Surface functionalization with phosphazene substrates, Part IV: Silica and Si(100) surface functionalization using cyclophosphazenes partially substituted with trialkoxysilane derivatives and PEG-750 monomethylether, 2,2,3,3-tetrafluoropropanol and 4-hydroxyazobenzene

This paper deals with the possibility of functionalizing the surface of silicon-based materials by exploiting cyclophosphazenes containing suitable substituent groups. Thus, phosphazene trimers were prepared, containing about 50% of the reactive sites substituted by gamma-amino-propyltriethoxy silane (APTES), while the residual positions in the cycle contain poly(ethylene glycol) monomethylether (MW approx. 750; PEG-750-ME), tetrafluoropropanol (TFP) and 4-hydroxyazobenzene (AzB). Using these novel materials we succeeded in surface functionalizing SiO2 beads in the coating of silicon wafers or sodalime slides and in the preparation of cyclophosphazene-based monoliths in the presence of hydrolyzed TEOS by sol-gel technique. The whole series of products has been characterized by standard spectroscopic (IR, UV-Vis, H-1-, C-13-, Si-29- and P-31-NMR, both in solution and in solid state) and thermal (DSC and DMTA) techniques. This approach to the surface functionalization of silicon-based materials containing carefully selected substituents is completely general and can be used to attach to the hydroxylated surfaces practically any type of nucleophile that can be supported on the cyclophosphazene ring.