Metathesis chemistry has emerged as versatile technology; facilitating cross-coupling reactions, ring closure, or polymerization under a broad range of reaction conditions. The growing interest in Ru-based methathesis stems from the high tolerance of Ru catalysts towards a variety of functional groups, air, and moisture. Because of this tolerance, Ru catalysts have been developed which mediate metathesis reactions in aqueous media, especially for applications in biological media or in aqueous dispersion polymerization. Most reports have involved the laborious preparation of a water-soluble Ru catalysts. Often, these modified catalysts exhibit poor performance in water due to slow dissociation kinetics of the solubilizing ligands. We recently reported an alternative strategy for conducing ring-opening metathesis polymerization (ROMP) in aqueous media. Our strategy involved polymerization of a water-soluble monomer in a water-miscible solvent to produce a water-soluble catalyst species. Chain extension of the resulting macrointiator proceeded with unprecedented control for all of the monomers tested. This strategy was further extended to prepare various nanoparticle morphologies (i.e., spherical micelles, worm-like micelles, or vesicles) directly in H2O via ring-opening metathesis polymerization-induced self-assembly (ROMPISA). To date, few compounds have been discovered which are useful as core-forming monomers in ROMPISA. Ideally, such monomers should be soluble in H2O from 1-10 wt%, but should form polymers that are hydrophobic. We developed a method to predict monomers for PISA using reversible addition-fragmentation chain transfer (RAFT) polymerization that evaluates changes in polymer hydrophobicity with increasing chain length. We have since adapted this method to predict monomers for ROMPISA. This computational treatment also gives information about the dependence of nanoparticle morphology on polymer hydrophobicity, which has facilitated the discovery of relationships between monomer structure and the nature of the resulting nanostructures. Our macroinitiator approach has also proven useful in the preparation of DNA-polymer conjugates. For example, DNA macromonomers comprised of native ssDNA have been readily polymerized under aqueous conditions without protection for the first time using ROMP. Based on these exciting results, we envision that our method will be generally useful for a broad variety of methathesis transformations in H2O.

Advances in aqueous metathesis chemistry

2019 Fall National Meeting

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