Photoinitiators and photoinitiation, 9 Photoinitiators for radical polymerization which counter oxygen‐inhibition

Abstract 1‐Alkanesulfonic and 4‐alkylbenzenesulfonic esters of α‐hydroxymethylbenzoin were shown to photoinitiate the polymerization and crosslinking of acrylates. The overall rate of polymerization in bulk and of crosslinking in solution, respectively, proved to be constant within each series of homologues. However, in thin films in an air atmosphere, the overall rate of crosslinking (curing rate) proved to increase with increasing alkyl chain‐length within each series of homologues. Moreover, the curing rate obtained with the 1‐hexanesulfonic ester and its higher homologues substantially surpassed the curing rates obtained with a number of established photoinitiators, provided a small amount of an alkali metal salt (preferably a lithium salt) is present. The curing mechanism of the sulfonic esters of α‐hydroxymethylbenzoin and the role of the alkali metal salt are explained.