Doctoral Dissertations

Date of Award

8-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

S. Michael Kilbey

Committee Members

Michael D. Best, Bin Zhao, Gila E. Stein

Abstract

Polymeric materials possessing specific functionality have been designed for use in applications such as membranes, biocompatible coatings, lubricants, and tissue engineering. Because the chemical nature of the repeat units set the properties offered by the polymer, the ability to reactively modify polymer chains to integrate specific functionality expands the range of potential applications. Thus, reactive modification of polymer thin films provides a useful route to confer new properties to the underlying material, with the range, strength and type of interaction across the interface dictated by the display of functional groups decorating the surface. To address the links between design, in situ functionalization, and properties, layers of end-tethered polymer chains, or polymer brushes, were created by grafting chains of poly (2-vinyl-4,4-dimethyl azlactone) (PVDMA) onto silicon substrates. The pendant azlactone rings of PVDMA readily react with nucleophiles, allowing in situ functionalization to be studied through the use of ellipsometry and neutron reflectivity measurements as a function of parameters that affect brush structure. The results indicate that the grafting density of chains and size of the functionalizing agent govern the extent of functionalization. In addition to an average view of the in situ functionalization process gained through ellipsometry measurements, the sensitivity of neutron scattering methods to isotopic substitution (of D for H) provides detailed insight into the location and amount of functional groups installed within the PVDMA brush by reactive modification. The resulting design-structure-property relationships provide a systematic basis for creating polymeric materials with desired properties, and this theme is advanced by the development of surface gradients. Designing and using gradient surfaces is an efficient approach for screening a wide variety of conditions and optimizing the extent of chemical functionality, which alters surface properties delivered by reactive modification. All of these studies yield relationships between extent of reaction in the confined environment (in a brush or thin film), the spatial display of functional motifs, and the swelling properties of the interfacial layer, as well as insight into general strategies that can be used to tailor frictional, adhesive, or biomimetic properties of polymer interfaces.

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