Low‐Frequency Vibration Damping Polyurethane Elastomers with High Mechanical Robustness via Constrained Pendant Chains

Low‐frequency vibration damping in polyurethane elastomers remains difficult to reconcile with mechanical robustness. Effective dissipation of low‐frequency vibration requires the characteristic relaxation time of polymer chains to match the timescale of slow external oscillations. However, such long‐timescale chain relaxation is typically associated with stress relaxation, creep and irreversible deformation, compromising mechanical robustness. Here, we report a polyurethane elastomer that addresses this trade‐off through a constrained pendant‐chain architecture, in which grafted pendant chains are locally constrained at their roots while retaining flexible terminal alkyl segments. This architecture is created by placing urea and urethane motifs at the pendant‐chain roots, where neighboring pendant‐chain units assemble into a reversible hydrogen‐bonded association network. This reversible network kinetically constrains pendant chain relaxation, shifts the characteristic relaxation toward longer timescales and thereby enhances low‐frequency damping. Meanwhile, the association network provides dynamic physical crosslinks that restrict backbone slippage and preserve structural integrity. The optimized polyurethane elastomer exhibits a loss factor of 0.98 at 1 Hz while maintaining a tensile strength of 60.2 MPa. These results establish constrained pendant chain engineering as a molecular design strategy for polyurethane elastomers that combine low‐frequency vibration attenuation with high mechanical performance.