Synthesis and characterization of soluble polyimides containing cyclohexylidene moiety with various alkyl-substituents

A series of novel aromatic diamines containing kinked cyclohexylidene moieties was synthesized by a HCl-catalyzed condensation reaction of excess aniline and corresponding alkyl-substituted cyclohexanone derivatives at 120-140 degrees C for 24 hours. The structures of monomers were identifield by H-1-NMR, C-13-NMR, and FT-IR. The yields of monomer preparation were above 70%. The polymers were synthesized from the obtained diamines and various aromatic dianhydrides by one-step polymerization in m-cresol at 200 degrees C for 6-8 hours. The inherent viscosities were in the range of 0.74-1.66 dL/g and the prepared polyimides showed excellent thermal stabilities as well as good solubility. That is, all polymers were readily soluble in common organic solvents such as dimethylacetamide, dimethylformamide, tetrahydrofuran, chloroform, etc. and the glass transition temperatures were in the range of 261-348 degrees C. The solubility and the glass transition temperature of the polymers increased as the bulkiness of the alkyl-substituents increased.