Synthesis and characterization of highly soluble and thermally stable new polyimides based on 3,5-diamino benzoyl amino phenyl-14H-dibenzo[a,j]xanthene

A new xanthene-containing diamine monomer was successfully synthesized in four steps by the condensation of β-naphthol and 4-nitrobenzaldehyde in the presence of p-toluenesulfonic acid catalyst, reduction of the nitro intermediate, the nucleophilic substitution reaction of amine compound and 3,5-dinitrobenzoyl chloride, and subsequent reduction of the dinitro compound. The diamine monomer could be obtained in quantitative yield. A series of novel organosoluble aromatic polyimides were prepared by direct polycondensation of synthesized diamine with four tetracarboxylic dianhydrides via a conventional two-step polymerization process. The polymers were obtained in quantitative yields with inherent viscosities of 0.20–0.74 dL/g. Most of the polymers dissolved in N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide and dimethyl sulfoxide. The resulting polyimides exhibited good thermal stability; no weight loss was detected before a temperature of 450 °C in nitrogen. Wide-angle X-ray diffraction measurements showed that these polyimides were predominantly amorphous.