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

Abstract

The temperature dependence of the conformational transition from a compact to expanded‐coil form of the alternating copolymer of maleic acid with styrene in aqueous 0.03M NaCl solution was studied at 15 to 40°C by pH titration, optical titration, and calorimetric measurements. The pH titration curve scarcely changed with temperature. The degree of dissociation of primary carboxyl groups in the copolymer at the midpoint of the conformational transition, determined by the optical titration, was almost independent of temperature. The standard enthalpy change of the transition at 25°C estimated from the calorimetric data was 0.363 kcal/mole, which may mean that the difference between the standard free energy changes of the transition at 20°C and 40°C does not exceed experimental error. The enthalpy change agrees well with the heat of transfer of benzene from the hydrophobic to the aqueous medium, and thus the compact form of the copolymer is considered to be stabilized by the hydrophobic interaction between the phenyl residues in the interior of the molecule.

Heat capacity measurements in carboxylic polyelectrolyte solutions

“…Thus, the role of the hydrophobic group and hydrophobic interactions in the conformational transition of these copolymers has been studied in detail. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] These investigations have led to the conclusion that a t low a the compact form of the polymer/chain is stabilized by hydrophobic interactions between the side chains, as can be shown for instance from the difference between the ethylene copolymer ( W t ) , where no conformational transition is observed, and the styrene copolymer (MASt), which has a conformational transition around a = 0.6. Partial molal heat capacity measurements have proven valuable in the study of aqueous solutions of ionic and nonionic s~l u t e s~~~~ and in micellar system^.^' Hydrophobic interactions and changes in hydration cause large changes in the molal heat capacity of the solute, and it seems useful to apply this method to the case of conformational changes in water-soluble polymers.…”

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

“…Consequently, the anomalous behavior of pK 1 shown in Figure 2 indicates a conformational transition which may be related to intramolecular hydrophobic interactions between phenyl and/or methyl groups. The values of the intrinsic dissociation constant of primary carboxyl groups (pK 1 °) estimated from Figure 2 seem con- siderably smaller than those for (MA-St), 9 • 12 The temperature dependence of the pH-titration of (MA-MSt), in 0.0878 M NaCl aqueous solution is, as in the case of (MA-St),, 13 scarcely recognized in the temperature range 15 to 35°C. Viscometric titration curves for fraction F-2 and F-4 in 0.0878 M NaCI aqueous solutions at 25"C are shown in Figure 3, in which the data in the range of IX 1 ' (degree of neutralization of the primary carboxyl group) below 0 were obtained by back-titration with HCI.…”

Conformational studies on poly(ethacrylic acid) in aqueous salts by potentiometric, viscometric, optical and1H-NMR measurements

“…Methods of the potentiometric, viscometric and optical titrations were previously described [7,9,23]. IH-NMR spectra were obtained by a 400 MHz 1H-NMR spectrometer, JEOL FX-400.…”