Synthesis and Degradation Mechanism of Self-Cured Hyperbranched Epoxy Resins from Natural Citric Acid.

Rapid and highly efficient degradation of cured thermoset epoxy resins is a major challenge to scientists. Here, degradable self-cured hyperbranched epoxy resins (DSHE-, = 1, 2, and 3) were synthesized by a reaction between 3-isocyanato-4-methyl-epoxy-methylphenylcarbamate and degradable epoxy-ended hyperbranched polyester (DEHP-) prepared from maleicanhydride, citric acid, and epichlorohydrin. The chemical structure of DSHE- was characterized by Fourier transform infrared and H NMR spectra. With an increase in DSHE- molecular weight, the adhesion strength of self-cured DSHE- films increases distinctly from class 1 to 4, and their pencil hardness remains about class B-2B. The study on the self-cured behavior and mechanism of DSHE- shows that the carbamate group of the DSHE- is decomposed into diamine group to react with epoxy group and form a cross-linked structure. The self-cured DSHE- films were degraded completely in 2 h at 90 °C in the mixed solution of hydrogen peroxide (HO) and ,-dimethylformamide under atmospheric pressure and produced the raw material citric acid, indicating good degradation performance and recyclable property of DSHE-.