Crystalline polymers solid mesomorphic forms

Let us finally remark the important role that solid mesophases play in manufacturing processes of polymeric materials. Polymers, in mesomorphic form, in fact, show enhanced mechanical properties and may be more easily processed, even at room temperature, than the stable crystalline forms. This allows obtaining manufactured objects at a low cost with high performances, which is not easy to obtain by processing the material directly in the stable crystalline state. 

The mesogenic structure of a benzoic acid dimer has been introduced as a noncovalent cross-linker for polysiloxanes [79]. Polymer 57 exhibits a smectic C phase due to the dynamics of H-bonding. In contrast, mesomorphic order is locked in the solid state of poly[(4-acryloyl)benzoic acid] by polymerization in its mesophase [128]. No liquid-crystalline state is observed for this material because of the lack of flexibility of the structures. Main-chain-type polymeric liquid-crystal associates are formed from carboxyl-bifunctionalized aromatic compounds [129]. 

Liquid crystal polymers (LCPs) were introduced over the last three decades. In the liquid state, either as a solution (lyotropic) or a melt (thermotropic), they lie between the boundaries of solid crystals and isotropic liquids. This polymeric state is also referred to as a mesomorphic structure, or a mesophase, a combined term adopted from the Greek language (mesos = intermediate morphe = form). This state does not meet all the criteria of a true solid or a true liquid, but it has characteristics similar to both a solid and a liquid. For instance, the anisotropic optical properties of LC polymeric fluids are like those of crystalline solids, but their molecules are free to move as in liquids. 

The mesomorphic state may be realized in two ways, namely, the two ways in which ordinary fluid phases are formed from solids dissolution and fusion. These two categories of mesomorphism are called lyotropism (liquid-crystalline solutions) and thermotropism (liquid-crystalline melts), respectively. The latter category consists of single-component substances and encompasses the large variety of low molecular weight mesogens used in LCDs. More recently, thermotropic specialty polymers... 

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