The correlation between the phase transition of block copolymers and the emulsion formation

The phase diagrams and the amount of emulsion phase in water/vinyl acetate (VAc)/block copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(e thylene oxide) (PEO-PPO-PEO) systems depend on temperature. In water/VAc mi xtures, the PEO-PPO-PEO block copolymers exhibit a phase transition (micell isation) at similar to 40 degrees C and a conformational transition at 55 d egrees C. At the phase transition temperature, the experimental findings, w hich have been obtained by dynamic light scattering (DLS), evidence the for mation of aggregates. In these mixtures, the onset of gel formation occurs at a lower polymer concentration than in the water. At temperatures higher than the phase transition temperature, water becomes a bad solvent for PEO and the disruption of the aggregates is produced by the contraction of PEO chains. The VAc molecules are eliminated outside the micelles. The restruct uring of the solvent in the micelles proximity is followed by the increase of the emulsion percentage. (C) 1999 Elsevier Science B.V. All rights reser ved.