Three investigations are available on sorption of CO₂ in the polyimide obtained from 3.3', 4,4'-biphenyltetracarboxydianhydride and 4.4'-oxydianiline known under the tradename Upilex R.^1-3 The authors studied commercial samples of Upilex R, but in one case specimens synthesized and pretreated under different conditions were investigated as well.³ For the temperature range 308-383 K and at pressures up to 3 MPa, the sorption isotherms can be described by parameters shown in the table which are based on data reported in two papers^1,3 by the same group. The results of Sada et al.² are somewhat different, particularly at lower temperatures.
Figures 82 , 83, and 84 show the temperature dependences of S,b, and k_D, respectfully.
A least squares treatment of the temperature dependence of k_D, b, and S resulted in the following values of enthalpies: ΔH_D = -11.10 kJ/mol
ΔH_H = -13.13 J/mol
ΔH_S = -27.35 kJ/mol.
The temperature dependence of Langmuir capacity adsorption parameter C'_H shows that it vanishes in the vicinity of 450 K or at temperatures much lower than the glass transition tensperatsre of this polymer. The dual mode sorption parameters can be found based on fugacity instead of pressure.² The values calculated in two cases do not differ greater than by 10%, although the enthalpies ΔH_D and ΔH_H are greater when the parameters are found via fugacity.
A study of the effects of pretreatment of the films indicated³ that the presence of the solvent led to the increase in the apparent solubility coefficient, while the annealing resulted in the opposite effect.