Defects distribution of metallocene and MgCl2-supported Ziegler-Natta isotactic poly(propylenes) as revealed by fractionation and crystallization behaviors

Abstract

The inter and intramolecular distribution of defects of poly(propylenes) of the Ziegler-Natta (ZN) and metallocene (M) types, with matched molar masses and overall defect concentrations, are inferred from the crystallization and polymorphic behavior of their narrow molecular mass fractions. The fractions obtained from the M-iPP display a range in molecular masses but the same concentration of defects and provide direct evidence of the uniform intermolecular defect distribution and the "single site" nature of the catalyst. The stereodefects of the ZN-iPP fractions are more concentrated in the low molecular mass fractions, corroborating a broad interchain distribution of the nonisotactic content. In addition, the invariance of the linear growth rates among the ZN fractions and very low contents of the gamma polymorph, developed even by the most defected ZN fraction, are consistent with a stereo blocky intramolecular distribution of defects in the ZN-iPP molecules. In contrast to the linear growth rates, which are sensitive to the defect microstructure, the overall crystallization rates correlate with nucleation density and not necessarily with the iPP chain microstructure.