Abstract: A process for the (co)polymerization of a monomer material, which includes at least an acrylonitrile monomer as an essential component, at a temperature of 80.degree. C. or higher by bulk or solution polymerization while allowing said monomer material to evaporate. The (co)polymerization is conducted while providing a vapor phase over a polymerization mixture in a reaction tank. During the (co)polymerization, the temperature of the vapor phase is maintained in a range of from 30.degree. C. to 65.degree. C. so that the polymerization is conducted without substantially releasing vapor, which is evaporated from the polymerization mixture, to outside of the reaction tank. By cooling the vapor phase of the reaction tank and maintaining its temperature in the above specific range in accordance with the present invention, it is possible to avoid mixing of a gelled polymer in a product and also to effectively remove reaction heat at the time of the (co)polymerization.

Abstract: A molding of an ABS-based resin is described. Rubber particles located at a depth of 0.5-1.5 .mu.m from a surface of the molding morphologically comprise at least the following two types of particles:(1) A particles having an a/b ratio not greater than 1.5, wherein a and b represent a major axis and a minor axis, respectively, and(2) B particles having an a/b ratio not smaller than 5, wherein a and b have the same meanings as defined abovewhen a section extending at the depth in parallel with the surface of the molding is observed in an electron micrograph taken by the ultrathin sectioning technique. Assuming that the total area of the rubber particles as observed in the electron micrograph is 100%, the total area of the A particles accounts for at least 10% and that of the B particles is in a range of 0.01-90%.