The solubility of gases and volatile liquids in polyethylene and polyisobutylene at elevated temperatures

The solubility of gases and volatile liquids in low-density polyethylene (LDPE) and polyisobutylene (PIB) at elevated temperatures has been correlated, using the experimental data available in the literature. In the present study, a Henry's constant K_p at a total pressure of approximately 1 atm defined as P₁ = K_PV, where P₁ is the partial pressure of the solute in the vapor phase and V is the solubility (cm³ solute/g polymer at 273.2 K and 1 atm), is correlated for nonpolar solutes with the following expressions: (1) For LDPE, ln(1/K_P) = ?1.561 + (2.057 + 1.438ω) (T_c/T)²; (2) For PIB, ln(1/K_p) = ?1.347 + (1.790 + 1.568ω) (T_c/T)², in which ω is the acentric factor and T_c the critical temperature of the solute. In obtaining the above correlations we have used 27 solutes covering 115 data points for LDPE, and 18 solutes covering 148 data points for PIB. We have calculated values of 1/K_p from the literature data reported in terms of the retention volume (V), weight-fraction Henry's constant (H₁), activity coefficient at infinite dilution (Ω), Flory–Huggins interaction parameter (χ), or V/P obtained from high pressure sorption experiments. The correlations obtained in this study permit one to estimate with reasonable accuracy the solubility of gases and volatile liquids in either LDPE or PIB, with information on the acentric factor (ω) and critical temperature (T_c) only. The relationship for LDPE is also applicable for solubilities in high-density polyethylene. Relationships for the heat of vaporization of solutes from infinitely dilute LDPE or PIB solutions are also derived from the temperature variation of 1/K_p.