Mechanochemical Synthesis of Ionic Polymers: Solid-State Ball-Milling Polymerization for Unrestricted Solubility Enabling Copolymerization of Immiscible Monomers

This study demonstrates the facile synthesis of ionic polymers using a solid-state mechanochemical ball milling method, which offers a straightforward, ecofriendly, and broad scope compared to conventional solution polymerization techniques. Unlike solution polymerization, which is limited by solvent selection and often results in poor efficiency, direct ball-milling polymerization enables the production of the desired product polymers from a broader range of ionic monomers without solubility and miscibility constraints. We employed free-radical polymerization of styrene and (meth)acrylic ionic monomers, as well as Ru-initiated ring-opening metathesis polymerization of norbornenyl ionic monomers, to demonstrate the effectiveness of the mechanochemical approach. Additionally, the study explored the mechanochemical copolymerization of immiscible monomer pairs such as sodium carboxylate/pyrene and ammonium sulfone betaine/porphyrin moieties, producing water-soluble porphyrin and pyrene polymers. Overall, this research showcases mechanochemistry's versatility and efficiency in synthesizing ionic polymers, anticipating its use in various applications.