Analytical Determination of Capacity

Determination of sulfur in the polysiloxane by elemental analysis is used to calculate the capacity of acidic groups in the polysiloxanes. Simple acid-base titration is often misleading if strong bases, e. g. NaOH, are used, because they react not only with the sulfonic acid but also with silanols and even with siloxane bonds, as shown in Eqs (3) and (4). 

To avoid these errors one determines the acid groups by back-titrating a small excess of base added to the stirred polysiloxane. 

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