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Crystal growth rates of spherulites or axialites of low molecular mass (MW = 15 OOO) and high molecular mass (MW = 300 000) isotactic polypropylene (i-PP) fractions crystallized from the melt have been investigated in an extensive supercooling range (20-70 K). On the basis of the regime theory, a transition between regimes I and I1 is found at AT Y 37 K for the low molecular mass fraction and a transition between regimes I1 and I11 is at AT = 48 K for both low and high molecular mass fractions of i-PP.Accordingly, the morphological changes observed by a polarized optical microscope at the supercooling range in the vicinity of regime transitions have been examined. The morphological change in this supercooling range does not correlate to the regime transitions.

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