Synthesis of a pyrrole‐based methine bridge type liquid‐crystalline conjugated polymer

Conjugated polymers consisting of pyrrole or an N‐substituted pyrrole bridged by methine with a mesogenic group were synthesized. Chemical structures of the products were confirmed with IR, NMR, UV–visible (UV–vis) spectroscopy, and gel permeation chromatography analysis. Liquid crystallinity was examined with differential scanning calorimetry measurements and polarizing optical microscopy observations. Liquid crystal domains of the polymer were macroscopically oriented in one direction by an external magnetic force (10 Tesla). The polymer orientation was confirmed by optical microscopy and X‐ray analysis. One of the polymers exhibited a striated fan‐shaped texture when observed with a polarizing optical microscope. This is attributed to the formation of a chiral smectic C (SmC^*) phase, which is a property of ferroelectricity. Spontaneous polarization of the polymer occurred at 110 nC/cm². © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 616–629, 2005     

Use of Transmission Electron Microscopy in Combinatorial Studies of Functional Oxides

Summary: The principles of combinatorial methodology are based on high‐throughput properties measurements (HTPM) of multiple compositions in combinatorial libraries, and are recently being increasingly applied in materials research. Nevertheless, the authors' view is that the involvement of detailed but time‐consuming investigation using transmission electron microscopy (TEM) should be an important part of combinatorial materials research. In this paper we present three examples from our combinatorial studies where the TEM investigation was essential in obtaining a detailed picture of microstructures and their relationship with the physical properties. In the study of microwave dielectrics such as BaTiO₃‐SrTiO₃, TEM provides essential information on the type and distribution of defects in the deposited films. In the case of the wide‐band semiconductor ZnO‐MgO, the distribution and morphology of the phases were studied and related to the measured electronic properties. Study of the manganates LaMnO₃‐CaMnO₃ with colossal magneto‐resistive properties showed an anisotropic distribution of the structural domains and the morphology of the film. The distribution of the domains and the absence of epitaxial stresses found are essential in the interpretation of magnetic measurements.

Cross‐sectional TEM (dark field) micrograph taken with the reflection of h‐(Zn,Mg)O at x = 0.5.     

Crystal‐structure dependence of electroactive properties in differently prepared poly(vinylidene fluoride/hexafluoropropylene) copolymer films

The electroactive properties of two random copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) were studied. The compositions were 95/5 and 85/15 mol % P(VDF/HFP). For each composition, three different film‐preparation methods were used—solvent casting, melt‐pressed quenched, and melt‐pressed slow‐cooled. The ferroelectric properties observed were strongly dependent on the preparation methods of the films as well as the HFP molar content of the samples. The highest remanent polarizations (P_r) obtained from electric displacement versus electric field (D‐E) hysteresis data are 80 and 50 mC/m² for the 5 and 15% HFP solvent‐cast samples, respectively. The slow‐cooled samples do not exhibit any ferroelectric behavior for either the 5 or 15% HFP copolymers. It was also observed that both the 5 and 15% HFP slow‐cooled samples have a smaller electrostrictive response relative to the other two types of samples. Wide‐angle X‐ray diffraction and DSC results suggest that the 5% HFP sample has a higher crystallinity relative to the 15% HFP sample for each preparation method. In addition, different crystal phases form in the samples resulting from the different preparation methods. Fourier transform infrared results suggest that the slow‐cooled samples are in the nonpolar α phase, whereas the quenched and solvent‐cast samples are more likely in the polar β phase. The slow‐cooled samples do not show a switching peak in their nonpolar α‐phase crystalline state. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2793–2799, 2001     

Advances in liquid crystalline conjugated polymers

We review advances in liquid crystalline (LC) conjugated polymers by focusing on (i) ferroelectric and (ii) photoresponsive LC conjugated polymers. In Part 1, LC polyphenylene derivatives were synthesized through substitution of fluorine‐containing chiral LC groups into side chains. Poly(para‐phenylene) [ P1 ] and poly(meta‐phenylene) [ P2 ] derivatives showed chiral smectic C phases responsible for ferroelectricity. They exhibited quick response to electric field, giving switching times of <1 s between two bistable states. The spontaneous polarization (P_S) of P2 remained unchanged even after the electric field became zero, affording the residual polarization (P_R) whose value was the same as that of P_S. This indicates that P2 has a potential memory function based on FLC nature. In Part 2, poly(para‐phenylenevinylene) [ P5 ] and poly(bithienylene‐phenylene) [ P6 ] derivatives were synthesized by introducing dithienylethene moieties into side chains. Drastic quenching of fluorescence occurred when the photoresponsive moiety changed from an open form to a closed one upon an irradiation of ultraviolet light. The quenched fluorescence was recovered through a photoisomerization from the closed form to the open one. Macroscopically aligned P6 film exhibited a linearly polarized fluorescence with significant anisotropy. Reversible quenching and emitting behavior in anisotropic fluorescence was controlled by the photochemical switching. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2463–2485, 2009