Process for the preparation of a copolymer comprising alpha-methylstyrene and acrylonitrile

In a process for the copolymerization of alpha-methylstyrene and acrylonitrile wherein said monomers are co-polymerized

• (a) in aqueous emulsion, and
• (b) in the presence of a free-radical-supplying compound and a chain-transfer agent, and
• (c) wherein the polymerization reaction is insufficiently cooled to remove all of the released reaction heat,
• the improvement in combination therewith consisting essentially in conducting said polymerization at a temperature of the aqueous emulsion maintained at a level of at most 110.degree. C. and while further maintaining the mean rate of temperature increase per hour, v, at a value in the range of between 5.degree. and 60.degree. C. per hour, wherein v is determined by the formula:
• ##EQU3## in which:
• T.sub.m =maximum temperature of the aqueous emulsion (.degree.C.),
• T.sub.o =temperature of the aqueous emulsion at the start of the polymerization (.degree.C.)
• t.sub.m =time in hours at which T.sub.m is reached, and
• t.sub.o =time in hours at which the polymerization is started,
• whereby the rate of monomer conversion is maximized, and whereby a heat resistant copolymer is obtained.