We report a thermal analysis study of the effect of molecular weight on the amorphous phase structure of poly(phenylene sulfide),
PPS, crystallized at temperatures just above the glass transition temperature. Thermal properties of Fortron PPS, having viscosity
average molecular weights of 30000 to 91000, were characterized using temperature modulated differential scanning calorimetry
(MDSC). We find that while crystallinity varies little with molecular weight, the heat capacity increment at the glass transition
decreases as molecular weight decreases. This leads to a smaller liquid-like amorphous phase, and a larger rigid amorphous
fraction, in the lower molecular weight PPS. For all molecular weights, constrained fraction decreases as the scan rate decreases.