Beschreibung:
Abstract: The formation of polymer single crystals has attracted a lot of interest in both academic and industrial research. With the regular close packing of building blocks over large distances, ordered crystalline structures provide important models for understanding the optimum properties of materials. Crystallization of polymers can be performed either from supercooled melts or from supersaturated solutions. However, since the crystallization behavior of polymers is highly depending on their chain-like structure and chemical details of the monomers, it has been a great challenge to form well-ordered crystals of polymers, especially when they have a rigid backbone or bulky side-groups. Unlike polyethylene and polypropylene which are known as classical model polymers for crystallization studies, polymers consisting of complex architecture or monomer features normally exhibit low mobility in the melt and, in some cases, a low thermal stability at high temperatures. Therefore, it is a challenge to find suitable experimental conditions for crystallization of such complex polymers. Furthermore, interaction forces between polymers play an important role in determining the resulting morphology of the obtained crystals. For example, because of strong π–π interactions between chains, conjugated polymers tend to form small-sized aggregates rather than large-sized crystals. In contrast, rather week van der Waals forces as, for example, in substituted polystyrenes rather cause a low nucleation probability and a slow crystal growth rate. Crystallization including nucleation and crystal growth is driven by the difference in chemical potential between the crystalline phase and the surrounding phase. For solutions, this difference is related to supersaturation of the solution. A supersaturated solution is metastable. Thus, a precisely controlled crystallization strategy is of great importance for complex polymers in this metastable regime. In this thesis, we investigated the formation of crystals from metastable solutions. Two polymers characterized by strong and weak interactions, respectively, were selected for a detailed crystallization study: poly(3-hexylthiophene) (P3HT) and poly(p-methylstyrene) (iPpMS)