Novel polyoxadiazoles with non-coplanar ortho-linked structures as highly CO2 permselective membranes

A novel class of polyoxadiazole membranes containing non-coplanar 1,1′-thiobis(2-naphthoxy) (S-BINOL) groups was synthesized using a versatile route and tested for CO2 separation. Dihydrazide monomer was obtained in a two-step high-yielding procedure and used in polycondensation reaction with terephthaloyl chloride to prepare a polyhydrazide, which was converted into amorphous and soluble polyoxadiazoles having an inherent viscosity of around 1 dL g−1 by a simple thermal cyclization without using any solvent or in solvent cyclization. The ortho-linked sulfide groups of the obtained polymers were subsequently oxidized to yield sulfone-containing polymers. Polyoxadiazole membranes demonstrated comparable CO2 separation properties to those of imide based polymers and almost better performance than commercial and modified polyethersulfones, and the previously reported polyoxadiazoles. The sulfone-containing polyoxadiazole membranes exhibited higher permeability, lower selectivity, and enhanced plasticization pressure compared to the corresponding sulfide containing one