Melt‐polymerized aliphatic‐aromatic copolyamides. I. Melting points of nylon 66 copolymerized with aromatic diamines and terephthalic acid

Measurements of melting points were made for melt‐polymerized aliphatic‐aromatic copolyamides; (i) N66PT, (ii) N66CT, and (iii) N66ST, i.e., nylon 66 [poly(hexamethylene adpamide)] copolymerized with three kinds of aromatic diamines, p‐phenylenediamine (P), bis (p‐aminophenyl) methane (C), and bis (p‐aminophenyl) sulfone (S), and terephthalic acid (T). As the mole fraction of copolymerized component n1, increases in the case of (ii) or (iii), the melting point decreases uniformly according to the relationship of Flory. In the case of (i), the melting point first decreases and then begins to increase after passing a minimum at n1 ≃ 0.2. A preliminary WAXD (wide‐angle X‐ray diffraction) study on N66PT crystals shows that the basal plane of the crystal lattice shifts from that of nylon 66 toward hexagonal packing with the increase of n1. It was suggested that the formation of mixed crystals for a series of N66PT will be attributed to their melting point behavior.