Phase Behavior of Linear-Bottlebrush Block Polymers

Block copolymers (BCPs) self-assembled into 3D network phases are promising for designing useful materials with multiple properties that rely on domain continuity. However, access to potential applications has been limited because network formation with linear BCPs tends to occur only over narrow compositional windows. Another constraint is slow self-assembly kinetics at higher molecular weights, which limits the network unit cell dimensions and the resulting material properties. Architecturally asymmetric, linear-bottlebrush BCPs have previously been demonstrated to promote self-assembly into complex micellar phases. The architectural asymmetry has been demonstrated to induce favorable curvature toward the linear block. However, linear-bottlebrush copolymer phase behavior and self-assembly into network phases have not been systematically studied. Here, we map the phase behavior of eight sets of diblock polymers with a linear-bottlebrush architecture in the expected vicinity of the double-gyroid phase. We demonstrate the effects of architectural asymmetry and the linear block cohesive energy density on self-assembly into double-gyroid, lamellar, and hexagonal phases. Through a combination of molecular and structural characterization techniques, we demonstrate that the shape of the polymer and the identity of the linear block provide significant control over the molecular factors that dictate network formation.