This study sought to aid in the development of an efficient, novel hybrid photoinitiator by examining the bond cleavage of 1-(arylmethyloxy)anthracenes 1 performing as a bichromophoric photoinitiator in the polymerization of styrene (St) and cyclohexene oxide (CHO) and classifying the cleavage as heterolytic or homolytic. The results indicated that the bichromophoric photoinitiator 1, containing no halogen or metal, induces radical and cationic polymerization reactions of St and CHO, respectively, to generate high yields of the corresponding polymers. In addition, an analysis of the effects of substituents on the photoreactivity and polymer yield of 1 indicated that the ability of the resultant radical or ion pair intermediate that was generated by the photolysis of 1 to initiate polymerization increased with the enhanced stability of the reactive intermediate. An analysis of the polymer end groups and photoproducts that were derived from specific initiators demonstrated that the arylmethyloxyl radical and arylmethyl carbocation are the reactive species involved in the initiation steps of the polymerization reactions for St and CHO, respectively. Polymer Journal (2012) 1 Much of the recent research has focused on novel photoinitiators that promote the initiation of both radical and cationic polymerizations, 2-8 because a combination of these two polymerizations could produce a hybrid polymer that is composed of radical-and cation-derived polymer units. For example, interpenetrating network polymers 9-11 combine the properties of these two polymer units and represent an attractive research area with many practical applications.Although some salt-type photoinitiators can initiate both cationic and radical polymerizations, [2][3][4][5]8,12,13 they have limited industrial application because they have low monomer solubility and require metal-or halogen-containing inorganic initiators. To overcome these limitations, nonsalt photoinitiators have been developed. Unfortunately, these photoinitiators are limited in their ability to induce hybrid polymerization. 6,7,14 A systematic study of the photoreactivity of O-substituted anthracene-9-methanol derivatives in methanol revealed that in the singlet excited state, an intramolecular charge-transfer interaction assisted in the heterolytic CH 2 -O bond cleavage to generate ion and radical pairs. 15 Therefore, these derivatives are good candidates for a novel hybrid-type photoinitiator that does not require halogen or metal. Although O-acyl anthracene-9-methanol functioned as a photoinitiator for