Local Structure Formation in Non-Cylindrical Bottlebrush Polymer Melts

Exploring macroscopic structure of bottlebrush polymers (BBPs) require large number of degree of freedom in computation to describe individual side-chains. We recently demonstrated a coarse-grained model describing a BBP as an wormlike cylinder model without explicit side-chains. These implicit side-chain (ISC) models drastically decrease the computational cost simulating BBP solution and melts.<span style="font-size:10.8333px"> In this study, we explored different designs of BBPs in melts using ISC model, particularly focusing on non-cylindrical shape. Asymmetric bottlebrush block copolymers are first analyzed, where one block is thicker than the other. We found that increasing the grafting density of one block effectively enhanced the size of the d-spacing, demonstrated by comparing with the experiments using synthesized with PS-b-PLA diblock BBPs. Next, we consider BBPs where the side-chain is varied along the backbone contour, leading them to exhibit non-cylindrical shapes. Even though there is no chemical incompatibility, different bottlebrush ‘shapes’ show local structures in homopolymer melts that are not observed for standard cylindrical bottlebrushes. The thinner part of the chain is segregated from the thicker part, which is attributed to an entropically-unfavorable packing of the mismatched bottlebrush thickness. The arrangement of different thicknesses in each shape results in different sizes of segregated local structures.