Structure and isothermal crystallization behavior of polypropylene prepared at high polymerization temperature

The structure, morphology, and isothermal crystallization behaviors of polypropylene (PP) prepared with heterogeneous Ziegler‐Natta catalyst at high temperature (100°C) were investigated with differential scanning calorimetry, wide‐angle X‐ray diffraction, temperature‐rising elution fractionation, gel permeation chromatography, and ¹³C NMR. The results reveal that the crystalline structure changes with variation of the composition of the PP. The isotactic PP (iPP)1 prepared with Et₃Al and “TMA‐depleted” methylaluminoxane crystallizes from the melt in the mixtures of the α and β forms, whereas each fraction obtained from pure PP1 does not show β‐PP crystal at the same crystallization condition. In addition, the γ‐PP crystal is appeared for the fractions of low mmmm%‐mmmm] (mmmm pentad content) values and molecular weight. Moreover, it was found that the iPP2 or iPP3 prepared with Hex₃Al crystallizes from the melt in mixtures of the α and γ forms, even at atmospheric pressure and for high molecular weight. The microstructure showed in the PP samples obtained at high temperature could be well explained with the shift in the alkylaluminium‐donor equilibrium reactions at high polymerization temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009