Preparation of sulfonyl aromatic polyamides and copolyamides by means of di‐ or triphenyl phosphite

High molecular‐weight aromatic polyamides were obtained by the direct polycondensation reaction of 4,4′‐sulfonyldibenzoic acid (SDA) with various aromatic diamines, by means of di‐ (DPP) or triphenyl phosphite (TPP) in N‐methyl‐2‐pyrrolidone (NMP)‐pyridine solution containing metal salts such as LiCl and CaCl2. The factors affecting the phosphorylation reaction were investigated, in particular for the reaction of SDA and 4,4′‐oxydianiline (ODA). For the polymerization by means of TPP, the optimum conditions are: molar ratio of TPP to diacid, higher than 2.3; concentration of metal salts, 8 wt % LiCl or 6 wt % CaCl2; reaction temperature, 100°C; and monomer concentration, 0.4 mol/L. For the polymerization by means of DPP, the optimum conditions are: molar ratio of DPP to diacid, higher than 3.8; concentration of metal salts of 8 wt % LiCl or 10 wt % CaCl2; reaction temperature, 110°C; and monomer concentration, 0.4 mol/L. Copolyamides were also prepared from the reaction of ODA with the mixed diacids of SDA and other dicarboxylic acids such as terephthalic acid, isophthalic acid, and 2,6‐naphthalene dicarboxylic acid by using TPP and DPP as the condensing agents.