Extensive research into the solubility of various solvents into a number of pure polymers has been conducted in the past; however, data for copolymer/solvent systems in literature are uncommon, especially systems involving polar solvents. Solubilities of benzene, chloroform, dichloroethane, and hexane in several copolymers (comprised of styrene, methyl methacrylate, ethyl methacrylate, butyl methacrylate and butadiene) at 298.15 K are presented in this study. Data for pure polymers for some of these solvents exist in the literature; however, as expected, copolymer data are unavailable. Each copolymer was spin-coated, as a film, on the surface of a thickness shear mode (TSM) resonator to a minute thickness that, upon exposure to all of the solvent concentrations, does not prompt a film mass exceeding the gravimetric or mass-loading regime of the TSM resonator. The experiments were conducted inside a specially designed stainless steel cell where the film-loaded TSM device was exposed to solvent vapors generated by 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 loading on the TSM resonator and, subsequently, 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. These models were UNIFAC-FV, Entropic-FV, and GK-FV and can be found in references [1, 2, and 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 the solubility of polar and non-polar systems.
References:
[1] Wibawa, G.; Hatano, R.; Sato, Y.; Takishima, S.; Masuoka, H. J. Chem. Eng. Data 2002, 47, 1022-1029.
[2] Bawn, C. E. H.; Wajid, M. A.; Trans. Faraday Soc. 1956, 52, 1658-1664.
[3] Saeki, S.; Holste, J. C.; Bonner, D. C. J. Polym. Sci. Polym. Phy. Ed 1981, 19, 307-320.