Effects of synthesis temperature and crystallization conditions on morphology of anisotacic poly(propylene)

The effect of polymerization temperature on the crystalline morphology of anisotactic PP synthesized in a liquefied monomer using a rac-EtInd 2 ZrCl 2 -methyaluminoxane system was studied. It was shown that, in the 20-30°C range, PP crystallizes into an α-modification. Anisotactic PP produced at elevated temperatures consists of a mixture of α- and γ-modifications. At a polymerization temperature of 70°C, the content of the γ-phase in the polymer is 75-80%. The development of the γ-phase in PP is related to the existence of steric irregularities corresponding to pentads [mrrm] and regiochemical errors such as 2-1 and 1-3 additions in the chain microstructure. The data on the ratios of crystalline modifications in the virgin polymer and in films prepared by hot pressing of a virgin powdered PP at various rates of cooling from melt are discussed. It was demonstrated for anisotactic PP that the γ-phase is thermodynamically more favorable.