Browsing by Subject "Copolymers"
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Item Block copolymers for vesicles: self-assembled behavior for use in biomimicry(2009-05-15) Gaspard, Jeffery SimonThe objective of this research is to investigate synthetic and polypeptide block copolymers, the structures they form, their response to various stimuli in solution and their capabilities for use in biomimicry. The self-assembled structures of both polymers will be used as a basis for the templating of hydrogels materials, both in the interior and on the surface of the vesicles. The resulting particles will be designed to show the structural and mechanical properties of living cells. The synthetic block copolymers are a polyethylene glycol and polybutadiene (PEO-b-PBd) copolymer and the polypeptide block copolymers are Lysine and Glysine (K-b-G) copolymers. Investigation of the structures synthetic block copolymers will focus on whether the polymer can form vesicles, how small of a vesicle structure can be made, and the formation of internal polymer networks. Subsequent investigations will look at the needed steps for biomimicry, using the synthetic block copolymers as a starting point and transitioning to a polypeptide block copolymer. The Lysine-Glysine copolymers are a new system of materials that form fluid vesicle structures. Therefore, we must characterize its assembly behavior and investigate how it responds to solution conditions, before we investigate how to make a cellular mimic from it. The size and mechanical behavior of the K-G vesicles will be measured to compare and contrast with the synthetic systems. The goals for creating a biomimic include a hollow sphere structure with a fluid bilayer, a vesicle that has controllable mechanical properties, and a vesicle with controllable surface chemistry. Overall, these experiments were a success; we showed that we can effectively control the size of vesicles created, the material properties of the vesicles, as well as the surface chemistry of the vesicles. Investigations into a novel polypeptide block copolymer were conducted and the block copolymer showed the ability to create vesicles that are responsive to changing salt and pH concentrations.Item Mechanistic studies of the metal catalyzed formation of polycarbonates and their thermoplastic elastomers(2009-05-15) Choi, WonsookStudies concerning the formation of industrially useful polycarbonates are the focus of this dissertation. Of particular importance is the biodegradable polymer, poly(trimethylene carbonate) which has a wide range of medical applications. The production of polycarbonates can be achieved by the ring-opening polymerization of cyclic carbonate, or the copolymerization of carbon dioxide and oxiranes or oxetanes. For the production of polycarbonates from these monomers, Schiff base metal complexes have been designed, synthesized, and optimized as catalysts. Detailed kinetic and mechanistic studies have been performed for the ring-opening polymerization of cyclic carbonates, as well as the copolymerization of carbon dioxide and oxiranes or oxetane. In addition, the copolymerization of cyclic carbonates and cyclic esters to modify the mechanical and biodegradable properties of materials used for medical devices has been studied using biocompatible metal complexes. In the process for ring-opening polymerizations of trimethylene carbonate or lactides, Schiff base metal complexes (metal = Ca(II), Mg(II) and Zn(II)) have been shown to be very effective catalysts to produce high molecular weight polymers with narrow polydispersities. Kinetic studies demonstrated the polymerization reactions to proceed via a mechanism first order in [monomer], [catalyst], and [cocatalyst] if an external cocatalyst is applied, and to involve ring-opening by way of acyl-oxygen bond cleavage. The activation parameters (?H?, ?S? and ?G?) were determined for ringopening polymerization of trimethylene carbonate, ring-opening polymerization of lactides, and copolymerization of trimethylene carbonate and lactide. In the process for copolymerization of carbon dioxide and oxetane, metal salen derivatives of Cr(III) and Al(III) along with cocatalyst such as n-Bu4NX or PPNX (PPN = bis(triphenylphosphine)iminium, and X = Br, Cl and N3) have been shown to be effective catalysts to provide poly(trimethylene carbonate) with only trace amount of ether linkages. The formation of copolymer is proposed not to proceed via the intermediacy of trimethylene carbonate, which was observed as a minor product of the coupling reaction. To support this conclusion, ring-opening polymerization of trimethylene carbonate has been performed and kinetic parameters have been compared with those from the copolymerization of carbon dioxide and oxetane.Item Synthesis & characterization of temperature- and pH- responsive nanostructures derived from block copolymers containing statistical copolymers of HEMA and DMAEMA(2008-05) Guice, Kyle B., 1982-; Loo, Yueh-Lin, 1974-; Sanchez, Isaac C.Hydrogels containing of 2-dimethylaminoethyl methacrylate, DMAEMA, exhibit changes in their swelling properties in response to both pH and temperature. Accordingly, these materials are useful for a variety of applications, such as tissue scaffolds, responsive lenses, separations and drug delivery. The response of DMAEMAcontaining hydrogels can be tuned by copolymerization with other monomers, such as 2-hydroxyethyl methacrylate, HEMA. We have developed methodologies for the controlled synthesis of poly(HEMAco-DMAEMA), PHD, statistical copolymers with uniform composition distributions, controlled molecular weights, and narrow molecular weight distributions using controlled free-radical polymerization techniques, such as atom transfer radical polymerization and radical addition-fragmentation chain transfer polymerization. We have also investigated the controlled synthesis and characterization of amphiphilic block copolymers containing PHD statistical copolymers. These block copolymers microphase separate to form periodic nanostructures such as alternating lamellae, cylinders on a hexagonal lattice, or spheres on a body-centered cubic lattice, depending on the volume fraction of each block, the interblock segregation strength, and the choice of casting solvent. When swollen with water, these microphase-separated PHD-containing block copolymers form model hydrogels with uniform composition distributions. Model block copolymer hydrogels containing PHD statistical copolymers are responsive to changes in pH or temperature. The response of these model block copolymer hydrogels can be tuned by adjusting of the DMAEMA content within the PHD block. Moreover, the response can be tuned by changing the hydrophobic block. Specifically, the use of a glassy hydrophobic block, such as polystyrene or poly(tert-butyl acrylate) at temperatures below its glass transition temperature, resulted in the preservation of the original block copolymer morphology during swelling. In contrast, the use of a hydrophobic block that is rubbery during swelling, such as poly(methyl acrylate), enabled reversible morphological transformations.