Synthesis and electron transporting properties of triblock copolymers consisting of polyfluorene and polystyrene

For the improvement of the electron transporting property of poly(9,9-di- n -octylfluorene) (PFO) as a conventional polymer light-emitting diode material, well-defined triblock copolymers of PFO [number-average molecular weight ( M n ) ≈ 10 000] with different chain length polystyrene (PSt) ( M n ≈ 1000, 2000, and 3000) were synthesized via a combined synthesis strategy of Suzuki–Miyaura reaction, atom transfer radical polymerization, and Steglich coupling reaction. Electron-only devices for homopolymer and triblock copolymers were fabricated by a solution process. It was demonstrated that triblock copolymer ( M n,PSt ≈ 2000) after annealing exhibited the highest electron mobility. Thermal, optical, electrochemical and morphological properties were investigated severally and revealed that the microphase separated structure was formed in block copolymers ( M n,PSt ≈ 2000, and 3000) after annealing, and the introduction of PSt raised the glass transition temperature ( T g ) and deepened the lowest unoccupied molecular orbital level.