Molecular Weight Induced Conformational Change and Its Impact on β-Phase Formation of Polydiarylfluorene in Dilute Solution

Polyfluorene derivatives have a characteristic conformation called the “β-phase,” with localized strong chain extension. Despite abundant research, the formation mechanism has not been fully clarified, particularly in the solution state. Using a gel permeation chromatography-static light scattering-viscometer integrated system, we investigated the β-phase formation mechanism of polydiarylfluorene (PODPF) in dilute solution. The formation was found to be sensitive to the molecular weight; it was significantly enhanced with lower molecular weight in a poor solvent. Molecular association was evident among the polymers that evinced prominent β-phase formation. Molecular weight induced conformational change (from rod-like to coil) was observed in the PODPF with increasing molecular weight. The conformational transition point lay at a rather high molecular weight, around 30 000, indicating that rod-like conformation in the lower molecular weight region enhances molecular association, resulting in the β-phase formation.