Correlation of the solubility of volatile liquids in molten polymers

Abstract

AbstractThe solubility of volatile liquids at infinite dilution (i.e., in the Henry's law region) in poly(vinyl acetate) (PVAc) and polystyrene (PS) at elevated temperatures has been correlated by plotting ln(1/Kp) against (Tc/T)2, where Tc is the critical temperature of the solute and Kp is Henry's constant at temperature T and a total pressure of approximately at 1 atm, defined as P1 = KpV10, where P1 is the partial pressure of the solute in the vapor phase and V10 is the solubility (cm3 solute per g polymer at 273.2 K and 1 atm). For this correlation, we have used experimental data available in the literature for 16 solutes covering 81 data points for PVAc and 17 solutes covering 82 data points for PS. We have calculated values of 1/Kp from the literature data reported in terms of the retention volume Vg0, weight‐fraction Henry's constant H1, and activity coefficient at infinite dilution Ω1∞. We have made the following observations: (1) for PVAc, ln(1/Kp) = −1.564 + B(Tc/T)2; and (2) for PS, ln(1/Kp) = −2.028 + B(Tc/T)2. In both cases, we found that values of B, the slope in the ln(1/Kp) versus (Tc/T)2 plots, vary with the acentric factor ω of the solutes. It has been found that, in both PVAc and PS at the same value of ω, values of B for slightly polar aromatic solutes are larger than those for nonpolar aliphatic solutes. Further, in PS at the same value of ω, values of B are smaller for strongly polar solutes than for slightly polar solutes, whereas in PVAc the opposite trend holds. This observation may be interpreted as that the solubility of strongly polar solutes in a polar polymer (e.g., PVAc) is greater than that of slightly polar and nonpolar solutes, whereas the solubility of strongly polar solutes in a nonpolar polymer (e.g., PS) is less than that of slightly polar solutes but greater than that of nonpolar solutes. The dependence of B on ω, observed in this investigation, is at variance with the correlations reported by Tseng, Lloyd, and Ward for PVAc and by Stiel and Harnish for PS.