Novel two-step synthesis of polybenzothiazoles via precursor polyamides from 2,5-bis(isopropylthio)-1,4-phenylenediamine and aromatic dicarboxylic acid chlorides

A novel two-step method for the synthesis of polybenzothiazoles has been developed starting from 2,5-bis(isoprophylthio)-1,4-phenylenediamine and aromatic dicarboxylic acid chlorides. The low-temperature solution polycondensation of these monomer pairs in N-methyl-2-pyrrolidone afforded the aromatic polyamides with pendant isopropylthio groups having inherent viscosities in the range of 0.8 and 2.4 dL/g. The soluble precursor polyamides were subjected to thermal cyclization to the corresponding polybenzothiazoles along with the elimination of propylene and water. The resulting polymers were also characterized.