The influence of 1,4-cyclohexanedicarboxylic acid on the thermal and mechanical properties of copolyamides

The present paper describes the novel aliphatic polyamide 6 (PA6) copolyamides by the melt polymerization reaction of our newly synthesized aliphatic diamine monomer: N¹,N⁶-Bis-(2-aminoethyl)adipamide (BAEA). The BAEA/CHDA (1,4-cyclohexanedicarboxylic acid) salt was prepared by pertinent long-chain polyamide with the cycloaliphatic ring and isolated as white solid, utterly characterized for the first time. The chemical structure of BAEA, BAEA/CHDA salt and copolyamides (PA6-BAEA/CHDA) was identified by ¹H NMR and FT-IR spectroscopy. Depending on the chemical compositions, the viscosity and molecular weight of the copolyamides were in the range of 19,447–13,536 g mol⁻¹ and 2.74–2.2 dL g⁻¹. With increasing BAEA/CHDA salt molar ratio in the synthesized copolyamides, their melting temperatures (T_m) decreased from 212.7 to 170.4 °C, and the glass transition temperatures (T_g) increased from 60 to 89.4 °C. Besides, the as-synthesized all copolyamides possess nearly similar thermal stability (T_d-50% = 439.59 − 443.38 °C) as neat PA6. Mechanical testing data revealed that with an increase in a proportion of BAEA/CHDA salt, Young’s modulus of copolyamides is increased from 698.54 to 1093.89 MPa, while the tensile strength is increased by 8.1%.