Mar Michael Meier

Star-shaped block copolymer stabilized palladium nanoparticles for efficient catalytic Heck cross-coupling reactions

Palladium nanoparticles of improved stability against aggregation were prepared using 5-arm star-shaped block copolymers with a poly(ethylene oxide) (PEO) core and a poly(epsilon-caprolactone) (PCL) corona as templates. The PEO core of these star-shaped block copolymers could be swollen with palladium acetate (Pd(OAc)(2)) in N,N-dimethylformamide (DMF), and Pd nanoparticles were obtained by reduction with NaBH4. This procedure resulted in well defined Pd nanoparticles that were stabilized against aggregation due to a barrier of PCL chains. Transmission electron microscopy (TEM) experiments strongly suggested that one Pd nanoparticle was formed inside each star-shaped block copolymer. The stability of the Pd nanoparticles with respect to aggregation was strongly dependent on the length of the PCL chains. Subsequently, these nanoparticles were evaluated for their capability to act as catalysts in Heck coupling reactions. These reactions were performed in an automated synthesizer and monitored by GC-MS revealing that these particles are highly active for the catalytic reactions mentioned. Up to 99% conversion was observed for the coupling of styrene with 4-bromoacetophenone within 24 h at a catalyst loading of 0.1 mol%.

Combinatorial polymer research and high-throughput experimentation: powerful tools for the discovery and evaluation of new materials

Polymer chemistry is very well suited for combinatorial approaches since a large parameter space has to be covered during synthesis, processing, blending or compounding. Moreover, a large variety of parameters need to be screened in order to evaluate structure–property relationships and to accelerate the design and development of new materials. Therefore, high-throughput experimentation and combinatorial approaches in polymer science have gained large attraction during the past few years since they might lead to shorter time-to-market periods for new polymeric materials as well as to a more profound understanding of quantitative structure–property relationships (QSPRs).

Combinatorial and high-throughput approaches in polymer science

Combinatorial and high-throughput approaches have become topics of great interest in the last decade due to their potential ability to significantly increase research productivity. Recent years have witnessed a rapid extension of these approaches in many areas of the discovery of new materials including pharmaceuticals, inorganic materials, catalysts and polymers. This paper mainly highlights our progress in polymer research by using an automated parallel synthesizer, microwave synthesizer and ink-jet printer. The equipment and methodologies in our experiments, the high-throughput experimentation of different polymerizations (such as atom transfer radical polymerization, cationic ring-opening polymerization and emulsion polymerization) and the automated matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS) sample preparation are described.

Polymeric nanocontainers with high loading capacity of hydrophobic drugs

Water soluble 4- and 6-arm star-shaped polymers with (bio) degradable hydrophobic cores and dense hydrophilic coronas were synthesized by a combination of ring opening polymerization (ROP) and atom transfer radical polymerization (ATRP). Their carrier abilities of different model compounds as well as active pharmaceutically ingredients in aqueous solutions were evaluated by UV/Vis and H-1 NMR spectroscopy studies. The highest loading capacities (up to 36 guest molecules per molecule of polymer) were, as expected, found for the 6-arm star-shaped polymers. The densely grafted poly[poly(ethylene glycol) methyl ether methacrylate] [p(mPEGMA)] shell stabilizes the host-guest complexes preventing undesired multimolecular aggregation. Dynamic light scattering (DLS) measurements evidenced the unimolecular character of all 4- and 6-arm polymers before and after loading with guest molecules. The (bio) degradability of the core was demonstrated under acidic conditions and in vitro using a lipase from Rhizopus Arrhizus. The dual-stimuli responsiveness of the hydrophobic core to enzymes and pH may facilitate increased control over in vivo drug release.

Fluorescent sensing of transition metal ions based on the encapsulation of dithranol in a polymeric core shell architecture

The encapsulation behaviour and the resulting transition metal ion sensing capabilities of a 5-arm star-shaped polymer bearing terpyridine ligands on its periphery are described.

Integration of MALDI-TOFMS as high-throughput screening tool into the workflow of combinatorial polymer research

The possibilities of an integration of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) as an high-throughput screening tool into the workflow of combinatorial materials research are discussed. A multiple layer sample preparation technique for MALDI is described in detail and its possibilities of automation and miniaturization are discussed. Automated MALDI sample preparation could be performed within an automated synthesizer robot as well as with an ink-jet printer. The first approach offers the possibility of online reaction monitoring, whereas the second approach gives the opportunity of applications in ultra-high-throughput environments. Moreover, an example of high-throughput screening of a polymerization reaction by MALDI-TOFMS is discussed.

Selected successful approaches in combinatorial materials research

Combinatorial materials research (CMR) is still a relatively young field of research. Nevertheless, it already provides successful strategies for a fast and accurate evaluation of a large variety of different research problems. Some of these approaches in CMR considering polymeric materials will be discussed and highlighted within this contribution by focussing on three prominent literature examples: structure-property relationships in biomaterials research, material properties evaluation utilizing thin film polymer libraries as well as the parallel and automated study of polymer based reversed unimolecular micelles and their application possibilities. These examples are meant to demonstrate the almost unlimited possibilities of combinatorial approaches in polymer science rather than to provide an extended overview of the field.