Doctor of Philosophy, University of Akron, 2023, Polymer Science

Polyurethanes are a versatile class of polymers that have been used in various applications ranging from coatings to medical devices. The chemical structure of polyurethane can be modified to obtain desired properties. Herein, we demonstrated the ability to modulate functional groups of polyurethanes to tailor their properties in two platforms, segmented polyurethane for degradable biomaterials and random polyurethane copolymers for enhancing the antimicrobial action of antibiotics. Medical devices made from segmented polyurethanes are generally bio-inert and have very low surface wettability. Although there are multiple approaches being employed for surface functionalization, each approach has significant deficiencies such as low surface functionalization or the need for complicated processes. Through this work, I was seeking to improve our fundamental understanding of how bulk functionalization will affect the presence of functional groups at the surface. The work sought to correlate the positional variation of the cationic amine group in either the soft or hard segment to the mechanical and surface properties of modified segmented polyurethanes. Furthermore, the degradation profile of cationic segmented polyurethanes in oxidative and hydrolytic environments was examined and correlations between the degradation profile and the the polyurethane compositions were developed. Antibiotic-resistant bacterial infections are one of the most pressing problems costing billions of dollars to the healthcare system. In particular, gram-negative bacterial infections are challenging to cure since gram-negative bacteria have an outer membrane acting as a selective membrane barrier. This work demonstrates how cationic polyurethanes can act as an outer membrane destabilizer. This work shows that the combination of a cationic polyurethane along with an antibiotic that is not able to traverse an intact outer membrane, is an effective treatment for multi-drug resistant bac (open full item for complete abstract)

Committee: Abraham Joy (Advisor); James Eagan (Committee Chair); Hazel Barton (Committee Member); Weinan Xu (Committee Member); Kevin Cavicchi (Committee Member) Subjects: Chemistry; Microbiology; Plastics

Doctor of Philosophy, University of Akron, 2018, Polymer Science

The emergence and increasing incidence of drug resistant strains of bacteria is a serious threat to human health. There is an urgent need for the development of new antimicrobial agents to combat bacterial infections that are different from the currently used small molecule drugs. Antimicrobial peptides, a broad family of peptides that are utilized by virtually every organism, are a promising source for new antimicrobial agents to fight pathogenic microorganisms. However, there are many limitations to the widespread use of these peptides, such as the cost of mass production and their rapid degradation in vivo by endogenous proteases. One viable way to overcome these limitations is through using synthetic mimics of these peptides. This work details the design of a new family of antimicrobial, water-soluble polyurethanes that were synthesized to mimic antimicrobial peptides using easily functionalized diols and the subsequent study of their in vitro antimicrobial properties. Studies were performed to determine the effects that a broad range of hydrophobic, uncharged polar, and charged polar pendant groups as well as the effects of molecular weight on the structure/property relationships of these antimicrobial polymers and how they impact antimicrobial efficacy, mammalian cell cytocompatibility, and mechanisms of action.

Committee: Abraham Joy Dr. (Advisor); Nita Sahai Dr. (Committee Chair); Hazel Barton Dr. (Committee Member); Li Jia Dr. (Committee Member); Michael Konopka Dr. (Committee Member) Subjects: Microbiology; Polymers

Doctor of Philosophy, University of Akron, 2006, Polymer Science

Carbon nanofiber (CNF) and carbon nanotube (CNT) composites have interesting mechanical and electrical properties that make these composites interesting for reinforcing applications. These applications require good dispersion of CNF within a polymeric matrix. Presently high shear methods, such as twin screw extrusion, are used to make well dispersed CNF composites but these methods reduce the physical properties due to a reduction in the aspect ratio of the CNF. Low shear methods to functionalize CNT and CNF have been used to obtain good dispersion while maintaining the high aspect ratio. In this research three ways of making CNF/polymer composites by low shear methods were explored. The first reaction used bisphenol A cyclic carbonate oligomer as a low molecular weight precursor. The oligomers were polymerized to disperse the CNF within the matrix. These composites were characterized by electrical resistivity, transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravametric analysis (TGA) and gel permeation chromatography (GPC). The composites had a percolation threshold at 6 wt % CNF decreasing the resistivity to 10 4ohm•cm. The second way used heterocoagulation where a cationic polystyrene latex was combined with anionically charged oxidized CNF. The composites were melt pressed and characterized using electrical resistivity, SEM, and TGA. The percolation threshold was 2 wt % and the resitivity dropped to 10 6ohm•cm. Finally, it was found that synthesizing a hyperbranched polyol was possible by chemically modifying oxidized CNF with glycidol and BF 3OEt 2. The resulting polyol CNF were characterized by TGA, Fourier transform infrared spectroscopy (FTIR), TEM, and X-ray photoelectron spectroscopy (XPS). The OH groups were reacted with heptafluorobutyryl chloride to determine the amount of OH in the sample. The resulting fluorinated composite was characterized by FTIR and elemental analysis. The amount of OH for the polyol CNF increased (open full item for complete abstract)

Committee: William Brittain (Advisor) Subjects: Chemistry, Polymer