The atom transfer radical polymerization (ATRP) of styrene and acrylates from silicon wafers
modified with an initiator layer composed of 2-bromoisobutyrate fragments is described. In the presence
of the proper ratio of activating and deactivating transition-metal species, controlled radical polymerizations of styrene were observed such that the thickness of the layer consisting of chains grown from the
surface increased linearly with the molecular weight of chains polymerized in solution in identical, yet
separate, experiments. The layer thickness increased linearly with reaction time for ATRP of styrene
and methyl acrylate due to both the extremely low initiator concentration relative to monomer and the
low monomer conversion. Further evidence for control was observed by the polymerization of blocks of
either methyl or tert-butyl acrylate from the polystyrene layer. Modification of the hydrophilicity of the
surface layer was achieved by hydrolysis of the poly(styrene-b-tert-butyl acrylate) to poly(styrene-b-acrylic
acid) and confirmed by decrease in water contact angle from 86° to 18°. The mechanistic aspects of ATRP
in the polymerization process were confirmed by the growth of very thick polystyrene films in the presence
of a pure copper(I) complex. Since no deactivator was present, the metal complex served only to facilitate
initiation by a redox process. Attempts to extend chain with methyl acrylate under controlled conditions
were unsuccessful in those films. The simulation of polymerization of surface layers suggests broader
molecular weight and chain end distributions, confirming XPS results on the progressive decrease of Br
absorption intensity.
Alumina-supported vanadium particles were prepared under ultrahigh vacuum (UHV) conditions and characterized with respect to their structural and CO adsorption properties. As supporting oxide, we used a thin, well-ordered alumina film grown on NiAl(110). This allows the application of scanning tunneling microscopy (STM), infrared reflection-absorption spectroscopy (IRAS), and X-ray photoelectron spectroscopy (XPS) without charging effects. Vanadium evaporation under UHV conditions leads to the growth of nanometer-sized particles which strongly interact with the alumina support. At very low vanadium coverages, these particles are partially incorporated into the alumina film and get oxidized through the contact to alumina. Low-temperature CO adsorption in this coverage regime permits the preparation of isolated vanadium carbonyls, of which we have identified mono-, di-, and tricarbonyls of the V(CO)(y)() type. A charge-frequency relationship was set up which allows one to quantify the extent of charge transfer from vanadium to alumina. It turns out that this charge transfer depends on the V nucleation site.
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