Peter Zugenmaier

Homogeneous and heterogeneous cellulose tri-esters and a cellulose triurethane: synthesis and structural investigations of the crystalline state

Abstract Structural investigations were carried out on new cellulose derivatives prepared by heterogeneous and homogeneous reactions. X-ray examination of heterogeneously prepared crystalline cellulose triesters and a triurethane provided new insights into the packing of chains in cellulose microfibrils and in these products. The results were compared with those given by the corresponding homogeneously prepared derivatives. The side-chain conformations for various triesters deviate to some extent from the all-trans arrangement of the bonds of the ester groups.

Temperature and bias-field dependences of dielectric behaviour in the antiferroelectric liquid crystal, (R)-MHPOBC

Temperature and bias-field dependences of dielectric behaviour in the antiferroelectric liquid crystal, R-MHPOBC, were investigated (see also previous paper). There are mainly two relaxation modes in the SmC*alpha and SmC* phases: one behaves as the soft-mode, which shows significant slowing down in the SmA* and SmC*alpha phases; the other one appears at lower frequencies and changes the dielectric strength remarkably, especially in the SmC* phase, which is considered to relate to the azimuthal phase-fluctuation of molecules in the parallel tilt sequences of the smectic layers. These two modes show different bias field dependences in different C* subphases. In the SmC*A phase, two other types of relaxation mode were observed, which are probably due to the in-phase and anti-phase azimuthal angle fluctuations of molecules in the anti-tilt pairs.

INVESTIGATIONS OF THE STRUCTURE OF A CHOLESTERIC PHASE WITH A TEMPERATURE INDUCED HELIX INVERSION AND OF THE SUCCEEDING SC-ASTERISK PHASE IN THIN LIQUID-CRYSTAL CELLS

Abstract Investigations of 4-[(S, S)-2, 3 epoxyhexyloxy]-phenyl-4-(decyloxy)-benzoate by polarizing microscopy, the Cano-Grandjean method, optical rotation dispersion and UV-VIS spectroscopy reveal a cholesteric phase with temperature induced reversal of the helical twist. Switching time experiments in the Sc* phase show that the intrinsic helix can be unwound reversibly and irreveribly by application of electric fields of different strengths.

Synthesis and Liquid-crystalline Behaviour of Tetrakis- and Octakis(13, 17-dioxa nonacosane-15-sulfanyl)Phthalocyanines

Abstract Tetra- and octa(13, 17-dioxa nonacosane-15-sulfanyl) substituted metal free- and Ni(II) phthalocyanines have been synthesized from the corresponding phthalonitrile derivatives in the presence the anhydrous metal salt(NiCl2) or a strong organic base. The new compounds have been characterised by elemental analyses, IR, NMR and electronic spectroscopy and mass spectra. The mesogenic properties of these new materials were studied by differential scanning calorimetry(DSC), optical microscopy and X-ray investigations. All compounds show a discotic mesophase in an extremely large temperature interval including room temperature. X-ray diffraction patterns of the mesophases confirm that tetra-substituted compounds(5a, 5b) form a hexagonal ordered columnar mesophases(Dho), whereas octa-substituted compounds(7a, 7b) lead to centered rectangular disordered columnar mesophases(Drd).

Synthesis and Characterization of Novel Tetra- and Octa-Triethyleneoxysulfanyl Substituted Phthalocyanines Forming Lyotropic Mesophases

Abstract Metal-free phthalocyanines and nickel phthalocyanines carrying four or eight oligo(ethyleneoxy)thia groups on peripheral positions have been synthesized from new phthalonitrile derivatives. These phthalocyanine derivatives were characterized both thermotropic and lyotropic mesophases by DSC and X-ray.

Materials of cellulose derivatives and fiber-reinforced cellulose-polypropylene composites: Characterization and application*

Cellulose is a biodegradable polymer produced sustainably in large quantities by nature. It has been used by mankind for centuries because of its favorable properties, but suffers disadvantages such as the high cost of production and limited processibility. For example, it cannot be melted and is only soluble in less common solvents. The latter limitation can be overcome through appropriate derivatization of cellulose, which increases the solubility range and may generate thermoplastic materials. This paper will review three new developments leading to enhanced utilization of cellulosics. Firstly, an overview is given of the progress in the formulation of fiber-reinforced thermoplastic cellulose composites to facilitate extrusion processing. Cellulose-polypropylene composites show enhanced properties in comparison with neat polypropylene, and offer scope for replacing composites containing glass fibers, owing to resultant advantages in weight, recyclability, and ease of disposal. Progress is also reported in improving the predictability of essential physical quantities and melt flow in cellulose esters. Finally, an account is given of the successful development of microcrystalline cellulose (CFM) derivatives, synthesized in a heterogeneous manner, as chiral recognition agents in liquid chromatography. The structural features of these materials are decisive for their use. A model is proposed for the morphology of the cellulosic fibrils.

HORIZONTAL CHEVRON CONFIGURATIONS IN FERROELECTRIC LIQUID-CRYSTAL CELLS INDUCED BY HIGH ELECTRIC-FIELDS

Abstract Application of a high electric field to a S∗c ferroelectric liquid crystal cell may cause the formation of horizontal chevron configurations with the smectic layers tilted by the amount of the chevron angle (in the case of the present investigation equal to the director tilt angle) with respect to the normal to the rubbing direction of the cell substrates. The layer structure resembles that of the well-known vertical chevron configuration, but in the plane of the substrate instead of perpendicular to it, and is similar to that recently reported for the stripe-shaped texture. Between crossed polarizers, the two domain types appear to switch in opposite directions when an a.c. electric field is applied. The temperature dependence of the observation of horizontal chevron structures was investigated and an explanation is proposed analogous to that for the stripe texture model.

Crystal and Molecular Structures of Six Differently with Halogen Substituted Bis (benzylimido) perylene

The structures of bis (3,5-dichlorobenzylimido) perylene, bis (3-chlorobenzylimido) perylene, bis (3-fluorobenzylimido) perylene, bis (3,5-difluorobenzylimido) perylene, bis (4-chlorobenzylimido) perylene, and bis (2,6-difluorobenzylimido) perylene were solved by single crystal analysis. The compounds crystallize in four different space groups, that is, in sequence of the compounds listed P1, P1, P2 1 /a, C2/c, Pbcn. P2 1 /n, respectively, although their chemical constitutions are very similar. The packing in different arrangements causes the twist of the benzene ring to differ with respect to the perylene ring and amounts to 111.4°, 112.3°, 98.6°, 105.1°, 80.3 °, 72.0° for the sequence of compounds listed, respectively. The first two compounds crystallizing in space group P1 are isomorphous in structure and exhibit the same dark blue color. The C-F bond distances lie between 1.36 and 1.38 A, the C-Cl bond distances between 1.73 and 1.75 A. For all six structures investigated the planes of two adjacent perylene skeleton planes are 3.43 to 3.50 A apart and the tilt angles versus the shortest unit cell dimension lie between 20 and 45°.

The molecular and crystal structures of a homologous series of bipolar, mesogenic biphenyls–HO(CH2)nOC6H4.C6H4CN

Abstract The crystal and molecular structures of eight 4,4′-disubstituted biphenyls of the general formula HO-(CH2)n-O-C6H4-C6H4-CN (n=3−5, 7−11) (HnCBPs) have been determined. All compounds investigated have a nearly parallel molecular arrangement in the crystalline state, with dipole-dipole interactions between the molecules. For n≥7, isomorphic layered structures are observed. The inter-molecular packing is different for odd and even numbers of methylene units in the spacer.

Axial chiral allenylacetates as novel ferroelectric liquid crystals

Liquid crystalline alkane-3,4-dienoates (allenylacetates) have been synthesized. Most compounds incorporate a heterocyclic 1,3,4-thiadiazole ring or a pyrimidine ring as a constituent of the rigid core. These axial chiral allene derivatives were at first obtained as racemic mixtures. Some of them were also synthesized in enantiomerically enriched form by enantioselective synthesis. The compounds were investigated by polarizing microscopy and by differential scanning calorimetry. The three-ring compounds exhibit broad regions of smectic C-phases. The optically active three-ring compounds show broad S c *-phases with moderate values of spontaneous polarization.