Gas sorption in poly(vinyl benzoate)

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Abstract
High‐pressure sorption (up to 50 atm) for CO2, N2, and Ar in poly(vinyl benzoate) (PVB) was studied at temperatures from 25 to 70°C by a gravimetric method utilizing an electromicrobalance. The results are described by Henry's law above the glass transition temperature Tg for all gases. The dual‐mode sorption model, Henry's law plus a Langmuir isotherm, applies to the sorption isotherms of N2 and Ar in the glassy state, and the dual‐mode parameters are given. For CO2, a new type of sorption isotherm is observed below Tg. The isotherm is concave to the pressure axis in the low‐pressure region and turns into a straight line with increasing CO2 pressure which can be extrapolated back to the coordinate origin. The linear part of the isotherm is characteristic of the rubbery state, while the nonlinear part stems from glassystate behavior. The “glass transition solubility” of CO2, at which PVB film changes from the glassy to the rubbery state, decrease as the temperature increases. The disappearance of microvoids, that is, the decrease of the Langmuir capacity, may be due to a large plasticizing effect of sorbed CO2. The difference between the N2 and Ar isotherms and the CO2 isotherm is discussed from this standpoint.