Microstructure in polypropylenes prepared with [formula omitted] and [formula omitted] catalytic systems

Abstract

Microstructures were studied for polypropylenes prepared with TiCl 4 MgCl 2 Et 3 Al and Ti(OBu)Cl 3 MgCl 2 Et 3 Al catalytic systems. Pentad tacticities, chain-end structures, and regioirregularity in these polypropylenes were determined from 13C n.m.r., 1H n.m.r., and INEPT (insensitive nuclei enhancement by polarization transfer) spectra. The propylene polymerization mechanism was statistically analysed on the basis of the two-site model from the pentad tacticities. It was confirmed that these polypropylenes are composed of the isotactic and atactic polymers produced at the IPP and APP catalytic sites, which produce the isotactic and atactic polymers, respectively. The optimum values of the two-site model parameters elucidated that the displacement of Cl ligand around the titanium by OBu reduces the strength of the steric control at the IPP site. The detected chain-end structures verified that the chain transfer of propagation species to the propylene monomer terminates the propagation reaction and regenerates initiation species. The two-site model analysis for the tactic structures at the chain-end indicated that the steric controls of the initiation reactions at both sites are as strong as those of propagation reactions. Further, it was found that these polypropylenes contain head-to-head and tail-to-tail structures whose contents (monomer unit per chain) are 10 −3 order.