Malleable, Recyclable, and Robust Poly(amide–imine) Vitrimers Prepared through a Green Polymerization Process

Abstract

The introduction of dynamic covalent bonds into chemically cross-linked networks is an effective strategy to solve intrinsic problems of inability to be reprocessed or recycled for thermosetting polymers. Imine bonds (also known as Schiff bases) are promising candidates for constructing covalent adaptable networks (CANs) because of their easily triggered exchange reactions. However, it remains a challenge for polyimine vitrimers to improve the creep resistance and thermal stability due to their unstable imine-based networks. In this work, we report a green strategy to prepare a series of partially bio-based, malleable, recyclable, and robust poly(amide–imine) vitrimers by bulk polymerization for the first time. The amide bonds are introduced into polyimine vitrimers for the improvement of mechanical property, thermal stability, and creep resistance. A series of H₂N-terminated prepolymers with tunable structures were first synthesized, which combined the amide and imine groups together. Then, a bio-based trimethyl citrate was selected as the curing agent to react with H₂N-terminated prepolymers for the construction of CANs with amide bonds as cross-linking points. The imine groups accompanied by a dynamic exchange nature endowed the poly(amide–imine) vitrimers with reprocessability, self-healing property, and degradability. Meanwhile, the amide groups with inherent intermolecular hydrogen bonding enhanced the mechanical properties, thermal stability, and creep resistance of poly(amide–imine) thermosets.