6-(4-Nitro­phen­oxy)hexa­nol

The title compound, C12H17NO4, features an almost planar mol­ecule (r.m.s. deviation for all non-H atoms = 0.070 Å). All methyl­ene C—C bonds adopt an anti­periplanar conformation. In the crystal structure the mol­ecules lie in planes parallel to (12) and the packing is stabilized by O—H⋯O hydrogen bonds

Phosphonated polyimides: enhancement of proton conductivity at high temperatures and low humidity

A new class of highly conductive and durable polymer electrolyte membranes have been developed for fuel cell applications under elevated temperature and/or low relative humidity (RH). Highly phosphonated and fully aromatic diamine monomer was prepared via three-step high-yielding procedure from previously synthesized phosphonated bisphenol: halogen displacement of 1-fluoro-4-nitrobenzene, reducing of nitro groups, and hydrolysis of phosphonate ester groups. A series of phosphonated copolyimide ionomers with ion exchange capacity (IEC) of 2.4–4.6 mequiv g−1 were obtained by a typical polycondensation reaction followed by solution casting to form transparent and flexible membranes. Proton conductivity of the phosphonated membranes was comparable to that of the commercial perfluorinated ionomer at 100% RH. Typically, the conductivity value of up to 125 mS cm−1 was obtained for the membrane with IEC of 3.5 mequiv g−1 at 100 °C. However, by reducing the relative humidity the merits of phosphonated polyimides became more evidence and their dry state conductivity was 1–3 order of magnitudes higher than Nafion 115 and substantially higher than the values reported for phosphonated membranes. Thermogravimetric analysis and long-term proton conductivity study of phosphonated copolyimides at high temperatures (up to 160 °C) and low humidity confirmed small amount of undesired self-condensation of phosphonic acid groups compared with other phosphonated membranes

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