Substantially enhanced stability against degrafting of zwitterionic PMPC brushes by utilizing PGMA-linked initiators

We present a simple method to prepare zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) brushes on silicon surfaces that exhibit excellent long term stability in aqueous environment. First, we attach poly(glycidyl methacrylate) (PGMA) to the substrate. Next, we couple 2-bromoisobutyryl bromide initiators to the modified substrate, which allows us to grow PMPC brushes using surface initiated atom transfer radical polymerization. Atomic force microscopy (AFM) is employed to evaluate the dry thickness of the PMPC brushes after incubation in water and solutions of various salts. The AFM results show that the PGMA-PMPC brushes are indeed very stable and that the brushes can stand being immersed for at least 4 weeks in physiological fluids (saline solution) and artificial sea water with only 1% decrease of their dry thickness. In view of potential applications, we demonstrate that the friction between these PGMA-PMPC brushes and a polystyrene colloid in water is extremely low: the friction coefficients are found to be 10(-3)-10(-4). Moreover, we show that our brushes keep their hydrophilic properties after immersion for 100,000 ppm hours in sodium hypochlorite solution, indicating their potential for employment as coatings on industrial membranes.