Neutron reflectivity is a powerful tool for exploring polymer dynamics above the glass-transition temperature at short diffusion times in layered thin-film systems. Recent studies of membrane-mediated interdiffusion in deuterium-labeled systems have shown that ultrathin membranes can track the position of the interface in binary polymeric diffusion couples and also can discriminate between perdeuterated and hydrogenous polymers of the same molecular weight. This report shows that similar dynamic information can be obtained for binary hydrogenous polystyrene (hPS) diffusion couples separated by an ultrathin (6-nm) isopentylcellulose cinnamate (IPCC) membrane on Si wafers (air//hPS/IPCC/hPS//Si, where "//" represents an interface between obviously different phases and "/" represents a dynamic interface between polymeric species). In particular, the air//hPS/IPCC/hPS//Si system provides the same information as perdeuterium-labeled polystyrene (dPS) diffusion couples separated by the same IPCC membrane (air//dPS/IPCC/dPS//Si). This technique has potential applications for the study of confinement effects on thin-film dynamics and macromolecular transport across membranes. (C) 2004 Wiley Periodicals, Inc.