Preparation of Liquid Crystalline Elastomers

The combination of rubber elasticity and anisotropic liquid crystalline order of liquid crystalline elastomers (LCEs) gives rise to exceptional physical properties, unknown for conventional solid-state materials. By selecting suitable chemistry of the liquid crystalline moieties, the liquid crystalline phase structure, and the chemistry of the macromolecular network structure, these physical properties can be optimized for specific applications like mechanics, optics, diffusional or electronic transport, etc. In this chapter we outline basic aspects to be considered when synthesizing LCEs, including some basic characterization techniques. We give an overview of the chemistry involved in synthesizing LCEs and the different techniques of chemical crosslinking developed for this purpose. The unique coupling of the polymer chain conformation and the anisotropic LC order in LCEs can be exploited to induce a macroscopic orientation of the LC phase structure by applying mechanical fields. By performing chemical crosslinking in the aligned state, the uniform macroscopic orientation can be fixed permanently. Different strategies are introduced to synthesize such liquid single-crystal elastomers (LSCEs), and illustrated by a wide range of examples. Orientation techniques based on external magnetic and electric fields or surface treatment are also included. We emphasize practical aspects and give advice for successful preparation of this fascinating class of materials. A promising future for LSCEs is expected because of their unique and as yet largely unexplored abilities to mimic living systems.