Grafting to reactions are one of the most investigated approaches to producing polymer brushes due to their unique capability to control both the brush thickness and grafting density. Despite their widespread use, some aspects of the grafting to reactions remain not fully understood. Among these, particularly relevant is the preferential grafting of the shortest chains in dispersed polymer systems. This phenomenon is investigated in the present paper by grafting on silicon oxide substrates polystyrene blends containing equimolar amounts of two telechelic polystyrenes with different molecular weights to model disperse polymer systems. Furthermore, for each blend, different end groups, namely, hydroxy or phosphate end groups, are considered. For hydroxy-terminated polystyrene blends, a preferential grafting of the shortest component is observed and derives from the lower entropy loss for short chains when the …