EFFECT OF POLARITY OF THE MEDIUM ON THE STEREOSPECIFIC POLYMERIZATION OF PROPYLENE BY ANSA-ZIRCONOCENE CATALYST

Propylene was polymerized with rac-ethylene-bis(1-eta'-indenyl)dichlorozirconium/methylaluminoxane in solvents of different polarity. The poly (propylene) formed was separated by solvent extraction; C-13-NMR and DSC measurements were made on the polymer fractions. The poly (propylene) in each solvent fraction has its characteristic molecular weight steric pentad distributions, melting transition temperature, and enthalpy for fusion irrespective of the polymerization medium. The results suggest that the medium dielectric constant does not affect the polymerization rate or the intrinsic stereoselectivity, propagation and chain transfer rates a given catalytic species but can alter the occurrence of steric insertion errors through shifting of distributions of the propagating species producing poly(propylenes) of different stereoregularities. (C) 1994 John Wiley & Sons, Inc.