Redox Initiated Cationic Polymerization: Reduction of Triarylsulfonium Salts by Silanes

A novel redox initiator system for carrying out the cationic polymerization of epoxide, oxetane and vinyl ether monomers has been developed. The redox couple is based on a triarylsulfonium salt as the oxidant with an organosilane as the reducing agent. The reaction between these two agents is markedly catalyzed by platinum and palladium complexes. Cationic polymerizations using this redox initiator system were carried out in a conventional manner with neat monomer or under solution conditions. This paper also describes the novel use of a two-component redox system in which the silane is delivered to the monomer sample in the vapor state. Optical pyrometry (infrared thermography) was employed as a convenient method with which to monitor the polymerizations. A study of the effects of variations in the structures of the triarylsulfonium salt, the silane and the type of noble metal catalyst were carried out. The use of this initiator system for carrying out commercially attractive cross-linking polymerizations for coatings, composites and electronic encapsulations is discussed.