Self-Assembly Behavior of PS- b -PMMA Bottlebrush Block Copolymers via Ring-Opening Metathesis Polymerization and Atom Transfer Radical Polymerization: The Critical Role of End-Group Chemistry

We report on the synthesis and self-assembly of thermally robust bottlebrush block copolymers (BBCPs) with enhanced pattern fidelity during high-temperature processing. The BBCPs were composed of glassy macromonomer side-chains of polystyrene (PS) and poly(methyl methacrylate) (PMMA) prepared via atom transfer radical polymerization (ATRP), followed by ring-opening metathesis polymerization (ROMP). Dehalogenation of PMMA and PS bromine terminated macromonomers was found to be the critical synthetic step to afford thermally stable BBCPs and phase-separated thin films. This subtle end-group modification was found to have dramatic consequences during the thermal processing of all-glassy segmented BBCPs, resulting in well-defined self-assembled morphologies. Atomic force microscopy and gel permeation chromatography with multiangle light scattering confirmed that the dehalogenated macromonomers and BBCPs exhibit excellent morphological stability. This strategy addresses a critical stability challenge in bottlebrush architectures and establishes a platform for defect-tolerant nanopatterning, advancing BBCPs toward practical applications in high-temperature directed self-assembly.