Lyotropic main-chain liquid crystal polymers

14 LYOTROPIC MAIN-CHAIN LIQUID CRYSTAL POLYMERS 

14 for partially chlorinated poly(l,4-phenylene-2,6-naphthalamide) dissolved in a 

FIGURE 11.14 Variation of the viscosity of solutions of partially chlorinated poly(l,4-phenylene-2, 6-naphthalamide) dissolved in a solvent mixture of hexamethylene phosphora-mide and iV-methylpyrrolidone containing 2.9% LiCl as a function of the solution concentration, showing the transition from isotropic to anisotropic solutions. (From Morgan, RW., Aromatic polyamides, CHEMTECH, 316, 1979. With permission of American Chemical Society, Washington, D.C.) 

A number of the polyamides have achieved commercial importance because of the very high tensile strengths of the fibers that can be spun from the nematic solutions. The additional chain orientation in the direction of the fiber long axis, obtained from the nematic self-ordering in the system, leads to a dramatic enhancement of the properties and makes them attractive alternatives to metal or carbon fibers for use in composites as reinforcing material. 

Poly( 7-phenylene isophthalamide), trade name Nomex  

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M. G. Northolt, D. J. Sikkema, Lyotropic Main Chain Liquid Crystal Polymers, Adv. Polym. Sci. 98,119 (1990)... 

Northolt MG and Sikkema DJ, "Lyotropic Main Chain Liquid Crystal Polymers", Adv Polym Sci 98 (1990)115. 

M. G. Northolt and D. J, Sikkema, Lyotropic main chain liquid crystal polymers, in Advances in Polymer Science , vol. 98, pp. 115-177. Springer-Verlag, Berlin, 1991. 

Despite the numerous confirmations of the negative phenomenon, it has still been widely stated that the flow of all polymer systems exhibits only positive primary normal forces (i.e. a positive Nj, the first normal stress difference) [8, 9]. Even subsequent reviews and research papers on the specific subject of lyotropic main chain liquid crystal polymers have not mentioned the confirmed negative effect [10], and even equivalent shear measurements on the identical solutions did not report the negative effect [11]. 

Lyotropic Main Chain Liquid Crystal Polymers... 

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