Calorimetric investigation of poly(methacrylic acid) and poly(acrylic acid) in aqueous solution

Abstract

The enthalpy of dissociation of poly(acrylic acid) and of poly(methacrylic acid) in water and in 0.5N NaCl at 25°C has been measured over a wide range of degrees of neutralization of the polyelectrolytes. In the case of poly(methacrylic acid) the calorimetric data permit the direct evaluation of the enthalpy of conformational transition of the polymer. For this transition, with the aid of standard free energy data derived from potentiometric titrations, the change in entropy was also estimated. The relative accuracy of the thermodynamic data, and the possibility of deriving therefrom information on the mechanism of transitions of the type, globular coils → expanded coils for partially hydrophobic synthetic polyelectrolytes in aqueous solution are discussed.

Effect of the Molecular Weight on the Dynamics of the Conformational Transition of Poly(methacrylic acid)

“…[1][2][3][4][5][6][7][8][9][10][11][12] The measurement of equilibrium properties, as a function of pH, has established that, at low pH, the macromolecule expands slowly as the charge density increases. At higher pH, after a certain expansion of the coil is achieved, a remarkable expansion of the PMA chain takes place.…”

Charged Carbon Nanomaterials: Redox Chemistries of Fullerenes, Carbon Nanotubes, and Graphenes

“…This hypothesis attributes the observed preferential dissolution of wider diameter SWCNTs at low charge ratios to the increased external area of the SWCNTs; other groups have attributed this phenomenon to electronic effects (section 6.1). It is likely that the specific free energies will vary between CCN salts (as they do for classic simple ionic salts 404 and polyelectrolytes 405 ), and both enthalpically and entropically driven dissolution may be possible in differing systems; further work is needed to elucidate the underlying physical chemistry.…”

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

“…At I% investigated here, PEA seems to be in the compact form at a < 0.1 and in the coil at a > 0.6, irrespective of L To determine the standard free energy change of transition, A G ~ the potentiometric behaviour of hypothetical coil in the whole region of a was assumed by extrapolation of the curve at a > 0.6 to the region of low a with the Henderson-Hasselbalch equation at each L An example of such hypothetical curves is shown at I = 0.01 in figure 1,by which the value of pK0 (at a = 0) could also be estimated. In table I are shown the values of AG ~ at the four I's and 25 ~ and those of the conventional PMA at I = 0 and 0.5 (NaC1) [15]. The compact form in PEA is more stable than in PMA.…”

“…Intermolecular aggregations were found only at very low ae 1 in aqueous salts of high ionic strength L On the other hand, poly(methacrylic acid) (PMA) is a typical hydrophobic polyacid. Its potentiometric, viscometric and optical titrations in aqueous salts have shown the pH-induced conformational transition similar to those of the maleic acid copolymers [12][13][14][15]. Results of solubility measurements [16] of hydrophobic dyes into PMA at low degree of ionization a of carboxyl groups and preferential binding [17] of organic solvents to PMA in aqueous solutions are consistent with the conclusion of the existence of the compact form at low a stabilized by hydrophobic interaction between methyl groups, although some authors have emphasized importance of hydrogen bond formation for stabilization of the acid form of PMA [18,19].…”