Crystallization behavior of poly(ethylene oxide) and its blends using time-resolved wide- and small-angle X-ray scattering

Time-resolved synchrotron wide- and small-angle X-ray scattering experiments were used to investigate the crystallization behavior and microstructure development of poly(ethylene oxide) and several melt-miscible PEO blends. Model blends were prepared with both weakly interacting poly(methyl methacrylate) and two strongly interacting random copolymers. Average SAXS long periods and lamellar thicknesses decreased at early crystallization times: by 2-3 nm for PEO and blends containing the low T_g diluent and by approx. 5-9 nm for blends containing higher T_g diluents. The latter appears to arise in part from additional restrictions placed on the growing lamellae by the stiff, high T_g amorphous polymeric diluents. The increase in final long period over that of near PEO was approx. 2-4 nm for the weakly interacting blends, as opposed to as large as 10 nm for the strongly interacting mixtures. In the former case, the changes are associated with interlamellar diluent placement, while in the latter they result primarily from an increase in lamellar thickness due to reduction in degrees of supercooling. In line with previous observations, there was a significant decrease in crystallization rates for blends containing strongly interacting diluents. Two Avrami expressions were generally required to fit the WAXD crystallinity - time data for PEO and as many as three for the blends. For neat PEO, the behavior is reminiscent of crystallization in mixtures of high and low molecular weight PEO fractions.