Bottlebrush polymers are macromolecules with densely grafted polymeric pendent groups attached to a polymeric backbone. Theses polymers are prepared using one of four synthetic strategies: grafting-from, grafting-to, transfer-to and grafting-through. The grafting-through process typically uses ring opening metathesis polymerization (ROMP) to synthesize the bottlebrush polymers with perfect grating density. We evaluated the effect of anchor group chemistry—the configuration of atoms linking the polymer to a polymerizable norbornene—on the kinetics of ROMP of polystyrene and poly(lactic acid) MMs initiated by (H2IMes)(pyr)2(Cl)2Ru=CHPh (Grubbs 3rd generation catalyst). We observed a variance in the rate of propagation of &gt;4-fold between similar MMs with different anchor groups. This phenomenon was conserved across all MMs tested, regardless of solvent, molecular weight (MW), or repeat unit identity. The observed &gt;4-fold difference in propagation rate had a dramatic effect on the maximum obtainable backbone DP, with slower propagating MMs reducing the maximum bottlebrush MW by an order of magnitude (from ~106 to ~105 Da). Experimental and computational studies indicated that the rate differences likely resulted from a combination of varying steric demands and electronic structure among the different anchor groups. Based on these data, the optimal anchor was chosen for a one pot two-step process in synthesizing large MW bottlebrush polymers with tunable sidechains and backbone DPs to yield well defined structures.

Synthesis and characterization of bottlebrush polymers: The importance of the Anchor Group

253rd National Meeting (2017)

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