Quantifying Cargo Partitioning and Exchange in Block Copolymer Micelles*

Block-copolymer micelles (BCMs) can carry molecular cargo in a nanoscopic package that is tunable using polymer structure in combination with cargo properties. For example, BCMs are used in targeted drug delivery due to their biocompatibility, in vivo degradability and prolonged circulation time. We are using NMR spectroscopy and diffusometry combined with SANS to investigate diblock poly (ethylene oxide)-b-(caprolactone) (PEO-PCL) and commercial triblock (PEO-PPO-PPO, aka Pluronic) micelle systems. We quantify populations and diffusion coefficients of coexisting micelles and free unimers over a range of temp. and solvent composition by NMR diffusometry, including mapping of micelle-unimer phase diagrams. Furthermore, we will present NMR measurements that quantify cargo (e.g., drug) partitioning and exchange rates in BCMs as a function of cargo hydrophobicity and size, and we observe that more hydrophobic cargos partition more strongly into micelles. We also observe with SANS that cargo loading and type differentially affects micelle structure. In summary, our NMR and SANS studies shed light on how intermolecular interactions fundamentally affect cargo partitioning and release, and micelle structure and dynamics.