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.