Poly(arylethynyl) Nanoparticles from Sonogashira Coupling in Aqueous Emulsion

Introduction The discovery of the conductive properties of conjugated organic polymers in the late 1970s initiated intense investigations of their synthesis, chemistry and physical properties. Today, they are widely studied for various applications, e.g. optoelectronics in displays or organic solar cells. Beyond academic interest in the generation and properties of unusual nanostructures, nanoparticles of conjugated polymers can be useful for the preparation of thin films, of highly disperse multiphase films, and of multilayer devices. 4,5,6 These examples illustrate that nanoparticles may contribute to resolve the issue of processing of conjugated polymers. Aqueous polymer dispersions are attractive in this context as they are compatible with printing techniques, also water is a non-solvent for the majority of organic compounds and polymers. The non-flammability and environmentally benign nature of water can be advantageous in some cases. Accordingly, the preparation of secondary dispersions, that is, postpolymerization emulsification of conjugated polymers has been studied. However, the necessity of polymer solubility in an organic solvent or of fusability, and the high viscosity of polymer melts and also of polymer solutions in organic solvents (which also have to be removed from dispersions subsequently) limit the scope of secondary dispersions. Polyanilines and polythiophenes are common conjugated polymers with heteroatoms in the main chain. They are accessible by oxidative polymerization, typically in water as a reaction medium. Aqueous dispersions of these polymers, that is colloidally stabilized particles of water-insoluble polyanilines and polythiophenes, have been studied. For A2 + B2 step growth reactions, a high molecular weight can only be achieved with exact monomer stoichiometry. Small variations result in a much lower molecular weight. Also, a high conversion of functional groups is required. In the case of catalytic reactions in emulsion, this requires a sufficient water-stability of catalysts. A suitable step-growth reaction that can be performed in aqueous systems for catalytic polymerizations is Sonogashira coupling. We report on the preparation of highly fluorescent polymer nanoparticles by Sonogashira coupling in aqueous miniemulsion.