Stability of Water/Poly(ethylene oxide)<sub>43</sub><i>-b-</i>poly(ε-caprolactone)<sub>14</sub>/Cyclohexanone
Emulsions Involves Water Exchange between the Core and the Bulk
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Abstract
The
formation of emulsions upon reverse self-association of the
monodisperse amphiphilic block copolymer poly(ethylene oxide)<sub>43</sub><i>-<i>b</i>-</i>poly(ε-caprolactone)<sub>14</sub> in cyclohexanone is reported. Such emulsions are not formed
in toluene, chloroform, or dichloromethane. We demonstrate by magnetic
resonance spectroscopy the active role of the solvent on the stabilization
of the emulsions. Cyclohexanone shows high affinity for both blocks,
as predicted by the Hansen solubility parameters, so that the copolymer
chains are fully dissolved as monomeric chains. In addition, the solvent
is able to produce hydrogen bonding with water molecules. Water undergoes
molecular exchange between water molecules associated with the polymer
and water molecules associated with the solvent, dynamics of major
importance for the stabilization of the emulsions. Association of
polymeric chains forming reverse aggregates is induced by water over
a concentration threshold of 5 wt %. Reverse copolymer aggregates
show submicron average hydrodynamic diameters, as seen by dynamic
light scattering, depending on the polymer and water concentration