Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (MSc)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1985. / Vita. Abstract. Includes bibliographical references (leaves 109-112). Also available via the Internet.

Thesis (Ph. D.)--University of Chicago, Dept. of Physics, March 2001. / Includes bibliographical references. Also available on the Internet.

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Several series of reversible physical networks based on polydimethylsiloxane (PDMS) chains and liquid crystalline (LC) structural units were synthesized and studied, which belong to three different architecture types: (1) LC-grafted PDMS (with LC quartets at the grafting sites), (2) LC-end-capped linear PDMS, (3) and linear 'infinite' LC-PDMS copolymers (with alternating LC and PDMS segments). PDMS spacers of different lengths of were tested, as well as 6 different polyaromatic mesogens of azo type and azo-free type. Hydrosilylation coupling of vinyl-functional mesogens, obtained as part of an international cooperation, with commercial Si-H-functional PDMS was employed to synthesize all the studied materials. The copolymers were physically crosslinked by the nano-aggregation of the LC units contained in their macromolecules. The thermotropic properties of the LC-nano-aggregates lent interesting physical properties to the whole material, making some of the copolymers attractive as potential smart materials. The PDMS spacer segments were selected for the sake of their extreme flexibility, which should provide elastic properties to the physically crosslinked copolymers, and also because of their (desired) incompatibility with the mesogens. This latter effect was highly helpful for achieving the...

In this dissertation, experiments are described which elucidate how the ordering of symmetric diblock copolymers affects the dynamics within various geometries. In all studies presented herein, experimental techniques are used to probe the dynamics of symmetric diblock copolymer systems as they progress toward equilibrium and to study the role that nanoscale ordering plays in these processes. In the majority of work presented herein, experiments were performed on symmetric diblock copolymer thin films. This work focuses on the effect of various sample preparation techniques on the equilibration kinetics of lamellar forming films. Films are prepared with varying thicknesses in the homogeneous, disordered state and annealed to form islands and holes as the surface decomposes to form commensurate thicknesses. Both nucleated and spinodal growth patterns were observed for this surface decomposition dependent on the initial thickness and intermediate morphologies formed upon ordering. We also prepare equilibrium commensurate films and induce a step change in surface interactions, switching from asymmetric to symmetric wetting boundaries. Upon equilibration, a perforated lamella forms at the free surface to mediate the order-order transition, inducing hole growth with a ramified shape. In the final project, the effect that lamellar order has on dynamics is studied within unstable polymer melt bridges. Liquid bridges are what is formed when a droplet is stretched between two surfaces, like spit between two fingers. Disordered diblock bridges are shown to evolve similar to their homopolymer counterparts. However, ordered diblock copolymer exhibits an enhanced stability with an inhibition of flow proposed to be induced by the isotropic orientational order within the bridge. As well, shear thinning is observed that is believed to be caused by an alignment of ordered domains along the bridge axis due to shear strain rates, providing pathways for flow of diblock copolymer out of the unstable bridge. / Thesis / Doctor of Philosophy (PhD)

Thesis advisor: Jeffery A. Byers / This dissertation covers the development of redox-switchable ring-opening polymerizations for the synthesis of copolymers of underutilized monomers. In Chapter one, the progress in the development of switchable methods for ring-opening polymerization and ring-opening copolymerizations. Chapter two describes a method for the redox-switchable copolymerization of L-lactide, propylene oxide and carbon dioxide. The benefits of this method are demonstrated through the facile synthesis of blocky and statistical copolymers of the three monomers. In Chapter three, a method for the redox-switchable polymerization of N-carboxyanhydrides is presented. A mechanistic analysis and copolymerizations of N-carboxyanhydrides and either lactones or epoxides follow the initial findings. Chapter four further expands the uses of N-carboxyanhydride redox-switchable polymerizations by immobilizing the catalysts onto semiconductor surfaces for the synthesis of surface bound polyamides. / Thesis (PhD) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

<p> It is well known that complex coacervates can be prepared by combining aqueous solutions of oppositely charged biopolymers, such as gelatin and gum arabic. There are few examples of synthetic polyelectrolytes that produce complex coacervates, however. Two series of anionic copolymers capable of forming complex coacervates with branched polyethylenimine (PEI) in water have been prepared. One series consists of binary copolymers containing methacrylic acid (MAA) and poly(ethylene glycol) monomethyl ether monomethacrylate (PEGMA) in molar ratios ranging from 20:80 to 80:20, as well as the two homopolymers, poly(MAA) and poly(PEGMA). Another series contains an equimolar amount of MAA and PEGMA, together with between one and ten percent of a third, hydrophobic monomer, butyl methacrylate (BMA).</p> <p> Both binary and ternary copolymers show lower critical solution temperatures, LCST's, ranging from 60.8°C to 1.5°C depending on composition. Furthermore, complex coacervation occurs upon addition of aqueous PEI to aqueous solutions of these copolymers. The percent volume of the liquid coacervate phase is independent of copolymer composition. However, with increasing MAA to PEGMA ratio in the binary copolymer, the concentration of the coacervate increases, reflecting an increased coacervation efficiency. The coacervate composition was not significantly affected by the BMA in the ternary copolymer series.</p> / Thesis / Master of Science (MSc)

<p> Attempts to prepare silicone oligonucleotide copolymers are complicated by the large difference in hydrophobicity in the two materials. Two approaches were followed to overcome this challenge. Initially, highly sterically hindered tetraisopropyldisiloxanes were used to bind 5'-0-(4,4'-dimethoxytrityl)-thyrnidine at the 5'-0H. These compounds proved to be hydrolytically more stable than the analogous dimethylsiloxane compounds, which were also prepared. Alternatively, Si-C bonds, which are hydrolytically stable, can be used to bind the two species together. Introduction of allyl ether by traditional Williamson conditions was followed by hydrosilylation with hydride terminated (Si-H) silicone, catalyzed by using platinum complexes, to give the nucleoside-functionalized silicone. We also introduced an epoxy group to one end of a silicone chain and found it to be stable to hydrolysis. Once the epoxy group binds nucleoside-functionalized silicone to solid phase, it is expected that the nucleoside-functionalized silicone via a trimethylene spacer linkage might be a starter for preparation of oligonucleotide-functionalized silicones in future work. </p> / Thesis / Master of Science (MSc)