monovinyl aromatic polymer compositions with a novel combination of rigidity and crack resistance Stress

A polystyrene composition modified with rubber comprising: a reaction product formed by the polymerization of a monomer mixture comprising at least 75 weight percent of one or monovinylaromatic more monomers in the presence of rubber particles to form a dispersion rubber particles in a vinylaromatic polymer; where dispersed rubber particles have an average particle diameter of from 6 to 10 microns; wherein the composition has a gel content of from 28% to 36% by weight; wherein the composition has a swelling ratio of less than 13; and wherein the composition contains a plasticizer in an amount of not more than 1%, said plasticizer consisting in mineral oil.