Synthesis and properties of modified aramids

The purpose of this study was to determine the influence of different kinds of main chain modification of aramids on their thermal properties and solubility. The properties of polyamides synthesized by direct polycondensation using phosphorylation reaction depend strongly on the chemical architecture of the macromolecules. Polymers thus obtained were characterized by viscosity measurements, differential scanning calorimetry, thermogravimetry and solubility tests. These polyamides were distinguished by inherent viscosities in the range of 0.12–1.67 dl/g. The thermal transitions decrease in all cases of modification and the solubility is improved. Furthermore, the liquid crystalline properties of the polyamides were investigated. Thermotropic liquid crystalline behavior can be stated for a polyamide composed of 4,4′-diaminodiphenylmethane (MDA) and sebacic acid (SEB) under shearing. Aromatic polyamides with kinks in their main chain exhibit lyotropic crystalline behavior whereas parallel displacement in the main chain prevent the formation of liquid crystals in solution.