Effect of nonelectrostatic interactions on the macromolecular behavior of polyelectrolytes. I. Potentiometric titrations of PLL in water and aqueous–organic mixtures

Abstract

The potentiometric and viscosity behavior of salt‐free solutions of the polycondensate between L‐lysine and 1,3‐benzenedisulfonyl chloride (PLL) and related polyelectrolytes, have been investigated in water and in aqueous–organic mixtures (acetone–water). The effects of counterions and solvent on the pH‐induced conformational transition is related to hydrophobic interactions. The transition from a compact state to a more extended one shifts towards high values of neutralization with increasing length of N‐tetraalkylammonium counterions. Moreover, the above transition gradually disappears as the percentage of acetone in the mixture is increased, which is interpreted as reflecting the breakdown of the compact structure due to hydrophobic interactions stabilized by bulky counterions. A linear decrease in the free energy variation ΔG_t° is observed with increasing percentage of acetone up to about 40% of acetone, and a value of 1200 cal/unit is obtained for PLL in water, which is a reasonable value compared to other data for hydrophobic polyelectrolytes.