EFFECTS OF MOLECULAR-WEIGHT ON THE STRUCTURE OF POLY(PHENYLENE SULFIDE) CRYSTALLIZED AT LOW-TEMPERATURES

We report a study of the effects of molecular weight on the structure and properties of poly(phenylene sulfide), PPS, crystallized from the rubbery amorphous state at temperatures just above the glass transitio n. PPS films were characterized using temperature-modulated differenti al scanning calorimetry (MDSC), small angle X-ray scattering (SAXS), a nd dynamic mechanical analysis (DMA). For samples crystallized so as t o have the same half-time, we find (1) the degree of crystallinity, ch i(e), is not dependent upon molecular weight and (2) as the molecular weight increases, the heat capacity increment at the glass transition increases. These results suggest that lower molecular weight PPS conta ins a greater fraction of the rigid amorphous phase, probably as a res ult of formation of taut tie molecules between crystals. It is found f rom DMA that molecular weight is the determining factor that affects t he Young's modulus value at the higher temperature. A lower E' is obse rved for the higher molecular weight material. MDSC data suggest that higher molecular weight PPS has a slower crystallization rate and reor ganization rate. The amount of crystals formed during heating is small er in higher molecular weight PPS, and this may be the explanation for the reduced Young's modulus above T-g.