Enhancement of the rates of onium salt photoinitiated cationic polymerizations of epoxides and vinyl ethers has been achieved through the use of oligomeric and polymeric electron-transfer photosensitizers. Poly(N-vinylcarbazole) (PVK) is an especially attractive and efficient photosensitizer. The use of PVK as a photosensitizer for the cationic photopolymerizations of vinyl ethers and epoxides was examined in detail. PVK functions as an electron-transfer photosensitizer for a wide variety of onium salt cationic photoinitiators, including diaryliodonium, triarylsulfonium, and dialkylphenacylsulfonium salts. The broadening of the spectral response through the use of these photosensitizers accounts for the observed rate enhancement of these polymerization reactions. Alternating copolymers prepared by the free radical polymerization of N-vinylcarbazole (NVK) with vinyl monomers also exhibit excellent photosensitization activity. Also described in this paper is the synthesis and use of a dimeric photosensitizer prepared by the hydrosilylation of N-vinylcarbazole with 1,1,3,3-tetramethyldisiloxane.