A Study of Reaction Kinetics by Near-Infrared Spectroscopy. 1. Comprehensive Analysis of a Model Epoxy/Amine System

An investigation of model epoxy/amine reactions was carried out by near-infrared (IR) spectroscopy. A comprehensive account of the origin, location, and shits during reaction of all major absorption peaks in the spectral range between 4000 and 7100 cm -1 is provided. Reaction kinetics derived from the near-IR data were in excellent agreement with the results obtained by HPLC. A most interesting and equally unexpected finding was the observed discrepancy between the kinetic predictions of near-IR and mid-IR analyses. It was established that the kinetics of epoxy/amine reactions can be accurately deduced from the near-IR data, while the «standard» mid-IR epoxy absorption band at 915 cm -1 was not a unique measure of the epoxy concentration, and hence its utilization in kinetic calculations is questionable unless appropriate corrections are made. Evidence was presented for the formation of hydrogen bonding that is directly related to a critical viscosity of the reactive mixture