In this paper, we model, on the mesoscopic level of description, the nonstandard behavior of mass transport into a binary mixture of two immiscible and rheologically different polymers. We formulate a model which explicitly incorporates the coupling between diffusion and the deformation of the interface and also of the two polymers. We use, for this purpose, four microstructural state variables, namely a scalar surface area Q and a covariant anisotropy second-rank tensor q for the dividing interface, and two contravariant symmetric second order conformation tensors A and B for the two immiscible polymers. A new expression for a 1D diffusion mass flux density is derived which involves four coupling functionnals. The results presented here show the possible occurrence of a non-Fickian behavior, in particular when the three involved diffusion Deborah numbers approach the unit.