Acceleration of the imine base/isocyanate (IBI)‐mediated polymerization of MMA caused by ionic liquid traces

The brutto rate of the imine base/isocyanate (IBI)‐mediated radical polymerization of methyl methacrylate (MMA) can be significantly increased by use of ionic liquid (IL) traces. At least, catalytic amounts of IL influence both the value of the brutto polymerization rate ν_Br,0 and the necessary reaction temperature of the used IBI mixture. Combinations of 2‐phenyl‐2‐oxazoline (POX) or 1‐methyl pyrazole (1MP) with isocyanates are IBI systems that usually do not initiate MMA at room temperature. By adding traces of 1‐ethyl‐3‐methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([Emim]FAP), polymethyl methacrylate (PMMA) with high average molecular weight can be obtained whereas the initiator mixture (imine base/isocyanate) concentration can be decreased by a factor of 10. The polymerization kinetics of several IBI combinations in the presence of ILs has been determined and a comparison to non‐IL containing initiator mixtures is given. Additionally, the temperature dependence of the IL‐containing polymerizations was measured. The interaction of the IL with MMA and the individual IBI initiator components is studied by means of attenuated total reflection Fourier transformation middle infrared spectroscopy (ATR FT MIR). Furthermore, the IBI brutto polymerization rate constants k_Br,0 were brought into relation to the IL hydrogen bond donating ability α. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Cyclodextrin derivatives and cyclofructan as ocular permeation enhancers

The positive influence of specific cyclodextrins and cyclofructan on the permeation of ophthalmic drugs through ocular tissues was demonstrated     

Crystal Structure and Electron Density Distribution in Niobium Carbide

In this paper the bonding properties, e. g. the charge distribution between the atoms and the deformation of niobium carbide densities have been studied. The crystal studied had the composition NbC_0.98. Careful and redundant data collection (74 unique reflections out of 2087 reflections measured) gave the basis for a detailed study. IAM models (independent atom model), high order and multipole refinements were made resulting in R values of R = 0.4% and R = 0.07%. In the corresponding deformation density maps electron accumulations between the niobium atoms were detected, but no bonding to the carbon atoms.     

Self‐Assembly of Tricuprous Double Helicates: Thermodynamics,Kinetics, and Mechanism

We report in this paper the coordination and kinetic properties of two oligobipyridine strands, which contain three 2,2′‐bipyridine subunits separated by oxydimethylene bridges, the 4,4′‐bis(CONET₂)‐substituted L and the 4,4′‐bis(CO₂Et)‐substituted L ′. Spectrophotometric measurements allowed the characterization of thermodynamic complexes and kinetic intermediates* which are involved in the self‐assembly process of L ₂Cu₃ and L Cu₃ helicates. The reaction presents positive cooperativity for the binding of two 2,2′‐bipyridine strands to the cuprous cations. While reactive kinetic intermediates* present distorted coordination geometries around Cu^I, the final rearrangement of the tricuprous bistranded helicates allows more closely tetrahedral coordination of each cation and reduces the interactions. Differences in the bulkiness and electronic properties of the L and L ′ substituents do not affect significantly the stability of the corresponding helicates, but greatly influence binding rates in the self‐assembly process.