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Title:Synthesis and kinetic processes in designed polymers
Author(s):Miller, Kali A.
Director of Research:Braun, Paul V.
Doctoral Committee Chair(s):Braun, Paul V.
Doctoral Committee Member(s):Evans, Christopher M.; Moore, Jeffrey S.; Zimmerman, Steven C.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Surface-initiated atom transfer radical polymerization
Polymer brushes
Silicon photonics
Acid amplified chain-shattering degradation
Fast relaxation imaging
Micro fabrications
Surface-enhanced infrared absorption spectroscopy
Abstract:Traditional polymers have been long used for commercial products from polyester shirts to polyvinyl chloride (PVC) pipes or even polytetrafluoroethane (Teflon) non-stick coatings. As the needs of our society grow and change, innovative solutions must be created to overcome the challenges that industry faces today. New polymers must be designed and engineered to perform specialized functions, improve on existent properties, or respond to changes in the environment. This thesis focuses on the synthesis and characterization of such polymer systems, with specific considerations for their kinetic processes. Selected material systems are individually described in paragraphs below, with applications in membranes and protective coatings, degradable materials, transport and concentration, and biocompatibility. Silicon photonic microring resonators have emerged as a promising technology for the sensitive detection of toxic and regulated substances. By functionalizing the surface of silicon photonic microring resonators with polymer brushes, we find that small molecules can selectively partition into the surface-confined sensing region of the optical resonators. This strategy leads to response enhancements in excess of 1000% percent, relative to non‐functionalized sensors, for representative targets including 4‐methylumbelliferyl phosphate, a simulant for highly toxic organophosphates, Bisphenol A, an industrial pollutant, as well as other small organic analytes of interest. Additionally, brush-modified resonators can be used utilized as a platform for the in-situ characterization of hydrophobic, hydrophilic, and stimuli-responsive polymer brush surfaces. Diffusion and partitioning of small molecules into the brushes was observed in real-time and conformation changes were quantified by measuring and fitting shifts in the resonance wavelength. With these techniques, we showed not only quantification of solvent compatibilities based on small molecule transport through the brush interface, but also extraction of polymer brush pKa as a function of brush length and solvent conditions. Thus, we also demonstrate that our technique allows for accessible characterization of diverse polymer layers in the present of complex analyte solvent interactions. The simultaneous growth in waste plastics, 3D-printing, and implantable biomaterials has challenged chemists to develop new polymers able to meet the demands of real-world applications. In particular, there is increasing demand for smart polymers that change their shape or properties or degrade in response to environmental stimuli. A renewed interest in degradable polymers, especially for biomedical and engineering applications has led to an extensive search for new mechanisms to breakdown polymers. Herein, we introduce the 3-iodopropyl acetal moiety as a simple cleavable unit that undergoes acid catalyzed hydrolysis to liberate HI and acrolein stoichiometrically. We show that integrating this unit into linear and network polymers gives a class of macromolecules that undergo a new mechanism of degradation with an acid amplified, sigmoidal rate. This trigger-responsive self-amplified degradable polymer undergoes accelerated rate of degradation and agent release. Fast relaxation imaging (FReI) is introduced as a novel technique to detect protein unfolding in situ by imaging changes in fluorescence resonance energy transfer (FRET) after temperature jump perturbations. Unlike bulk measurements, diffraction-limited epifluorescence imaging combined with fast temperature perturbations reveals the impact of local environment effects on protein-biomaterial compatibility. Our experiments investigated a crowding sensor protein and phosphoglycerate kinase to quantify the confinement effect of the cross-linked hydrogel and reveal the effect of noncovalent interactions of the protein with the polymer surface. Additionally, we demonstrate that a biomedically-relevant zwitterionic polymer in solution can interact with proteins directly through utilizing fluorescence techniques. Polymer-dependent changes in the tryptophan fluorescence spectra of three structurally-distinct proteins reveal that the polymer interacts directly with all three proteins and changes both the local polarity near tryptophan residues and the protein conformation. Thermal denaturation studies show that the protein melting temperatures decrease and that protein folding cooperativity increases upon interaction with the polymer. We demonstrate the exact extent of the changes is protein-dependent, as some proteins exhibit increased stability, whereas others experience decreased stability at high polymer concentrations. These results suggest that the polymer is not universally protein-repellent and that its efficacy in biotechnological applications will depend on the specific proteins used. Vibrational resonances of microelectromechanical systems can serve as means for assessing physical properties of ultrathin coatings in sensors and analytical platforms. Most such technologies exist in largely two-dimensional configurations with a limited total number of accessible vibration modes and modal displacements, thereby placing constraints on design options and operational capabilities. Our study presents a set of concepts in 3D microscale platforms with vibrational resonances excited by Lorentz-force actuation for purposes of measuring properties of thin-film coatings. Nanoscale films including photodefinable epoxy, cresol novolak resin, and polymer brush with thicknesses as small as 270 nm serve as the test vehicles for demonstrating the advantages of these 3D MEMS for detection of multiple physical properties, such as modulus and density, within a single polymer sample. The stability and reusability of the structure are demonstrated through multiple measurements of polymer samples using a single platform, and via integration with thermal actuators, the temperature-dependent physical properties of polymer films are assessed. Numerical modeling also suggests the potential for characterization of anisotropic mechanical properties in single or multilayer films. The findings establish unusual opportunities for interrogation of the physical properties of polymers through advanced MEMS design. Nanoantenna-based surface-enhanced infrared absorption is a powerful platform for the detection of biological and chemical species due to its ability to strongly enhance infrared absorption of a relatively narrow band of vibrational modes. However, SEIRA only detects molecules within order of 100 nm of the nanoantenna, and thus requires diffusion of analyte into the local vicinity of the nanoantenna to provide enhanced sensing. Here, we demonstrate the use of a polyacrylamide hydrogel film with imbedded radial chemical gradient to locally concentrate analytes in the local vicinity of SEIRA-active nanoantenna to improve the detection limit over that provided by SEIRA along. Using a positive charge gradient, embedded in a hydrogel film, a nerve agent simulant, 4-methylumbelliferyl phosphate, was concentrated 15-fold above a SEIRA active array of nanoantenna. The combined effect of molecular concentration and SEIRA resulted in the potential ability to detect the agent of interest at concentrations two orders of magnitude below that provided by ATR using a conventional, gradient-free substrate.
Issue Date:2019-06-19
Rights Information:Copyright 2019 Kali A. Miller
Date Available in IDEALS:2019-11-26
Date Deposited:2019-08

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