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Document Type

Thesis

Publication Date

4-30-2026

Disciplines

Chemistry

Advisor

Claire Otteson

Abstract

The accumulation of non-recyclable thermoset plastic waste demonstrates a need for high- performance materials that bridge the gap between the reprocessability of thermoplastics and the durability required for industrial materials. Previous research has produced high-strength and recyclable hydrogenated nitrile butadiene rubber (HNBR) materials using boronic ester crosslinks, but the susceptibility of the Lewis acidic boron atom makes it vulnerable to hydrolysis which limits longevity in humid or aqueous environments. The proposed research aims to target covalent adaptable networks (CANs) based on the boronic ester interaction, and their instability in water. Three structurally modified crosslinkers are proposed to incorporate into a previously researched hydrogenated epoxidized nitrile butadiene rubber (HENBR) network to evaluate the structure-property relationship between crosslink composition and hydrolytic stability. Electron- withdrawing fluorine groups, electron-donating methoxy groups, and bulky tert-butyl groups were chosen to evaluate their effects on the Lewis acidity and steric shielding of the boron atom. Dynamic, mechanical, and thermal analyses are predicted to show that increased steric shielding and reduced Lewis acidity will increase the activation energy for hydrolysis, and accelerated aging under controlled humidity conditions are expected to show that the bulky tert-butyl groups will shield the boron atom and preserve mechanical integrity in aqueous conditions. The novel aspect of this work is the comparative investigation of molecular shielding effects that moves beyond small molecule studies into fully formulated materials. The information gained will provide key insights into creating more robust moisture-resistant sustainable materials for industrial manufacturing, thereby reducing thermoset waste accumulation. This work will address a key barrier in the development of recyclable thermosets, and future work will explore applications of these optimized boronic ester materials.

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