Disclosed are rubber-modified monovinylidene aromatic polymers with improved toughness and rigidity as well as a process for the process thereof. The polymer comprises: a) a monovinylidene aromatic polymer matrix, b) rubber particles dispersed therein, characterized in that the rubber particles are produced from a dine rubber having I) from 20 to 80 percent, based on the total weight of said rubber particles, of a high solution viscosity component having a viscosity value ranging from 110 to 500 centipoise and II) from 80 to 20 percent, based on the total weight of said rubber particles, of a low solution viscosity component having a viscosity value ranging from 1 to 100 centipoise, further characterized in that the ratio of solution viscosity of high solution viscosity component to the solution viscosity of low solution viscosity ranges from 1.1 to 500, wherein both component I and II have a 1,4 cis content of greater than 30 percent, and III) the rubber is grafted with monovinylidene aromatic polymer to the extent that there is at least 30 percent monovinylidene aromatic polymer present as grafts on the rubber.