Hydrothermal synthesis as green route towards amide- and imidazole-based organic materials

Abstract

In order to enable the development of future technologies, it is essential to create new materials with adjustable properties. In many cases it is of paramount importance that these materials are not only functional but also lightweight and highly resistant towards various external influences. Organic high-performance materials (HPMs) are highly sought after to meet these requirements, as they are composed of abundant, lightweight elements that formstable moieties. However, the synthesis of organic HPMs typically requires harsh and harmful conditions.In recent years, it has been successfully demonstrated that so-called hydrothermal (HT) conditions allow to directly synthesize highly crystalline low-molecular weight carbonyl dyesas well as linear polyimides. Enhancing the crystallinity of an organic HPM by applying such a “green” strategy is not only highly intriguing but also of significant importance for amultitude of practical applications. In general, the thermal and chemical stability of materials improves with increasing crystallinity, allowing the materials to with stand more extreme working conditions.Due to their ability to generate outstandingly high crystallinity in organic low-molecular weight compounds as well as linear polymers, HT methods can also be considered as highly promising for realizing crystalline frameworks and conjugated ladder polymers.In this thesis, the development and synthesis of crystalline frameworks and conjugated ladder polymers using three different linkages were achieved through HT method.The goal of the first and second part was to synthesize crystalline frameworks with benzimidazole and amide linkages using HT synthesis. It was observed that under HTconditions, crystalline and thermally stable polyamide and polybenzimidazole materials were produced. However, instead of achieving long-range extended frameworks, the synthesis led to the formation of short-range fused macrocycle structures.The third part focused on the preparation of conjugated ladder polymers with imidazopyrrolone linkages using HT synthesis. The synthetic procedure was modified by incorporating microwave (MW) synthesis, resulting in a faster and less tedious synthesis process that yielded thermally stable, processable, yet amorphous polymers.In summary, this thesis aims to develop "green" and innovative pathways toward organic HPMs with various linkages using only water under high-temperature and high-pressure conditions.