Micellization of Block Copolymers in Dilute Near-Critical Solutions: How Model Impurities and Drugs Partition Between Micellar and Solvent Phases

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CBET-0828472RadoszNear-critical solvents are compressed and compressible fluids used either below or above their critical temperatures. If such a compressible fluid is selective enough with respect to the blocks that form a block copolymer, it will lead to near-critical solution in which micelles can be formed not only by decreasing temperature, which leads to micellization temperature, but also by decreasing pressure, which leads to micellization pressure. The goal of the proposed research is to understand the micellar and bulk phase transitions of model copolymers composed of blocks that differ in polarizability or polarity or both, such as styrene-block-diene, an example of a uniform and well-characterized material, and polyethylene glycol-block-polycaprolactone, an example of a drug-delivery material, both in selective near-critical solvents. This is crucial to understand and exploit the pressure-sensitive micellization that can lead to novel drug- and gene-delivery nanoparticles. Such micellization processes are fast and reproducible because polymer solutions in near-critical solvents have low viscosity and high diffusion rates. The micelles produced from such processes are not only easy to separate from the near-critical solvent, but also reliably retain their structure upon recovery and subsequent dissolution in aqueous formulations. The proposed experimental tasks evolve around characterizing the bulk cloud-point, crystallization, melting, and micellar phase transitions of the model block copolymer samples. The bulk and micellar transitions will be determined from high-pressure dynamic light scattering. This work will help understand drug and impurity partitioning in compressible micellar systems, and hence help transform the science and engineering platform for making unique polymeric nanoparticles. Broader Impact The proposed project will enable two doctoral students working on this subject to continue their projects on characterizing self assembling molecules that lead to nanostructured materials. These students will not only be exposed to the experimental characterization methods in the PI's lab, but also to the synthesis and neutron scattering facilities at the Oak Ridge National Laboratory. Furthermore, the high-pressure dynamic light scattering method of characterizing micellar solutions of blocky polymers will be incorporated in the graduate and undergraduate thermodynamics and polymer science classes. This project will also advance a novel micelle-based nanoparticle technology (patent pending) by providing basic understanding how to form and recover dry drug-loaded micelles from near-critical solvents, without having to freeze the solvent, which is essential to manufacturing drug and gene delivery nanoparticles.