2001 Technology for a Sustainable Environment: NSF/EPA Partnership for Environmental Research: Design and Optimization of Non-Fluorous CO2-Philic Polymers (TSE01-F)

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AbstractCTS-012440Beckman, EricU of PittsburghDesign and Optimization of Non-Fluorous CO2-Philic Polymers The application of CO2 to chemical processing continues to elicit significant interest, as CO2 generally poses fewer hazards than conventional organic solvents. At one time it was thought that CO2 could simply replace many organic solvents, but subsequent work showed that CO2 is a rather feeble solvent, and hence unrealistically high pressures are needed to dissolve compounds of interest. The discovery during the 1990's of "CO2-philes" suddenly rendered a number of applications technically possible, greatly raising interest in CO2 as a solvent. These new CO2-philes, primarily fluoropolymers, allowed a host of new applications for CO2, from heterogeneous polymerization to homogeneous catalysis. Although fluorinated amphiphiles were technically successful, their high cost renders the economics of a process unfavorable unless the "CO2-phile" can be recycled at greater than 99% efficiency. The drawbacks inherent to the use of fluorinated precursors have greatly inhibited the commercialization of most new applications for CO2, and thus the full promise of CO2-based technology has yet to be realized. Consequently, we have investigated the design of non-fluorous CO2-philes. First, a set of thermodynamic heuristics for the design of non-fluorous CO2-philes was developed. The applicability of these rules-of-thumb was demonstrated by the design of poly(ether-carbonates), polymers that exhibit lower miscibility pressures in CO2 than perfluoropolyethers and are biodegradable. The method of synthesis of these materials readily allows generation of surfactants and other functional molecules, opening the economical use of CO2 to a variety of processes. To date, we have used our simple heuristics to design three types of non-fluorous CO2-phile; we expect that others will ultimately be found, greatly broadening the applicability of CO2 as a solvent. The number of possible design variables (copolymer composition and topology) creates an impractically large program if we continue to synthesize and test all potentially useful structures. Further, conventional thermodynamic models are incapable of predicting the behavior of all of the possible permutations. Consequently, we propose to conduct a program whose ultimate aim is to fully understand the effect of composition and topology on the phase behavior of our new CO2-philes in carbon dioxide. We propose to combine targeted synthesis, measurement of selected thermophysical properties, high pressure FT-IR, and development of an accurate potential function from first principles to mathematically describe the thermodynamics of mixing of our materials with CO2. Success will allow us to numerically optimize the structure of non-fluorous CO2-philes.Research at the University of Pittsburgh will focus on the synthesis of model materials, investigation of phase behavior, and creation of a thermodynamic model that describes the effects of molecular structure on phase behavior. These tasks will be coordinated with research underway at Auburn University (C.R. Roberts), where high pressure IR measurements will be employed to evaluate the strength of specific interactions of CO2 with the Lewis base groups incorporated into our model polymers. The high pressure IR work provides input both to the synthetic design and the construction of an accurate potential model for CO2-polymer interactions.