Date of Award
12-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
School
Polymer Science and Engineering
Committee Chair
Dr. Jeffrey Wiggins
Committee Chair School
Polymer Science and Engineering
Committee Member 2
Dr. Xiaodan Gu
Committee Member 2 School
Polymer Science and Engineering
Committee Member 3
Dr. Zhe Qiang
Committee Member 3 School
Polymer Science and Engineering
Committee Member 4
Dr. Sergei Nazarenko
Committee Member 4 School
Polymer Science and Engineering
Committee Member 5
Dr. Derek Patton
Committee Member 5 School
Polymer Science and Engineering
Abstract
Benzoxazines represent a versatile class of thermosets with tunable thermal and mechanical performance, yet rational design remains challenging due to the complex polymerization and network formation. In this dissertation, a systematic evaluation of monomer purity, meta substitution, and backbone molecular weight in diamine-based benzoxazines was conducted to investigate their effects on melt processability, network development, and structure–property relationships.
Six benzoxazine monomers derived from aryl ether diamines were synthesized, with controlled levels of meta substitution and varying numbers of ether-bridged phenyl rings. Meta substitution was found to suppress crystallinity in high-purity benzoxazine monomers and lower onsets of polymerization were observed due to meta positioning of the terminal diamine rings. Terminal diamine meta substitution also led to higher polymerization enthalpies, attributed to the emergence of a secondary polymerization mechanism, which increased the glass transition temperature up to 75 °C and delayed the onset of mass loss degradation. At high glass transition temperatures approaching 200 °C, however, degradation of Mannich bridges during cure imposed an upper bound on achievable network stability.
Degradation of polybenzoxazines was further explored in reference to the production of polymer-derived carbon. TGA revealed that meta substitution of nitrogen increased effective carbon yield when compared to para substitution. Further analysis with x-ray diffraction of carbon derived from polymerization and pyrolysis of high-purity benzoxazine monomers revealed that aromatic substitution and molecular weight between cross-links have little impact on the resulting size of graphitic crystallites. Together, these findings help establish molecular-level design rules that link benzoxazine structure, polymer network evolution, and carbon microstructure, providing a framework for the rational design of next-generation benzoxazines for extreme environments.
Copyright
Charles M. Davis, 2025
Recommended Citation
Davis, Charles M., "Network Formation and Thermal Degradation of Aryl Ether Diamine Polybenzoxazines" (2025). Dissertations. 2430.
https://aquila.usm.edu/dissertations/2430