Solutions of lyotropic liquid crystalline polymers

Solutions of the aromatic polyamides (PpBA, PpPTA and PmPTA), the polybenzazoles (PBT and PBO), poly(benzyl glutamate) (PBG) and hydroxypropylcellulose (HPC) are the most studied main chain lyotropic systems and our understanding of the behaviour of lyotropics is based on investigations of this relatively small number of materials (Moldenaers, 1996). They form main chain liquid crystals because of their rigid molecular structure in the appropriate solvents. Two kinds of solvents are used (Collyer, 1996)  

Powerfully protonating acids such as 100% sulphuric acid, chlorofluoro acid, methanesulphonic acid and anhydrous hydrogen fluoride 

Aprotic dipolar solvents such as dimethylacetamide containing about 2.5% of a salt as lithium chloride or calcium chloride 

Moreover, in order to obtain a nematic mesophase instead of an isotropic solution several conditions have to be fulfilled  

A polymer concentration above a critical concentration cnem ccrit 

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