This procedure determines the carboxyl end group content in a PET sample.
The procedure involves the titration of the carboxyl end groups with potassium hydroxide in an o-cresol/chloroform medium to a bromophenol blue endpoint. A known weight of PET sample is dissolved in o-cresol then chloroform and bromophenol blue are added to the solution. The solution is then titrated with potassium hydroxide until the color changes to blue as a result of the end group reaction. Based on the amount of KOH required for the titration, the quantity of carboxyl end groups is calculated.