ISO International Standard

This International Standard specifies methods for the measurement of the acidity of aromatic isocyanates and

prepolymers used as polyurethane raw materials. Method A is a straightforward titration without a blank and is

primarily applicable to products derived from crude or modified methylene-bis-(4-phenylisocyanate), polymethylene

polyphenylisocyanates and toluene diisocyanate having moderate to high (> 100 mg/g ) levels of acidity. Method B is

applicable to refined, crude or modified isocyanates derived from methylene-bis-(4-phenylisocyanate), polymethylene

polyphenylisocyanate and toluene diisocyanate having low (< 100 mg/g ) levels of acidity, and a blank is employed.

These methods can also be used for isomeric mixtures of toluene diisocyanate, methylene-bis-(4-phenylisocyanate)

and polymethylene polyphenylisocyanate. Other aromatic isocyanates may be analysed by this method if

precautions are taken to verify suitability.