The chain-extension behavior of 2,2'-bis(2-oxazoline) (BOZ) was studied to evaluate the coupling effect on polyamide-6 (PA6) in a Haake Rheocord mixer and an extruder. The relative torque of PA6 dramatically increased within 1-2 min, and the results were similar whether the added amount of BOZ in PA6 was the theoretical amount or twice as much at 240 degrees C; however, after 5 min, the coupling results showed an optimal dosage of the chain extender, a lack of which caused a deficiency of chain extension and an excess of which led to a greater blocking reaction. The final torque was 2.16 times as much as that of a control sample when the reaction temperature was 240 degrees C, and the added amount of BOZ in PA6 was 1.156%; at the same time, the initial carboxyl content of the chain-extended products decreased to 40% for PA6, and this corresponded to the intrinsic viscosity of PA6 increasing to 1.636 dL/g, whereas that of the control sample was 1.384 dL/g. Furthermore, the effects of BOZ on the thermal and mechanical properties of chain-extended PA6 were investigated. The degree of crystallinity decreased as the chain extender was added to PA6. The Izod impact strength, tensile strength, and elongation at break of the resultant products dramatically improved under wet conditions. (c) 2007 Wiley Periodicals, Inc.