Crystallization, melting, and relaxation of modified poly(phenylene sulfide). I. Calorimetric studies

The crystallization, melting, and glass-rubber relaxation characteristics of a series of random poly(phenylene sulfide) (PPS) copolymers based on sodium hydrosulfide (NaSH) and 1,4- and 1,3-dichlorobenzene monomers have been investigated; sample compositions included the PPS homopolymer, and copolymers incorporating 5%, 8%, and 10% meta-phenylene linkages. The introduction of increasing levels of meta-phenylene units led to a modest decrease in amorphous glass transition temperature (from 86°C [0%] to 74°C [10%]) and a strong decrease in equilibrium melting temperature as determined by Hoffman-Weeks extrapolation (from 331°C [0%] to 273°C [10%]). Wide-angle x-ray scattering (WAXS) studies indicated that the meta units were excluded as defects from the bulk crystal structure, with no variation in unit cell parameters. Measurements of glass transition temperature for the crystallized polymers revealed a significant positive offset in T_g with the presence of crystallinity owing to the constraints imposed by the crystallites on the amorphous phase. The magnitude of this offset was observed to decrease with increasing meta-phenylene incorporation, suggesting that the meta defects act to loosen the constraints imposed at the crystal lamellar surface. Determination of the rigid amorphous phase fraction at T_g, however, revealed no dependence on copolymer composition.