Master of Science, Miami University, 2024, Chemistry and Biochemistry

Chapter 1 introduces carbodiimide-driven anhydride formation from carboxylic acids, a useful reaction in a variety of non-equilibrium systems. It also introduces established techniques for regulating this reaction. Multiple strategies to control deactivation (anhydride hydrolysis) rates have been reported, but control over activation (anhydride formation) rates is limited. It also explores the role that pyridine already plays within established carbodiimide systems. Chapter 2 explores the reversible reaction of pyridine derivatives with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide methiodide in water to form adducts. These adducts are unreactive with carboxylic acids and thus reduce the anhydride formation rate while prolonging carbodiimide lifetime. The best results are obtained with 4-methoxypyridine. We demonstrate that this strategy can be used to control the formation of transient polymer network hydrogels, in one example increasing the time to reach peak modulus by 86% and the lifetime by 43%. Chapter 3 concludes and summarizes the work completed in Chapters 1-2 and provides future directions and opportunities with the carbodiimide adduct system. The appendix includes supporting information.

Committee: C. Scott Hartley (Advisor); Dominik Konkolewicz (Committee Member); Rock Mancini (Committee Member); David Tierney (Committee Member) Subjects: Chemistry; Organic Chemistry

Master of Science in Polymer Engineering, University of Akron, 2017, Polymer Engineering

Star polymers have been widely used in our lives. One of the more well-known applications for which star polymers in solution are widely used is hydrogels. Star polymers are used here because it is easier for them to form a network. A hydrogel is a chemically or physically crosslinked, water-swollen, natural or synthetic network. Because of their outstanding bio-compatibility and water solubility,hydrogels have the potential to transform many biomedical applications, including contact lenses, wound dressing, drug delivery and tissue engineering. But some problems limit the development of hydrogels - high expense and low mechanical properties. The first goal of this research is to focus on star polymer properties in the melt. As opposed to the star polymers in solution, we will use molecular dynamics to simulate the star polymer in the melt, with an interest in studying dynamics. Will the relaxation times of the star polymers change for different shapes of linear chain?Will star polymers have different dynamics in the vicinity of the center as compared to the free ends? Will the glass transition temperature fit with the free volume theory of Flory and Fox? Then we will study star polymers in solution, forming cross-linked hydrogels connected by permanent chemical bonds. We will kinetic control different variables to demonstrate how the chemically crosslinked network changes and what the structual features are. The simulation will be done on two kinds of hydrogels, reversible and irreversible, using Brownian dynamics to simulate the environment of crosslinking process. The variables are initial concentration, then length of precursor polymer and the rate of reaction. With the help of LAMMPS, AMDAT and MATLAB software, we hope to fully understand different properties of the star polymer in the melt and solution.

Committee: David Simmons (Advisor); Kevin Cavicchi (Committee Member); Min Younjin (Committee Member) Subjects: Engineering; Polymers