Dielectric studies of photodegradation and photooxidation of polystyrene

The effects of vacuum photolysis at 254 nm and the short‐(λ = 254 nm) and long‐wave (λ > 300 nm) photooxidations on the dielectric constants (ϵ′) and dielectric losses (ϵ″) of polystyrene have been investigated at 25 ± 1°C. Dielectric constants generally increase on photodegradation, but more pronounced increases occur in the low‐frequency region on vacuum photolysis. It is suggested that such increases are associated with Maxwell‐Wagner‐Sillars polarization. Increases in dielectric losses are observed in three main frequency regions: around 102 Hz, 104 Hz, and at 3 × 106 Hz. The lowest frequency loss which occurs in both the vacuum‐irradiated and in the photooxidized samples is attributed to a combination of the effects of interfacial polarization and of the increased direct‐current conductivity of the polymer which occurs as a result of these reactions. The 104 Hz dispersion associated only with photooxidation is related to the presence of small, volatile, polar oxidation products, like ketones. The loss peak overlaps the intrinsic γ‐relaxation of polystyrene, and it appears that the motions of small molecules, or of relaxing dipoles in these, are coupled to the phenyl group rotational vibrations. The high‐frequency losses (3 × 106 Hz) are ascribed to orientation polarization of carbonyl dipoles attached to chain ends, these compounds being produced as a result of hydroperoxide decompositions. A good correlation between the carbonyl dipole relaxation strength and carbonyl concentration is observed. It would appear that relaxation strength measurements could provide quantitative kinetic information for polystyrene oxidation.