Strategies for Synthesis of Elastomeric Polypropylene: Fluxional Metallocenes with C₁-Symmetry

Abstract

The effects of replacing one of the 2-phenylindenyl-type ligands in bis(2-phenylindenyl)zirconium dichloride, (2-PhInd)2ZrCl2 (7), a catalyst precursor for the production of elastomeric polypropylene (ELPP-7), with a cyclopentadienyl-type ligand have been studied. The mixed-ring compounds: (pentamethylcyclopentadienyl)(2-phenylindenyl)zirconium dichloride, Cp*(2-PhInd)ZrCl2, (8), (pentamethylcyclopentadienyl)(1-methyl-2-phenylindenyl)zirconium dichloride, Cp*(1-Me-2-PhInd)ZrCl2 (9), and (cyclopentadienyl)(2-phenylindenyl)zirconium dichloride, Cp(2-PhInd)ZrCl2 (10), have been synthesized through the reaction of the corresponding lithium indenide with C5R5ZrCl3 (8 and 9: R = CH3; 10: R = H). Crystal structures have been determined for complexes 8 and 9. The behavior of the catalysts derived from complexes 8, 9, and 10 upon their activation by methylaluminoxane (MAO) for ethylene and propylene polymerization has been studied. Of all mixed-ring catalysts only 8/MAO produces elastomeric polypropylene (ELPP-8) with properties consistent with a stereoblock microstructure. The stereosequence distributions in ELPP-8 determined from 13C NMR spectra are very similar to those in elastomeric polypropylene generated with 7/MAO under comparable conditions. However, the melting points and IR indices of 8/MAO-derived samples are significantly lower than for samples of ELPP-7 with similar isotacticity which may be attributable to shorter isotactic block lengths in ELPP-8. At the same time, comparison of 8/MAO to another metallocene system capable of producing elastomeric polypropylene rac-MeHC(Me4Cp)(Ind)TiCl2/MAO, 1/MAO, described by Chien reveals significant similarities both in the catalyst symmetry and properties of generated polypropylene. The increase of isotacticity of ELPP-8 with propylene pressure similar to the trend observed for ELPP-7 favors the two-state mechanism of stereoblock formation with 8/MAO.

Zirconocene complexes with a biphenyl substituted cyclopentadienyl ligand: synthesis, characterization, and olefin polymerization behavior

“…b Cp 0 (1); the plane of C(1-5), Ph (1); the plane of C (8)(9)(10)(11)(12)(13), Ph (2); the plane of C (14)(15)(16)(17)(18)(19).…”

“…1). Followed by this important finding, they extensively investigated the effects of the 2-aryl groups on the indenyl ligand [9] and the nature of the metal [10] and cyclopentadienyl ring fragment [11], including mixed-ring complex systems [12] on the production of elastomeric polypropylene.…”

Nucleation and Crystallization of Low Isotatic Polypropylenes with Statistically Distributed Stereoerrors

“…Compared to other low isotactic polypropylenes 14,42,[83][84][85] an elastic recovery of ! rev > 70% found for the investigated polypropylenes with statistically distributed steroerrors is high.…”

“…[26][27][28] Futhermore, it has been shown that in case of isotactic polypropylenes the formation of crystalline domains is correlated to the length of the isotactic blocks. 27,[29][30][31][32][33][34] Using specific metallocene catalysts at varying polymerization conditions, such as monomer concentration temperature, nature of cocatalyst, 1 low isotactic polypropylenes can be obtained containing different amounts and combinations of stereoerrors leading to high molecular weight atactic polypropylene, 29,[35][36][37] polypropylenes with an intermediate isotactic-atactic microstructure, 6,29,38-40 stereoblock isotactic-atactic polypropylenes 7,8,12,14,41 or stereoblock isotactic-hemiisotactic polypropylenes. 42 Beside those, a new type of high molecular weight, low isotactic polypropylene has been synthesized by Rieger et al [43][44][45] Due to the random incorporation of stereoerrors, these polypropylenes contain statistically distributed, isotactic sequences.…”

Zirconocene-catalyzed copolymerizations of ethylene with 5-methyl-1,4-hexadiene as non-conjugated diene

“…6 More recent improvements in a synthetic challenge are the successful syntheses of polyolefin elastomer using a sandwich type of metallocene catalyst and of linear low density polyethylene by Insite ® Technology. 7,8 The excellent reviews for other dinuclear metallocene compounds as catalysts for preparation of polyolefins have been reported. 9,10 These advances may contribute to expansion of the application fields of the final products.…”