Abstract
AbstractThe microstructure of propene/1‐pentene copolymers prepared with the metallocene catalysts rac‐Et(Ind)2ZrCl2 and rac‐Me2Si(2‐MeBenz‐[e]Ind)2ZrCl2 was studied by 13C NMR spectroscopy. Both catalysts lead to the formation of random copolymers although rac‐Me2Si(2‐MeBenz‐[e]Ind)2ZrCl2 favors a somewhat higher incorporation of 1‐pentene than rac‐Et(Ind)2ZrCl2. Surprisingly, the presence of 1‐pentene has a significant influence on the stereoregularity of the copolymers formed with rac‐Me2Si(2‐MeBenz‐[e]Ind)2ZrCl2. Propene/1‐pentene copolymers produced with rac‐Et(Ind)2ZrCl2 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‐Me2Si(2‐MeBenz‐[e]Ind)2ZrCl2 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.
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