NONINTEGRAL AND INTEGRAL FOLDING CRYSTAL-GROWTH IN LOW-MOLECULAR MASS POLY(ETHYLENE OXIDE) FRACTIONS .2. END-GROUP EFFECT - ALPHA,OMEGA-METHOXY-POLY(ETHYLENE OXIDE)

Differential scanning calorimetry (DSC) and in situ small-angle x-ray scattering (SAXS) indicate that in an alpha, omega-methoxy-poly (ethylene oxide) (MPEO) fraction (MW 3000) a transient nonintegral folding (NIF) crystal initially forms during crystallization throughout a wide range of crystallization temperatures. Subsequent transformations of the NIF to IF (integral folding) crystals at low temperatures occur mainly through isothermal thickening or thinning via perfection processes or, at higher temperatures, through primary crystal formation. The NIF crystal is thermodynamically the least stable state among the crystal forms, but its growth is the most rapid. The overall crystallization and crystal melting of this MPEO fraction reveal that the NIF crystal and the NIF --> IF crystal transformations are common to low-molecular mass PEO fractions without regard to the end group. Nevertheless, diffusion coefficient and viscosity measurements provide clear evidence of an end-group effect in PEO and MPEO fractions. The difference in the overall crystallization and isothermal thickening and thinning kinetics of low-molecular mass PEO and MPEO fractions can lead to further understanding of end-group effects.