Organic vapours sorption, diffusion and swelling in poly-trimethyl-silyl-norbornene

oly-trimethyl-silyl-norbornene is an high free volume glassy polymer, whose vapor sorption levels are extremely high: this property makes it attractive for the application to gas separation membranes. Sorption and dilation experiments of n-alkane vapors were performed at 35°C using, respectively, a pressure decay apparatus and an optical device. During sorption, a wide relaxation stage was observed for both penetrants. The diffusion coefficients estimated from transient sorption show a concentration dependence which is more pronounced for the larger penetrant. The pseudo-equilibrium solubilities, calculated at the end of the relaxation stage, are very high, like for Poly-trimethyl-silyl-propyne (PTMSP). The solubility isotherms were then compared with the NELF model predictions for gas solubility in glassy polymer. The Lattice Fluid parameters were obtained from a collection of infinite dilution solubility coefficients available for different hydrocarbons: fitting these data with the NELF model, one obtains that p*= 359.82 MPa, T*= 405.98 K and rho*= 1.345 Kg/L. The model results are more than satisfactory, being in good agreement with experimental data in the whole pressure range. The polymer shows a dilation behaviour typical of the glassy state and the experimental swelling coefficients are in excellent agreement with those calculated through the NELF model.