The optimum conditions for preparing poly(styrene-co-divinylbenzene) were determined and the variation of the mechanical properties of the networks with the crosslinking density was evaluated. The molecular weight between crosslinks was in the 800-12,000 range. The flexural modulus and flexural strength were 5000 and 110 MPa, respectively, for the more crosslinked materials. When liquid rubber (hydroxyl-terminated polybutadiene) was incorporated into the glassy matrix, these values dropped to 2500 and 70 MPa, respectively, but the impact resistance increased to 70 J/m. These values were comparable to some commercial grade high impact polystyrene resins. The particle size of the dispersed rubber phase was on the nanometer scale, and attempts to increase its dimensions should provide further improvement in the impact properties.