Dynamic covalent polymer brushes: reversible surface modification of reactive polymer brushes with alkoxyamine-based dynamic covalent bonds

Abstract

Reactive poly(methacrylate)-based polymer brushes with radically exchangeable alkoxyamine units in the side chains were prepared on flat silicon substrates and their reactivity and surface properties were investigated. The reactive polymer brushes were prepared by surface-initiated atom transfer radical polymerization (ATRP) and the graft density of the brushes was estimated to be approximately 0.36 chains per nm². Radical crossover reactions among the alkoxyamine units in the side chains of the polymer brushes and at the ends of the fluorinated polymer chains were carried out to produce polymer brushes with low surface free energies. Angular-dependent X-ray photoelectron spectroscopy (XPS) measurement suggested that the fluorinated polymer chains were predominantly attached to the outermost surface because of the size exclusion from the high graft density. In addition, the de-grafting reaction of the fluorinated polymer chains was also performed to confirm the reversibility of the radical crossover reactions. The surface properties of the polymer brushes after the grafting and de-grafting processes were characterized by XPS and contact angle measurements. The composition calculated from the XPS indicated that the reversible grafting of the fluorinated polymer chains proceeded successfully. The surface wettability of the polymer brushes also changed after the grafting of the fluorinated polymers. Furthermore, after the de-grafting of the fluorinated polymer chains, the peaks attributed to fluorine atoms completely disappeared from the XPS spectrum and the wettability of the surface after the de-grafting returned to that obtained before grafting.