Anionically-polymerized-rubber-modified styrene copolymers.

摘要

Disclosed is a rubber-modified styrene copolymer which contains as an impact strength modifier a rubbery polymer having a viscosity of 2-250 centipoises as measured at 25 DEG C as a 5 wt.% styrene solution and a styrene insoluble content lower than 0.1 wt.%, produced by anionic polymerization and dispersed in a continuous phase of a styrene-acrylonitrile copolymer. The rubbery polymer contains small particles of the same styrene-acrylonitrile copolymer occluded in the form of cells. The areas of particles in each of which the maximum cell diameter is smaller than 0.1 mu m are at least 40% of the area of all the particles of the rubbery polymer and the volume average particle size of these particles is 0.1-0.4 mu m. The weight ratio of the monomers in the styrene-acrylonitrile copolymer is 90/10 >/= styrene/acrylonitrile >/= 55/45. Per 100 parts by weight of the copolymer, the proportions of polymers having a molecular weight greater than 1,000,000 is smaller than 0.5 part by weight while the proportion of polymers having a molecular weight greater than 1,200,000 is smaller than 0.01 part by weight.