Microstructure of Metallocene-Catalyzed Propene/1-Pentene Copolymers

✍ Scribed by Maria Carmela Sacchi; Fabrizio Forlini; Simona Losio; Incoronata Tritto; Udo M. Wahner; Ioan Tincul; Dawie J. Joubert; Emmanuel R. Sadiku

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 137 KB
• Volume: 204
• Category: Article
• ISSN: 1022-1352
• DOI: 10.1002/macp.200350024

✦ Synopsis

Abstract

The microstructure of propene/1‐pentene copolymers prepared with the metallocene catalysts rac‐Et(Ind)~2~ZrCl~2~ and rac‐Me~2~Si(2‐MeBenz‐[e]Ind)~2~ZrCl~2~ was studied by ^13^C NMR spectroscopy. Both catalysts lead to the formation of random copolymers although rac‐Me~2~Si(2‐MeBenz‐[e]Ind)~2~ZrCl~2~ favors a somewhat higher incorporation of 1‐pentene than rac‐Et(Ind)~2~ZrCl~2~. Surprisingly, the presence of 1‐pentene has a significant influence on the stereoregularity of the copolymers formed with rac‐Me~2~Si(2‐MeBenz‐[e]Ind)~2~ZrCl~2~. Propene/1‐pentene copolymers produced with rac‐Et(Ind)~2~ZrCl~2~ retained the isotacticity of polypropene and featured only the stereoerror pentads mmmr, mmrr and mrrm typical for enantiomorphic site control. However, propene/1‐pentene copolymers obtained with rac‐Me~2~Si(2‐MeBenz‐[e]Ind)~2~ZrCl~2~ are characterized by a gradual loss of tacticity which is concurrent with an increase in the amount of all irregular pentads. It is proposed that the presence of 1‐pentene can lead to a reversible loss of stereocontrol over a whole sequence of inserted monomer units. Subsequently, more or less atactic blocks are formed besides isotactic blocks.

Percentage of 1‐pentene in the copolymer as function of the feed composition for 1‐pentene/propene copolymers prepared with EI and MBI.

magnified imagePercentage of 1‐pentene in the copolymer as function of the feed composition for 1‐pentene/propene copolymers prepared with EI and MBI.