Preparation of the Unsaturated Polyester

1-2 g of the polyester (without styrene) are dissolved by warming with 50 ml acetone and, after cooling, are titrated as quickly as possible with 0.1-N alcoholic potassium hydroxide using phenolphthalein as indicator, until the red color remains for a few seconds. 

The alkali consumption of the solvent is determined in a blank experiment.The acid number is given by the weight of KOH in mg, required to neutralize 1 g of substance. 

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