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Bicontinuous microstructures are essential to the function of diverse natural and synthetic systems. Their synthesis has been based on two approaches: arrested phase separation or self-assembly of block copolymers. The former is attractive for its chemical simplicity and the latter, for its thermodynamic robustness. Here we introduce elastic microphase separation (EMPS) as an alternative approach to make bicontinuous microstructures. Conceptually, EMPS balances the molecular-scale forces that drive demixing with large-scale elasticity to encode a thermodynamic length scale. This process features a continuous phase transition, reversible without hysteresis. Practically, EMPS is triggered by simply supersaturating an elastomeric matrix with a liquid, resulting in uniform bicontinuous materials with a well-defined microscopic length scale tuned by the matrix stiffness. The versatility of EMPS is further demonstrated by fabricating bicontinuous materials with superior mechanical properties and controlled anisotropy and microstructural gradients. Overall, EMPS presents a robust alternative for the bulk fabrication of homogeneous bicontinuous materials.

Covalent mechanophores are molecular motifs that contain weak bonds, which are preferentially cleaved in response to the application of a mechanical force. Specially designed motifs can signal such bond scission events by changing their optical absorption or emission characteristics and thus exhibit mechanochromism. Here, we report the synthesis of three triarylmethane benzyl ether derivatives and their use as mechanochromic cross-linkers in elastomeric networks. Mechanical stimulation of these polymers triggers the heterolytic cleavage of the C–O ether bond of the triarylmethanes, which leads to the formation of resonance-stabilized carbocations that absorb light in the visible range. The materials adopt blue, yellow, or red coloration depending on the chemical design of the triarylmethane mechanophore. The color palette can be further expanded by simple combinations of these three colors. Thus, our work demonstrates the versatility of the triarylmethane platform in polymer mechanochemistry.