Molecular architecture directs linear-bottlebrush-linear triblock copolymers self-assemble to soft, reprocessable elastomers

Linear-bottlebrush-linear (LBBL) triblock copolymers represent an emerging system for creating multifunctional nanostructures. Their self-assembly depends on molecular architecture but remains poorly explored. We synthesize polystyrene-block-bottlebrush polydimethylsiloxane-block-polystyrene triblock copolymers with controlled molecular architecture, and use them as a model system to study the self-assembly of LBBL polymers. Unlike the classical stiff rod-flexible linear block copolymers that are prone to form highly ordered nanostructures such as lamellae, at small weight fractions of the linear blocks, LBBL polymers self-assemble to a disordered sphere phase regardless of the bottlebrush stiffness. Microscopically, the characteristic lengths of the self-assembled nanostructures increase with the stiffness of bottlebrush block by a power law, which is captured by a scaling analysis. Macroscopically, the formed nanostructures are ultrasoft, reprocessable elastomers with shear moduli of about 1 kPa, two orders of magnitude lower than that of conventional polydimethylsiloxane elastomers. Our results provide insights on exploiting the self-assembly of LBBL polymers to create soft functional nanostructures.