Side-chain mesogens

Macromolecules with Side-Chain Mesogenic Groups... 

Schematically the arrangement of a macromolecule with side-chain mesogenic groups in the liquid crystalline state is shown in Fig. 13. Flexible spacers give the mesogenic group its mobility. It is of interest to note that in such liquid crystals all positional mobility of the mesogen is based on conformational motion of the flexible spacer and backbone. Restricting this mobility either prohibits ordering, or freezes the order into the glassy state.

The transition behavior of a number of liquid crystals with side-chain mesogens is summarized in Table 5. The most obvious feature of macromolecular liquid crystals is the frequent absence of fully ordered crystals at low temperatures. If fully ordered crystals are observed, crystallization is incomplete, i.e. the observed phase states are to be described by an area on the right side of Fig. 3. Glass transitions, which were hard to find in low molecular weight liquid crystals (see Table 3), are now prominent. 

Table 5. Transition Parameters of Mesophases of Macromolecules with Side-Chain Mesogens... 

Scheme 11 Doubly hydrogen-bonded side-chain mesogens [19]...

Fig. 35 Color change of polystyrene-fcZocfc-polyfmethacrylic acid) and imidazole-terminated side-chain mesogens PS-h-PMAA(LC) (Scheme 13) due to a shift in photonic handgap accompanying isotropization [171]...

Fig. 1. Thermotropic Polymers with Either Main Chain or Side Chain Mesogenic Units...

A supramolecular approach is usually employed in the preparation of such materials. Commonly used base polymers are ionomers containing sulfonate groups, such as poly(styrenesulfonate). Azo-containing molecules are frequently employed for the side-chain mesogen [95]. 

Fig. 5,11. Order distribution-functions of various parts of a polyacrylate with side-chain mesogen (phenylene-4-hydroxybenzoate) separated by a flexible spacer (hexamethylene). Determined from the angular dependence of the deuterium NMR line-shape. Presented by H. W. Spiess, Dechema Tagung 1987, see also Refs. The angle p is defined between the ma etic field and the...

Polymers with Side-Chain Mesogens Linked at the Main Chain Spacer... 

Figure 6. Schematic representation of LC elastomers prepared from chiral combined main-chain/side-chain copolymers, d] main-chain mesogens Idl side-chain mesogens chiral groups [7],...

As an alternative concept to combined LC polymers, polymers with the side-chain mesogens linked at the main-chain mesogen were prepared [24] (see Figure 5, type B). 

These were prepared by a solution polycondensation of a (phenol) and a bis(acid chloride) as shown in Scheme 3 [24, 25]. The resulting polymers (Table 2) again show broad LC phases due to the synergistic interaction of the main-chain and side-chain mesogenic groups. However, compared to the other types of combined LC... 

Table 2. Structure, molecular weight and phase behaviour of the combined polymers in which the side-chain mesogen is linked to the main-chain mesogen.

In order to understand the synergistic interaction of the main-chain and side-chain mesogens, NMR [21] and neutron scattering [27] experiments have been performed on selectively deuterated samples. NMR [21] (see Volume 1, Chapter Vlll, Sect. 1 of this Handbook) shows clearly that the main-... 

Figure 11. The temperature dependence of the quadrupole splitting Av ( H NMR) of combined LC polymers selectively deuterated at either the main-chain (A) or the side-chain ( ) mesogen [21, 25].

Skeletal muscles are anisotropic, that is, they exhibit contraction and elongation along the fiber axis. Naciri et al. (2003) described a method of preparing LC fibers from a side-chain LC terpolymer containing two side-chain mesogens... 

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