Influence of the Coil Block on the Properties of Rod−Coil Diblock Copolymers with Oligofluorene as the Rigid Segment

Abstract

Rod−coil diblock copolymers of 2-hydroxyethyl methacrylate (HEMA) with well-defined oligofluorene initiator were synthesized using the atom transfer radical polymerization (ATRP) technique. The resulting copolymers were characterized using spectroscopic (1H NMR, GPC), optical (UV, photoluminesence), and thermal (DSC) techniques. The incorporation of the initiator into the polymeric chain was confirmed by spectroscopic methods, while strong evidence for microphase separation was obtained both from DSC and AFM. A detailed AFM study of the surface morphology in thin films was performed using rod−coil diblock copolymers having different flexible blocks, namely HEMA and polystyrene. Common solvents for both rod and coil blocks were used as a function of the solutions concentration of the diblock copolymers. By increasing the concentration of a selective solvent, formation of either islands, a stringlike morphology, and honeycomblike structures was observed. The optical properties of the HEMA copolymers from THF solution show no change in the emission spectra as we move from solution to the solid state. However, when ethanol was used as a solvent, a red shift of 10 nm was observed going from solution to the solid state, which is a strong indication for phase separation and organization of the diblock copolymers in alcoholic solutions. Annealing of the copolymers at 160 °C for 30 min resulted in green light emission due to the appearance of a new band at 535 nm in the case of OFPHM 6.0, while when polystyrene was used as coil block in OFPS copolymer pure blue light is emitted even after this treatment.

About Supramolecular Assemblies of π-Conjugated Systems

“…The polymers can be applied in LEDs displaying stable blue light emission, Figure 25. 192 Stupp et al reported the synthesis and characterization of triblock rod-coil molecules 74-78 consisting of diblock coil segments of polystyrene and polyisoprene and oligo(p-phenylenevinylene)s (OPVs) as rod segments. On the basis of TEM and X-ray diffraction data, 75-78 formed self-organized nanostructures ( Figure 26) whereas 74 lacked any order, showing that π aggregation of OPV units is not the dominant factor in the self-assembly process.…”

Polyfluorenes

“…Rod-coil block copolymers consisting of conjugated segments connected with flexible segments have been the subject of extensive studies because of their unusual morphologies and photophysical behavior in both solution and solid state [171][172][173][174][175][176]. For this kind of block copolymers, a combination of complementary virtues from both rod and coil blocks can be envisioned.…”

Fluorene-based macromolecular nanostructures and nanomaterials for organic (opto)electronics

“…The increase in solvent polarity and evaporation rate causes an increase in nanoribbon dimensions. Oligo-or PF-based rod-coil diblock copolymers of PF-37-42 have been observed to form nanowires and nanofibres with widths of several 10 nm, and chain packing in the assembled entities has been studied by AFM, XRD and theoretical modelling [244,245,[259][260][261][262][263][264][265]. Rod-coil co-PFs of PF-42 enable morphological transformation through the variation of coil-segment fractions and the amount of immiscible solvent [246] Recently, nanowire thin films have been obtained via nanoscale phase separation of fully conjugated block copolymers such as PF-28, 29 [266].…”