Wolfgang H. Meyer

Proton mobility in oligomer-bound proton solvents: imidazole immobilization via flexible spacers

Abstract A completely new approach for obtaining high proton conductivity in polymers based on proton solvating heterocycles covalently bound via flexible spacers is presented. Imidazole-terminated ethyleneoxide (EO) oligomers as model materials have been characterized with respect to their conductivity by ac impedance spectroscopy and with respect to 1 H- and 19 F-diffusion coefficients by pulsed magnetic field gradient-NMR (PFG-NMR). Comparison of conductivity and NMR diffusion coefficients of pure and acid doped materials shows ‘structure diffusion’ (intermolecular proton transfer and structural reorganization by hydrogen bond breaking and forming processes) to be the dominant conduction process, which gives rise to proton conductivities of up to 5×10 −3 S cm −1 at 120°C in completely waterfree materials.

Proton conducting blends of poly(4-vinylimidazole) with phosphoric acid

The synthesis, thermal, and conduction properties of blends prepared from poly(4-vinyl-imidazole), P-4VI, and phosphoric acid are reported. The number of moles of phosphoric acid per polymer repeat unit, x, was varied from 0≤x≤2. These blends can be cast into homogeneous films. Thermogravimetric analysis (TGA) illustrates that these blends are chemically stable up to about 150°C. Differential scanning calorimetry (DSC) shows that the softening temperature of the blends decrease from 77°C for x=1 to −8°C for x=2. The DC conductivity increases with x and reaches ∼10−4 S/cm for x=2 at ambient temperature.

Proton-conducting polymer electrolytes based on phosphoric acid

Abstract The synthesis, thermal, mechanical and conduction properties of blends of a cationic polyelectrolyte, poly(diallyldimethylammonium-dihydrogenphosphate), ‘PAMA + H 2 PO 4 − ’, and phosphoric acid are reported. Blends of ‘PAMA + H 2 PO 4 − x H 3 PO 4 ’ with 0.5≤ x ≤2.0 can be cast into amorphous films, which are stable up to 150°C. DSC results show that the softening temperatures of the blends decrease from 126°C for x =0.5 to −23°C for x =2.0. The dc conductivity increases with x and reaches 10 −4 S/cm at ambient temperature and 10 −2 S/cm at 100°C for PAMA + H 2 PO 4 − 2H 3 PO 4 . The 1 H- and 31 P-self-diffusion coefficients of PAMA + H 2 PO 4 − x H 3 PO 4 for x =1,2 were determined by PFG-NMR. D (H) is always at least one order of magnitude larger than D (P) , which means that inter-phosphate H + transfer plays an important role in the samples. D (H) coincides quite well with the conductivity diffusion coefficient D σ which is obtained from the conductivity data via the Nernst–Einstein relationship, assuming that the charge carrier concentration is equal to the repeat unit concentration. Since with the same assumption the charge carrier concentration is only (3 x +2) −1 times the concentration of all the phosphate protons, the result D σ / D (H) ≈1 is rather surprising and indicative of cooperative proton transfer which does not contribute to the conductivity. D (H) / D (P) in the blends is much larger than D (H) / D (P) in pure phosphoric acid. This means that the phosphate moieties are considerably more immobilized in the blends as compared to H 3 PO 4 . This immobilization effect is more pronounced in blends with low phosphoric acid content and decreases with increasing temperature.

Proton Conductivity in Acid-Blended Poly(4-vinylimidazole)

The temperature and pressure dependent conductivities of poly(4-vinylimidazole) (P4VI) blended with H 3 PO 4 or H 2 SO 4 have been studied. The influence of the temperature on the conductance and activation volume is discussed. The temperature dependent conducti samples in the glassy state can be fitted with a simple Arrhenius relation. The logarithm of relative conductance for P4VI blended with H 3 PO 4 decreases linearly with increasing pressure. With decreasing temperature the conductance decrease becomes more pronounced. It is proposed that the proton transport in P4VI with low acid concentrations is mainly controlled by a proton hopping mechanism. At high acid levels the proton transport is controlled by both proton hopping and segmental motion of the polymer. The glass transition marks a change in the proton transport mechanism, which is also reflected in the abnormal behavior of the activation volume of the conductance. The conductivities of P4VI blended with H 3 PO 4 and H 2 SO 4 are compared. The conductivity of H 3 PO 4 blended P4VI is lower than that of H 2 SO 4 blended P4VI at the same acid concentrations.

Micelle formation of poly(acrylic acid)-block-poly(methyl methacrylate) block copolymers in mixtures of water with organic solvents

The micelle formation of poly(acrylic acid)-block-poly(methyl methacrylate) (AA-MMA) block copolymers in mixtures of water with organic solvents was investigated by non-radiative energy transfer (NRET). In the case of block copolymers with 70 hydrophobic MMA units, which form strongly aggregated micelles in pure water, the addition of a non-selective organic solvent (methanol or 1,4-dioxane) induces a micelle-unimer transition within a relatively small range of solvent composition without significantly increasing the rate of chain exchange between micelles close to this transition region. The addition of 2 vol.-% dimethyl adipate (a solvent with chemical similarity to the PMMA block and only limited solubility in water) does not speed up the chain exchange in this system either. In contrast, this solvent promotes the aggregation of smaller block copolymers (20 or 40 MMA units) which are mainly present as single chains in pure water. In the case of the block copolymer with 40 MMA units the so formed micelles show a very slow chain exchange extending over many days. These observations prompt us to assume that the rate of the micelle-unimer exchange equilibrium is not kinetically hindered (i.e., determined by the T g of the core material of the micelle) but controlled by a strong thermodynamic preference for the aggregated state.

The local free volume, glass transition, and ionic conductivity in a polymer electrolyte: A positron lifetime study

The size of free-volume holes in neat poly[(ethylene glycol)23dimethacrylate] [poly((EG)23DMA)] and in the same polymer doped with 0.6 mol/kg LiCF3SO3 have been studied as a function of temperature in the range between 100 and 370 K using positron annihilation lifetime spectroscopy. The results are compared with differential scanning calorimetry and ionic conductivity measurements. In both systems, the hole volume νh shows a typical glass-transition behavior, i.e., a small linear increase with temperature below the glass transition temperature Tg and a steeper increase above Tg. From these measurements Tg was estimated to be 233 K (neat polymer) and 240 K (polymer with salt) and the coefficients of the thermal expansion of the hole volume were determined. The fractional free volume (f=0.080) and the number density of holes (Nh=0.6 nm−3) were also estimated. Below Tg the average hole volume of the polymer electrolyte is larger than in the neat polymer. This is consistent with the bulky character of the CF3...

Nafion ® Membranes: Molecular Diffusion, Proton Conductivity and Proton Conduction Mechanism

H-PFG-NMR diffusion and proton conductivity data for NAFION ® 117 is presented as a function of temperature and water content. From this, H 2 O diffusion on a molecular scale is concluded to be similar to the one in bulk water. But “geometrical” restrictions of diffusion lead to a decreasing pre-exponential factor, i.e. decreasing macroscopic diffusion coefficient with decreasing water content. It is shown that proton conductivity is correlated with water diffusion for low degrees of hydration (vehicle mechanism). With increasing hydration there is an increasing contribution from “structure diffusion” culminating in an amplification factor of A = 2.5 for fully hydrated protonic NAFION ® 117 at room temperature. The bonding of water in NAFION ® as well as the local environment (hydration) of the acidic proton are concluded to be similar as in acidic aqueous solutions.

Polypyrrole for use in information storage

Abstract It is shown that conducting polypyrrole can be used for information storage if the information is stored in the form of a surface relief pattern. The preparation of the film with the relief pattern as well as the expected storage time of the information are also briefly discussed.

Thermal and dielectric properties of glassy ionenes

Abstract Poly[(dialkylimino)alkylene] salt (‘ionenes’) −[−( CH 2 ) N − N ( R ) 2 −] n q.n.X where m = 6 or 10, R = CH3 or CH2CH3 and X = monovalent (q = 1) or bivalent (q = 0.5) counterions, form amorphous glassy films when quenched from the melt or cast from solution followed by rapid evaporation of the solvent. The glass transition temperature, Tg, was found to be between 295 and 350 K depending on the structure of the polymer and the type of counterion. The dielectric properties were studied in the frequency range 10–107 Hz and in the temperature range − 170

Block copolymer micelles as seed in emulsion polymerization

The size of aggregates formed by poly(acrylic acid)-block-poly(methyl methacrylate) block copolymers was determined and the applicability of these block copolymers as stabilizers in emulsion polymerization was investigated. The analytical methods included transmission electron microscopy, light scattering, and analytical ultracentrifugation. Polymers with a hydrophilic poly(acrylic acid) block of equal or larger size than the hydrophobic poly(methyl methacrylate) block are efficient as stabilizers down to block copolymer-to-monomer ratios of less than 1 wt.-%. From the influence of the block copolymer-to-monomer ratio on the latex particle size, from the relation between the number of block copolymer molecules per latex particle and the aggregation number of the block copolymer micelles, and from fluorescence studies we conclude that micelles consisting of block copolymers with 35 or more hydrophobic MMA units act as a seed in the emulsion polymerization of acrylic and methacrylic monomers.