Conformational transitions of the hydrophobic polyacids.
The conformational transitions of the alternating maleic acid copolymers with styrene (MA-St)n, and alpha-methyl styrene (MA-MSt)(n) in aqueous solutions were studied by means of various methods. The following results were obtained: 1) The conformational transitions of (MA-St)n from the compact to extended coil form are observed in various salt solutions, as in aqueous NaCl, and the compact form is stabilized by Rb+ and Cs+, but destabilized by Li+. The coions, Br-, I-, ClO4- and SCN- affect scarcely the stability of the compact form. 2) The temperature coefficient of viscosity d In [eta]/dT of (MA-St)n in 0.09 M NaCl was positive for the compact form, but negative for the coil form, and it reflects the transition. 3) The difference between specific heats for the compact and coil forms of (MA-St)n in 0.03 M NaCl is determined to be about 15% of the corresponding heat of transfer of benzene to aqueous medium. 4) A remarkable dilution of the bound monomeric acridine orange to the compact form (MA-St)n is observed and the dimerization free energy of the dye in the compact form is about -2.1 kcal mole at 25 degrees C. 5) Potentiometric, dilatometric and viscometric titrations of (MA-MSt)n in aqueous NaCl at 25 degrees C show a similar conformational transition to that of (MA-St)n. Also, the difference in the molar extinction coefficient at 261 nm indicates the transition. The compact form of (MA-MSt)n is more unstable than that of (MA-St)n. From the results, the compact conformations and the transition mechanism of both the polyacids were discussed in comparison with the results for the maleic acid copolymers with n-alkyl vinyl ethers.
Sugai
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Department of Polymer Science, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060, Japan.
Ohno
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