Sulfonium-containing polymers prepared from dibenzothiophene and diphenyl sulfide were applied as both alkylating agents and latent initiators for the cationic polymerization of glycidyl phenyl ether. The alkylation of acetonitrile proceeded smoothly with poly(S-n-octyl-2-vinyldibenzothiophenium tetrafluoroborate) (4; 64 mol % octyldibenzothiophenium tetrafluoroborate unit) to give N-(n-octyl)acetamide in an excellent Yield on the basis of the starting octyldibenzothiophenium tetrafluoroborate unit in 4. The cationic polymerization of glycidyl phenyl ether was also carried out in the presence of poly(S-methyl-2-vinyldibenzothiophenium tetrafluoroborate) or poly(S-n-octyl-4-vinyldiphenylsulfonium tetrafluoroborate) to confirm their moderate thermal latent activity.