Copolymers of styrene and alphamethyl styrene and process for making the same

摘要

Copolymers of styrene and alpha-methyl styrene are made by heating a mixture of 10 to 50 per cent. by weight of alpha-methyl styrene and from 90 to 50 per cent. of styrene in bulk, to a temperature not greater than that defined by the equation:-t = 147 - 0.78X where t represents a temperature in degrees centigrade and X represents the percentage by weight of alpha-methyl styrene in the starting materials, until a copolymer which is solid at ordinary temperature and pressure or a solution of copolymer in monomers is obtained, feeding the polymeric product into a zone of reduced pressure where the copolymer is heated to a temperature between 200 and 280 DEG C. at an absolute pressure of less than 50 millimetres for a time not greater than 60 minutes while vaporizing volatile ingredients from the polymeric product and leave in the copolymer 1 per cent. or less of methanol soluble residues, separately withdrawing vapours of the volatile ingredients and the copolymer from the zone of reduced pressure and cooling the copolymer. The polymerization may be effected in a tank provided with a propeller agitator or in a sheet metal container which is submerged in a heated liquid bath until a solid polymer is formed and the can stripped from the solid resin and solid polymer crushed and fed to the zone of reduced pressure, e.g. a vacuum chamber. The polymeric material may be mechanically worked in the zone of reduced pressure and removed from the zone via an extrusion die, e.g. as described in Specification 672,667, [Group II]. Alternatively the heated polymeric product may be fed by the pressure of an extruder into the upper portion of a vacuum chamber and the volatiles removed by allowing the product to fall in the form of thin ribbons, threads and/or bands into the lower part of the chamber. A suitable form of apparatus is described in U.S.A. Specification 2,146,532. The polymerization may be effected in the presence of catalysts such as benzoyl peroxide, lauroyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide or t-butyl perbenzoate.