AbstractThis article describes work with model polymers to explore the effects of long branches on polyethylene melt rheology. Dynamic moduli were measured at two or more temperatures on melts, blends, and solutions of linear (L) and star (B) hydrogenated polybutadiene (HPB). Enhancement factor Γ and temperature coefficient (flow activation energyEa) were determined from viscosity data and correlated with arm molecular weightMband volume fraction of the star component Φ. As in other species, Γ for a given branch point functionality is roughly an exponential function of Φ11/6Mbin entangled melts and solutions. In contrast with other species, however, (Ea)Band (Ea)Lare different; (Ea)B– (Ea)Lis directly proportional to ΦMb, and the degree of thermorheological complexity varies primarily with (Ea)B– (Ea)L. In blends with linear HPB of comparable viscosity, Γ for the star component remains essentially constant, and (Ea)B– (Ea)Lis directly proportional to the volume fraction of the sta