Synthesis and properties of high performance polyimides derived from a novel diamine containing a N -octylcarbazole unit and two 3,5-diarylimidazole groups

Abstract

A novel heterocyclic diamine based on carbazole and imidazole rings, 5,5′-(9-octyl-carbazole-3,6-diyl)bis[4-phenyl-2-(4-amino-phenyl)-1H-imidazole], was synthesized from readily available compounds through a multi-step procedure in high yield. The obtained diamine was fully characterized and its polycondensation reaction with different aromatic dianhydrides via the conventional two-step method, ring-opening polycondensation and chemical imidization, led to preparation of novel photoactive and heat resistant polyimides with improved solubility. The effects of the heteroaromatic rings into the main chain of the prepared polyimides were evaluated through the study of their solubility, thermal and optical properties. The inherent viscosities of the resulting polyimides were in the range of 0.39–0.51 dL g⁻¹, and all of  them were soluble in common polar aprotic solvents. Meanwhile, they had good thermal stability with glass transition temperature (T _g) values of 312–330 °C, the temperature at 10% weight loss of 475–495 °C, and the residue at 700 °C of 61–65% in nitrogen. These polymers exhibited strong UV-vis absorption, and their photoluminescence (PL) spectra showed maxima at 413–426 nm in solution and at 429–438 nm in the solid state. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous.