(276a) Organic Vapor Sorption by Copolymers of Poly(Styrene-Butadiene) Using a Quartz Crystal Microbalance

Knowledge of the solubilities of solvents in polymers is needed for the design as well as operation of polymer processing plants to meet environmental, health and safety regulations. Solubility data for copolymer systems are rare in literature, especially for systems with polar solvents. Solubilities of benzene, hexane, dichloroethane, and chloroform in copolymers of poly(styrene-butadiene) at 294.15 K are presented in this study. Literature data exist for pure polymer of poly(styrene) and poly(butadiene) for some of these solvents; however, copolymer data are unavailable. The copolymers investigated had compositions of twenty-one percent, forty-five percent, and eighty-five percent of polystyrene in poly(butadiene). The experiments were conducted using a quartz crystal microbalance (QCM) along with a flow-type, vapor generation apparatus. Quartz crystal parameters were measured using an impedance analyzer (Agilent 4294A) to allow for equivalent circuit analysis of the coated and solvent-exposed crystal. These parameters were utilized to establish the mass-balance regime of the QCM to gather thermodynamic sorption data. Solvent activities were represented with a modified Flory-Huggins model to within experimental error. Free volume activity coefficient models should adequately represent sorption at these low pressures, hence, the applicability of several free volume models to the polymer solvent systems was determined by a comparison of these model solubility predictions to experimental results. The free volume models which were compared to experimental data were UNIFAC-FV, Entropic-FV, and GK-FV and can be found in literature [1, 2, 3]. The Flory Huggins model combinatorial term does not account for free volume changes, however, these free volume models account for the changes in the free volume due to mixing solvents and polymers. UNIFAC-FV and Entropic-FV models were tested for their accuracy in predicting solubilities of polar and nonpolar systems. Experimental results were found to agree well with these predictive free volume models.

References

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2. Elbro, H. S., A. Fredenslund, P. Rasmussen. A New Simple Equation for the Prediction of Solvent Activities in Polymer Solutions. Macromolecules. 1990 (23): 4707-4714.

3. Kontogeorgis, G. M., A. Fredenslund, D. P. Tassios . Simple Activity Coefficient Model for the Prediction of Solvent Activities in Polymer Solutions. Ind. Eng. Chem. Res. 1993 (32): 362-372.