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

Abstract

Kinetic 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 at 25.0°C 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 at the ionic strength 0.09 and 25.0°C. Such values are compared with those determined from pH‐titration data on other hydrophobic polyelectrolytes.

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

“…It has been shown that in the presence of organic molecules the chains of PMA aggregate around the fluorescent probe forming a cluster. These (15) clusters are formed at low pH, 13 and they are stable up to pH 6. 31 Therefore, we can conclude that the conformational transition that takes PMA from an extended to the contracted state occurs in at least three different steps involving different structures: The first is very fast and cannot be observed by the stopped-flow technique.…”

“…1,14,15 In this model, the transition is described as occurring between two forms, A and B, in which the polymer subunits may exist. At low values of R the form A dominates, and after passing the transition region the B form will occur predominantly.…”

“…[17][18][19] However, just a few data have been published on the kinetics of the pH-induced conformational transition of synthetic polyelectrolytes. 9,14,15,[20][21][22] The kinetics of the conformational transition of an alternating maleic acid-styrene copolymer was studied by Ohno et al, and the transition was observed to occur in approximately 500 ms. 14,15 Different fluorescent probes have been used to study the expansion of PMA following a pH jump, where the fluorescence intensity change is assumed to monitor the rate of polymer coil expansion. 9,21,22 Part of the process could not be followed because it was faster than 1 ms, but most of the transition occurs in the range 600-1000 ms.…”

Effect of Hydrophobic Bonding on the Conformational Transition and Properties of Intramolecular Micelles Formed by Copolymers of Maleic Acid and Styrene

“…Polyelectrolytes with hydrophobic groups attached to the side chain may give rise to intramolecular micelles under appropriate conditions. Such polymers have been called "polysoaps", and typical examples are the n-dodecyl derivatives of poly(4-vinylpyridine); 1 copolymers of maleic acid with alkyl vinyl ethers, [2][3][4][5][6][7] styrene, [8][9][10][11] or R-methylstyrene. 12 These polymers are known to form hydrophobic microdomains as a consequence of a pH-induced conformational transition, and this process has been studied by different measuring techniques.…”

“…6,12,13 A similar pH-induced conformational transition has been observed in an alternating copolymer of maleic acid and styrene. [8][9][10][11] In this polymer, the compact form is stabilized by hydrophobic interaction between phenyl groups, and the transition occurs near R 1 ) 0.3.…”