The Investigation of the Structure - Phase Transformations of Poly(Propylene Imine) Dendrimer of Second Generation

Liquid crystal poly(propylene imine) dendrimer of second generation (D2) was investigated by X-ray diffraction method in the range from room temperature to isotropic melting temperature. The effects of both magnetic and electric fields on an orientation of the dendrimer were considered. An analysis of diffraction patterns was carried out with the use of paracrystal model of Hosemann. Structural simulation and diffraction calculations ≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡ some structural parameters during phase transformations were considered. It was determined that the dendrimer has fan-shaped conformation and forms two liquid crystal phases: SmI and N C . The dendrimer does not crystal-lize, but does vitrify with the structure of the previous SmI phase. It was established that the dendrimer can not be oriented either by magnetic field 1,2 T or electrostatic field 2 MV/m. The identification of LC phases and their structure parameters have been confirmed by diffraction calculations. The phase transitions of the dendrimer are G → 55–66 о С → SmI → 101 о С → N С → 274 о С → Iso. The SmI → N С phase transition is the phase transition of mixed order (the phase transition of both the first-order and the second-order). Temperature dependencies of structural parameters in the vicinity of the SmI → N С phase transition and in the vicinity of the region of vitrifying contain features of a two-phase behavior of the dendrimer.