UV‐induced crosslinking and cyclization of solution‐cast polyacrylonitrile copolymer

An alternative, rapid stabilization route for polyacrylonitrile (PAN) precursors is reported based on UV‐induced crosslinking and cyclization reactions. Two mechanisms of photoinitiation were investigated: homolytic cleavage and hydrogen abstraction. Solution‐cast PAN copolymer samples were irradiated for different durations (100, 300, and 600 s) and temperatures (～65 and 100°C, below and above glass transition temperature respectively). FTIR spectra show the formation of carbon–oxygen, carbon–nitrogen, and carbon–carbon double bonds (1450–1700 cm^?1 region) attributed to the development of cyclized structure. Conversion indices estimated from the FTIR spectra indicate samples containing hydrogen abstraction photoinitiator show higher extents of cyclization among the three main set of samples. This observation was also confirmed by higher gel percentages measured on the same set of samples. FTIR conversion indices of samples UV‐treated above glass transition temperature were higher compared with that for the same specimens UV‐treated below glass transition temperature. DSC results show that samples containing hydrogen abstraction photoinitiator enable a higher extent of post‐UV thermal cyclization. FTIR spectra of the UV treated samples were compared with conventional thermal stabilized specimens. This comparison confirms that the addition of 1 wt % photoinitiator to PAN followed by 5 min of UV treatment increases the rate of the cyclization reaction and reduces the thermal oxidation time by over an hour, which could significantly reduce the conventional stabilization time by half. These results indicate the potential for an energy‐efficient, cost‐effective route for producing carbon fibers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013