Semi-Micro Hydroxyl Equivalent Weight Methods.

Most hydroxyl equivalent weight analyses call for relatively large prepolymer samples which may be impractical when dealing with small research products. The following describes a semi-micro procedure using an acetic anhydride/N-methylimidazole (AA/NMIN) esterification. The semi-micro procedure when compared to the macro version had more scatter but accuracy was not significantly affected. The AA/NMIM method requires a polar solvent system which is necessary to form an ion intermediate, hence esterification of nonpolar prepolymers cannot be accomplished. Also presented is a semi-micro technique for determining the hydroxyl equivalent weight of nonhydrogen bonding prepolymers by measuring the free hydroxyl infrared absorbance. When the technique was compared to titrimetric methods, the differences were no greater than 6%. (Author)