Photocross-linking of polymers initiated by benzylsulphonium salts as cationic initiators

Abstract

Photocross-linking of poly(1,3-dioxolane-4-methyl methacrylate) and copolymers with methyl methacrylate initiated by benzylsulphonium salt (BSS) has been explored. On photoirradiation, BSS directly produces benzyl cations which are capable of initiating cationic polymerization of side-chain cyclic ketals. The homopolymer and the copolymers were doped with BSS in the concentration range 0.05–5 mol % on the basis of the ketal units and the resulting films were irradiated at > 300 nm in air. The course of the photocross-linking of the sample films was followed spectroscopically by measuring the absorbance due to BSS (ultraviolet) and the absorbance due to dioxolane (infrared) as well as thermal analysis (differential scanning calorimetry) and chemical titration (ketal content). It was found that BSS is effective in inducing the cross-linking of the polymers, and the present system might be a promising candidate for a highly sensitive negative photoresist with an aqueous developing system.