Thermotropic mesophase reactions

Hydrosilylation reactions have been performed with PFSs containing Si-H functionalities to attach mesogenic azobenzene groups. This has allowed the preparation of calamitic thermotropic side-chain liquid crystalline materials that display a nematic mesophase between ca. 53 and 250... 

The thermal reaction of cobalt polymers 4.28 with isocyanates at 120 °C leads to 2-pyridone-containing polymers such as 4.30 [70]. Well-characterized, yellow polyesters 4.31 containing skeletal (cyclobutadiene)cobalt moieties in the main chain have been prepared by interfacial polycondensation approaches [73]. The use of solubilizing alkoxy substituents R afforded materials with Mn = 5,400-16,300 (PDI = 1.3-1.8). Analogous materials to 4.31 with a 1,3-disposition of the main-chain substituents on the cyclobutadiene ligands have also been studied [73, 74]. Thermotropic liquid crystallinity was detected by polarizing microscopy, with, in some cases, mesophases stable over the temperature range from about 110 to >250°C. 

In the formation of carbonaceous mesophase by thermolysis (pyrolysis) of isotropic molten pitch, the development of a liquid-crystalline phase is accompanied by simultaneous aromatic polymerization reactions. The reactivity o/pitch with increasing heat treatment temperature and its thermosetting nature are responsible for the lack of a true reversible thermotropic phase transition for the bulk mesophase in most pitches. Due to its glass-like nature most of the liquid-crystalline characteristics are retained in the super-cooled solid state. 

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