Whereas the polymer solution without the additive turned brownish-yellow after only 30 secs. at the boiling temperature of the dimethyl acetamide, scarcely any coloration was visible in the polymer solution with the above additives even after boiling for 5 minutes.
Example 6 In a 2 litre!circular flask with a blade stirrer and B gas inlet tube, 5 parts of partl-~ saponified polyvinyl acetate ~Mowiol N 70-80, commerciai product made by Farbwerke Hoechst) are dissolved in 1000 parts of de-ionised _ 14 ~ ~ ~o~ , .. ~

1~)69~44 water and heated to 75G~ with stirring, using a water bath.
At this temperature, the monomer phase~ consisting of 350 parts of acrylonitrile 15~ parts of ethyl acrylate 2.5 parts of azoisobutyronitrile 2.5 parts of isophorone diisocyanate and 1.5 parts of bis-(2-methoxycarbonylethyl)-sulphide is added and dispersed in the water phase by the gravity of the stirrer. The polymerisation time is 110 mins. at 75C, with a further 60 mins. at 85C for additional heating.
After cooling, the bead pol~mer formed is collected in a suction filter, washed with de-ionised water and dried.
The bead polymer is pure white in appearance. By contrast, a bead polymer produced without the addition of -isophorone diisocyanate has a distinct yellow tinge. After 30 minutes' heating to 150 in the air, the bead polymer with the additive is yellowish, whereas the material with no additive has turned brownish-yellow.

~ . I :

v . : . ' . . :
, :

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Polymer materials comprising (a) a homopolymer of acrylonitrile or a copolymer of acrylonitrile and at least one further copolymerisable monomer, the copolymer containing at least 20% by weight of units of acrylo-nitrile; and (b) at least one alkyl, cycloalkyl or aryl isocyanate in an amount sufficient to inhibit or prevent thermal discoloration of the said materials.

2. Polymer materials as claimed in claim 1 wherein said isocynate is selected from the group consisting of isobutyl isocyanate, octyl isocyanate and hexamethylene isocyanate.

3. Polymer materials as claimed in claim 1 wherein said isocyanate is selected from the group consisting of cyclohexyl isocyanate and isophorone di-isocyanate.

4. Polymer materials as claimed in claim 1 wherein said isocyanate is selected from the group consisting of phenyl isocyanate and toluene di-isocyanate.

5. Polymer materials as claimed in claim 1 wherein said isocyanate is present in an amount of 0.05 to 5% by weight of said materials.

6. Polymer materials as claimed in claim 2 wherein said isocyanate is present in an amount of 0.05 to 5% by weight of said materials.

7. Polymer materials as claimed in claim 3 wherein said isocyanate is present in an amount of 0.05 to 5% by weight of said materials.

8. Polymer materials as claimed in claim 4 wherein said isocyanate is present in an amount of 0.05 to 5% by weight of said materials.

9. Polymer materials as claimed in claim 5 wherein said isocyanate is present in an amount from 0.1 to 2% by weight of said materials.

10. Polymer materials as claimed in claim 6 wherein said isocyanate is present in an amount from 0.1 to 2% by weight of said materials.

11. Polymer materials as claimed in claim 7 wherein said isocyanate is present in an amount from 0.1 to 2% by weight of said materials.

12. Polymer materials as claimed in claim 8 wherein said isocyanate is present in an amount from 0.1 to 2% by weight of said materials.

13. Polymer materials as claimed in claim 1 wherein said further co-polymerisable monomer comprises at least one monomer selected from the group consisting of styrene, .alpha.-methyl-styrene, butadiene, isoprene, esters of acrylic and methacrylic acids and methacrylonitrile.

14. Polymer materials as claimed in claim 13 wherein said isocyanate is selected from the group consisting of cyclohexyl isocyanate and isophorone di-isocyanate.

15. Polymer materials as claimed in claim 13 wherein said isocyanate is selected from the group consisting of phenyl isocyanate and toluene di-isocyanate.

16. Polymer materials as claimed in either of claims 13, 14 or 15 wherein said isocyanate is present in an amount of 0.05 to 5% by weight of said materials.

17. Polymer materials as claimed in either of claims 13, 14 or 15 wherein said isocyanate is present in an amount of 0.1 to 2% by weight of said materials.

18. Polymer materials as claimed in claim 1 wherein said copolymer contains 20 to 85% by weight of acrylonitrile units.

19. Polymer materials as claimed in either of claims 13, 14 or 15 wherein said copolymer contains 20 to 85% by weight of acrylonitrile units.

20. Polymer materials as claimed in claim 1 wherein said copolymer contains 50 to 85% by weight of acrylonitrile units.

21. Polymer materials as claimed in either of claims 13, 14 or 15 wherein said copolymer contains 50 to 85% by weight of acrylonitrile units.

22. Polymer materials as claimed in either of claims 13, 14 or 15 wherein said isocyanate is present in an amount from 0.05 to 5% by weight of said materials and wherein said copolymer contains 20 to 85% by weight of acrylonitrile units.

23. Polymer materials as claimed in either of claims 13, 14 or 15 wherein said isocyanate is present in an amount from 0.1 to 2% by weight of said materials and wherein said copolymer contains 20 to 85% by weight of acrylonitrile units.

24. Polymer materials as claimed in either of claims 13, 14 or 15 wherein said isocyanate is present in an amount from 0.05 to 5% by weight of said materials and wherein said copolymer contains 50 to 85% by weight of acrylonitrile units.

25. Polymer materials as claimed in either of claims 13, 14 or 15 wherein said isocyanate is present in an amount from 0.1 to 2% by weight of said materials and wherein said copolymer contains 20 to 85% by weight of acrylonitrile units.

26. Polymer materials as claimed in claim 1 which further contain at least one aliphatic thioether.

27. Polymer materials as claimed in either of claims 3, 7 or 14 which further contain at least one aliphatic thioether.

28. Polymer materials as claimed in either of claims 3, 7 or 14 which further contain bis-(2-methoxycarbonylethyl)-sulphide or-propyl-sulfide.

29. Polymer materials as claimed in claim 1 which further contain at least one nitroalkane.

30. Polymer materials as claimed in claim 29 wherein said nitroalkane contains 1 to 8 carbon atoms.

31. Polymer materials as claimed m claim 1 wherein said further copolymerisable monomer comprises at least one monomer selected from the group consisting of vinyl esters, unsaturated ketones, vinylalkyl esters, vinyl chloride and vinylidene chloride.

32. Polymer materials as claimed in claim 31 wherein said copolymer contains 20 to 85% by weight of acrylonitrile units.

33. Polymer materials as claimed in claim 31 wherein said isocyanate is present in an amount of 0.05 to 5% by weight of said materials.

34. Polymer materials as claimed in either of claims 31, 32 or 33 wherein said isocyanate is selected from the group consisting of cyclohexyl isocyanate, isophorone-di-isocyanate, phenyl isocyanate, and toluene di-isocyanate.

35. Polymer materials as claimed in either of claims 13, 14 or 15 wherein in addition to said further copolymerisable monomer, said copolymer comprises a minor amount of at least one monomer selected from the group consisting of divinylbenzene, trialkyl cyanurate and glycol dimethacrylate.

36. Polymer materials as claimed in either of claims 13, 14 or 15 wherein , said isocyanate is present in an amount from 0.05 to 5% by weight of said materials, said copolymer contains 20 to 80% by weight of acrylonitrile units and in addition to said further copolymerisable monomer said copolymer comprises a minor amount of at least one monomer selected from the group consisting of divinylbenzene, trialkyl cyanurate and glycol dimethyacrylate.

37. Polymer materials as claimed in claim 1 which further contain one or more dyes, pigments, stabilisers or plasticisers.

38. Polymer materials as claimed in claim 1 in the form of a solution thereof.

39. Polymer materials as claimed in claim 38 in the form of a solution thereof in dimethyl formamide or dimethyl acetamide.

40. Polymer materials as claimed in claim 1 comprising (a) a copolymer of acrylonitrile and at least one further copolymerisable monomer selected from the group consisting of methyl methacrylate, ethyl acrylate and styrene and (b) an isocyanate selected from the group consisting of cyclohexyl isocyanate, isophorone di-isocyanate and 2, 4 di-ioscyanatotoluene wherein said copolymer contains 20 to 85% by weight of acrylonitrile units and said isocyanate is present in an amount from 0.05 to 5% by weight.

41. Polymer materials as claimed in claim 40 wherein in addition to said further copolymerisable monomer, said copolymer comprises a minor amount of at least one monomer selected from the group consisting of divinylbenzene, trialkyl cyanurate and glycol dimethacrylate.

42. A process for the preparation of polymer materials as claimed in claim 1 which comprises incorporating an effective amount of at least one alkyl, cycloalkyl or aryl isocyanate in a monomer composition comprising acrylonitrile and, if desired, at least one further copolymerisable monomer, (or in a partially polymerised composition derived therefrom), the monomer composition containing at least 20% by weight of acrylonitrile; and polymerising the said composition.

43. A process as claimed in claim 42 wherein the said composition is bulk polymerised.

44. A process as claimed in claim 42 wherein a mixture of the isocyanate and the said composition is suspended in the form of droplets in an aqueous phase and subsequently bead polymerised.

45. A process as claimed in claim 42 wherein the said composition is solution polymerised in a solvent for the resulting polymer material.

46. A process as claimed in claim 45 wherein the solvent comprises dimethylformamide or dimethylacetamide.

47. A process for the preparation of polymer materials as claimed in claim 1 which comprises admixing at least one alkyl, cycloalkyl or aryl isocyanate with a homopolymer of acrylonitrile or a copolymer of acrylonitrile and at least one further copolymerisable monomer, the copolymer containing at least 20% by weight of units of acrylonitrile; the isocyanate being employed in an amount sufficient to inhibit or prevent thermal discoloration of the resulting materials.

48. A process as claimed in claim 47 wherein the homopolymer or co-polymer is in pulverulent form.

49. A process as claimed in claim 47 or claim 48 wherein the isocyanate is employed in the form of a vapour, solution or emulsion thereof.

50. A process as claimed in claim 47 wherein the homopolymer or copolymer is in the form of a solution.

51. Moulded articles produced from polymer materials as claimed in claim 1.

52. Moulded articles as claimed in claim 51 having a wall thickness of at least 0.5 mm.

53. Moulded articles as claimed in claim 52 having a wall thickness of 3-5 mm.

54. A process as claimed in claim 42 wherein said isocyanate is select-ed from the group consisting of isobutyl isocyanate, octyl isocyanate and hexamethylene isocyanate.

55. A process as claimed in claim 42 wherein said isocyanate is select-ed from the group consisting of cyclohexyl isocyanate and isophorone di-isocyanate.

56. A process as claimed in claim 42 wherein said isocyanate is selected from the group consisting of phenyl isocyanate and toluene di-isocyanate.

57. A process as claimed in claim 42 wherein the isocyanate is in-corporated in an amount of from 0.05 to 5% by weight of said materials.

58. A process as claimed in either of claims 54, 55 or 56 wherein the isocyanate is incorporated in an amount of from 0.05 to 5% by weight of said materials.

59. A process as claimed in claim 42 wherein the isocyanate is incorporated in an amount of from 0.1 to 2% by weight of said materials.

60. A process as claimed in either of claims 54, 55 or 56 wherein the isocyanate is incorporated in an amount of from 0.1 to 2% by weight of said materials.

61. A process as claimed in claim 42 wherein said further copolymerisable monomer comprises at least one monomer selected from the group consisting of styrene,.alpha.-methyl-styrene, butadiene, isoprene, esters of acrylic and methacrylic acids and methacrylonitrile.

62. A process as claimed in claim 61 wherein said isocyanate is selected from the group consisting of cyclohexyl isocyanate, isophoron, di-isocyanate, phenyl isocyanate and toluene di-isocyanate.

63. A process as claimed in claim 62 wherein the isocyanate is incorporated in an amount of from 0.05 to 5% by weight of said materials.

64. A process as claimed in either of claims 42 or 63 wherein said monomer composition contains 20 to 85% by weight acrylonitrile.

65. A process as claimed in either of claims 42 or 63 wherein said monomer composition contains 50 to 85% by weight acrylonitrile.

66. A process as defined in claim 42 wherein said further copoly-merisable monomer comprises at least one monomer selected from the groups consisting of vinyl esters, unsaturated ketones, vinylalkyl esters, vinyl chloride and vinylidene chloride.

67. A process as claimed in claim 66 wherein said monomer composition contains 20 to 85% by weight acrylonitrile.

68. A process as claimed in claim 66 wherein said isocyanate is present in an amount of 0.05 to 5% by weight of said materials.

69. A process as claimed in either of claims 66, 67 or 68 wherein said isocyanate is selected from the group consisting of cyclohexyl isocya-nate, isophorone-di-isocyanate, phenyl isocyanate and toluene di-isocyanate.

70. A process as claimed in claim 47 wherein said isocyanate is selected from the group consisting of isobutyl isocyanate, octyl isocyanate and hexamethylene isocyanate.

71. A process as claimed in claim 47 wherein said isocyanate is selected from the group consisting of cyclohexyl isocyanate and isophorone di-isocyanate.

72. A process as claimed in claim 47 wherein said isocyante is selected from the group consisting of phenyl isocyanate and toluene di-isocyanate.

73. A process as claimed in claim 47 wherein the isocyanate is employed in an amount of from 0.05 to 5% by weight of said materials.

74. A process as claimed in either of claims 70, 71 or 72 wherein the isocyanate is employed in an amount of from 0.05 to 5% by weight of said materials.

75. A process as claimed in claim 47 wherein the isocyanate is employed in an amount of from 0.1 to 2% by weight of said materials.

76. A process as claimed in either of claims 70, 71 or 72 wherein the isocyanate is employed in an amount of from 0.1 to 2% by weight of said materials.

77. A process as claimed in claim 47 wherein said further copolymerisable monomer comprises at least one monomer selected from the group consisting of styrene,.alpha.-methyl-styrene, butadiene, isoprene, esters of acrylic and methacrylic acids and methacrylonitrile.

78. A process as claimed in claim 77 wherein said isocyanate is selected from the group consisting of cyclohexyl isocyanate, isophorone di-isocyanate, phenyl isocyanate and toluene di-isocyanate.

79. A process as claimed in claim 78 wherein the isocyanate is incor-porated in an amount of from 0.05 to 5% by weight of said materials.

80. A process as claimed in either of claims 47 or 79 wherein said copolymer contains 20 to 85% by weight of acrylonitrile units.

81. A process as claimed in either of claims 47 or 79 wherein said copolymer contains 50 to 85% by weight of acrylonitrile units.

82. A process as defined in claim 47 wherein said further copolymerisable monomer comprises at least one monomer selected from the group consisting of vinyl esters, unsaturated ketones, vinylalkyl esters, vinyl chloride and vinylidene chloride.

83. A process as claimed in claim 82 wherein said copolymer contains 20 to 85% by weight of acrylonitrile units.

84. A process as claimed in claim 82 wherein said isocyanate is present in an amount of 0.05 to 5% by weight of said materials.

85. A process as claimed in either of claims 82, 83 or 84 wherein said isocyanate is selected from the group consisting of cyclohexyl isocyanate isophorone-di-isocyanate, phenyl isocyanate and toluene di-isocyanate.