Mikto-Brush-Arm Star Polymers via Cross-Linking of Dissimilar Bottlebrushes: Synthesis and Solution Morphologies.

A convergent brush-first ring-opening metathesis polymerization (ROMP) approach for the synthesis of mikto-brush-arm star polymers (MBASPs) via cross-linking of dissimilar bottlebrush polymers is reported. Living bottlebrush polymers prepared via ROMP of norbornene-terminated poly(ethylene glycol) (PEG) or polystyrene (PS) macromonomers (MMs) were mixed together in a desired ratio and exposed to a bis-norbornene cross-linker to yield MBASPs with narrow size distributions. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed that the solution morphologies of MBASPs depended on the feed ratio of the PEG and PS bottlebrush polymers at the cross-linking stage. This work provides a robust and modular strategy for the synthesis of a new type of miktoarm star polymer wherein the star arms are bottlebrush polymers.