title: Ultraviolet/Ozone as a Tool To Control Grafting Density in Surface-Initiated Controlled-Radical Polymerizations via Ablation of Bromine.
abstract: We used an ultraviolet-ozone (UVO) cleaner to create substrates for atom-transfer radical polymerization (ATRP) with varying surface initiator coverage. We collected complementary time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) measurements to investigate the precise chemical origin of the variation in grafting density. At short exposure times, the atomic composition underwent minor changes except for the relative amount of bromine. At longer UVO exposure times, there is clear evidence of exposure-dependent surface initiator oxidation. We interpret these data as evidence of a bromine ablation process within the UVO cleaner, with additional oxidative modification of the rest of the surface. We then used these substrates to create a series of poly(methyl methacrylate) (PMMA) brushes varying in grafting density, demonstrating the utility of this tool for the control of polymer brush density. The measured brush grafting densities were correlated with the bromine concentration measured by both ToF-SIMS and XPS. XPS and brush thicknesses correlated strongly, following an exponential decay with a half-life of 18 ± 1 s.
authors.affiliation: Material Science and Engineering Division and ‡Material Measurement Science Division, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Sheridan
authors.affiliation: Material Science and Engineering Division and ‡Material Measurement Science Division, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
authors.forename: Sara V
authors.initials: SV
authors.lastname: Orski
authors.affiliation: Material Science and Engineering Division and ‡Material Measurement Science Division, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
authors.forename: Shin
authors.initials: S
authors.lastname: Muramoto
authors.affiliation: Material Science and Engineering Division and ‡Material Measurement Science Division, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Stafford
authors.affiliation: Material Science and Engineering Division and ‡Material Measurement Science Division, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Beers