Thermotropic Liquid Crystals of Polyesters Having a Mesogenic p,p‘-Bibenzoate Unit. 7. Chain Folding in the Smectic Phase of BB-6

Abstract

The solid state morphology of the main-chain liquid crystal BB-6 polyester was studied by the small angle X-ray scattering (SAXS) method. The BB-6 polyester forms isotropic, smectic A, and crystal phases in the order of decreasing temperature; thereby its crystallization is taking place from the smectic A phase. The SAXS for the crystalline specimens prepared by cooling the isotropic melt at a rate of 10 °C min-1 shows the well-defined reflection maxima which are attributable to the stacked lamellar structure. The lamellar spacings are distributed around 250 Å so that an appreciable number of chain foldings are included in a chain. The lamellar size is increased by annealing the crystal like in other crystallizable polymers. In contrast, it is not essentially altered by annealing the smectic A phase. The results show that the chain foldings exist at a thermodynamic equilibrium in the smectic A phase. The correlation length between the chain foldings is assumed approximately to be 250 Å, which corresponds to 15 times the length of the repeat unit.

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

“…The long period is about 80 Å which is five times as long as the repeat unit length of BB-5(3-Me) (16.4 Å ). This lamella spacing is much smaller than those of around 250 Å proposed for the S A phase in the previous part of this section, 16,17,19 suggesting that shear flow in the smectic liquid crystal may affect the lamellar thickness. Here, it should be stated that the spacing of 80 Å is comparable to the value estimated by a theoretical treatment of the effects of shear flow on the parallel oriented lamellae at microscopic level where the lamellar spacing (d) is connected with the critical stress for the layer collapse (disorientation) (ð _ Þ c ) and the lamellar binding energy (K) as 61,62 …”

“…[50][51][52][53] This section represents the solid state morphology of BB-6 by small-angle X-ray scattering (SAXS) method and discusses the chain configuration in the smectic phase. [16][17][18][19] Chain Folding Lamellar Structure in BB-6 Crystal Formed from S A Melt Six specimens with different molecular weights, BB-6-I to BB-6-VI, were prepared. All the polymers exhibit the well-defined transition behavior as listed in Table II.…”

“…16,17,19,22,23 The results of DMA obtained for the two oriented fibers of A and B are shown in Figure 34, where only tan are presented because the small cross section of the fibers prevents determining the accurate value of Young's modulus. Considerable mechanical anisotropy with tan of fiber B larger than that of fiber A can be seen for the -relaxation while the intensities of and relaxations are similar.…”

Frustrated Smectic Phase with Unusual Density Modulation along Layer Observed in Main Chain Type of Polymers

“…What is interesting with respect to this point is that shearing the smectic phase produces the preferred uniplanar orientation where the chain orients parallel to the glass surface and perpendicular to the shear direction 14 and the tilt direction of the mesogenic groups lies parallel to the surface (see Figure 4a). This type of uniplanar orientation is characteristic of a biaxial smectic phase 19 and the X-ray analysis provides a choice between the two models.…”

Chain Folding of Main-Chain Polyesters in the Smectic A and CA Phases with a Liquid-Like Association of Biphenyl Mesogens within a Layer.

“…We have treated the following main-chain LC polyesters designated as BB-n where n is the carbon number of the methylene spacer [1][2][3][4][5][6][7][8][9][10][11][12][13] . These BB-n polyesters invariably form smectic mesophases when n varies from 3 to 9.…”