Coalescence of polymer particles is a key phenomenon in many powder processing technologies. Both the extent and the rate of coalescence between particles govern the production cycle and the performance of the end-product. It is well accepted that both processing conditions and material formulation affect the morphology of molded parts and consequently their mechanical properties. The interest of this study is to evaluate the impact that changes in morphological features caused by the imposition of different thermal treatments as well as by the addition of a nucleating agent (bis 3,4 dimethylbenzylidene sorbitol) have on the coalescing behavior of ethylene copolymers produced from Ziegler-Natta and metallocene catalyst technologies. Results showed that samples produced using slower cooling rates exhibited higher crystallinity and increased thermal stability. Variations in thermal treatments, however, only resulted in minor changes in the coalescing behavior of the resins considered in this work. However, the addition of the nucleating agent to Ziegler-Natta ethylene copolymers led to the formation of crystalline structures with increased material thermal stability, but reduced chain mobility, and consequently resulted in a slower coalescing rate. These effects, however, are dependent on the molecular structure of the copolymers. The addition of the sorbitol nucleating agent influenced the morphological structure of the metallocene copolymer used in this work but did not result in any significant changes in the coalescence behavior of the resin. (c) 2006 Wiley Periodicals, Inc.