We designed a new type of styrenyl compound applicable to conventional photopolymerization systems, aiming at the production of polymers with improved mechanical properties, resistance to chemicals, and elevated glass-transition temperatures (T-g's). A series of styrenyl monomers bearing 2,5-dithio-1,3,4-thiadiazole groups were prepared, and their reactivity was studied in solid-state photopolymerization initiated by 2-(4'-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine. These monomers exhibited much higher polymerization rates than usual, and the final conversion nearly reached completion, despite the relatively high T-g of the solid-state photopolymerization system. Even at temperatures below T-g, the polymerization proceeded without a ceiling phenomenon. These features were explained by intermolecular interactions between the monomers that induced monomer alignments effective for solid-state polymerization, large excess free volumes arising from rotation around the methylthio groups, and intramatrix radical migration leading to encounters with the remaining monomers. (C) 2003 Wiley Periodicals, Inc.