Gregor Trimmel

Cross-linking of poly(methyl methacrylate) by oxozirconate and oxotitanate clusters

Radical polymerization of methyl methacrylate with 0.5 - 2 mol% of the (meth)acrylate-substituted oxozirconium and oxotitanium clusters Zr 6 (OH) 4 O 4 (OMc) 12 (OMc = methacrylate), Zr 4 O 2 (OMc) 12 , Ti 6 O 4 (OEt) 8 (OMc) 8 and Ti 4 O 2 (OPr 1 ) 6 (OAcr) 6 (OAcr = acrylate) results in an efficient cross-linking of the organic polymers. The obtained inorganic-organic hybrid polymers exhibit a higher thermal stability due to inhibited depolymerization reactions. Contrary to undoped poly(methyl methacrylate), the cluster cross-linked polymers are insoluble but swell in organic solvents. The solvent uptake upon swelling decreases with an increasing amount of polymerized cluster. The impedance spectra of PMMA doped with various proportions of Zr 4 O 2 (OMc) 12 show that the capacitance of the polymers decreases with an increasing proportion of the cluster. The polymer doped with 2 mol% of Zr 4 O 2 (OMc) 12 shows an increase in conductivity to 0.9.10 -7 S.cm -1 at 74 °C.

Sol-gel processing of alkoxysilyl-substituted nickel complexes for the preparation of highly dispersed nickel in silica

Nanocomposites containing nickel nanoparticles in silica were obtained by sol-gel processing of Ni(NO3)2, Ni(OAc)2 (OAc = acetate), NiCl2, or Ni(acac)2 (acac = acetylacetonate), a complexing silane [(EtO)3Si(CH2)3NHCH2CH2NH2, (EtO)3Si(CH2)3NH2 or (RO)3Si(CH2)3NHCH2CH2NHCH2CH2NH2] and Si(OEt)4, followed by calcination of the metal-complex-containing xerogels in air and reduction in hydrogen. Two types of nanocomposite materials were prepared, both containing about 8–8.5 wt % of elemental nickel: (i) Ni/SiO2 nanocomposite powders in which the silica matrix is mainly formed from Si(OR)4, and (ii) Ni particles on pre-formed silica spheres. The latter were prepared by impregnating silica spheres with sols from the particular complexing silane–nickel salt combination followed by calcination and reduction. In both types of materials, the average nickel particle size is influenced by the composition of the precursor mixture, particularly the counter-ion of the employed nickel salt. The smallest particles (diameter below 3 nm) were obtained from Ni(NO3)2 [and Ni(OAc)2 for the powders], while the use of Ni(acac)2 and NiCl2 resulted in larger nickel particles. The variation of the nickel particle diameters was much larger for the powders than for the impregnated spheres.

Sol-gel processing of tethered metal complexes: influence of the metal and the complexing alkoxysilane on the texture of the obtained silica gels

Abstract The metal complexes [M(AEAPTS)2]2+ or [M(TRIAMIN)2]2+ are formed by reaction of cobalt, nickel or copper acetate (or 1:1 mixtures thereof) with two molar equivalents of [N-(aminoethyl)aminopropyl]trimethoxysilane (AEAPTS) or [N((N-aminoethyl)aminoethyl)aminopropyl]trimethoxysilane (TRIAMIN). Sol–gel processing of [M(AEAPTS)2]2+/Si(OEt)4 or [M(TRIAMIN)2]2+/Si(OEt)4 (1:6) mixtures results in xerogels in which the metal complexes are tethered to the silica gel network. The gelling behavior of the mixtures is influenced by the presence of metal ions and depends very strongly on the kind of complexing silane. For comparison, xerogels were also prepared from metal acetate/Si(OEt)4 mixtures without a complexing silane. While the xerogels prepared from M(TRIAMIN)22+/Si(OEt)4 mixtures are essentially non-porous, the xerogels prepared from M(AEAPTS)22+/Si(OEt)4 mixtures or in the absence of a complexing silane are porous and have high surface areas. The latter samples have distinctly larger pores than the samples prepared in the presence of the complexing silanes. The xerogels were calcined in air at 550 °C to remove the organic groups and to obtain metal oxide/silica nanocomposites. The presence of the metal ions promotes the thermal degradation of the organic groups, i.e., both the onset and the end of the thermal degradation of the organic groups is shifted to lower temperatures. The decomposition temperature depends on the kind of metal. Calcination results in an increase of porosity, mainly by creation of micropores. Reduction at 500 °C results in metal/silica nanocomposites. The reduction step has only a minor influence on the texture; the proportion of micropores is only slightly reduced. Re-examination of the surface and pore structure of the xerogels and the metal oxide/silica nanocomposites after 2 years showed that the porosity had strongly decreased upon storage at ambient conditions, mainly due to the disappearance of micropores.

EXAFS investigations on nanocomposites composed of surface-modified zirconium and zirconium/titanium mixed metal oxo clusters and organic polymers

Summary. The surface-modified oxometallate clusters Zr6(OH)4O4(OMc)12, Ti4Zr4O6(OBu)4 (OMc)16, and Ti2Zr4O4(OBu)2(OMc)14 (OMc = methacrylate) as well as their nanocomposites with polystyrene, poly(methacrylic acid) and poly(methyl methacrylate) were investigated by EXAFS. Studies on the nanocomposites revealed that the structure of the cluster core is retained in the hybrid materials.

Inorganic-Organic Hybrid Polymers from Surface-Modified Oxometallate Clusters

Inorganic-organic hybrid polymers were prepared by radical polymerization of methacrylic acid or methyl methacrylate with the (meth) acrylate-substituted oxozirconium and oxotitanium clusters Zr 6 (OH) 4 O 4 (OMc) 12 (OMc = methacrylate), Zr 4 O 2 (OMc) 12 , Ti 6 O 4 (OEt) 8 (OMc) 8 and Ti 4 O 2 (OPr i ) 6 (OAcr) 6 (OAcr = acrylate). A few mol% of cluster is sufficient for an efficient cross-linking of the polymer chains. Small-angle X-ray scattering data indicate that the cluster size is retained in the polymers and that the microstructure of the cluster cross-linked samples can be described by a dispersion of identical spherical or disk-shaped clusters in the polymer. The obtained hybrid polymers exhibit a higher thermal stability because depolymerization reactions are inhibited. Contrary to undoped poly (methyl methacrylate), the cluster cross-linked polymers are insoluble but swell in organic solvents. The solvent uptake upon swelling decreases with an increasing amount of polymerized cluster.

Copper Nanoparticles in Silica

Copper nanoparticles in a silica matrix are prepared by a three-step procedure. In the first step a copper salt is reacted with an alkoxysilane of the type (RO)3Si(CH2)nA, where A is a coordinating organic group. The obtained metal complexes {[(RO)3Si(CH2)nA]xCu]2+ are used as precursors for sol-gel processing, with Si(OR)4 as co-reactant to adjust the metal:silica ratio. In the second step, the metal complex-containing gels are calcined in air at high temperatures, and metal oxide nanoparticles in a silica matrix are formed. Finally, the metal oxide nanoparticles are reduced to metal nanoparticles.