POLYMERS WITH ENHANCED PHOTOSTABILITY - PHOTOREACTIONS OF POLY(O-ISOBUTYRYLSTYRENE) IN THE LONG-WAVE REGION

Poly(o-isobutyrylstyrene) (POIS) was exposed in the solid state to lon g-wave UV radiation (lambda greater than or equal to 300 nm) under hig h vacuum conditions at 25 +/- 1 degrees C. Transient spectral measurem ents indicate the presence of two distinct enols, i.e. the syn and ant i, which have lifetimes of 163 ns and 4.5 mu s respectively. The most important photoprocess is photoenolization, and although the syn carbo nyl triplet is principally involved, experimental data indicate that t he corresponding singlet may also contribute to the process. The anti carbonyl triplet appears to play a relatively passive part in photoeno lization; however, it is involved in alpha-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 fo r 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 deplete d to a minimal extent; thus, in terms of photodegradation, POIS appear s to be a relatively photostable polymer.