Franz René Kogler

Control of the ratio of functional and non-functional ligands in clusters of the type Zr6O4(OH)4(carboxylate)12 for their use as building blocks for inorganic–organic hybrid polymers

The methacrylate ligands of the cluster Zr6O4(OH)4(methacrylate)12 undergo degenerate exchange with methacrylic acid in solution. Addition of propionic or isobutyric acid allows partial or complete exchange of the methacrylate ligands for propionate or isobutyrate. The mixed-carboxylate cluster Zr6O4(OH)4(OMc)8(isobutyrate)4(BuOH) was independently prepared by reaction of Zr(OnBu)4 with a mixture of methacrylic acid and isobutyric acid. The structures of Zr6O4(OH)4(OMc)8(isobutyrate)4(BuOH) and Zr6O4(OH)4(isobutyrate)12(H2O) consist of an octahedral Zr6(μ3-O)4(μ3-OH)4 core with one of the carboxylate ligands being monodentate. The H2O or ROH molecule is coordinated to the neighbouring zirconium atom and, at the same time, hydrogen bonded to the monodentate carboxylate. A mechanism for the carboxylate exchange is suggested based on the structural observations.

Ring-opening metathesis polymerizations with norbornene carboxylate-substituted metal oxo clusters

The clusters Ti6O4(OPr)8(endo,exo-OOC–Norb)8, Zr6O4(OH)4(endo-OOC–Norb)12 and Zr6O4(OH)4(exo-OOC–Norb)12(BuOH) were prepared by the reaction of 5-norbornene-2-carboxylic acid (HOOC–Norb) with Ti(OPr)4 or Zr(OBu)4 and were characterized by X-ray structure analyses. Ring-opening metathesis polymerization was performed with Zr6O4(OH)4(OOC–Norb)12 either in the absence or in the presence of norbornene. Highly crosslinked polynorbornene was obtained in the latter reactions. The onset of thermal decomposition of the polynorbornene crosslinked by 1–5 mol% of the cluster was about 40–45° higher than that of pristine polynorbornene. Small-angle X-ray scattering investigations showed that the clusters are randomly distributed in the polymer.

Surface-modified Zirconium Oxide Clusters and their Use as Components for Inorganic-Organic Hybrid Materials

Pre-formed transition metal oxide clusters with methacrylate ligands were polymerized in the presence of organic co-monomers to form inorganic-organic hybrid polymers. The number of polymerizable ligands and thus the crosslinking density of the hybrid polymers can be varied for a given cluster type by partially exchanging the methacrylate ligands for non-reactive ones. The properties of the hybrid polymers can also be varied by adjusting the conditions of the polymerization reaction, especially by a pre-polymerization procedure. It is shown that the thermal stability of polystyrene crosslinked by Zr 6 O 4 (OH) 4 (OMc) 12 is thus greatly improved.