Origin of the Anisotropy and Structure of Ellipsoidal Poly(fluorene) Nanoparticles

Annika Sickinger  and Stefan Mecking

Polymer nanoparticles with a nonspherical shape are difficult to access and rare. Heterophase Suzuki–Miyaura polycondensation can yield distinct ellipsoidal poly(9,9′-dioctylfluorene) nanoparticles. We reveal the origin of this unusual particle shape by a combination of experimental approaches. Given sufficient chain mobility, enabled by the choice of a suitable organic solvent, also prefabricated oligomers with a DPn ≥ ca. 10 and polymers can form ellipsoidal nanoparticles. This agrees with the finding that high molecular weights are reached very rapidly in the aforementioned polymerizations, despite their step-growth character. Introduction of cross-links during the polymerization disturbs the evolution of nonspherical particles. Overall, the formation of anisotropic particle shapes (as observed by TEM) strongly correlates with the formation of β-phase regimes with an ordered polymer packing in the particles (as observed by UV/Vis absorption and fluorescence spectroscopy).