Aligned Core–Shell Gyroid in an ABC Bottlebrush Triblock Terpolymer by Shearing and Epitaxial Growth

ABC bottlebrush triblock terpolymers exhibit unique periodic mesoscopic morphologies with unit cell dimensions that can exceed 100 nm, a length scale that is challenging to achieve with linear block copolymers. Similar to conventional block copolymers, these self-assembled morphologies are typically polygrain, with randomly oriented grains that render the material globally isotropic. In this study, we applied a reciprocating shear field to a poly(ethylene- alt -propylene)- b -polystyrene- b -poly( d l -lactide) (PEP-PS-PLA) bottlebrush triblock terpolymer synthesized via ring-opening metathesis polymerization (ROMP) of macromonomers prepared by living anionic polymerization (PEP, PS) and ring-opening polymerization (PLA). Small-angle X-ray scattering (SAXS), conducted in situ while shearing the material, and transmission electron microscopy (TEM) revealed a rapid transition from a core-shell gyroid (CSGYR) morphology to coexisting core-shell hexagonally packed cylinders (CSHEX) and cylinders-in-undulating-lamellae (CUL), occurring by a two-step alignment process. Reciprocating shearing oriented the CSHEX and CUL phases, with the cylinder axes coincident with the shear direction and the (10) lattice planes preferentially arranged parallel to the shear plane. Subsequent high-temperature annealing induced a CSHEX/CUL-to-CSGYR transition via epitaxial growth, yielding an aligned CSGYR phase with the [111] lattice direction aligned along the shear direction. This work provides insight into the shear-induced phase behavior of bottlebrush multiblock polymers and presents a feasible strategy for achieving aligned morphologies in these materials.