Abstract
Thermodynamics of sorption of n-alkanes C 4–C 11 in poly(5,6-bis(trimethylsilyl)norbornene) was studied using the Inverse Gas Chromatography (IGC). Temperature dependences of the specific retention volume V g and solubility coefficient S of various alkanes were obtained in the range 60–140 °C. For solubility coefficients, the following equation holds: ln S = 3.44 ( T c / T ) 2 − 3.90 , where T c is the critical temperature of solutes, T is the experimental temperature and S is expressed in cm 3(STP)/cm 3 atm. The partial molar enthalpies Δ H m and entropies Δ S m of mixing of different n-alkanes in this glassy polymer vary in much wider range than in rubbers and display positive correlations: for more exothermic mixing process the larger negative Δ S m values are observed. It was shown that the Δ H m in poly(5,6-bis(trimethylsilyl)norbornene) pass through a minimum, when the size of solutes increases. The coordinates of Δ H m at minimum versus solute size provide an estimate of the size of free volume elements in this polymer. This conclusion was supported by variation of permeability in different glassy polymers studied using IGC and by the results of other methods for probing free volume in glassy polymers.
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