Thermally rearranged polymers are formed from the solid-state thermal reaction of polyimides and polyamides that contain reactive groups ortho position to their diamine. These polymers have shown outstanding transport properties for gas separation applications. The thrust of this work is to critically examine the chemical and morphological structure of these polymers and to identify the fundamental contributions of gas sorption to permeability. To accomplish this goal, a series of TR polymers and TR polymer precursors have been synthesized and investigated for transport properties. As a function of conversion, diffusivity increases more dramatically than sorption, which explains the outstanding permeabilities observed for these samples. Modifications to the polymer backbone structure, which can be achieved by adding rigid functional groups such as hexafluoroisopropylidene-functional linking groups, can further be used to improve permeabilities. The precursor used to form TR polymers has dramatic effects on the final polymer transport properties. Despite having nearly identical polymer structure, TR polymers formed from polyamide precursors have lower combinations of permeability and selectivity than TR polymers formed from polyimide precursors. In addition to structure-property studies with TR polymers, this thesis also present comparisons of permeability, diffusivity, and sorption of sparingly soluble gases (i.e., hydrogen and helium) for hydrocarbon-based polymer, highly fluorinated polymers, perfluoropolymers, and a silicon-based polymer. An explanation for the unique transport properties of perfluoropolymers is presented from the standpoint of the solution-diffusion model, whereby perfluoropolymers have uniquely different solubility selectivities than hydrocarbon-based polymers. Additionally, a large database of sorption, diffusion, and permeability coefficients is used to determine the contributions of free volume on solubility selectivity in polymers. / text

<p>Thermal, non-catalytic conversion of light olefins (C2= - C4=) was originally utilized in the production of motor fuels at several U.S. refineries in the 1920-30’s. However, the resulting fuels had relatively low-octane number and required harsh operating conditions (T > 450 oC, P > 50 bar), ultimately leading to its succession by solid acid catalytic processes. Despite the early utilization of the thermal reaction, relatively little is known about the reaction products, kinetics, and initiation pathway under liquid-producing conditions. </p> <p>In this thesis, thermal ethylene conversion was investigated near the industrial operating conditions, i.e, at temperatures between 320 and 500 oC and ethylene pressures from 1.5 to 43.5 bar. Non-oligomer products such as propylene and/or higher odd carbon products were observed at all reaction temperatures, pressures, and reaction extents. Methane and ethane were minor products (< 1 % each), even at ethylene conversions as high as 74 %. The isomer distributions revealed a preference for linear, terminal C4 and C5. The reaction order was found to be 2nd order with a temperature dependent activation energy ranging from 165 to 244 kJ/mol. The importance of diradical species in generating free radicals during a two-phase initiation process was proposed. The reaction chemistry for ethylene, which has only strong, vinyl C-H bonds starkly contrasted propylene, which possesses weaker allylic C-H bonds and showed preference for dimeric C6 products over C2-C8 non-oligomers. </p> <p>Extending this work further, the thermal oligomerization of ethylene was enhanced using high surface area supports such as silica and alumina. Both supports resulted in order of magnitude rate increases compared to the gas phase reaction, however the ethylene conversion rate with alumina was superior to silica by a factor of between 100 and 1,000. Additionally, the alumina evidently confers a catalytic function, resulting in altered product distributions, notably an increase in branched products such as isobutene and isopentenes. The oligomerization chemistry with alumina appears to reflect the involvement of Lewis acid sites rather than traditional Brønsted acid or transition metal catalysis, which operate via carbenium ion and metal-alkyl intermediates, respectively. </p>

Thermal reactions and flash photolysis are used to study the olefin bond-migration promoted by tungsten carbonyls. Substitution of piperidine (pip) by 2- allylphenyldiphenylphosphine (adpp) in the cis-(pip)(η^1- adpp)W(CO)-4 complex was investigated, and no olefin bond-migration was observed. This suggests that a vacant coordinated site adjacent to the coordinated olefin is an essential requirement for olefin bond rearrangement. The rates of olefin attack on the photogenerated coordinatively unsaturated species, cis-[(CB)(η^1-ol- P)W(CO)-4] (CB = chlorobenzene, p-ol = Ph-2P(CH-2)-3CH=CH-2; n = 1-4) were measured. Kinetics data obtained both in pure CB and in CB/cyclohexane mixtures support a dissociative mechanism in which the W-CB bond is broken in the transition state. In contrast to results observed in studies of other related systems, no olefin bond-migration is noted. This observation is attributed to P-W coordination at all stages of the reaction, which precludes formation of a reactive intermediate containing a vacant coordination site adjacent to a P-ol bond.