GB1558835A - Process for preparing polymers having high molecular weight - Google Patents

Description

(54) PROCESS FOR PREPARING POLYMERS HAVING HIGH MOLECULAR WEIGHT (71) We, JAPAN SYNTHETIC RUBBER CO., LTD., a Japanese body corporate of 2-11-24, Tsukiji, Chuo-ku, Tokyo, Japan, 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 a process for preparing a homopolymer or copolymer of an aromatic alkenyl compound, an < -unsaturated carboxylic acid ester or a conjugated diolefin, having a narrow molecular weight distribution and a high molecular weight, by emulsion polymerisation.

The production of polystyrene, styrenebutadiene rubber, polyisoprene, and the like by emulsion polymerisation is well known.

However, to date it has so far proved impossible to obtain a polymer having a relatively narrow molecular weight distribution and a high molecular weight of from millions to several tens of millions by known emulsion polymerisation techniques. Recently, it was reported that polystyrene having such a high molecular weight was obtained by combining triethylenetetramine with polypropylene powder which had been prepared by oxidising polypropylene with ozone after completely removing atactic polypropylene therefrom, followed by hydroperoxidation [European Polymer J. 10, 551 (1974) and Makromol.

Chem. 175. 2091(1974)]. This process, however, has proved difficult to operate with respect to industrial production of the hydroperoxidised polypropylene and recovery thereof.

On the other hand, it is known that a polymer having a narrow molecular weight distribudon can be obtained by an anionic polymerisation method. Polystyrene and the like having a narrow molecular weight distribution are commercially available as a standard sample in gel permeation chromatography for characterising high polymers. The polystyrene seems to be obtained by polymerising using anions and purifying the resulting polymer using, for example, a fractional precipitation method. In the anionic polymerisation method, an initiator is used in an amount inversely proportional to the molecular weight of the polymer to be produced. Since the initiator loses its activity by reaction with a very small amount of impurities such as water in the polymerisation system, it requires a fine technique to produce polymers having a high molecular weight of millions to several tens of millions by the anionic polymerisation method and therefore the industrial scale production of such polymers has so far proved very difficult.

The present invention provides a process for preparing a homopolymer or copolymer having a weight-average molecular weight, Mw, of 3,000,000 to 50,000,000 with a narrow molecular weight distribution, the ratio of weight-average molecular weight, Mw, to number-average molecular weight, Mn, i.e.

Mw/Mn being 1 to 2, which process comprises emulsion polymerising a monomer or monomers selected from an aromatic alkenyl compound, an a,p-unsaturated carboxylic acid ester or a conjugated diolefin, using an initiator comprising (a) at least one peroxide which is a dialkyl peroxide having one, two or four groups of the formula: (O-O-C(CH,),-R (i) wherein R1 is methyl or phenyl, and (b) at least one reducing agent which is an acyclic alkyl primary amine, an acyclic alkyl tertiary amine, a p olyalkylenepolyamine, a polyalkyleneimine, an alkanolamine, an alkyl primary amine sulphonic acid or an alkali metal salt thereof, a quaternary ammonium hydroxide, a quaternary ammonium bromide, hydrazine, dextrose, an alkali metal salt of sulphurous acid, oxalic acid or imidazole, at a polymerisation temperature of from 0 to 700 C, and employing from 0.001 to 1 mole % of the reducing agent (b) based on said monomer or monomers.

Since there has been no suitable decomposition accelerator for dialkyl peroxides, they have previously been used alone either for crosslinking of silicone rubber and ethylene-propylene rubber and curing of unsaturated polyesters of thermal decomposition, or for polymerisations over 1000 C (H. Warson: The Application of Synthetic Resin Emulsions, Benn, London, page 14, (1972)).

Examples of dialkyl peroxides which can be used in the process of the invention are: Those having one group of the formula (i) -- di-t-butyl peroxide, t-butyl cumyl peroxide and dicumyl peroxide.

Those having two groups of the formula (i) - aJo( - dis(t - butylperoxy)p - diisopropyl- benzene, 2,5 - dimethyl - 2,5 - di(t - butylperoxy)hexane, 2,5 - dimethyl - 2,4 - Sdi(t- butylperoxy) - hexyn - 3,1,1 - bis(t - butylperoxy) - 3,3,5 - trimethyl cyclohexane, n - butyl 4,4 - bis(t - butylperoxy)valerate, 2,2 - bis(t- butylperoxy)butane and 1,1 di(t - butylperoxy)cyclohexane.

Those having four groups of the formula (i) - 2,2 - bis(4,4 - di- t - butylperoxy cyclohexyl)propane.

Among the above dialkyl peroxides, t-butyl cumyl peroxide, 2,5 - dimethyl - 2,5 - di(tbutylperoxy)hexane and 2,2 - bis(4,4 - di butylperoxy cyclohexyl ) propane are particularly preferred.

In contrast to the present invention when other peroxides such as hydroperoxides, diacyl peroxides and ketone peroxides are used the polymers produced have lower molecular weight or are produced at very low yields.

The amount of peroxide used in the process of the present invention is preferably 0.0001 to 1 mole %, more preferably 0.005 to 0.5 mole % based on the monomer or monomers used. If the amount of the peroxide is lower than 0.0001 mole%, the yield decreases, while if the amount of the peroxide is over 1 mole %, the molecular weight of the polymer produced decreases.

Where the reducing agent used in the process of the present invention is an acyclic alkyl primary amine, those having an alkyl group of 1 to 16 carbon atoms are preferred.

Examples of these acyclic alkyl primary amines having one amino group are methylamine, ethylamine, propylamine, butylamine, amylamine, laurylamine and cetylamine. Examples of polyalkylenepolyamines are ethylenediamine, trimethylenediamine, tetramethylenediamine and hexamethylenediamine.

Where the reducing agent is an acyclic alkyl tertiary amine, those having an alkyl group of 1 to 6 carbon atoms are preferred. Examples of these are trimethylamine, triethylamine, tripropylamine, tri-n-butylamine, triamylamine and triethylenediamine.

Where the reducing agent is a polyalkylenepolyamine there is preferably used diethylenetriamine, triethylenetetramine, dipropylenetriamine or tripropylenetetramine.

Where the reducing agent is a polyalkyleneimine, there is preferably used polyethyleneimine or polypropyleneimine.

Where the reducing agent is an alkanolamine those having 1 to 6 carbon atoms are preferred.

Examples of these are ethanolamine, propanolamine, n-propanolamine, isopropanolamine, diethanolamine and triethanolamine.

Where the reducing agent is an alkyl primary amino sulphonic acid or an alkali metal salt thereof, there is preferably used aminoethyl sulphonic acid or sodium aminoethyl sulphonate.

Where the reducing agent is a quaternary ammonium hydroxide or bromide, there is preferably used choline, tetramethylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium hydroxide or tetraethylammonium bromide.

Other reducing agents which can be used in the process of the present invention are hydrazine, dextrose, alkali salts of sulphurous acid such as sodium sulphite and potassium sulphite, oxalic acid and imidazole.

Among the above reducing agents, laurylamine, hexamethylenediamine, triethylamine, tri-n-butylamine, triethylenediamine, triethylenetetramine, polyethyleneimine, ethanolamine, n-propanolamine, triethanolamine, tetramethylammonium bromide, tetraethylammonium bromide, tetraethylammonium hydroxide, and dextrose are particularly preferred.

Aromatic amines such as aniline, N-methylaniline, p-aminophenol and diphenylamine; alkyl secondary amines such as diethylamine and di-n-butvlamine; and quaternary ammonium chlorides such as phenyltriethylammonium chloride, tetramethylammonium chloride and tetraethylammonium chloride cannot be used in the process of the present invention, although they may be analogous to the reducing agents mentioned above. Further such compounds as alicyclic amines, e.g. cyclohexylamine; phenylhydrazine, diphenylhydrazine, e-caprolactam, thiourea and ammonium sulphate cannot be used in the process of the present invention.

The amount of reducing agent used in the process of the present invention is 0.001 to 1 mole %, preferably 0.01 to 0.5 mole % based on the monomer or monomers used. Where the reducing agent is a polymeric compound such as polyethyleneimine, the repeating unit is regarded as the molecule for calculation purposes. If the amount of reducing agent is less than 0.0at mole %, its effect as an initiator decreases, while amounts of more than 1 mole % are decreasingly less economical.

The peroxide (a) and the reducing agent (b) are preferably used in amounts such that the product of the mole percentages of (a) and (b) is from 0.00001 to 1, preferably from 0.0001 to 1. If this product is less than 0.00001, their effect as an initiator is diminished, and if this product is more than 1, the molecular weight of the polymer produced is lowered.

The monomer used in the process of the present invention is an aromatic alkenyl compound such as styrene, methyl styrene, or alpha-methyl styrene; an a,8-unsaturated carboxylic acid ester such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate or butyl acrylate; or a conjugated diolefin such as butadiene, isoprene or chloroprene. Among these monomers, styrene, butadiene, isoprene, ethylacrylate and methyl methacrylate are particularly preferred.

On the other hand, vinyl acetate, vinyl chloride, or vinylidene chloride are hardly polymerised or do not produce a polymer having a high molecular weight. Thus, these monomers cannot be used in the process of the present invention.

According to the process of the present invention, if styrene or methyl methacrylate, for example, is polymerised alone, a homopolymer can be obtained. If two or more monomers are polymerised, a copolymer such as a random copolymer or a block copolymer can be obtained. For example, a styrene-butadiene copolymer or a methyl methacrylate-butadiene copolymer having a high molecular weight and a narrow molecular weight distribution can be produced according to the process of the present invention. If the polymerisation Is carried out in the presence of two or more monomers, a random copolymer can be obtained. If one monomer is polymerised almost completely, then another monomer is added, and the polymerisation continued, a block copolymer can be obtained.

The block copolymer may have the poly (aromatic alkenyl) block (A) and the poly (conjugated diolefin) block (B) in the form of A-B, A-BA, A-B-A-B or B--AA-B. Among these block copolymers, styrene-butadiene block copolymers and styrene-isoprene block copolymers are particularly preferred.

Emulsifiers used in the process of the present invention may be of any type, whether anionic, cationic or non-ionic. Preferred are non-ionic and anionic emulsifiers from the view-point of giving a high polymerisation rate. Examples of anionic emulsifiers are fatty acid salts, higher alcohol ester sulphates, aliphatic alcohol ester phosphates and alkyl aryl sulphonates; examples of non-ionic emulsifiers are polyoxvethylene alkyl esters, polyoxyethylene alkyl phenol ethers, polyoxyethylene alkyl esters and sorbitan alkyl esters; and examples of cationic emulsifiers are aliphatic amine salts and quaternary ammonium salts. Among these, sodium dodecylbenzene sulphonate, sodium lauryl sulphate, polyoxyethylene oleyl ether and polyoxyethylene nonyl phenol ether are preferred. The emulsifier is preferably used in an amount of from 0.1 to 10% by weight based on the weight of the monomer used as in the case of conventional emulsion polymerisations.

Since the presence of impurities such as chlorine and phosphoric compounds in the water to be used in the emulsion polymerisation is undesirable as in the case of conventional processes, it is preferred to use pure water or deionised water. The water may be used in an amount of from 0.5 to 10 times, preferably 1 to 5 times, the weight of the monomer used.

The polymerisation is carried out at a temperature of 0 to 700 C, preferably 50 to 60 C. Since the polymerisation is carried out in an aqueous system, a temperature lower than 0 C can not be used because of freezing.

If the temperature is higher than 70" C, the molecular weight of the polymer product becomes lower and its distribution broadens.

After the polymerisation, a shortstop and/or an anti-oxidant may be added to the emulsion and the unreacted monomer removed accord ing to conventional techniques. The resulting polymer may be used in the form of a latex, or conventional techniques of coagulation and drying may be used to process it further.

The homopolymer or copolymer prepared by the process of the present invention has a high molecular weight (Rw) of 3,000,000 to 50,030,000, and a ratio of w/lZn of 1 to 2, preferably 1 to 1.3.

The homopolymers or copolymers having a high molecular weight prepared by the pro cess of the present invention have good mould ability and thin films can be produced there from. A solution of these polymers is remark ably viscous even at a low concentration and has good spinnability. These polymers can be used not only as a standard sample in gel permeation chromatography for characterising high polymers but also as (or in) adhesives, films, sheets, paints, moulding materials and polymer modifiers for improving mechanical properties by mixing with other polymers.

The molecular weight and narrow molecular weight distribution characteristic of the polymers produced by the process of the present invention was identified by comparing with samples of commercially available polystyrene, in intrinsic viscosity (5), GPC (gel permeation chromatography) curve and ultracentrifugation tests.

The process of the invention is illustrated by the following Examples in which all percentages are by weight unless otherwise stated.

Examples 1-7 and Comparative Examples 1-8.

Into a 100-ml branched ampule previously washed and dried and filled with nitrogen were placed 4.2 ml of styrene, 22.5 ml of an aqueous solution of sodium dodecylbenzene sulphonate (concentration 2.5%), and a peroxide and a reducing agent as listed in Table 1, and the ampule was sealed. The polymerisation was carried out for 3 hours while rotating the ampule in a thermostat at 400 C. Then the ampule was opened and 1 ml of an aqueous solution of N,N-diethylhydrosylamine (concentration 0.1 mole/l.) was added to terminate the polymerisation. The thus-obtained polymer latex was dropped into methanol to precipitate the polymer, which was washed with water and dried under reduced pressure sufficiently to enable its yield, intrinsic viscosity (X1) in toluene at 30 C, and gel permeation chromatogram using tetrahydrofuran as a solvent at 330 C to be measured. The results are as shown in Table 1.

The accompanying drawing shows GPC curves of the polystyrene produced by Example 3 (curve I) and a standard sample of commercially available polystyrene having an aver .ge molecular weight of 5,500,000, and Mw/Rn = 1.06 produced by Pressure Chemical Co. Ltd. (Curve II).

As is clear from the results in Table 1, only peroxides which are dialkyl peroxides as defined above produce a polymer having a narrow molecular weight distribution and d high molecular weight in the above defined ranges.

TABLE 1 Peroxide Reducing agent Mol.** Mol.*** weight weight Amount* Amount* yield (Mw distri- Kind of No. Name (mole %) Name (mole %) (%) x10-4) bution peroxide Comparative t-Butyl hydroperoxide 0.5 Triethylene- 1.0 95 30 # Hydro Example 1 tetramine peroxide " 2 p-Menthane hydro- 0.5 " 1.0 60 18 # " peroxide " 3 Cumene hydroperoxide 0.5 " 1.0 93 15 # " " 4 2,5-Dimethylhexane- 0.5 " 1.0 21 2 # " 2,5-dihydroperoxide " 5 Benzoyl peroxide 0.5 " 1.0 0 - - Diacyl peroxide " 6 Acetyl peroxide 0.5 " 1.0 41 55 # " " 7 Lauroyl peroxide 0.5 " 1.0 16 13 + " " 8 Methyl ethyl ketone 0.5 " 1.0 0 - - Ketone peroxide Example 1 Di-t-butyl peroxide 0.5 " 1.0 95 900 ++ Dialkyl peroxide " 2 Di-cumyl peroxide 0.5 " 1.0 93 570 ++ " " 3 2,5-Dimethyl-2,5-di- 0.5 " 1.0 96 960 +++ " (t-butylperoxy)-hexane TABLE 1 (Continued) Peroxide Reducing agent Mol.** Mol.*** weight weight Amount* Amount* Yield (Mw distri- Kind of No. Name (mol %) Name (mole %) (%) x 10-4) bution peroxide Example 4 t-Butyl cumyl peroxide 0.5 Triethylene 1.0 87 1100 +++ Dialkyl tetramine peroxide " 5 1,1-Bis(t-butylperoxy)- 0.5 " 1.0 91 530 ++ " 3,3,5-trimethyl cyclohexane " 6 2,2-Bis(4,4-di-t-butyl 0.5 " 1.0 75 630 +++ " peroxy cyclohexyl)propane " 7 2,5-Dimethyl-2,5-di- 0.5 " 1.0 96 450 ++ " (t-butylperoxy)hexyne-3 Note) * : Based on the monomer used, ** : Molecular weight was calculated from intrinsic viscosity.

*** : Molecular weight distribution was determined by GPC comparing with three standard samples of polystyrene Sample (a) : Pressure Chemical Co. Ltd. Mw = 550 x 104, Mw/Mn = 1.06 Sample (b) National Bureau of Standards. Mw = 26 x 104, Mw/Mn = 2.1 Sample (c) : National Physical Laboratory. 1 x 104 < Mw < 150 x 104, Mw/Mn = 3.5, +++ : equal to or narrower than Sample (a) ++ : broader than Sample (a) but narrower than Sample (b) + : broader than Sample (b) but narrower than Sample (c) # . equal to or broader than Sample (c) Examples 8-30, Comparative Examples 9-24 Into a 100-ml branched ampule previously washed and dried and filled with nitrogen, were placed 4.2 ml of styrene, 22.5 ml of an aqueous solution of polyoxyethylene oleyl ether (concentration 1.5%) and a peroxide and a reducing agent as listed in Table 2, and the ampule was sealed. The polymerisation was carried out for 4 hours while rotating the ampule at 250 C. Then the ampule was opened and 1 ml of an aqueous solution of N,N-diethylhydroxylamine (concentration 0.1 mole/l.) was added to terminate the polymerisation. The thus obtained polymer latex was dropped into methanol to precipitate the polymer, which was washed with water and dried under reduced pressure sufficiently to enable the same measurements as described in Example 1 to be carried out. The results are as shown in Table 2.

As is clear from Table 2, reducing agents which are alkyl primary amines, alkanolamines alkyl primary amino sulphonic acids or alkali metal salts thereof, quatemary ammonium hydroxides or bromides, hydrazine, dextrose, alkali metal salts of sulphurous acid, oxalic acid and imidazole are effective for producing polymers having high molecular weight and a narrow molecular weight distribution as defined above.

TABLE 2 Peroxide Reducing agent Amount Amount Yield Mol. weight Mol. weight No. Name (mole %) Name (mole %) (%) (Mw x 10-4) distribution Comparative B 0.5 Ferrous chloride 1.0 nil Example 9 " 10 " " Ferrous sulfate " " " 11 " " Aniline " " " 12 " " Methylaniline " " " 13 " " Sodium thiosulfate " " " 14 " " Cobalt naphthenate " " " 15 " " Hydroquinone " "

16 Sodium ferricyanide 0.5 80 18 # " " " # Sodium pyrophosphate 0.5 " 17 " " Phenylhydrazine 1.0 nil " 18 " " Tetraethylammonium chloride " " " 19 " " Thiourea " " " 20 " " p-Aminophenol " " " 21 " " Cyclohexylamine " " " 22 " " Diethylamine " " " 23 " " Di-n-butylamine " " TABLE 2 (Continued) Peroxide Reducing agent Amount Amount Yield Mol. weight Mol. weight No. Name (mole %) Name (mole %) (%) (Mw x 10-4) distribution Example 8 B 0.5 Triethylenediamine 1.0 78 1800 +++ " 9 " " Ethanolamine " 73 1100 +++ " 10 " " Triethanolamine " 69 950 ++ " 11 " " n-Propanolamine " 70 1300 +++ " 12 " " Tetraethylammonium hydroxide " 85 530 +++ " 13 " " Ethylamine " 83 420 ++ " 14 " " Hydrazine " 90 350 ++ " 15 " " Tetramethylammonium bromide " 60 630 +++ " 16 " " Aminoethyl sulfonic acid " 53 730 ++ " 17 " " Oxalic acid " 55 550 ++ " 18 " " Sodium aminoethyl sulfonate " 52 470 ++ " 19 " " Diethylenetriamine " 49 620 ++ " 20 " " Sodium sulfite " 52 760 ++ " 21 " " Potassium sulfite " 53 830 ++ " 22 " " Imidazole " 52 990 ++ TABLE 2 (Continued) Peroxide Reducing agent Amount Amount Yield Mol. weight Mol. weight No. Name (mole %) Name (mole %) (%) (Mw x 10-4) distribution Example 23 B 0.5 Dextrose 1.0 49 1200 +++ " 24 " 1.0 Triethylenetetramine " 93 1300 +++ " 25 " 0.5 Laurylamine 0.5 89 860 +++ " 26 " " Trimethylenediamine " 75 450 ++ " 27 " " Hexamethylenediamine " 69 660 +++ " 28 " " Tetramethylammonium hydroxide " 83 730 ++ " 29 " " Tetramethyl ammonium bromide " 76 1050 +++ " 30 " 0.01 Triethylenetetramine 0.01 70 1680 +++ Comparative Example 24 " " " 0.0005 nil Note) B: 2,5-Dimethyl-2,5-di(t-butyl peroxy)hexane Examples 31-38, Comparative Examples 25-27.

Using the same procedure as described in Example 1, but using as a peroxide 0.5 mole 0/ of 2,5 - dimethyl - 2,5 - di(t - butylperoxy)hexane based on the monomer used, as a reducing agent 1.0 mole % of triethylenetetramine based on the monomer used, and a monomer as listed in Table 3, the polymerization was carried out for 24 hours. The results are as shown in Table 3.

As is clear from Table 3, vinyl acetate, vinyl chloride and vinylidene chloride, which can be polymerized in a usual emulsion polymerization, are not polymerized.

TABLE 3 Yield Mol. weight Mol. weight No. Monomer (O/o) CMw x 10-4) distribution Example 31 aMethyl styrene 91 450 ++ 32 32 Methyl methacrylate 89 990 33 33 Butadiene 95 2500 " 34 Isoprene 90 1300 +++ 35 35 methyl styrene 89 2100 +++ 36 36 Methyl acrylate 97 800 ++ 37 37 Ethyl acrylate 91 730 +44 38 38 ChlDroprene 85 1300 ++ Comparative Example 25 Vinyl acetate 0 26 26 Vinyl chloride 0 27 Vinylidene chloride 0 Note) Marks or signs are the same as defined in Note of Table 1.

Claims (17)

WHAT WE CLAIM IS:

1. A process for preparing a homopolymer or copolymer having a weight-average molecular weight of 3,000,000 to 50,000,000 with a narrow molecular weight distribution, the ratio of weight-average molecular weight to number-average molecular weight being 1 to 2, which process comprises emulsion polymerising a monomer or monomers selected from an aromatic alkenyl compound, an X unsaturated carboxylic acid ester and a conjugated diolefin, using an initiator comprising (a) at least one peroxide which is a dialkyl peroxide having one, two or four groups of the formula: -C-O-O-C( CH3 ) 2-R1 (i) wherein R1 is methyl or phenyl, and (b) at least one reducing agent which is an acyclic alkyl primary amine, an acyclic alkyl tertiary amine, a polyalkylenepolyamine, a polyalkyleneimine, an alkanolamine, an alkyl primary amino sulphonic acid or an alkali metal salt thereof, a quaternary ammonium hydroxide, a quaternary ammonium bromide, hydrazine, dextrose, an alkali metal salt of sulphurous acid, oxalic acid or imidazole, at a polymerisation temperature of from 0 to 700 C, and employing from 0.001 to 1 mole % of the reducing agent (b) based on said monomer or monomers.

2. A process according to claim 1, wherein the reducing agent (b) is selected from an acyclic alkyl tertiary amine and a polyalkyleneimine.

3. A process according to claim 1, wherein the reducing agent (b) is selected from an acyclic alkyl primary amine, an alkanol-amine, an alkyl primary amino sulphonic acid or an alkali metal salt thereof, a quaternary ammonium hydroxide, a quaternary ammonium bromide, hydrazine, dextrose, an alkali metal salt of sulphurous acid, oxalic acid and imidazole.

4. A process according to claim 1, wherein the reducing agent (b) is a polyalkylenepolyamine.

5. A process according to claim 1, wherein the reducing agent (b) is laurylamine, hexamethylenediamine, triethylamine, tri-n-butylamine, triethylenediamine, triethylenetetramine, polyethyleneimine, ethanolamine, n-propanoi- amine, triethanolamine, tetramethylammonium bromide, tetraethylammonium bromide, tetraethylammonium hydroxide or dextrose.

6. A process according to any one of the preceding claims, wherein there is used from 0.0001 to 1 mole % of the peroxide (a) based on said monomer or monomers.

7. A process according to claim 6, wherein there is used from 0.005 to 0.5 mole % of the peroxide (a) based on said monomer or monomers.

8. A process according to any one of the preceding claims, wherein there is used from 0.01 to 0.5 mole % of the reducing agent (b) based on said monomer or monomers.

9. A process according to any one of claims 1 to 6, wherein the peroxide (a) and the reducing agent (b) are used in amounts such that the product of the mole percentages of (a) and (b) is from 0.00001 to 1.

10. A process according to claim 9, wherein the peroxide (a) and the reducing agent (b) are used in amounts such that the product of the mole percentages of (a) and (b) is from 0.0001 to 1.

11. A process according to any one of the preceding claims wherein the polymerisation temperature is from 50 to 600 C.

12. A process according to any one of the preceding claims, wherein the homopolymer or copolymer produced has a ratio of weightaverage molecular weight to number-average molecular weight of from 1 to 1.3.

13. A process according to any one of the preceding claims, wherein the monomer or monomers are selected from styrene, butadiene, isoprene and methyl methacrylate.

14. A process according to any one of the preceding claims, wherein the dialkyl peroxide is t-butyl cumyl peroxide, 2,5 - dimethyl2,5 - di - (t - butylperoxy)hexane, or 2,2 his (4,4 - di - t - butylperoxy cyclohexyl)propane.

15. A process according to claim 1 substantially as hereinbefore described with reference to any one of Examples 1, 3, 5, 7 to 9, 11 to 13, 15 to 17, 19, 20, 22 to 24, 31 to 36 and 38.

16. A process according to claim 1 substantially as hereinbefore described with reference to any one of the specific Examples other than as claimed in claim 15.

17. A homopolymer or copolymer as defined in claim 1 when prepared by a process according to any one of the preceding claims.