Unimolecular Nanostructures Formed by Self-Association of Side-Chain End-Functionalized Bottlebrush Polymers in Dilute Solutions

Bottlebrush polymers (BBPs) functionalized with associating side-chain end groups exhibit strong potential for diverse applications, e.g., in biomedical area such as unimolecular carriers. The properties and performance of such materials strongly depend on the BBPs conformation and associating groups organization. In this work, we employed extensive coarse-grained molecular dynamics simulations to investigate the structure and properties of associating BBPs in dilute solutions as functions of the fraction of associating side-chain end groups, side-chain length, and association strength. We found that increasing the fraction of associating end groups or the association strength drives a conformational transition from an expanded cylindrical worm-like structure to a compact globule with reduced radius of gyration. While higher associating end-group density or stronger association strength promotes clustering, longer side chains suppress clustering and favor an expanded worm-like BBP conformation. This is because reduction of the fraction of associating end groups or an increase in the side-chain length effectively dilutes the density of associating sites, thereby diminishing intramolecular interactions. Based on our simulations, we have constructed a diagram of states that delineates distinct regimes of bottlebrush globule, wrapped multicluster, coiled bottlebrush (with clusters), and wormlike bottlebrush, by analyzing the average radius of gyration of clusters of associating groups in comparison with that for the bottlebrush as a whole. Our results predict equilibrium conformation of intramolecularly self-associating BBPs depending on the association energy, extent of functionalization, and side-chain lengths and provide guidance on how different conformations can be achieved for specific applications.