Association properties of diblock copolymers of ethylene oxide and 1,2-butylene oxide in aqueous solution. Copolymers with oxyethylene-block lengths in the range 100-400 chain units

Copolymers E96B18, E184B18, E315B17, and E398B19 (E = oxyethylene unit, B = oxybutylene unit) were synthesized and characterized by gel permeation chr omatography (for distribution width) and C-13 NMR spectroscopy (for absolut e molar mass and composition). Dynamic and static light scattering was used to determine micellar properties in dilute aqueous solution at three tempe ratures (25, 40, and 50 degrees C): that is, hydrodynamic radius and hydrod ynamic expansion factor, mass-average molar mass, and thermodynamic expansi on factor. At a given temperature, the values of the radii and expansion fa ctors increased as E-block length was increased, whereas values of the mice lle association number decreased. The tube-inversion method was used to def ine the mobile-immobile (hard gel) phase boundary. At room temperature (20 degrees C), hard gels were formed in the concentration range 3.5-8 wt % cop olymer depending on E-block length, the lowest value being for the copolyme r with the longest E block (E398B19).