Preparation and characterization of new soluble benzimidazole–imide copolymers

Abstract

The present necessity to use heat-resistant materials in electronics justifies the scientific interest in different heterocyclic polymers. This paper is especially concerned with the preparation of novel heat-resistant polyimides having bisbenzimidazole moieties in the main chain and their applications as dielectric films. A soluble copolyimide was prepared by a two-step synthesis from aromatic dianhydrides and aromatic diamines. The bisbenzimidazole diamine was prepared by reduction of the corresponding dinitro compound. The diamine was reacted with various aromatic dianhydrides to prepare a series of alternating benzimidazole–imide copolymers via the poly(amic acid) precursors and thermal or chemical imidization. Monomers and polymers were characterized by conventional methods and their physical properties such as solution viscosity, solubility properties, thermal stability and thermal behaviour were studied. All copolymers were obtained in high yields having inherent viscosities ηinh that ranged from 0.60 to 0.98 dL g−1. Thin films of the copolymer were tough and flexible, having tensile strengths as high as 100 MPa. Glass transition temperatures were observed between 275 and 328 °C. Thermogravimetric analyses indicated that the thermal degradation of poly(benzimidazole–imide) occurs around 530 °C, which is ca. 80 °C higher than polyimide, confirming that the introduction of the bisbenzimidazole component improved the thermal stability of polyimide.