Synthesis of epoxidized soybean oil-derived covalent adaptable networks through melt Schiff base condensation

Abstract

Thermosets derived from epoxidized soybean oil (ESO) are restricted drastically because they have inferior mechanical properties, are not reprocessable, and are difficult to recycle due to their irreversible cross-linking structures. Herein, we report malleable and recyclable poly(epoxy imine) covalent adaptable networks (CANs) with tunable mechanical properties synthesized via a novel two-step procedure with ESO, vanillin (VAN), and diamines as raw materials. In the first step, ESO was reacted with VAN to generate aldehyde-terminated ESO (VESO). In the second step, poly(epoxy imine) CANs containing dynamic imine bonds were obtained by Schiff base condensation of VESO with diamines. The structure of poly(epoxy imine) CANs can be easily controlled by simply changing the structure of diamine, which in turn enables their mechanical properties to be regulated conveniently. Soft poly(epoxy imine) CAN with tensile strength (σ) and elongation at break (ε) 6.61 MPa and 54% was obtained by using flexible aliphatic diamine. Tough and strong poly(epoxy imine) CANs with σ and ε of higher than 25 MPa and 22% were achieved by using rigid aromatic diamines. All the poly(epoxy imine) CANs synthesized with different diamines showed various functionalities including reprocessability, recyclability, and weldability owning to the dynamic imine bonds. The tunable mechanical properties and excellent integrated functionalities make the biobased poly(epoxy imine) CANs more attractive than traditional ESO-derived thermosets. • A new approach was designed to synthesize epoxy covalent adaptable networks (ECANs). • The structure and property of the ECANs can be easily regulated by changing diamines. • The ECANs showed excellent reprocessability and weldability.