Polyacetylene and Novel Conjugated Derivatives through the Metathesis Polymerization of 1,3,5,7-Cyclooctatetraenes

Citation

Klavetter, Floyd L. (1989) Polyacetylene and Novel Conjugated Derivatives through the Metathesis Polymerization of 1,3,5,7-Cyclooctatetraenes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/wqc2-mk42. https://resolver.caltech.edu/CaltechETD:etd-05222007-110626

Abstract

A Diels-Alder adduct of cyclooctatetraene and benzyne has been polymerized through ring-opening metathesis by titanium methylidene sources to produce a soluble polyacetylene precursor. The polymerization proceeds through first order kinetics and linear increase in molecular weight, providing a route into conjugated polyene segments of various and controlled length.

A versatile and convenient route to polyacetylene has been developed through the condensed phase metathesis polymerization of cyclooctatetraene. Dissolution of catalyst in "neat" cyclooctatetraene provides a means of transforming the liquid into a highly lustrous film at ambient temperature and pressure. These films have physical and spectral properties very similar to films prepared by the Shirakawa methodology. Iodine-doped films exhibit conductivities greater than 300 Ω⁻¹/cm. New processing modes and novel morphologies for polyacetylene have been discovered. Novel polyacetylene derivatives have been prepared to demonstrate the versatility of the method. Both electron-releasing and electron-withdrawing groups have been attached to carbons in the π-conjugated system. These organic materials have been used in the fabrication of solid state devices.

The mechanism of metathesis polymerization with a well-defined tungsten carbene catalyst has been explored, using cyclooctatetraene and its soluble analogue 1,5-cyclooctadiene as monomers. A new phenomenon referred to as "cycloextrusion" has been discovered, and its influence upon the statistical distribution of isomers and the cis-trans polymer stereochemistry delineated. Cycloextrusion is a dilute solution phenomenon, limited to cycloolefins containing an unhindered diene moeity in the ring. The thermodynamics and kinetics of the catalyst in the presence of a reversibly binding ligand have been intensively researched. Tetrahydrofuran serves as the reversibly binding ligand which deactivates the catalyst to an extent dependent upon concentration of tetrahydrofuran present. The metathesis of cyclooctadiene with this tungsten carbene can thus be sufficiently retarded to show that the polymerization kinetics involves a catalyst-monomer bound complex, followed by regeneration of catalyst.

Linear copolymers are prepared in both random and block form from the metathesis polymerization of 1,5-cyclooctadiene/cyclooctatetraene and norbornene/cyclooctatetraene solutions, respectively. The average conjugation length in the random copolymers can be varied systematically by varying the mole fraction of cyclooctatetraene in the copolymerization solution. Raman spectroscopy, UV-Vis, NMR, electrical conductivity, and non-linear optical measurements all indicate a progression of conjugation length in the copolymer with increasing mole fraction cyclooctatetraene.

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