Conformational transition of the copolymer of maleic acid and styrene in aqueous solution

The pH‐induced conformational transition of maleic acid–styrene copolymer in aqueous NaCl solutions has been investigated by potentiometric titration, viscosimetry, and dilatometry. The dependence of the intrinsic viscosity on the degree of neutralization of the primary carboxyl group indicates that the transition is from a compact to a loosely coiled form. From titration data, the standard free energy change ΔG° per monomole, for the transition from the uncharged compact from to the hypothetical uncharged loosely coiled one is estimated to be about 370–280 cal/monomole for concentrations ranging from 0.0092 to 0.2739N in NaCl. The value of ΔG° decreases slightly with increasing temperature in the temperature range from 15 to 30°C. The volume change associated with the transition was found to be −0.6 ml in 0.01N NaCl and −0.9 ml in 0.09N NaCl per monomole, respectively. From viscosity data, changes of molecular dimensions and the long‐range interaction parameter through the transition region have been discussed.