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A series of fluorene-based copolymers containing hole blocking/electron transporting diphenyloxadiazole units were synthesized by means of Suzuki-Miyaura coupling of selected aromatic dibromo- and diboronato- derivatives catalyzed with a Pd(PPh3)4 catalyst. All of the copolymers with various composition of main-chain units were characterized by SEC chromatography, NMR, UV–vis, fluorescence and IR spectroscopy, and DSC. The emission stability of fluorene copolymers was improved by the replacement of alkyl groups on the C-9 carbon of fluorene with aryl groups or by the incorporation of anthracene units into the copolymer main chain. A comparison of luminescence properties of pristine and annealed thin layers of studied copolymers was performed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4532–4546, 2009

Organic photovoltaic (PV) cells composed of a perylene derivative, N , N ′-di(pentan-3-yl)-perylene-3,4:9,10-bis(dicarboximide), PTCDI, acting as an acceptor and a π-conjugated polymer poly{1-phenyl-2-[4-(trimethylsilyl)phenyl]acetylene}, PDPA, acting as a donor of photogenerated free electrons are presented. Two types of starting double-layer samples were prepared: samples I composed of a spin-cast PDPA thin film bottom layer and a PTCDI upper layer deposited by the vacuum sublimation, and samples II composed of a spin-cast mixed PDPA/PTCDI layer and a vacuum-sublimation deposited PTCDI upper layer. The samples were treated with toluene vapors to induce changes in the morphology of heterojunctions due to recrystallization of PTCDI, which have been monitored by the optical absorption spectra and AFM images, and the influence of the morphology changes on photovoltaic characteristics of the samples has been studied. A short-time (2–5 min) toluene-vapor treatment positively influences the PV efficiency of system I due to a formation of larger PTCDI crystals, which improves the collection efficiency of the upper layer. However, a longer-time treatment of a system I results in a decrease in its PV efficiency owing to a significant decrease in the PDPA–PTCDI interfacial area accompanying further growth of PTCDI crystals, which lowers the photogeneration efficiency of the system. A combination of molecularly dissolved (in PDPA) and crystalline PTCDI in the system II has been proved to provide better PV efficiency due to a combination of improved free charge carrier photogeneration in the composite bottom layer and the collection efficiency of charge carriers of the upper layer.

The stabilizing effect of Au nanoparticles on electrical conductivity of poly(3-octylthiophene-2,5-diyl) based composite films was investigated. For the content of Au nanoparticles 1 vol %, the turning point where the conductivity starts to decrease, shifts to 110°C, compared with 50°C for the neat polymer. At low temperatures, the composites show the common activation energy of conductivity E a = 0.3 eV independent of the Au nanoparticle concentration. It corresponds to the activation energy of neat polymer and suggests that the conductivity of the composite is controlled by the same mechanism.

A two-phase method has been adapted for the preparation of polymer composites consisting of regioregular poly(3-octylthiophene-2,5-diyl) and Au or Ag nanoparticles. This work compares optical and morphological properties of nanocomposites formed by mixing metal organosols and polymer solution (type I composites) with nanocomposites formed by in-situ reduction in polymer solutions (type II composites). Both types contained very small metal nanoparticles (1-10 nm). Interestingly, more than ten-fold enhancement of Raman scattering of the polymer by the electromagnetic (EM) mechanism of SERS (surface-enhanced Raman scattering) resulted from the coupling of the polymer with plasmonic Au nanoparticles into a nanocomposite system.

A new series of associating polymers were prepared by grafting highly hydrophobic side chains: poly( n -butyl acrylate), PNBA ; poly( n -butyl methacrylate), PNBMA ; and poly( N -( tert -butyl)acrylamide), PTBA of different sizes onto a poly(sodium acrylate), PAANa , backbone. Due to the strong hydrophobic character of the stickers, the dynamics of the associations is very slow as compared to more conventional water-soluble polymers modified with short alkyl chains and the physical associations mainly behave as chemical ones in the experimental conditions. As a consequence, all the copolymers readily self-assemble in aqueous solution forming clusters in very dilute conditions and then gels at higher concentrations. From dynamic measurements, it was shown that the copolymer solutions follow the same scaling relation η ∗ ∼ c a , where a is a frequency dependent exponent. In these conditions, all the copolymer solutions exhibit a sol–gel transition which obeys the main rules of the percolation theory. For each copolymer, the critical gel concentration c g depends strongly on the hydrophobic character of the stickers and a single master curve can be drawn by plotting the complex viscosity vs. the reduced concentration, c / c g . Although the temperature dependence of the viscoelastic properties is very weak, due to the slow dynamics of the associations, it was clearly evidenced that the alkyl acrylamide derivative (PAANa- g -PTBA) exhibits a slight thermothickening behavior which contrasts with the thermothinning behavior of alkyl(meth)acrylate derivatives (PAANa- g -PNBA and PAANa- g -PNBMA). The opposite type of behavior is explained by the presence of the amide function which is known to play an important role in the LCST (lower critical solution temperature) phase diagram of N -alkyl derivatives.

The solution behavior and self-assembly of a ‘hairy’ heteroarm star copolymer polystyrene/poly(2-vinylpyridine) containing 20 fairly short polystyrene and 20 long poly(2-vinylpyridine) arms was studied in 1,4-dioxane–methanol mixtures and in acidic aqueous solutions. The copolymer forms reversible micelles in 1,4-dioxane–methanol mixtures. Since the conformation of the unimolecular heteroarm star (unimer) with collapsed insoluble PS arms and stretched soluble PVP arms resembles the spherical core/shell micelle, the solubility of the copolymer in the selective solvent is fairly high and the multimolecular micelles are formed by only few heteroarm stars. Both heteroarm stars (in pure 1,4-dioxane) and micellar systems (composed of both micelles and unimolecular heteroarm stars (unimers) in 1,4-dioxane–methanol mixtures) may be transferred in acidic aqueous media by dialysis. Polyelectrolyte behavior of unimer stars was studied in detail in acidic aqueous media. Static and dynamic light scattering measurements show that heteroarm stars interact electrostatically over long distances in low ionic strength solutions. Experimental data indicate that the charged stars may form temporary shell interacting (electrostatically stabilized) aggregates at elevated concentrations.

Self-assembling properties of poly(sodium acrylate) grafted with dodecyl [C12], PAAgC12, or poly(N-isopropylacrylamide) [PNIPA] side chains, PAAgPNIPA, were studied in unentangled semidilute aqueous solution. While PAAgC12 self-associates through hydrophobic interactions, the gelation of PAAgPNIPA is triggered by heating in response to the lower critical solution temperature of PNIPA (LCST ∼ 32 °C). The local structure of the physical networks was investigated by small-angle neutron scattering, and the scattering patterns were described using a polydisperse sphere model taking into account hard-sphere interactions. This model allow us to draw a realistic picture of physical gels with quantitative information concerning the size of hydrophobic cores, the volume fraction of stickers in the aggregates, the fraction of stickers which take part in the aggregation process, the range of repulsive interactions, and the structural modifications induced by temperature. The description of the network is in good agre...

The polyelectrolyte behavior of kinetically frozen multimolecular polystyrene-block-poly(methacrylic acid), PS−PMA, micelles has been studied in detail by a combination of light scattering, fluorescence correlation spectroscopy, and atomic force microscopy and by conductometry in aqueous solutions at low ionic strength. Experimental studies reveal important intermicellar electrostatic interactions. The experimental data are interpreted with help of computer studies, which combine mechanistic lattice Monte Carlo simulations and indirect treatment of electrostatic forces. The shell is modeled as a brush of self-avoiding chains tethered to the micellar core. Electrostatic interactions are obtained by solving the Poisson−Boltzmann equation.

Hybrid polymeric micelles with compact polystyrene cores (PS) and mixed poly(methacrylic acid)/poly(ethylene oxide) shells (PMA/PEO) were prepared by mixing PS−PMA and PS−PEO linear diblock copolymer samples in 1,4-dioxane (80 vol %)/water. The mixture is a mild selective precipitant for PS and micelles with swollen PS cores, and either PMA or PEO shells form in both systems before mixing. Both types of micelles coexist in a mobile equilibrium with unimers and, because PMA and PEO are fairly compatible, hybrid micelles PS−(PMA/PEO) form spontaneously after mixing the individual micellar solutions. Hybrid micelles differing in the composition of the mixed shell were stepwise dialyzed into aqueous buffers. In aqueous media, the unimer−micelle equilibrium is kinetically frozen and the micelles behave as independent polymeric nanoparticles with glassy PS cores and mixed polyelectrolyte/nonelectrolyte shells. A number of experimental techniques (size-exclusion chromatography, capillary zone electrophoresis, an...

Polyelectrolyte behavior of the inner part of poly(methacrylic acid) shell and microscopic properties of the interface between the hydrophobic core and the hydrophilic shell in polystyrene-block-poly(methacrylic acid) micelles were studied by UV−vis spectroscopy and by the steady-state and time-resolved fluorometry using two fluorescent probes, 5-(N-octadecanoyl)aminofluorescein (OAF) and 5-(N-dodecanoyl)aminofluorescein (DAF). Two almost identical copolymer samples of polystyrene-block-poly(methacrylic acid), PS-PMA and PS-DPA-PMA, were used in the study, except that the latter was fluorescently tagged between blocks by a pending p-vinyl-9,10-diphenylanthracene group (DPA), which allows also for studying the OAF binding in the interfacial region by means of nonradiative energy transfer from DPA to fluorescein head-groups of either OAF or DAF. Pronounced shifts in pKa of both OAF and DAF, which were observed after binding to polymeric micelles, are explained by a competition of two effects. The first effe...