Cubic Phase in a Connected Micellar Network of Poly(propylene oxide)−Poly(ethylene oxide)−Poly(propylene oxide) Triblock Copolymers in Water

Abstract

Small-angle neutron scattering studies are presented in the solid aqueous gel phase of the Pluronic-R polymer, 25R8, which is a triblock copolymer with a central poly(ethylene oxide) block symmetrically surrounded by poly(propylene oxide) blocks: PO15EO156PO15. 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 °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 PEO. 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.