Effect of heterogeneous distribution of lamellar stacks in semi-crystaline polymers on amorphous relaxations

Recent SAXS experiments have shown that the ideal two-phase model is inadequate in space filling spherulitic systems. A model of amorphous materials heterogeneously filled with lamellar stacks, is consistent with the SAXS data. The strength of glass transitions in semi-crystalline materials are used to directly give the total `rigid' fraction which does not contribute to the glass transition. Comparison with the rigid fraction calculated from the SAXS model of heterogeneously dispersed lamellar stacks, shows that the inter-lamellar `amorphous' species do not contribute to the glass transition. No other `rigid amorphous fractions' are needed to describe the data, under crystallization conditions where the lamellar stacks are relatively well developed. PEEK, PET, and a polyimide are used as examples. In situations of very high crystallinities or systems with a highly constrained amorphous phases due to defective or high surface area lamellar stack morphologies, a RAF in addition to the rigid interlamellar amorphous species is needed to describe the data.