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

Abstract

AbstractAB‐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.