Multibranched star-shaped polyethers

Synthesis of multibranched star-shaped polyethers having poly(ethylene oxide)s (PEO) arms is described. The novel method of preparing these multibranched macromolecules consists in reaction of the -OH ended oligomers with dicyclic compounds; e.g. monoalkyl ethers of poly(ethylene oxide) with diepoxides in the presence of a basic catalyst, converting a part of the ∼OH groups into ∼OC^σ end groups (alkoxide anions). Analysis of the structure of these macromolecules was mostly based on ¹H NMR, MALDI-TOF, and SEC with triple detection. The absolute values of M_w (LS), M_w/M_n, and [η] are given, indicating formation of macromolecules of high molar mass and highly branched. The number of branches was estimated by several methods, including comparison of the Mark-Houwink (M-H) dependencies of the obtained products with the M-H dependence for PEO stars with exactly known number of arms. The final stars were phosphorylated at the −OH ended branches. Almost exclusively monoesters of phosphoric acid were found in ³¹P (¹H) NMR.     

Activated monomer propagation in cationic polymerizations

New mechanism of cationic polymerization of cyclic ethers and acetals consisting in the activated (e.g. protonated) monomer addition to the electrically neutral macromolecule e.g.: is discussed. It is shown, that when the -OH in the tail-group is more nucleophilic than monomer itself this mechanism has chances to dominate over the traditional mechanism of propagation, involving tertiary oxonium ion. Kinetics of the polymerization process, elementary reactions, competition with the tertiary oxonium ion growth are discussed. Examples are given, based on the work on ethylene oxide and epichlorohydrin polymerization, showing how to apply the theory of the activated monomer in order to avoid side reactions, namely cyclization and disproportionation of the chains.     

Solvent effect on the polytype structure of CdI2 crystals

Single crystal platelets of cadmium iodide have been grown from alcohols: n-propyl, isobutyl and isoamyl and from their aqueous solutions. The structures of 880 crystals has been identified and the effect of solvent on the polytype structure of CdI₂ has been discussed regarding: the stability of the basic structures 2H and 4H, the structure of complex polytypes, the effect of the solvent on the structure of faults, the period of polytypes. Some relations indicating the role of the solvent in the formation of polytype structure of CdI₂ have been found.     

Holographic recording in chiral and linear isomers of single-component phototropic liquid crystals: an experiment and theoretical approach

Phototropic liquid crystals (PtLC) comprising one component are a new class of liquid crystals (LC) which due to the phenomenon of photochemical phase transition are of special interest, especially in view of their potential applications in photonic devices. So far, however, only a little attention has been paid to these materials. In this paper, we discuss holographic recording in chiral and linear single-component PtLCs from the family of 4-alkyl-4?-alkoxyazobenzene and we develop the one-dimensional mathematical model describing the formation of the diffraction grating. The grating formation process and its dynamics, resulting from the photoinduced isotropic-to-nematic phase transition, have been described by the mechanism that assumes the formation and growth of the liquid-crystalline domains of different sizes induced by the sinusoidally modulated Gaussian light intensity distribution. We show that the model is based on one parameter, that is the incubation time which can be easily obtained experimentally and which can be used for the fitting of the experimental data. Reporting new PtLCs materials and the model that describes the processes of holographic recording in these types of materials can be useful in the design of new phototropic LC materials and for optimisation of the experimental conditions.     

Electrical conductivity and phase transformations in the composite ionic conductors AgI : α-Al2O3 prepared via a high-pressure route

Silver ion conducting composites of the general formula xAgI : (1 − x)α-Al₂O₃, where 0.2 ≤ x ≤ 0.8 (vol fraction) were prepared using a high-pressure synthesis route (T = 400 °C, p = 7.5 GPa). The microstructure of as-received rigid, non-brittle and dense samples was investigated by SEM. Other studies — DSC, XRD and impedance spectroscopy, were done as a function of temperature in the 20-200 °C temperature range. Close correlations were observed between the temperature dependences of the XRD patterns, the electrical conductivity and events seen on DSC traces. It was found out that the electrical conductivity at room temperature of all as-received composite materials was higher (by a factor between 7 and 100, depending on composition) than that measured after the heating-cooling cycle. This effect and other observed correlations were explained referring to the residual stress concept.     

Identification of the structure parameters applying a moving load

An approach to the flexural stiffness identification of a linear structure is proposed. The idea of the presented approach is to transform the dynamical problem into a static one by integrating the input and output signals. The output signal is the structure displacement due to different kinds of loads such as a pulse acting at a given point, moving a load of deterministic or random type. The obtained solution for the one-point force can be easily generalized to a set of point forces, which can be a model of the pressure of vehicle axes. The presented method can be applied to the identification of structure parameters of bridges. It allows also to take into account some stochastic disturbances following the movement of vehicles through the pavement roughness.