Toughened and Recyclable Epoxy Networks Featuring Nanostructures and Dynamic Covalent Bonds

Two aromatic diamines featuring boronic ester bonds were designed and synthesized. The first one was synthesized via the reaction of 1,4-butanediol diglycidyl ether with 2,2-bis(hydroxymethyl)propionic acid, followed by the reaction with 3-aminobenzeneboronic acid. The second diamine was an alpha,omega-diaminophenyl PCOE telechelic, which was synthesized via the ring-opening polymerization of cyclooctene (COE), followed by the reaction with 3-aminobenzeneboronic acid. The former was used as the hardener whereas the latter as the modifier to generate the nanophases in the epoxy networks derived from diglycidyl ether of bisphenol A (DGEBA). It was found that the epoxy-PCOE networks had nanostructures, in which the PCOE component was organized into the nanodomains with the size of 20-100 nm. The mechanical tests showed that the epoxy-PCOE networks had the fracture toughness superior to that of the control epoxy. Furthermore, the epoxy-PCOE networks exhibited excellent reprocessability, attributable to the dynamic exchange of boronic ester bonds. It was demonstrated that the incorporation of PCOE microdomains facilitated the recycling of epoxy networks. In addition, the epoxy-PCOE networks showcased shape memory properties with a moderate shape transition temperature. With the aid of boronic ester bonds, the original shape of the shape memory networks can be reprogrammed.