Degrafting of Poly(poly(ethylene glycol) methacrylate) Brushes from Planar and Spherical Silicon Substrates

Densely grafted, hydrophilic polymer brushes produced via surface-initiated controlled radical polymerization have been shown to undergo degrafting upon exposure to aqueous media. This degrafting process has been proposed to involve swelling-induced, mechanochemically facilitated hydrolysis of bonds located at the brush substrate interface. While a number of reports have described degrafting of hydrophilic polymer brushes, only little is known about the key structural parameters of these thin films that dictate this process. Using a series of PPEGMA and PPEGMEMA brushes produced by surface-initiated atom transfer radical polymerization (SI-ATRP), this report investigates the influence of three parameters: (i) the chemical structure of the ATRP initiator, (ii) the molecular weight of the surface-grafted polymer chains, and (iii) surface curvature. Studies performed with PPEGMA and PPEGMEMA brushes grown from substrates modified with different ATRP initiators indicated that hydrolysis of both siloxane as well as ester/amide bonds contributes to degrafting. Finally, experiments with PPEGMEMA-modified silica nanoparticles revealed the influence of surface curvature and suggested that degrafting is more pronounced as surface curvature decreases.