Polymer brushes by living anionic surface initiated polymerization on flat silicon (SiO_x) and gold surfaces: Homopolymers and block copolymers

The formation of homopolymer and block copolymer brushes grafted from Au and Si (SiO_x) surfaces via living anionic surface-initiated polymerization (LASIP) is described. The initiator precursor 1,1-diphenylethylene (DPE) was functionalized with alkylsilane or alkylthiol and grafted onto planar Si wafer and Au surfaces, respectively, by self-assembled monolayer techniques. n-BuLi was used to activate the DPE initiator for anionic polymerization of monomers at the interface. A high-vacuum reactor was used for polymerization at surface under anhydrous solution conditions. By a careful sequence of monomer introduction, reaction, and termination, homopolymer and block copolymer tethered polymer brushes were obtained. The grafted polymer chains were investigated using surface sensitive techniques such as ellipsometry, contact angle measurements, atomic force microscopy, Fourier transform infrared spectroscopy, surface plasmon spectroscopy, and X-ray photoelectron spectroscopy. The importance of activation of the grafted initiator, control of polymerization conditions, and removal of excess BuLi is emphasized. Interesting differences in morphology, thickness, grafting density, and polymerization conditions contrast LASIP from solution and other surface-initiated polymerization mechanisms. The formation of block copolymer sequences highlights the unique utility of a living anionic polymerization technique on surfaces.