Interfacial polycondensation. V. Polyterephthalamides from short‐chain aliphatic, primary, and secondary diamines

Abstract

Abstract High molecular weight polyterephthalamides were synthesized from a homologous series of primary diamines (ethylenediamine to hexamethylenediamine) by the interfacial polycondensation method. These polymers were found to be extremely high‐melting (300–450°C). and difficult to dissolve. Fibers were prepared by dry spinning from solutions in trifluoroacetic acid. A study of the polymer melting points and the fiber modulus as a function of the diamine chain length showed an alternation of properties with the number of carbon atoms, odd or even, in the diamine chain. All the polymers were highly crystalline and gave orientable fibers. As a comparison to the highly intractable polyterephthalimides from the primary diamines, a series of polymers from secondary diamines ( N,N ′‐dialkyl ethylenediamine to N,N ′‐dialkyl hexamethylenediamine) were prepared. In contrast to the polymers from the primary diamines, these N ‐alkylated derivatives were extremely soluble. In fact, some of them were even water‐soluble when prepared as low molecular weight products (η inh ≤ 0.2). The N ‐alkylated polymers melted at least 70°C. lower than the corresponding polyterephthalamides from the primary diamines. The N ‐methylated derivatives were crystalline, while the N ‐ethylated ones were amorphous. These results illustrate the importance of hydrogen bonding in determining the melting points and solubility characteristics of polymers.