Kinetically-Controlled Dynamics in Block Polymer Micelles

Amphiphilic block polymers consist of covalently-bonded hydrophobic and hydrophilic polymer segments.  Akin to small molecule amphiphiles, these macromolecules self-assemble into a variety of well-defined structures in aqueous solution such as micelles and vesicles.  However, the macromolecular hydrophobic block leads to very slow and seemingly nonexistent micelle dynamics.  This kinetic entrapment is an attractive advantage of amphiphilic block polymers for applications in drug delivery; however, it also leads to path-dependent solution assembly.  Consequently, careful optimization of preparation conditions are necessary to produce well‑defined, uniform, and reproducible macromolecular solution assemblies.  We are interested in understanding the effects of common processing conditions on the structure, dynamics, and long-term stability of block polymer micelles.  In particular, we found that organic cosolvent removal led to an unexpected micelle growth, in which the sizes evolved through a distinct bimodal distribution separated by multiple fusion events.  These studies revealed that the micelle stability was critically dependent on stirring the solution, which motivated a detailed investigation into the effects of solution agitation on the chain exchange dynamics in polymer micelles.  The results presented here demonstrate the influence of kinetically-controlled processes on block polymer micelle dynamics, and emphasize the importance of selecting and controlling processing conditions when preparing these assemblies.