Investigations of the origin of stereocontrol in syndiospecific Ziegler-Natta polymerizations
| Data(s) |
2001
|
|---|---|
| Resumo |
<p>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 [SiMe<sub>2</sub>]- bridged ligand array (1,2-SiMe<sub>2</sub>)<sub>2</sub>{C<sub>5</sub>H-3,5-(CHMe<sub>2</sub>)<sub>2</sub>} (where R = t- butyl, tBuThp; where R = i-propyl, iPrThp) are described. The structures of tBuThpY(µ-Cl)<sub>2</sub>K(THF)<sub>2</sub>, tBuThpSc(µ-Cl)<sub>2</sub>K(Et<sub>2</sub>O)<sub>2</sub>, tBuThpYCH(SiMe<sub>3</sub>)<sub>2</sub>, Y<sub>2</sub>{µ<sub>2</sub>-(tBuThp)<sub>2</sub>}(µ<sub>2</sub>-H)<sub>2</sub>, and tBuThpSc(µ-CH<sub>3</sub>)<sub>2</sub> have been examined by single crystal X-ray diffraction methods. Ansa-yttrocenes and scandocenes that incorporate the singly [CPh<sub>2</sub>]-bridged ligand array (CPh<sub>2</sub>)(C<sub>5</sub>H<sub>4</sub>)(C<sub>13</sub>H<sub>8</sub>)(where C<sub>5</sub>H<sub>4</sub> = Cp, cyclopentadienyl; where C<sub>13</sub>H<sub>8</sub> = 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.</p> <p>A series of ansa-tantalocenes have been prepared as models for Ziegler-Natta polymerization catalysts. A singly bridged ansa-tantalocene trimethyl complex, Me<sub>2</sub>Si(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>TaMe<sub>3</sub>, 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.</p> |
| Formato |
application/pdf |
| Identificador |
http://thesis.library.caltech.edu/8161/1/Zubris_dl_2001.pdf Zubris, Deanna Lynn (2001) Investigations of the origin of stereocontrol in syndiospecific Ziegler-Natta polymerizations. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:03242014-152154971 <http://resolver.caltech.edu/CaltechTHESIS:03242014-152154971> |
| Relação |
http://resolver.caltech.edu/CaltechTHESIS:03242014-152154971 http://thesis.library.caltech.edu/8161/ |
| Tipo |
Thesis NonPeerReviewed |
