Relaxation phenomena in the vicinity of the glass transition of poly (p-phenylene sulfide)

Abstract

Thermally stimulated depolarization current (TSDC), thermal sampling (TS) TSDC, and dielectric spectra of poly(p-phenylene sulfide) (PPS) were measured in the vicinity of the glass transition temperature Tg. The global TSDC spectra of amorphous PPS with varying the poling temperature revealed the presence of two TSDC peaks. Only a very intense peak associated with the α relaxation (the glass transition) was observed at 367 K in the global TSDC spectra poled at above 360 K, while an additional peak was observed at around 330 K in those spectra poled at below 355 K. This additional peak observed at below Tg was considered to be originated from the secondary sub-Tg relaxation. Both the sub-Tg and the α relaxations were analyzed from elementary TSDC spectra obtained by the TS technique. It was found that the temperature dependence of the relaxation times in both relaxations was ruled by the same compensation law. The physical meaning of the compensation temperature is discussed in relation to the thermal-expansion coefficient. Moreover, the dielectric constant ε′ and dielectric loss factor ε″ of amorphous PPS are calculated using the relaxation parameters derived from the TS-TSDC analysis. Numerical results of dielectric data are represented by three-dimensional and/or two-dimensional spectra and are compared with the available experimental data. The simulated dielectric spectra forecast that the sub-Tg relaxation should appear as a peak or shoulder of ε″ at lower-temperature and ultra-low-frequency regions in the ac measurements.