Synthesis and physical properties of N -substituted polyimides based on imidazole

Abstract

AB-type monomers based on imidazole for the preparation of polyimides were synthesized by carrying out a substitution at the 1-position of 2-amino-4,5-dicyanoimidazole, followed by hydrolysis. Thus, pendant groups such as hexyl and 2,4-dinitrophenyl as an aliphatic long chain and an electron-withdrawing group, respectively, were introduced at the 1-position of the imidazole monomer. A solid-state polymerization was employed to prepare the poly(imidazoleimide)s in the form of a film from poly(imidazoleamic acid chloride)s by heating up to 180–200°C. The carbonyl stretching peaks of the imide ring appear at 1808 (sym) cm −1 and 1756 (antisym) cm −1 . The effects of monomer structure on reactivity and the degree of imidization were investigated by comparing the viscosity of the resultant polymers and intensity of carbonyl peak at 1808 cm −1 . The difference in the hydrolysis rate between polyimides having short or long aliphatic pendant groups at the 1-position was observed using FT-IR. The inherent viscosity of the N -hexyl polyimide was 1.26 dL/g in N -methyl pyrrolidinone (NMP) and 0.22 dL/g in the case of N -2,4-dinitrophenyl poly(amic acid) in methanesulfonic acid at 30°C. The structural, physical, and material properties of the polyimides were characterized by infrared, nuclear magnetic resonance, luminescence, viscosimetric methods, differential scanning calorimetry, thermogravimetric analysis, optical microscopy, and wide angle x-ray scattering. Solution properties were also investigated by monitoring the viscosity as a function of time at 30°C. Luminescence spectroscopy of the poly(1-methyl imidazole imide) and poly(1-methyl imidazoleamic acid) films shows an emission band centered at 535 and 505 nm, respectively. Thermal properties are described comparing the weight loss and decomposition temperature as a function of the polymer structure and the degree of imidization. © 1993 John Wiley & Sons, Inc.