Synthesis and Characterization of Low Molecular Weight Ethylene–Propylene Copolymers Prepared Using Metallocene Catalysts

Abstract

The synthesis in a liquid propene phase of ethylene–propylene copolymers of low molecular weights (3 000–20 000 g mol−1) is accomplished using three different metallocenes containing bridged bis(indenyl) moieties: (A) rac‐dimethylsilylbis(4,5,6,7‐tetrahydro‐1‐indenyl)zirconium dichloride, (B) rac‐ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl)zirconium dichloride, and (C) rac‐ethylenebis(indenyl)zirconium dichloride. Hydrogen pressures higher than 1 bar were required to drop the molecular weight below 25 000 g mol−1. Metallocene B gives rise to the copolymers with lower molecular weights (<5 000 g mol−1), irrespective of the ethylene content, due to the presence of a hydrogenated six membered ring in the indenyl moiety as well as a CH2 bridge. DSC experiments indicate that for low ethylene contents (below 4 wt%), metallocene A gives rise to copolymers with the highest melting temperatures and the lowest melting enthalpies, suggesting the existence of longer isotactic propylene sequences into the copolymer backbone.