The transport of monodisperse, atactic polystyrene-d (aPS-D) into atactic polystyrene (aPS) melts and isotactic polystyrene (iPS) semicrystalline matrices has been characterized by a quantitative ATR-FTIR technique.; Values of aPS-D tracer diffusion coefficients in aPS melts compare very well with previous literature indicating the effects of (i) diffusant molecular weight holding constant the matrix molecular weight and (ii) matrix molecular weight holding constant the diffusant molecular weight. Semicrystalline morphologies of iPS were characterized extensively by DSC, microscopy, and SAXS as a function of temperature. Non-Fickian transport kinetics are observed during the imbibition of aPS-D into semicrystalline iPS at low temperatures and high penetrant molecular weights. There are two apparent time regimes of non-Fickian kinetics. The first regime of imbibition kinetics occurs at early times, where the uptake can be described by Fickian mutual diffusion kinetics. Later, there is a decrease in the imbibition rate and the rates of continued imbibition are no longer Fickian. The transition to a slower transport kinetics regime can be identified with a time scale over which penetrant macromolecules in amorphous pockets explore the bottlenecks between crystalline, dendritic obstacles.