In this work, a novel synthetic path for preparing semi-armotic components modified polyamide 6 was developed by caprolactam as solvent of purified terephthalic acid and 1,6-hexanediamine. First, the ring opening reaction and poly-addition of caprolactam were initiated by 1,6-hexanediamine to generate a prepolymer containing amino groups in both ends, then followed by the poly-condensation reaction with purified terephthalic acid, a long chain copolymer was produced, which the reaction time was reduced by 4 h compared with conventional hydrolytic ring-opening polymerization of pure caprolactam. By varying the ratio of terephthalic acid and 1,6-hexanediamine, a series of copolymers with different number average molecular weight and physical properties were prepared. Analytical results showed that the conversion percentage of caprolactam is significantly increased by the proposed method. Furthermore, this new copolymers exhibited excellent transparence and high decomposition temperature. Besides, the copolymers with average molecular weight 15,000 present good mechanical properties, making it a potentially useful application in plastics, textile yarn, and membranes. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 959-967