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

Abstract

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 ones.