Removal of Hydrogen Bonding Interferences in the near Infrared Spectroscopic Determination of Dicarboxylic Acids in Diols

Abstract

Although several NIR spectroscopic methods exist for following the synthesis of polyesters, they are all used at the reaction temperature of between 240 and 260°C where reaction still proceeds, they also employ near equimolar concentrations of diacids and diols. A poor correlation, however, is obtained when analysing dilute diacid solutions in diols, this is attributed to hydrogen bonding between the carboxyl and hydroxyl groups. The removal of hydrogen bonding by addition of chloroform to the solution gave excellent correlation of the absorbance of the second overtone carbonyl bands with acid concentration.