Potentiometric titration was carried out in a thermostatic cell using a I-130 pH meter (Belarus) supplied with the standard glass and reference Ag/AgCl electrodes. The analysis procedure was as follows: a sample of peroxide copolymer was dissolved in an excess amount of 0.1N KOH aqueous solution for complete neutralization of the carboxylic group. Peroxide copolymer salt solution in the concentration range of 5-10 mmol/L (in moles of MA units contained in the copolymer composition) was thus obtained, afterwards an excess of KOH was titrated with 0.1N aqueous hydrogen chloride.