STRUCTURAL POLYMORPHISM OF AMPHIPHILIC COPOLYMERS - 6 LYOTROPIC LIQUID-CRYSTALLINE AND 2 SOLUTION PHASES IN A POLY(OXYBUTYLENE)-B-POLY(OXYETHYLENE)-WATER-XYLENE SYSTEM

Six lyotropic liquid crystalline and two solution (equilibrium) phases can be formed (at 25 degrees C) by an amphiphilic diblock copolymer c omposed of poly(ethylene oxide) and poly(butylene oxide) in the presen ce of water (selective solvent for PEG) and ''oil'' (p-xylene, a selec tive solvent for PBO). Oil-in-water (''normal'') micellar solution (L( 1)), micellar cubic liquid crystals (I-1), hexagonal liquid crystals ( H-1), and a lamellar structure (L(alpha)) are formed with an increase of the copolymer concentration along the oil-lean side of the ternary phase diagram. A micellar solution (L(2)), micellar cubic liquid cryst als (I-2), hexagonal liquid crystals (H-2), and bicontinuous cubic liq uid crystals (V-2), all of the water-in-oil (''reverse'') morphology, are formed in the water-lean part of the phase diagram with increasing copolymer concentration and in the presence of some water. The oil-in -water [water-in-oil] structures can accommodate up to 0.33 [0.40] g o f oil [water]/g of copolymer. The formation of a reverse micellar cubi c phase (I-2), indexed to the crystallographic space group Fd3m (face- centered), is an important feature of this phase diagram as it is one of the first times that such a structure has been identified. The norm al micellar cubic structure (I-1) is body-centered (Im3m). The microst ructure in the bicontinuous cubic region (V-2) can be described in ter ms of a multiply-connected amphiphile bilayer consistent with the Gyro id minimal surface (Ia3d). The absence of a ''preferred curvature'' in the self-assembly of this macromolecular amphiphile distinguishes it from typical low-molecular weight surfactants and bestows this remarka ble structural polymorphism.