PHASE-BEHAVIOR OF POLY(ETHYLENE OXIDE)-POLY(PROPYLENE OXIDE)-POLY(ETHYLENE OXIDE) TRIBLOCK COPOLYMERS IN WATER

Phase behavior of ethylene oxide (EO)-propylene oxide (PO)-ethylene ox ide triblock copolymers in water has been investigated, by using H-2 N MR and polarizing microscopy, as functions of both concentration and t emperature. Seven copolymers, having wide variations of composition an d molecular weight, are used. It has been demonstrated that formation of liquid crystalline phases above certain polymer concentrations is a rather common feature for the EO-PO-EO triblock copolymer-water syste ms. The liquid crystalline phases formed are cubic, hexagonal, and lam ellar phases. A cubic phase which may possess a;bicontinuous-type stru cture has been identified. Four factors are important for controlling the phase behavior. They are molecular weight, polymer chemical compos ition, temperature, and concentration. A minimum molecular weight of t he copolymer is needed in order to form the liquid crystalline phases. Moreover, a dose relationship between the cloud point of the copolyme r and the mesophase structures has been indicated.