Catalyst-Free Covalent Adaptable Polyester Networks Based on Dissociative Transesterification Chemistry

In this study, diethyl 1,3-acetonedicarboxylate (DAC), derived from naturally occurring citric acid, is investigated as a building block for the synthesis of covalently adaptable networks (CANs). The kinetic model studies reveal that DAC undergoes a catalyst-free transesterification reaction (TER) following the dissociative pathway with an activation energy of 104.96 ± 2.73 kJ mol−1. This knowledge is transferred to synthesize CANs by simply one-pot melt polycondensation of a mixture of DAC and polyols with varied stoichiometries. Importantly, these networks could be readily reprocessed by hot-pressing at 150 °C within 5 min. This fast reprocessability is in sharp contrast with the prolonged reprocessing time required for most vitrimers based on traditional TER, which can be correlated to the low viscosity provided by the temporary dissociation of the networks. Benefiting from the catalyst-free, dissociative TER, closed-loop recycling was achieved by two depolymerization-repolymerization methods: degradation in excess polyols, followed by reintroducing complementary DAC and repolymerized, or degradation in excess DAC, followed by reintroducing complementary polyols and repolymerized. In addition, the catalyst-free TER allows for highly selective depolymerization of these materials and recovery of the highly pure starting monomers from mixed waste plastic streams, achieving closed-loop recycling. Similarly, the carbon fiber reinforced polymers (CFRPs) based on them could be selectively depolymerized, giving the recovered carbon fiber without obvious damage and the initial monomers in high yields.