The grafting-through method for making bottlebrush polymers (aka, molecular brushes) often relies on ring-opening metathesis polymerization (ROMP) to form the bottlebrush polymer backbone. The level of control over molecular weight and molar mass dispersity in this ROMP step depends heavily on the nature of the macromonomer because ROMP catalysts have finite lifetimes. Thus, even moderately sized bottlebrush polymers can be inaccessible via this route, and synthesis of more complex architectures (e.g., tapered bottlebrush polymers) is also limited. Our aim is to increase livingness in ROMP grafting-through by increasing the relative rates of propagation to termination (the kp/kt ratio). We explore various parameters that influence these rates in the ROMP grafting-through step, including the effect of solvent, concentration of the macromonomer, the nature of the macromonomer side chain (e.g., styrenic, acrylic, etc.), and the type of anchor group (the atoms connecting the side chain polymer to the polymerizable unit, usually a norbornene). This systematic approach to optimization of ROMP grafting-through has revealed strategies to enable the construction of bottlebrush polymers with larger backbone degrees of polymerization and larger side chains than are accessible using commonly employed methods.

Optimizing ROMP grafting-through in bottlebrush polymer synthesis

ACS Spring 2022

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