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On the basis of time-resolved synchrotron small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) experiments, a nonintegral-folding chain (NIF) crystal can be found in low molecular weight poly (ethylene oxide) (PEO) fractions. This crystal grows first as a transient state, and integral-folding chain (IF) crystals form later through an isothermal thickening or thinning process. In a PEO fraction with MW = 4250, it is observed that either isothermal thickening to the IF(n=0) crystal or thinning to the IF(n=l) crystal occurs depending upon the thermodynamic stability of the NIF crystal. At low crystallization temperatures, the main process is isothermal thinning; at intermediate temperatures, both thickening and thinning processes are observed; only isothermal thickening can be seen at high temperatures.This observation indicates that the NIF crystal exists as an initial step of the crystal growth over a wide crystallization temperature range. The fold length of this NIF crystal is crystallization temperature de-pendent, a behavior similar to the observed changes of fold length of polymer lamellar crystals. Systematic study in changes of fold length from the NIF to IF crystals with the time has resulted in a kinetic map of such transitions. This process is related to the chain molecular motion along the crystallographic c-axis in the solid state.

The long‐time regime coarsening in a phase‐segregated blend of hydrogenated polybutadiene (HPB) with high‐density polyethylene (HDPE) was studied. The blend consisted of 10 wt% of HPB in a HDPE matrix. The morphology of the system was studied by etching the HPB particles from the HDPE matrix and observing the etched specimens in a scanning electron microscope. The average volume of the HPB particles was found to increase with storage time in the melt, and to follow a temporal exponent of 1 in agreement with the predictions of the Ostwald ripening theory. This indicated that the particles coarsen by the evaporation‐condensation mechanism on which the Ostwald ripening theory is based. The rate constant from the Ostwald ripening theory was calculated and compared to the rate constant determined from the experimental data. The theoretical rate constant, K, calculated from Ostwald ripening theory, was 3.6 × 10−18 cm3/s compared to an experimentally determined rate constant of 4.8 × 10−18 cm3/s. The agreement between the theoretical and experimental rate constants was quite good. The significance attached to the good agreement between the theoretical and experimental rate constants might be mollified to some extent by the uncertainty involved in the parameters used to calculate the theoretical rate constant; viz. the interfacial tension, mutual‐diffusion coefficient, and equilibrium concentration of the HPB in the matrix phase that are not known to high accuracy. In reality, because other theories were used to determine the interfacial tension, mutual‐diffusion coefficient, and equilibrium phase compositions, this study was a test of several theories simultaneously. However, the agreement of the experimental temporal exponent and rate constant with the predictions of Ostwald ripening theory strongly indicates that the HPB/HDPE system coarsens by the evaporation‐condensation mechanism upon which the Ostwald ripening theory is based. © 1994 John Wiley & Sons, Inc.

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