Polymerization of metallocene-catalyzed long-chain branched and functional polypropylene

Abstract

Propylene was polymerized with homogeneous and heterogeneous metallocene catalysts. In addition to homopolymerizations, copolymerizations were conducted with α-olefins, dienes and functional comonomers.

Propylene/1,9-decadiene copolymers were polymerized with racemic dimethylsilanylbis(2-methyl-4-phenyl-1-indenyl)zirconium dichloride supported on methylaluminoxane-modified silica. Rheological tests showed long-chain branching in the copolymers, even with comonomer incorporations of less than 1 mol %.

Hydroxyl functional propylene/10-undecen-1-ol copolymers were polymerized with homogeneous racemic dimethylsilanylbis(2-methyl-4-phenyl-1-indenyl)zirconium dichloride. Addition of triisobutylaluminum eliminated the drop in molecular weight with increasing comonomer content, and the interactions between the active center and the hydroxyl group at the end of the comonomer chain were more efficiently blocked. Catalyst activity was improved by increase in the proportion of methylaluminoxane in the cocatalyst mixture. Functionality contents up to 2 mol % were obtained by lowering pressure.

The functional polypropylene exhibited significantly enhanced peel strength and paintability relative to a reference homopolypropylene. Adhesion properties were improved not only in the copolymer but also in a blend consisting of propylene homopolymer and functional polypropylene, even when functionality content was only 0.17 wt %. The functional polypropylene slightly increased the adhesion between polypropylene and polyamide phase or silica filler, although the effect on impact strength was not as good as desired.

In copolymerization with metallocene catalysts, the comonomer distribution is uniform along the polypropylene backbone and the stereospecificity is maintained. The properties of the polypropylene are dramatically affected even with comonomer incorporations less than 1 mol %, regardless of whether the comonomer is a non-conjugated diene to induce long-chain branching or contains a functional group to improve adhesion properties.