Hindered piperidine amine (HPA) and tertiary amine (TA) were introduced into hydrolytic polymerization of caprolactam, and polyamide 6 (PA 6) modified by additives [HPA/TA = I : I (w/w)] was obtained. The effects of additives on the melt, light, and heat stability of PA 6 were studied. The results showed that with an increase in additive content, the viscosity of PA 6 increased and the elastic response decreased. Thus, the drawing property of PA 6 fibers during melt spinning was improved. With the addition of 0.1%-0.2% additives, the degree of variation in amino end group content and relative viscosity decreased during the process going from resin to fiber, indicating the modified PA 6 had improved melt stability. During light and heat aging, the ratio of retained frac0.1%-0.4% additives. Scanning electron microscopy showed that the surface morphology of the modified fiber remained almost the same, whereas that of the unmodified fiber was seriously destroyed when exposed to xenon light it for 8 days heated to 180 degrees C in air for 1.5 h. The degree of variation of relative viscosity of the PA 6 fiber also decreased after modification by 0.1%-0.2% additives under oxidative degradation. Y, these results indicate PA 6 had better melt, light, and heat si stability when modified by additives. (c) 2006 Wiley Periodicals Inc.