The intermolecular defect distribution of poly(propylenes) of the Ziegler-Natta (ZN) and metallocene (M) types is assessed by classical fractionation and analysis of the fractions by GPC and 13C NMR. In addition, the linear growth rates, a property sensitive to differences in defects distribution in the poly(propylene) chain, are used to infer the stereoblock-like intramolecular distribution of defects in industrial type ZN iPPs and their fractions. The behavior of fractions from a matched metallocene iPP provide direct evidence of the single-site nature of the catalyst. Metallocene poly(propylenes) enable a quantitative assessment of the molecular, thermodynamic and kinetic factors that govern the formation and concentrations of the a and g polymorphs. Short continuous crystallizable sequences and high crystallization temperatures favor the formation of this polymorph in homo poly(propylenes) and random propylene copolymers. Differences in the partitioning of the comonomer between the crystalline and non-crystalline regions leads to contents of the gamma phase that differ among the copolymers at any given crystallization temperature. Qualitatively these differences can be used to assess the degree to which a counit participates in the crystallite.
Metallocene; Ziegler-Nata; crystallization; polypropylenes
