Several Interesting Fields Exploited through Understanding of Polymeric Effects on Liquid Crystals of Main-Chain Polyesters

Abstract

ABSTRACT:We review our experimental results on the structural characteristics of polymeric liquid crystals collected through our studies on the main-chain liquid crystalline polyesters with mesogenic biphenyl groups connected by flexible alkyl spacer. The polyesters studied, designated as BB-n where n is the number of carbon atoms in the alkyl spacer unit, form smectic mesophases. Of interest is that the type of smectic phase alters depending on the odd-even parity of n. An ordinal smectic A phase is formed by BB-n with even n, whereas BB-n with odd n forms a new type of smectic phase, so called smectic CA phase, in which the long axis of the mesogen is tilted against the layer normal and the tilting direction is opposite between neighboring layers. Finding of smectic CA phase with specific packing symmetry leads to a distinct discovery of ferroelectric and antiferroelectric phases in achiral molecular systems. In these smectic phases, the polymer chain assumes more extended conformation. Such an extended conformation, however, does not continue over the whole length of the polymer and hairpin folding arises to gain entropy. In the smectic phases, the hairpin foldings are located at a limited space, forming chain folded lamellae. Unusual shear flow orientation and anomalous crystallization behavior are explained based on the chain folded lamellar structure. Solid state morphology of liquid crystalline polymer is also presented. Since the degree of liquid crystallinity is almost 100%, the solid phase cooled through the formation of liquid crystals is composed of crystal and liquid crystal glass. Liquid crystal glass is studied and properties are discussed in a comparison with those of conventional isotropic glass.

High-Performance Segmented Liquid Crystalline Copolyesters

“…Table contains the maximum q values for each peak and corresponding Bragg spacing. The calculated Bragg spacing values correlated well with previously reported BB 6 homopolymer lamellar spacing values of 225–294 Å . The consistent spacing between BB 6 and BB6P10R5 y series suggested the scattering peak corresponds to the hard segment and further confirmed the microphase‐separated morphology of these segmented copolyesters.…”

Smectic liquid crystal Schlieren texture in rapidly cooled poly(butylene naphthalate)

“…Importantly, the smectic LC phase has been suggested to exist only below the glass transition temperature of the system, possessing a frozen liquid crystalline structure. As such, the mesophase is more precisely classified as an LC glass [14,15]; heating the LC glass to above its T g (65 °C) at a rate of 4 K/min caused transformation into -crystals at slightly higher temperature. Later on, the conditions of mesophase formation were further evaluated by FSC and fast X-ray diffraction experiments [16].…”

Control over Internal Structure of Liquid Crystal Polymer Nanofibers by Electrospinning

“…The WAXD pattern of the annealed fiber ( D = 0.69 ± 0.11 µm, annealed at 50 °C for 1 day) shown in Figure 3a is very similar to that of the melt‐spun fibers (Figure 2b). 10, 11 Figures 3b and c show the annealing‐time dependence of the WAXD profiles for the meridian and the azimuthal direction at 2 θ ∼ 20 °, respectively. As seen in Figure 3b, the annealing decreased the reflection peak intensity with a spacing of 24.0 Å, and increased that with a spacing of 17.0 Å.…”

“…The main‐chain polyester with the biphenyl group as a mesogen, designated as BB‐ n , in which n is the number of carbon atoms in the alkyl spacer, forms smectic mesophases. For BB‐ n , the effects of the flexible spacer on mesophase formation have been extensively studied 9–11. In the present study, we used the main‐chain liquid crystal polyester, BB‐5(3‐Me), to control the internal structure and molecular orientation of electrospun fibers.…”