Synthesis and structure–property relationships of polydimethylsiloxane bottlebrush elastomers

Molecular bottlebrushes are composed of polymeric side chains densely grafted onto a single backbone in a way that steric repulsion between the side chains extends the backbone and suppresses interchain entanglement. Bottlebrush networks bearing polydimethylsiloxane (PDMS) side chains are particularly attractive because they access a supersoft regime lying below the modulus limit imposed by entanglements in solvent-free linear PDMS and can reproduce the nonlinear strain-stiffening response of biological tissues. This review summarizes the synthesis and structure–property relationships of PDMS bottlebrush elastomers. On the synthetic side, physical crosslinking, chemical crosslinking of precisely synthesized bottlebrushes, one-pot network formation, and dynamic bond strategies are compared with respect to the structural variables that each route places under control and the modulus range that each has been reported to reach, to discuss the trade-off between structural precision and process simplicity. Regarding structure–property relationships, the effect of entanglement suppression arising from side-chain crowding on network modulus, finite extensibility, and the decoupling of softness from firmness is outlined. Finally, the remaining challenges, including processability, durability, and the quantification of network defects, are highlighted.