Non-isothermal crystalliztion kinetics of poly(phenylene sulfide) with low crosslinking levels

Poly(phenylene sulfide) (PPS) with different crosslinking levels was successfully fabricated by means of high-temperature isothermal treatment (IT). The crosslinking degree of PPS was increased with IT time as revealed by Fourier-transform infrared spectroscopy and dynamic viscosity measurements. Its influence on the non-isothermal crystallization behaviors of PPS was studied by differential scanning calorimeter (DSC). The crystallization peak temperature of PPS with 6 h IT was 15 K higher than that of the one with 2 h IT at 30 K/min cooling rate. The non-isothermal crystallization data were also analyzed based on the Ozawa model. The Ozawa exponent m decreased from 3.5 to 2.2 at 232°C with the increase of the IT time, suggestive of intensive thermal oxidative crosslinking reducing the crystallite dimension as PPS crystal grew. The reduced cooling crystallization function K(T) was indicative of the larger activation energy of crosslinked PPS chain diffusion into crystal lattice, resulting in a slow crystal growth rate. Additionally, the overall crystallization rate of PPS was also accelerated with the increase of crosslinking degree from the observation of polarized optical micrograph. These results indicated that the chemical crosslinked points and network structures formed during the high-temperature isothermal treatment acted as the effective nucleating sites, which greatly promoted the crystallization process of PPS and changed the type of nucleation and the geometry of crystal growth accordingly.