Self-Healable and Microstructure-Programmable Vitrimeric Nonisocyanate Polyurethane Foams via Decoupled Fabrication

Abstract

The intrinsic kinetic coupling between cross-linking and foaming presents a fundamental challenge for the production of nonisocyanate polyurethane (NIPU) foams, limiting independent control over their microstructure and properties. Here, we report a sequential fabrication strategy that decouples these processes to produce high-performance, recyclable NIPU foams. Stable cyclocarbonate-functionalized prepolymers are synthesized as processable intermediates, and a rheological protocol is developed that uses the viscosity explosion point (VEP), defined as the extremum of the first derivative of tan δ with respect to time, as a quantitative indicator to time foaming initiation. In addition, 1,4-phenylenediboronic acid (BDBA) is incorporated to introduce dynamic boronic ester bonds, creating a covalent adaptable network. The VEP-guided strategy yields foams with homogeneous closed-cell morphology, tunable density (0.302–0.498 g/cm3), compressive strength up to 3.03 MPa, and enhanced glass transition temperature. The dynamic boronic ester bonds impart self-healing efficiency above 83% and closed-loop recyclability without sacrificing mechanical integrity. Furthermore, the prepolymer intermediate shows good storage stability and can be shaped by compression molding, producing uniform foams with tailored thermomechanical properties. This work provides a science-based framework for decoupling competing kinetics in the design of sustainable polymer foams.