High flexible propylene/ethylene copolymers and process for preparing same

• Main Authors: KERSTING; MEINOLF, MUELLER; PATRIK
• Format: Patent
• Language: English
• Published: 21.04.1998
• Edition: 6
• Subjects: CHEMISTRY; COMPOSITIONS BASED THEREON; MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVINGCARBON-TO-CARBON UNSATURATED BONDS; METALLURGY; ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP

Highly flexible propylene/ethylene copolymers having a high rubber content are obtainable by two-stage 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 an aluminum compound as a cocatalyst, in a first polymerization stage, propylene being polymerized at from 15 to 40 bar and from 50 DEG to 90 DEG C. and during an average residence time of the reaction mixture of from 0.5 to 5 hours and then, in a second polymerization stage, a mixture of propylene and ethylene being polymerized with the polymer discharged from the first polymerization stage, at from 5 to 30 bar, this pressure being at least 2 bar below the pressure of the first polymerization stage, and at from 60 DEG to 100 DEG C. and during an average residence time of the reaction mixture of from 0.5 to 5 hours, the ratio of the partial pressure of propylene to that of ethylene being brought within the range from 0.5: to 5:1, the weight ratio of the monomers reacted in the first polymerization stage to those reacted in the second polymerization stage being from 0.9:1 to 0.4:1 and the polymerization in the second polymerization stage being carried out in the presence of a C1-C8-alkanol.