Quantitative determination of the distribution of free hydroxylic and carboxylic groups in unsaturated polyester and alkyd resins by 31P‐NMR spectroscopy

Quantitative 31P‐NMR spectroscopy is used to measure the hydroxyl and carboxyl content of some polyester resins (short‐ and long‐oil alkyds, polyols, polyesters) through derivatization of the —OH protons with 2‐chloro‐4,4,5,5‐tetramethyldioxaphospholane I. This methodology is shown to be superior to titration methods, since it can (a) discriminate between primary and secondary hydroxyl groups, (b) identify individual alcohols and acids present, (c) measure the amount of free fatty acids in oil‐modified alkyds, and (d) provide lower limits for the number‐averaged molecular weight of the resins and exact values for linear polyesters. A major advantage of the technique is that the NMR measurements are made on unmodified resins in their final product form supplied by the manufacturer. The information obtained is important for the characterization of the alkyd resins and affects drastically their physical properties and performance as products.