EXTENDED CHAIN CRYSTAL-GROWTH OF LOW-MOLECULAR MASS POLY(ETHYLENE OXIDE) AND ALPHA,OMEGA-METHOXY POLY(ETHYLENE OXIDE) FRACTIONS NEAR THEIR MELTING TEMPERATURES

For low molecular mass poly(ethylene oxide) (PEO) and alpha,omega-methoxy poly(ethylene oxide) (MPEO) fractions, extended chain crystals can grow when isothermal crystallization temperatures are near their melting temperatures (supercooling DELTA-T = T(m) - T(c) is in the range of a few degrees). Experimentally, observed lamellar thicknesses of the extended chain crystals are constants in this supercooling region. Linear relationships between crystal growth rate (G) and supercooling (DELTA-T) can be observed. Absolute values of the slopes of these relationships decrease with increasing molecular length. Additionally, MPEO fractions generally have higher slope values when compared with their PEO counterparts. Nevertheless, this difference between PEO and MPEO fractions gradually vanishes with increasing molecular length. Extended chain single lamellar crystals are highly faceted in these temperature regions, and their aspect ratios vary with supercooling as well as molecular length. Nucleation theory for the growth of extended chain crystals is applied. The transient chain-end surface free energy, sigma', and the lateral surface free energy, sigma, for the PEO and MPEO fractions possess entropic origins. The rough surface growth model is also discussed.