Liborius Born

On the physical crosslinking of amine-extended polyurethane urea elastomers: A crystallographic analysis of bis-urea from diphenyl methane-4-isocyanate and 1,4-butane diamine*)**)

The substance under investigation is taken as a model for hard segments consisting of MDI 1) and 1,4-butane diamine. It crystallizes in the triclinic space group P¯1 witha=4.6297;b=5.8259;c=25.286 Å;α=90.721;β=91.580;γ=102.90 degrees andZ=1. Bond distances and angles are given, together with some data on the conformation.The most significant finding is that neighbouring molecules in one and the same plane are linked to one another by means of bifurcated hydrogen bonds.A comparison with the corresponding data for an analogous bis-urethane provides a plausible explanation of the main differences between diamine and glycol extension in polyurethane elastomers.

The physical crosslinking of polyurethane elastomers studied by X-ray investigation of model urethanes

Polyurethane elastomers extended with aliphatic glycols or diamines, show a characteristic fluctuation in their thermal and hydrothermal properties which is dependent on the number of CH2 groups in the chain extender (“even” or “odd”).The causes of this behavior are examined in the following report using X-ray crystallographic analyses of single crystals of model urethanes. These model compounds were prepared by reaction between diphenylmethane -4-mono-isocyanate and glycoles of the HO-(CH2)n-OH structure withn=2 to 6.Whilst strain-free hydrogen bonds can form between neighboring molecules in urethanes with “even” chain extenders, significant strains occur in urethanes containing “odd” chain extenders which result in reduced stability of the physical crosslinking system.

Diisocyanato dicyclohexylmethane: structure/property relationships of its geometrical isomers in polyurethane elastomers

Abstract4,4′-Diisocyanato dicyclohexylmethane (HMDI) is a commercially available diisocyanate used as a building block for polyurethane products that require excellent light stability and hydrolysis resistance. It consists of a mixture of three geometrical isomers, the trans,trans-, cis,trans-, and cis,cis-isomers. We found that the trans,trans-isomer leads to some interesting properties in polyurethane elastomers. Surprisingly, the hardness and percent elongation (properties that usually follow an inverse relationship) both increase with increasing trans,trans- HMDI contents. We also observed dramatic increases in the ultimate tensile strength, split-tear strength, resilience, and solvent resistance. Also, the melting temperature of the elastomers increases with increasing trans,trans content. X-ray analysis of model hard segments showed that the hard segment based ont,t-HMDI is highly ordered, leading to higher melting temperatures and better separation between the hard- and soft-segment phases.

Neuartige 3,5-diarylpyridone und ihre strukturzuordnung

Summary Novel 3,5-diarylpyridones have been synthesized; their structures were determined from their characteristic spectroscopic behaviour and confirmed by X-ray crystallographic studies.

Crystal structure of 1,4,5,8-naphthalene-tetracarboxylic- dianhydride (NTDA)

The crystal structure of the title compound has been determined at room temperature. The crystals are monoclinic, space group P2i/c, Ζ = 2, with a = 7.867(2), b = 5.305(1), c = 12.574(2) Ä and β = 72.73(2)°. The structure was refined to R = 0.042 for 589 observed reflections. The molecule is on an inversion center. The agreement among chemical equivalent bond lengths is generally very good, thus confirming the short carbonyl distance (1.185 Ä). The crystal is built of stacks of only partially overlapping NTDA molecules along b. Introduction 1,4,5,8-Naphthalene-tetracarboxylic-dianhydride (NTDA), C 1 4 H 4 0 6 (1), has been reported to form radical-anion salts with numerous organic cations (Heywang et al., 1989). To gain a better understanding of crystal structure determinations of these complexes, reasonably accurate distance and angle information for the NTDA molecule will be needed. The packing mode of the molecule without cations is also of interest. 148 Liborius Born and Gerhard Heywang Table 1. Positional parameters and their estimated standard deviations.

New radical cation salts of substituted pyrenes

Abstract Pyrenes with alkylthio substituents represent a new class of relatively cheap donor compounds which can be reacted to very stable radical cation salts with high conductivity (up to 677 S/cm).

4-Biaryl-substituted dihydropyridines with an unusual antiperiplanar conformation

Abstract We report X-ray crystal structures and NMR solution data of the unusual antiperiplanar conformation of 1,4-dihydro-5-cyano-2,6-dimethyl-4-biaryl-3-pyridine carboxylic acid esters with 3′-(4′-(1″- or 2″-naphthyl)pyridyl)- and 2′-(9″-anthracenyl) phenyl-residues as the biaryl moiety. This class might serve as a biological tool to identify which DHP-rotamer is responsible for the interaction with the biological receptor.

PHOTOCHEMISTRY OF PESTICIDES, 71. REGIOSELECTIVE PHOTODIMERIZATION OF o,o-DIETHYL-o-(3-CHLORO-4-METHYLCOUMARIN-7-YL)-THIOPHOSPHATE (COUMAPHOS)

Abstract UV-irradiation (λ > 313 nm) of o,o-diethyl-o-(3-chloro-4-methyl-coumarin-7-yl)-thiophosphate (Coumaphos; 1) in chloroform results in an regioselective dimerization reaction to afford the head-to-tail anti-dimer 2. The structure of 2 is established by single crystal x-ray diffraction. Singlet oxygen does not affect the formation of 2.