Cyclic acetals as coinitiators in CQ-induced photopolymerizations

A series of cyclic acetals were investigated with regard to their ability to function as coinitiators in free-radical photopolymerization induced by camphorquinone (CQ). Among these cyclic acetals, the reactivity of 2-hexyl-1,3-benzodioxole (HBDO) was the highest, according to the quantum yield of CQ. However, the most efficient coinitiator was l,3-benzodioxolane, which has a reactivity significantly exceeding that of HBDO. The polymerization efficiency of the coinitiators did not correlate with the efficiency of the photoinduced formation of the initiating radicals. The reasons for this lack of correlation were discussed in terms of how the reactivity of the radicals formed affected the various stages of polymerization. Further studies with a cleavage-type photoinitiator in the presence of cyclic acetals provided supporting evidence for the role of the chaintransfer reaction in the polymerization of the CQ/cyclic acetal systems. Polymer Journal (2010) 42, 450–455; doi:10.1038/pj.2010.29; published online 12 May 2010