Catalyst-Free\nDynamic Covalent Polyester Networks\nwith Dissociative Transesterification

Most\nvitrimers based on transesterification (TER) require external catalysts.\nMoreover, their slow relaxation rates necessitate a high reprocessing\ntemperature and prolonged reprocessing time, resulting in issues like\ndegradation or side reactions. Herein, a spider-like bisenol tetraester\n(E4) is investigated as a building block to synthesize dynamic covalent\nnetworks (DCNs). One of the highlights of E4 is that it can undergo\na catalyst-free TER following the dissociative pathway at high temperatures.\nUsing this dissociative TER, a series of DCNs were prepared by melt\ncuring of E4 and different alkanediols. Remarkably, these DCNs exhibit\nultrafast stress relaxation rates at 190 °C, with rather short\nrelaxation times (1.4–3.1 s) and relatively high viscous flow\nactivation energies (142.7–167.1 kJ mol<sup>–1</sup>). This allows for fast reprocessing of them at 180 °C within\n8–10 s, a considerably shorter time frame as compared to the\nlong reprocessing time required for vitrimers based on conventional\nTER. Lastly, the catalyst-free TER allows highly selective depolymerization\nof these DCNs and the carbon fiber-reinforced polymers (CFRPs) based\non them, achieving eco-friendly and low-cost recovery of initial monomers\nfrom the mixed plastic waste stream.