A silacyclobutane having a five-membered cyclic carbonate structure (SBMC) was prepared, and its transition metal-catalyzed ring-opening polymerization at the four-membered carbosilane unit was investigated as well as formation of carbosilane networked polymers and polymer gel electrolytes. The SBMC was synthesized by epoxidation of 1-(4-butenyl)-1-methylsilacyclobutane followed by insertion of CO2 to the epoxide. Ring-opening polymerization of the silacyclobutane moiety in the SBMC readily proceeded by a transition metal catalyst such as platinum divinyltetramethyldisiloxane complex. A flexible networked polymer film was obtained by copolymerization of the SBMC with a small amount of crosslinker, hexamethylene-1,6-bis(1-methylsilacyclobutane) (HMBS). The copolymerization of SBMC and HMBS in 1 M LiPF6 solution in ethylene carbonate and diethyl carbonate (3/7 v/v) gave a gel polymer electrolyte, which showed good ionic conductivity and could be applied to lithium ion batteries. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012