Photochemical Processes in a Copolymer of 2-(2'-Hydroxy-4'-methacryloyloxyphenyl)-2H-benzotriazole and Methyl Methacrylate

The temperature-dependent (10-300 K) fluorescence behaviour of films of a copolymer of 2-(2′-hydroxy-4′-methacryloyloxyphenyl)-2H-benzotriazole and methyl methacrylate (HMPB-co-MMA) has been studied. The emission spectra consist of a short-wavelength band and a highly Stokes-shifted emission with maxima at 390 and 550 nm respectively. The temperature- insensitive 390 nm emission is assigned to a non- intramolecular hydrogen-bonded form of HMPB while the red-shifted emission is due to the species formed following excited-state intramolecular proton transfer. The temperature dependence of the 550 nm fluorescence is complex and does not allow a linear Arrhenius plot. Possible mechanisms for the temperature-dependent deactivation processes are proposed. Irradiation studies indicate that the non-planar HMPB entities are more photolabile than the intramolecularly hydrogen-bonded form. The relevance of the results to the application of HMPB as an ultraviolet absorber and photostabilizer in polymers is discussed.