Azobenzene-Containing Polymers for Photoswitching Applications: Design, Synthesis and Characterization

Abstract

In this thesis two properties of azopolymers are investigated. In the first part azopolymers with absorption in the visible range of the light spectrum are synthesized, characterized and possible applications of these polymers are illustrated. In the second part, the isothermal, photoinduced solid-to-liquid transition of azopolymers is investigated and associated to differences between the trans and cis forms of the azopolymers. For the preparation of an azopolymer with absorption in the visible light region, an azobenzene molecule, which absorbs visible light, is incorporated into a polymethacrylate backbone. For this purpose, a monomer based on a methacrylate and containing the just mentioned azobenzene molecule is synthesized first. The azobenzene molecule is linked to the methacrylate via six methylene groups. In the following, solid state properties and light switching in polymer films are investigated and the advantages of the new polymer will be demonstrated by comparison with a conventional azopolymer. Based on these properties, information storage and solar energy storage are shown as possible applications. The thermal properties, in particular the glass transition temperature, of azopolymers are examined in more detail in the second part. For certain azopolymer structures, a solid-to-liquid transition is observed depending on their conformation (trans or cis), which is associated with the glass transition temperature. In order to better understand this phenomenon, the thermal properties of several different azopolymers are determined by different methods. The azopolymers differ in their polymer backbone, length of the side chain or azobenzene substituents. Furthermore, possible applications based on photoinduced solid-liquid transitions are demonstrated.