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- Chain-Growth Polymerization of 3-Hexylthiophene Towards Well-Defined Semiconductor Block Copolymers (2011)
- The central point of this thesis is the control of the P3HT synthesis using Kumada catalyst transfer polymerization (KCTP). Kinetic studies of the active monomer formation via Grignard metathesis revealed that this reaction is rather slow, however, its completion is essential for controlled end groups. It was shown that LiCl accelerates this reaction and allows 100% H/Br end groups without long reaction times. MeOH as a quenching reagent was found to cause chain-chain coupling via disproportionation of the Ni-catalyst species. For non-functionalized P3HTs HCl was identified as the best quenching agent. The identification of these factors now allows the fast synthesis of any molecular weight with 100% homogeneous functionalizable H/Br end groups. In the second part these well-defined P3HTs were used to investigate their equilibrium bulk structures and aggregation in solution. A temperature dependent phase diagram of the crystalline regions in P3HT was obtained in bulk. Further, the order of the P3HT side chains was elucidated for the first time as tilted and non-interdigitated. The analysis of the semicrystalline order of P3HT showed extended chain crystals as the equilibrium structures up to a molecular weight of ~20 kDa. The study of the aggregate formation in solution revealed that the amount of aggregates and their nature depends on the used solvent, the molecular weight and the synthetic method. The maximum fraction of aggregates in solution seemed to indicate the resulting charge carrier mobility measured in organic thin film field effect transistors. For the well-defined P3HTs, even low molecular weight samples allow for high charge carrier mobility. In the third part the bromine end groups were used to introduce valuable carboxylic end groups in one single, selective and quantitative post-polymerization step. Thus, carboxylated polymers with a charge carrier mobility as high as 10 3 cm2/Vs were obtained. These functionalized polymers can be anchored onto surfaces, can coordinate nanoparticles or can be used as end cappers for the formation of block copolymers. Additionally, a correlation of the melting enthalpies with the charge carrier mobilities indicated that the crystallinity is the determinant factor for the molecular weight dependence of the charge carrier mobility. A great challenge for the synthesis of P3HT containing block copolymers is to combine KCTP with other controlled polymerization methods. Especially conjugated blocks with high molecular weights are difficult to incorporate, because of their lower solubility and lower percentage of end groups. Here, it was demonstrated that copper catalyzed azide-alkyne cycloaddition, a so-called click reaction, is a simple and efficient approach to create high molecular weight P3HT macroinitiators for nitroxide mediated radical polymerization. First, the synthesis of alkyne functionalized P3HT was optimized. HCl as a quenching reagent caused hydrohalogenation and hydration reactions and MeOH proved to be the quenching reagent of choice. In the second step, P3HT-alkyne was combined with an azide functionalized alkoxyamine to form the macroinitiator in one single post-polymerization step. Two different types of block copolymers were realized. The first type is amphiphilic P3HT-b-P4VP with a polar coil block, which is able to coordinate to inorganic particles. Thermal analysis showed that the crystallite size of P3HT is hardly influenced by the coil content when such long P3HT rod blocks are used. Preliminary investigations of the self-assembly in solution, demonstrated that colloidal structures with crystalline P3HT cores are obtained in P4VP selective solvents. Thus, P3HT b P4VP is an interesting system for hybrid photovoltaics and for investigating structure formation of rod-coil block copolymers in bulk and solution. The second type of block copolymers are fully-functionalized P3HT-b-PPerAcrs, with PPerAcr as an electron conducting second block. With the new synthetic approach it was possible to get an exclusively P3HT-b-PPerAcr diblock copolymer with a high molecular weight. In this context a high content of PPerAcr of 64wt% was realized which is important for a balanced charge transport in OPVs. The pure diblock, the high molecular weight and, hence, a high chiN parameter enabled for the first time the formation of a hexagonally ordered cylindrical bulk structure for a fully-functionalized crystalline-crystalline block copolymer. Additionally, in thin films, order-disorder transition and microphase separation was observed with domain sizes in the range of the exciton diffusion length. In conclusion, the optimization of the synthesis of P3HT allowed a better understanding of fundamental aspects about its molecular weight dependent structures and the resulting properties. Further, new end groups could be introduced to widen its applications. Additionally, long P3HT blocks were efficiently incorporated into well-defined diblock copolymers.