Polydiacetylene (PDA) are polymers known to switch from blue to red when exposed to environmental stimuli. This paper reports on electrospun composite nanofibers of polyacrylonitrile (PAN) and a high temperature PDA. The effect of PAN on the thermal and thermochromic properties of the PDA was studied. PDA to PAN mass ratio in the composites was varied and an unusually high loading of 30 wt% PDA was achieved. Scanning and transmission electron microscopies (SEM, TEM) revealed a randomlypacked morphology of nanofibers with well dispersed PDA particles inside. Through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), the heat resistant PAN nanofibers were found to increase the reversible temperature range of the embedded PDA while also improving its thermal stability. Naked eye observations suggested that the composite thermochromic sensor can be reversed from temperatures around 200 degrees C - a big improvement from just 156 degrees C - while ultraviolet -visible spectroscopy (UV-vis) studies showed that there was a progressive deterioration of the conjugated PDA backbone which ultimately resulted in complete loss of reversibility and colorimetric character at 230 degrees C. (C) 2018 Elsevier Ltd. All rights reserved.