Controlled polymerisation of sulfonate-containing monomers via Atom Transfer Radical Polymerisation

Anti-fouling is a key element in the development of biomedical materials. Poly(ethyleneglycol) is commonly used as an integral part of biomaterials for this very purpose. However polyethers can be problematic as they can autooxidise relatively rapidly, especially in the presence of oxygen and transition metal ions, present in most biochemically-relevant solutions. Zwitterionic-based materials have shown potential as biomaterials. For example phosphorylcholine-based polymers, such as - methacryloyloxyethylphosphorylcholine (MPC), have been used to produce commercial biocompatible materials. However, MPC has been reported as difficult to synthesise and handle. Another class of zwitterionic monomer used in the literature is based on the sulfobetaine moiety. The resulting polysulfobetaines have also been reported as having low protein absorption and as being easier to handle, they therefore have potential for biomaterial applications. One such sulfobetaine monomer is N,Ndimethyl- N-(2-acryloylethyl)-N-(3-sulfopropyl) ammonium betaine (SPDA). Very few studies have been carried out on the controlled polymerisation of SPDA in aqueous media. However there have been a number of studies on N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N dimethylammonium betaine (Figure 1), also known as sulfobetaine methacrylate (SBMA), which is the methacrylate analogue of SPDA. Zhang et al.2, 4 grafted two zwitterionic polymers, PSBMA and poly(carboxybetaine methacrylate), from glass and gold substrates via Atom Transfer Radical Polymerisation (ATRP). The initiators were immobilised to the substrates using 2-bromo-2-methyl-N-3-[(triethoxysilyl)propyl]propanamide (BrTMOS). The catalyst system for polymerisation was CuBr with 2,2’-bipyridine (bpy). These studies were carried out in a degassed solvent of pure water and methanol (1:1 volume ratio). The PSBMA grafts were demonstrated to have high resistance to protein absorption, as effective as PEG and MPC-based polymers.