Photoreactions of poly( o-propionylstyrene in the long-wave UV region

Abstract

Films of poly( o-propionylstyrene) (POPS) were exposed to long-wave ultraviolet radiation under high vacuum at 25 °C. Gaseous products were quantitatively analyzed by mass spectrometry, and molecular weight measurements were carried out on the polymer residue. POPS undergoes a Norrish Type I decomposition; however, the extent of degradation is limited by the competition from photoenolization of the carbonyl triplet. Transient spectra indicate the presence of the syn-enols and anti-enols which have lifetimes of 125 ns and 4 μs respectively. Molecular weight data indicate that cross-linking occurs, but the extent is considerably lower than that observed for the isomeric poly ( p-propionylstyrene) (PPPS). It is proposed that photoenolization competes with the Norrish Type I reaction, thus lowering the concentrations of macroradicals. Interactions of these radicals are also subject to adverse steric effects, their mutual approach being inhibited by their proximity to the polymer chain. POPS is, however, considerably more photostable than the isomeric PPPS.