Development of functional polymers for ion exchange membranes

Abstract

Random and block sulfonated poly(meta-phenylene isophthalamide)s copolymers were synthesized with different degrees of sulfonation (DS) through the Higashi-Yamazaki phosphorylation method using a sulfonated monomer. Creasable polymer films were obtained by solvent casting, and ion exchange membranes were prepared by ion exchange of the films. Thermogravimetric analysis demonstrated the thermal stability of the membranes with five percent weight loss above 380 °C. The sulfonated block copolymer showed lower water uptake with higher water durability than the random polymer with the same DS. Both types of materials showed higher proton conductivities at high temperature than that of Nafion® 117 under 95% relative humidity. Poly(N, N-dimethylpiperidinium sulfone)s (PDMPS-x) with different ion exchange capacities (x) were prepared by polycondensation using a piperidine functional monomer followed by quaternization of solvent cast films. The water uptake, ionic conductivity, and chemical stability in the hydroxide form were evaluated. The chloride forms of the membranes were thermally stable to more than 200 °C. The membrane PDMPS-1.7 displayed good conductivity of 64 mS/cm at 80 °C in water and remained unchanged over 28 days in 1M KOH solution at 80 °C. Trimethylcyclohexylammonium-functionalized polysulfones (PSU-CyTMA-x) with the different IECs were synthesized from a functional monomer followed by quaternization of solvent cast films. Polymer synthesis and membrane preparation were similar to that for the PDMPS-x membranes. The hydroxide form of the membranes showed low water uptake with good conductivity and good chemical stability under high-temperature conditions. The membrane PSU-CyTMA-1.8 showed water uptake <70 wt.% with hydroxide conductivity of 64 mS/cm at 80 °C in water. Approximately 73% of conductivity remained after 20 days in 1M KOH solution at 80 °C. Amphiphilic polybutadiene-block-poly(4-vinylpyridine) copolymers with high 1,4-polybutradiene content were synthesized through living anionic polymerization by changing polymerization solvents for each block. Polymers were hydrogenated to prepare polyethylene-block-poly(4-vinylpiperidine) copolymers. The hydrogenation conditions were determined, and hydrogenations of both blocks were confirmed by FTIR. The polymers were prepared for subsequent preparation of polyethylene-block-poly(dimethylpiperidinium) copolymers that could be used as base-stable anion exchange membranes.