Oxidative Degradation of Thermosets Based on Thioketal Cleavable Linkages in Aqueous Environment
Mohamed Abdelrahim, Jun Zhang, Quan Gao, Wael A. Zordok, Ji Liu, Jin Geng
Abstract
Thermosets are rigid, infusible, and unmolded materials containing three-dimensional (3D) cross-linked structures. They are considered a fundamental pillar in the international economy, which are produced by 65 million tons annually. The responsive cross-linking moieties provide the thermosets characterized with outstanding physicochemical properties such as stiffness, degradability, and chemical and thermal resistance. We prepared degradable thermoset materials using thioketal (TK) cross-linkers, which underwent main-chain or side change degradation in the presence of hydrogen peroxide in water. TK cross-linkers at different concentrations (5, 10, and 20% wt %) were polymerized with 2-hydroxyethyl acrylate (HEA) or with 2-hydroxyethyl methacrylate (HEMA) and 1-vinyl-2-pyrrolidone (PD) to produce cross-linked poly(HEA) and poly(HEMA-PD) by free radical polymerization, respectively. The resultant polymer materials completely degraded in hydrogen peroxide/water (3–30%, vol). Using isophorone diisocyanate, we also produced degradable polyurethane based on TK-bearing diol. We prepared a 3D degradable thermoset using the Direct-Ink-Writing (DIW) 3D printing technology, which was charged by diethylene glycol diacrylate (15%, wt %) and a prepolymer (isophorone diisocyanate terminated by acrylate moieties) containing diol-thioketal linkage (15%, wt %). Finally, we found that TK-poly(HEA) underwent microbial degradation by Lactobacillus jensenii at 37 °C, which indicates a benign eco-friendly effect.