Effects on sorption and diffusion in PTMSP and TMSP/TMSE copolymers of free volume changes due to polymer ageing

Solubility isotherms for n-pentane and n-hexane were measured in pure poly[1-(trimethylsilyl)-1-propyne] (PTMSP) and in 1-trimethylsilyl-1-propyne/1-trimethylsilyl-1-n-hexyne 70/30 copolymer, using freshly prepared samples as well as aged films, at different temperatures. The experimental values of penetrant diffusivity, mobility and heat of mixing have been reported and discussed, based on direct positron annihilation lifetime spectroscopy information, Dual Mode Sorption Model and Non-Equilibrium Lattice Fluid model. The ageing effect is more pronounced in PTMSP, where it leads to a significant solubility and diffusivity reduction, than in the copolymer where the effect is less important. In the activity range inspected the diffusion coefficient and the heat of mixing are almost concentration independent for PTMSP, while they increase appreciably with concentration in the copolymer, as an effect of the great difference in the free volume present in the two matrices.