Coarse-Grained Models for the Solution Self-Assembly of Block Copolymer Polymer Bottlebrushes

A class of 'bottlebrush' polymers consist of linear backbones with a high grafting density of side-chains, where the repulsions between side-chains stiffen the molecular conformation and suppress the effects of molecular entanglement. This has advantages for polymer self-assembly, where block bottlebrushes can rapidly form ordered morphologies with relatively large length scales of O(100nm) unimpeded by slow entangled dynamics. Despite continued interest in the community on using bottlebrushes for self-assembly, it remains a challenge to efficiently model the side-chain degrees of freedom important for bottlebrush structure in multi-chain systems. Our group has recently developed a systematic coarse-graining scheme that can capture the single-molecule properties of bottlebrush polymers in a simplified 'implicit side-chain' model. Instead of the O(10⁵) beads required for synthetically-relevant bottlebrush polymers when side-chains are explicitly included, we can represent these same molecules with as few as O(10¹) beads per molecule. We leverage this model to capture the self-assembly properties of block bottlebrush molecules, developing a phase diagram for these solutions systems as a function of block fraction and concentration. These coarse-grained bottlebrush models are consistent with experimental x-ray scattering on synthesized bottlebrush molecules, capturing the dimensions of self-assembled lamellae and their order-disorder concentration.