Synthesis of Soluble Anion-Exchange Copolyimides and Nanofiltration Membrane Performances

Abstract

Novel soluble anion-exchange copolyimides were synthesized by the two-step method. Copolyimides had inherent viscosities between 0.35 and 0.42 dL/g. Ion exchange capacity (IEC) of the polyimides was 0.18−0.33 mequiv/g. These IEC values were well explained with the degree of substitution. All polyimides were soluble in polar solvents such as N -methyl-2-pyrrolidone, N, N -dimethylformamide, and N, N -dimethylacetamide and showed amorphous patterns in X-ray diffraction studies. Soluble copolyimides synthesized in this study had glass transition temperatures between 220 and 265 °C. All unmodified polyimides were thermally stable below 560 °C. 10% weight loss temperatures were recorded in the range 560−600 °C in nitrogen. However, the 2-hydroxypropyl group of anion-exchange copolyimides was degraded at around 260 °C. The anion-exchange copolyimide nanofiltration membranes prepared from a cosolvent of diethylene glycol dimethyl ether and N -methyl-2-pyrrolidone showed better salt removal behavior than that of neutral copolyimides nanofiltration membranes.