Synthesis and properties in solution of ruthenium(II) coordination polymers

Synthetic strategies are presented for the preparation of readily soluble ruthenium(II) coordination polymers of high molecular weight. The constitutional homogeneity of the polymers is proved using high-resolution NMR spectroscopy, and their molar masses are estimated from ¹H NMR spectra, viscosity data and SAXS investigations. The polymers are shown to be conformationally rigid, and to form either densely packed coils or rods. It is mainly this difference in shape which causes the very specific properties of the respective polyelectrolytes in the solid state as well as in dilute solution. Finally, the UV-vis absorption spectra of some of these materials are presented.     

Counterion mobility and effective charge of polyelectrolytes in solution

Polyelectrolytes are macromolecules containing dissociable or charged groups. The charge, that is effectively accessible, is determined by counterion condensation, which is strongly influenced by the ionic strength of the solution under study. In general a rapid exchange between free and condensed counterions is expected. In the present study diffusion and electrophoretic mobility of poly(diallyldimethylammoniumchloride) and perfluorinated succinic acid have been monitored simultaneously. Condensation of the perfluorinated succinic acid to the macroion shows in the electrophoretic mobility of succinic acid monitored by pulsed field gradient NMR. In the concentration dependence of the averaged diffusion coefficient and electrophoretic mobility an exchange fast on the time scale of the NMR experiment is manifested.     

Synthesis and solution properties of rodlike polyelectrolytes

The synthesis and the solution behavior of rigid, rodlike cationic polyelectrolytes having (i) poly(p-phenylene) backbones and (ii) main chains composed of 4,4“-bis(2,2′:6′,2”-terpyridine)2′,5′-dihexyl-p-terphenyl moieties and ruthenium(II) centers are presented. All these polymers are shown to have a homogeneous constitution and degrees of polymerization of up to P_n ≈ 70. Their solution properties were analyzed using viscosimetry, small-angle X-ray scattering (SAXS) and osmometry. Pronounced polyelectrolyte effects were found in salt-free solutions using viscosimetry. Small-angle X-ray scattering demonstrated directly the strong correlation of the counterions and the macroions. The osmotic coefficients measured in salt-free solution as function of polyelectrolyte concentration were found to be lower than predicted by the cell model.     

Anomalous viscosity behavior of rodlike polyelectrolytes: Partially sulfonated poly(2-benzoyl-1,4-phenylene)s in aqueous solution

Two stereoisomeric poly(2-benzoyl-1,4-phenylene)s were synthesized. Polymer I has exclusively a head-to-tail structure; however, polymer II contains both head-to-head and head-to-tail units. The sulfonation reaction of polymers I and II was found to occur mainly on the meta position of the benzoyl group on the phenylene backbone. The viscosities of polymers Ia (27% sulfonated) and Ic (51% sulfonated) in aqueous solutions at 25°C were measured with and without NaBr addition. Upon the addition of NaBr (0.05 and 0.1M), the reduced viscosities were found to increase gradually and reach a constant value in each case after standing at room temperature for 30–40 h. Without NaBr, the time effect was not found. The reduced viscosities of solutions with NaBr were also higher than those without the salt. These results are quite different from the typical “polyelectrolyte” behavior. A possible explanation of the salt effect of rigid rodlike polymers such as sulfonated poly(2-benzoyl-1,4-phenylene) is discussed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1425–1429, 1998     

Synthesis and aqueous solution properties of hydrophobically modified anionic acrylamide copolymers

In this investigation, hydrophobically modified polyacrylamide with low amounts of anionic long‐chain alkyl was synthesized by the free radical polymerization in deionized water. This water‐soluble copolymerization method is more convenient compared with the traditional micellar copolymerization methods. The copolymers were characterized using Fourier transform infrared, ¹H NMR, and the molecular weight and polydispersity were determined using gel permeation chromatography. The solution behavior of the copolymers was studied as a function of composition, pH, and added electrolytes. As NaCl was added to solutions of AM/C₁₁AM copolymers or pH was lowered, the shielding or elimination of electrostatic repulsions between carboxylate groups of the C₁₁AM unit lead to coil shrinkage. The steady shear viscosity and dynamic shear viscoelastic properties in semidilute, salt‐free aqueous solutions were conducted to examine the concentration effects on copolymers. In addition, the shear superimposed oscillation technique was used to probe the structural changes of the network under various stresses or shear conditions. We prepared hydrophobically modified polyacrylamide with N‐alkyl groups in the aqueous medium. The advantage of this method is that the production is pure without surfactants. These results suggest that the unique aqueous solution behavior of the copolymers is different from conventional hydrophobically associating acrylamide. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2465–2474, 2008     

Interaction of the low-molecular weight salts with cationic polyelectrolytes

The interaction of several mono-, di-, and trivalent anions with cationic polyelectrolytes having different contents in N,N-dimethyl-2-hydroxypropylen ammonium chloride units (polymer A) or tertiary amine N-atoms and PEG (polymer PEGA) in the main chain was studied by viscosimetric and conductometric measurements. Both methods have shown a stronger interaction for tri- and bi- than for univalent counterions. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2571–2581, 1997     

Diffusion behavior of polyelectrolytes in dilute solution: coupling effects of hydrodynamic and Coulomb interactions

The diffusion behavior of polyelectrolytes in dilute salt-free solution is studied through a hybrid mesoscale simulation technique that combines the molecular dynamics method and the multiparticle collision dynamics approach. To elucidate the effects of hydrodynamic interactions (HI), we compare results for hydrodynamic and random solvents. When HI are taken into account, we find that the chain diffusivity decreases initially and then increases gradually with the increasing strength of the Coulomb interaction. By contrast, when HI are switched off, the electrostatic-dependent diffusivity shows three distinct regions, and a plateau of approximately constant diffusivity manifests between two decreasing regions. The findings reveal that the dynamics of polyelectrolytes in dilute solution depend on the coupling effects of hydrodynamic and Coulomb interactions, and that these dynamics can be understood by considering the conformational changes of chains, the counterion condensation, and the dynamics of counterions.     

Structure and properties of thin films of binary rodlike/flexible polyimide mixtures

Binary mixtures of a rodlike poly(p-phenylene pyromellitimide) (PMDA-PDA) and a flexible 6F-BDAF polyimide synthesized from hexafluoroisopropylidene diphthalic anhydride and 2,2-bis(4-aminophenoxy-p-phenylene) hexafluoropropane were prepared by solution-blending of the meta-PMDA-PDA poly(amic ethyl ester) and 6F-BDAF poly(amic acid) precursors, followed by solvent evaporation and thermal imidization. Mixtures containing different molecular weights of 6F-BDAF poly(amic acid) were studied. The size scale of the phase separation, as measured by light scattering, is ca. 1 μm or smaller in most cases. The domain size is primarily set by the demixing of the precursor polymers during solvent evaporation, with no significant coarsening observed during the thermal imidization. The observed variation of the domain size with molecular and process parameters such as composition, molecular weight, and film thickness is discussed in terms of the miscibility of the precursor polymers, rate of solvent evaporation, and solidification. Dynamic mechanical thermal analysis and dielectric relaxation measurements indicate that the glass transition temperature of 6F-BDAF is unaffected in all of the mixtures studied, indicating complete demixing of rodlike and flexible polyimides in agreement with theory. X-ray photoelectron spectroscopy results show a strong surface segregation of 6F-BDAF in mixtures containing as low as 10% by weight of the 6F-BDAF component in the bulk. The mixtures with PMDA-PDA as the major matrix component therefore exhibit excellent mechanical toughness, dimensional stability up to 500°C, low coefficients of thermal expansion (< ca. 10 ppm/°C), and low dielectric constants (<3.0). On the other hand, the surface properties of the mixtures are dominated by the flexible 6F-BDAF, resulting in excellent polymer/polymer self-adhesion (lamination) properties between fully imidized films.     

Osmotic deswelling of microgels by linear polyelectrolytes

Polyacrylate microgels used as absorbers or viscosifiers in water are known to have these useful qualities reduced in the presence of linear poly-electrolytes. An osmotic deswelling mechanism is postulated whereby the counterions from linear chains sterically excluded from the gel act to draw solvent from the gel phase. This postulate is tested using intrinsic viscosity measurements of Carbopol microgels, made with the linear polyelectrolyte considered as parr of the solvent. The intrinsic viscosity is used to calculate the swollen-to-dry volume ratio for the microgel in the presence or absence of 0.1% linear sodium polyacrylate over a range in ionic strength. Simultaneously, a standard treatment for the free energy of a network of non-Gaussian chains containing fixed charges is modified to include the osmotic effect of the excluded counterions. In the absence of linear polymer, the theory is fit to the data, the fitting parameter being the 3100 monomer units between crosslink sites in the network. In the presence of high (350 000) molecular weight linear polymer, good agreement is found between the observed deswelling and that predicted if the linear chains are totally excluded. Lower molecular weight linear chains are found to give a reduced deswelling which is shown to be self-consistent with their partitioning into the network.Presented in part at the 64th Colloid and Surface Science Symposium, Lehigh University, June 1990     

Synthesis and optical and electroluminescent properties of novel conjugated polyelectrolytes and their neutral precursors derived from fluorene and benzoselenadiazole

Novel copolymers derived from amino‐functionalized fluorene‐ and selenium‐containing heterocycles [2,1,3‐benzoselenadiazole (BSeD)] were synthesized by the palladium‐catalyzed Suzuki coupling method. Their quaternized salt polyelectrolytes of corresponding compositions were obtained by a postpolymerization treatment. The resulting copolymers were soluble in polar solvents. An efficient energy transfer due to exciton trapping on the BSeD sites was observed. Devices from such copolymers emitted orange‐red light peaked at 560–610 nm. All the polymers showed good device performance with high‐work‐function metal Al as a cathode without the use of an additional electron‐injection layer and are promising candidates for polymer light‐emitting diode applications. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2521–2532, 2006     

Conformations and solution structure of polyelectrolytes in poor solvent

Using extensive Molecular Dynamics (MD) simulations we study the behavior of polyelectrolytes in poor solvents, where we take explicitely care of the counterions. The resulting pearl-necklace structures are subject to strong conformational fluctuations, only leading to small signatures in the form factor, which is a severe obstacle for experimental observations. In addition we study how the necklace collapses as a function of Bjerrum length. At last we demonstrate that the position of the first peak in the inter-chain structure factor varies with the monomer density close to for all densities. This is in strong contrast to polyelectrolyte solutions in good solvent.     

Synthesis and solution properties of poly(methacrylate)s with semipolar structures on the side chains

Poly{2‐(N,N‐dimethylamino)ethyl methacrylate [poly(DMMA)]}, which was prepared by radical polymerization initiated with dimethyl 2,2‐azobis(2‐methylpropionate), was reacted with hydrogen peroxide, diethyl sulfate, and chloroacetic acid to yield poly[N,N‐dimethyl‐N‐(2‐methacryloyloxyethyl)amine N‐oxide] [poly(DMANO)], poly[N‐ethyl‐N,N‐dimethyl‐N‐(2‐methacryloyloxyethyl)ammonium ethyl sulfate] [poly(EDMES)], and poly[N,N‐dimethyl‐N‐(2‐methacryloyloxy)ethylammonioacetate] [poly(DMEAA)] as ion‐containing water‐soluble polymers, respectively. The solution properties of these charged polymers were compared via the reduced viscosities of these three charged polymers in aqueous solutions as a function of the concentration. Poly(EDMES) showed typical polyelectrolyte behavior, and the other two polymers [poly(DMANO) and poly(DMEAA)] exhibited antipolyelectrolyte behavior. Furthermore, the antipolyelectrolyte behavior was different for poly(DMANO) and poly(DMEAA); that is, poly(DMANO) was less dependent on small electrolytes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 129–141, 2005     

Synthesis and properties of highly branched polycations with an aliphatic polyether scaffold

Cationic polyelectrolytes with pyridinium and 1,2‐dimethylimidazolium functionalities based on a hyperbranched polyglycerol scaffold with a narrow polydispersity were prepared by a polymer analogous reaction in a one‐pot synthesis. By the variation of the spacer lengths between the cationic functionalities and polyether scaffold, a simple method was developed to adjust the charge density and flexibility of the polycations, as reflected by their glass‐transition temperature. The polyelectrolytes were further characterized in detail by ¹H NMR, ¹³C NMR, and IR spectroscopy, as well as thermogravimetric analysis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4609–4617, 2005     

Separation of polyelectrolyte chain dynamics and dynamics of counterion attachment by EPR spectroscopy

Rotational dynamics and local enrichment of counterions close to polyelectrolyte chains were studied by EPR spectroscopy in solvents of different viscosity. The results confirm previous findings (D. Hinderberger, G. Jeschke, and H. W. Spiess, Macromolecules 2002, 35, 9698) that electrostatic attachment of counterions to the chains is dynamic with lifetimes of contact ion pairs shorter than 1 ns. While in low-viscosity solvents linewidths for a dianionic nitroxide probe and their dependence on polyelectrolyte concentration are dominated by the gradient of local concentration in the vicinity of the chain, they are more strongly influenced by changes in rotational dynamics in a glycerol/water mixture. The slowdown of dynamics at higher viscosity strongly depends on polyelectrolyte concentration, suggesting that the lifetime of the attached state increases. The linewidths of trianionic triarylmethyl probes and of the center line of the nitroxide probes are dominated by local counterion enrichment both at low and high viscosity. Comparison of these linewidths and of the extent to which the lineshapes are non-Lorentzian indicates build-up of larger concentration gradients at higher viscosity.     

Rheological properties of multisticker associative polyelectrolytes in semidilute aqueous solutions

Multisticker associative polyelectrolytes of acrylamide (≈86 mol %) and sodium 2‐acrylamido‐2‐methylpropanesulfonate (≈12 mol %), hydrophobically modified with N,N‐dihexylacrylamide groups (≈2 mol %), were prepared with a micellar radical polymerization technique. This process led to multiblock polymers in which the length of the hydrophobic blocks could be controlled through variations in the surfactant‐to‐hydrophobe molar ratio, that is, the number of hydrophobes per micelle (N_H). The rheological behavior of aqueous solutions of polymers with the same molecular weight and the same composition but with two different hydrophobic block lengths (N_H = 7 or 3 monomer units per block) was investigated as a function of the polymer concentration with steady‐flow, creep, and oscillatory experiments. The critical concentration at the onset of the viscosity enhancement decreased as the length of the hydrophobic segments in the polymers increased. Also, an increase in the N_H value significantly enhanced the thickening ability of the polymers and affected the structure of the transient network. In the semidilute unentangled regime, the behavior of the polymer with long hydrophobic segments (N_H = 7) was studied in detail. The results were well explained by the sticky Rouse theory of associative polymer dynamics. Finally, the viscosity decreased with an increase in the temperature, mainly because of a lowering of the sample relaxation time. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1640–1655, 2004     

Electrophoretic evidence for a new type of counterion condensation

A systematic capillary electrophoresis study uncovered how polyelectrolyte effective charge density varies with backbone charge spacing and solvent dielectric constant. The study primarily focused on aliphatic ionenes, a special class of polyelectrolytes, which possess regularly spaced quaternary ammonium groups in the backbone. Complete ionization of functional units and good solvency in water or mixtures of water with lower dielectric constant solvents (methanol, acetonitrile) enabled continuous measurements of ionene effective charge density through the onset of counterion condensation. Ionenes with both uniform and alternating charge spacing were examined. As expected, effective charge density rose linearly with fixed charge density to a critical value, above which effective charge density remained constant. Deviating from expectation, the onset of condensation did not occur at a critical fixed charge density. Instead, condensation initiated at a constant critical Bjerrum length. The same onset condition was found for quaternized poly(vinyl pyridine)s. These experimental results suggest a new form of condensation, one driven by ion-pairing of polyelectrolyte with counterions. In support of this hypothesis, the onset of condensation appeared to correlate with counterion size. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3616–3627, 2004     

Liquid crystalline complexes of an azo-containing surfactomesogen with oppositely charged polyelectrolytes

A triethyl-ammonium functionalized 4-nitro-4′-alkoxy azobenzene mesogen with a 10-carbon spacer (azo10Q, a ‘surfactomesogen’) was complexed in equimolar proportions to a variety of oppositely charged polyelectrolytes, and studied by differential scanning calorimetry (DSC), polarizing optical microscopy, and X-ray diffraction. The complexation generates a single-layer smectic A mesophase over a very wide temperature range from a surfactomesogen that, alone, melts directly to the isotropic phase. The clearing temperatures, ranging from 130 to 190 °C and generally higher than the melting point of azo10Q, are dependent on the nature of the polyelectrolyte as well as its molecular weight. In contrast, a prominent glass transition near ambient temperature appears to be independent of molecular weight, but varies somewhat with the type of polyelectrolyte. A second T_g-like transition of much lower intensity is detectable at higher temperatures (generally above 100 °C), and, with literature support, is tentatively attributed to nanophase separation involving sublayer planes in the lamellar packing structure. A series of nonequimolar complexes was also investigated, and it was found that, with decreasing azo10Q content, the clearing temperature viewed by DSC decreases rapidly in intensity (and somewhat in temperature) and then disappears although birefringence remains, whereas the lower glass transition increases rapidly in temperature to finally merge with the upper one. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3421–3431, 2005     

Aromatic and rigid rod polyelectrolytes based on sulfonated poly(benzobisthiazoles)

Aromatic polyelectrolytes based on sulfonated poly(benzobisthiazoles) (PBTs) have been synthesized by a polycondensation reaction of sulfo-containing aromatic dicarboxylic acids with 2,5-diamino-1,4-benzenedithiol dihydrochloride (DABDT) in freshly prepared polyphosphoric acid (PPA). Several sulfonated PBTs, poly[(benzo[1,2-d:4,5-d′]bisthiazole-2,6-diyl)-2-sulfo-1,4-phenylene] sodium salt (p-sulfo PBT), poly[(benzo[1,2-d:4,5-d′]bisthiazole-2,6-diyl)-5-sulfo-1,3-phenylene] sodium salt (m-sulfo PBT), their copolymers, and poly[(benzo[1,2-d:4,5-d′]bisthiazole-2,6-diyl)-4,6-disulfo-1,3-phenylene] potassium salt (m-disulfo PBT), have been targeted and the polymers obtained characterized by ¹³C-NMR, FT-IR, elemental analysis, thermal analysis, and solution viscosity measurements. Structural analyses confirm the structures of p-sulfo PBT and m-disulfo PBT, but suggest that the sulfonate is cleaved from the chain during synthesis of m-sulfo PBT. m-Disulfo PBT dissolves in water as well as strong acids, while p-sulfo PBT dissolves well in strong acids, certain solvent mixtures containing strong acids, and hot DMSO. TGA indicates that these sulfonated PBTs are thermally stable to over 500°C. Free-standing films of p-sulfo PBT, cast from dilute neutral DMSO solutions, are transparent, tough, and orange in color. Films cast from basic DMSO are also free standing, while being opaque and yellow-green. p-Sulfo PBT was incorporated as the dopant ion in polypyrrole, producing conductive films with conductivities as high as 3 S/cm and electrical anisotropies as high as 10. © 1996 John Wiley & Sons, Inc.     

Conjugated polyelectrolytes and neutral polymers with poly(2,7‐carbazole) backbone: Synthesis,characterization, and photovoltaic application

Poly(2,7‐carbazole) neutral polymers (PC‐N, PC‐NOH, and PC‐P) and polyelectrolytes (PC‐NBr and PC‐SO₃Na) with hydrophilic pendant groups of ammonium, phosphonate, and sulfonate were synthesized as interlayers for cathode modifications in bulk‐heterojunction photovoltaic cells (BHJ PVCs). The absorptions of the polymers were determined by the poly(2,7‐carbazole) backbone, showing absorption peaks at ～390 nm for their solutions and films. Because of large intermolecular interactions, excimer emissions with wavelengths higher than 500 nm were found in the photoluminescence spectra of the films of the polymers, which weakened the light emissions of the polymers. PC‐N, PC‐NBr, PC‐NOH, and PC‐P possessed comparable HOMO levels of ?5.23 eV and LUMO levels of ?2.4 eV, but HOMO and LUMO levels of PC‐SO₃Na were up‐lying to ?4.91 and ?2.12 eV, respectively. PC‐N, PC‐NBr, PC‐NOH, and PC‐P were selected to construct thin interlayers in BHJ PVCs with PFO‐DBT35:PCBM = 1:4 as the active layer. Compared with traditional Al cathode, bilayer cathodes with the interlayers showed improvements of open‐circuit voltages and short‐circuit currents of the PVCs. PC‐NOH was the best for the photovoltaic performances and over 20% increase of power conversion efficiency (PCE) was achieved. The bilayer cathodes would have great potential to further elevate PCE of BHJ PVCs with other active layer materials. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011