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

Abstract

SynopsisKinetic studies of the pH-induced conformational transition of the hydrophobic copolyelectrolyte of maleic acid and styrene in aqueous NaCl at ionic strength 0.09 were performed by an optical method a t 25.OoC with a rapid reaction analyzer of high resolving power. A pH jump applied to a solution, in which the molecule is in the compact form, gives a kinetic trace from which, by appling the general kinetic theory of cooperative transitions, two mean relaxation times are determined. Plots of these relaxation times against the degree of ionization of the primary carboxyl groups of the maleic acid units agree well with theoretical predictions from the linear Ising model, where the molecule in the compact form is described as a random coil with hydrophobic "pockets." The initiation parameter for a pocket obtained from the kinetic data is 0.036. On the other hand, the parameter calculated from the previous pH-titration results by applying Zimm-Rice theory is 0.015 a t the ionic strength 0.09 and 25.0°C. Such values are compared with those determined from pH-titration data on other hydrophobic polyelectrolytes.transition. The standard enthalpy change, AH:, estimated by calorimetry at 25.0"C was reported to be similar to the heat of transfer of benzene from the hydrophobic to the aqueous medium.13 The difference spectrum between the

Conformational Transition of the Copolymer of Maleic Acid and α-Methylstyrene in Aqueous Solution

“…The modified pH-titration curves for fraction F-2 at 25°C and various ionic strengths are shown in Figure 2; these curves show anomalous behavior around o: 1 = 0.25 and greatly resemble the case of (MA-St)" reported earlier. 9 Similar titration curves were also obtained for unfractionated F-0 and fraction F -4. The polymer concentration ( CP) dependence of the titration curve was found to be very small in the range of CP from 0.0048 to 0.0149 monomole dm - 3 at constant ionic strength.…”

“…The other reagents used here and the preparation method of polymer stock solution were identical to those described previously. 9 …”

“…The temperature was controlled within ± 0.0 I oc_ The KCl liquid-junction, the standardization of the instrument, and the procedure of pH-titration have been described previously. 9 • 19 The analysis of titration data was also identical to that described previously 9 The total molarity of primary carboxyl groups was determined from the first peak of the differential titration curve. The correction for hy-720 drogen ion concentration was made directly from a blank titration; the results at various ionic strengths agree very closely with the previous data.…”

“…The temperature of both the sample and reference was controlled within ± 0. I oc_ Volume changes were measured at 15 to 35°C in a similar manner to that described previously, 9 with a Carlsberg type dilatometer immersed in a wellcontrolled thermostat ( ± 0.001 °C).…”

Molecular concepts, self-organisation and properties of polysoaps

“…Alternatively, a well balanced ratio of hydrophobic to hydrophilic units is achieved by controlled, limited dissociation e.g. of carboxylic groups, as in poly(methacrylic acid) [186,304] or in poly(styrene-a/Mnaleic acid) [305,306] or by controlled, limited quarternization of amino groups, like in poly([thio-l-(diethylamino)methyl] ethylene) [307,308]. Still, it appears that the hydrophobic domains in such polymers with very short tails are less shielded than in surfactant micelles or in polysoaps with "normal" tail lengths [258,303].…”