TABLE OF CONTENTS Van Houwelingen [13] discussed the determination of anhydride groups in a resin derived from octadecene-1 and maleic anhydride:
The common method for anhydride groups involving reaction with an excess of aniline and subsequent backtitration of the excess [102] is unsuitable, as the reactivity of the anhydride group is low. Even after hydrolysis with aqueous pyridine (containing 40% v/v of water) in a Parr bomb at 150 C for 4 hours, anhydride groups are still seen in the infrared spectra.
A suitable method for determining the anhydride group is titration with aqueous potassium hydroxide in pyridine after previous esterification of the carboxyl group with diazomethane. This esterification is carried out in diethyl ether methanol (9 + 1). After methylation, which takes about 10 minutes for 0.5 g of sample, the solvents are removed by evaporation and a portion of the derivatised polymer is dissolved in pyridine and titrated. In the infrared spectra of the resin before and after methylation it can be seen that the absorption band of the acid group at 5.84 ?m disappears and a carbonyl band of the ester at 5.74 ?m is formed. The acid content of the sample is found from the difference in titres of an unmethylated and a methylated product.
