Synthesis and Characterization of Thianthrene-Based Polyamides

Thianthrene-2,7- and -2,8-dicarboxylic acids plus a synthetic intermediate, 4,4'-thiobis[3-chlorobenzoic acid], have been synthesized in good yields via nucleophilic aromatic substitution of Na2S on N,N-dimethyl-3,4-dichlorobenzamide. New aromatic polyamides having inherent viscosities of 1.29-2.39 dL/g were prepared by the direct polycondensation reaction of the dicarboxylic acids with 4,4'-oxydianiline and 1,4-phenylenediamine in N-methyl-2-pyrrolidinone (NMP) using triphenyl phosphite (TPP) and pyridine. The fused-ring thianthrene-based polyamides were more soluble than analogous poly(thioether amide)s. Polymer films were cast from either N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAc)/LiCl solutions and analyzed by FTIR and NMR. All prepared aramids displayed good thermal stability by DSC and TGA.