Photoinitiators with functional groups. VII. Covalently bonded camphorquinone—amines

Camphorquinone (CQ), a widely used photoinitiator (PI) in dental applications, was covalently bonded to aromatic amines to enhance the rate of electron and proton transfer effect due to the close vicinity of the diketone and the amine group. 10‐bromocamphorquinone and 10‐bromomethylcamphorquinone were selected as suitable precursors for esterification with the carboxyl group containing aromatic amines based on 4‐dimethylaminobenzoic acid. Properties of the new photoinitiating systems were investigated by UV spectroscopy and differential scanning photocalorimetry in lauryl acrylate. Compared to physical mixtures, in all cases similar or even better performance was obtained. Surprisingly, 10‐acetyl derivatives 7 – 9 and 18 especially, were found to be highly reactive. Compared to CQ/ethyl 4‐dimethylaminobenzoate, the rate of photopolymerization was increased by a factor of up to 2. Intramolecular reaction was confirmed by photo‐differential scanning calorimetry experiments with varying PI concentrations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4948–4963, 2004     

An algebraic approach to manifold-valued generalized functions

We discuss the nature of structure-preserving maps of varies function algebras. In particular, we identify isomorphisms between special Colombeau algebras on manifolds with invertible manifold-valued generalized functions in the case of smooth parametrization. As a consequence, and to underline the consistency and validity of this approach, we see that this generalized version on algebra isomorphisms in turn implies the classical result on algebras of smooth functions.     

GC-MS and HPLC analyses of lignin degradation products in biomass hydrolyzates

Summary The gas-chromatographic separation of lignin degradation products of hydrolytically degraded biomass (e. g. poplar wood) and their mass spectrometric identification are described. For routine analysis of lignin degradation products of biomass hydrolyzates, a time saving HPLC gradient method using a UV-detection system (280 nm), is described. In addition to reference samples, solutions of hydrothermally degraded biomass were analyzed.

---

GC-MS- und HPLC-Analytik von Ligninabbauprodukten in Biomassehydrolysaten

Zusammenfassung Die gas-chromatographische Trennung von Ligninabbauprodukten nach hydrolytischer Spaltung von Biomasse (z.B. Pappelholz) sowie die massenspektrometrische Identifizierung werden beschrieben. Für eine routinemäßige Analytik der Ligninabbauprodukte in Biomassehydrolysaten wird weiterhin die Trennung mittels einer Gradienten-HPLC-Methode aufgezeigt. Die Detektion erfolgte bei 280 nm. Neben Referenzproben wurden hydrothermale Abbaulösungen untersucht.

     

Visibly transparent & radiopaque inorganic organic composites from flame-made mixed-oxide fillers

Radiopaque composites have been produced from flame-made ytterbium/silica mixed oxide within a crosslinked methacrylate resin matrix. The refractive index of the filler powder increased with ytterbium oxide loading. A high transparency was achieved for a matching refractive index of the filler powder and the polymer in comparison to commercial materials with 52 wt% ceramic filling. It was demonstrated that powder homogeneity with regard to particle morphology and distribution of the individual metal atoms is essential to obtain a highly transparent composite. In contrast, segregation of crystalline single-oxide phases drastically decreased the composite transparency despite similar specific surface areas, refractive indices and overall composition. The superior physical strength, transparency and radiopacity compared to composites made from conventional silica based-fillers makes the flame-made mixed-oxide fillers especially attractive for dental restoration materials.     

Photoelectron yield of small silver and gold particles suspended in gas up to a photon energy of 10 eV

The photoelectric yieldY of clean Ag and Au particles suspended in He-gas has been measured up to photon energieshv=10 eV.Y shows strong deviations from the bulk in the case of Ag but not in the case of Au. Surface adsorbates generate dramatic changes inY, pointing to the decisive role of the surface electron density profile on the optical properties.     

Monitoring adsorption on small particles

A review on the application of photoelectron emission from small particles suspended in a gas to monitor the adsorption properties and to detect adsorbates on the particles is given. The relation between surface coverage with an adsorbate and the shift in photothreshold and photoelectric yield is demonstrated by two examples: The adsorption of O₂ on silver particles and of perylene on carbon particles. A third example concerns the detection of polyaromatic hydrocarbons (PAH) on particles arising from combustions.     

Aqueous olefin metathesis

According to popular belief, oxygen and water are the natural enemies of organometallic reactions and therefore must be excluded rigorously from the reaction vessel. This belief is founded in the case of the highly reactive nucleophilic metal alkylidene complexes that were used in early catalytic olefin metathesis. However, owing to the high stability of the ruthenium carbene complexes introduced by Grubbs, metathesis in water has become reality.