Application of lateral sol–gel type crosslinking to a polyurethane copolymer

A triethoxysilyl (TES) group was attached to polyurethane (PU) as a side group through allophanate bonding. The PUs were crosslinked by a sol–gel reaction between the triethoxysilyl groups after acidic hydrolysis, and the tensile strength and shape memory properties were tested for a series of PUs with a different TES group contents. The tensile stress suddenly increased at a critical TES content level, and the tensile strain was rather increased with increasing stress. The shape recovery at 45 °C remained above 90 % for the entire range of TES group contents. The low temperature flexibility of the TES crosslinked PUs was better than that of the linear PU without crosslinking. The extraordinary characteristics of the sol–gel crosslinked PUs are discussed.