Dissociation of carboxyl-terminated cascade polymers: Comparison with theory

The dissociation of carboxyl-terminated cascade polymers (generations 1-4) in 0.10 M NaCl has been studied by potentiometric titration. Experimental surface potentials were compared to the theoretical values calculated from the nonlinearized Poisson-Boltzmann equation. Experimental values are smaller than those predicted by theory for generations 2-4 in NaCl. The lower experimental potential is attributed in part to the effect of counterion binding, which is supported by the fact that significantly larger surface potentials are observed when Na+ is replaced by tetramethylammonium ion (TMA(+)). Potentials higher than those predicted by theory were observed at high degree of dissociation for generations 3 and 4 in TMACl, which may be due to the effect of the high surface charge density of cascade polymers on the local dielectric constant.