Investigation of conformational changes in styrene-maleic acid copolymer macromolecules during ionization in aqueous solutions

Abstract

Potentiometric titration was used in an investigation of the conformational transition occurring during ionization of styrene-maleic acid copolymers. At 25° the free energy of the globule-coil transition is 175 cal/mole in pure water and 265 cal/mole in a 0·1 n KCl solution. Upon adding dioxan the macromolecules uncoil, but the addition of tetraethylammonium bromide stabilizes the globular conformation. These facts point to hydrophobic interactions having a definite role to play in the stabilization of the globules. Investigation of the temperature dependence of the free energy for the conformational transition showed that at 10–50° the globule-coil transition entropy is positive, which points to the possibility of intramolecular H-bonds contributing to the stabilization of the globular conformation of the macromolecules.