Controlled formation of the β-phase in poly(9,9-dioctylfluorene) by blending with low-molecular-weight polystyrene

Abstract

The poly(9,9-dioctylfluorene) (PFO) solid film exhibits various phases including disordered α-phase and well-ordered β-phase. Especially, the formation of the β-phase in PFO is crucial for enhancing its carrier transport properties. Recently, the β-phase conformation of the PFO chains was reported to be formed by blending PFO with polystyrene (PS). Here, the weight-average molecular weight (Mw) of PS was investigated to clarify the formation mechanism of the β-phase conformation in a PFO:PS blend film. The β-phase conformation was formed only when PFO was blended with low-Mw PS. The temperature for the formation of the β-phase in the PFO:PS blend film was likely to be reduced to near room temperature owing to the thermal properties of low-Mw PS. Furthermore, we demonstrated that the amount of conformational change and the content of β-phase of the PFO chains in the PFO:PS blend film can be controlled by adjusting the blending ratio of low-Mw PS.