Toward Truly Water‐Soluble Rodlike Polyelectrolytes: Protonation–Deprotonation Equilibria in Aqueous Solutions of Poly(para‐phenylenes) Wrapped in Ethylene oxide and Amino Side Groups
Ernst‐Berl‐Institut für Technische und Makromolekulare Chemie, Technische Universit?t Darmstadt, Darmstadt, Germany
Abstract:
The protonation/deprotonation behavior of rodlike poly(p‐phenylene)‐based polyamines is analyzed in aqueous solution using NMR spectroscopy and potentiometry. The observed features cannot be explained by a single acid constant, but shifting electrostatic potential—generated by the protonated ammonium side groups—has to be taken into account additionally. Consequently, the density of ionic groups attached to the polymer backbones and the ionic strength of the solutions contribute to the polybase behavior as well: the shift of basicity as observed with increasing degrees of protonation can be quantified by an apparent ionization constant, pKapp, for each value of pH. Due to intrinsic rigidity of the polymer backbone and true solubility in water effectuated by the highly polar side chains, the electrostatic effects influencing the polybase behavior can be observed free from conformational effects and over the whole range of accessible pH and degree of protonation for the first time.
