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There has been a growing demand for specific linear alpha olefins in the polyethylene industry in order to control polymer rheology. This growing demand thereby increases the need for highly active and selective ethylene oligomerization catalysts. Chromium-based catalysts continue to be of high interest for this application due to this metal’s versatility in both selective and non selective ethylene oligomerization. Ligand design is an important consideration in oligomerization chemistry: the ability of the ligand to stabilize low valent chromium and to support a two-electron redox process will allow the catalytic systems to follow the selective ring expansion mechanism for oligomerization. Chelating aminophosphane based ligands, previously studied by our group, have been shown to support both tri- and tetramerization of ethylene. We have explored modifications of one of the NP arms by replacing with a different coordinating group in an attempt to further stabilize the monovalent state of chromium and increase selectivity. Other ligands explored in this work are pyrrole based ligands, which have shown high activity and selectivity towards ethylene oligomerization. One example of this is the commercial Chevron-Phillips system. Recently, the co-polymerization of CO2 with epoxides has been studied as an environmentally friendly route to convert CO2 into biodegradable polymers. The first successful catalytic system to achieve these results consisted of a diethyl-zinc complex. More recently, aluminum, chromium, cadmium and cobalt have been studied as polycarbonate catalysts. To date, the only reported chromium catalysts for CO2-epoxide copolymerization are Cr-salen and Cr-porphyrin complexes, studied by Darrensbourg and Holmes, respectively. We were particularly interested in finding new chromium-based complexes able to catalyze epoxide/CO2 copolymerization by using molecules with the nitrogen donor motif embedded in different functions such as neutral pyridines with anionic pendants, pyrroles with either imine or amine pendants, or a combination of these.

This thesis describes the synthesis of soluble Polymer of Intrinsic Microporosity (PIM-1), fluoro-endcapped PIM-1 (F-PIM-1) and copolymers of F-PIM-1 with poly(ethylene glycol) monomethyl ether (MeOPEG). The main aim of the project was to alter the porosity of microporous PIM-1 in three ways: (a) synthesis of copolymers of F-PIM-1 with MeOPEG (b) blending of PIM-1 with MeOPEG in various proportions; and (c) adsorption of MeOPEG from aqueous solution byPIM-1. PIM-1 and F-PIM-1 were synthesized by step growth polymerization of tetrafluoroterephthalonitrile (TFTPN) with 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane (THSB), using the conventional method and a newly reported high shear mixing method. F-PIM-1 oligomers were then coupled to poly(ethylene glycol) monomethyl ether (MeOPEG). The products were analyzed by NMR, IR, MALDI ToF MSS, TGA and polystyrene based GPC as well as multidetector GPC techniques. The high shear technique generally produced high molar mass products and yields. This method was also more successful for copolymerization.Blending of PIM-1 and MeOPEG in different proportions resulted in macrophase separation. Copolymer products were used to facilitate mixing of blends (as compatibilizers), however only 5% of MeOPEG could be solubilised into a PIM-1 phase. The effect of compatibilizer was found to be affected by interaction between PIM-1 and copolymer. However, N2 adsorption studies showed that after thermal removal of MeOPEG, PIM-1 regained stable porosity with significant BET surface area.Fluorescence studies were aimed at applications of PIM-1 and copolymers in sensors. PIM-1 and copolymers, spin-coated on the polyester-based substrate Melinex, were studied with and without methanol treatment in an environment of different solvent vapours. The effect of time and volume on wavelength shift and change in intensity was studied. Polar solvents tended to cause a red shift with decrease in intensity while less polar solvents behaved otherwise. Based on fluorescence experiments, solvent profiles for PIM-1 and copolymers were established.

Gas separations are often required in chemical processes, e.g. air separation, ethylene production, etc. These are often challenging and costly processes because of the low temperature and high pressure needed if vapour-liquid phase separations are involved. This thesis focuses on hybrid membrane-distillation separations as an opportunity to develop more energy-efficient separation processes. In a typical ethylene plant, recovery, the separation and purification of the cracked product are economically important. The focus of this thesis is on the ‘C2splitter’ which separates the desired product, ethylene, from ethane. Cryogenic distillation, which is currently used to separate the binary ethylene-ethane mixture, is extremely expensive in terms of both capital and operating costs, especially because of refrigerated cooling requirements. Hybrid membrane-distillation processes are able to effectively separate low-boiling compounds and close-boiling mixtures and to reduce energy consumption, relative to cryogenic distillation. However, hybrid membrane-distillation processes present challenges for process modelling, design and operation. There are two major challenges associated with the modelling of hybrid processes for low temperature separations: i) the complex interaction between the process and the refrigeration system and ii) the large number of structural options, e.g. conventional column, membrane unit or hybrid membrane-distillation separation, where the distillation column can be integrated with the membrane unit to form a sequential, parallel, ‘top’or ‘bottom’ hybrid scheme. This thesis develops a systematic methodology to design, screen, evaluate and optimise various design alternatives. Schemes are evaluated with respect to energy consumption, i.e. power consumption of process and refrigeration compressors, or energy costs. In the methodology, process options are screened first for feasibility, based on numerous simulations and sensitivity analyses. Then, the feasible options are evaluated in terms of energy consumption and compared to the performance of a conventional distillation column. Finally, economically viable schemes are optimised to identify the most cost-effective heat-integrated structure and operating conditions. The methodology applies models for multi-feed and multi-product distillation columns, the membrane, compressor and refrigeration system; heat recovery opportunities are systematically captured and exploited. For the separation of relatively ideal mixtures, modified shortcut design methods, based on the Fenske-Underwood-Gilliland method are appropriate because they allow fast evaluation without needing detailed specification of column design parameters (i.e. number of stages, feed and side draw stage locations and reflux ratio). The modifications proposed by Suphanit (1999) for simple column design are extended to consider multi-feed and/or multi-product columns. The complex column designs based on the approximate calculations method are validated by comparison with more rigorous simulations using Aspen HYSYS. To design the hybrid system, a reliable and robust membrane model is also needed. To predict the performance of the module model, this work applies and modifies detailed membrane model (Shindo et al., 1985) and approximate method (Naylor and Backer, 1955) to avoid the need for initial estimates of permeate purities and to facilitate convergence. Heat integration opportunities are considered to reduce the energy consumption of the system, considering interactions within the separation process and with the refrigeration system. A matrix-based approach (Farrokhpanah, 2009) is modified to assess opportunities for heat integration. The modified heat recovery model eliminates the need to design the refrigeration cycle and uses a new simple, linear model that correlates the ideal (Carnot) and a more accurately predicted coefficient of performance. This work develops a framework for optimising important degrees of freedom in the hybrid separation system, e.g. permeate pressure, stage cut, side draw molar flow rate and purity, column feed and side draw locations. Heat recovery options between: i) column feeds and products; ii) the membrane feed and products and iii) the associated refrigeration system are considered. A deterministic and a stochastic optimisation algorithm are applied and compared for their efficiency of solving the resulting nonlinear optimisation problem. The new approach is demonstrated for the design and optimisation of heat-integrated sequential and parallel hybrid membrane-distillation flowsheets. Case study results show that hybrid scheme can reduce energy cost by 11%, compared to distillation, and that parallel schemes have around 8% lower energy costs than sequential hybrid schemes. These results suggest hybrid membrane-distillation processes may be competitive with distillation when applied for ethylene-ethane separations, but that further development of suitable membranes may still be needed.

This research aimed to develop technology and processes to further beneficiate two southern African bentonites for applications in polymer/clay nanotechnology. The bentonites were from the Koppies mine in South Africa, and the Boane mine in Mozambique. The work was divided into two parts: (i) preparation of organomodified nanoparticulate smectite clays, and (ii) preparation of their poly(ethylene-co-vinylacetate) nanocomposites. Nanoparticulate organobentonites were prepared using purified bentonites. The conventional organomodification process uses a very low concentration of bentonites at 80 oC. In this study, a novel method was developed: concentrated slurries of naturally occurring Ca-bentonite partially activated with soda ash in the presence of a proprietary dispersant were contacted at ambient temperature with quaternary ammonium surfactants. A known amount of bentonite dispersion was placed in a planetary mixer before the mixture. Likewise, a known amount of surfactant, up to 50% excess, based on the estimated cation exchange capacity (CEC) of the bentonites, was added while mixing the dispersion. The surfactants added were either in solution or in powdered form. The intercalated bentonite was recovered by centrifugation and washed repeatedly with water until halide ions could not be detected using a 1M silver nitrate solution. The solids were dried at ambient temperature and humidity, and then crushed and milled into a fine powder using a mortar and pestle. Several instrumental techniques were used to characterise and examine the properties of the bentonite samples before and after organic treatment.The X-ray diffraction (XRD) results were consistent with: (i) paraffin-type extended chain intercalation; and (ii) interdigitated monolayer intercalation of the C12 and C14 single-chain alkyl surfactants and bilayer intercalation of the single-chain C16 surfactant and the surfactants with double alkyl chains. Fourier transform infrared (FTIR) spectroscopy analysis of the organobentonite powders confirmed disordered chain conformations. XRD also detected significant amounts of cristobalite in the samples of Boane bentonite (from Mozambique). This impurity could not be removed cost-effectively. The onset decomposition temperature ofthe present organobentonites was around 200 ºC, which is within the typical range of polymer/organoclay processing temperatures. The thermal stability of the organobentonites was independent of both the number of alkyl chain substituents and their length, and also independent of the degree of clay intercalation. SURFACTANT INTERCALATED KOPPIES AND BOANE BENTONITES FOR POLYMER NANOTECHNOLOGY ii Poly(ethylene-co-vinylacetate) nanocomposites were prepared with South African Koppies bentonite, organomodified with single-chain C12 (and polar 2-hydroxyethyl side chain) and double-chains C18 alkyl ammonium cationic surfactants. The later surfactant was intercalated both below and above the clay CEC. Nanocomposites were prepared by twin-screw melt compounding. Transmission electron microscopy (TEM) indicated the presence of mixed nanoand micron-sized clay morphologies. XRD studies revealed that the crystallinity of the particles improved and that the d-spacing values increased on incorporation of the modified bentonites in the polymer matrix. It is postulated that, rather than indicating polymer co-intercalation, this was caused by further intercalation of either excess surfactants or surfactant residues that were released by shear delamination of the clays during compounding. Improved mechanical properties were realised, especially when using the bentonite containing the longer double-chains surfactant intercalated at levels in excess of the CEC of the clay. The nanocomposites showed improved tensile modulus and elongation at break values at the expense of a reduction in impact strength, while tensile strength was about the same as for the neat polymer. / Thesis (PhD)--University of Pretoria, 2013. / gm2014 / Chemistry / unrestricted

Ionomers are polymers that contain ionic groups in relatively low concentrations along the polymer backbone. These ionic groups, in the presence of oppositely charged ions, form aggregates that lead to novel physical properties of the polymer. React-A-Seal® and Surlyn® are poly(ethylene-co-methacrylic acid) (EMAA) ionomer-based materials and Nucrel® is the EMAA acid copolymer neutralized to produce Surlyn®. React-A-Seal® , Surlyn® , and Nucrel® recover into their original shapes following a high impact puncture at velocities ranging from 300 to 1200 ft/s ("self-healing"). This self-healing process may be of great benefit in space applications where structures are exposed to matter impacts. A thermal IR camera indicated a temperature increase to 98°C for Nucrel® 925, Surlyn® 8940, React-A-Seal® , and Surlyn® 8920 after initial penetration. To understand and generalize the observed phenomena, questions concerning the mechanism of the puncture resealing must be answered. One suggestion is that the elastic character of the melt created by the puncture drives the self-healing. This inference is based on the observed temperature rise of ~3°C above the melting temperature of the samples (~95°C) during the impact. With the expectation of gaining additional insight into the self-healing phenomenon, a thermodynamic and viscoelastic investigation was conducted using primarily DSC and DMA. Surlyn® and React-A-Seal® showed the characteristic order-disorder transition at ~52°C that has been reported in literature. Master curves were constructed from the creep isotherms for the four EMAA samples. An aging study was performed to investigate the irreproducibility and ®tailing effect” observed in the creep data. The aging study indicated that, with increased aging time and temperature, changes in the polyethylene matrix lead to complexities in morphology resulting in changes in the magnitude and shape of the creep curves. As a result of the thermodynamic, viscoelastic, and high-speed impact experiments it has been theorized that self-healing can occur in Nucrel® 925, Surlyn® 8940, React-A-Seal® , and Surlyn® 8920 because of two features, ionic aggregation and complex flow behavior. / Master of Science

Ethylene is an endogenously synthesized plant hormone that dissipates quickly in field conditions and seldom exceeds five nmol mol-1. Ethylene can accumulate to 1000 times this level in closed environments. The best-known effects of ethylene are its impacts on fruit ripening and senescence, yet ethylene influences growth and development throughout the plant life cycle. At low, continuous concentrations (20 to 50 nmol mol-1), ethylene reduces yield of many plants. Clean-air treatment during critical stages of floral development, silver thiosulfate (STS), and 1-methylcyclopropene (1- MCP) may delay flower senescence and reduce the detrimental effects of ethylene on peas and tomatoes grown in continuous ethylene. There is evidence of species differences in ethylene sensitivity, but limited information on cultivar differences. To address these issues, ethylene sensitivity of two dwarf tomato cultivars, Micro-Tom and Micro-Tina, and one dwarf pea cultivar, Earligreen, was examined. Ethylene by temperature interactions were examined in tomatoes at 0, 20, and 40 nmol mol-1 ethylene and 22 and 28°C. Three-day-long clean-air treatments were applied to tomatoes from germination through fruit set to identify the most ethylene-sensitive stage of floral development. The actions and toxicities of STS and 1-MCP were compared. Ethylene sensitivities of the two closely related dwarf tomato cultivars were examined. At 22°C, the 20 and 40 nmol mol-1 red fruit yields were 51 and 11 % of control. At 28°C, yields were 37 and 4% of control. Vegetative growth at 20 and 40 nmol mol-1 was 96 and 91 % of control, at both temperatures. Three-day-long clean-air treatments from days 22 to 33 (axillary flower opening) improved fruit set and final yield. Floral bud abortion in elevated ethylene occurred primarily at or before microsporogenesis. Floral bud initiation and vegetative development were not significantly affected. Tomato plants grown in continuous 70 nmol mol-1 ethylene conditions retained only 3% of the total number of floral buds initiated. STS-treated plants retained 50 to 54% of their floral buds. Leaf area of plants subjected to 100 nmol mol-1 ethylene was 26% of control, and plants subjected to 200 nmol mol-1 ethylene were 21 % of control. When plants were treated daily for 10 hours with 35 nmol mol-1 l-MCP, leaf area improved to 81 and 64% of control. Manipulating temperature had neither a statistically nor a biologically significant effect on ethylene sensitivity. Ethylene reduced yield primarily by arresting floral bud development and causing early floral bud senescence. Both STS and 1-MCP looked promising for improving yield in high ethylene environments, but concentrations and durations of application need to be further refined. Yield of Micro-Tom was significantly less sensitive to ethylene than Micro-Tina. These results indicate that solving ethylene sensitivity issues in controlled environments may be accommodated by cultivar choice as well as timely control of environmental ethylene, chemical inhibitors, and genetic manipulation.

Indiana University-Purdue University Indianapolis (IUPUI) / Stiffening and softening of extracellular matrix (ECM) are critical processes governing many aspects of biological processes. The most common practice used to investigate these processes is seeding cells on two-dimensional (2D) surfaces of varying stiffness. In recent years, cell-laden three-dimensional (3D) scaffolds with controllable properties are also increasingly used. However, current 2D and 3D culture platforms do not permit spatiotemporal controls over material properties that could influence tissue processes. To address this issue, four-dimensional (4D) hydrogels (i.e., 3D materials permitting time-dependent control of matrix properties) are proposed to recapitulate dynamic changes of ECM properties. The goal of this thesis was to exploit orthogonal enzymatic reactions for on-demand stiffening and/or softening of cell-laden hydrogels. The first objective was to establish cytocompatible hydrogels permitting enzymatic crosslinking and stiffening using enzymes with orthogonal reactivity. Sortase A (SrtA) and mushroom tyrosinase (MT) were used sequentially to achieve initial gelation and on-demand stiffening. In addition, hydrogels permitting reversible stiffening through SrtA-mediated peptide ligation were established. Specifically, poly(ethylene glycol) (PEG)-peptide hydrogels were fabricated with peptide linkers containing pendent SrtA substrates. The hydrogels were stiffened through incubation with SrtA, whereas gel softening was achieved subsequently via addition of SrtA and soluble glycine substrate. The second objective was to investigate the role of dynamic matrix stiffening on pancreatic cancer cell survival, spheroid formation, and drug responsiveness. The crosslinking of PEG-peptide hydrogels was dynamically tuned to evaluate the effect of matrix stiffness on cell viability and function. Specifically, dynamic matrix stiffening inhibited cell proliferation and spheroid formation, while softening the cell-laden hydrogels led to significant increase in spheroid sizes. Matrix stiffness also altered the expression of chemoresistance markers and responsiveness of cancer cells to gemcitabine treatment. markers and responsiveness of cancer cells to gemcitabine treatment.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Includes bibliographical references. / by Michael Stoukides. / Ph.D.

The effect of preharvest foliar applications of ethephon and postharvest curing on baked sweet potatoes (Ipomoea batata) were analyzed. Ethylene had negative effects on appearance of baked roots while curing increased the total phenolics in sweet potatoes. Panelists preferred the non-ethylene treated and green or cured over ethylene treated sweet potatoes with respect to texture, color and flavor. No differences in chemical or color properties were found between treatments. The effect of curing time (0, 7, 14 days) on baked sweet potatoes was studied. Curing caused more browning on flesh of sweet potatoes. Moreover, panelists preferred the texture of the green over the cured roots but did not find any differences in flavor sensory quality. The effect of hot water treatment on sprouting and spoilage of cured sweet potatoes was investigated. The most effective treatment was at 53-56 °C for less than 10 min, resulting in less than 60% (control=80%).