Date of Award

Fall 2020

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

First Advisor

Brian C. Benicewicz

Abstract

The modification of inorganic nanoparticles with organic polymer chains has become a significant field of study for the engineering of advanced nanocomposite materials. This dissertation presents the design, synthesis, and characterization of novel polymer grafted silica nanoparticles as new strategies to combat bacterial resistance. Described herein is the synthesis of monomers that have been graft polymerized onto silica nanoparticles that can be used as a delivery drug vehicle for biomedical applications. The polymerization of these monomers was performed via reversible addition-fragmentation chain transfer (RAFT) polymerization. The molecular design of the RAFT agents that are attached to the surfaces of the nanoparticles has the main role in controlling the molecular weight and dispersity of the polymer chains grafted to the surface of the nanoparticles. The method of attachment of the RAFT agents additionally controls the surface graft density. The important properties of nanocomposites can be exploited in many different areas, such as biomedical applications.

In the first chapter of this work, the overall background of antimicrobial polymers, the functionalization of nanoparticles using RAFT polymerization, and the concept of the modification of silica nanoparticles to afford a bimodal brush system is described. The second chapter focuses on designing a new type of stimulus-responsive polymer that can work as antibiotic-delivery carriers in biomedical applications. We reported pH-responsive “controlled release” polymers that were grafted on silica nanoparticles using reversible addition-fragmentation chain transfer (RAFT) polymerization. Two monomers 2-((2-(propionyloxy) propanoyl)oxy)ethyl methacrylate (HEMA-LA) and 4-(2-(methacryloyloxy)ethoxy)-4-oxobutanoic acid (HEMA-SA), containing hydrolytically sensitive ester linkages were synthesized to functionalize on the surface of silica nanoparticles. The degradation rate was monitored by attaching dyes at the end of these monomers in each repeat unit to study the release rate, thus assessing the use of these monomers as delivery vehicles for anti-bacterial applications.

In the following chapter, bimodal polymer chains grafted on the surface of silica nanoparticles was developed via RAFT polymerization to create water-dispersible nanoparticles that have additional advantages as antibiotic-delivery vehicles in biomedical applications. Two different polymer chains populations were attached to silica nanoparticles; the first population is high graft density with low molecular weight, which is a pH-responsive controlled release polymer derived from two possible monomers (HEMA-LA) and (HEMA-SA), both containing a hydrolytically sensitive ester linkage: the second population is a water-dissolvable polymer of methacrylic acid (MAA) at low graft density with high molecular weight. Fluorescent dyes were conjugated to the controlled release polymers to monitor the nanoparticles in biological systems.

Finally, in the fourth chapter, we described a new approach using two different RAFT agents, 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPDB), and 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDSS) to create bimodal polymer brush grafted nanoparticle. These novel bimodal brush silica nanoparticles were designed successfully to combat antibiotic-resistant bacteria. The first population polymer brush is based on two potential “controlled release” monomers 2-((2-((2-hydroxy propanoyl)oxy) propanoyl)oxy) ethyl methacrylate (HEMA-LA), 2-(methacryloyloxy)ethyl succinate (HEMA-SA) containing a hydrolytically sensitive ester linkage as a high graft density, short brush to work as antibiotic-delivery carriers. However, the second population polymer brush was based on a sugar-containing monomer, 2-methacrylamido glucopyranose (MAG), as a low graft density, long brush to enhance bacterial uptake of nanoparticles.

Included in

Chemistry Commons

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