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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. 1 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 types of polymerizations could produce a hybrid polymer composed of radical-and cation-derived polymer units. For example, interpenetrating network polymers 9-11 that combine the properties of these two polymer units present an attractive research subject due to potential practical applications.While some salt-type photoinitiators can initiate both cationic and radical polymerizations, [2][3][4][5]8,12,13 they have limited industrial application because of problems such as low solubility in monomers and the need for metal-or halogen-containing inorganic initiators. To overcome these problems, nonsalt-type photoinitiators have been developed, but they induce only minor hybrid polymerization. 6,7,14 A systematic study on the photoreactivity of O-substituted anthracene-9-methanol derivatives in methanol revealed that an intramolecular charge transfer interaction in their singlet excited states assists heterolytic CH 2 -O bond cleavage to generate ion pairs along with radical pairs.15 Therefore, these derivatives are good candidates for a novel hybrid-type photoinitiator containing no halogen or metal. While O-acyl anthracene-9-methanol functioned as a photoinitiator for the radical polymerization of styrene (St), the cationic photopolymerization of cyclohexene oxide (CHO) was induced only to a minor extent.14 This finding suggests that the much lower polarity of CHO compared with that of methanol results in inefficient heterolytic bond cleavage in the singlet excited state. Therefore, an investigation was undertaken to develop a hybrid-type photoinitiator that would undergo much more efficient heterolysis in CHO. To accomplish this, 2-arylmethyloxy-6-...

An investigation was undertaken to shed much light on the bond‐cleavage mode (heterolysis vs homolysis) of bichromophoric photoinitiators in styrene (St) and 1,2‐epoxycyclohexane (EpC) and then to develop a highly efficient hybrid‐type photoinitiator. Excited‐state 2‐(9‐anthrylmethyloxy)‐6‐cyanonaphthalene in toluene and 1,2‐dimethoxyethane, which were used instead of St and EpC, respectively, underwent both homolytic ArOCH2 bond cleavage and heterolytic ArOCH2 bond cleavage to give the corresponding radical‐pair and ion‐pair intermediates. The charge‐separated state characteristic of the naphthol chromophore in the singlet excited state was found to play a pivotal role in this heterolytic bond‐cleavage mode. An inspection of the radical (St) and cationic (EpC) photopolymerization behavior observed in the presence of some 2‐arylmethyloxy‐6‐cyanonaphthalenes led us to conclude that the aforementioned 9‐anthrylmethyloxy‐substituted naphthalene derivative is a candidate for a functional hybrid‐type photoinitiator containing no halogen and/or metal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 25–31, 2006

This study explored the abilities of 1‐(9‐anthrylmethyloxy)‐2‐pyridone and related compounds, which absorb long‐wavelength light (>350 nm), to photochemically initiate radical and cationic polymerizations. It was found that the irradiation of the title compounds initiates the radical polymerization of styrene whereas the cationic polymerization of oxetane proceeds in the presence of these photoinitiators to a negligible extent. The behavior of 9‐anthrylmethyloxyl and amidyl radicals in the photopolymerization process of styrene was discussed based on 1H NMR, UV, and fluorescence spectral data. In addition, the photoinitiation ability of the anthrylmethyloxyl end group was also investigated by using its model compound. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2859–2865, 2004

Hydroxy-substituted aromatic nitrone derivatives were used for the photochemical control of the refractive index of poly(methyl methacrylate) (PMMA) films. Upon irradiation with 366-nm light in solution, these derivatives underwent rearrangement reactions, which eventually produced N,N-diarylformamide derivatives in quantitative yields. Similar photoreactions of the aromatic nitrones in the PMMA films lowered the refractive index of the films by as much as 0.014. The magnitude of the observed refractive-index change was enough for hydroxy-substituted nitrones to be used as additives for the fabrication of gradedindex-type polymer optical fibers. In addition, the refractive index of the PMMA films remained almost constant at any conversion of the starting nitrone derivatives for at least 70 days at room temperature.