The variations of the cross-linking agent, initiator, and molar ratio in the synthesis of a semi-interpenetrating polymer network (IPN) of polyurethane-starch/polymethyl methacrylate (PMMA) were studied for their viscoelastic and morphologic properties. The synthesized semi-IPNs were evaluated by means of dynamic mechanical analysis (DMA), finding that a relationship exists between the quantity of cross-linker and the storage module, where alpha and beta relaxations are present in the polymethyl methacrylate's rigid chains, and this peak widens upon increasing the quantity of PMMA in the semi-IPN. The morphology of the semi-IPNs shown by SEM and AFM micrographies suggests that 0.5wt.% of initiator and 3wt.% of cross-linker demonstrate uniform surfaces.