Synthesis, Electron Transport Behavior, and Enhanced Blue Light Stability of Polyfluorene-Poly(Methyl Methacrylate) Diblock Copolymers

Poly(9,9-di-n-octylfluorene) (PFO) suffers from interchain aggregation, which degrades its blue spectral stability and charge transport. To address this, a series of rod-coil diblock copolymers (PFO-b-PMMAs) with varying poly(methyl methacrylate) (PMMA) chain lengths were synthesized via Steglich coupling. The non-conjugated PMMA blocks act as bulky steric spacers in the solid state, effectively suppressing detrimental PFO aggregation and enhancing pure blue emission stability. Furthermore, moderate PMMA blocks (PFO-b-PMMA1 and PFO-b-PMMA2) promote favorable β-phase formation and ordered crystalline packing. This microstructural optimization yields a maximum electron mobility of 1.98 × 10−6 cm2/(V·s) for PFO-b-PMMA2, markedly higher than the PFO-2 homopolymer (4.13 × 10−7 cm2/(V·s)). However, an overlong PMMA block (PFO-b-PMMA3) introduces excessive steric hindrance (Tg = 66 °C) that disrupts crystallization, acting as an insulating barrier that reduces mobility. Thus, precisely tuning the non-conjugated block length effectively maximizes both the blue spectral stability and electron transport capabilities of PFO-based materials.