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Dynamics of Micelles of the Triblock Copolymers Poly(ethylene oxide)-Poly(propylene oxide)-Poly(ethylene oxide) in Aqueous Solution

Zana, R.; Marques, C.M.; Johner, A.

Adv. Coll. Int. Sci., 2006, 123, 345.

A number of results reported on the kinetics of exchange of triblock copolymers poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene
oxide), PEO–PPO–PEO, between micelles and the intermicellar aqueous solution are reviewed and analyzed to extract the rate constants k^+ for
the entry of a copolymer into a micelle and k^- for the exit of a copolymer from a micelle. Contrary to what is generally observed for conventional
surfactants, the rate constant for the entry of a copolymer into a micelle is slower to much slower than for a diffusion-controlled process and
decreases as the degree of polymerization of the PO block, nPO, increases. The effect of the degree of polymerization of the EO block, n_{EO}, on the
two rate constants is significant only for low values of n_{EO}. The variation of k^- with n_PO strongly suggests that the free copolymer molecule
adopts a conformation where the PO block is tightly coiled with little contact with water and not a fully extended and hydrated conformation, in
contrast to what is commonly assumed when analyzing the dependence of the cmc on the polymerization degree of the hydrophobic block.

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