Electrospun polyacrylonitrile (PAN) copolymer nanofibers (particularly those after the post-spinning stretching process) are expected to be an innovative type of precursors for making continuous carbon nanofibers with superior mechanical properties. In this study, three types of unidirectionally aligned PAN-based nanofibers including homo-PAN, binary-PAN (a PAN copolymer with itaconic acid units), and ternary-PAN (a PAN copolymer with itaconic acid and methyl acrylate units) were prepared by the electrospinning technique; thereafter, the nanofibers (in the form of bundles) were stretched into 3 times of their original lengths in hot water at 97 degrees C. The effects of chemical composition and post-spinning stretching process on morphological, structural, and thermo-chemical properties of these precursor nanofibers were investigated. The results indicated that, the stretched electrospun binary-PAN nanofibers possessed the most desired thermo-chemical properties, macromolecular regularity, crystal and macromolecule orientations, and dimensional stability; and thus they are suitable for the development of high-performance carbon nanofibers. (C) 2015 Elsevier Ltd. All rights reserved.