Step-growth reactions for monodisperse conjugated polymer particles

• Stufenwachstumsreaktionen für monodisperse konjugierte Polymerpartikel

Ciftci, Sibel; Martin Möller, Prof. Dr. (Thesis advisor); Alexander Kuehne, Prof. Dr. (Thesis advisor)

Aachen (2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2019

Abstract

Inspired by colloidal photonic crystals found in nature, the production of monodisperse particles, which spontaneously self-assemble into artificial colloidal crystals, has always been an inspiring challenge for scientists. Such colloidal crystals have been prepared from a wide variety of dielectric materials and find application in fields, ranging from sensors and fibre optical components to jewelry. In this work, I present novel dispersion polymerization approaches for the production of monodisperse nanoparticles consisting of semiconducting conjugated polymers. These conjugated polymer particles can self-assemble into photonic crystals without elaborate and costly nanofabrication methods. In the first part, I generate monodisperse hard sphere conjugated polymer nanoparticles (CPNs) via palladium catalyzed Heck cross-coupling dispersion polymerization. These particles self-assemble into photonic crystals and are applied as a gain medium and resonator in an organic laser. However, the Pd-catalyzed cross-coupling reaction produces metal residues as an inevitable by-product within the synthesized particles. These are disadvantageous for optical applications. In the following chapters of this thesis, I therefore rigorously focus on metal-free approaches. Using metal-free Knoevenagel dispersion polymerization I create hybrid particles by seeding the particle nucleation with dielectric SiO2 particles, enabling the generation of silica-core conjugated-polymer-shell particles. These hybrid particles act as whispering gallery mode resonators (WGM) and show emission of laser light. Finally, the Horner-Wadsworth-Emmons reaction is investigated as a metal-free dispersion polymerization, offering shape tunable conjugated CPNs. The shape can be controlled between highly monodisperse amorphous CPNs to crystalline platelet-like particles and porous conjugated organic framework particles. This method does not only proceed without any metal catalyst but also takes place at room temperature. Moreover, I investigate the kinetics of particle formation for all aforementioned step growth dispersion polymerizations. This data helps to understand, under which conditions monodisperse particles can be obtained using step growth polycondensation applied to a dispersion polymerization protocol. This work opens up pathways for tailor-made synthesis of CPN and their application in optoelectronic devices or in bio-imaging experiments in the near future.