1-(Arylmethyloxy)-9,10-anthraquinones: Photoinitiators for Radical and Cationic Polymerizations

Abstract

An investigation was undertaken to gain understanding of the type of bond cleavage (heterolysis versus homolysis) of 1-(methoxy-substituted arylmethyloxy)-9,10-anthraquinones (1) as bichromophoric photoinitiators of styrene (St) and cyclohexene oxide (CHO) polymerization to aid development of a novel and efficient hybrid photoinitiator. Results indicated that the 4-methoxynaphthalen-1-ylmethyl-substituted photoinitiator 1 containing no halogen or metal induces radical and cationic polymerization reactions of St and CHO, respectively, to give the corresponding polymers in reasonable yields. This initiator also accomplished hybrid photopolymerization of an equimolar mixture of St and CHO, although the ability to initiate polymerization was reduced. Analysis of the photoproducts derived from specific initiators as well as of the polymer end groups substantiated that the arylmethyloxyl radical and arylmethyl carbocation are major reactive species initiating the polymerization of St and CHO, respectively. In addition, the charge-separated state characteristic of the 9,10-anthraquinon-1-yloxy chromophore in the singlet excited state played a pivotal role in the heterolytic bond-cleavage in the latter monomer.