Thermal Switching of Polymer Topology Enables Programmable Mechanical Properties in Soft Materials

Soft materials with on-demand mechanical tunability remain challenging to realize, particularly those capable of large, reversible, and programmable changes within a single material system. In this work, a synthetic elastomer is designed that undergoes thermally reversible topological network reconfiguration, switching between brush- and linear-like architectures, thereby enabling a reversible transition from soft to stiff mechanical states. This reconfiguration is achieved by grafting crystallizable side chains onto a polymer backbone via Diels-Alder (DA) adducts at low annealing temperatures to form brush-like networks, while retro-DA reactions at higher temperatures release the side chains, yielding a linear topology. The brush architecture suppresses crystallization, whereas the linear form facilitates crystallinity to form an additional crystalline framework, leading to a reversible rubbery-to-glassy transition. As a result, the elastomers undergoing annealing cycles between 60 and 130 °C exhibit reversible enhancements in stiffness and strength by up to 286-fold and 25-fold, respectively. Coarse-grained molecular dynamics (CGMD) simulations reveal that the significantly improved stiffness and strength originate from the formation of a crystalline framework that effectively bears mechanical load and impedes crack propagation. This thermally programmable strategy enables dynamic control of mechanical behavior, offering a novel paradigm for designing intelligent materials with tailored and on-demand performance.