Synthesis and electron transporting properties of triblock copolymers consisting of polyfluorene and polystyrene
Jin Cheng, Shinji Kanehashi, Kenji Ogino
Abstract
Abstract 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.