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Thesis (MSc.(Chemistry)) - University of Pretoria, 2006.

Typescript. Includes vita and abstract. Includes bibliographical references (leaves 153-159). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

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The alkali metal graphite intercalates and the conducting polymers polyacetylene and polypyrrole are reviewed and compared. Polyacetylene was synthesized by Luttinger's method and doped by exposure to caesium vapour. The doped and undoped polyacetylene were characterized by neutron powder diffraction. Hydrogen absorption and subsequent pyrolysis of caesium doped polyacetylene were studied. Mass spectrum analysis of the gases evolved at 300°C showed methane and other alkanes, indicating H₂ addition to the polymer chain followed by methane elimination. The graphite intercalates C₈Cs and C₂₄Cs reacted irreversibly with acetylene, neutron powder diffraction indicating graphite and two new substances. Mass spectrum analysis of gases evolved on heating showed ethylene, butene and butadiene, suggesting a polymerization. Polypyrrole was synthesized electrochemically and characterized by cyclic voltammetry. Gram quantities of polypyrrole doped with BF^-₄ and C10^-₄ were prepared electrochemically under high vacuum conditions to achieve high purity and avoid oxygen doping. Perchlorate doped polypyrrole prepared in an oxygen-free environment proved dangerously unstable, especially when dry. The neutron scattering law for a harmonic oscillator and the energy level splitting pattern of a 1-D rotor in a cos3θ hindering potential are reviewed and applied to solid acetonitrile. Intense lines in the neutron spectrum at 140 and 190 cm^-1 are assigned to methyl group torsions with barriers to rotation of 400 and 734 cm^-1. Hydrogen is reversibly physisorbed by intercalates C₂₄K, C₂₄Rb and C₂₄Cs at 100K to form compounds C₂₄M(H₂)₂. Neutron spectra of H₂, HD and D₂ physisorbed by C₂₄Rb and C₂₄Cs at energy transfers between 0.3-3 meV and 10-200 meV (1 meV = 8.065 cm^-1) were measured and assigned to rotational tunnelling and librations of hydrogen molecules in two sites of different dimensions. The cos2θ barriers to rotation were 57 and 78 meV respectively in C₂₄Rb(H₂)_x and 51 and 78 meV in C₂₄Cs(H₂)_x. A structural model is proposed for the metal layers with the hydrogen molecules in the layers and perpendicularly oriented.

New procedures for preparation of polyacetylenes with highly luminescent naphthalimide groups that might be potentially utilized in optoelectronics and sensors are developed within the framework of present doctoral thesis. The procedures provide luminescent a) linear polyacetylenes that can be processed from solutions, and b) mesoporous network polyacetylenes with high pore volume. Two paths to soluble polyacetylenes are used: (i) copolymerization of ethynyl- functionalized naphthalimide (monomer PN) and a monoethynyl aromate catalyzed with [Rh(nbd)acac], and (ii) modification of poly(disubstituted acetylene)s carrying -chloroalkyl pendants involving the exchange of chlorine atoms for azido groups and subsequent "click"- reaction of Huisgen type of azido groups with ethynyl groups of PN. The PN does not homopolymerize but copolymerizes with ethynylaromates. The highest possible molar fraction of the PN units in copolymers is of 0.5, which suggests the absence of PN dyads or longer sequences in copolymers and the alternating arrangement of PN units in the copolymers of the composition of 0.5. Surprisingly, ethynylarenes that give insoluble homopolymers gave soluble copolymers with PN. The modification procedure requires knowledge on the effect of the monomer structure symmetry and substituent...

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In the work described in this thesis, the Feynman-Dyson perturbation theory, developed from quantum field theory, was employed in semiempirical calculations on trans - polyacetylene. A variety of soliton-like excited states of the molecule were studied by the PPP-UHF-RPA method. The results of this study provide useful information on the nature of these states, which are thought to account for the unique electrical conduction properties of trans - polyacetylene and similar conducting polymers. Feynman-Dyson perturbation theory was also used to extend Hartree-Fock theory by the inclusion of time-independent second-order self-energy insertions. The results of calculations on polyenes show that consideration of this approach is warranted, as the contribution of the second- order terms is significant. The computer program, written during the course of the research reported here, is discussed as well. / Ph. D.

3 ABSTRACT Complexes [Rh(cycloolefin)(acac)] (cycloolefin = norborna-2,5-diene, cycloocta- 1,5-diene and cyclooctatetraene) were investigated as catalysts of polymerization of monosubstituted acetylenes into stereoregular cis-transoid polyacetylenes. All complexes were highly active in arylacetylenes polymerizations in both coordinating and non-coordinating solvents. Selection of solvent and cycloolefin ligand of the catalyst allowed the control over polymer MW. The onset of initiation in the [Rh(cycloolefin)(acac)]/monomer systems proceeded as the proton transfer from the monomer molecule to the acac ligand under the release of acetylacetone and coordination of -C≡CR ligand to Rh(cycloolefin) moiety. Cis-transoid poly(phenylacetylene) and poly[(2,4-difluorophenyl)acetylene]s with required initial MW were prepared with these catalysts and submitted to the long-term ageing in which the polymers were exposed to the atmosphere and diffuse daylight either dissolved in tetrahydrofuran or in the solid state. Tightly connected processes of cis-to-trans isomerization of the polymer main-chains double bonds and oxidative degradation were found to proceed during polymers ageing in the solution. Besides, the formation of corresponding cyclotrimers accompanied the polymers ageing. However, the cyclotrimers amount was...