Polymers with enhanced photostability: photoreactions of poly( o-isobutyrylstyrene) in the long-wave region

Abstract

Poly( o-isobutyrylstyrene) (POIS) was exposed in the solid state to long-wave UV radiation ( λ≥300 nm) under high vacuum conditions at 25±1 °C. Transient spectral measurements indicate the presence of tow distinct enols, ie. the syn and anti, which have lifetimes of 163 ns and 4.5 μs respectively. The most important photoprocess is photoenolization, and although the syn carbonyl triplet is principally involved, experimental data indicate that the corresponding singlet may also contribute to the process. The anti carbonyl triplet appears to play a relatively passive part in photoenolization; however, it is involved in α-scission which leads to the formation of isopropyl radicals which, in turn, give rise to propane (principal product), propene and 2,3-dimethylbutane. Quantum yields for the formation of these products are low (10 −5), and this reflects the extent of competition from photoenolization. Similarly, the extent of cross-linking is very small. The carbonyl concentration is depleted to a minimal extent; thus, in terms of photodegradation, POIS appears to be a relatively photostable polymer.