Rectangular Centered Cylinders-in-Undulating-Lamellae from ABC Bottlebrush Block Terpolymers*

Bottlebrush block polymers with side chains densely grafted on a backbone have attracted extensive attention mainly due to the large self-assembled domain spacings (several hundred nanometers) never achieved with linear block polymers (usually d < 50 nm). However, the ordered morphologies in diblock bottlebrushes have been limited to lamellar and cylindrical phases. Motivated by our previous work where a core-shell gyroid network was experimentally found in ABC bottlebrush block terpolymers, we investigated the morphologies of two ABC bottlebrushes, poly(ethylene-alt-propylene)-b-polystyrene-b-poly(_DL-lactic acid) (PEP-PS-PLA) and PEP-b-PS-b-poly(ethylene oxide) (PEP-PS-PEO) synthesized by ring-opening metathesis polymerization (ROMP). An unprecedented rectangular centered cylinders-in-undulating-lamellae (RCCUL, space group c2mm) was found in both systems at a compositional region where an orthorhombic Fddd single network occurred in linear ABC counterparts. The RCCUL unit cell parameters can be adjusted over a considerable range, with the b/a value spanning 1 to √3. This study demonstrates that stiff bottlebrush architectures can spawn new materials with attractive morphologies and properties.