Surface-initiated anionic polymerization of styrene by means of self assembled monolayers

A synthetic concept of preparing dense polymer brushes on planar surfaces is described, in which a self-assembled monolayer (SAM) of biphenyllithium moieties on gold substrates is used to initiate anionic polymerization of styrene. The thickness of the resulting dry polystyrene brush, as estimated by ellipsometry and atomic force microscopy (AFM), is 18 ± 0.2 nm. These techniques also reveal a smooth, homogeneous polymer surface throughout the entire substrate on the macroscopic, as well as on the microscopic, scale, with a roughness of 0.3-0.5 nm (rms). On the basis of results from in situ swelling experiments, monitored by ellipsometry, a polymerization degree of N = 382 and a grafting density of approximately 7-8 chains/R(g)², or 3.2-3.6 nm²/chain, were calculated with use of mean-field theory. Polarized external reflection (ER) FTIR spectra of the grafted layer confirm highly stretched preferentially oriented polystyrene chains. Upon annealing, spin-coated polystyrene films dewet immediately the brush surface to give polymer droplets with a contact angle of 3°. All obtained results indicate that the described synthetic approach yields densely grafted polymer brushes whose experimental investigations were till now very limited.