Phase segregation in melt-extruded blends of polyethylenes that differ considerably in molecular weight was found to exert diverse degrees of influence on various measured mechanical properties. The development of phase segregated morphology was found to depend on blend component viscosity in conjunction with blend composition. The instantaneous tensile deformation properties were insensitive to phase segregation while the high-strain tensile deformation behavior was strongly and adversely influenced by phase segregation. In certain instances, phase segregation was found to favor plane stress fracture resistance. Finally, the bulk crystallization kinetics of such blends also revealed signatures of phase segregation in the form of incomplete co-crystallization of the blend components. (c) 2007 Elsevier Ltd. All rights reserved.