The aim of this study was to define a block copolymer micellar system with a high solubilization capacity for poorlysoluble aromatic drugs. Ethylene oxide and phenyl glycidyl ether were sequentially polymerized to form the diblockcopolymer G
5E
67 (G = phenyl glycidyl ether, OCH
2CH(CH
2OC
6H
5); E = oxyethylene, OCH
2CH
2; subscripts denotenumber-average block lengths in repeat units). The association properties in aqueous solution over the range 20-50
C were investigated by surface tensiometry and light scattering, yielding values of the cmc, hydrodynamic radius,and association number; gel boundaries in concentrated micellar solution were investigated by tube inversion. Thesolubilization capacity of G
5E
67 for the poorly water-soluble drug griseofulvin was higher than that of a triblock EGEcopolymer of
longer G block length and considerably higher than that achieved with poloxamers (E
mP
nE
m, P =oxypropylene).