Synthesis and characterization of high molecular weight hexafluoroisopropylidene‐containing polybenzimidazole for high‐temperature polymer electrolyte membrane fuel cells

A high molecular weight, thermally and chemical stable hexafluoroisopropylidene containing polybenzimidazole (6F‐PBI) was synthesized from 3,3′‐diaminobenzidine (TAB) and 2,2‐bis(4‐carboxyphenyl) hexafluoropropane (6F‐diacid) using polyphosphoric acid (PPA) as both the polycondensation agent and the polymerization solvent. Investigation of polymerization conditions to achieve high molecular weight polymers was explored via stepwise temperature control, monomer concentration in PPA, and final polymerization temperature. The polymer characterization included inherent viscosity (I.V.) measurement and GPC as a determination of polymer molecular weight, thermal and chemical stability assessment via thermo gravimetric analysis and Fenton test, respectively. The resulting high molecular weight polymer showed excellent thermal and chemical stability. Phosphoric acid doped 6F‐PBI membranes were prepared using the PPA process. The physiochemical properties of phosphoric acid doped membranes were characterized by measuring the phosphoric acid doping level, mechanical properties, and proton conductivity. These membranes showed higher phosphoric acid doping levels and higher proton conductivities than the membranes prepared by the conventional membrane fabrication processes. These membranes had sufficient mechanical properties to be easily fabricated into membrane electrode assemblies (MEA) and the prepared MEAs were tested in single cell fuel cells under various conditions, with a focus on the high temperature performance and fuel impurity tolerance. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4064–4073, 2009     

Controlling the outcome of overacylation of N-protected aminooxyacetic acid during the synthesis of an aminooxy-peptide for chemical ligation

An aminooxy-containing peptide, the nucleophile partner for oxime ligations, is usually grafted on a NH₂-peptide resin by activating a protected aminooxyacetic acid as an active ester. Here, we have shown that its subsequent coupling to NH₂-peptide resin competes with the overacylation of the -NH-O- nitrogen and that the overacylation level increases with the basicity of the reaction mixture. Moreover, we found that overacylation is prevented when the COOH of the Aoa-derivatives is engaged in an amide bond.     

Remarks on global existence for the supercritical nonlinear Schrödinger equation with a harmonic potential

This paper is concerned with the nonlinear Schrödinger equation with a harmonic potential which describes the attractive Bose–Einstein condensate under the magnetic trap. By combining the best constant of Gagliardo–Nirenberg's inequality with the characteristic of this equation, we derive out a global existence condition for the supercritical equation which coincides with the critical case.