Upon the application of the temperature-jump technique, the protonation of polymethacrylic acid is studied at pH = 7.0 in the presence of bromthymol blue (BTB) as indicator. Rate constants an determined for the proton transfer from carboxylate groups to the dianion of BTB (k(ex) = 3.4 x 10(6) M(-1)s(-1)), for the association of a proton with a carboxylate group (k(L) = 2.1 x 10(9) M(-1)s(-1)), and for association of a proton with the dianion of BTB (k(ln) = 5.0 x 10(10) M(-1)s(-1)).