A kinetic study was conducted of the independent photoinitiated cationic polymerization of a number of epoxide monomers and mixtures of these monomers with N-vinylcarbazole. The results show that these two different classes of monomers undergo complex synergistic interactions with one another during polymerization. It was demonstrated that N-vinylcarbazole as well as other carbazoles are efficient photosensitizers for the photolysis of both diaryliodonium and triarylsulfonium salt photoinitiators. In the presence of large amounts of N-vinylcarbazole, the rates of the cationic ring-opening photopolymerization of epoxides are markedly accelerated. This effect has been ascribed to a photoinitiated free-radical chain reaction that results in the oxidation of monomeric and polymeric N-vinylcarbazole radicals by the onium salt photoinitiators to generate cations. These cations can initiate the ring-opening polymerization of the epoxides, leading to the production of copolymers.