Core-Shell Gyroid in ABC Bottlebrush Block Terpolymers

Block polymer self-assembly provides a robust toolkit for creating useful materials with 3D periodic network morphologies. However, the network dimensions are limited in linear copolymers due to the coil conformations and the slow self-assembly kinetics at high molecular weights. A block bottlebrush architecture can circumvent both shortcomings owing to extended chain conformations and molecular dynamics substantially free of chain entanglements. However, until now network morphologies have not been reported in bottlebrush block polymers. In this work, we systematically explore the phase behavior of poly(ethylene-alt-propylene)-b-polystyrene (PEP-PS) diblock and PEP-PS-b-poly(ethylene oxide) (PEP-PS-PEO) triblock bottlebrush polymers prepared by ring-opening metathesis polymerization (ROMP). No network phases were found in the diblocks, whereas the addition of minor bottlebrush PEO blocks led to a substantial core-shell double gyroid (GYR) phase window. Encouragingly, the GYR unit cell dimensions increased as d ~ N_bb^0.92 with the backbone degree of polymerization N_bb, portending the ability to access larger network dimensions than previously obtained with linear polymers. Besides the GYR network, several new intriguing phases also appeared in triblock bottlebrush terpolymers.