Self-assembly behavior of bottlebrush block copolymers in thin film

Bottlebrush polymers (BBPs) have attracted significant interest over the past two decades due to their distinctive physical and solution properties. Recent advancements in synthetic techniques now enable precise control over their three-dimensional architectures using diverse monomers. Compared to linear block copolymers (BCPs), bottlebrush block copolymers (BBCPs) exhibit unique structural characteristics, including a higher entanglement molecular weight, which facilitates rapid ordering dynamics and broadens their application potential. In this study, poly(styrene-b-methyl methacrylate) (PS-b-PMMA) BBCPs were synthesized via atom transfer radical polymerization (ATRP) and ring-opening metathesis polymerization (ROMP), with nanostructured patterns formed through thermal annealing. However, bromine groups at the chain termini, introduced during ATRP, promoted cross-linking during annealing, leading to significant defects in the BBCP patterns. This issue arose due to the considerably higher bromine density per chain in BBCPs compared to linear BCPs. To address this issue, a dehalogenation reaction was employed to remove the bromine groups, enhancing the thermal stability of BBCPs. Consequently, defect-free nanostructured BBCP patterns were successfully obtained, demonstrating their potential for applications such as directed self-assembly in nanolithography.