Preparation and properties of aramids based on naphthalenedicarboxylic acid and their molecular composites with amorphous nylon

Abstract

AbstractTwo naphthalene‐aromatic polyamides were prepared from 2,6‐naphthalenedicarboxylic acid and various aromatic diamines by a modified Higashi phosphorylation reaction. The first polymer, poly(4,4′‐diaminobenzanilide‐2,6‐naphthalamide)** (DBNA), was synthesized by the reaction of 2,6‐naphthalenedicarboxylic acid with 4,4′‐diaminobenzanilide. The second polymer, 50/50 copoly(1,4‐phenylene/1,4‐bis(4′‐phenoxy)benzene‐2,6‐naphthalamide)*** (PBNA), is a copolymer synthesized using an equimolar ratio of 1,4‐phenylene diamine and 1,4‐bis(4′‐aminophenoxy)benzene. These two polymers have inherent viscosities of 4.17 and 2.32 dL g‐1, respectively, and dissolve in N‐methyl‐2‐pyrrolidone (NMP)containing LiCl. Highstrength films were obtained by casting from these polymer solutions. Blends of DBNA/amorphous nylon and of PBNA/amorphous nylon were prepared by rapidly precipitating the ternary NMP solution into deionized water, and hot‐pressing to films at 185°C. The compatibility, morphology, and mechanical properties were investigated by dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), and tensile tests. The results revealed that both DBNA and PBNA were partially compatible with amorphous nylon. DBNA formed microfibrils in the amorphous nylon matrix, and its mechanical properties, tensile strength and modulus, improved with increasing DBNA content. PBNA had no reinforcing effect, perhaps because it did not form microfibrils in the amorphous nylon matrix.