Photochemistry of ring substituted polystyrenes—Part IV: Photolyses of poly( o-, m-, p-methylstyrenes)

Abstract

The photodegradations of films (2 × 10 −4 cm thick) of poly( o-, m- and p-methylstyrenes) with 254 nm radiation under high vacuum at 25°C are studied. In all cases the principal gaseous product is hydrogen but smaller quantities of methane, and very small amounts of ethane, are also formed, indicating that fission of bonds between the ring and the methyl groups is also involved. Ultraviolet and visible spectra of degraded films indicate the presence of unsaturated groups and of coloured species. Solubility data indicate that crosslinking and chain scission occur simultaneously. Rates of crosslinking are greater than those for polystyrene and this is attributable to the participation of the substituted phenyl radicals (formed by phenyl-CH 3fission) in addition reactions. However, crosslinking is inhibited sterically to some extent in the poly( o-methylstyrene). Quantum yields for gaseous product formation and probabilities of chain scission and crosslinking are determined. Mechanisms are advanced that correlate the rate of product formation and chain scission with the effect of the particular methyl substituent on the stabilities of the radical intermediates.