Use of dielectric spectroscopy for real-time in-situ reaction monitoring

Coating resin manufacturing requires knowledge of the extent of reaction during resin synthesis so the appropriate actions can be taken (addition of the next reactant, reaction termination, etc.). This article reports the results from experiments conducted to survey the utility of dielectric spectroscopy (DES) as a real-time, in-situ technique to monitor the extent of reaction during synthesis of three low molecular weight resins that are representative of components used in coatings formulations. The resins made were based on very different chemistries: (1) a 100% solids polyacrylate functional oligomer from the Michael reaction between a polyacrylate monomer and an acetoacetate ester; (2) an acrylate functional monomer from the reaction between an epoxy ester and acrylic acid; and (3) a solvent-based isocyanate-terminated polyurethane prepolymer from the reaction between a mixture of diols and excess diisocyanate. In all three cases, very good to excellent correlations were found between continuous real-time DES output and the values of characteristic QC parameters (viscosity, acid number, epoxy equivalent weight, % NCO, ATR-FTIR peak heights for reactants and products, and GPC data) determined by off-line analysis of samples taken periodically during the reactions.