The nylon 612/6 copolymer was synthesized by melt polymerization using a 5L polymerizer. The effects of different mass fractions of caprolactam (CPL) on the mechanical properties of nylon 612/6 copolymer were investigated. The reasons for the influence of CPL addition on the mechanical properties of nylon 612/6 copolymer were determined by end group titration

section moisture content and X-ray diffraction(XRD)test. The mass fraction of CPL was determined to be 15% nylon 612/6 copolymer can obtain better mechanical properties. Compared with nylon 612: the notched impact strength is improved by 113%; the elongation at break is increased by 127%; the tensile strength is decreased by 8%; the bending strength is decreased by 28%; and the isothermal crystallization behavior of nylon 612 and nylon 612/6 with a mass fraction of 15% CPL was analyzed by Avrami equation. The Avrami index n was between 2.02~2.53 and 2.23~2.38

respectively. Isothermal crystallization process of nylon 612 and nylon 612/6 copolymers is secondary nucleation. After nucleation

it grows along the crystal nucleus in two dimensions. At the same time

the Arrhenius equation is used to determine the isothermal crystallization activation energy ΔE was —756.38kJ/mol and —115.09kJ/mol

respectively.