Thermotropic liquid crystalline elastomers

Aragrag N (2010) Synthesis and characterisation of thermotropic liquid crystalline elastomers. PhD thesis, University of Reading... 

Lenz and his coworkers have prepared some thermotropic liquid crystalline elastomers (TLCE) having mesogenic groups at terminal chain ends in oligomers having average molecular weight of several thousand. However, no experiment has been made to elucidate their phase structure and mechanical properties. 

Saikrasun S, Bualek Limcharoen S, Kohjiya S, Urayama K. 2005. Anisotropic mechanical properties of thermoplastic elastomers in situ reinforced with thermotropic liquid crystalline polymer fibers revealed by biaxial deformations. J Polym Sci Part B Polym Phys 43 135 144. 

S. Saikrasun, S. Bualek-Limcharoen, S. Kohjiya, and K. Urayama. Thermotropic liquid-crystalline copolyester/thermoplastic elastomer in situ composites. I. Rheology, morphology, and mechanical properties of extruded strands. J. Appl. Polym. ScL, 89 2676-2685, 2003. 

S. Saikrasun and T. Amomsakchai. Phase behavior and properties of in situ-reinforcing elastomer composites based on thermoplastic elastomers and thermotropic liquid crystalline copolyester. J. Appl. Polym. ScL, 101 1610-1619, 2006. 

Shivakumar E, Das C, Segal E, Narkis M. Viscoelastic properties of ternary in situ elastomer composites based on fluorocarbon, acrylic elastomers and thermotropic liquid crystalline polymer blends. Polymer 2(X)5 46(10) 3363-71. 

In conclusion, we note that although many problems in the theory of liquid-crystalline ordering in polymer systems have already been solved, this area is still in the initial stage of development on the whole. Among the most important directions of further research (cf. [139] for more detail) are the rheology of thermotropic polymer liquid crystals, the theory of liquid-crystalline elastomers, the statistical physics of the surface in liquid-crystalline polymers, the theory of smectic ordering in polymer systems, and the kinetics of phase transitions in liquid-crystal polymCTS. 

Qin Y, Brydon DL, Mather RR, Wardman RH (1993) Fibers fi-om polypropylene and liquid crystal polymer blends 2. Effect of extrusion and drawing conditions. Polymer 34 1202 Seo Y, Hwang SS, Hong SM, Park TS, Kim KU (1995) Effect of die geometry on the structural development of a thermotropic liquid crystalline polymer in a thermoplastic elastomer matrix. Polym Eng Sci 35 1621... 

Donnio B, Wermter H, Finkelmann H (2000) A simple and versatile synthetic route for the preparation of main-chain liquid-crystalline elastomers. Macromolecules 33 7724—7729 Finkelmann H (1987) Liquid crystal polymers. Chap 1. In Gray GW (ed) Thermotropic liquid crystals. Wiley, Chichester, pp 1-27... 

Jeong H M, Kim B K and Choi Y J (2000) Synthesis and properties of thermotropic liquid crystalline polyurethane elastomers. Polymer 41 1849-1855. 

Table 6 and Figure 20 reprinted from Polymer, Vol. 41, 2000, Authors Jeong H M, Kim B K and Choi Y J, Title Synthesis and properties of thermotropic liquid crystalline polyurethane elastomers, pp. 1849-1855, Copyright (2004), with permission from Elsevier Science. 

In the phrase liquid-crystalline, the crystalline adjective refers to the faa that these materials are sufSdentiy ordered to diffract an X-ray beam in a way analogous to that of normal crystalline materials. On the other hand, the liquid part specifies that there is frequently sufSdent disorder for the material to flow like a liquid. liquid crystals can be divided into thermotropic, that exhibit a phase transition with change of temperature, and lyotropic, that exhibit phase transition as a function of both temperature and concentration of the LC molecules in a solvent. Both low molecular wdght materials and polymers " can show liquid crystallinity. In the case of polymers, it frequently occurs in very stiff chains such as the Kevlars and other aromatic polyamides. It can also occur with flexible chains, however, and it is these flexible chains in the elastomeric state that are the focus of the present discussion. LC networks of flexible chains have the following three properties (1) they can be extensively deformed (as described for elastomers throughout this book), (2) the deformation produces alignment of the chains, and (3) alignment of the chains is central to the formation of LC phases. Elastomers of this type have been the subject of numerous studies, as described in several detailed reviews. ... 

To obtain the liquid crystalline state in a polymer network, several strategies are conceivable. They are all based on well known principles evaluated during the last few decades for linear liquid crystalline polymers. The monomer units of the network have to consist of mesogenic moieties, which are either rigid rods or discs in the case of thermotropic polymorphism or amphiphiles in the case of lyotropic polymorphism. The mesogenic units can be attached either as side chains to the monomer units yielding side chain elastomers (Fig. la, b) or directly linked... 

---