Synthese von chinoxalin- und indol-2,3-dicarbonsäureimiden

Quinoxaline- and indole-2,3-dicarboxyclic imides 7, 8 are prepared by reaction of halogenactive maleimides 1, 2 with sodium azide. Further derivatives of these heterocyclic series are available by secondary reactions of the imides.     

Morphology and rheology of peel of model adhesives

The morphology of surfaces produced during peel experiments was studied to increase the understanding of peel phenomena. Thin films of polystyrenes of narrow molecular-weight distribution and a polydisperse polyester on flexible supports were peeled from rigid substrates at temperatures above their glass transitions with equipment that also permitted quenching and preservation of the peeled surfaces which then could be studied by scanning electron microscopy. The results show many types of cavitation including foams and the coalescence of cavities to form fibers. Cavitation occurred throughout and beyond the region of transition from cohesive to interfacial failure where peel force decreased abruptly; however, cavity growth was abruptly restricted as the failure mode changed. The master curves and shift factors obtained in this work provided strong evidence that the quenching used to preserve the peeled surfaces did not introduce large perturbations in the results. The reason was that failure occurred at or close to the heated substrate.     

Propagation of spin information at the supramolecular scale through heteroaromatic linkers

We report an in-depth study on how spin information propagates at supramolecular scale through a family of heteroaromatic linkers. By density-functional theory calculations, we rationalize the behavior of a series of Cr7Ni dimers for which we are able to systematically change the aromatic linker thus tuning the strength of the magnetic interaction, as experimentally shown by low temperature micro-SQUID and specific heat measurements. We also predict a cos2 dependence of the magnetic coupling on the twisting angle between the aromatic cycles in bicyclic linkers, a mechanism parallel to charge transport on similar systems [L. Venkataraman et al., Nature (London) 442, 904 (2006)].     

Efficient and robust strong-field control of population transfer in sensitizer dyes with designed femtosecond laser pulses

We demonstrate control of electronic population transfer in molecules with the help of appropriately shaped femtosecond laser pulses. To this end we investigate two photosensitizer dyes in solution being prepared in the triplet ground state. Excitation within the triplet system is followed by intersystem crossing and the corresponding singlet fluorescence is monitored as a measure of population transfer in the triplet system. We record control landscapes with respect to the fluorescence intensity on both dyes by a systematic variation of laser pulse shapes combining second order and third order dispersion. In the strong-field regime we find highly structured topologies with large areas of maximum or minimum population transfer being insensitive over a certain range of applied laser intensities thus demonstrating robustness. We then compare our experimental results with simulations on generic molecular potentials by solving the time-dependent Schr?dinger equation for excitation with shaped pulses. Control landscapes with respect to population transfer confirm the general trends from experiments. An analysis of regions with maximum or minimum population transfer indicates that coherent processes are responsible for the outcome of our excitation process. The physical mechanisms of joint motion of ground and excited state wave packets or population of a vibrational eigenstate in the excited state permit us to discuss the molecular dynamics in an atom-like picture.     

Synthesis and Characterization of Thermoplastic Polyurethaneureas based on Polyisobutylene and Poly(tetramethylene oxide) Segments

New thermoplastic polyurethaneureas (TPUU) based on polyisobutylene (PIB) and poly(tetramethylene oxide) (PTMO) segments have been synthesized possessing tensile properties comparable to conventional PTMO based TPUs. PIB based TPUU containing 35 weight (wt)% hard segment was synthesized by chain extension of H₂N-Allyl-PIB-Allyl-NH₂ with 4,4′ -methylene bis(phenylisocyanate) (MDI) and 1,4-butanediol (BDO) in toluene. The ultimate tensile strength (UTS) = 12 MPa and ultimate elongation = 70% were inferior to PTMO based polyurethane (UTS = 35 MPa, elongation at break = 600%). H₂N-Allyl-PIB-Allyl-NH₂ and HO-PTMO-OH in different proportions were chain extended in presence of MDI and BDO to obtain TPUUs containing 35 wt% hard segment. The polymers exhibited M _ns = 84000–138000 with polydispersity indices (PDIs) = 1.7–3.7. The UTS = 23–32 MPa and elongation at break = 250–675% was comparable to that of PTMO based polyurethane and significantly higher than the PIB based TPUU with the same Shore hardness. The Young's modulus of the polymers was strongly dependent and directly proportional to the PIB wt% in the SS of the TPUUs.     

Stilbene-Based Fluorescent Sensor for Detection of Organophosphorus Warfare Nerve Agents

In this paper, we report the synthesis of stilbene-based fluorophore, 3,4-dihydroxy-4′-aminostilbene (DHAS) for the detection of chemical warfare agents such as organophosphorus nerve gases. DHAS was characterized by various spectroscopic methods and grafted on to electrospun nanofibers. The interaction of DHAS with nerve agents simulant, diethyl chlorophosphate (DCP) was investigated in solution and vapor phase by fluorescence spectroscopy.     

Living Carbocationic Polymerization of Styrene in the Presence of Proton Trap

Abstract

The living polymerization of styrene was achieved with the 2,4,4-trimethyl-2-pentyl chloride/TiCl₄/MeCl:methylcyclohexane 40:60 v:v/?80°C polymerization system in the presence of di-tert-butylpyridine in concentrations comparable to the concentration of protic impurities. It was determined that the living nature of the polymerization is not due to carbocation stabilization. The polymerization is second order in TiCl₄. Side reactions, namely polymerization by direct initiation and intermolecular alkylation, are operational, and a careful selection of experimental conditions is necessary to minimize their effect and obtain apparently living behavior. Polymerization by direct initiation can be minimized by increasing the initiator concentration, and intermolecular alkylation can be reduced by quenching the polymerization system when the conversion reaches close to 100%.