Catalyst-Free Dynamic Covalent Polyester Networks with Dissociative Transesterification

Abstract

Most vitrimers based on transesterification (TER) require external catalysts. Moreover, their slow relaxation rates necessitate a high reprocessing temperature and prolonged reprocessing time, resulting in issues like degradation or side reactions. Herein, a spider-like bisenol tetraester (E4) is investigated as a building block to synthesize dynamic covalent networks (DCNs). One of the highlights of E4 is that it can undergo a catalyst-free TER following the dissociative pathway at high temperatures. Using this dissociative TER, a series of DCNs were prepared by melt curing of E4 and different alkanediols. Remarkably, these DCNs exhibit ultrafast stress relaxation rates at 190 °C, with rather short relaxation times (1.4–3.1 s) and relatively high viscous flow activation energies (142.7–167.1 kJ mol^–1). This allows for fast reprocessing of them at 180 °C within 8–10 s, a considerably shorter time frame as compared to the long reprocessing time required for vitrimers based on conventional TER. Lastly, the catalyst-free TER allows highly selective depolymerization of these DCNs and the carbon fiber-reinforced polymers (CFRPs) based on them, achieving eco-friendly and low-cost recovery of initial monomers from the mixed plastic waste stream.