Gelation Crystallization of Polymers from Supercritical Solution as a Route Toward Useful Materials

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This proposal studies the materials which are formed during the crystallization of polymers dissolved in a supercritical fluid. Polymers such as linear polyethylene and polypropylene are completely miscible with toluene under supercritical conditions. As the mixture is cooled and depressurized, polymer crystals form in a linked network. The gaseous solvent is removed by depressurization, leaving the crystalline network intact. The result is a solvent-free gel or foam of uniform structure, and with a broad range of porosities and mechanical strengths which can be varied depending upon the crystallization conditions. The process has the advantage over liquid phase crystallization where removal of the solvent usually destroys the crystalline network. The proposal will study the mechanical strength and microstructure of these gels formed from a variety of different polymer precursors, including polymer blends.