This article reports a new needleless emulsion electrospinning method for scale-up fabrication of ultrathin core–shell polyacrylonitrile (PAN)/isophorone diisocyanate (IPDI) fibers. These core–shell fibers can be incorporated at the interfaces of polymer composites for interfacial toughening and self-repairing due to polymerization of IPDI triggered by environmental moisture. The electrospinnable PAN/IPDI emulsion was prepared by blending PAN/N,N-dimethylformamide and IPDI/N,N-dimethylformamide solutions (with the solute mass fraction of 1 : 1). The electrospinning setup consisted of a pair of aligned metal wires as spinneret (positive electrode) to infuse the PAN/IPDI emulsion and a rotary metal disk as fiber collector (negative electrode). The formed ultrathin core–shell PAN/IPDI fibers were collected with the diameter in the range from 300 nm to 3 μm depending on the solution concentration and process parameters. Optical microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy were used to characterize the core–shell nanostructures. Dependencies of the fiber diameter on the PAN/IPDI concentration, wire spacing, and wire diameter were examined. Results show that needleless emulsion electrospinning provides a feasible low-cost manufacturing technique for scalable, continuous fabrication of core–shell nanofibers for potential applications in self-repairing composites, drug delivery, etc. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40896.