Studies on reactions of the N‐phosphonium salts of pyridines. XIV. Wholly aromatic polyamides by the direct polycondensation reaction by using phosphites in the presence of metal salts

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Abstract
Poly‐p‐benzamide of high molecular weight (ηinh = ∼ in H2SO4) was obtained by the direct polycondensation reaction of p‐aminobenzoic acid (p‐ABA) by means of diphenyl and triaryl phosphites in N‐methylpyrrolidone (NMP)‐pyridine solution containing lithium and calcium chlorides. Molecular weight of polymer varied with the amount of these salts, showing maximum values at the concentration of about 4 wt‐% of LiCl or about 8 wt‐% of CaCl2 in the reaction mixture. The reaction temperature at around 80°C gave a polymer of the highest viscosity. The polycondensation reaction was also affected by monomer concentration, solvents, and tertiary amines like pyridine. Similarly, aromatic polyamides with high molecular weight (ηinh values up to 1.34 in H2SO4) were prepared from isophthalic acid and aromatic diamines, whereas terephthalic acid gave only low‐viscosity polymers.