Two‐Step Divergent Synthesis of Monodisperse and Ultra‐Long Bottlebrush Polymers from an Easily Purifiable ROMP Monomer

The longest bottlebrush polymers reported so far (up to 7 μm in length) were synthesized in two steps from a norbornene derivative bearing two 2‐bromoisobutylate moieties (NB). The key to this achievement is the excellent reactivity of NB in ring opening metathesis polymerization, which proceeded in a well‐controlled manner with quantitative conversion of NB for monomer‐initiator ratios ranging up to 10,000. The resultant polymer derived from NB was readily converted to various bottlebrush polymers in a divergent synthetic route by grafting vinyl monomers from the 2‐bromoisobutylate units in NB via atom transfer radical polymerization. The structure of the ultra‐long bottlebrush polymer was directly observed using atomic force microscopy. Monodisperse bottlebrush polymers with lengths of several μm were synthesized in two steps from a simple norbornene derivative that served as a ROMP monomer and as an ATRP initiator. This divergent synthesis produced bottlebrush polymers with tunable lengths, diameters, and chemical structures. The ultra‐long shape (up to 7 μm) of the bottlebrush polymer was visualized by AFM.