Hydrophilic/Hydrophobic substrates induce enrichment of short/long chains in brushes by grafting to reactions of polymers with polar reactive end-groups

Grafting to reaction consists in the chemical attachment of end-functionalized polymers on reactive substrates, thus providing anchored polymer brushes. The characteristics of the obtained brushes are mainly influenced by the molecular weight of the polymer, the mass distribution, the chemistry of the reactive end-group and the type of substrate. Recently, the grafting to reaction of phosphate-terminated polymers was used as a promising method to tune the amount of phosphorus atoms carried on silicon substrates for deterministic doping applications in microelectronics. While, for these dopant-polymers, the effects of the molecular weight and dispersity on the final properties of the grafted brush were already investigated, the role played by the substrate remains unexplored. In this work, not-deglazed and deglazed silicon substrates are considered, with not-deglazed silicon consisting in silicon covered by a thin layer of native oxide, which is instead removed in deglazed silicon by a hydrofluoric acid treatment. The thickness of the polymer brushes obtained by grafting phosphate-terminated polystyrenes on these two substrate is evaluated. Furthermore, largely disperse systems were simulated by blending polystyrenes with different molecular weights. The thickness and the composition of the brushes obtained by grafting these blends were also investigated, resulting in a preferential grafting of the shortest component on not-deglazed silicon and in the opposite situation of long chain enrichment on deglazed silicon. The origin of these opposite behaviours are discussed.