Solubility and diffusivity of low molecular weight compounds in semi-crystalline poly-(2,6-dimethyl-1,4-phenylene)oxide: The role of the crystalline phase

The transport properties , i.e. sorption isotherm and diffusivity, of propane and methanol in totally amorphous polyphenyleneoxide (aPPO) and semi-crystalline nanoporous PPO (bPPO), obtained by treating with benzene vapours the amorphous sample, have been evaluated gravimetrically. In contrast to what is commonly observed in semi-crystalline polymers, bPPO shows a larger sorption capacity and faster sorption kinetics as compared to the totally amorphous sample: this behaviour, observed also in the case of sorption of liquid methanol, is discussed in terms of the morphology of the samples attributing the observed peculiarities prevalently to the non negligible sorption capacity of nanoporous crystalline domain. The nanoporous nature of crystalline phase has been confirmed also by DSC analysis, which points out that the crystalline domain displays a very low melting temperature. Sorption experiments indicate that semi-crystalline PPO is a promising candidate for use as membrane material in gas separation processes, in view of the remarkably high values of solubility and diffusivity. Finally, in the case of propane, the sorption experiments were repeated at different temperatures, to quantify the sorption enthalpy aPPO and bPPO.