@article{OrgzallLorenzMikatetal.1999,
  author    = {Orgzall, Ingo and Lorenz, Bernd and Mikat, J{\"u}rgen E. R. and Reck, G{\"u}nter and Knochenhauer, Gerald and Schulz, Burkhard},
  title     = {Phase transition in 1,3,4-oxadiazole crystals under high pressure},
  year      = {1999},
  abstract  = {Crystalline 2,5-di(4-nitrophenyl)-1,3,4-oxadiazole (DNO) has been investigated at pressures up to 5 GPa using Raman and optical spectroscopy as well as energy dispersive X-ray techniques. At ambient pressure DNO shows an orthorhombic unit cell (a = 0.5448 nm, b = 1.2758 nm, c = 1.9720 nm, density 1.513 g cm-3) with an appropriate space group Pbcn. From Raman spectroscopic investigations three phase transitions have been detected at 0.88, 1.28, and 2.2 GPa, respectively. These transitions have also been confirmed by absorption spectroscopy and X-ray measurements. Molecular modeling simulations have considerably contributed to the interpretation of the X-ray diffractograms. In general, the nearly flat structure of the oxadiazole molecule is preserved during the transitions. All subsequent structures are characterized by a stack-like arrangement of the DNO molecules. Only the mutual position of these molecular stacks changes due to the transformations so that this process may be described as a topotactical reaction. Phases II and III show a monoclinic symmetry with space group P21/c with cell parameters a = 1.990 nm, b = 0.500 nm, c = 1.240 nm, ß = 91.7°, density 1.681 g cm-3 (phase II, determined at 1. 1 GPa) and a = 1.890 nm, b = 0.510 nm, C = 1.242 nm, ß = 89.0°, density 1.733 g cm-3 (phase 111, determined at 2.0 GPa), respectively. The high-pressure phase IV stable at least up to 5 GPa shows again an orthorhombic structure with space group Pccn with corresponding cell parameters at 2.9 GPa: a = 0.465 nm, b = 1.920 nm, c = 1.230 nm and density 1.857 g cm-3 . For the first phase a blue pressure shift of the onset of absorption by about 0.032 eV GPa has been observed that may be explained by pressure influences on the electronic conjugation of the molecule. In the intermediate and high-pressure phases II-IV the onset of absorption shifts to increased wavelengths due to larger intermolecular interactions and enhanced excitation delocalization with decreasing intermolecular spacing.},
  language  = {en}
}
@article{LavrenkoAndreevaStrelinaetal.1999,
  author    = {Lavrenko, Peter N. and Andreeva, Katharina A. and Strelina, Irina A. and Garmonova, Tatjana I. and Schulz, Burkhard},
  title     = {Optical anisotropy and flexibility of poly(m-phenylene oxadiazole) in sulfuric acid},
  year      = {1999},
  language  = {en}
}
@article{ReicheFreydankHelmsetal.1999,
  author    = {Reiche, J{\"u}rgen and Freydank, Anke-Christine and Helms, Andreas and Geue, Thomas and Schulz, Burkhard and Brehmer, Ludwig and Stiller, Burkhard and Knochenhauer, Gerald},
  title     = {Vacuum deposition films of oxadiazole compounds : formation and structure investigation},
  year      = {1999},
  abstract  = {The search for alternative routes of organic thin film formation is stimulated by the outstanding properties of these films in such fields as nonlinear optics, photonic data processing and molecular electronics. The formation of highly ordered multilayer structures by thermal vacuum deposition (VD) of organic compounds is an essential step toward the application of supramolecular organic architectures in technical systems. The VD of an amphiphilic substituted 2,5- diphenylene-1,3,4-oxadiazole 1 onto silicon substrates at defined temperature was used for the formation of ultrathin films. The structural data obtained for the VD-films of oxadiazole 1 by means of X-ray reflectivity, X-ray grazing incidence diffraction and atomic force microscopy (AFM) investigations indicate the formation of well ordered oxadiazole multilayers. The structure of the VD-multilayers is compared with that of Langmuir-Blodgett (LB) films and thermally treated LB-multilayers prepared from the same compound.},
  language  = {en}
}
@article{LavrenkoOkatovaSchulzetal.1999,
  author    = {Lavrenko, Peter N. and Okatova, Olga V. and Schulz, Burkhard and Andreeva, Katharina A. and Strelina, Irina A.},
  title     = {Hydrodynamic and dynamo-optical properties of poly(1,3-phenylene-1,3,4-oxadiazole) molecules in sulphuric acid},
  year      = {1999},
  abstract  = {Translational diffusion of the macromolecules, intrinsic viscosity and flow birefringence induced in dilute solutions of poly(1,3-phenylene-1,3,4-oxadiazole) (PMOD) in conc. sulphuric acid has been investigated. Molecular-weight dependences of hydrodynamic and dynamo-optical properties are established over the M range from 8.1 103 to 87 103. Experimental data agree well with the theories developed for translational friction and intrinsic viscosity of the wormlike chains with the following molecular parameters: mass per chain unit ML = 22.7 Dalton/{\AA}, the Kuhn segment length A = 59 ± 4 {\AA}, the chain diameter d = 4 ± 1.5 {\AA}. Hindrance to intramolecular rotation is characterized by the parameter s = 1.7. The shear optical coefficient was found to be approximately 1.7 times lower the value of that obtained in the same solvent for the para-phenylene isomer of this polymer, being in good agreement with higher equilibrium flexibility of the PMOD molecule chains in solutions as determined herein from the hydrodynamic data.},
  language  = {en}
}
@article{BrumaSchulzKoepnicketal.1999,
  author    = {Bruma, Maria and Schulz, Burkhard and K{\"o}pnick, Thomas and Stiller, Burkhard and Mercer, Frank W.},
  title     = {Study of thin films made from aromatic polyamides with silicon and phenylquinoxaline rings in the main chain},
  year      = {1999},
  abstract  = {Aromatic polyamides containing silicon and phenylquinoxaline rings in the main chain have been prepared by polycondensation reaction of a silicon-containing diacid chloride, namely bis(p-chlorocarbonylphenyl) -diphenylsilane, with various aromatic diamines having preformed phenylquinoxaline units. These polymers were easily soluble in polar aprotic solvents, such as N-methylpyrrolidinone (NMP) and dimethylformamide (DMF), and in tetrahydrofurane. They showed high thermal stability with decomposition temperature being above 450°C and glass transition temperature in the range of 253-304°C. Polymer solutions in NMP were processed into thin films having the thickness of tens of nanometer to 10 mm, by spin-coating onto glass plates or silicon wafers. The films had strong adhesion to substrates and exhibited very smooth surfaces, free of pinholes, in atomic force microscopy (AFM) studies. The free-standing films had dielectric constant in the range of 3.48-3.69. Thermal treatment of the films up to 350°C rendered them completely insoluble in organic solvents, while maintaining their smoothness and strong adhesion to the silicon substrate, and with no Tg in DSC experiments. Their FTIR spectra did not show any changes compared to the untreated films, meaning that polymers maintain their structural integrity at high temperature. {\´O} 1999 Elsevier Science S.A. All rights reserved.},
  language  = {en}
}
@article{BrumaHamciucSchulzetal.1999,
  author    = {Bruma, Maria and Hamciuc, Elena and Schulz, Burkhard and K{\"o}pnick, Thomas and Stiller, Burkhard and Mercer, Frank W.},
  title     = {Synthesis of fluorinated poly(phenylquinoxaline-amide)s and study of thin films made therefrom},
  year      = {1999},
  abstract  = {A series of five fluorinated poly(phenylquinoxaline-amide)s were synthesized by a polycondensation reaction of a diacid chloride containing the hexafluoroisopropylidene (6F) group, namely 2,2-bis(p-chlorocarbonylphenyl)- hexafluoropropane, with various aromatic diamines incorporating two phenyl-substituted quinoxaline rings. These polymers were easily soluble in polar aprotic solvents such as N-methylpyrrolione (NMP), dimethylformamide (DMF), and tetrahydrofurane (THF), and showed a high thermal stability with decomposition temperatures above 400 °C and glass transition temperatures in the range of 260-290 Tg. Polymer solutions in NMP were processed into free-standing films that showed low dielectric constant values, in the range of 3.4-3.9, and good mechanical properties, with tensile strength in the range of 40-80 MPa and elongation to break in the range of 22-55\%. Very thin films, in the range of tens of nanometer, which were deposited onto silicon wafers exhibited very smooth surfaces, free of pinholes when studied by atomic force microscopy (AFM).},
  language  = {en}
}
@article{BrumaSchulzKoepnicketal.1999,
  author    = {Bruma, Maria and Schulz, Burkhard and K{\"o}pnick, Thomas and Stiller, Burkhard and Belomoina, Nataliya and Mercer, Frank W.},
  title     = {Synthesis and study of aromatic polyamides containing silicon and phenylquinoxaline rings in the main chain},
  year      = {1999},
  abstract  = {New poly(phenylquinoxaline-amide)s with silicon in the main chain have been prepared by polycondensation reaction of a diacid chloride, namely bis(p-chlorocarbonyl-phenyl)-diphenylsilane, with aromatic diamines containing one or two phenylquinoxaline rings separated by a flexible bridge such as ether or methylene. These polymers were easily soluble in polar aprotic solvents such as N-methylpyrrolidinone (NMP) and dimethylformamide (DMF) and showed high thermal stability with decomposition temperature being above 450°C and glass transition temperature in the range of 260- 304°C. Polymer solutions in NMP were processed into thin flexible films which exhibited very smooth surfaces, free of pinholes when studied by atomic force microscopy. The free-standing films showed a dielectric constant in the range of 3.6-3.7.},
  language  = {en}
}
@article{OkatovaAndreevaSchulzetal.1999,
  author    = {Okatova, Olga V. and Andreeva, Katharina A. and Schulz, Burkhard and Lavrenko, Peter N.},
  title     = {Degradation of poly(m-phenylene oxadiazole) in concentrated sulfuric acid},
  year      = {1999},
  language  = {en}
}