Study on Blocking and Deblocking Kinetics of Diisocyanate with ε-Caprolactam Using FTIR Spectroscopy

摘要

These blocking and deblocking reactions of toluene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI) and dicyclohexylmethylmethane-4,4'-diisocyanate (HMDI) blocked with e-caprolactam were directly traced by FTIR spectroscopy at different temperatures respectively. Taking advantage of the relationship between the concentration of reactants and absorbance of NCO group according to Lambert-Beer law, the change with time for concentration was calculated under different temperatures. The results showed that the reaction rate constants for toluene diisocyanate, MDI blocked with e-caprolactam were 4.05 x 10~(-3) and 6.53 x 10~(-2) at 60 °C respectively, while the reaction rate constant for HMDI with catalyst was 3.56 x 10~(-3) at 140 °C, the class of reaction kinetics for diisocyanate (TDI and MDI) blocked with e-caprolactam were first order and second order respectively and the reaction of blocked HMDI was second order reaction selecting stannous octoate as catalyst. The Arrhenius equation was employed to acquire the activation energies of blocked diisocyanate (TDI, MDI and HMDI) respectively. The process of deblocking for blocked diisocyanate was also studied by TGA and FTIR.