Green dipolar aprotic solvents for the dynamic polycondensation of high-performance polyimide membranes†

Abstract

The legislation is limiting the use of harmful organic solvents in industrial processes. The establishment of clear guidelines for minimizing solvent residues and the development and implementation of circular methodologies, together with growing environmental and health awareness, will promote the replacement of traditional solvents by more sustainable alternatives. In general, high-performance polymers, such as polyimides, are synthesized under specific reaction conditions. This work defines and develops clear guidelines, integrating them into a decision map to evaluate the potential of an alternative solvent for application in the synthesis of polyimides. Since every industrial application demands explicit criteria, our study focused on the development of polyimides for the membrane industry. More than 130 solvents were evaluated, and 10 solvents were found to have the potential to be employed in the synthesis of polyimides. The outcome was verified with 7 of those solvents, namely, γ-valerolactone (GVL), cyrene (Cy), dimethyl carbonate (DMC), dimethyl isosorbide (DMI), dimethyl sulfoxide (DMSO), 3-methoxy-N,N-dimethylpropanamide (commercially known as KJCMPA®-100), and the reference N-methyl-2-pyrrolidone (NMP), and tested for the synthesis of 3 polyimides (6FDA-HAB, 6FDA-6FpDA and 6FDA-DAM), obtaining extremely consistent outcomes. This work found four solvents, GVL, DMI, DMSO, and KJCMPA, that could substitute NMP, and other harmful solvents, in the synthesis of high-performance polymers. GVL provided even better results in terms of the molecular weight of the polyimides than the reference NMP, showing a realistic potential for its direct substitution. This work also reports more than 40 alternative solvents derived from the identified solvents. Finally, the key action points that should be taken into account for imminent advances in the subject were recognized.