Bulk Synthesis of Bottlebrush Polymers via Ring-Opening Metathesis Polymerization

Ring-opening metathesis polymerization (ROMP) of macromonomers is widely used to synthesize bottlebrush polymers (BBPs) with a well-defined chain sequence and remarkable physical/chemical properties. However, a large volume of highly purified organic solvent is required to dissolve the macromonomers and enable living ROMP, which raises serious economic and environmental issues. In this study, the bulk polymerization of macromonomers was investigated by using both reactive molecular dynamics (MD) simulations and experiments. MD simulations revealed that catalyst dispersion was the key factor in achieving living polymerization in bulk with a narrow dispersity. Further experiments confirmed that the living ROMP could be achieved by tuning the catalyst activity and reaction conditions. Homopolymers, statistical copolymers, and block copolymers with a narrow dispersity were successfully synthesized in bulk. Following this strategy, a reactive twin-screw extruder was also used to conduct the bulk ROMP of the macromonomers. Additionally, the synthesis of macromonomers and their polymerizations were performed sequentially in bulk to realize one-pot polymerization. We believe that this work provides an efficient approach to synthesizing BBPs with well-defined structures via bulk ROMP, offering insights into green ROMP technology and the mass production of BBPs.