Reversible addition fragmentation transfer (raft) polymerization for coatings in capillary electrophoresis

Capillary electrophoresis is a powerful tool for biomolecule separation. In CE it is necessary to control electroosmotic flow in order to fully exploit the potentiality of the technique in the separation of proteins. In some cases, for instances at high pH, the EOF can lead to elution of the analytes before separation has occurred. In other circumstances the negatively charged wall can cause adsorption of cationic solutes through coulombic interactions. In order to minimize these problems, a new capillary coating was developed. Brush polymers, obtained by grafting from approach, were grown on the capillary surface via Reversible Addition Fragmentation Transfer (RAFT) polymerization. RAFT is a controlled/living polymerization process used to synthesize well-defined polymers with low polydispersity index (PDI). In this approach, polymer chains grow directly from the surface leading to formation of chains covalently attached, by one end, to the silanols of the substrate. The process involves a conventional free radical polymerization onto modified silica surface in the presence of thiocarbonylthio compounds of general structure RS(S=C)Z. A systematic investigation of different polymerization conditions (type of silanating agent, monomer type and concentration, characteristics of the various RAFT agents, etc.) has been carried out. Different coatings generated by RAFT polymerization were compared with conventional coatings obtained by physisorption and chemisorption. The capillary surface was silanized by agents bearing different functional groups such as radical initiators (AzoBis compound) or radical carriers (thiol group). A new RAFT chain transfer agent, bearing a silanating group, able to initiate the growth of polymer chains directly on the silica surface, was used to generate polymer coatings. The brush polymers, obtained in this way, generated thick films of reduced surface charge and protein-wall interaction. The poster will present the results obtained in terms of EOF suppression coating stability and separation efficiency achieved in protein separations