Polyoxyolefin-based amphiphilic block copolymer surfactants are commercially available, inexpensive and are used in a variety of solution-based applications. But their use as templates for nanostructured materials in the melts phase is limited by their low molecular mass, presence of impurities, and weak segregation strength that lead to order-disorder transition temperatures (ODTs) at or below room temperature. Recently we demonstrated that that the effective segregation strength of such copolymer melts can be enhanced significantly by blending with a homopolymer that selectively associates with one of the segments. For example, blending Pluronic F108, P105, and P123 surfactants with poly(acrylic acid), poly(hydroxy styrene), and other homopolymers induces phase segregation in disordered melts and can increase ODTs by more than 150 °C relative to the neat copolymer. Here, we further show that the molecular weight of added homopolymer has little influence on the melt phase behavior of poly (oxyethylene-oxypropylene-oxyethylene) type block copolymers as determined small-angle x-ray and neutron scattering experiments when the homopolymer is selectively miscible with the majority phase. The effect of molecular weight when the homopolymer is instead added to the minority phase of polyoxyolefin block copolymer melts will also be discussed.