Mesoscopic Morphologies in Frustrated ABC Bottlebrush Block Terpolymers

Bottlebrush block polymers, featuring densely grafted side chains, have garnered significant attention mainly for their large self-assembled domain spacings, up to several hundred nanometers, rarely achieved with linear counterparts. However, the structures observed in AB diblock bottlebrushes are limited to simple lamellae and cylindrical phases. We synthesized a library of ABC bottlebrush triblock terpolymers, poly(_DL-lactide)-b-poly(ethylene-alt-propylene)-b-polystyrene (PLA-PEP-PS) using macromonomers and ring-opening metathesis polymerization (ROMP). This creates a frustrated system, where the mandatory interfaces (PLA/PEP) have larger interfacial energies than PLA/PS. Morphological characterization revealed intriguing mesoscopic structures, including layered microstructures, core-shell hexagonally packed cylinders (CSHEX, plane group p6mm), alternating tetragonally packed cylinders (ATET, p4mm), and an unprecedented morphology, rectangular centered cylinders-in-undulating-lamellae (RCCUL, c2mm). Varying molecular weight led to a wide range of unit cell dimensions (exemplified by RCCUL) from 40 nm to over 130 nm. This work highlights the potential of multiblock bottlebrushes for creating materials with innovative structures and diverse domain dimensions.