Metathesis chemistry has emerged as versatile technology, facilitating polymerization under a broad range of reaction conditions. To date, numerous catalysts have been developed which mediate metathesis in aqueous media. However, most reports involve the laborious preparation of water-soluble Ru-based catalysts, which often exhibit poor performance in water due to slow dissociation of the solubilizing ligands. We recently reported an alternative strategy for conducting controlled ring-opening metathesis polymerization (ROMP) in aqueous media. Our strategy involved polymerization of a water-soluble monomer in a water-miscible solvent to produce an active catalytic species. Chain-extension of the resulting macroinitiator in water proceeded with unprecedented control for all of the monomers tested. This strategy was further extended to prepare nano-objects of various morphologies via ROMP-mediated polymerization-induced self-assembly (ROMPISA).
To date, a limited number of compounds have been identified that are suitable as core-forming ROMPISA monomers. Recently, we developed a methodology to predict monomers for RAFT-mediated PISA that evaluates changes in polymer hydrophobicity with increasing chain length. We have since adapted this method to predict monomers for aqueous ROMPISA. This computational strategy also provides 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 ROMPISA approach has also been successfully applied for the development of tubular polymersomes via 1D fusion of spherical counterparts. This out-of-equilibrium morphology was found to arise spontaneously during ROMPISA, and the composition of each formulation could be manipulated simply by targeting different core-block degrees of polymerization. We termed this unique phenomenon “polymerization-induced polymersome fusion”, which operates via the build-up of membrane tension exerted by the growing polymer chains. Based on our findings, we envision that our methodology will be generally useful for a broad variety of biotechnological applications.

Robert Mathers

Penn State University

Appearances