Synthesis of high‐molecular‐weight rodlike polyamides and block copolymers

High‐molecular‐weight polyamides containing p‐benzamide units can be obtained by polycondensation of monomers having preformed amide linkages in N‐methylpyrrolidone with added CaCl2 and LiCl in the presence of pyridine and triphenylphosphite (the conditions used by Higashi et al.). For example, the polyterephthalamide of 4,4′‐diaminobenzanilide having ηinh = 5.4 was obtained. Similarly, polycondensation of p‐phenylenediamine with N,N′‐bis(p‐carboxyhenyl)terephalamide produced a polymer having ηinh = 5.15. These results constitute the first demonstration that the phosphorylation reaction can be used to prepare rodlike polymers containing p‐benzamide units of molecular weights adequate for commercial‐quality fibers. Polymerization of p‐aminobenzoic acid using either Yamazaki or Higashi conditions does not lead to a polyamide having a high inherent viscosity. Block copolyamides having rigid and semiflexible blocks were prepared by using both Yamazaki and Higashi conditions. Block copolymers composed of p‐ and m‐benzamide units, and having ηinh = 3.0–3.1, were synthesized by using a rigid prepolymer obtained by applying the Yamazaki reaction to a monomer containing a preformed amide linkage, 4‐N‐(4′‐aminobenzamido)‐benzoic acid. Use of monomers having preformed amide linkages with Higashi conditions afforded block copolymers having inherent viscosities of up to 4.75.