High‐molecular‐weight poly( p ‐phenyleneterephthalamide) by CaCl 2 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 CaCl 2 and tertiary amines. The inherent viscosity of the polymer obtained varied with the amount of CaCl 2 and tertiary amines added. The reaction, when effectively promoted by CaCl 2 , proceeded homogeneously in the early state of polycondensation, and then resulted in a highly swollen gel. CaCl 2 had to be present in the PPD.2HCl/tertiary amines/NMP solution as well as in the TPA/SOCl 2 /NMP mixture for the polycondensation to proceed to high molecular weight. Complexes of CaCl 2 , PPD.2HCl, and tertiary amines in NMP similar to the well known complex, CaCl 2 · n NH 3 ( n = 2, 4, 8) was proposed to facilitate the polycondensation.