Abstract
The pH titration was made at various temperatures for two compounds with different densities of charged groups, carboxymethyl cellulose (CMC-H) and partially anionized polyacrylamide (PAAm-H). The effects of the density of charged groups and temperature on the ionization were quantitatively investigated by determining the apparent ionization constant (Kapp) and the variation of electrostatic free energy of ionization (ΔGiel). The result indicates that pKapp increases for CMC-H and the PAAm-H series with low density of charged groups as the temperature increases. The ΔGiel values for both CMC-H and PAAm-H are proportionate to the density of charged groups. The value of ΔGiel for CMC-H increases with an increase in temperature. As the temperature increases, however, ΔGiel decreases for the PAAm-H series with high density of charged groups, while that for the PAAm-H series with the low density is constant as low as 1/10 that for other series. It became clear that such a relationship between the temperature and ΔGiel reflects the temperature dependence of the dielectric constant and polymer chain flexibility.
