Cubic phase in a connected micellar network of poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) triblock copolymers in water

Small-angle neutron scattering studies are presented in the solid aqueous gel phase of the Pluronic-R polymer, 25B8, which is a triblock copolymer with a central poly(ethylene oxide) block symmetrically surrounded by poly(propylene oxide) blocks: PO(15)EO(156)PO(15). At copolymer concentrations of the order of 50-65 w/w %, these copolymers associate into a homogeneous phase constituting an interconnected network of micelles, in which micellar cores of hydrophobic poly(propylene oxide) are interconnected by hydrophilic poly(ethylene oxide) strands. At temperatures below 40 degrees C, the materials form three solid gel phases. Neutron scattering shows that two of these phases have characteristics of cubic structures. The third phase constitutes a mixture of ordered micelles and a lamellar phase of crystalline PEG. The cubic phase close to the order-to-disorder transition can by shear be aligned into a mono (or twin) domain structure, resulting in a novel polymer network in which the knots are positioned on a lattice.