Versatile levulinic acid-derived dynamic covalent thermosets enabled by in situ generated imine and multiple hydrogen bonds

Abstract

Bio-based dynamic covalent thermosets have attracted extensive attention as they are expected to break conventional thermosets' reliance on fossil resources and address the recycling issue after disposal. However, there has always been a contradiction between using bio-based feedstocks and possessing high properties, as well as a conflict between high performance and rapid recycling (reprocessing and degradation). In this work, a simple approach was developed to prepare bio-based thermosets with high performance, rapid reprocessing, high flame retardancy, and antibacterial properties enabled by in-situ generated dynamic covalent imine (Schiff base) bonds and multiple hydrogen bonds. The levulinic acid epoxy (ELA) was successfully synthesized and cured with 2-(4-aminophenyl)-1H-benzimidazol-5-amine (BIA) containing benzimidazole structures. The high concentration of Schiff bases and multiple hydrogen bonds of ELA-BIA endowed it with high glass transition temperature and mechanical properties, as well as satisfactory catalyst-free malleability, rapid reprocessing and repairing. Furthermore, due to the combined effect of the in-situ Schiff base and benzimidazole structure, ELA-BIA exhibited excellent condensed phase char formation ability, resulting in intrinsic flame retardancy with a limiting oxygen index of 33.8 % and a UL-94 V-0 rating, both of which were significantly higher than 4, 4′-diaminodiphenyl methane (DDM) cured ELA or DDM cured bisphenol A epoxy. Moreover, the Schiff bases bonded in the networks provided 100 % of the intrinsic antibacterial rates. This work provides a feasible and simple strategy for the preparation of high-performance and versatile bio-based dynamic covalent thermosets.