Evolution of Viscoelasticity in a Reversibly Photo-Cross-Linked Elastomer Network

Network topology and chain mobility govern the viscoelastic response of dynamic polymer networks, yet their evolution during reversible cross-linking remains poorly understood. Here, a UV light-responsive polyurethane containing anthracene moieties is developed to construct reversible networks through UV light-induced [4 + 4] cycloaddition and thermal cleavage. Dynamic rheology combined with time–temperature superposition reveals systematic changes in storage and loss moduli, relaxation time, and activation energy with increasing cross-linking density. UV-thermal cycling regulates network topology and chain mobility, resulting in enhanced elasticity, improved thermal stability, and retained dynamic behavior required for thermal reprocessing. These findings establish a direct correlation between reversible network evolution and viscoelastic response, providing mechanistic insight into the design of recyclable polyurethane elastomers with programmable mechanical properties.