Olefin metathesis represents a powerful class of reactions for the controlled synthesis, degradation, and functionalization of a variety of monomeric and polymeric substrates. In particular, polybutadienes comprised of predominantly 1,4 isomers experience chain cleavage and ring-closure upon exposure to Grubbs’ catalysts, leading to a reduction in a molecular weight. We demonstrate that this phenomenon can be exploited to induce rapid morphological transitions in aqueous, self-assembled aggregates of poly(butadiene-b-ethylene oxide) (PB-PEO). When pre-formed PB-PEO aggregates are exposed to Grubbs’ catalyst, the catalyst is sequestered within the hydrophobic PB cores. As metathesis subsequently occurs, the associated reduction in PB molecular weight increases the preferred interfacial curvature of the aggregate. Small angle x-ray scattering, dynamic light scattering, optical microscopy, and transmission electron microscopy show that the aggregate morphology transforms from vesicles or wormlike micelles to spherical micelles within minutes. The ultimate morphology and its characteristic length scales are highly controllable via the ratio of catalyst to polymer. In addition, the degraded PB chain ends within the aggregated cores are functionalized with a Ru ligand, enabling further metathesis reactions (e.g., polymerization of a new species) to be initiated. In this manner, we believe that olefin metathesis can be exploited as a new strategy by which to synthetically mimic unique, dynamic behaviors exhibited by important biological particles, such as microtubules.

Rapid morphological transitions in poly(butadiene-b-ethylene oxide) aggregates induced by olefin metathesis

256th National Meeting (2018)

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