PHOTO-DECOMPOSITION OF POLY(STYRENE) HYDROPEROXIDE .2. REACTIONS IN THE SOLID-STATE

The long-wave (lambda > 300 nm) photo-decomposition of the hydroperoxi de of poly(styrene) was investigated in the form of thin films, which were irradiated at 20 +/- 1-degrees-C. Under high-vacuum, hydroperoxid e decomposition which was measured directly was accompanied by concomi tant increases in concentrations of carbonyl and other hydroxylic prod ucts. A variety of low molecular compounds was formed, including H2O, CO, CO2, O2, benzaldehyde, benzene and benzophenone, but H2O was most abundant. Molecular weight and gel permeation chromatography (GPC) mea surements showed that chain scission was restricted to the very early stages of the reaction, cross-linking rapidly overwhelming its effects . In addition, the distribution rapidly became skewed to higher molecu lar weights. That the decompositions did not conform to the expected u nimolecular kinetics, together with their higher-than-expected values of the quantum yield; i.e. 2 +/- 0.25 mol (einstein)-1 suggested that sensitized decomposition was also occurring. This can be brought about by the interactions of the hydroperoxide with the initially formed hy droxyl (and perhaps also alkoxy) radicals, and more importantly, by th ose with ketonic products. The large differences between the behaviour of the hydroperoxide in the solid state and in the form of a dilute s olution can be attributed largely to the effects of facile cross-linki ng, secondary decompositions being inhibited by the increasing rigidit y of the system.