Effects of peroxide bonds and their degradation products on the dielectric relaxations of polystyrene

Polystyrene radically polymerized in atmosphere of air is composed of bisegment (C-A) or trisegment (C-A-C) block copolymers consisting of styrene segment (A) and styrene peroxide segment (C). Dielectric measurements of a system of copolymers of styrene and oxygen were obtained above the glass temperature. Three primary relaxations, a, b, and c, in order of descending temperature, were found corresponding to three microphases: styrene phase (phase a), styrene peroxide phase (phase c), and an intermediate phase (phase b) which contains a low concentration of peroxide bonds. An alternating copolymer of styrene and oxygen exhibits the relaxation c alone. With heat treatment above the glass temperature, relaxation c and subsequently relaxation b vanish with thermal degradation of peroxide bonds. The sum of relaxation strengths is linearly related to the content of peroxide bonds which was evaluated by the elementary analysis and DTA. Below the glass temperature, the temperature dependence of dielectric loss of carefully purified polystyrene without peroxide bonds shows very weak peaks which correspond to γ (200°K at 10 kHz) and δ (50°K at 10 kHz) peaks, respectively, in the activation plot. When low molecular degradation products of peroxide bonds are occluded or impurities such as benzaldehyde are added into the specimen, the height of the γ peak is appreciably enhanced, indicating that the reorientation of small polar molecules in polystyrene accompanies the vibration of the phenyl group about the C? C₆H₅ bond which gives rise to the γ relaxation.