Propylene-ethylene copolymers made from three different constituents

US6300434A · kind A · utility

Assignee

• Basell Polyolefine GmbH · DE

Inventors

• Harald Schwager · Speyer, DE
• Juergen Kerth · Eisenberg (Pfalz), DE

Key dates

• Filing date: Sep 6, 1995
• Grant date: Oct 9, 2001
• Expiry date: Sep 6, 2015

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C08F297/086
• WIPO field: Macromolecular chemistry, polymers
• WIPO sector: Chemistry

Abstract

Propylene-ethylene copolymers obtainable by three-step polymerization from the gas phase in an agitated fixed bed by means of a Ziegler-Natta catalyst system which, in addition to a titanium-containing solid component, also contains, as cocatalyst, an aluminum compound, where, in a first polymerization step, propylene is polymerized at from 60 to 90.degree. C. and at from 20 to 40 bar and at a mean residence time of the reaction mixture of from 0.5 to 5 hours, then, in a second polymerization step, a mixture of propylene and ethylene is polymerized onto the polymer obtained from the first polymerization step at from 40 to 110.degree. C. and from 5 to 30 bar, this pressure being at least 7 bar below the pressure in the first polymerization step, and at a mean residence time of the reaction mixture of from 0.2 to 4 hours, and then, in a third polymerization step, ethylene or a mixture of ethylene and propylene is polymerized onto the polymer obtained from the second polymerization step at from 40 to 110.degree. C. and from 5 to 30 bar and at a mean residence time of the reaction mixture of from 0.1 to 5 hours, the weight ratio between the monomers reacted in the first and second poly…