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Structures and Properties of Brush Polymers Bearing Biomolecules

Structures and Properties of Brush Polymers Bearing Biomolecules
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Polymer materials have several advangtages such as easy process at low cost, high flexibility, high mechanical strength, and good scalability. Furthermore, their properties can be controlled by various syntheic methods. Through chemical bonding of specific molecules to the polymer backbone, side chain or functional groups, the function of polymer can be changed. First brush polymers were reported as aliphatic polymers with n-alkyl side chains in the 1940s.The n-alkyl side chains have self-assembly character. The macroscopic properties on film surfaces were managed through control of microscopic structures in polymer structure by self-assembly character. In consideration of high potential application of various brush polymer system, such as biomaterials, microelectronics, solar cells, adhesives, and gas separation membranes, the structure analysis with surface characteristic is very important. In the area of biomaterials, biomolecule-mimicking brush polymers may be useful in a variety of solid forms as biocompatible coating materials, tissue culture materials, biomedical sensor materials, protein separation membranes, and gene delivery carriers. Most of these applications require formation of nanoscale thin films with control over the nanostructures. In Chapter II, A series of well-defined brush polymers with quaternary ammonium were synthesized. These polymers have self assembled structure by interaction of quaternary ammonium groups and from multi-layer structures, providing hydrophilic cationic surfaces. Because of quaternary ammonium groups and long brush alkyl chain, the polymer films have bactericidal properties and selective protein adsorption properties by positively charged surfaces. However, in vitro and in vivo result of each polymers were different. The polymer which has high amount of QA showed unfavorable environment to cells but the polymer with a small number of quaternary ammonium showed good biocompatibility. These results indicate that the control of surface characters by functional groups of brush polymers and self assembled characters are important for biomedical applications. In Chapter III, X-ray reflectivity (XR) study of brush polymers with various number of bristle ends incorporating phosphorylcholine (PC) moieties was performed in thin films supported on silicon substrates. As a result of self assembled structure, Bragg reflections were observed and a quantitative analysis was conducted for multilayer structure using Parratt formalism. This analysis provides detail information about structure and interface across the film thickness of the lamellar structure with varying mole fraction of PC moieties. The structures of the polymer thin films were extensively changed as adding the PC moieties and increasing mole fraction at the alkyl side end. As a result, highly ordered multilayer lamellar structure was leaded. In Chapter IV, In this study, neutron reflectivity study of brush polymers with bristle ends incorporating phosphocholine (PC) moieties was performed in dry, liquid, and protein solution on quartz substrate. Before neutron reflectivity measurements, X-ray reflectivity measurements were carried out to confirm the multilayer structure of each film and film conditions. As a result of self-assembled structure, strong Bragg peaks were observed in both X-ray reflectivity and neutron reflectivity measurement. Though certain Bragg peaks in liquid condition was not shown because of water swelling, surface of polymer films were shown excellent functional character. Indeed, thickness variation by water sorption was also well displayed difference of functionalized polymers. As a result, protein resist surface was leaded by self assembled structure. In Chapter V, In this study XR study of brush polymers was performed on water surface. By the mixing of hydrophilic and hydrophobic group, different structure transitions were shown during surface compression. The thickness of LB monolayer was confirmed by XR and structure model was supported by IR measurement. Alkyl chain packing and disordering was observed and hydrogen bonding between polymer and water was also observed. Inverse structure and double layer structure were suggested for each polymer at high surface pressure area to agreement with experiment results. As a result, unique LB monolayer structure was purchased. In Chapter VI, XR studies were conducted to characterize the thin films of brush polymers with various number of bristle ends incorporating 0, 25, 50, 75 and 100 % of quaternary ammonium (QA). The films were coated on silicon wafer substrates by spin-coating. Because of interaction of QA ends and alkyl chain, each polymer has self assembled multi layer structure and Bragg reflections were observed. The results indicate that structure of polymer films were dramatically changed as adding the QA ends. Especially, due to the carboxylic group between alkyl chain and QA, bent alkyl chain structures with crystalline QA groups or stand alkyl chain structure with interdigitate QA groups were presented. These analysis provide detail information about structure and interface across the film thickness of the lamellar structures.
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