One of the challenges polymer blends may face is their morphological instability. Among the many polymer blends that have been studied in academia and industries, polyamide 6 (PA6) based polymer blends have probably received the most attention. This work shows for the first time that graft copolymers with PA6 as grafts are highly instable under melt polymer blending conditions. Therefore, the structural instability of such graft copolymers can be another crucial factor that dictates the morphology and properties of PA6 based polymer blends as well as their stability, especially those of nano-structured ones. (C) 2010 Elsevier Ltd. All rights reserved.