Permanent Orientation of the Main Axis

The orientation of polydomain polymers by mechanical or viscous flow fields can be achieved easiest if a macroscopic chain anisotropy that coincides with the local symmetry of the LC phase structure is induced and fixed by chemical crosslinking. Eor nematic or Sa main chain polymers which locally show a prolate (see Sect. 3) chain anisotropy, a uniaxial deformation leads to a globally prolate chain conformation. If the chain conformation of the LC polymer is locally oblate, a globally oblate chain conformation can be induced by either uniaxial compression or -equivalently - biaxial stretching of the sample (Lig. 9). 

In some cases it is also possible to induce a global chain conformation of the LSCE opposite to the local chain conformation of the polymeric starting material which will be discussed for cholesteric and smectic-A side chain elastomers. 

In the following, several examples of the preparation of LSCEs will be given. Lor selected preparation techniques we will also discuss some practical aspects which are important to produce high quality elastomer samples. The examples are ordered according to their different phase stmctures. 

This robust synthetic approach has frequently been used to produce LSCEs in the last few years as it works well for side chain as well as main chain elastomers. It is also applicable for polymer networks of different LC phase structures (smectic, cholesteric, lyotropic hexagonal) as long as they exhibit prolate chain conformations. We will therefore give a more detailed description in the following paragraphs. 

In order to produce LSCEs, the crosslinking/casting reaction is interrupted before completion. At that time a lightly crosslinked gel is obtained which is swollen with organic solvent and thus isotropic. A macroscopic orientation can now be induced by deswelling the gel under uniaxial mechanical load at room temperature. The gel is removed from the casting setup, hung vertically, and has a 

---