Surface-confined living radical polymerization for coatings in capillary electrophoresis

Surface-confined living radical polymerization is shown to be a controlled means of covalently bonding both linear and cross-linked polymer films on silica. CuCl/bipyridine initiates radical formation through atom transfer with a self-assembled monolayer of benzyl chloride, onto which polymer then grows. The polymerization is intrinsically confined to the surface, avoiding problems associated with polymer formed in the solution. The surface-confined polymerization scheme is generally applicable to radical polymerization of vinyl monomers and was studied here for the case of acrylamide. Infrared spectroscopy shows that the film growth is controllable, and atomic force microscopy reveals that smooth films are prepared. The surface-confinement polymerization scheme was tested for both linear and cross-linked polyacrylamide. Capillary electrophoresis of strongly basic proteins confirms that the coated capillaries provide the high efficiency expected for polyacrylamide. The cross-linked coating exhibits higher reproducibility with respect to migration time than does the linear coating. Surface-confined living radical polymerization prepares linear and cross-linked polymer films without danger of clogging narrow capillaries and will ultimately facilitate cross-laboratory comparisons by enabling control of film thickness.