Metallization of nanosized objects
Conducting and
semi-conducting nanoparticles are currently a topic of intense
research due to their novel properties, which are significantly
different from those of the corresponding bulk materials. Since the
unique properties of these nanoparticles are directly related to
their size, a precise control over the size, size polydispersity,
shape and internal structure is required. As a typical example, the
band gap of a semi-conductor nanoparticle is reported to depend on
particle size.
Five arm star-shaped block copolymers with a poly(ethylene oxide)
(PEO) core and a poly(ε-caprolactone) (PCL) corona were
used as templates for the preparation of gold and palladium
nanoparticles of improved stability against aggregation. The PEO
core of these star-shaped block copolymers could be swollen with
KAuCl4 or
Pd(OAc)2 in
N,N-dimethylformamide (DMF) and Au or Pd nanoparticles were
respectively obtained by reduction. The resulting well defined Au
or Pd nanoparticles were stabilized against aggregation thanks to a
barrier of PCL chains. Transmission electron microscopy (TEM)
experiments strongly suggested that one Au or Pd nanoparticle was
formed inside each star-shaped block copolymer. The stability of
the accordingly prepared nanoparticles over aggregation was however
strongly dependent on the length of the PCL
chains.
Schematic
representation of the five-arm PEO-b-PCL copolymer used as template
for the synthesis of Au or Pd nanoparticles. A typical TEM picture
of gold nanoparticles templated in this copolymer is also
shown.
The
Pd nanoparticles were evaluated for their capability to act as
catalysts in Heck catalyzed coupling reactions utilizing automated
synthesizer techniques in combination with GC-MS high-throughput
screening. High activities and up to 99% conversion were observed
for the coupling of styrene with 4-bromoacetophenone within 24
hours at a catalyst loading of 0.1 mol %.
Researchers
involved: Mariam
Filali
Collaborations:
Ulrich Schubert
(Eindhoven), Michael Meier (Eindhoven)
Relevant
papers:
"Star-block copolymers as templates for the preparation of stable
gold nanoparticles"
M. Filali, M. A. R. Meier, Ulrich S. Schubert, J.-F.
Gohy
Langmuir
2005, 21,
7995-8000
"Star-shaped block copolymer stabilized palladium nanoparticles for
efficient catalytic Heck cross-coupling reactions"
M. A. R. Meier, M. Filali, J.-F. Gohy, U. S.
Schubert
J. Mater.
Chem.
2006, 16,
3001-3006
"Star-shaped block copolymers stabilized Pd-nanoparticles and their
catalytic activity: a high-throughput approach"
M.A. R. Meier, M. Filali, J.-F. Gohy, U. S.
Schubert
Polymer
Preprints
2006, 47,
931-932