INSOLUBLE POLYMERIC BENZOPHENONE - SURFACE PHOTOPHYSICAL STUDIES USING DIFFUSE-REFLECTANCE LASER-FLASH PHOTOLYSIS (DRLFP)

Diffuse-reflectance laser-flash photolysis (DRLFP) studies of solid samples of benzoylated cross-linked (2% DVB) polystyrene (insoluble polymeric benzophenone) are reported. They show that the transients generated by the pulsed-laser excitation are the benzophenone triplet and a radical (benzhydryl radical). Different loadings with the benzophenone chromophores result in different contribution to the transient absorption by each species, and at intermediate loadings the major contribution to the transient absorption is due to the triplet state of benzophenone. A map of the distribution of the functional groups in the polymeric beads is proposed which accounts for these results. Since the polymers were prepared following the concept of the solid-phase synthesis, the map can be extended to any functionalized cross-linked (2% DVB) polystyrene obtained by this method. DRLFP is shown to be a sensitive method for the detection of transient signals from an extremely low-loaded polymer; for example, a polymer carrying only one benzoylated phenyl group out of 10 000 pendant phenyl groups of the polystyrene chain has been studied here using DRLFP and shown to give useful results.