Jeremy Herman, Brad Howard Jones, George Bachand, Sun Hae Ra Shin
Sandia National Laboratories
The dynamic self-assembly of block copolymers in selective solvents including water has been explored for years now. While olefin metathesis is routinely used in the synthesis and modification of block copolymers, there have been surprisingly few attempts to harness such chemical transformations to alter self-assembly in situ. Along these lines, we show that olefin metathesis can be used to change the morphology of self-assembled poly(butadiene-b-ethylene oxide) (PB-PEO) in different solvents, through direct addition of a Hoveyda-Grubbs catalyst. When this catalyst is added to PB-PEO dispersions, there is depolymerization of the PB block by olefin metathesis, causing rapid and controllable changes in the aggregate size and shape. With PB-core aggregates in water, the morphologies are characterized by rapidly decreasing hydrodynamic sizes and increasing interfacial curvature. Transitions from bilayer vesicles to cylindrical micelles to spherical micelles can be achieved in a timespan of minutes. With PB-corona aggregates in hexane or heptane, the morphologies are characterized by increasing hydrodynamic sizes and decreasing interfacial curvature. In such cases, we believe that transitions from spherical micelles to cylindrical micelles or bilayer vesicles may be achieved over similar time scales. In either case, the final morphology can be finely tuned by catalyst concentration, a feature that we suspect arises advantageously from catalyst instability. We anticipate that this approach to precisely manipulate morphology on demand in block copolymer micelles may have important implications for biomimicry and nanotechnology, among other applications.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.