GB1564453A

GB1564453A - Crosslinkable polymers

Info

Publication number: GB1564453A
Application number: GB2044477A
Authority: GB
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1976-05-22
Filing date: 1977-05-16
Publication date: 1980-04-10
Also published as: DE2623128A1; JPS5334892A; FR2352006A1

Description

(54) CROSSLINKABLE POLYMERS (71) We, BAYER AKTIEN GESELLSCHAFT, a body corporate organised under the laws of the Federal Republic of Germany of 509 Leverkusen, Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to crosslinkable acrylonitrile polymers which contain at least one N-methylol compound of an unsaturated urethane or bis-urethane in copolymerised form as a crosslinking component.

It is already known that methylol alkyl ethers of acid amides readily crosslink in the presence of acids or acid donors (E.P.

Muller et al, Makromol. Chemie 57, 27 (1962). It is also known that spontaneously crosslinking polymers can be stabilised by the addition of an a-aminocarboxylic acid during or after polymerisation (DT-OS No.

1,911,360). This process gives storable emulsions of homopolymers or copolymers of olefinically unsaturated amides containing methylol groups.

In the process described in FR-PS No.

1,500,101, crosslinking during polymerisation is avoided by the addition of mineral salts as stabilisers. The addition of mineral salts also prevents crosslinking' during drying.

According to published Japanese Patent Application Sho-43 82768, the crosslinking of a copolymer of at least 85% by weight of acrylonitrile and at most 15% by weight of a methylol compound of an unsaturated amide during its actual production is prevented by carrying out polymerisation in a concentrated salt water solution containing zinc chloride as its main constituent and in the presence of zinc oxide.

Stabilisation such as this is necessary because undesirable crosslinking can occur very quickly, even during the polymerisation of acrylonitrile and Nmethylol ethers of (meth)acrylamides, especially in cases where polymerisation is carried out in acid medium, as is normally the case. However, one disadvantage of this approach is that the polymer obtained has to be treated with a very large quantity of washing agent in order to remove at least most of the salt added. In addition, small residues of salts in the polymer adversely affect its properties, for example by vacuole formation.

Accordingly, an object of the present invention is to provide crosslinkable copolymers of acrylonitrile and a process for their production which does not have any of the disadvantages referred to above.

It has now surprisingly been found that acrylonitrile can be polymerised with Nmethylol compounds of unsaturated urethanes or bisurethanes and, optionally, other comonomers without any difficulties, i.e. in the absence of crosslinking, even when the polymerisation reaction is carried out in the absence of the known stabilising additives. According to the invention, Nmethylol compounds of unsaturated monocarboxylic or dicarboxylic acid derivatives containing one or two urethane groups are used as the unsaturated urethanes or bis-urethanes.

Accordingly, the present invention provides copolymers of at least 65% by weight of acrylonitrile; from 0.5 to 10% by weight of at least one copolymerisable Nmethylol derivative (or an alkyl ether or alkyl ester thereof) of an unsaturated monocarboxylic or dicarboxylic acid, the Nmethylol derivative containing one or two urethane groups; and, optionally, at least one other comonomer.

The present invention also provides a process for the production of crosslinkable copolymers of acrylonitrile and one or more other comonomers, wherein at least 65% by weight of acrylonitrile is copolymerised with from 0.5 to 10% by weight of at least one copolymerisable N-methylol derivative (or an alkyl ether or an alkyl ester thereof) of an unsaturated monocarboxylic or dicarboxylic acid, the N-methylol derivative containing one or two urethane groups, and, optionally, at least one other comonomer.

The invention also relates to the use of polymers having the above-mentioned composition for the production of filaments, fibres and films.

Particularly suitable crosslinking components are N-methylol compounds and the corresponding alkyl ethers or alkyl esters of unsaturated urethanes or bisurethanes corresponding to the general formula:

in which R represents hydrogen or methyl, R' represents hydrogen, methyl or the radical:

R2 represents hydrogen, methyl, phenyl or halogenated alkyl, such as -CH2CL, R3 represents hydrogen or a straightchain or branched Cl~6-alkyl radical, preferably a C14-alkyl radical, a cycloalkyl radical, preferably with 6 carbon atoms, or an optionally substituted phenyl radical, and R4 represents hydrogen, a linear or branched Cl~6-alkyl radical, preferably methyl, or a radical of the formula:

where R5 represents a linear or branched C16- alkyl radical, preferably a Cl~3-alkyl radical.

Examples of particularly preferred unsaturated N-methylol compounds are given in the following:

The compounds of formulae (II) to (V) are particularly preferred.

The production of the described Nmethylol compounds of these unsaturated mono- or bisurethanes is known and is carried out, for example, by reacting the hydroxy alkyl esters of unsaturated carboxylic acids with isocyanates to form the unsaturated urethanes, followed by reaction with formaldehyde to form the N methylol compounds. The less reactive N methylol alkyl ethers or esters are obtained by reacting the N-methylol compounds with primary alcohols in the presence of hydrochloric acid or by reaction with acid anhydrides. The compounds of formulae (VI), (VII) and (XIV) may be obtained, for example, by reacting the hydroxy alkyl esters of unsaturated carboxylic acids with methoxy methyl isocyanate.

Another group of suitable N-methylol compounds, namely the N-methylol compounds of unsaturated carboxylic acid derivatives containing urethane groups, correspond to the general formula:

in which R6 represents hydrogen or methyl, R7 represents hydrogen, methyl or the radical:

R8represents hydrogen or methyl, R9. R10, which may be the same or different, represent hydrogen or C14-alkyl, R11 represents a straight-chain or branched C, l8-alkyl radical, preferably a C~5-alkyl radical, R12 represents hydrogen or a straightchain or branched C,~,-alkyl radical or a radical of the formula:

where R13 represents a C, 6-alkyl radical, preferably a C,~3-alkyl radical, and n=O, 1 or 2.

The following are examples of these unsaturated N-methylol compounds:

The unsaturated N-methylol compounds of general formula (XV) are produced by reacting unsaturated ester isocyanates known from the laterature (German Patent Specification No. 1,018,050) with alcohols to form unsaturated ester urethanes, followed by reaction with formaldehyde to form the corresponding N-methylol compounds. The less reactive N-methylol alkyl ethers or esters may be obtained by reacting the N-methylol compounds with primary alcohols in the presence of acids or by reaction with acid anhydrides, preferably acetic acid anhydride.

The other comonomers optionally used are, in particular, those monomers commonly used in the production of acrylonitrile fibres. Preferred monomers of this type are acrylic and methacrylic acid alkyl esters, for example methyl(meth)acrylate and ethyl (meth)acrylate. These monomers are generally incorporated in the polymer in quantitites of up to 10% by weight and preferably in quantities of from 3 to 8 ", by weight. It is also possible to incorporate the usual dye-receptive additives, for example unsaturated sulphonic acids, preferably methallyl sulphonic acid, vinyl sulphonic acid or styrene sulphonic acid and their alkali metal salts, in the coipolymers in quantities of, for example up to 3 n by weight.

Other comonomers optionally used are preferably comonomers which may serve as crosslink acceptors, i.e. which are able to react with the methylol urethane groups built into the polymer chain in the presence of acids and/or under heat. Examples of these copolymerisable crosslink acceptors are unsaturated amides such as, for example, acrylamide and methacrylamide, unsaturated urethanes such as, for example, allyl methyl urethane, 1,3 - di (methylaminocarboxy) - 2- methylene propane or compounds corresponding to the formulae

and also unsaturated ureas, hydrazides and semicarbazides, although the unsaturated amides and urethanes are preferred.

The copolymers according to the invention may be produced by the usual polymerisation techniques, for example solution polymerisation, dispersion polymerisation or suspension polymerisation. Polymerisation is preferably carried out in a precipitant or suspending agent, preferably water. In this case, from 0.5 to 10% by weight and preferably from 1 to 6% by weight of at least one copolymerisable N-methylol compound of the unsaturated urethanes or bis-urethanes or their N-methylol alkyl ethers or Nmethylol alkyl esters, and preferably at least one other comonomer, are polymerised together with at least 65% by weight and preferably with at least 80 /n by weight of acrylonitrile.

The initiators used are the known redox systems, preferably potassium and sodium peroxodisulphate/potassium or sodium bisulphite. The molar ratio between the two components of the initiator system is with advantage between 4:1 and 1:4, whilst the absolute quantity in which the initiator system is used amounts with advantage to 0.5 to 6% by weight, based on the quantity of monomers.

Polymerisation is preferably carried out at a pH-value of from 3 to 4.5, more preferably from 3.5 to 4, and at a temperature of from 30 to 70"C, more preferably from 50 to 60"C. After a polymerisation time of about 3 to 10 hours, preferably from 5 to 7 hours, the polymers are isolated in the usual way by filtration under suction, precipitation or concentration of the solvent. The polymer is then dried for 5 to 15 hours at 30 to 800C. It is particularly advantageous to wash the polymer until it is neutral, preferably with lower alcohols, for example methanol, after isolation and before drying.

Whereas conventional polymerisation processes, in which N-methylol compounds or their derivatives, such as N-methylol alkyl ethers, are polymerised, require additions of stabilisers, for example soluble salts or zinc oxide, to prevent crosslinking during the actual polymerisation reaction, the polymers according to the invention may be produced in the total absence of stabilising additives without any significant crosslinking taking place. This must be regarded as extremely surprising.

It is also surprising that the free methylol compounds of the unsaturated urethanes or bis-urethanes described above may be incorporated into the polymer without crosslinking occurring during the actual polymerisation reaction, although it is known that the reactivity of free methylol groups is considerably greater than that of protected, i.e. etherified or esterified, methylol groups (E. Muller et al.

Makromolekulare Chemie 57, 27 (1962).

The new polymers are eminently suitable for the production of filaments, fibres and films with excellent mechanical properties.

For example, they may be dry or wet spun into filaments by standard methods, dimethyl formamide, dimethyl acetamide and dimethyl sulphoxide preferably being used as solvents for this purpose. The spun filaments may then be further processed into fibres. Crosslinking is initiated during further processing by the action of acids, for example mineral acids, and/or heat.

Although it is possibie in principle to vary the molecular weights of the polymers according to the invention within wide limits by known methods, polymers with Kvalues of from 70 to 90 are particularly suitable for the production of filaments and fibres.

In the following Examples, parts by weight are to parts by volume as grams are to millilitres, and the percentages are by weight.

EXAMPLE 1 498.4 parts by weight of acrylonitrile, 56 parts by weight of 2 - (N - methyl - N hydroxymethylaminocarboxy) - propyl methacrylate corresponding to the formula:

and 5.6 parts by weight of sodium methallyl sulphonate are dissolved in 7440 parts by weight of water at 500C while a gentle stream of nitrogen is passed through. The pH-value is adjusted to 3.3 with 20% sulphuric acid and the polymerisation reaction is initiated by the addition of 5 parts by weight of potassium peroxodisulphate and 20 parts by weight of sodium disulphite. After 6 hours, the polymer is filtered off under suction, washed with water until neutral and dried in vacuo at 50 to 60"C. Yield: 510 parts by weight (92 X" of the theoretical), K-value: 83.

A 279:, solution of this polymer in dimethyl formamide is spun into a precipitation bath of water and dimethyl formamide. The coagulated filament is then.

drawn through a warm bath (500 C) containing 0.5 , of sulphuric acid, washed in a water bath, dried and wound into package form. The filaments obtained are no longer soluble in dimethyl formamide.

The 2 - (N - methyl - N hydroxymethylaminocarboxy) - propyl methacrylate is produced as follows: 2 - (N - methylaminocarboxy) - propyl methacrylate is quantitatively obtained by the addition reaction of methyl isocyanate with 2-hydroxy propyl methacrylate in anhydrous benzene. It is then reacted with an equimolar quantity of formaldehyde in water at 0 to 30C in the presence of barium hydroxide. The 2 - (N - methyl - N hydroxymethylaminocarboxy) - propyl methacrylate is isolated in a yield of 95 /n by extraction with methylene chloride.

EXAMPLE 2 390 litres of water are boiled under nitrogen for 30 minutes in a 450 litre enamel vessel, followed by cooling to 50"C. This is followed by the successive addition at that temperature of 28.5 kg of acrylonitrile, 1.2 kg of 2 - (N - methyl - N - hydroxymethylaminocarboxy) - ethyl methacrylate corresponding to the formula:

and 0.3 kg of sodium methallyl sulphonate.

The pH-value is adjusted to 3.3 with 20% sulphuric acid. Polymerisation is initiated by the addition of 0.33 kg of potassium peroxodisulphate and 1.32 kg of sodium disulphite. After 6 hours, the suspension is cooled to room temperature and filtered under suction through a 250 litre vacuum filter. The residue is washed with water until neutral and dried in vacuo at 50 to 600 C.

Yield: 28.2 kg (94 X" of the theoretical), Kvalue: 84.

A solution of 26.5 parts by weight of the polymer in 73.5 parts by weight of dimethyl formamide is maintained for 6 hours at a temperature of 50"C in a thermostat. The ball drop time is measured at hourly intervals. The ball drop time is the time in seconds which a 1/8" ball takes to drop a distance of 7 cm in the warm solution (800 C). The ball drop times are substantially constant over a period of 6 hours. (A description of the ball drop method may be found in K. Jost, Rheologica Acta, Vol. 1, No. 2-3 (1958), page 303).

If 5% of an organic or inorganic acid, based on the solids content, is added to a second sample of the same solution, followed by maintaining for 6 hours at a temperature of 80"C, the ball drop times increase considerably as a result of crosslinking.

Acid: p-toluene sulphonic acid Tempering time in hours: 1 2 3 4 5 6 Ball drop times in sec: 63 73 78 87 95 102 A film is cast from a 25% solution of the above polymer and treated with 1% aqueous hydrochloric acid. The film is tempered at 130 to 150"C. Thereafter only small fractions of the film dissolve in DMF; the polymer is crosslinked.

EXAMPLE 3 A solution of 526.4 parts by weight of acrylonitrile, 28 parts by weight of 2 - (N methyl - N - hydroxymethyl aminocarboxy) - ethyl acrylate corresponding to the formula:

and 5.6 parts by weight of sodium methallyl sulphonate in 7440 parts by volume of water is adjusted to pH 3.3 at 500C with 20% sulphuric acid. Polymerisation is initiated under nitrogen by the addition of 6 parts by weight of potassium peroxodisulphate and 24 parts by weight of sodium disulphite.

After 6 hours, the polymer is filtered off under suction, washed until neutral and dried. Yield: 510 parts by weight (91% of the theoretical), K-value: 89.5.

A 25% solution of this polymer in dimethyl formamide is heated to 80"C in a thermostat and tempered for 6 hours at that temperature. The ball drop time is measured at hourly intervals. The solution does not show any significant increase in viscosity after 6 hours. The ball drop time amounts to between 58 and 63 seconds.

The same spinning solution is spun through a 50-bore spinneret (individual bore diameter 100 ) into a precipitation bath.

The coagulated filament is then drawn through warm (50"C) 1% hydrochloric acid, washed in a water bath, dried at 1500C and wound into package form. The filaments thus treated are no longer soluble in dimethyl formamide.

EXAMPLE 4 498 parts by weight of acrylonitrile, 28 parts by weight of 2 - (N - methyl - N hydroxymethyl)- aminocarboxy)- propyl acrylate corresponding to the formula:

28 parts by weight of acrylamide and 5.6 parts by weight of sodium methallyl sulphonate are dissolved in 7440 parts by volume of water. The solution is then heated to 50"C, the pH-value is adjusted to 3.3 with dilute sulphuric acid and the polymerisation reaction is initiated by the addition of 5 parts by weight of potassium peroxodisulphate and 20 parts by weight of sodium disulphite. After 6 hours the polymer is filtered off under suction, washed until neutral and dried in vacuo at 50"C. Yield: 515 parts by weight (92 /" of the theoretical), K-value: 86.

When a 27% solution of this copolymer in DMF is tempered at 80"C, the ball drop times remain substantially constant at 61 to 66 seconds over a period of 6 hours.

A 27% solution of the polymer is wet spun and the filaments are aftertreated in 0.1N sulphuric acid, washed and dried at 1500C.

The fibre material thus obtained is no longer soluble in dimethyl formamide.

EXAMPLE 5 540.4 parts by weight of acrylonitrile, 14 parts by weight of bis - (N - methyl N - hydroxymethylaminocarboxyethyl) - itaconate corresponding to the formula:

and 5.6 parts by weight of sodium methallyl sulphonate are dissolved at 50"C in 7440 parts by volume of water. The pH-value is then adjusted to 3.3 with 20% sulphuric acid and the polymerisation reaction is initiated by the addition of 6 parts by weight of potassium peroxodisulphate and 24 parts by weight of sodium disulphite. After 6 hours, the polymer is filtered off under suction, washed until neutral and dried. Yield: 493 parts by weight (88% of the theoretical), Kvalue: 91.5.

27.5 parts by weight of this acrylonitrile copolymer are dissolved in dimethyl formamide and the resulting solution is spun into a precipitation bath of water/dimethyl formamide. After treatment in 1% hydrochloric acid, the filaments are washed and dried at 150"C. They are insoluble both in cold and in warm dimethyl formamide.

EXAMPLE 6 540.4 parts by weight of acrylonitrile, 14 parts by weight of 2 - (N - methyl - N hydroxymethylaminocarboxy) - 3 chloropropyl acrylate corresponding to the formula:

and 5.6 parts by weight of sodium methallyl sulphonate are dissolved under nitrogen at 50"C in 7440 parts by volume of water. The pH-value is adjusted to 3.5 with 20% sulphuric acid and the polymerisation reaction is initiated by the addition of 6 parts by weight of potassium peroxodisulphate and 24 parts by weight of sodium disulphite. The polymer is filtered off under suction after 6 hours, washed until neutral and dried. Yield: 515 parts by weight (92% of the theoretical), K-value: 86.

10 parts by weight of the polymer are stirred for 2 hours at 200C/pH 2.5 in 150 parts by volume of a 10% formaldehyde solution, followed by filtration and drying at 140"C. The polymer thus treated is no longer soluble in dimethyl formamide.

EXAMPLE 7 526.4 parts by weight of acrylonitrile, 28 parts by weight of 2 - (N methoxymethylaminocarboxy) - ethyl methacrylate corresponding to the formula:

and 5.6 g of sodium methallyl sulphonate are dissolved at SOOC/pH 3.5 in 7440 parts by volume of water. The polymerisation reaction is initiated by the addition of 5 parts by weight of potassium peroxodisulphate and 20 parts by weight of sodium disulphite. After 6 hours, the polymer is filtered off under suction, washed until neutral and dried. Yield: 498.5 parts by weight (89% of the theoretical), Kvalue:87.

The drop ball times of a 27.5% solution of the polymer in dimethyl formamide at 800C remain constant over a period of 6 hours. If 5% of an organic or inorganic acid is added to this solution, the ball drop times increase considerably as a result of crosslinking.

The 2 - (N - methoxymethylamino carboxy) - ethyl methacrylate can be quantitatively produced by reacting 2hydroxy ethyl methacrylate with methoxy methyl isocyanate in anhydrous benzene at boiling temperature.

EXAMPLE 8 526.4 parts by weight of acrylonitrile, 28 parts by weight of 2 - (N - acetoxymethyl N - methylaminocarboxy) - ethyl methacrylate corresponding to the formula:

and 5.6 parts by weight of sodium methallyl sulphonate are dissolved under nitrogen at 50"C in 7440 parts by volume of water and the pH-value of the resulting solution is adjusted to 3.5 with dilute sulphuric acid.

After the addition of 5 parts by weight of potassium peroxodisulphate and 20 parts by weight of sodium disulphite, the polymerisation mixture is stirred for 6 hours, after which the polymer is filtered off under suction, washed until neutral and dried. Yield: 498 parts by weight (89% of the theoretical), K-value: 88.

The ball drop time of a 26% solution of the polymer in dimethyl formamide at 800C remains substantially constant over a period of 6 hours and only increases following the addition of 1% of acid.

The 2- (N - acetoxymethyl- N methylaminocarboxy) - ethyl methacrylate is prepared as follows: 217 parts by weight of 2 - (N - methyl N - hydroxymethylaminocarboxy) - ethyl methacrylate produced as described in Example 1 are added dropwise at 1000C to 500 parts by weight of acetic acid anhydride, followed by stirring for 5 hours at 1000C.

The excess acetic acid anhydride is then distilled off. This acetylation is quantitative.

EXAMPLE 9 930 parts by volume of water, 65.8 parts by weight of acrylonitrile, 3.5 parts by weight of 2 - (N - hydroxymethyl - N methoxycarbonylamino) - ethyl methacrylate, corresponding to the formula:

and 0.7 part by weight of sodium methallyl sulphonate are dissolved at 500 C, the pM- value is adjusted to 3.3 and polymerisation is initiated by the addition of 0.5 part by weight of potassium peroxodisulphate and 2.0 part by weight of sodium disulphite.

After filtration under suction, the polymer is washed until neutral and dried at 50 to 600 C. Yield: 63 parts by weight (90% of the theoretical), K-value: 84.5.

A 27.5% solution of the acrylonitrile copolymer in dimethyl formamide is spun into a precipitation bath of water and DMF, and the coagulated filament is drawn through a warm (600C) bath containing 0.1N formic acid, subsequently washed and dried. The filament thus treated is crosslinked and is no longer soluble in dimethyl formamide.

2 - (N - hydroxymethyl - N methoxycarbonylamino) - ethyl methacrylate is obtained by heating a mixture of benzene ahd methanol to boiling point and adding methacrylic acid ethyl ester isocyanate dropwise, stirring for 5 hours and then distilling off the benzene and the unreacted methanol. The intermediate unsaturated ester urethane is reacted with formaldehyde.

EXAMPLE 10 512.4 parts by weight of acrylonitrile, 42 parts by weight of 2 - (N - methyl methoxymethylaminocarboxy) - ethyl methacrylate corresponding to the formula:

and 5.6 parts by weight of sodium methallyl sulphonate are dissolved at 50 C/pH 3.5 in 7400 parts by volume of water and polymerisation is initiated by the addition of 4.5 parts by weight of potassium peroxodisulphate and 18 parts by weight of sodium disulphite. After 6 hours, the polymer is isolated by filtration under suction. Yield: 490 parts by weight (87.5% of the theoretical), K-value: 87.

The polymer is dissolved in dimethyl formamide to form a 26% by weight solution, and the solution is wet-spun by a standard method. After the precipitation bath, the filament is passed through a bath containing 0.1N sulphuric acid, subsequently washed, dried at 150"C and wound into package form. The crosslinked filaments are no longer soluble in dimethyl formamide.

WHAT WE CLAIM IS: 1. A copolymer comprising, in copolymerised form, at least 65% by weight of acrylonitrile; from 0.5 to 10% by weight of at least one copolymerisable N-methylol derivative (or an alkyl ether or an alkyl ester thereof) of an unsaturated monocarboxylic or dicarboxylic acid, the N-methylol derivative containing one or two urethane groups; and, optionally, at least one other comonomer.

2. A copolymer as claimed in Claim 1, wherein the N-methylol derivative corresponds to the general formula (I):

in which R represents hydrogen or methyl, R' represents hydrogen, a methyl group or the radical

R2 represents hydrogen, methyl, phenyl or halogenated alkyl, R3 represents hydrogen, a straight-chain or branched C,~6-alkyl radical, a cycloalkyl radical or an optionally substituted phenyl radical, and R4 represents hydrogen, a straight-chain or branched C,~6-alkyl radical or a radical corresponding to the formula:

where R5 represents a C, 3-alkyl radical.

3. A copolymer as claimed in Claim 1, wherein the N-methylol derivative corresponds to the general formula (XV):

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

through a warm (600C) bath containing 0.1N formic acid, subsequently washed and dried. The filament thus treated is crosslinked and is no longer soluble in dimethyl formamide.

2 - (N - hydroxymethyl - N methoxycarbonylamino) - ethyl methacrylate is obtained by heating a mixture of benzene ahd methanol to boiling point and adding methacrylic acid ethyl ester isocyanate dropwise, stirring for 5 hours and then distilling off the benzene and the unreacted methanol. The intermediate unsaturated ester urethane is reacted with formaldehyde.

EXAMPLE 10 512.4 parts by weight of acrylonitrile, 42 parts by weight of 2 - (N - methyl methoxymethylaminocarboxy) - ethyl methacrylate corresponding to the formula:

and 5.6 parts by weight of sodium methallyl sulphonate are dissolved at 50 C/pH 3.5 in 7400 parts by volume of water and polymerisation is initiated by the addition of 4.5 parts by weight of potassium peroxodisulphate and 18 parts by weight of sodium disulphite. After 6 hours, the polymer is isolated by filtration under suction. Yield: 490 parts by weight (87.5% of the theoretical), K-value: 87.

The polymer is dissolved in dimethyl formamide to form a 26% by weight solution, and the solution is wet-spun by a standard method. After the precipitation bath, the filament is passed through a bath containing 0.1N sulphuric acid, subsequently washed, dried at 150"C and wound into package form. The crosslinked filaments are no longer soluble in dimethyl formamide.

WHAT WE CLAIM IS: 1. A copolymer comprising, in copolymerised form, at least 65% by weight of acrylonitrile; from 0.5 to 10% by weight of at least one copolymerisable N-methylol derivative (or an alkyl ether or an alkyl ester thereof) of an unsaturated monocarboxylic or dicarboxylic acid, the N-methylol derivative containing one or two urethane groups; and, optionally, at least one other comonomer.
2. A copolymer as claimed in Claim 1, wherein the N-methylol derivative corresponds to the general formula (I):

in which R represents hydrogen or methyl, R' represents hydrogen, a methyl group or the radical

R2 represents hydrogen, methyl, phenyl or halogenated alkyl, R3 represents hydrogen, a straight-chain or branched C,~6-alkyl radical, a cycloalkyl radical or an optionally substituted phenyl radical, and R4 represents hydrogen, a straight-chain or branched C,~6-alkyl radical or a radical corresponding to the formula:

where R5 represents a C, 3-alkyl radical.
3. A copolymer as claimed in Claim 1, wherein the N-methylol derivative corresponds to the general formula (XV):

in which R5 represents hydrogen or methyl, R7 represents hydrogen, methyl or the radical:

R8 represents hydrogen or methyl, R9, R'O, which may be the same or different, represent hydrogen or C1~4-alkyl, R11 represents a straight-chain or branched C,~,8-alkyl radical, and R12 represents hydrogen or a straightchain or branched C,~6-alkyl radical or a radical of the formula:

where R13 represents a C,~6-alkyl radical, and n=0, 1 or 2.
4. A copolymer as claimed in Claim 1, substantially as hereinbefore described with reference to any of the Examples.
5. A process for the production of a crosslinkable copolymer of acrylonitrile, which comprises copolymerising at least 65% by weight of acrylonitrile with from 0.5 to 10% by weight of at least one copolymerisable N-methylol derivative or an alkyl ether or an alkyl ester thereof) of an unsaturated monocarboxylic or dicarboxylic acid, the N-methylol derivative containing one or two urethane groups, and, optionally, at least one other comonomer.
6. A process as claimed in Claim 5, wherein the N-methylol derivative is of the general formula (I), as defined in Claim 2.
7. A process as claimed in Claim 5, wherein the N-methylol derivative is of the general formula (XV), as defined in Claim 3.
8. A process as claimed in Claim 5, substantially as hereinbefore described with reference to any of the Examples.
9. A copolymer when produced by a process as claimed in any one of Claims 5 to 8.
10. Filaments, fibres and films comprising a copolymer as claimed in any one of Claims 1 to 4 and 9.