Polymerization of a silacyclobutane having an epoxy moiety and its application to networked polymer synthesis were examined. Four-membered ring-opening polymerization of silacyclobutane having a 3,4-epoxybutyl group on the silicon atom (OBMSB) was achieved by using a platinum vinyldisiloxane complex with keeping the epoxy ring unchanged. Copolymerization of 1,1-diethylsilacyclobutane (DESB) with OBMSB by using the same catalyst effectively gave the corresponding copolymers [poly(DESB-co-OBMSB)]. Thermal properties of the polyOBMSB, polyDESB, and poly(DESB-co-OBMSB) were investigated by DSC and TGA. Cast films of the obtained polymers with 1-naphthylmethylmethyl-p-hydroxyphenylsulfonium hexafluoroantimonate, a small amount of thermally latent acid generator were prepared. Heating the films at 80 degrees C for 2 h gave crosslinked networked polycarbosilanes through cationic ring-opening of the epoxy moieties. Thermal and mechanical properties of the networked polymers were investigated by TGA, DSC, and tensile strength measurements. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3400-3405