Hydroxyl number is a term that reflects the number of hydroxyl groups in a molecule. Hydroxyl number determination is important in polymer analysis to determine the extent of reaction or number of hydroxyl groups available for further reaction. There exist many methods for chemical determination, and these vary with polymers, degree of solubility, ease of reaction, and catalyst. There also exist other methods including GC, GPC, and IR methods. Other methods for hydroxyl determination in oils and with the use of near-IR have been reported. The wet chemical methods for hydroxyl number determination in polymers are accurate and precise but can take hours to run. Although this time can be reduced by running several samples simultaneously, running just one sample would take about 3–4 h because of required reaction and titration times. The chemical method requires the use of pyridine, dimethylaminopyridine, and acetic anhydride, which are irritating, highly toxic, and corrosive chemicals. In order to reduce these problems with the chemical hydroxyl number determination, the feasibility of an analysis of the polymers by infrared (IR) spectroscopy was studied with the use of the Nicolet PLS Quant program.
Kathryn A. B. Lee, Steve M. Hurley, Robert A. Siepler, Richard D. Mills, Kristy A. Handrich, and John J. Conway, "Determination of Hydroxyl Number in Polymers by Infrared Spectroscopy," Appl. Spectrosc. 44, 1719-1721 (1990)