Lamellar Mesophases Formed by Thermotropic Liquid Crystalline Ionic Polymer Systems without Mesogenic Units

Mixtures consisting of polyamine (branched polyethyleneimine (PEI) and polyallylamine (PAA)) and n-alkanoic acid (C n: n = the carbon number of alkanoic acid) were prepared and their thermal and liquid crystalline properties were examined. The occurrence of proton transfer from the carboxylic acid to the amine groups was found by IR measurement of the mixtures. The polyamines and C n exhibited no mesophase. Also, PEI/C n with n = 3, 4, 5, which are mixtures of PEI and C n, did not show a liquid crystalline phase. However, PEI/C n with n> 5 clearly displayed a lamellar fluid liquid crystal phase having a layer structure with low order inside the layer, due to ion–ion interactions. In the lamellar mesophase, PEI/C n showed a focal-conic fan texture which resembles the fan-shaped textures in smectic A and C phases. PEI/C n with 5 < n < 13 formed a bilayer structure in the lamellar mesophase. On the other hand, a tilted bilayer structure is proposed as a packing model of PEI/C n with 13 < n< 19. PAA/C18 consisting of polyallylamine and C18 also showed a lamellar fluid mesophase and formed a similar layer structure to PEI/C18.