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Investigations of the origin of stereocontrol in syndiospecific Ziegler-Natta polymerizations

Citation

Zubris, Deanna Lynn (2001) Investigations of the origin of stereocontrol in syndiospecific Ziegler-Natta polymerizations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/j7gk-0s22. https://resolver.caltech.edu/CaltechTHESIS:03242014-152154971

Abstract

In order to expand our understanding of the mechanism of stereocontrol in syndiospecific α-olefin polymerization, a family of Cs-symmetric, ansa-group 3 metallocenes was targeted as polymerization catalysts. The syntheses of new ansa-yttrocene and scandocene derivatives that employ the doubly [SiMe2]- bridged ligand array (1,2-SiMe2)2{C5H-3,5-(CHMe2)2} (where R = t- butyl, tBuThp; where R = i-propyl, iPrThp) are described. The structures of tBuThpY(µ-Cl)2K(THF)2, tBuThpSc(µ-Cl)2K(Et2O)2, tBuThpYCH(SiMe3)2, Y22-(tBuThp)2}(µ2-H)2, and tBuThpSc(µ-CH3)2 have been examined by single crystal X-ray diffraction methods. Ansa-yttrocenes and scandocenes that incorporate the singly [CPh2]-bridged ligand array (CPh2)(C5H4)(C13H8)(where C5H4 = Cp, cyclopentadienyl; where C13H8 = Flu, fluourenyl) have also been prepared. Select meallocene alkyl complexes are active single component catalysts for homopolymerization of propylene and 1-pentene. The scandocene tetramethylaluminate complexes generate polymers with the highes molecular weights of the series. Under all conditions examined atactic polymer microstructures are observed, suggesting a chain-end mechanism for stereocontrol.

A series of ansa-tantalocenes have been prepared as models for Ziegler-Natta polymerization catalysts. A singly bridged ansa-tantalocene trimethyl complex, Me2Si(η5-C5H4)2TaMe3, has been prepared and used for the synthesis of a tantalocene ethylene-methyl complex. Addition of propylene to this ethylene-methyl adduct results in olefin exchange to give a mixture of endo and exo propylene isomers. Doubly-silylene bridged ansa-tantalocene complexes have been prepared with the tBuThp ligand; a tantalocene trimethyl complex and a tantalocene methylidene-methyl complex have been synthesized and characterized by X-ray diffraction. Thermolysis of the methylidene-methyl complex affords the corresponding ethylene-hydride complex. Addition of either propylene or styrene to this ethylene-hydride compound results in olefin exchange. In both cases, only one product isomer is observed. Studies of olefin exchange with ansa-tantalocene olefin-hydride and olefin-methyl complexes have provided information about the important steric influences for olefin coordination in Ziegler-Natta polymerization.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Ziegler-Natta polymerizations ; Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Bercaw, John E.
Thesis Committee:
  • Grubbs, Robert H.
  • Gray, Harry B.
  • Rees, Douglas C.
Defense Date:10 July 2000
Record Number:CaltechTHESIS:03242014-152154971
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:03242014-152154971
DOI:10.7907/j7gk-0s22
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8161
Collection:CaltechTHESIS
Deposited By: Benjamin Perez
Deposited On:25 Mar 2014 16:34
Last Modified:16 Apr 2021 22:10

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