Living Anionic Polymerization of Styrene Derivatives para-Substituted with π-Conjugated Oligo(fluorene) Moieties

The anionic polymerization of styrene monomers para-substituted with π-conjugated mono-, di-, and tri(9,9-dihexylfluorene) moieties, St-Fl, St-Fl₂, and St-Fl₃, was examined under the conditions either in THF at −78 °C or in tert-butylbenzene at 20 °C with sec-BuLi as an initiator. The polymerization of both St-F_l and St-Fl₂ was found to proceed in a living manner to quantitatively afford the corresponding polymers with predictable molecular weights and narrow molecular weight distributions (M_w/M_n < 1.08). The anionic polymerization of St-Fl₃ was also indicative to proceed in a living manner but with an unpredictable molecular weight. Both AB and BA diblock copolymers with the well-defined and expected structures could be successfully prepared by the sequential addition of St-Fl or St-Fl₂ followed by styrene and vice versa. The block copolymerization results clearly indicate the living nature of the anionic polymerization of St-Fl and St-Fl₂ and the almost same anionic polymerization behaviors of both monomers as styrene in reactivities of monomer(s) and propagating chain-end anion(s). Solubilities, intrinsic viscosities, and glass transition temperatures of the poly(St-Fl) and poly(St-Fl₂) herein prepared were measured. The optical absorption and luminescence spectra of the studied polymer films showed well-resolved vibronic structures and the peak maxima was progressively increased as the fluorene chain length increased. The luminescence spectra also showed reduced aggregation/excimer emission in comparison with that of parent polyfluorene. The present study suggests that living anionic polymerization could be employed to polymerize other styrene derivatives with π-conjugated moieties in a controlled manner and such polymers may exhibit precisely defined physical properties.