Polymerization of PPTA in Ionic Liquid/Cosolvent Mixtures

1-Octyl-3-methylimidazolium chloride ([C8MIM][Cl]) shows the greatest potential to replace N-methylpyrrolidone/CaCl2 as solvent for the synthesis of poly(p-phenylene terephthalamide) (PPTA), a high-strength material when spun into a fiber. Coordinating anions are crucial to prevent precipitation of the polymer during synthesis. Additionally, the imidazolium cations play an essential role in gelation of the reaction mixture and enable the polycondensation reaction to continue in a gel state. Analysis of Kamlet–Taft parameters and Gutmann donor and acceptor numbers of ionic liquids and various solvents showed that balanced interactions between the secondary amide bonds of the polymer, anion, cation, and solvent are required to form a network of hydrogen bond interactions throughout the reaction mixture. This hypothesis was supported by the fact that tri-n-butyl phosphate (TBP), containing similar Kamlet–Taft and Gutmann solvent parameters as N-methylpyrrolidone, was able to produce PPTA with an inherent viscosity as high as 1.86 dL/g in combination with [C8MIM][Cl]. Such a high value without the use of N-methylpyrrolidone or hexamethylphosphoramide has not yet been reported.status: publishe