Conjugated core–shell bottlebrush polymers that exhibit crystallization-driven self-assembly

Abstract

Bottlebrush polymers are complex architectures with densely grafted polymer side chains along polymeric backbones. The dense and conformationally extended chains in bottlebrush polymers give rise to unique properties, including low chain entanglement, low critical aggregation concentrations, and elastomeric properties in the bulk phase. Conjugated polymers have garnered attention as lightweight, processible, and flexible semi-conducting materials. They are promising candidates in electronic devices and sensors, but their optoelectronic properties depend on adequate polymer ordering, π–π interactions, and crystallization. Crystallization-driven self-assembly of conjugated polymers has become a prominent method to optimize properties including band energies, redox potentials, and exciton diffusion and transport. Much progress has been made in controlled block copolymer self-assembly, but despite their promising properties, reports of conjugated bottlebrushes have been limited, and their self-assembly is relatively unexplored. For the first time, we report the synthesis of conjugated core–shell bottlebrush polymers. These materials contain poly(3-hexylthiophene) (P3HT) and poly(ethylene glycol) (PEG) in either core or shell position. We demonstrate that the use of P3HT as a crystallizable conjugated polymer and PEG as a colloidally stabilizing and disaggregating block facilitates their self-assembly into a number of unique crystalline morphologies with longer conjugation lengths and lower exciton bandwidths relative to analogous diblock copolymers. These include intramolecularly self-assembled segregated bottlebrush polymers, short nanofibers formed by end-on-end stacking of bottlebrush molecules, extremely long >20 μm nanofibers formed exclusively by end-on-end stacking, and >15 μm nanoribbons formed from both end-on-end and side-by-side stacking of bottlebrush polymers.