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

Abstract

The longest bottlebrush polymers reported so far (up to 7 mm 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 2bromoisobutylate units in NB via atom transfer radical polymerization. The structure of the ultra-long bottlebrush polymer was directly observed using atomic force microscopy.

Comparison of Polypentenamer and Polynorbornene Bottlebrushes in Dilute Solution

“…Another study that utilized ATRP grafting-from of PNB reported 95% grafting efficiency of a bulky monomer, t -butyl methacrylate when two ATRP handles per repeat unit were present. 84 Their success, even when the steric impedance was high, provides further confidence in the robust nature of the grafting-from technique. Finally, as a means to explore the influence of graft chemistry, MA was grafted-from PCPBIB(61) with comparable N sc ≈ 11–72 ( Figure S18 ) to compare PCPBIB(61)- g -MA to the PCPBIB(61)- g -S series ( Table 4 ).…”

“…This indicates that near-quantitative initiation of PS grafts was achieved within the signal-to-noise limits of the NMR analysis. Another study that utilized ATRP grafting-from of PNB reported 95% grafting efficiency of a bulky monomer, t -butyl methacrylate when two ATRP handles per repeat unit were present . Their success, even when the steric impedance was high, provides further confidence in the robust nature of the grafting-from technique.…”