Design Principles of Stimuli-Responsive Covalent Adaptable Networks

Covalent adaptable networks (CANs) are sustainable polymeric materials that combine mechanical robustness with reprocessability through dynamic covalent bonds. Their mechanical behavior is governed by the kinetics and thermodynamics of bond reactions. Existing continuum models for CANs, based on classical rubber-like elasticity, often focus on steady-state behavior and overlook stress contributions from newly formed strands by assuming they are load-free. This limits their ability to predict behaviors like tensile recovery and actuation during transitions. To address these limitations, we develop a mean-field framework that connects microscopic bond reactions and molecular packing-induced conformational changes to macroscopic elastic behavior. Our model captures topological evolution and mechanical response of responsive networks undergoing bond reactions, validated using light-induced living polymer networks (LILPNs). To interpret the tensile recovery observed in LILPNs during transitions, we propose a conformation switch (CS) mechanism, which incorporates stress contributions from predeformed new strands due to molecular packing during transitions. The CS modeling reproduces key features of tensile recovery observed in experiments. Leveraging this framework, we also investigate the effects of molecular weight and functionality on LILPN dynamics. This work provides a predictive platform for designing responsive and adaptive polymer networks with tailored properties.