A new structural subclass of constrained geometry catalysts for the polymerization of olefins /
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| Other Authors: | |
| Format: | Thesis eBook |
| Language: | English |
| Published: |
[College Station, Tex.] :
[Texas A&M University],
[2006]
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| Subjects: | |
| Online Access: | Link to OAK Trust copy |
| Abstract: | The sterically expanded octamethyloctahydrodibenzofluorene moiety, C₂₉H₃₈(Oct), has been incorporated into ansa-metallocenes and constrained geometry catalysts(CGC's). Utilization of this sterically expanded version of fluorene has resulted in solidstate anomalies for both systems. The ansa-metallocenes Me₂C(n⁵-C₅H₄) (n⁵-C₂₉H₃₆)MCl₂, M = Zr, Hf and Me₂C(n⁵-C₅H₄)(n⁵-C₂₉H₃₆)ZrBn₂ demonstrate crystal motifs expected for ansa-metallocenes while Me₂C(n⁵-C₅H₄)(n⁵-C₂₉H₃₆)MMe₂, M=Zr, Hf exhibit diffuse diffraction, a phenomenon that is extremely unusual for organometallic complexes. This crystalline anomaly is the result of a disorder restricted to two dimensions caused by the rare pillared motif of the system. The best solution for this system consists of parallel and anti-parallel pillars present in a 60:40 ratio. The solid state anomaly observed for the Oct-CGC's occurs on a molecular level. The parent Oct-CGC, Me₂Si(n¹-C₂₉H₃₆)(n¹-N-[superscript]tBu)ZrCl²·OEt², demonstrates an unprecedented n¹ ligation to the fluorenyl-based ring. Systematic derivatization of this system via halide substitution, alkylation, and exchange of Zr for Hf has revealed that the n¹ ligation persists for systems with small substituents on the metal center capable of retaining a coordinated ether. It is hypothesized that the unusual structure of this new Oct-CGC results in Me₂Si(n¹-C₂₉H₃₆)(n¹-N-[superscript]tBu)ZrCl₂·OEt₂/MAO (MAO = methylaluminoxane) being six times more active in the homopolymerization of 1-octene than ethylene. When compared to the prototypical Ti-CGC Me₂Si(n⁵-C₅Me₄)(n¹-N-[superscript]tBu)TiCl₂/MAO, the Oct-CGC is 85 times more reactive in the homopolymerization of 1-octene and 52 times more active in the copolymerization of 1-octene and 4-methyl-1-pentene. The high reactivity of the Oct-CGC towards alpha-olefins results in the observation of an unyielding comonomer effect in the copolymerization of these olefins with ethylene. In addition, the Oct-CGC is perhaps the most syndioselective catalyst known. With an enantiofacial selectivity of 99.7% and a remarkably high activity towards alpha-olefins, the Oct-CGC is capable of producing the highest melting syndiotactic polypropylene (T[subscript]m = 165⁰C, annealed = 174⁰C) reported thus far. The high activity and syndioselectivity of the Oct-CGC can be extended to the production of syndiotactic poly(4-methyl-1-pentene) with the highest melting point thus far reported (T[subscript]m = 215⁰C). |
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| Item Description: | "Major Subject: Chemistry" Title from author supplied metadata (automated record created on Apr. 14, 2006.) Vita. Abstract. Electronic resource. |
| Format: | Mode of access: World Wide Web. System requirements: World Wide Web access and Adobe Acrobat Reader. |
| Bibliography: | Includes bibliographical references. |