2003
DOI: 10.1021/ma0303972
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Propylene Polymerization with 1,2‘-Bridged Bis(indenyl)zirconium Dichlorides

Abstract: A series of C1 symmetric, 1,2′-bridged bis(indenyl)zirconium dichlorides were prepared to study the effect of ligand substitution, symmetry, and bridge identity on the stereoselectivity of propylene polymerization. Unsubstituted [1-(1-indenyl)-2-(2-indenyl)ethane]zirconium dichloride, Et(2-Ind)(1-Ind)-ZrCl 2 (1), was synthesized, and its propylene polymerization behavior was compared to three 2-phenylsubstituted complexes with different bridges: (4). The polymerization activity, polypropylene molecular weight,… Show more

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Cited by 15 publications
(9 citation statements)
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“…Kaminsky pointed out that the angle between the bridged ligand and its various substitutions can play a pivotal role for activity and stereospecificity. 15 This was verified by the experimental result that Et(2-Ind)(2-Ph-1-Ind)ZrCl 2 (Et = C 2 H 4 ) gave polypropylenes with higher isotacticity 16 ([mmmm] = 74%) than anti C 2 symmetric Me 2 Si(2-Ph-1-Ind) 2 ZrCl 2 ([mmmm] = 58%).…”
Section: Introductionmentioning
confidence: 61%
“…Kaminsky pointed out that the angle between the bridged ligand and its various substitutions can play a pivotal role for activity and stereospecificity. 15 This was verified by the experimental result that Et(2-Ind)(2-Ph-1-Ind)ZrCl 2 (Et = C 2 H 4 ) gave polypropylenes with higher isotacticity 16 ([mmmm] = 74%) than anti C 2 symmetric Me 2 Si(2-Ph-1-Ind) 2 ZrCl 2 ([mmmm] = 58%).…”
Section: Introductionmentioning
confidence: 61%
“… ,− We had proposed that the temperature and monomer concentration dependence of the stereospecificity of these catalysts is due to a competition between monomer insertion and conformational isomerization of the metallocene and proposed that the interconversion between enantiomeric anti conformers and at least one syn conformer was responsible for the generation of isotactic and atactic stereosequences (Scheme ). Indirect support for this proposal was provided by the polymerization behavior of the MAO-activated silyl-bridged rac ( anti ) and meso ( syn ) analogues, which produce isotactic and atactic polypropylene, respectively. , Recently, Busico has proposed, on the basis of microstructural analysis of these polymers, that the achiral syn isomer can be disregarded as a source of the atactic stereosequences and that the generation of isotactic and atactic stereosequences is the results of the interconversion of chiral anti isomers at a rate competitive with propylene insertion. According to this proposal, short atactic stereosequences are generated by kinetic states where the rate of conformational isomerization is faster than propylene insertion.
1 Expected Low-Energy Conformations of [(2-PhInd) 2 Zr(polymeryl) + ] Based on Calculated Low-Energy Conformations of the Neutral Catalyst Precursor (2-PhInd) 2 ZrCl 2 a a For simplicity, the counteranion has not been depicted here.
…”
Section: Introductionmentioning
confidence: 99%
“…The syntheses of these complexes as well as their propylene polymerization are described elsewhere. 40 Copolymerizations were carried out in neat R-olefin monomer with a constant overpressure of ethylene at 20 °C. Ethylene/propylene feed compositions were determined using gas fugacities as described by Kravchenko.…”
Section: Resultsmentioning
confidence: 99%