Preparation of polyamide‐imides via the phosphorylation reaction. II. Synthesis of wholly aromatic polyamide‐imides from N‐[p‐(or m‐) carboxyphenyl]trimellitimides and various aromatic diamines

Wholly aromatic polyamide‐imides with high molecular weight (ηinh up to 1.7 dL/g in DMAc–5% LiCl) were obtained by the direct polycondensation reaction of N‐[p‐( or m‐) carboxyphenyl]trimellitimide [p‐(or m‐)CPTMI] and aromatic diamines by means of di‐ or triphenyl phosphite in N‐methyl‐2‐pyrrolidone (NMP)‐pyridine solution in the presence of lithium or calcium chloride. The factors affecting the phosphorylation reaction were investigated, in particular for the reaction of p‐CPTMI and 4,4'‐oxydianiline (ODA). Molecular weight of polymers varied with the amount of metal salts and showed maximum values at the concentration of 10‐15 wt % in the reaction mixture. Monomer concentration of 0.2 mol/L produced polymer of the highest viscosity. Higher concentrations produced gelation and yielded polymers of low molecular weight. A reaction temperature of about 120°C gave the best results. Among the solvents tested, NMP was significantly the most effective for the reaction. The highest inherent viscosity values, ηinh = 1.35 and 1.58 dL/g, were obtained with triphenyl phosphite (TPP)/monomer and diphenyl phosphite (DPP)/monomer molar ratios of 2.0. Excessive addition of phosphites did not cause a serious deleterious effect on the molecular weight of polymer. Polycondensations of several combinations of p‐or m‐CPTMI and aromatic diamines were carried out with satisfactory results.