Cooperative Semi-Interpenetrating Polymerization toward Boroxine-Based Dynamic Covalent Networks with Tunable Properties and Chemical Recyclability

The dynamic chemistry of covalent boron-oxygen bonds has been extensively leveraged to construct cutting-edge dynamic covalent polymer networks (DCPNs) with self-healing, repairable, and reprocessable properties. However, the inherent poor water resistance of the resulting structural units, such as boronic esters or boroxines, severely limits the widespread application of boron-containing DCPNs. Herein, a novel and effective H2O-induced cooperative semi-interpenetrating polymerization (sIPP) was successfully developed by using diisocyanates (DIC) and linear boronic acid-contained polyesters (P-BA) as starting materials, thus constructing a series of well-mixed and water-resistant dynamic covalent semi-interpenetrating polymer networks (P-sIPNs-DIC) composed of boroxine-based DCPNs and linear polyureas. Additionally, precise control over structural unit composition, sequence distribution, and carbon–carbon double-bond geometry enables tunable mechanical properties of the resultant P-sIPNs-DIC between thermoplastic elastomers and robust plastics. Impressively, P-sIPNs-DIC enable effective acidic depolymerization to selectively recover the pristine P-BA with excellent yield, which can be directly employed to regenerate P-sIPNs-DIC with performance matching the original, thus achieving a closed-loop lifecycle from linear polymers to polymer networks and back to linear polymers.