Photoreactivity of diarylnitrone additive/pendant in poly(methyl methacrylate) film and photocontrol of refractive index for this polymer film

Photoreactivities of hydroxy-substituted diarylnitrones (1a-f) in solution and methyl methacrylate(MMA)-derived polymer film were studied. The methyl group introduced at the ortho-position on the N-aryl benzene ring of 1 (1c-e) was found to exert a great steric effect on the photoreaction pathway to eventually give a different photoproduct distribution. This steric effect also contributed to suppressing a decrease in the refractive index of PMMA polymer film. The irradiation at 366 nm of MMA-derived copolymer film (bearing the diarylnitrone pendants) lowered the refractive index of this film by −Δn = 0.0152, which was much larger than the refractive-index decrease of PMMA polymer film containing 1c-e as additives (−Δn = 0.0017-0.0044).