The effect of different cyclic substituents on the properties of recyclable acetal-containing epoxy resins

Vitrimers represent an emerging field warranting comprehensive investigation into fundamental aspects of dynamic covalent bond design. Herein, three acetal-containing cycloaliphatic epoxides (ACEs) with different cyclic substituents (cyclopentyl, furyl, and phenyl groups) were synthesized. These three liquid ACEs have different viscosities and refractive indices. After curing with anhydride, the cured ACEs show elevated glass transition temperature of up to 189 degrees C, and superior tensile strengths of up to 71 MPa. Interestingly, the dangling groups attached to the acetal bonds have a significant impact on the structure dynamics, reprocessability, degradation rates and hot wet aging resistance of cured ACEs. The effect of different dangling groups on the dynamic behaviors of acetal bonds was verified by small molecular modeling reactions. Among them, the epoxy resin containing the furyl group shows the fastest stress relaxation rate at the same temperature. The epoxy resin containing the phenyl group has the highest retention of tensile strength after reprocessing or hot wet aging, while the epoxy resin containing the cyclopentyl group exhibits the fastest degradation rate in various acid solutions. These cured ACEs can also be effectively repaired and welded owing to their dynamic structures. These noteworthy discoveries provide essential insights for understanding the structure-property relationship of acetalcontaining recyclable thermosetting polymers.