A Physically-Based Model for Viscoelastic Behavior of Covalent Adaptive Network Elastomers

Covalent adaptive network (CAN) elastomers, exemplified by polyimine, exhibit unique viscoelasticity due to dynamic covalent bond reorganization under mechanical loading. This study presents a physically based constitutive model integrating bond dissociation kinetics and chain diffusion to unravel the energy dissipation mechanisms governing their rate-dependent behavior. The model is distinctively embedded within an eight-chain network framework, enabling a simplified yet physically consistent description of network evolution. Through systematic experimental characterization and theoretical modeling, we demonstrate that polyimine’s viscoelastic response arises from the interplay between connected (“on”) chains and dissociated (“off”) chains. The model accurately captures key phenomena, including biphasic stress relaxation (rapid diffusion-driven decay followed by delayed bond-detachment dissipation) and cyclic loading-induced hysteresis with progressive residual strain accumulation. Quantitative analysis of chain density evolution reveals strain-accelerated dissociation kinetics for “on” chains and strain-independent relaxation dynamics for “off” chains. Notably, prolonged relaxation drives the network toward equilibrium, evidenced by convergence to Gaussian chain statistics. These findings establish a microstructure-informed framework for tailoring the viscoelastic performance of CAN elastomers in applications demanding dynamic mechanical adaptability.