Reactivity of substituted S-phenyl thiobenzoates as photoinitiators of radical polymerization

Abstract

The reactivity in the excited state of new radical photoinitiators, S-phenyl thiobenzoates, was investigated. Laser flash photolysis experiments on various substituted compounds allowed both thiyl and benzoyl radicals to be observed. These two radicals arose from the α-cleavage of the CS bond in the first excited triplet state. The ability to initiate radical polymerization was followed by dilatometry. From the results, it is found that the S-phenyl thiobenzoate photoinitiators can be even more reactive than benzoin ethers because of their better u.v. light absorption.