Room-Temperature, Aqueous-Phase Fabrication of Poly(methacrylic acid) Brushes by UV-LED-Induced, Controlled Radical Polymerization with High Selectivity for Surface-Bound Species

Poly(methacrylic acid) (PMAA) brushes were grafted from Si/SiO2 substrates by means of immobilized-photoiniferter-mediated controlled radical polymerization. The employed UV setup was based on ultraviolet light-emitting diodes (UV-LEDs), which allowed for a precise control of the brush height with irradiation time, as observed by in situ quartz crystal microbalance experiments with dissipation monitoring (QCM-D). In contrast to many alternative approaches, it was shown that the novel UV source in combination with a photoiniferter renders lengthy postcleaning steps of the synthesized brushes unnecessary. Following characterization of the polymer layers by means of variable-angle spectroscopic ellipsometry (VASE) and static contact angle measurements, the lubrication properties of the PMAA brushes were investigated in macroscopic tribological experiments under low-contact-pressure, aqueous conditions. Results indicated that PMAA brushes have the potential to dramatically reduce sliding friction in an aqueous environment.