Ring-Opening Metathesis Polymerization with Tungsten Based Catalysts: Kinetics, Thermodynamics and Mechanism

Citation

Claverie, Jérôme (1996) Ring-Opening Metathesis Polymerization with Tungsten Based Catalysts: Kinetics, Thermodynamics and Mechanism. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/h6fj-1t43. https://resolver.caltech.edu/CaltechTHESIS:11052019-172741776

Abstract

Ring-opening metathesis polymerization (ROMP) is instrumental in the synthesis of a variety of polymers. Since the appearance of well defined metathesis catalysts, the synthesis and characterization of ROMP polymers has been greatly improved.

In the first chapter, the kinetics and the thermodynamics of such polymerizations are presented. When a living ROMP polymerization is effected in the presence of a chain transfer-agent, the molecular weight distribution is governed by the kinetics of the polymerization. The molecular weight distribution has been evaluated numerically, and the numerical results have been compared to experimental ones. The living polymerization of norbornene by Mo(=CHR)(=N-1,3-i-Pr-C₆H₃)(O-t-Bu)₂ (R = -t-Bu, -C(CH₃)₂Ph) in the presence of neohexene and styrene has been used as a model experiment. When the ROMP catalyst is too active, chain transfer to the polymer occurs, and the molecular weight distribution is dependent upon the thermodynamics of the polymerization. The theoretical thermodynamic product distribution has been predicted, and compared to experimental results for the polymerization of 1,5-cyclooctadiene (COD) and cyclooctene. The results have been applied to the synthesis of short polyacetylene oligomers by ROMP of sec-butylcyclooctatetraene.

In the second chapter, the synthesis of monodisperse substituted polyacetylenes is described. For this synthesis, one has to use very active ROMP catalysts which appreciably initiate the polymerization. The new class of tungsten vinyl alkylidenes allows such a polymerization. Synthesis, characterization and catalytic properties of tungsten imido and oxo vinyl alkylidenes is described.

In the third chapter, reactivity of tertiary alcohols with tungsten vinyl alkylidenes and neopentylidenes is examined. These alcohols are found in trace amounts in all the samples of these tungsten carbenes. The role of the alcohols in ROMP is studied for polynorbornene, polycyclooctadiene and polyacetylene. Activation of these catalysts has been observed, even by trace amounts of alcohol, and has important consequences in the microstructure of the resulting polymer. Mechanistic implications toward a general scheme of acid activation of the well defined tungsten carbenes is proposed.

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