Commercial poly(p-phenylene sulfide) (PPS) was thermally cured, which resulted in an increase of molecular weight due to cross-linking. Non-isothermal crystallization studies of samples cured for up to 7 days at 250?C...Commercial poly(p-phenylene sulfide) (PPS) was thermally cured, which resulted in an increase of molecular weight due to cross-linking. Non-isothermal crystallization studies of samples cured for up to 7 days at 250?C showed a monotonous increase of crystallization temperature compared to pure PPS. However, a further increase of curing time decreased the crystallization temperature. The change in the half-crystallization time (t1/2) was similar to the crystallization temperature. Thus, the cross-linking of PPS affected crystallization behaviors significantly. To a certain extent, crosslinks acted as nucleation agents, but excessive cross-linking hindered the crystallization. Morphologies observed by polarized optical microscopy suggested that thermal curing for as little as 1 day contributed to the spherulitic structure having a smaller size, that was not observed with pure PPS.展开更多
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 ...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.展开更多
Thermal transition and decomposition behaviors of polyetheretherketone,polyethersulfone,poly(phenylene sulfide),poly(phenylene sulfide ketone) have been investigated.The melting point,glass transition temperature,deco...Thermal transition and decomposition behaviors of polyetheretherketone,polyethersulfone,poly(phenylene sulfide),poly(phenylene sulfide ketone) have been investigated.The melting point,glass transition temperature,decomposition temperature and activation energy of decomposition reaction have been reported.From these results,the thermal resistant order of these four polymers has been estimated.展开更多
文摘Commercial poly(p-phenylene sulfide) (PPS) was thermally cured, which resulted in an increase of molecular weight due to cross-linking. Non-isothermal crystallization studies of samples cured for up to 7 days at 250?C showed a monotonous increase of crystallization temperature compared to pure PPS. However, a further increase of curing time decreased the crystallization temperature. The change in the half-crystallization time (t1/2) was similar to the crystallization temperature. Thus, the cross-linking of PPS affected crystallization behaviors significantly. To a certain extent, crosslinks acted as nucleation agents, but excessive cross-linking hindered the crystallization. Morphologies observed by polarized optical microscopy suggested that thermal curing for as little as 1 day contributed to the spherulitic structure having a smaller size, that was not observed with pure PPS.
基金financially supported by the National Science Fund for Distinguished Young Scholars (No.50925311)the National Natural Science Foundation of China (No.20976112)
文摘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.
文摘Thermal transition and decomposition behaviors of polyetheretherketone,polyethersulfone,poly(phenylene sulfide),poly(phenylene sulfide ketone) have been investigated.The melting point,glass transition temperature,decomposition temperature and activation energy of decomposition reaction have been reported.From these results,the thermal resistant order of these four polymers has been estimated.
