Fractionation and Crystallization of Isotactic Polypropylenes Prepared Using Homogenous Metallocene Catalyst

Abstract

A series of polypropylenes were prepared using rac-ethylene-bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride (Et(H4Ind)2ZrCl2 (EI(4H)) as a homogeneous metallocene catalyst. The molecular weight of the polypropylene polymers was controlled using molecular hydrogen which was used as a transfer agent. To obtain materials with differing molecular weight and tacticities, polymers were fractionated with prep-TREF. Polypropylene polymers and fractions were fully characterized using various analytical techniques: differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), 13C nuclear magnetic resonance spectroscopy (13C-NMR) and high temperature gel permeation chromatography (HT-GPC). It was found that the addition of molecular hydrogen to propylene polymerizations catalyzed using EI(4H) catalyst system resulted in a reduction in polymer molecular weight and isotacticity. Furthermore, the molecular weight, the isotacticity and the degree of crystallinity of the TREF fractions increased significantly with increasing elution temperature for all samples. Also, only the  crystal form existed in all TREF fractions of different samples.