Photodecomposition of polystyrene hydroperoxide: Part I—Reactions in dilute solution

Abstract

The long-wave ( λ > 300 nm) photodecomposition of polystyrene hydroperoxide (PSOOH) in dilute solution (benzene) at 20 ± 1°C was studied under high-vacuum conditions. Although water was by far the most abundant low-molecular-weight product, trace amounts of a number of others, such as CO, O 2, CO 2, benzaldehyde and acetophenone, were also formed. New absorbances due to macromolecular ketonic and hydroxylic species were detected by a number of spectroscopic techniques. Molecular weight ( M n ) and gel-permeation chromatography measurements indicated that although random chain scission predominates in the earlier stages of the degradation, some crosslinking, as indicated by a broadening of the molecular weight distribution, also occurs. The kinetics of the reaction were investigated from the points of view of PSOOH concentration and chain scission, and found to be complex, particularly in the former case. Decomposition rates of PSOOH accelerate with reaction time, and the quantum yield is 1·6 ± 0·2 mol einstein −1. These observations are consistent with sensitized decomposition, the initially formed hydroxy and alkoxy radicals from the PSOOH and, more importantly, the ketonic reaction products interacting with the PSOOH in a number of ways, to increase the overall rate of decomposition. Mechanisms of the sensitized decomposition, chain scission and crosslinking are discussed in the light of experimental observations.