Fast Reprocessing of Acetal Covalent Adaptable Networks with High Performance Enabled by Neighboring Group Participation
Qiong Li, Songqi Ma, Pengyun Li, Binbo Wang, Zhen Yu, Hongzhi Feng, Yanlin Liu, Jin Zhu
Abstract
Covalent adaptable networks (CANs) represent a transition material combining favorable features of thermosets and thermoplastics. However, it is still a huge challenge to simultaneously achieve fast reprocessability and high performance for CANs. Here, we designed catechol-based acetal CANs to achieve continuous reprocessing without sacrificing thermal and mechanical properties. A small-molecule model study demonstrated the significantly accelerated acetal exchange by neighboring group participation (NGP) of phenolic hydroxyl. Using this internally catalyzed acetal chemistry, a series of CANs with a broad range of properties were simply prepared from bio-based epigallocatechin gallate (EGCG) and tri(ethylene glycol) divinyl ether (TEGVE) via one-step “click” cross-linking without using catalysts or releasing small-molecule byproducts. The dynamic nature of the CANs was confirmed via stress relaxation and multiple recycling methods including extrusion. While the dense cross-link density and high rigidity of the network provided high solvent resistance and mechanical properties. This work provides a promising and practical method to produce fast-reprocessing dynamic covalent polymer networks with dense cross-link density and superior performance.