Itaconic acid-based hyperbranched polymer toughened epoxy resins with rapid stress relaxation, superb solvent resistance and closed-loop recyclability

Abstract

The development of epoxy vitrimers with excellent overall properties and recyclability has been a great challenge. In this work, an itaconic acid-based hyperbranched polymer (IAHBP) was synthesized and incorporated as a curing agent for diglycidyl ether of bisphenol-A (DGEBA) to prepare epoxy vitrimers. The tensile strength, flexural strength and impact strength of DGEBA/IAHBP were 91.0 MPa, 121.8 MPa and 18.4 kJ m⁻² respectively. The hyperbranched topological structure of IAHBP promoted dynamic transesterification and DGEBA/IAHBP exhibited outstanding malleability, shape reconfiguration and reprocessibility. DGEBA/IAHBP showed high shape fixity (R_f ∼ 97%) and recovery ratio (R_r ∼ 99%) over ten shape memory cycles, which involved grasping and loosening motions and the recovery of complex objects such as flower-shaped and 3D butterfly-shaped objects. Due to the increased free volume and crosslinking density, DGEBA/IAHBP demonstrated excellent solvent resistance. DGEBA/IAHBP can be efficiently degraded using sodium hydroxide aqueous solution, with the degraded epoxy reused to cure DGEBA to produce new epoxy vitrimers. The recycled epoxy vitrimers presented similar mechanical properties and T_g to the original samples. This work demonstrated a green and convenient strategy for the production of epoxy vitrimers with excellent mechanical performance and environment friendly reprocessibility.