Thermo-sensitive hydrogels based on interpenetrating polymer networks made of poly(N-isopropylacrylamide) and polyurethane.

A series of interpenetrating polymer networks (IPNs) of vinyl-terminated polyurethane (VTPU) and poly(N-isopropylacrylamide) (PNIPAAm) was prepared by free radical polymerization. The effects of IPN composition and cross-linking density on the thermo-responsive and mechanical properties have been studied in terms of particle size, dynamic mechanical thermal properties, transmittance, swelling and de-swelling behavior and water transport mechanism. Results showed that the swelling ability of hydrogels increased over four orders of magnitude in terms of diffusivity, and phase transition became faster with increasing N-isopropylacrylamide (NIPAAm) content. Regarding the mechanical reinforcement of swollen gel, a significant increase in compression properties has been obtained by forming IPNs with polyurethane, which was tailor-made depending on the IPN composition and structure of polyurethane. Furthermore, a cross-linking density increase in the NIPAAm domain augmented rubbery modulus, decreased water swelling and increased water deswelling of the IPNs.