PHASE-BEHAVIOR AND STRUCTURE OF TERNARY AMPHIPHILIC BLOCK COPOLYMER-ALKANOL-WATER SYSTEMS - COMPARISON OF POLY(ETHYLENE OXIDE) POLY(PROPYLENE OXIDE) TO POLY(ETHYLENE OXIDE) POLY(TETRAHYDROFURAN) COPOLYMERS

The phase behavior of amphiphilic copolymer-alkanol-water ternary syst ems was investigated for triblock copolymers of similar molecular weig ht and the same hydrophilic block [poly(ethylene oxide), E] but having different hydrophobic blocks [poly(propylene oxide), P, or poly(n-but ylene oxide) = poly(tetrahydrofuran), T]. The alkanol used (butan-1-ol ) was comparable in terms of chemical composition to the hydrophobic s egments. A rich phase behavior was obtained for the polymer with the P middle block (Pluronic F127, E100P70E100): five different one-phase r egions, i.e., micellar (L-1) and reverse micellar (L-2) solutions, and (micellar) cubic (I-1), hexagonal (H-1), and lamellar (L-alpha) lyotr opic liquid crystalline regions, were detected. The microstructure in the liquid crystalline regions was established from small-angle X-ray measurements; I-1 was found to be primitive cubic. The alkanol molecul es are most likely anchored with their OH- group at the E-P interface, increasing the apparent volume of the P blocks relative to that of th e E blocks, and thus causing a decrease in the polymer layer curvature from spherical to cylindrical. Only a single one-phase region, extend ing from the water to the alkanol corner, was observed in the E100T27E 100 ternary phase diagram. The extent of the one-phase regions decreas ed for both E100T27E100 and E100P70E100 systems when the alkanol molec ular weight increased.