In supercritical polymerization processes, polymer chains grow to molecular weights determined by their solubility under the prevailing density (or pressure and temperature) conditions of the solvent. Further growth in the chain length results in phase separation and leads to precipitation. In this project, polymerizations will be conducted under isopycnic conditions by adjusting the density of the solvent environment to be identical to the density of the polymer formed. This iso- density operation is expected to insure levitation by buoyancy and prevent precipitation of the phase-separated polymer. Density adjustments are readily achievable for supercritical solvents through manipulation of either the pressure of the temperature, of the solvent composition (if mixtures are used), and isopycnic conditions for a variety of polymers and polymerization systems are possible. This is a way to simulate the micro gravity environment of space-based processes on earth. The objective of the research project is to make polymeric materials of precise geometries and morphologies by synthesizing them in a supercritical fluid of precisely the same density as the product polymer. This would prevent precipitation of the polymer and permit polymerization of molecules of any desired structure to be fabricated. The research will focus on testing his hypothesis by synthesizing polystyrene and crystallizing polyethylene in isopycnic supercritical fluid solvents. He will explore using mixtures of fluids such as carbon dioxide or butane with fluids of higher density such as xenon or sulfur hexafloride.
