Hyperbranching polymerization of aziridine on silica solid substrates leading to a surface of highly dense reactive amine groups

Silica solid substrates such as fused silica, silicon wafers with a natural oxide layer, and glass were treated with aziridine to produce reactive primary amine groups on the top surface. We found that the hydroxyl group on the substrate was able to initiate the ring-opening polymerization of aziridine, resulting in highly branched poly(ethyleneimine) on the surface. In dichloromethane, the thickness of the organic film reached 25 Å in 20 h and the absolute density of the primary amine group on the surface was 23 amines/nm 2. Atomic force microscopy shows an embossed morphology after the polymerization in dichloromethane, while use of toluene gives a rather smooth surface. The resulting organic layer shows high thermal and pH stability.