Inherent Tensile Strength and Stretchability of Unentangled Elastomers

Elastomers, as three-dimensional cross-linked polymer networks, are essential materials in a wide range of applications. Strength and stretchability are fundamental mechanical properties of elastomers, but how they are determined by the network structure remains inadequately understood. In this work, we combine theoretical analysis with extensive molecular dynamics (MD) simulations to investigate the single-chain mechanics and large-strain mechanical behavior of unentangled elastomers. We show that the rupture of individual polymer chains follows a mechanochemical process governed by an external force-dependent energy barrier E_b. We derive the relationship between macroscopic tensile stress, the conformational statistics of network strands, and the force–extension behavior of individual chains for unentangled elastomers. This relationship is corroborated by our MD simulations. The inherent strength σ_inh of elastomers is found to be 1–2 orders of magnitude lower than the theoretical ideal strength σ_is, as only a small fraction of strands bear significant stretching tensions during network rupture. During deformation, strand scission is driven by the straightening and rupture of the shortest paths (SPs) in the polymer network, and the critical stretch ratio λ_d marking the onset of scission can be predicted through topological SP analysis of the undeformed network. Our findings hold for unentangled elastomers with varying chain lengths, network junction functionalities, and fractions of topological defects. This work promotes the fundamental understanding of the strength, damage evolution, and stretchability of polymer networks, and also provides valuable guidance for designing elastomers with tailored strength and stretchability.