Novel sulfonium salts, 1-naphthylmethyl-, cinnamyl-, 9-fluorenyl tetramethylene sulfonium hexafluoroantimonates, and dimethylsulfonium hexafluoroantimonates, were synthesized by the reaction of tetrahydrothiophene and dimethylsulfide with the corresponding bromides or chloride, followed by anion exchange with KSbF6. These sulfonium salts polymerized epoxy monomers at a temperature lower than previously reported for benzyltetramethylenesulfonium hexafluoroantimonate. They initiated radical photopolymerization as well as cationic polymerization. The photopolymerization was accelerated by the addition of aromatic compounds such as p-methoxyphenol, 4-methoxy-1-naphthol, 2-ethyl-9,10-dimethoxyanthracene, N-ethylcarbazole, and phenothiazine as photosensitizers. (C) 2003 Wiley Periodicals, Inc.