Copolymerization behavior of direct polycondensation of AB₂ and AB monomers that forms hyperbranched aromatic polyamide copolymers

The copolymerization behavior of the one‐step direct polycondensation of 3,5‐bis‐(4‐aminophenoxy)benzoic acid (AB 2 monomer) and 3‐(4‐aminophenoxy)benzoic acid (AB monomer) was investigated by IR and 13 C NMR measurements. IR measurements revealed that the content of the AB 2 units in the polymer was higher in the early stages of polymerization. 13 C NMR spectra of the polymers indicated that the number of dendritic units increased slowly with increasing reaction time. The stepwise copolymerization of the AB 2 and AB monomers was also carried out, and the structure was analyzed by 13 C NMR measurements. Copolymer synthesized stepwise by adding AB 2 monomer first (polymer II ) had more dendritic units and less terminal units as compared with the one‐step copolymer (polymer I ). Copolymer synthesized stepwise by adding AB monomer first gave a resulting copolymer (polymer III ) composed of long AB chains. The solubility of the stepwise copolymers was low, and the inherent viscosity was high in comparison with the one‐step copolymer as a result of the difference in architecture of the copolymers.