Browsing by Subject "Polymerization"
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Item A study of controlling resistances during initial solvent evaporation period of asymmetric membrane formation.(Texas Tech University, 1975-05) Majid, S. M ANot availableItem A study of controlling resistances during initial solvent evaporation period of asymmetric membrane formation.(Texas Tech University, 1975-05) Majid, S. M ANot availableItem Adventures in main group chemistry: from molecules to materials(2008-05) Findlater, Michael; Cowley, Alan H.Three synthetic methods have been explored for the preparation of several novel boron-substituted amidinates and guanidinates. The extension of heterocumulene insertion chemistries to boron-aryl, boron-metallocene and boron-transition metal moieties has also been achieved and the mechanism of such insertions is addressed via density functional theory modeling techniques. The reactivity of these complexes is also explored, mainly through halide abstraction methodologies to generate boron cations, which are potent Lewis Acids and may be useful in promoting organic transformations or in the polymerization of ethylene. The synthesis and characterization of the elusive monomeric low valent carbenoid boron(I), a compound with a formal lone pair located upon the boron center, has been lacking. The suitability of the guanidinate ligand system to support such a species is also discussed and a combined experimental and theoretical approach to this highly topical problem is also presented. Thirdly, the use of photovoltaics (devices which convert solar energy directly into electricity) as an alternative source of energy outwith fossil fuel technologies is a rapidly growing area of interest. Initial efforts to use a novel approach, which incorporates inorganic nanocrystals wired into a conducting polymer matrix, are also presented. Successful synthetic approaches to the gallium, aluminum and indium monomeric precursors suitable for electropolymerization were developed. These compounds proved to be effective starting points for the generation of conducting polymers with embedded III/VI (Ga₂S₃) nanocrystals with further studies currently underway as to their III/V (InP, GaAs) compatriots. Finally, a retrospective of projects that may best be described in terms of the moniker "Loose Ends and Future Directions" will be presented. The aim of which will be to serve as a useful guidepost for further studies in the fields and topics discussed.Item Axisymmetric flow of dilute xanthan gum polymer solutions through media(Texas Tech University, 1984-08) Duran, Stephen LynnNot availableItem Design and synthesis of new C1 and C2-symmetric ansa-metallocene catalysts for isotactic-polypropylene formation(Texas A&M University, 2006-04-12) Al-Bahily, Khalid ASeveral ansa C1-symmetric cyclopentadienyl-fluorenyl metallocenes based on zirconium have been prepared with different substituents at position 3 on the cyclopentadienyl ring. Isotactic polypropylene production from these systems depends highly on the size of these substituents. Therefore, large groups such as 1-methyl-4-tbutylcyclohexyl (metallocene 6), 1-methyl-cyclohexyl (metallocene 7), 1,3,3,5- tetramethylcyclohexyl (metallocene 8), and 2,3,4-trimethyl-3-pentyl (metallocene 9) have been investigated. In combination with methylaluminoxane (MAO), they showed good activity and produced high molecular weight of isotactic polypropylene. In terms of the tacticity of the polymers, metallocene 6 made the best isotactic polypropylene with ~88% mmmm pentad content. Also, it has been found that if the size of this substituent is large as in 2,3,4-trimethyl-3-pentyl (metallocene 9), then it will block the polymerization active site which will deactivate the metallocene. New synthetic pathways for the synthesis of cyclopentadienyl-fluorenyl metallocenes based on titanium have been achieved. Anchoring these types of ligands onto titanium by following the conventional method of using TiCl4 in the metallation step has failed for the production of Me2C(3-(diphenylmethyl)-C5H3)(C13H8)TiCl2 (metallocene 12), Ph2C(C5H4)(C13H8)TiCl2 (metallocene 14), and Ph2C(C5H4)(C13H8)TiMe2 (metallocene 15); this is possibly due to the high reactivity of TiCl4. Therefore, TiCl4??2THF has been prepared and used in that step to produce these new titanocenes with good yields. A new ansa-C2-symmetric substituted bis-indenyl metallocene for isotactic polypropylene production has been successfully prepared. It is known that ansa-C2- symmetric metallocenes are good catalysts for isotactic polypropylene production, but in general, their synthesis suffers from the production of the meso Cs-stereoisomer of these catalysts, which generally produces only atactic polypropylene. Therefore, the meso stereoisomers must be removed and this is considered a loss of the material that increases the cost of the catalysts. Addition of bulky substituents on the indenyl groups as in Me2Si(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenz(f)indenyl)2ZrCl2 (metallocene 5) has prevented the meso stereoisomer production. 5/MAO produces isotactic polypropylene with up to ~80% mmmm pentad content.Item Design, synthesis, and characterization of functional block copolymers containing fluorinated or hydrophilic segments by ATRP(2008-08) Bucholz, Tracy Laine, 1981-; Loo, Yueh-Lin, 1974-; Sanchez, Isaac C., 1941-Well-defined functional block copolymers containing either a fluorinated or a hydrophilic segment can be synthesized via a controlled free-radical technique, known as atom transfer radical polymerization (ATRP). Their self assembly characteristics in the solid state and in solution were examined in this work with the aim of developing ultralow dielectric constant materials and templates for conductive polymer synthesis, respectively. We demonstrated the controlled synthesis via ATRP of block copolymers containing poly(pentafluorostyrene) (PPFS) and a degradable polymer, such as poly(methyl methacrylate) (PMMA), poly([epsilon]-caprolactone) (PCL), or poly(D,L-lactide) (PLA). These block copolymers microphase separate in the solid state to form periodic nanostructures, such as alternating lamellae, a bicontinuous gyroid on a cubic lattice, cylinders on a hexagonal lattice, or spheres on a body-centered-cubic lattice, depending on the volume fraction of each block and the interblock segregation strength. Additionally, we quantified the interblock segregation strength of PPFS/PMMA, demonstrating that this block copolymer is only approximately twice as segregated as its nonfluorinated counterpart poly(styrene-[beta]-methyl methacrylate) due to the symmetric placement of the polar C-F bonds on the benzene ring in PPFS. We also showed that the self-assembly characteristics of PPFS-containing block copolymers can be used to create nanoporous fluorinated films with ultra-low dielectric constants in the range of 1.7 - 1.9. The dielectric constants are tunable through manipulation of the volume fraction of the degradable block in the parent block copolymers. We also demonstrated the controlled synthesis via ATRP of block copolymers containing poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAMPSA) with either poly(oligo(ethylene glycol) methyl ether methacrylate) (PEGMA) or poly(methyl acrylate) (PMA). We showed that PEGMA/PAAMPSA formed well-ordered nanostructures in the solid state when cast from strong hydrogen bond accepting solvents, such as DMSO and DMF. PEGMA/PAAMPSA can also be used as the acid dopant in the synthesis of conductive polyaniline (PANI). Additionally, we studied the micelle formation of PMA/PAAMPSA and subsequently used these micelles as templates to create spherical conductive PANI nanoparticles. The size and size distribution of these PANI nanoparticles were dictated by the corresponding characteristics of the micellar template.Item Electrochemical study of the catalytic properties of cobalt 2,2'-bipyridine complexes with n-alkyl bromides and selected olefins(Texas Tech University, 1982-05) Caron, Linda MarieNOT AVAILABLEItem Frictional study of polymeric textiles(2007-08) Rajanala, RanjeetThe frictional properties of textile materials have been of interest to material scientists and textile technologists for a number of years. Friction is defined as the resistance to motion when two bodies in contact are set to a relative motion. Friction is the principal physical property- that holds the fibers together to form a fabric. Friction is a complex physical and mechanical phenomenon. Polymeric materials such as textiles fail to obey the classical Amontons' law of friction. This thesis work endeavors to prove the failure of Amontons' classical law of friction using a statistical approach. The nonlinearity between the friction force and the normal load resulted in the de\'elopment of a normalized friction factor, "R" The novel normalized friction factor has been used to evaluate the frictional properties of a set of woven and nonwowen fabrics. In addition, research efforts also focused on understanding the surface mechanical properties of needlepunched-thermalbonded nonwoven substrate. The sliding friction apparatus has been conveniently used to characterize the frictional properties of the nonwoven fabric. Results on the frictional study of the nonwoven fabric have been very promising and have proved the effectiveness of the novel friction factor. The thesis also presents a critical appreciation of previous works on the frictional properties of polymeric textiles.Item Micro/nano fabrication of polymeric materials by DMD-based micro-stereolithography and photothermal imprinting(2006) Lu, Yi; Chen, ShaochenItem Modeling and optimization of the batch free-radical polystyrene polymerization process(Texas Tech University, 1990-05) Zheng, DongleiNot availableItem Nonlinear process-model-based control and optimization of batch polymerization reactor(Texas Tech University, 1994-05) Choi, Jin Y.Polymers (Ray and Laurence, 1977) have been synthesized in the laboratory for more than 150 years. When the commercial importance of polymers was realized in the early twentieth century, production began by scale-up from successful laboratory experiments. Because so little was understood about the polymerization step and the product was so difficult to characterize, a successful polymerization process was one which could reproduce the same recipe for every batch, thus producing reasonable product uniformity from batch to batch. As might be expected, even minor modifications of the recipe produced a different product, so that a great plethora of product lines, each of small market volume, began to evolve. As the total demand for polymer products has vastly increased over the last 40 to 50 years, the method of production became more and more expensive. Thus in the last 20 years, polymer manufacturers have been working to improve the quality of their products and the efficiency of their operation through efforts: (1) to improve their ability to characterize the chemical makeup and corresponding physical properties of the various polymer products; (2) to quantitatively understand the influence of the reaction conditions on the polymer produced; and (3) where necessary, to develop more effective reactors. These efforts have required a much better understanding of polymerization kinetics and optimum recipes. The scope of this work is not to investigate a new fact about the polymerization reaction or its physical properties or aspects of reactor design, but to effectively utilize some known facts to guide the course of a polymerization processes. Therefore, our objective is to find out the best process recipes, typically feed rate (i.e., monomer, solvent, initiator) and temperature profile, and effectively maintain them during the batch time. Consequently, it requires a process control and optimization technique.Item Novel N-heterocyclic carbene architectures for use in carbene based polymers and redox swithcable : catalysis(2008-08) Kamplain, Justin Wade, 1980-; Bielawski, Christopher W.The central focus of this dissertation pertains to the synthesis and study of novel N-Heterocyclic carbene architectures. This pursuit has led to advances in carbine structure and bonding, and application of NHCs in materials chemistry in the role of monomer and catalystItem Phase behavior of ethylene/low-density polyethylene mixtures(Texas Tech University, 1976-08) Harmony, Stephen CNot availableItem Polymer phase equilibrium calculation of a differential method(Texas Tech University, 1977-05) Khalafi, Seyed AbbasNot availableItem Studies of solvent-solute interactions in the photophysics of laser dyes(Texas Tech University, 1988-12) Casey, Kelly GambleThe fluorescence lifetime of rhodamine B in the normal alcohols (C1-C10) and normal nitriles (C2,C5,C6,C8,C9) has been measured using a picosecond laser system. The lifetime measuring technique is time-correlated single photon counting (TCSPC). Absorption and emission spectra of rhodamine B in the alcohols and nitriles have also been determined, thus allowing calculation of quantum yields, radiative, and nonradiative rates. The rotation of the dye's diethylamino groups is related to the nonradiative rate. A decreasing nonradiative rate corresponds to a greater energy barrier to rotation. The behavior of the nonradiative rates, and thus the rotational energy barrier, is modelled as a function of (1) solvent viscosity and (2) solvent polarity. The polarity-dependent model shows better cortelation with the data. The nitrile data differs from the alcohol data in that the barrier appears to be constant and therefore independent of solvent viscosity and polarity. Hydrogen bonding is used to explain the differences between the alcohols and nitriles. Rotational relaxation times of two laser dyes (cresyl violet and oxazine-1) in polymer solution (poly(ethylene oxide) and methanol) has been measured using the transient absorption spectroscopy (TAS) method. TAS is a pump-probe technique using a picosecond laser system. The pump beam optically bleaches the sample and the probe beam monitors the transient response. The effect of increasing polymer concentration is seen as an increasing rotational relaxation time. This result is examined with respect to the Debye-Stokes-Einstein (DSE) equation governing viscosity-dependent, rotational reorientational times. The greater increase in the rotational times of cresyl violet is explained on the basis of increased polymer-dye interaaion, specifically hydrogen bonding.Item Synthesis and metal cation separation of chelating polymers containing crown ether units(Texas Tech University, 1995-05) Zhao, QiangEach of the three parts of this dissertation research involves organic synthesis, monomer polymerization and polymer characterization, analytical chemistry and host-guest chemistry. The overall goal is to synthesize several different types of novel monomers and polymers which contain crown ether units and then study their complexation behavior with metal cations by sorption measurement, liquid-liquid or liquid-solid extraction or membrane transport techniques. The types of crown ether polymers described in the dissertation include formaldehyde condensation crosslinked resins, linear styryl-type polymers and polyamides. In the first part of the research, the influence of adding alkali-metal cations in the formaldehyde polymerization of dibenzo polyethers was investigated. It was found that cation complexation of the dibenzocrown ether monomer diminished the efficiency of the polymerization process, neutral crown ether resins and crown ether carboxylic acid resins with different levels of crosslinking were also prepared and their alkali-metal ion sorption efficiency and selectivity have been studied. Lastly, formaldehyde dibenzo- 18-crown-6 resins with varying levels of phosphonic monoacid and diacid group substitution were also prepared. The effect of the identity and level of the phosphonic acid groups on alkali-metal cation sorption by the resins was investigated. The second part of the research in the dissertation was the synthesis of some novel linear styryl-type crown ether polymers, some of which include ion-exchange sites in the polymer structure. The influence on metal picrate extractions for variation of the crown ether substituent group, side arm and spacer group between crown ether unit and polymer backbone in the polymers was studied. Factors, including the introduction of crown ether units and preorganization of the ion-exchange site relative to crown ether cavity, were also examined with regard to their effects on the metal cation sorption behavior of the ion-exchange crown ether polymers. The final part of the research in the dissertation involves the synthesis and characterization of a number of novel crown ether polyamide esters and acids. The crown ether units were incorporated within the polymer backbones. Some of the prepared polyamides could be cast to form mechanically strong membranes. This feature is crucial for potential applications in industry. Alkali-metal cation sorption by the crown ether polyamide acids and transport of alkali-metal cations across crown ether polyamide carboxylic acid membranes were investigated.Item Synthesis of alcohol substrate for [3,3]- and [3,5]-sigmatropic rearrangements and indenyl yttrium complexes as models for olefin polymerization catalysts(2012-05) Mehra, Rudhran; Birney, David M.; Bradley, Christopher A.Sigmatropic rearrangements are an important class of pericyclic reactions. These rearrangements can provide “clean” products as they can be easily carried out at relatively low temperatures and/or under photochemical conditions. Pericyclic reactions can be explained using several theories - Frontier Molecular Orbital (FMO) theory, Woodward- Hoffmann rules and Aromatic Transition State theory. In 1976, Lemal and co-workers coined the term “pseudopericyclic” for a class of rearrangements that were distinguished by the presence of “orbital disconnections”. Beginning nearly 20 years later, Birney and co-workers have further shed light on the nature of these rearrangements. The transition states observed in these reactions also differ from planar to almost planar which affects the degree of pseudopericyclic character. The exact nature of pseudopericyclic reactions, however, continues to be of interest to the scientific community. The first part of the thesis discusses the background and current work done on pseudopericyclic reactions. The second part of the manuscript discusses a series of [3,3]- and [3,5]-rearrangements that have been designed to further elucidate their pericyclic/pseudopericyclic character. These systems could have six- and eight- member transition structures via [3,3]- and [3,5]-sigmatropic rearrangements The synthesis involves making the acetate, trichloroacetimidate, dimethyl thiocarbamate, xanthate and vinyl ether of a substrate dienol. The synthesis of the dienol is also discussed. The third part of the thesis discusses the synthesis of a novel indenyl yttrium complexes used as a model for active catalyst in Group 3 olefin polymerizations. A number of ligands have been discussed and synthesized. Using these ligands as ancillary supports, we have synthesized an indenyl yttrium complex that mimics the active species in olefin polymerization. Specifically, attempts have been made to study the insertion of a Y-carbon bond into the indenyl benzo ring at different temperatures and the β-elimination step. One of the biggest potential drawbacks of the indenyl complexes is the deactivation of the catalyst via insertion into the ligands; which directly affects the chain length, stereochemistry and molecular weight of the polymer. This in turn can drastically impact the mechanical, chemical, and physical properties of the polymer.Item Synthesis of crown ether-containing polymers and functionalized crown ethers(Texas Tech University, 1985-05) Son, ByungkiNot availableItem The effect of structural modifications on solvent interactions with siloxane polymers(Texas Tech University, 1978-05) Chen, Ko-ChiGas-Liquid chromatography (GLC) was used to investigate the sensitivity of GLC data to structural modification in a series of alkyl- and fluoroalkyl- substituted siloxane polymers. Experimental data at 55°C, 70°C, 85°C and essentially atmospheric pressure for each solute in the siloxane polymer systems at infinite dilution are presented. Infinite-Dilution pseudo activity coefficients (Ω∞) and thermodynamic quantities (e. g., ∆Hm, ∆Gm, ∆Sm) were obtained from data taken at 55°C, 70°C and 85°C. The significance of the results to melting transition in polymers, glass transition in polymers, polymer solubility, and the effect of polymer structural modification with solubility are discussed. It is concluded that gas chromatography is a valuable tool for studying the structure of polymers and their interaction with compounds of lower molecular weight.Item Thermally-responsive interpenetrating polymer network nanoparticles as intelligent therapeutic systems(2006) Owens, Donald E., 1979-; Peppas, Nicholas A., 1948-; Richards-Kortum, Rebecca, 1964-