bimodal and monovinylidene aromatic polymers of high resistance to impact rubber modified rubbers.

A monovinylidene aromatic polymer modified with rubber produced from a vinyl aromatic monomer and a diene rubber having two distinct molecular structures, wherein 25 to 75 percent by weight of diene rubber, having a linear structure, and 75 to 25 weight percent having a branched structure, wherein the diene rubber has a broad distribution of weight average molecular weight yet monomodal, and the Mw of the rubber having a branched structure is higher than the rubber having a structure linear.