Transition Temperatures and Textures

The crystal-to-smectic, smectic-to-smectic and smectic-to-nematic and smectic-to-isotropic transitions are rarely observed for this class of polymers. The nematic-to-isotropic transition, is also not frequently observed because it usually occurs at such a temperature that thermal degradation precedes this transition. The phenomenon of observation of smectic (high order)-to-smectic (low order) and smectic-to-nematic transitions, known as polymesomor-phism, is common to low molar mass LCs (LMLCs). In contrast, LC 

The polarizing light microscopy is the simplest method available to identify LC phases. This optical method has been used since the discovery of liquid crystals and has led to nematic, cholesteric and smectic classifications. The appearance of a specific texture of the melt is usually a function of the types of LC phase, and it is often possible to directly identify the type of LC phase present in a polymer melt by this optical method. The textures of various LC phases are caused by the existence of different types of defect present in the LC phases. It should be noted that microscopic observations are sometimes misleading because the development of specific textures in an LC phase can occur with great difficulty. This problem arises owing to their multiphase nature (the coexistence of polycrystalline and amorphous phases), polydispersity and/or higher viscosities of LCPs melts compared with those of LMLCs. In most cases, LCPs must be annealed for hours or days at suitable temperatures to develop specific textures. 

Mostly thermotropic polyesters show a nematic phase with a typical appearance that is called a marbled texture, a Schlieren texture, a threaded texture, or, a nematic droplets depending on the thickness and temperature of the polyester. Only in a few cases, they exhibit low-order smectic phases [100], which are identified through the observations of fan-shaped and broken fan textures in their LC phases. No report of higher-order smectic phases has been observed in this class of pol)nners. It is worth mentioning that nematic texture can simply be frozen into a glassy state in the case where there is no interference from the crystallization process. An intriguing property of an LC polyester is its biphase structure over 

Crystallization of main-chain LCPs is considerably different from that of conventional polymers, such as polyethylene or PET. LCPs 

The overall crystallization process includes two steps, primary nucleation followed by crystal growth. The process can be well described by the Avrami equation [107] as shown  

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