Selective inhibition of the photoinitiated cationic ring-opening polymerization of epoxides by dialkyl sulfides has provided dual systems that can be "activated" by UV irradiation and then subsequently be polymerized by the application of heat. It is proposed that dialkyl sulfides terminate the initial or growing polyether chains at an early stage to form stable trialkylsulfonium salts. These systems are dormant at room temperature but on thermolysis, the sulfonium salts are capable of reinitiating ring-opening polymerization. These dual photo- and thermal cure systems have potential applications in adhesives, potting resins, and composites. (c) 2006 Wiley Periodicals, Inc.