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Abstract Most elastomers undergo strain‐induced crystallization (SIC) under tension; as individual chains are held rigidly in a fixed position by an applied strain, their alignment along the strain field results in a shift from strain‐hardening (SH) to SIC. A similar degree of stretching is associated with the tension necessary to accelerate mechanically coupled, covalent chemical responses of mechanophores in overstretched chains, raising the possibility of an interplay between the macroscopic response of SIC and the molecular response of mechanophore activation. Here, thiol‐yne‐derived stereoelastomers doped covalently with a dipropiolate‐derivatized spiropyran (SP) mechanophore (0.25–0.38 mol%) are reported. The material properties of SP‐containing films are consistent with undoped controls, indicating that the SP is a reporter of the mechanical state of the polymer. Uniaxial tensile tests reveal correlations between mechanochromism and SIC, which are strain‐rate‐dependent. When mechanochromic films are stretched slowly to the point of mechanophore activation, the covalently tethered mechanophore remains trapped in a force‐activated state, even after the applied stress is removed. Mechanophore reversion kinetics correlate with the applied strain rate, resulting in highly tunable decoloration rates. Because these polymers are not covalently crosslinked, they are recyclable by melt‐pressing into new films, increasing their potential range of strain‐sensing, morphology‐sensing, and shape‐memory applications. 

Abstract Thermoset toughness and deconstructability are often opposing features; simultaneously improving both without sacrificing other mechanical properties (e.g., stiffness and tensile strength) is difficult, but, if achieved, could enhance the usage lifetime and end‐of‐life options for these materials. Here, a strategy that addresses this challenge in the context of photopolymer resins commonly used for 3D printing of glassy, acrylic thermosets is introduced. It is shown that incorporating bis‐acrylate “transferinkers,” which are cross‐linkers capable of undergoing degenerative chain transfer and new strand growth, as additives (5–25 mol%) into homemade or commercially available photopolymer resins leads to photopolymer thermosets with substantially improved tensile toughness and triggered chemical deconstructability with minimal impacts on Young's moduli, tensile strengths, and glass transition temperatures. These properties result from a transferinker‐driven topological transition in network structure from the densely cross‐linked long, heterogeneous primary strands of traditional photopolymer networks to more uniform, star‐like networks with few dangling ends; the latter structure more effectively bear stress yet is also more easily depercolated via solvolysis. Thus, transferinkers represent a simple and effective strategy for improving the mechanical properties of photopolymer thermosets and providing a mechanism for their triggered deconstructability.