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The micellization and gelation properties of oxyethylene/oxybutylene diblock copolymers E40B10 and E41B8 in aqueous K2SO4 solutions were investigated. The thermodynamic and hydrodynamic volumes of the micelles in salt solutions of various concentrations up to 0.4 mol dm−3 were determined by static and dynamic light scattering, respectively. The related changes in the gelation behavior of concentrated micellar solutions of the copolymers were explained as thermodynamic (excluded) volume effects. The thermodynamic volumes of micelles measured in moderately concentrated solution were used successfully to predict the critical gel concentrations of concentrated solutions. ©1995 John Wiley & Sons, Inc.

A series of diblock copolymers E,oBn, with n in the range 3 to 16, was prepared by sequential anionic polymerization, and the association behavior of the copolymers in aqueous solution was investigated, as was the gelation of their concentrated micellar solutions. At temperatures in the range 30-50 'C, a minimum B-block length of four to five units was required for micellization. Gelation of micellar solutions of the copolymers was observed for copolymers with B-block lengths of six to seven units or more. The relationships between (i) standard Gibbs energy of micellization and molecular characteristics and (ii) critical gelation concentration and micellar characteristics were explored.

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The thermally-reversible gelation of aqueous solutions of diblock copolymers of ethylene oxide (E) and tw-lactide (L), E42L12, E3*L16, E39L20, E41L26. E7,LI4 and E77L26, has been studied using gelation temperature measurements, polarised light microscopy and NMR spectroscopy. The solutions showed a high temperature gel-sol boundary but no low temperature gel-sol boundary. Polarised light microscopy showed that the gel phase was isotropic, and the dependence of sol-gel temperature on concentration suggested that the micelles were prolate ellipsoidal, rather then spherical. NMR spectroscopy showed that below ca. 60 "C, the L block in the micelle core became highly restricted. It is tentatively suggested that this is due to the L blocks forming an ordered structure, thus explaining the absence of a low temperature gel-sol boundary.