The mechanical properties of polymethyl methacrylate and copolymers formed with both ethyl methacrylate and butyl methacrylate were investigated. Six polymers were produced by bulk polymerization, measured for molecular weight and glass transition temperature, T(g) and assessed for modulus of elasticity and fracture toughness. Increasing the concentration of ethyl methacrylate or butyl methacrylate resulted in a linear decrease in the glass transition temperature, modulus of elasticity, and fracture toughness. A comparison of testing environments revealed that the modulus of elasticity was reduced when conditioned and tested in water at 37-degrees-C compared to ambient laboratory conditions for all polymers. Similar comparisons of the fracture toughness showed an increase for testing in water at 37-degrees-C; however, this was not significant for the lower T(g) compositions. Both modulus of elasticity and fracture toughness were strongly correlated with the glass transition temperature and composition.