Spectroscopic analysis reveals kinetics and quenching mechanisms in epoxy-amidoamine dispersions, indicating unexpected side reactions alter coating properties.
Molecular weight advancement and epoxy conversion in epoxy‐amidoamine resins have been characterized in solutions and in aqueous dispersions using viscosity, light scattering, and near‐infrared spectroscopy. By measuring the intensity of the 4532 cm−1 band in the near infrared, it is possible to determine the concentration of epoxy groups in these resins at low levels in the presence of amine and acid groups as well as solvents and other species. The epoxy‐amine reaction in these resins is found to be second order with an activation energy of around 13 kcal/mole. The addition of one mole of carboxylic acid per mole of amine functionality was sufficient to quench the epoxy‐amine reaction. Preparation of aqueous dispersions suitable for electrocoat formulation required that the extent of epoxy reaction be within a given range. Although the addition of acid completely quenched the epoxy‐amine reaction, a slow side reaction was discovered which consumes epoxy groups and ultimately changes the physical properties of coatings made from these dispersions.
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Qaderi et al. (1987) studied this question.
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