NONINTEGRAL AND INTEGRAL FOLDING CRYSTAL-GROWTH IN LOW-MOLECULAR MASS POLY(ETHYLENE OXIDE) FRACTIONS .3. LINEAR CRYSTAL-GROWTH RATES AND CRYSTAL MORPHOLOGY

Correlations of the linear crystal growth rates with the change in crystal morphology for poly (ethylene oxide) (PEO) (MW 3000) and alpha,omega-methoxy-poly (ethylene oxide) (MPEO) (MW 3000) fractions have been established over a wide range of supercooling (DELTA-T = 25 K). Two linear crystal growth rates were measured, namely, the linear crystal growth rate of spherulites or hedrites and the lateral (linear) crystal growth rate of single lamellar crystal along different crystalline planes (below DELTA-T = 11-12 K). At a low supercooling of 5 K, the crystal growth rate of the MPEO fraction passes through a minimum. Subsequently, the rate increases abnormally and reaches a maximum at even lower supercooling. This crystal growth retardation has been attributed to the competition between differing chain conformations during crystal growth. In this case, particularly, these conformations are the extended chain and the once-folded chain conformations. This retardation is not observed in the PEO fraction, since in this low supercooling region any once-folded chain conformations formed during crystal growth are of the double-layer lambella type. The change in morphology in this region supports this judgement. Above DELTA-T = 7.6 K, the crystal growth behavior in these two fractions can be described by the present nucleation theory on flat crystal growth faces. Below that DELTA-T, however, different crystal growth mechanisms can be clearly seen. This may be associated with the crystal growth on the highly serrated growth faces in these two fractions.