Covalently Attached Monolayers of Oligo(dimethylsiloxane)s on Silica: A Siloxane Chemistry Approach for Surface Modification

Abstract

This work describes the synthesis of oligo(dimethylsiloxane) [−Si(CH3)2O−]n monolayers supported on silica. The fundamental properties of siloxane (Si−O−Si) backbones, for example, high flexibility and high thermal stability, set siloxane monolayers apart from self-assembled monolayers derived from long-chain alkylsilanes, alkylthiols, and so forth and provide attractive features for using “siloxane chemistry” for the modification of surfaces. Oligo(dimethylsiloxane) surfaces were prepared by reaction of low molecular weight α,ω-dichloro-dimethylsilane/oligo(dimethylsiloxane)s [Cl[Si(CH3)2O]n−Si(CH3)2Cl, n = 0, 1, 2, 3, 4] with mesoporous precipitated silica (pore diameter 15 nm). Reactions with silicas of different degrees of hydration (dried at 200 °C in a vacuum, “as received”, and saturated with water vapors) were studied under two conditions: (1) in the vapor phase and (2) in solution. Reactions of Cl[Si(CH3)2O]n−Si(CH3)2Cl with dry silicas yield surfaces with bonding densities of 2.35 ± 0.15 [Si(CH...