Isotope effects on hydrophobic interaction in hydrophobic polyelectrolytes

Abstract

An alternating copolymer of maleic acid and perdeuteriostyrene was prepared, and the pH-induced conformational transition from the compact to extended coil form was observed by pH, optical, viscometric, and NMR titrations in 0.01-0.27 mol/L aqueous NaCl at 5-45 °C. The transition curves were calculated from the pH and optical data in terms of the coil fraction in the molecule vs. degree of ionization of the carboxyl groups. Also, thermodynamic parameters of the conformational transition were determined from the pH-titration curves and their temperature dependence, taking into consideration dissociation of the secondary carboxyl groups. The transition curve, transition free energy, and difference of specific heats between the compact and coil forms at 0.03 M NaCl were compared with those for the maleic acid-nondeuterated styrene copolymer. All results are consistent with a more enhanced hydrophobic stabilization of the compact form in the deuterated copolymer than in the nondeuterated copolymer. Possible reasons for the enhancement of the hydrophobic interaction between the aromatic substances by deuteration are discussed.

Conformational Characterization of A Maleic Acid Copolymer with An Inflexible Side Chain

“…The degree of polymerization was estimated to be ~ 640 by use of the intrinsic viscosity of the anhydride copolymer in tetrahydrofuran at 30°C r MALEIC ACID COPOLYMER 863 and the MW- [JJ] relationship for the maleic anhydride-styrene copolymer [20]. Aqueous NaCl solutions of (MA-Ind) n were prepared by the method described previously [11][12][13][14][15][16][17][18].…”

“…Potentiometric, viscometric, and optical titration data were obtained by using the same methods as in our previous studies on maleic acid copolymers [11][12][13][14][15][16][17][18]. The concentrations of (MA-Ind),, used were approximately 1.0 X 10" 2 , 1.8 X 10" 2 , and 1.6 X 10" 3 monomol/dm 3 for pH, viscometric, and optical measurements, respectively.…”

“…The hydrophobic polyacids studied previously are maleic acid copolymers of hydrophobic vinyl compounds. Strauss et al [2][3][4][5][6][7][8][9][10] studied the transition of copolymers with longer alkyl vinyl ethers than propyl, and our group [11][12][13][14][15][16][17][18] has studied aromatic vinyl compounds such as styrene. The side chains in the alkyl vinyl ether copolymers are flexible in the coiled form, and even the side chains of our aromatic copolymers were found to be flexible according to NMR measurements [17].…”

Contraction of the Copolymer Gel of Maleic Acid and Styrene in the Range of Degree of Ionization above 0.5

“…The dimension of the protons and hydroxyl ions (in the solution / the gel) estimated from the pH measured, and the total moles of carboxyl groups in the gel estimated on the assumption that the pH increment per a was at a maximum at a Å 0.5, respectively. A jump in pH at a Å 0.5 has commonly been observed for polymers composed of maleic acid (1)(2) / and OH 0 were approximated with those in the absence of the gel. The gel volume V t was determined by the relation V t Å W g /r, where W g and r were the weight and the density of the gel, and the latter was assumed to be identical with the density of the outer solution.…”

“…The polymer of maleic acid and the copolymer of maleic acid polymerization was initiated by a, a-azobis(isobutyroniwith styrene or alkylvinyl ether that the viscosities show trile) and was carried out at 60ЊC. Gels synthesized in a maxima in the vicinity of half-ionization of the ionizable glass tube (3 mm diameter) and cut into a rod form (3 group (1)(2). According to the theory of the viscosity of a mm length) were rinsed thoroughly with THF solution.…”