Photochemistry in Polymer Solids V. Decay of Benzophenone Phosphorescence in Polystyrene and in Polycarbonate

Abstract

ABSTRACT:Decay curves and lifetimes of benzophenone phosphorescence in polystyrene and in bisphenol A polycarbonate (BPA-PC) at 80----433 K significantly reflect change in the molecular motion of matrix polymers such as glass transition, /3-transition, and }'-transition. The non-singleexponential decay. curves were observed in both polymers at temperatures between T, and T., and analyzed using the diffusion-controlled rate coefficient with a time dependent transient term for the dynamic quenching process of benzophenone triplet by phenyl or phenylene groups in the matrix polymers. The diffusion coefficients, D, of the reacting functional groups in polystyrene and BPA-PC for the wide temperature range below T. are much larger than that in PMMA in the same temperature range, showing a higher quenching ability of these polymers for the benzophenone triplet.

Gelation of Copolymers with Pendent Benzophenone Photo-Cross-Linkers

“…The high E c for PS (30.1 ± 6.3 J/cm 2 , nearly 3 times larger than any other material) despite the presence of what should be a quite reactive 3°benzylic position suggests a steric effect here as well. While quenching of AmBP triplet by the styrenic polymer 77 could also contribute to lower reactivity, we note that the incorporation of a 1°benzylic position pendent to the polymer chain as in poly(pmethylstyrene) (PpMS) lowers E c considerably (11.8 ± 0.7 J/cm 2 ). Together with the aforementioned results for PiBA and PiBMA, these findings paint a consistent picture that steric effects lead to generally reduced reactivity of backbone hydrogens.…”

Photochemistry in polymer solids. 8. Mechanism of photoreaction of benzophenone in poly(vinyl alcohol)

“…These temperature dependences of the decay profiles of benzophenone triplet in poly(vinyl alcohol) are similar to those previously observed in poly(methyl methacrylate) and other acrylic polymers2 and in polystyrene and polycarbonate. 4 Though there seem to be no physically quenching groups in poly-(vinyl alcohol), in contrast to the case of previously measured polymers, the tertiary hydrogen atom in the main chain of poly(vinyl alcohol) (PVA) is supposed to be easily abstracted by benzophenone triplet (3BP*), forming benzophenone ketyl radical (BPH') and poly(vinyl alcohol) on-chain radical (PVA"), based on the model hydrogen abstraction reaction12 of benzophenone triplet from 2-propanol.…”

“…In eq 3 D is the sum of the diffusion coefficient for the carbonyl group in benzophenone and that for hydrogen in poly (vinyl alcohol), R is the reaction radius between the two reacting groups, k is the intrinsic (chemical) rate constant for hydrogen abstraction, and N is the Avogadro number divided by 103. When k& is controlled by the diffusion process of the two groups (k » 4irRDN), eq 3 is reduced to (4) with A = 4irRDN and B = 4R2(ttD)1/!2N. The rate coefficient k& includes a time-dependent term that is important at the very early stage of reaction where the steady-state diffusion flux of the reacting group is not yet attained.…”

“…Figure4. Arrhenius plots of diffusion coefficients, D, of reacting groups for hydrogen abstraction by benzophenone triplet in poly (vinyl alcohol) calculated from l/ (O) or B (©).…”