This thesis describes the covalent modification of carbon electrodes with a monolayer of polymerisation initiators and the growth of polymer brushes by surface initiated atom transfer radical polymerisation (SI-ATRP). Monolayer modification was sought to preserve the underlying electrode properties and topography and to produce a well-organised layer from which the polymer brushes can be grown. This work investigated two approaches for immobilising a monolayer of polymerisation initiators. Firstly, the electrochemical grafting of protected aryl diazonium salts produced a covalently anchored monolayer of tether groups that can participate in subsequent amide coupling and click reactions, to covalently anchor the polymerisation initiator. Secondly, specific reactions between the electrode surface and appropriate polymerisation initiator derivatives have been used to covalently anchor the initiators. For most systems, electro-active ferrocene (Fc) groups were reacted with modified surfaces as model reactants to enable the electrochemical estimation of the surface concentration of the polymer initiator groups. Film thickness measurements of the ethynylaryl (Ar-Eth) monolayer were carried out using atomic force microscopy confirming a monolayer. XPS analysis confirmed the presence of bromine on most of the polymerisation initiator modified samples. Modification of surfaces with polymer brushes can introduce new surface properties, such as switchable wettability, while maintaining the underlying bulk substrate properties. This work focused on examining SI-ATRP at each of the polymerisation initiator monolayers, with the aim to identify the most promising system(s) for further investigation. Polymer brushes of poly(3-(methacryloylamino)propyl)-N,N’-dimethyl(3-sulfopropyl)-ammonium hydroxide) (PMPDSAH) were grown from initiators tethered through the aryl diazonium salts modification procedure. Redox probe voltammetry and XPS analysis indicated that the grafting from polymerisation by the copper catalysed SI-ATRP was successful. Polymer brushes of poly(methyl methacrylate) PMMA were grown from the Ar-Eth modified monolayer by three SI-ATRP procedures: a standard procedure, an electrochemically mediated SI-ATRP method and a one-pot copper catalysed azide-alkyne click (CuAAC) reaction and SI-ATRP reaction from the Ar-Eth monolayer. Redox probe voltammetry and AFM images provided evidence for the growth of polymer brushes by these three methods. The successful one-pot CuAAC/SI-ATRP reaction for simultaneous coupling of the polymerisation initiator to the surface and polymerisation is a new approach for the production of polymer brushes and it minimises the number of surface modification steps needed. This method appears most promising for further development.

Polymer brushes generated via "grafting-from" approach emerged as an attractive surface modification tool offering chemical stability, synthetic flexibility and unprecedented control over the polymer grafting density, thickness, chemical composition and functionality. They display interesting features to many applications in regenerative medicine including cell culture, tissue engineering and as delivery systems due to exquisite control of physicochemical and biological properties. Cationic polymer brushes are particularly attractive in the field of designing effective vectors for gene delivery as polymer brush allows the design and coating of a variety of particles with well-defined core-shell architecture and chemistry to efficiently condense and deliver nucleic acids. This thesis concentrates on designing safe and efficient gene delivery vectors based on 'graft from' cationic polymer brush and understanding the interaction of nucleic acids with polymer brush. Chapter one presented fundamental knowledge of polymer brush and its biomedical application. The first part of this chapter describes the definition of polymer brush, the preparation strategies, mechanism of atom transfer radical polymerisation and the responsiveness of polymer brush including solvent, pH and ionic strength. The second part discusses the state-of-art applications of polymer brush in regenerative medicine including protein resistant polymer brush for tissue engineering and as drug/gene delivery systems.

Thesis (Ph. D. in Chemistry)--Vanderbilt University, Dec. 2007. / Title from title screen. Includes bibliographical references.

There is an increasing demand for materials that are physically robust, easily recovered, and able to perform a wide variety of chemical functions. By combining hard and soft matter synergistically, organic-inorganic hybrid materials are potentially useful for a number of applications (e.g. catalysis, separations, sensing). In this respect, organic/ordered mesoporous silica (OMS) hybrids have attracted considerable attention, with an increasing emphasis on complex organic moieties achieved through multi-step reactions and polymerizations. It is on this front that we have focused our work, specifically in regard to polypeptides. Polypeptides are well suited organic components for hybrids as they provide a wide range of possible side chain chemistries (NH2, -SH, -COOH, -OH, etc.), chirality, and have conformations that are known to be responsive to external stimuli (pH, electrolytes, solvents, etc.). Our work has shown that N-carboxyanhydride chemistry offers a facile single step approach to the incorporation of dense polypeptide brushes in OMS. Modifying the initiator loading, pore size, pore topology, and monomer identity significantly impacted the properties of the obtained composites and peptide brush layers. Extending this work, a synthesis paradigm for preferentially grafting poly-L-lysine to the external and internal surfaces of SBA-15, a widely used OMS material, was developed. We observed that the pores of these hybrids could be opened and closed by the reversible swelling of the polypeptide layer. Similarly, novel bifunctional hybrids were synthesized by grafting polypeptides to the external surface of monodisperse OMS spheres that contain a thiol-functionalized core. The accessibility of the internal thiols to a fluorescent dye shows the potential of these hybrids for applications such as controlled uptake/release.

This research focuses on the modeling of surfaces decorated by grafted polymers in order to understand their structure, energetics, and phase behavior. The systems studied include flat and curved surfaces, grafted homopolymers and random copolymers, and in the presence of solvent conditions, homopolymer melt conditions, and diblock copolymer melt conditions. We use self-consistent field theory to study these systems, thereby furthering the development of new tools especially applicable in describing curved particle systems and systems with chemical polydispersity. We study a polymer-grafted spherical particle interacting with a bare particle in a good solvent as a model system for a polymer-grafted drug interacting with a blood protein in vivo. We calculate the energy of interaction between the two particles as a function of grafting density, particle sizes, and particle curvature by solving the self-consistent field equations in bispherical coordinates. Also, we compare our results to those predicted by the Derjaguin approximation. We extend the previous study to describe the case of two grafted particles interacting in a polymer melt composed of chains that are chemically the same as the grafts, especially in the regime where the particle curvature is significant. This is expected to have ramifications for the dispersion of particles in a polymer nanocomposite. We quantify the interfacial width between the grafted and free polymers and explore its correlation to the interactions between the particles, and use simple scaling theories to justify our results. In collaboration with experimentalists, we study the behavior of the glass transition of polystyrene (PS) films on grafted PS substrates. Using the self consistent field theory methods described above as well as a percolation model, we rationalize the behavior of the glass transition as a function of film thickness, chain lengths, and grafting density. Grafting chemically heterogeneous polymers to surfaces in melt and thin film conditions is also relevant for both particle dispersion and semiconductor applications. To study such systems, we model a random copolymer brush in a melt of homopolymer that is chemically identical to one of the blocks. We modify the self-consistent field theory to take into account the chemical polydispersity of random copolymer systems and use it to calculate interfacial widths and energies as well as to make predictions about the window in which perpendicular morphologies of diblock copolymer are likely to form. We also explore the effect of the rearrangement of the chain ends on the surface energy and use this concept to create a simple modified strong stretching theory that qualitatively agrees with our numerical self-consistent field theory results. We explicitly study the system that is most relevant to semiconductor applications - that of a diblock copolymer melt on top of a substrate modified by a random copolymer brush. We explore the morphologies formed as a function of film thickness, grafting density, chain length, and chain blockiness, and make predictions about the effect of these on the neutral window, that is, the range of brush volume fractions over which perpendicular lamellae are expected to occur. / text

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The issue of skin friction related injuries has been one of the problems challenging the artificial sports turf industry. It has been identified by users as a major factor impeding acceptance of artificial turf at the professional level. However, information explaining the mechanisms for skin-turf abrasion is limited and little progress has been made, it appears, to derive an appropriate testing method for product approval or in evidence of improvement of the skin-friendliness of these products in sport surface surfaces. This research project focused on exploring the potential for improving the skin-friendliness of artificial turfs through a multi-faceted approach: identifying the contribution of the abrasive-components in modern artificial turf surfaces through mechanical testing; while critically evaluating currently available skin friction standards , evaluating strategies for polymer material modifications to reduce the skin-surface friction; and the designing of an appropriate bench-top set-up for the lab-based assessment of material skin-friendliness. The lack of understanding of skin-turf interaction was addressed by identifying the turf-component that has the greatest influence on the skin-turf friction with the mechanical device used in the current industry standard. The skin -turf frictional profiles of a series of third generation (3G) turf surfaces were examined, in combination with independent measurements of the silicone skin surface roughness pre- and post-friction testing. Results indicated that turf carpets without any infill material exhibited the highest frictional values while surfaces completely filled with either sand or rubber displayed similarly low frictional values, independent of infill type. Morphological measurements also showed the largest decrease in surface roughness for skin samples tested on carpet-only surfaces, indicating a smoothening effect via abrasion. This abrading effect is alleviated with the addition of infill to the surface, with fully-filled surfaces having the least damage to the skin s. This unprecedented study suggests that the carpet may have the largest influence on the overall frictional behaviour of an artificial turf surface narrowing down the turf component to be targeted when applying product improvements to address skin-friendly properties. The strategy of material surface modification was then employed, to study the effect of polyzwitterionic brushes on improving the skin-friendliness of the identified polypropylene substrate. To address the intended application for artificial turfs, a bench-top test was developed to investigate the frictional properties of the hydrated samples outside of commonly used aqueous environments, where an excess of lubricating water molecules is absent. Photo-grafted poly(sulfobetaine methacrylate) (pSBMA) brushes of various irradiation durations were prepared and the improvement in frictional properties was studied. Frictional measurements using silicone skin tips, under both dry and hydrated surface conditions, showed that the applied modification was capable of forming a stable lubrication layer in the absence of excess water, significantly reducing the coefficient of friction by up to 78.8 %. The pSBMA brushes also provided the additional advantage of antifouling exhibiting resistance towards pathogenic Staphylococcus aureus with almost zero surface colonization for well-grafted samples. The low skin -sample friction under ambient conditions and desirable fouling-resistance highlights the potential of pSBMA brushes as a modification strategy for achieving skin-friendly surfaces targeted at reducing the risk of skin abrasions. The tribological implications of counter-surface selection were investigated. Frictional assessments of the pSBMA-modified samples were carried out using standard steel tribo-tips, in addition to the skin tips used. Measurements with the skin tips showed that the hydrated pSBMA brushes were successful in reducing initial skin -sample friction though the effect diminishes with extended testing, attributed to the drying of the interfacial water. The standard steel tribo-tips were unable to reciprocate these results, returning consistently low frictional values regardless of extent of surface modification or hydration. These observations draw attention to the importance of counter-surface selection in frictional assessments, highlighting how appropriate test materials can identify characteristic surface properties while providing an interaction that simulates that of the intended application. The simple experimental set-up used may potentially be enhanced as an intermediate product qualification method in the manufacturing of skin-friendly artificial turf yarns.

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