yTwo dialkyl fumarate monomers were copolymerized with styrene and methyl methacrylate. The reactivity ratios of the monomers were calculated, and the glass transition temperature-composition diagrams for the copolymers were measured. The experimental T-g data of the copolymers were fitted to several empirical equations proposed in the literature. A comparison is made between the copolymers and the blends of the corresponding polymers.