High-molecular-weight poly(p-phenyleneterephthalamide) by CaCl2 promoted direct polycondensation with thionyl chloride in N-methylpyrrolidone

The direct polycondensation of terephthalic acid and p‐phenylenediamine hydrochloride (PPD.2HCl) with thionyl chloride was found to be significantly promoted in N‐methylpyrrolidone (NMP) by dissolved CaCl2 and tertiary amines. The inherent viscosity of the polymer obtained varied with the amount of CaCl2 and tertiary amines added. The reaction, when effectively promoted by CaCl2, proceeded homogeneously in the early state of polycondensation, and then resulted in a highly swollen gel. CaCl2 had to be present in the PPD.2HCl/tertiary amines/NMP solution as well as in the TPA/SOCl2/NMP mixture for the polycondensation to proceed to high molecular weight. Complexes of CaCl2, PPD.2HCl, and tertiary amines in NMP similar to the well known complex, CaCl2 · nNH3 (n = 2, 4, 8) was proposed to facilitate the polycondensation.