A new structural subclass of constrained geometry catalysts for the polymerization of olefins

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Title: A new structural subclass of constrained geometry catalysts for the polymerization of olefins
Author: Irwin, Levi Jacob
Abstract: The sterically expanded octamethyloctahydrodibenzofluorene moiety , C29H38 (Oct ) , has been incorporated into ansa -metallocenes and constrained geometry catalysts (CGC's ) . Utilization of this sterically expanded version of fluorene has resulted in solidstate anomalies for both systems . The ansa -metallocenes Me2C (n5 -C5H4 ) (n5 -C29H36 )MCl2 , M = Zr , Hf and Me2C (n5 -C5H4 ) (n5 -C29H36 )ZrBn2 demonstrate crystal motifs expected for ansametallocenes while Me2C (n5 -C5H4 ) (n5 -C29H36 )MMe2 , M=Zr , Hf exhibit diffuse diffraction , a phenomenon that is extremely unusual for organometallic complexes . This crystalline anomaly is the result of a disorder restricted to two dimensions caused by the rare pillared motif of the system . The best solution for this system consists of parallel and anti -parallel pillars present in a 60 :40 ratio . The solid state anomaly observed for the Oct -CGC's occurs on a molecular level . The parent Oct -CGC , Me2Si (1 -C29H36 ) (1 -N -tBu )ZrCl2 ?OEt2 , demonstrates an unprecedented n1 ligation to the fluorenyl -based ring . Systematic derivatization of this system via halide substitution , alkylation , and exchange of Zr for Hf has revealed that the n1 ligation persists for systems with small substituents on the metal center capable of retaining a coordinated ether . It is hypothesized that the unusual structure of this new Oct -CGC results in Me2Si (1 -C29H36 ) (1 -N -tBu )ZrCl2 ?OEt2 /MAO (MAO = methylaluminoxane ) being six times more active in the homopolymerization of 1 -octene than ethylene . When compared to the prototypical Ti -CGC Me2Si (n5 -C5Me4 ) (n1 -N -tBu )TiCl2 /MAO , the Oct -CGC is 85 times more reactive in the homopolymerization of 1 -octene and 52 times more active in the copolymerization of 1 -octene and 4 -methyl -1 -pentene . The high reactivity of the Oct -CGC towards alpha -olefins results in the observation of an unyielding comonomer effect in the copolymerization of these olefins with ethylene . In addition , the Oct -CGC is perhaps the most syndioselective catalyst known . With an enantiofacial selectivity of 99 .7 % and a remarkably high activity towards alpha -olefins , the Oct -CGC is capable of producing the highest melting syndiotactic polypropylene (Tm = 165oC , annealed = 174oC ) reported thus far . The high activity and syndioselectivity of the Oct -CGC can be extended to the production of syndiotactic poly (4 -methyl -1 -pentene ) with the highest melting point thus far reported (Tm = 215oC ) .
URI: http : / /hdl .handle .net /1969 .1 /3106
Date: 2006-04-12

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A new structural subclass of constrained geometry catalysts for the polymerization of olefins. Available electronically from http : / /hdl .handle .net /1969 .1 /3106 .

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