(32a) Architectural Control of Configurational Entropy in a/B Block Copolymer Self-Assembly: The Case of Core-Shell Bottlebrushes

The spatially periodic nanoscale morphologies arising from block copolymer self-assembly offer enticing opportunities for scalable production of isoporous materials with tailored pore sizes for membrane and nanotemplating applications. Linear AB diblock copolymer undergo composition-dependent self-assembly into lamellae, hexagonally packed cylinders, network, and spherical micelle morphologies, which reflect a delicate balance of the A/B segment repulsions and the entropy of chain stretching to minimize these unfavorable segment contacts. For a selected monomer chemistry, this thermodynamic balance sets the minimum degree of polymerization and smallest accessible pore size. We describe the melt phase self-assembly behaviors of core-shell bottlebrush (csBB) polymers, which derive from linking narrow dispersity AB diblock arms by living ring-opening metathesis polymerization of a norbornyl chain end functionality. We quantitatively demonstrate how the thermodynamic stabilities of self-assembled csBB morphologies depend on copolymer arm composition (f_A) and degree of polymerization (N_arm), as well as the brush backbone degree of polymerization (N_bb) and arm grafting density. These studies highlight how pre-organization of the AB diblock arms into a brush architecture entropically stabilizes the ordered morphology in a previously unrecognized manner.