Tuning moduli of hybrid bottlebrush elastomers by molecular architecture

Polymeric elastomers made of bottlebrush chains are soft, solvent-free materials with precisely controllable moduli by network topology. However, fabrication methods of bottlebrush networks with precisely programmable topology are lacking. The aim of this study is to achieve precise control over the modulus of hybrid elastomers containing bottlebrush and linear strands by integrating a versatile experimental synthesis approach with Molecular Dynamics (MD) simulations. In this study, polydimethylsiloxane (PDMS) networks (G′=10−328 kPa) are made by crosslinking prepared and purified bottlebrush molecules where the precursors, side chains and backbone, are synthesized using well-controlled living anionic polymerization. This approach allows independent programming of the crucial topological parameters of bottlebrushes, such as length of both sides chain and backbone and grafting density. In addition to this versatile synthesis, MD simulations reveal the influence of network defects inevitably present in all polymer networks. This novel combining of fabrication method and simulation yields experimentally-measured structural shear and Young's moduli which are in better agreement with theoretical predictions. Importantly, these bottlebrush-containing networks have no solvent or additives and notably, by removing ungrafted side chains impurities before network formation, results in soft, solvent-free elastomers with Young's moduli as low as E∼30 kPa with adhesiveness far lower than commercial silicone products of similar stiffness.