Toughing 3D‐Printable Elastomers Through End‐Constraint Shifted Deformation

ABSTRACT Facilitating entropic elastic deformation is central to strengthening the mechanical resilience of 3D‐printable elastomers. Despite extensive efforts that have focused on enhancing entropy‐driven responses through regulating inter‐chain interactions, the role of dangling chain conformational constraints in modulating elastic energy dissipation and mechanical reinforcement has remained largely overlooked. Herein, we challenge this prevailing convention by constraining polymer chain termini, thereby eliminating unbound ends and creating a fully connected molecular network. This end‐constraint reweights the deformation response by suppressing slippage and enhancing entropic elasticity, unlocking a unique combination of high modulus, creep resistance, and toughness unattainable with conventional designs. By coupling terminal constraint and interchain physical crosslinking, 3D‐printable elastomers achieve enhancement of over 571.1% and 388.2% in strength and toughness, while preserving printability and resilience. This work establishes chain‐end engineering as a powerful principle for molecular design, opening avenues toward recyclable, durable, and high‐performance soft materials for 3D printing, wearable electronics, and soft robotics.