Surface-initiated thermal radical polymerization on gold

We report surface-initiated thermal radical polymerization from cross linke d monolayers of azo-initiators on Au. Initial attempts to graft polymer lay ers from initiators attached to alkanethiol monolayers yielded polymer film s with thicknesses less than 5 nm. Efficient grafting from such surfaces is not possible because initiator-containing monolayers are somewhat unstable under thermal radical polymerization conditions, and desorbed thiols may s erve as efficient chain-transfer reagents that inhibit radical polymerizati on. In addition, reactive radicals can attack the Au-S bonds that link the initiator monolayer to the surface. To overcome these problems, we employed mercaptopropyltrimethoxysilanes to form an adhesion layer for initiator at tachment. Cross-linked poly(siloxane) layers apparently stabilize the initi ator layer, allowing well-defined surface radical polymerization to occur f rom Au substrates. We characterized the grafted polymer layers with ellipso metry, reflectance Fourier transform infrared spectroscopy, and atomic forc e microscopy.