Synthesis of Poly-p-phenylene Terephthalamide (PPTA) in Ionic Liquids

Several ionic liquids (ILs) were tested for their suitability to synthesize the aramid polymer poly-p-phenylene terephthalamide (PPTA) in an attempt to diminish the dependence on the toxic N-methylpyrrolidone (NMP) that is currently used in industry. The room-temperature IL 3-methyl-1-octylimidazolium chloride ([C8MIM][Cl]) showed the highest promise as, with this medium, the polycondensation reaction proceeds with a mechanism similar to how it occurs in the solvent mixture of NMP with CaCl2. With this IL, PPTA polymer with an inherent viscosity of 1.95 dL/g was obtained in a low-temperature polycondensation reaction. This is the highest reported molecular mass of PPTA to date that was obtained by polymerization in an ionic liquid. An extended X-ray absorption fine structure (EXAFS) and solid-state NMR spectroscopic study showed that [C8MIM][Cl] and the current industrial solvent of NMP and CaCl2 show similar characteristics when it comes to the synthesis of PPTA.