Melt viscosity of oligomeric triblock copolymers (type PEP) of ethylene and propylene oxides

Melt viscosity η at 25°C of four oligomeric triblock copolymers consisting of a central block of ethoxamer units and two end blocks of propoxamer units (PEP) (M_n × 10^?3 = 1 and 2; mole fraction of ethoxamer units x_E = 0.41, 0.57, and 0.74) was analyzed in terms of the theory advanced by Berry and Fox. The structure-dependent factor F(X) was deduced from the intrinsic viscosity data, and the mean friction factor per friction center ζ was computed from η and F(X). At a fixed molecular weight, it increases with increasing x_E. The dependence of ζ versus x_E was compared with curves computed from the data for homopolymers. The best agreement was obtained if the following values of the inherent friction factor (log ζ₀) were used: ?10.25 for poly(ethylene oxide) PEO and ?10.65 for PPO. © 1994 John Wiley & Sons, Inc.