The amide-salt solvent system containing N-methyl pyrrolidone and LiCl or CaCl2 is generally used for the synthesis of PPTA. In this paper the associationdisassociation equilibrium and solvation existing in the solvent system were studied. The experimental results showed that there were multiple association-disassociation equilibrium in the solvent system and strong solvation of the cations. The higher the free-ion concentration and the solvation effect

the higher the molecular weight of the polymer was obtained.