Acetylation and Phthalation Procedures

In these procedures, the hydroxyl-containing polymer is reacted with an excess of a standard non-aqueous solution of acetic anhydride or phthalic anhydride, sometimes in the presence of a catalyst such as p-toluene sulfonic acid. After ester formation is complete, an excess of water is added to convert excess anhydride to the free carboxylic acid. The acid is titrated with aqueous or alcoholic standard potassium hydroxide to the phenol phthalein end-point to determine unconsumed acid. A blank run is carried out in which the sample is omitted. The hydroxyl 

As mentioned above, organic isocyanates react with hydroxyl groups to produce 

In many practical situations, distinguishing between primary and secondary hydroxyl groups in polymers is necessary. The reaction product of a glycerol-propylene oxide condensate tipped with ethylene oxide would therefore contain both types of hydroxyl group  

Differences in reaction rate between primary and secondary hydroxyl groups with phenyl isocyanate are the basis of methods for carrying out this determination (see next) [5, 6]. 

The reaction is carried out under standard conditions in which a calculated weight of the polyol (depending on its hydroxyl number) is reacted with an excess of a standard toluene solution of phenyl isocyanate in the presence of a basic catalyst. 

Chemical methods for the determination of hydroxyl groups in polymers are based on acetylation [1-12], phthalation [2], perchloric acid catalysed acetylation [2, 4, 5], reaction with beta-nitro phthalic, anhydride [5, 8], pyromellitic anhydride [6] and reaction with phenyl isocyanate [2, 5] or when two adjacent hydroxyl groups are present in the polymers, by reaction with potassium periodate [1]. 

The reactions on which these methods are based are as follows  

Molecular weight p-Toluene sulfonic acid catalysed acetylation method Phthalation method [2] Reaction with phenyl isocyanate 

The Stetzler and Smullin [2] method is applicable to polyoxyethylene, polyoxypropylene and ethylene oxide tipped glycerol/propylene oxide condensates. Compounds of this type in the molecular range 500 to 5000 can be analysed by this procedure. 

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