PHOTOREACTIONS OF POLY(O-BUTYRYLSTYRENE) IN THE LONG-WAVE REGION

Poly(o-butyrylstyrene) (POBS) was exposed in the form of thin films to long-wave UV radiation (lambda greater-than-or-equal-to 300 nm) under high vacuum at 25+/-1-degrees-C. Ethylene was the principal low-molec ular-weight product, but much smaller amounts of CO, methane, ethane a nd propane were also formed. Quantum yields for gaseous product format ion were low, indicating that the Norrish type I and II reactions, whi ch lead to their production, are subject to competition from the relat ively favourable photoenolization. Transient spectra indicate the pres ence of the syn- and anti-enols, which have lifetimes of 140 ns and 4. 7 mus respectively. Molecular weight data indicate that crosslinking o ccurs, but to a much lesser extent than in the isomeric p-acylstyrene polymers, both the Norrish type II reaction and photoenolization compe ting with free radical production. Other spectroscopic measurements in dicate a minimal depletion of the carbonyl concentration, which is con sistent with the predominance of these reactions. In terms of photodeg radation, POBS is a relatively photostable polymer.