Self-assembly of poly(oxybutylene)-poly(oxyethylene)-poly(oxybutylene) (B6E46B6) triblock copolymer in aqueous solution

Laser light scattering and small-angle neutron scattering were used to study poly(oxybutylene)-poly(oxyethylene)-poly(oxybutylene) triblock copolymers (B6E46B6) in aqueous solution from low to high concentrations and over a range of temperatures from 5 to 35 degrees C. B6E46B6 molecules exist as unimers at low concentrations and low temperatures. At higher concentrations and at low temperature (less than or equal to 15 degrees C), they associate in small numbers and scattering evidence shows that molecular associates with open structures might form. At higher temperatures, typical flowerlike micelles form. The critical micelle concentration decreases with increasing temperature while the association number increases. At high polymer concentrations (e.g., at 35% in mass), further entanglements form among the micelles, yielding another slow mode in dynamic light scattering, which can be attributed to the bridging of two hydrophobic end blacks located iu two different hydrophobic clusters by the hydrophilic middle block. However, these cross-linkings were quite weak and free micelles were still the majority in solution. When the temperature is lowered, a very slow process of microphase separation occurs. The self-assembly behavior of B6E46B6 is compared with that of other BEB type triblock copolymers.