Independently Tuning Elastomer Softness and Firmness by Incorporating Side Chain Mixtures into Bottlebrush Network Strands

Softness and firmness are opposing traits that synergistically define the elastic response of biological systems. Currently, no single class of synthetic materials including elastomers and gels provides independent control of these mechanical characteristics, particularly without altering chemical composition. To address this challenge, we explore a hierarchical bottom-up approach via architectural modulation of bottlebrush mesoblocks followed by their self-assembly into linear–brush–linear triblock copolymer networks. By judiciously incorporating side chains of different lengths, we seamlessly demonstrate full control over elastomer firmness at a fixed Young’s modulus, thus bypassing the infinitely laborious synthesis of targeted side chain lengths. This industrially scalable iteration upon the design-by-architecture approach to network construction delivers thermoplastic elastomers with unprecedented softness–firmness combinations desired in soft robotics, flexible electronics, and biomedical devices.