Formation of Hydrophobic Region by Oligosoap and the Variation of Partial Molal Volume in Aqueous Solution

Abstract

Various kinds of anionic oligosoaps were synthesized from alternating cooligomers of alkyl vinyl ethers with maleic anhydride or diethyl maleate. The variations of apparent (φυ) and partial base molal volumes (φυ0) of these oligosoaps in aqueous solution were investigated to discuss the degrees of the formation of their hydrophobic regions.1) The observed dependence of φυ on the concentration of oligosoaps indicated that the cooligomer derivatives with shorter alkyl ethers behaved as polyelectrolytes (remarkable extension of molecules due to electrostatic repulsion), while those with longer alkyl ethers formed hydrophobic regions.2) The values of φυ0 depended on saponification degrees and the kind of gegen ions (K or Na). This may be interpreted by the difference of the effective bulkiness of gegen ions fixed by oligomer anions.3) It was found that increments of φυ0 (Δφυ0) per methylene group of alkyl chain in the vinyl ethers scattered in the range of 1617 ml/methylene, while those of various monosoaps were found to be almost the same. These results seem to reflect the variety of hydrophobic region of oligosoaps in water.4) Effects of chemical structures and the number of repeating-units of the alternating cooligomers on φυ, φυ0 and Δφυ0 have also been discussed.