To establish the reaction condition under which the radical copolymerization of methyl methacrylate (MMA) with alpha-(2-hydroxy-4-methacryloyloxyphenyl)-N-(2,6-dimethylphenyl)nitrone (HMDN) proceeds smoothly to give photoreactive copolymers, the effects of the nitrone chromophore on the extent to which the radical polymerization of MMA is inhibited were investigated. It was found that the reversible addition of initiating radical to the CH=N+(-O-) moiety in the nitrone chromophore readily occurs to give the nitroxyl radical. It was also found that the latter radical undergoes an efficient coupling reaction with propagating radical to inhibit the radical copolymerization of MMA with HMDN. However, on raising the reaction temperature and the radical concentration, the copolymerization was successfully carried out. This polymerization condition allowed us to prepare the HMDN/MMA, HMDN/styrene, and HMDN/cyclohexyl acrylate copolymers in good yields. The photoirradiation of the copolymer film prepared on a silicon wafer lowered its refractive index by 0.003-0.023, depending on the relative composition of the diarylnitrone chromophore in these copolymers. (c) 2005 Wiley Periodicals, Inc.