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In this dissertation, the results of the synthesis of new polymer-metal nanoparticle-hybrid materials, the development and employment of new characterization methods and important groundwork for future research are presented.
Spherical silver nanoparticles with a diameter of 2-4 nm were stabilized with thiol-endfunctionalized polystyrene with molecular weights between 500 and 91.000 g/mol. The synthesis could be scaled up to 100-gram batches with quantitative yield. The resulting polymer-stabilized silver nanoparticles were characterized with common polymer-analytical methods. In addition to that, the exceptionally high morphological and chemical stability of the particles in dispersion and in solid state was characterized. It was possible to co-extrude the particles with conventional polystyrene at 190 °C and to process the blend, resulting in a very homogenous distribution of silver nanoparticles in the polystyrene matrix.
As a development of these results, palladium nanoparticles with polystyrene shell were synthesized and characterized. The shell was attached over a 2,2´-bipyridyl-end group. Surprisingly, the resulting palladium nanoparticles showed a worm-shaped morphology with a diameter of about 2 nm and lengths of about 10 nm. These “nanoworms” were stable in dispersion and in melt and it was possible to show that the worm shape results from linear aggregation of spherical palladium nanoparticles. The results were transferred to α-mercapto-polystyrene and nanoworms with diamters of 10 nm and lengths of up to 120 nm were observed.
The concept of polymer-stabilized silver nanoparticles was transferred to telechelic polymers. This led to nanoparticle-crosslinked materials. α,ω-dimercapto-polyisoprene with high cis content of more than 80 % was synthesized with a near-quantitative degree of functionalization and yield and was crosslinked by in-situ synthesized silver nanoparticles. This crosslinking led to an elastomer, which mechanical properties were heavily dependent on the nanoparticle content. The e-module as a direct result of crosslinking increased with increasing amount of silver nanoparticles, reached a maximum at a level of nanoparticle saturation and dropped quickly with nanoparticle oversaturation. These results were verified by swelling experiments. The resulting material was thermoplastic and was processible reversibly at temperatures above 90 °C. The concept of nanoparticle-crosslinking of polymers was successfully transferred to other metals and other endfunctionalized polymers.
In the last part of the presented work, methylcoumarin-endfunctionalized polystyrene was attached to a gold nanoparticle by surface polymerization, resulting in an “artificial molecule”. For this, the new material class of endfunctionalized polymer-azo-initiators was developed and characterized. Each particle was functionalized with exact one methylcoumarin group, attached via a single polystyrene chain as spacer. This was proven by a self-developed GPC-method. During synthesis, the measured molecular weight of a gold nanoparticle increased by the molecular weight of exactly one polystyrene block.