Novel syntheses of 1-propenyl ethers and dialkylphenacylsulfonium salts and their applications in cationic photopolymerization

Two investigations in the area of photoinduced cationic polymerization have been conducted. These research efforts were intended to provide efficient, low cost preparation of cationically polymerizable monomers and cationic photoinitiators and to evaluate these compounds in photopolymerization applications.; In the first project, a new, convenient method for the isomerization of allyl ethers and related compounds has been developed. Alkyl and aryl allyl ethers can be smoothly isomerized to the desired 1-propenyl ethers by refluxing in a basic ethanol/water solution containing pentacarbonyliron as a catalyst. This method was combined with Williamson ether synthesis to make 1-propenyl ether compounds in a one-pot fashion. Further, cationic polymerizations of aryl 1-propenyl ethers were studied using diaryliodonium salt photoinitiators. These compounds fail to undergo efficient cationic polymerization due to chain-transfer by Friedel-Crafts alkylation.; The second project involves the development of a new, simplified method for the synthesis of dialkylphenacylsulfonium salt cationic photoinitiators. This novel method was successfully used for the preparation of dialkylphenacylsulfonium salts bearing a wide variation in the length and structure of the alkyl chains as well as the light absorbing aryl ketone chromophores and the anions. Photopolymerization studies revealed that these photoinitiators are capable of initiating the cationic polymerization of a wide variety of epoxy and vinyl ether monomers directly on irradiation with UV light or by using visible light irradiation in the presence of photosensitizers. Kinetic studies show that they compare favorably with respect to their reactivity to diaryliodonium and triarylsulfonium salt photoinitiators in the polymerization of epoxides. The photopolymerizations of vinyl and 1-propenyl ethers display a marked induction period consistent with termination of the growing chains by reaction with the photogenerated ylides. Preliminary studies have demonstrated that these compounds can also be employed as thermal initiators for the cationic ring-opening polymerization of epoxides at moderate temperatures.