Determination of Hydroxyl Number in Polymers by Infrared Spectroscopy: Comparison of Near-IR and Mid-IR

A comparison of near-infrared (NIR) and mid-infrared (mid-IR) techniques for the determination of hydroxyl number in polyesters was made. Both of these analyses are faster and involve less exposure to irritating, highly toxic, and corrosive chemicals than the chemical analysis, although both techniques rely on developing calibration files. The mid-IR procedure consisted of making thin films of polymer on IR crystals by spin coating and taking transmission spectra. The program used for the analysis, Nicolet PLS Quant, compensated for the resulting indeterminate pathlength. The NIR procedure consisted of taking transmission spectra of the clear, viscous polymers in 4-mm cuvettes and using standard regression analysis of the spectra.