UTILIZING FUNCTIONALIZATION TO ACCESS ADVANCED MATERIALS PROPERTIES Public Deposited

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  • March 19, 2019
Creator
  • Jackson, Anne-Martine
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • While there are many materials that can perform a single selected task very well, there is a growing need for smart materials to advance technology in a variety of fields. Smart materials are often inspired by complex biological systems, and thus need to respond to external stimuli and perform multiple functions. It is desired that these materials have the ability to respond to changes in temperature, pressure, pH, light, magnetic field and the presence of other chemicals. A few of the functions that these materials are to perform include sensing, actuating, self-healing, recognition, self-cleaning, and optical switching. To produce materials with the range of tasks that are needed, new and elegant ways to integrate functionality into polymeric systems are needed. Functionality can be integrated into existing polymers either chemically or physically. When modifying an existing polymer chemically, the chemical functionality as well as the placement needs to be considered. The same chemical moiety integrated either into the bulk, on the surface or as an endgroup will achieve drastically different effects. Alternatively, to introduce physically functionality, a material must be able to change potential energy, topography or mechanical properties upon the application of an external stimulus. In both cases, the properties of a material and the functions that it can perform are highly dependent on structure and the molecular functionality of the polymer. This thesis describes the functionalization of polymeric materials via three synthetic routes, surface, bulk and endgroup functionalization, to achieve unique physical and chemical properties. Specifically, grafting of polymeric brushes was utilized to achieve simultaneous control of surface wetting and wrinkling effects (Chapter I), unique iodinated monomers were copolymerized with methyl methacrylate to achieve bulk x-ray contrast in bone cement materials (Chapter II), and aromatic polyesters were endcapped with ureidopyrimidinone moieties to achieve end-functionalized materials with variable properties (Chapter III). Grafting of polymeric brushes from surfaces has been extensively investigated on static surfaces, but studies of brushes on physically mobile surfaces have been limited. Chapter I will investigate the wrinkling effects observed after grafting a shape memory substrate in a strained conformation with poly(oligo ethylene glycol) methacrylate brushes. Using this method, we have been able to systematically change the contact angle of the surface as a function of grafting time and induce wrinkled topographical features on the surface due to the system's inherent strain. Two types of wrinkling were observed. In the temporary shape, randomly oriented wrinkles with sizes of 4.9-6.2 μm were formed during brush synthesis due to swelling/deswelling of the substrate. Linear wrinkles with wavelengths of 27-33 μm were observed when the grafted substrate underwent a shape memory transition to return to the primary shape due to the strain difference between the substrate and the brush layer. This is the first report of grafting from a shape memory material demonstrating that shape memory and anisotropic polymer brushes can create wrinkles on multiple length scales, forming complex surface topographies with controllable wetting behavior. In Chapter II, an intrinsically radiopaque monomer was synthesized and incorporated into acrylic bone cements to aid in the in vivo visualization of bone cement materials. Acrylic bone cements are most commonly comprised of radiolucent poly(methyl methacrylate) (PMMA) and inorganic fillers (e.g. BaSO4 or ZrO2). While the inorganic fillers aid in the in vivo x-ray visualization of these materials, they also have deleterious effects on the mechanical and biological properties. To avoid the use of inorganic fillers, the copolymerization of a novel, non-aromatic iodine-containing monomer with methyl methacrylate was employed to synthesize intrinsically radiopaque bone cements. The kinetics of the suspension copolymerization were studied, and the results confirmed that the polymerization proceeds in a random fashion. In addition, we show that these materials have excellent x-ray contrast, ~4x that of PMMA, at 16 mol% incorporation. Importantly, the mechanical properties of the formulated bone cements utilizing the iodine-containing copolymer do not significantly differ from the PMMA materials. This is the first report of a wholly aliphatic iodine-containing monomer being used in bone cement materials, and shows promise to create materials with excellent x-ray opacity and mechanical properties. In Chapter III, the structure-property relationships of an aromatic polyester, poly(ethylene terephalate) (PETG), with glycol modifications and hydrogen bonding endgroups are investigated. The ureidopyrimididone (UPy) group, a quadruple hydrogen bonding moiety, has been used extensively to end-functionalize low molecular weight, low glass transition temperature polymers to create supramolecular telechelic materials with improved tensile properties and thermoreversibility. High molecular weight engineering plastics have excellent properties, but are often difficult and expensive to process, so creating low molecular weight materials with similar mechanical properties to high molecular weight materials is highly desirable. While the effect of the UPy endgroup has been investigated on many aliphatic materials, the effect of these groups has not been broadly investigated for high performance aromatic polymers with glass transition temperatures. We show that endgroup functionalization of low molecular weight PETG with the UPy moiety enhanced mechanical properties.
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  • In Copyright
Advisor
  • Sheiko, Sergei
  • Lopez, Rene
  • You, Wei
  • Ashby, Valerie
  • Nicewicz, David
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2015
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  • Chapel Hill, NC
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