Convenient approach to novel functional substituted and branched poly(silylenemethylenes)

Novel poly(silylenemethylenes) have been prepared by the ring-opening polymerization of 1,3-disilacyclobutanes followed by a protodesilylation reaction with triflic acid. The silicon–aryl bond cleavage could be controlled by using different leaving groups, for instance phenyl- and para-anisyl substituents. The reactions of the triflate derivatives with organomagnesium compounds, LiAlH₄, amines, or alcohols gave functional substituted poly(silylenemethylenes). Hydrosilylation reactions or reductive coupling with potassium–graphite led to organosilicon network–polymers, which may serve as suitable precursors for silicon carbide and Si/C/N-based materials. The structures of the polymers were identified by NMR spectroscopy (²⁹Si, ¹³C, ¹H). © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 725–735, 1998     

Mass spectrometric and quantum mechanical analysis of gas-phase formation, structure, and decomposition of various b2 ions and their specifically deuterated analogs

B ions represent an important type of fragment ions derived from protonated peptides by cleavage of an amide bond with N-terminal charge retention. Such species have also been discussed as key intermediates during cyclic peptide fragmentation. Detailed structural information on such ion types can facilitate the interpretation of multiple step fragmentations such as the formation of inner chain fragments from linear peptides or the fragmentation of cyclic peptides. The structure of different b₂ ion isomers was investigated with collision-induced dissociations (CID) in combination with hydrogen/deuterium (H/D) exchange of the acidic protons. Special care was taken to investigate fragment ions derived from pure gas-phase processes. Structures deduced from the results of the CID analysis were compared with structures predicted on the basis of quantum chemical density functional theory (DFT) calculations to be most stable. The results pointed to different types of structures for b₂ ion isomers of complementary amino acid sequences. Either the protonated oxazolone structure or the N-terminally protonated immonium ion structure were proposed on the basis of the CID results and the DFT calculations. In addition, the analysis of different selectively N-alkylated peptide analogs revealed mechanistic details of the processes generating b ions.     

A deuteron NMR study on order and phase behaviour of liquid-crystalline copolymers

Liquid-crystalline (LC) block copolymers of lamellar morphology were prepared via anionic polymerization of polystyrene-block-1,2-polybutadiene and subsequent introduction of a deuterated mesogen by polymer analogous reaction. Deuteron NMR measurements show that the first-order nematic/isotropic transition in the block copolymer is changed to a critical behaviour under the influence of shear. In the nematic phase the order parameter is reduced with respect to the homopolymer, and there is no evidence of an isotropic boundary layer of the LC-block at the nematic/isotropic interface.     

Fire retardants and fire safety how can tests reflect reality?

In the standard test methods, the thermal action proceeds even today in most cases under the conditions of the well ventilated fire. The intensity of the thermal action varies widely, however, depending on the designed safety level. In the last few years, the outstanding purpose was to test the behaviour of products under the action of fire, in particular the time to the flash-over. The intensity of the fire action rises accordingly, despite the possibility of further free ventilation, to such a degree that the test conditions in laboratory processes can reflect reality only under certain conditions. This philosophy is drawn from the results of statistical investigations in the U.S. is that the time to the flash-over in a room is equal to the time to untenability, because most of the victims of the fire were not present in the room where the fire broke out. Test methods on a real scale that serve this designed safety level will therefore have to work with the high fire action on the products to be tested. In contrast, however, in some European countries the philosophy underlying the adoption of designed safety levels is that the main purpose is to protect human beings who are present in the room where the fire breaks out. According to this philosophy, a fire development that threatens to become dangerous must always be prevented. Consequently, interest is focused mainly on restricting the spread of fire and thus preventing a flash-over. The test methods to be designed with this purpose in view should, therefore, simulate the conditions of the starting fire or the developing fire. The efficiency of a fire retardant can then be evaluated according to whether the fire spread is restricted or not. Under these conditions, the question of the time to be flash-over is of no significance. With standard tests, it is impossible to make a statement as to how far the fire safety of products can be improved by the use of fire retardants unless the safety-relevant range of application for the test method has been defined.     

The thermal susceptibility of poly(chloroethyl methacrylates)

The non-oxidative thermal degradation kinetics and mechanism of poly(2-monochloro, 2, 2-dichloro and 2, 2, 2, -trichloroethyl methacrylates) were studied. The influence of the antioxidant IRGA-NOX 1010 on the thermal degradation of the monochloroethyl derivative was also investigated. Initial hydrolysis data on the major degradation products, the corresponding monomers, were obtained.