Polyethylene (PE) has relatively poor adhesion with polar polymeric materials. In an effort to improve the adhesion between PE and thermoplastic polyurethane (TPU), maleic anhydride (MA), hydroxyl (OH), and secondary amine (NHR) functionalized PEs were blended into nonmodified PE. These functional groups will react with urethane linkages in TPU at the temperature of melt processing. We bonded these PEs to TPU via lamination and coextrusion. To compare the two processes, we determined the interfacial copolymer density Sigma considering both advection and interfacial area generation. We found that the development of adhesion in coextrusion was much faster in comparison with lamination at the same temperature. This difference was attributed to the extensional and compressive flow in coextrusion overcoming the diffusion barrier at the interface and forcing reactive species to penetrate the interface. The effects of functional group reactivity and processing variables on adhesion were correlated with interfacial copolymer coverage. Amine functionalized PE showed dramatic adhesion improvement even at 1 wt %. (C) 2011 American Institute of Chemical Engineers AIChE J, 57: 3496-3506, 2011