Process for preparing rubber-modified styrene copolymers by suspension copolymerization

A process for the production of ABS type copolymers, comprising a copolymer of vinyl aromatic monomer, acrylonitrile monomer, and rubbery polymer having improved surface appearance and impact properties by suspension copolymerization, consisting essentially of the steps of:

• (a) forming an aqueous suspension of an admixture of polymerizable materials comprising said vinyl aromatic monomer, said acrylonitrile monomer and said rubbery polymer;
• (b) suspension polymerizing said admixture of polymerizable materials at a temperature between about 60.degree. to 150.degree. C. to a residual monomer content less than about 2% by weight to produce an ABS copolymer comprising polymerized monomers dispersed in a gel-containing rubber phase;
• (c) recovering beads of said copolymer containing cross-linked rubber and having a high macrogel content from said suspension;
• and
• (d) causing phase inversion of said copolymer by melt extruding said copolymer under extrusion conditions having a shear force sufficient to cause phase inversion and produce a substantially gel-free ABS copolymer comprising a continuous phase comprising vinyl aromatic monomer-acrylonitrile copolymer in which grafted rubber polymer is homogeneously dispersed therethrough.