Carboxyl-containing homopolyimides based on 3,5-diaminobenzoic acid and different tetracarboxylic acid dianhydrides have been synthesized by one-step high-temperature polycondensation in N -methyl-2-pyrrolidone. The effect of the dianhydride structure on the properties of the obtained polymers has been studied and the possibility of their use in situ to manufacture highly thermostable primary coatings for quartz waveguides has been shown.

Homo- and copolyimides containing F, Cl, or Si atoms and COOH, OH, and cardo groups are synthesized by one-step high-temperature polycyclocondensation. It is shown that the structure of the polymer affects its solubility, thermal, mechanical, and optical properties and use as a coating. The resulting polymers with ηinh = 0.3–1.3 dL/g are characterized by high heat resistance and thermal stability (240°C ≤ Tg ≤ 375°C, 440°C ≤ T10% ≤ 580°C) and also form high-strength films (55 MPa ≤ σ ≤ 140 MPa; 1.1 GPa ≤ E ≤ 2.8 GPa). The developed polyimides are promising as new highly thermostable protective coatings, in particular, of optical fibers, whose mechanical properties do not change after prolonged exposure at 300°C.