Concentration effects in the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline in N,N‐dimethylacetamide

The monomer concentration for the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline in N,N‐dimethylacetamide was optimized utilizing high‐throughput experimentation methods. Detailed ¹H‐NMR spectroscopic investigations were performed to understand the mechanistic aspects of the observed concentration effects. Finally, the improved polymerization concentration was applied for the synthesis of higher molecular weight (> 10,000 Da) poly(2‐ethyl‐2‐oxazoline)s. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1487–1497, 2005     

Mikrochemie

Ohne Zusammenfassung     

Erbium incorporation in LiNbO3 by diffusion-doping

 The erbium incorporation into LiNbO₃ by diffusion doping is investigated in detail by means of Secondary Ion Mass Spectrometry, Secondary Neutral Mass Spectrometry, Rutherford Backscattering, Atomic Force Microscopy, X-ray Standing Wave technique and optical site-selective spectroscopy. The diffusion of erbium in LiNbO₃ can be described by Fick’s laws of diffusion with a concentration-independent diffusion coefficient. The diffusion constants and activation energies for Z-cut (X-cut) LiNbO₃ are 4.8×10^-5 cm²/s (12.0×10^-5 cm²/s) and 2.28 eV (2.44 eV), respectively. A limited solubility of erbium in LiNbO₃ has to be taken into account increasing exponentially with rising temperature. During the first step of diffusion an Er _x Nb _y -oxide layer is formed at the surface of the sample acting as diffusion reservoir. Erbium is incorporated into LiNbO₃ on vacant Li-sites slightly shifted from the original Li-position along the (-c)-direction. Site-selective spectroscopy found four distinguishable energetically different erbium centres at this lattice site resulting from locally different symmetries of the crystal field. Received: 21 March 1996 / Accepted: 12 August 1996     

Elementarerweichungen in Amorphen Polymeren

Thermally stimulated recovery behaviour of amorphous polymers is described in terms of a continuous distribution of sharply defined elementary softening processes in the polymer. It is proposed that each of these elementary processes is the result of a co-operative site-change mechanism. On exceeding the activation temperature for the process, the viscoelastic time constants fall abruptly by many orders of magnitude, as opposed to following an Arrhenius-type law. The implications of this type of behaviour are discussed.

Prof. Schwarzl zum 60. Geburtstag gewidmet.     

The crystal and molecular structure of ferricinium tetrachloroferrate

The crystal and molecular structure of ferricinium tetrachloroferrate was studied by X-ray diffraction. The compound crystallizes in space group Pna2₁ with 4 molecules C₁₀H₁₀Cl₄Fe₂ per unit cell. Data analysis was relatively difficult and direct methods of phase determination were very useful in the interpretation of the Patterson synthesis. The two rings in ferricinium are nearly parallel. The structural parameters are very similar to those previously published by others for ferrocene. This molecular structure and its vibrational properties seem to be in contrast to a general rule previously formulated by others for the infrared spectra of cyclopentadienyl compounds.