The process of adsorption-diffusion in polymer solutions is analysed by proposing a new phenomenological model. The important feature of the model is the incorporation of the phenomenon of disengagement of the chains at the pore mouth from the adsorbed entangled chains present around the porous adsorbent particle. This feature is shown to lead to the development of an intermediate plateau before an equilibrium plateau is reached in the adsorption kinetic curves, a prediction not obtainable by conventional models. The model has been validated by using the experimental data obtained in this work and also that from the literature. This work brings in a new feature of an "optimum" pore radius for maximum adsorption rate in polymeric systems.