Synthese und Charakterisierung neuartiger Hybridmaterialien aus Polymer-geschützten Goldnanopartikeln

In this dissertation, the synthesis and characterization of polymer-stabilized gold nanoparticles is presented. The protection of gold nanoparticles with polymers was realized both by coordination of the gold surface by a functional end group of the polymer and by coordination of the polymer main chain, which was either realized by commercially available polymers or the polymers were prepared prepared on the particle surface by polymerization of small ligands. In case of coordination by a functional end group, a tailored monomer was used, which was coupled with the natural product L-menthol. This monomer was polymerized by ATRP with a disulfide-containing co-initiator, yielding a polymer with a natural product bound to the main chain and a disulfide bridge in the middle of the molecule. Gold nanoparticles were prepared by addition of gold acid followed by dropwise addition of a reduction agent. The polymer was linked to the gold surface via its sulfur-containing group. It was not possible to determine whether the disulfide bridge underwent an in situ cleavage to form the corresponding thiol or if the disulfide remained intact and coordinated to the gold surface in its original form. Characterization of the as-prepared nanoparticles by GPC indicated a dynamic equilibrium between free and particle-bound polymer. Protection of gold nanoparticles by coordination with a polymer main chain was started with a simple example. Citrate-stabilized gold nanoparticles were prepared in an aqueous system and prevented against aggregation during removal of the solvent by addition of PVA. The highly concentrated gold nanoparticle dispersion containing about 50 wt % gold was used for electrospinning. The as-prepared fibers with high gold contents could be transferred to gold nanowires by thermal degradation of the matrix polymer. Characterization by TEM and HIM showed continuous, crystalline wires comprising a diameter range from about 30 – 200 nm. The electrical conductivity was interrupted by some defects. Another approach for protection of gold nanoparticles by coordination of the polymer main chain was carried out by polymerization of vinyl ligands on the particle surface. In the first step, gold nanoparticles were prepared by Brust-Schiffrin method, using 4-mercaptostyrene as a ligand. In the following, the ligands were polymerized by free radical surface polymerization. Providing that the radical polymerization proceeds much faster than the cleavage of the azo-initiator, it was assumed that each particle was polymerized by only one radical, which means that each particle contains only a single functional group from the initiator end group. Hence, an artificial molecule with a defined stoichiometry was prepared, which can be used as a building block for more complex structures. As one project, the surface polymerization was carried out using a macroinitiator containing a methyl coumarin end group, building an artificial molecule from a gold nanoparticle with exactly one single methyl coumarin functionality, which is connected via a polymer spacer. Connection of methyl coumarin to the particle and purity of the compound was proved by GPC analysis applying a diode array detector. In a second project, an artificial molecule with a single vinyl group was synthesized and thus could be used as macro monomer. It was copolymerized with MMA to yield a novel nanoparticle-polymer-hybrid material. Proof of gold nanoparticle being connected to the polymer chain was given by GPC. The resulting elugram of the copolymer displayed significant differences to the elugram of the corresponding blend. AFM clearly showed structures nanoparticles and polymer strands.