STRUCTURE OF LIQUID CRUSTAL POLY(PROPYLENE IMINE) DENDRIMERS OF THE LOWEST GENERATIONS BY X-RAY ANALYSIS

Liquid crystal poly(propylene imine) dendrimers of zero (D-0) and first (D-1) generations exposed to the magnetic field influence were investigated by X-ray diffraction method. Analysis of diffraction patterns was carried out with the use of the paracrystal model of Hosemann and the cluster model of Fonk. Structural simulation and diffraction calculations on the models were used for determining of the layer structure parameters of the dendrimers. Temperature behavior of the structural parameters was considered in the interval from room temperature to isotropic melting temperature. It was determined that only the dendrimer of zero generation can be oriented by magnetic field. This dendrimer forms crystalline phase, but at the same time D-0 is capable to partial vitrifying preserving the structure of smectic C phase. D-0 has orthorhombic crystalline lattice with parameters: a = 39,2 angstrom, b = 9,76 angstrom, c = 14,25 angstrom. There are four molecules in the elementary cell. The calculated specific density is 1,09 g/sm(3). The space group of a symmetry is P2(1)2(1)2. Increase of generation number results in more advanced liquid crystal polymorphism. D-1 forms two smectic phases: SmC and SmF. D-1 does not crystallize, but vitrifies preserving the structure of smectic F phase. Structural models confirmed by diffraction analysis suppose an elongated molecular conformation in all phase states of both D-0 and D-1. The phase transformations of the dendrimers look like: Cr -> 159 degrees C -> SmC -> 274 degrees C -> Iso of D-0 and G -> 55-66 degrees C -> SmF -> 108 degrees C SmC -> 274 degrees C Iso of D-1. Temperature dependences of structural parameters of the dendrimers near the phase transitions Cr -> SmC of D-0 and SmF -> SmC of D-1 contain features of a two-phase behaviour of the dendrimers (this effect is less expressed for D-1).