Exploring polymer architecture for self-assembly of bottlebrush polymers: coarse-grained, implicit side-chain model in melts

Recent advances in polymer chemistry have enabled the synthesis of densely grafted polymers, opening new frontiers in polymer design. These 'bottlebrush polymers' have a wide materials design space, but any physical understanding of how molecular architecture affects macroscopic properties must account for many individual side-chains. We recently demonstrated that it is possible to describe a bottlebrush as a linear semi-flexible chain based on the wormlike cylinder (WLCy) model. However, our original model was designed to consider solution bottlebrush assembly, and was therefore not applicable to the self-assembly of bottlebrush in melts.

In this study, we expand the capability of the ISC model to melt bottlebrush copolymer assembly.² We first consider homopolymer bottlebrush melts to establish the melt ISC framework. Using single-chain in mean-field (SCMF) simulations, the end-end distance and radius of gyration are obtained to parameterize an ISC model with wormlike cylinder model parameters.^1,2 Each architecture could be mapped to a unique set of wormlike cylinder model parameters, so that they can be represented by an ISC model.² The effective pairwise interaction potential for this ISC model was determined by using an iterative Boltzmann inversion (IBI) procedure to match with the structural features in the ESC model.² The resulting interaction potential determined by IBI was consistent with key features of the original architectures, showing similar forms relative to the width .² Next, in order to incorporate the incompatibility of different species for bottlebrush copolymer, we introduced the Flory-Huggins parameter χ into the pairwise interaction potential by considering additional SCMF simulations on bottlebrush binary blends. The IBI procedure is applied to the incompatible pairs to generate pair potentials as a function of χN. We found that the χN effect can be parameterized for different architectures and scaled from the homopolymer interaction potential. The predicted interaction potential for in ordered self-assembly structure led to predictions consistent with the self-assembled structure of bottlebrush block copolymers in experiments.