Beyond Cationic Systems: Inverse Vulcanization with Anionic and Zwitterionic Monomers

Globally, millions of tons of excess elemental sulfur are produced each year, with limited large-scale industrial applications, creating a need for new technologies that can utilize sulfur while mitigating long-term storage concerns. Inverse vulcanization harnesses this sulfur to form high sulfur-content polysulfides through solventless polymerization with a variety of monomers. Prior work has shown that an array of cationic monomers become miscible with sulfur to form charged polysulfides. Many of these cationic polysulfides demonstrated enhanced water solubility compared to other inverse vulcanized polymers. However, the inclusion of anionic and zwitterionic monomers has only been reported with the use of catalysts or alternate initiation mechanisms. Here, the inclusion of cationic monomers enhanced miscibility and reactivity between sulfur and an array of anionic and zwitterionic monomers. This led to the formation of fully polymerized, charged terpolymers with as little as 5% of the cationic component. These polymers have been characterized to determine the impact of the ammonium-based cationic and the anionic monomers on the polymerization kinetics and final polymer properties. The resulting terpolymers all contained measurable water-soluble fractions ranging from semi-soluble (25%) to mostly soluble (83%). Monitoring the polymerization kinetics between an array of polymerizable groups (e.g., vinyl, allyl, acrylate, etc.) revealed that reaction rates were impacted by both the cationic and anionic components. Although some polymerizations followed trends predicted by established monomer reactivity ratios, others displayed markedly different behavior, highlighting the complex interplay between monomer structure, charge, and sulfur reactivity. Additionally, the wide array of monomers enabled the exploration of the role of the polymer structure and the charged group in metal binding. Nearly all terpolymers had similar metal binding properties, showing effective mercury, silver, and gold sorption with no clear trends based on monomer structure. Overall, this work substantially broadens access to charged, water-soluble polysulfides, expanding the possible applications of sulfur-based polymers.