Preparation and Application of Polyurethane-Modified Epoxy Based on a Synergistic Effect of Dual Dynamic Bond Networks with Long and Flexible Chains
Lu Li, Lei Rong, Yuhuan Nie, Tingxi Zhang, Zhichao Xia, Qibin Chen
Abstract
Epoxy resins always suffer from high brittleness and poor resistance to crack initiation and propagation due to their high cross-linked density. In this work, a highly tough, self-healable, degradable, and recyclable polyurethane-modified epoxy material was successfully prepared via combining long and flexible chains with dual dynamic covalent bond/hydrogen bond cross-linking networks into the epoxy resin. Polyurethane with amide-based terminal epoxy groups (AETPU) was first synthesized by using a diol containing amide bonds ( N, N -bis(2-hydroxyethyl)-3-amino propenamide, OH-AAM–OH) as a chain extender, and then incorporated into the epoxy resin network. The effect of various quantities of AETPU on the performance of the epoxy resin was investigated. Results demonstrate that adding AETPU improves the toughness, self-healing ability, degradability, and recyclability of the modified epoxy resin. The sample EP50, with the 50 wt % AETPU addition, shows a 394.2% increase in elongation at break and a 368.4% improvement in toughness compared to pure epoxy resin, while it has only a 45.3% reduction in tensile strength and a 41.8% decrease in Young’s modulus. When the amount of AETPU increases, the self-healing performance of the material improves; scratches on the EP50 sample almost disappear after healing at 120 °C for 1 h. In addition, EP50 rapidly degrades at room temperature in mixed dithiothreitol/ N, N -dimethylformamide solvent. The combining strategy of a dynamic covalent/noncovalent dual cross-linked network with the long, flexible chain has great potential to improve the multiple performances of materials and lays a foundation for further exploitation of multifunctional epoxy resins.