Constitutional isomerism: Synthesis and characterization of ordered polyamides from isophthalic acid and N-phenylethylenediamine by direct polymerization

An ordered (head-to-head (H-H) or tail-to-tail (T-T)) polyamide was prepared by direct polycondensation of a symmetric monomer, isophthalic acid (1) with N-phenylethylenediamine (2) as a non-symmetric monomer using the condensing agent diphenyl(2,3-dihydro-2-thioxo-3-benzoxazolyl)phospho The polycondensation was carried out by slow addition of (1) to (2), and gave polyamide (3d) with an inherent viscosity of 0.29 dl g(-1). On the other hand, authentic II-II or T-T ordered polyamide (3a) and H-T ordered polyamide (3b) were obtained by a multi-step route. Random polyamide (3c) was synthesized by mixing isophthaloyl chloride and 2 all at once in N-methyl-2-pyrrolidinone. The microstructure of the polymers was investigated by H-1 and C-13 NMR spectroscopy, It was found that their spectra were different due to their different constitutions, while polymer 3d obtained by direct polycondensation had the expected H-H or T-T sequence. Furthermore, the model reactions were studied in detail to demonstrate the feasibility of selective amidation and polymer formation.