PRODUCTION OF THERMOPLASTIC COPOLYMER

Process for the preparation of thermoplastic copolymers of alpha -methylstyrene and acrylonitrile by continuous bulk copolymerization of A. 30 to 50 mol % of alpha -methylstyrene and B. 70 to 50 mol % of acrylonitrile at temperatures from 60 DEG to 120 DEG C. with average residence times of 4 to 12 hours in the presence of initiators which supply free radicals, carried out in at least two continuously operated mixed tank reactors, characterized in that 100 molar parts of a monomer mixture of A0. 34 to 52 mol % of alpha -methylstyrene and B0. 66 to 48 mol % of acrylonitrile are fed continuously into the first tank reactor per unit time, and, with back-mixing, are copolymerized up to a conversion of 5 to 30 molar parts to give a copolymer of the composition A1. 49 to 53 mol % of alpha -methylstyrene and B1. 51 to 47 mol % of acrylonitrile, and the mixture consisting of 70 to 95 molar parts of the monomers A and B and 5 to 30 molar parts of the copolymer of the composition A1-B1 is transferred continuously to the second tank reactor and is polymerized there up at a further conversion of 5 to 55 molar parts to a total conversion of 20 to 60 molar parts to give further copolymer of the composition A1. 49 to 53 mol % of alpha -methylstyrene and B1. 51 to 47 mol % of acrylonitrile, 0,5 to 11.5 molar parts of acrylonitrile being removed from the vapor condenser of the second tank reactor and recycled to the first tank reactor per unit time.