Microstructure development and crystallization of poly(ethylene oxide) and melt-miscible PEO blends

Time-resolved (TR) small-angle X-ray (SAXS) experiments were conducted to monitor the development of microstructure and crystallinity in neat PEO and a representative composition from four, melt-miscible PEO blends. Although crystal thickening was not observed directly during the time scale of the experiments, comparison of the microstructural parameters obtained from the analysis of the TRSAXS data with those determined from static SAXS (for well -crystallized samples) indicated different rates of crystal thickening for rapidly vs slowly crystallizing systems. An Avrami-like expreseion was used to track the kinetic evolution of experimental invariants during crystallization. A generalized four-parameter model was proposed which, in addition to the two "Avrami" exponents, included factors that account for the nonzero crystallinity at the start of the SAXS run and finite lamellar stacks at the end of the run. The model is reduced to three parameters for zero initial crystallinity. The three-parameter version could be need successfully to fit the TRSAXS data of the blende (which do not exhibit initial crystallinity), while the four-parameter approach offered a better fit for neat PEO crystallized at 45 °C. The model was further used to estimate bulk crystallinities as a function of time for neat PEO and the strongly interacting blends. These values agree favorably with those measured using DSC.