Synthesis and Formation of a Supramolecular Nematic Liquid Crystal in Poly(<i>p</i>-phenylene−sulfoterephthalamide)−H₂O

Abstract

The formation of lyotropic solutions in water has yet to be reported for polyaramides. In this work, we investigate the synthesis and properties of a water-soluble polyaramid via the inclusion of a sulfonated monomer in the backbone of the polymer chain. Using sulfonated terephthalic acid (sTA) together with a diamine and a diisocyanate enables us to produce a lyotropic water-soluble polyaramid poly( p -phenylene−sulfoterephthalamide). Two different synthetic routes are presented: (1) the reaction between sTA and p -phenylene diisocyanate (PPDI) and (2) the reaction of activated sTA using triphenyl phosphite and p -phenylenediamine (PPD). Polymers with various molar masses up to 15 000 g mol -1 using both methods have been obtained. We have examined the optimal reaction conditions for the synthesis of these polymers, in particular the effect of reaction temperature, concentration of monomers and reactants, type of counterions, and solvents. The polymers obtained are mostly soluble in water, up to high concentration (10 wt % without an alkali counterion on the sulfonic acid group), and surprisingly lyotropic nematic behavior has been observed independent of the molar mass of the polymer. The phase diagram of these materials in water has been investigated, and the lyotropic phase has been characterized using optical polarized microscopy.