Cost-effective Synthesis of Bottlebrush Block Copolymers from endo-exo Mixture Macromonomers

Abstract

The synthesis of bottlebrush block copolymers (BBCPs) via ring-opening metathesis polymerization (ROMP) typically relies on exo-nor-bornene-terminated macromonomers to achieve high polymerization rates. However, norbornene derivatives synthesized via the Diels-Alder reaction were obtained as mixtures of exo and endo isomers, with the endo isomer predominating. This presents a significant challenge for the preparation of well-defined BBCPs from such mixtures because of the inherently low ROMP reactivity of endo-norbornene. Here, we demonstrate that polymerization kinetics are strongly influenced by the solvent, temperature, and configuration of the norbornene end group. By optimizing these parameters, the complete conversion of endo/exo macromonomer mixtures can be achieved within a short time, enabling the efficient synthesis of well-defined BBCPs. The resulting BBCPs exhibited self-assembly behavior comparable to those prepared from purely exo-norbornene-terminated macromonomers, forming structurally colored polymer microspheres that function as eco-friendly photonic pigments. This study provides an efficient and cost-effective strategy for the synthesis of BBCPs using commercially available norbornene derivatives.