Thermally stimulated current (TSC) study of the Tg and Tll transitions in anionic polystyrenes

Abstract

AbstractThe thermally stimulated current (TSC) technique has been used to investigate three anionic polystyrenes of M̄n 17,000, 71,700, and 1.55 × 106, i.e., M < Mc, M > Mc, and M ≫ Mc, where Mc is the entanglement molecular weight. A current maximum near Tg designated TMg, has relaxation times which follow an Arrhenius equation. A second current maximum at T > Tg appears to be the Tll process and is designated TMll. Relaxation times for it follow a Vogel equation. TMg and TMll vary with molecular weight, increasing below Mc and leveling off above Mc at a temperature of about 170°C. Values of TMg and TMll are compared with values of Tg and Tll obtained from torsional braid analysis, which involves melt flow; and with differential‐scanning‐calorimetric values on fused films, where there is no transport of polymer. It is concluded from such cross‐comparisons that TSC, at least for polystyrene, is a quasistatic test which may involve microscopic viscosity. Macroscopic viscosity does not play a role. The ratio TMll/TMg is in the range 1.10–1.16, similar to Tll/Tg values by other methods. A few comments about Tll in atactic poly(methyl methacrylate) by the TSC method are given.