Elastomeric Polypropylene from Unbridged 2-Arylindenyl Zirconocenes:  Modeling Polymerization Behavior Using ansa-Metallocene Analogues

Abstract

Bis(2-arylindenyl)zirconium dichlorides activated by methylaluminoxane (MAO) produce elastomeric polypropylene. The elastic properties of this material are proposed to arise from a stereoblock microstructure. The silyl bridged catalysts rac- and meso-dimethylsilyl(bis(2-phenylindenyl))zirconium dichloride were prepared and used to model the polymerization behavior of the unbridged catalysts. The meso isomer is approximately twice as productive as the rac isomer in propylene polymerization. Additionally, blends of isotactic and atactic polypropylene were prepared by using varying amounts of the rac and meso isomers until the IR and NMR characteristics matched polypropylenes produced from bis(2-phenylindenyl)zirconium dichloride. These studies suggest (1) that the rac isomer is favored in the isomerization equilibrium for the unbridged catalysts and (2) that the larger fraction of atactic polymer in the elastomeric polypropylene is a consequence of the higher rate of polymerization for the meso isomer.

High-Melting, Elastic Polypropylene: A One-Pot, One-Catalyst Strategy toward Propylene-Based Thermoplastic Elastomers

“…5−7 Additional approaches toward PP with elastic properties were conducted by Collins et al applying a bridged, C 1 -symmetric metallocene framework, 8,9 whereas the directed synthesis of a PP− i PP block structures using unbridged bis(2-phenylindenyl)zirconium dichloride with an oscillating stereocontrol mechanism constituted a breakthrough regarding the synthesis of pure propene-based elastomers. 10,11 In the past decade, the concept of tailored polyolefin block structures even passed the threshold toward industrial application regarding the implementation of a chain shuttling mechanism into the polymerization setup using two catalysts of different selectivity in combination with a chain shuttling agent. 12 An alternative approach to design polyolefin block structures is provided by a living coordinative polymerization mechanism and facilitates a variety of promising polyolefin products.…”

“…In the late 1980s, scientists of DuPont reported on high molecular weight elastic polypropylene ( e PP) produced along with isotactic polypropylene as an ether-soluble fraction using metal oxide supported group IV metal compounds. , Back in those days, the application of metallocene complexes for tailored polypropylene structures received accretive attention evoking several successful approaches toward the directed synthesis of e PP. In this context, the group of Chien et al developed a series of C 1 -symmetric indenyl­cyclopentadienyl-based ansa -metallocene complexes in the early 1990s comprising different cyclopentadienyl derivatives and chiral methylene bridges. − Additional approaches toward PP with elastic properties were conducted by Collins et al applying a bridged, C 1 -symmetric metallocene framework, , whereas the directed synthesis of a PP– i PP block structures using unbridged bis­(2-phenylindenyl)­zirconium dichloride with an oscillating stereocontrol mechanism constituted a breakthrough regarding the synthesis of pure propene-based elastomers. , In the past decade, the concept of tailored polyolefin block structures even passed the threshold toward industrial application regarding the implementation of a chain shuttling mechanism into the polymerization setup using two catalysts of different selectivity in combination with a chain shuttling agent . An alternative approach to design polyolefin block structures is provided by a living coordinative polymerization mechanism and facilitates a variety of promising polyolefin products. − However, the economic inefficiency to be limited to one polymer chain per catalyst molecule displays the major drawback auf this strategy …”

Applications of Zirconium(IV) Chloride in Organic Synthesis

“…Zirconium(IV) chloride were complexed with chirally rigid BINOL ethers 227 to give ansa-zirconocenes 228, which represent a class of chiral organometallic reagents or catalysts in organic synthesis (Scheme 120). [167][168][169] Scheme 120…”

Bis(2-phenylindenyl)zirconium Dichloride

“…17 These catalysts were created to model the effect of ligand rotation on polymerization in comparison to the unbridged (PhInd) 2 ZrCl 2 by virtue of their stereorigidity locking them into a single form. This study allowed the researchers to conclude that the rac isomer is favored in the isomerization equilibrium for unbridged catalysts, and the higher rate of polymerization of the meso isomer results in a larger fraction of atactic polymer.…”