The dependence of the acid dissociation constants on the tacticity of poly(vinylamine hydrochloride), prepared from tert-butyl N-vinylcarbamate, was determined by 13C and 15N NMR pH titrations. The 13C NMR titration for the CH2 diads produced typical sigmoidal curves, whereas the CH titration curves were bell-shaped, one for each triad configuration. The 15N NMR pH titration curves were generally sigmoidal. However, the curve for well-resolved mm sequence was bisigmoidal, and the break in the curve coincided with the maximum of the corresponding CH titration curve. A two-stage titration process was used to fit the data, yielding pKx = 5.3, 5.3, and 5.0 for the first stage and pK“2= 10.8, 10.3, and 9.3 for the second stage for the mm, mr, and rr configuration, respectively. A model was proposed to account for this titration process which involves a conformation change of the polymer mediated by hydrogen bond formation near half-neutralization. © 1987, American Chemical Society. All rights reserved.