Influence of the coil block on the properties of rod-coil diblock copolymers with oligofluorene as the rigid segment

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 (H-1 NMR, GPC), optical (UV, photo-luminesence), 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 degreesC 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.