Relaxation times and in situ kinetic analysis during network evolution of epoxy via a nickel catalyst of imidazole

A research work has been conducted to investigate relaxation time changes with curing schedule, time, and concentration of DGEBA cured with Im6NiBr2. Our results demonstrate that low field NMR relaxometry is a facile and easy protocol to evaluate storage stability of one-pot epoxy based compositions. The DGEBA–Im6NiBr2 mixtures consistently display a greater degree of latency and a slower rate of the relaxation time decrease over the parent DGEBA–imidazole mixture. The results obtained on storage stability using NMR method are in reliable agreement to those reported previously using DSC and FT-IR approaches [1]. High field NMR techniques at elevated temperatures were utilized to determine the rate constants of both polymerization stages. The results exhibit that the rate constant of the first step is more sensitive, in comparison to the second stage, to the isothermal temperature used. By reference to the reaction between DGEBA and Im6NiBr2, 1H NMR at elevated temperature was shown to be a simple technique, available for on-line process monitoring, for obtaining the degree of cure enabling kinetic parameters. This study highlights the usefulness of the high temperature bulk 1H NMR technique in kinetic studies of epoxy-metal organic curing agent systems.

Research highlights
► Changes in the NMR relaxation times with cuing schedule on DGEBA/Im6NiBr2 cure was clarified.
► Low field NMR relaxometry enables to determine storage stability of epoxy based mixtures.
► Kinetic parameters of the reaction have been evaluated by in situ1H NMR measurements.