Hydrophobic Interaction of the Water-Soluble ABA-Type Block Copolymer Composed of 2-Hydroxyethyl Methacrylate and Ethylene Oxide and Its Conformational Transition

Abstract

ABSTRACT:The water-soluble ABA-type block copolymer composed of a hydrophobic poly(2-hydroxyethyl methacrylate) and a hydrophilic poly(ethylene oxide) was synthesized. The correlation between the structure of the block copolymer in dilute aqueous solution and its hydrophobic interaction was studied in comparison with random copolymers whose hydrophobic groups are statistically distributed along the chain. Fluorometric measurements using ANS as a probe for hydrophobic region were carried out on the aqueous solution of the block copolymer in the monomolecular state. The hydrophobic domain structure of the monomolecular block copolymer is discussed with respect to the change in the thermodynamic parameters for the binding process of ANS to the polymer chain. The binding ability of the block copolymer for an ANS molecule was found to be larger than that of corresponding random copolymers. This indicates that the mode of the arrangement of hydrophobic groups along the chain affects the hydrophobic interaction and that the block copolymer forms the large hydrophobic region which results from the aggregation of these hydrophobic blocks. It was observed that the temperature dependence of the binding constant of the block copolymer displayed a sharp transition within a narrow temperature range, indicating that the structural change takes place within a molecule. The thermodynamic parameters for both states of the block copolymer below and above the transition temperature were determined independently from the temperature dependence of the binding constant. This means that the hydrophobic domain of the block copolymer becomes larger in the lower temperature range than in the higher, presumably because of the segregation between the hydrophobic and the hydrophilic blocks.KEY WORDS Water-Soluble Block Copolymer / Telomerization / 2-Hydroxyethyl Methacrylate / Poly(ethylene oxide) / Hydrophobic Interaction / Fluorescent Probe / Hydrophobic Domain / Segregation / Polymers consisting of both the hydrophilic and hydrophobic portions have characteristic properties,1 often referred to as the amphiphilic property. Only a few papers, however, have been published on the relation between the polymer structure and this property. The condition for the occurrence of either the hydrophilic or the hydrophobic functions still remains unclear and so it is desirable to study more extensively the influence of intramolecular interaction on the solution properties. may thus be expected that the mode of arrangement of hydrophobic groups in a polymer chain affects the occurrence of hydrophobicity in polymers.It has been reported that the hydrophobic interaction of a water-soluble amphiphilic polymer is influenced not only by the chemical structure and composition of the hydrophobic groups but also by the distribution of these groups along the chain. 2 • 3 ItThe study on the conformation and intramolecular interaction of block copolymers consisting of an incompatible homopolymer pair in dilute solution has been the subject of extensive investigati...

Shifts in Redox Formal Potentials Accompanying the Incorporation of Cationic Complexes in Perfluoro Polycarboxylate and Polysulfonate Coatings on Graphite Electrodes

“…The positive value of AAH ~ for incorporation of the Ru(NH3)6 ~+/~+ couple by polyelectrolyte II (Table III) represents the net result of a variety of coulombic and dipolar interactions whose individual contribution to the measured values of AAH~gs ~ it would be extremely difficult to disentangle. However, it may be worth noting that the behavior we have observed is similar to that reported for the incorporation from aqueous solution of an organic sulfonate (8-anilino-1-naphthalene sulfonate) by the hydrophobic portion of a block copolymer of polyethylene oxide and poly(2hydroxyethyl methacrylate) (20). The incorporation, which is free of direct electrostatic binding between fixed charge groups and the incorporating ions, is also governed by a positive entropy change that overcomes a corresponding increase in enthalpy.…”

“…However, it may be worth noting that the behavior we have observed is similar to that reported for the incorporation from aqueous solution of an organic sulfonate (8-anilino-1-naphthalene sulfonate) by the hydrophobic portion of a block copolymer of polyethylene oxide and poly(2-hydroxyethyl methacrylate) (20). The incorporation, which is free of direct electrostatic binding between fixed charge groups and the incorporating ions, is also governed by a positive entropy change that overcomes a corresponding increase in enthalpy.…”

Hydrophobic domain structure of water-soluble block copolymer. 2. Transition phenomena of block copolymer micelles

“…However, it is known that in the crystalline state iPS adopts a threefold helical conformation, with a repeat distance of 6.6 Á along the chain, and that this helical character is substantially maintained in good solvents. 4 Keller et al5,6 reported a new X-ray diffraction pattern from gels of iPS prepared from irons-decalin. The characteristic features were a meridional reflection of 5.1-Á spacing and a layer line distance of 30.6 Á.…”