Dehydrofluorination mechanism, structure and thermal stability of pure fluoroelastomer (poly(VDF-ter-HFP-ter-TFE) terpolymer) in alkaline environment

[Display omitted] •Dehydrofluorination mechanism, structure and thermal stability of pure fluoroelastomer in alkaline environment were systematic researched.•The structures of samples, especially the sequence types of double bonds and positions in chains were identified by ATR-FTIR, 1H and 19F NMR.•The contents of double bonds were quantified by the improved “Chlorine Iodine Method”.•Demonstrated that dehydrofluorination was mainly conformed to Hofmann’s rule and accompanied with oxidation reaction.•Demonstrated that the effect of oxygen-containing groups on thermal stability of fluoroelastomer was much higher than that of double bonds. This study evaluates the dehydrofluorination mechanism, structure and thermal stability of pure fluoroelastomer which was dissolved by organic solvent and reacted with different concentrations of KOH at 20∼60°C. The sequence types and contents of double bonds and other oxygen-containing groups of samples were analyzed and investigated by Attenuated total reflectance/Fourier transform infrared (ATR-FTIR), 1H nuclear magnetic resonance (NMR), 19F-NMR spectroscopy and chemical titration method; thermal decomposition temperatures of samples were analyzed by thermogravimetric analysis (TGA). The results revealed that dehydrofluorination of fluoroelastomer would accompain with oxidation reaction whereby some double bonds conforming to Hofmann’s rule had been converted to hydroxyl groups, wherein the temperature and alkali concentration were the important factors. The double bonds generated in seven positions of molecular chains, sequence types were mainly conformed to Hofmann’s rule and Zaitsev’s rule supplemented. With the increase of reaction temperature and concentration of KOH, the thermal stability of fluoroelastomer decreased obviously since hydroxyl groups had a greater effect on it. Finally, the mechanism of reaction was also deduced.