Synthesis and characterization of poly(vinylphosphonic acid) for proton exchange membranes in fuel cells

Vinylphosphonic acid (VPA) was polymerized at 80 ºC by free radical polymerization to give polymers (PVPA) of different molecular weight depending on the initiator concentration. The highest molecular weight, Mw, achieved was 6.2 x 104 g/mol as determined by static light scattering. High resolution nuclear magnetic resonance (NMR) spectroscopy was used to gain microstructure information about the polymer chain. Information based on tetrad probabilities was utilized to deduce an almost atactic configuration. In addition, 13C-NMR gave evidence for the presence of head-head and tail-tail links. Refined analysis of the 1H NMR spectra allowed for the quantitative determination of the fraction of these links (23.5 percent of all links). Experimental evidence suggested that the polymerization proceeded via cyclopolymerization of the vinylphosphonic acid anhydride as an intermediate. Titration curves indicated that high molecular weight poly(vinylphosphonic acid) PVPA behaved as a monoprotic acid. Proton conductors with phosphonic acid moieties as protogenic groups are promising due to their high charge carrier concentration, thermal stability, and oxidation resistivity. Blends and copolymers of PVPA have already been reported, but PVPA has not been characterized sufficiently with respect to its polymer properties. Therefore, we also studied the proton conductivity behaviour of a well-characterized PVPA. PVPA is a conductor; however, the conductivity depends strongly on the water content of the material. The phosphonic acid functionality in the resulting polymer, PVPA, undergoes condensation leading to the formation of phosphonic anhydride groups at elevated temperature. Anhydride formation was found to be temperature dependent by solid state NMR. Anhydride formation affects the proton conductivity to a large extent because not only the number of charge carriers but also the mobility of the charge carriers seems to change.Vinylphosphonsäure (VPA) wurde bei 80 °C durch freie radikalische Polymerisation polymerisiert. Es wurden Polymere (PVPA) mit verschiedenen Kettenlängen erhalten. Das höchste Molekulargewicht, Mw, das erreicht wurde, war 6.2x104 g/mol, das mittels statischer Lichtstreuung bestimmt wurde. Hochauflösende NMR-Spektroskopie wurde verwendet, um Informationen über die Mikrostruktur der Polymerketten zu erhalten. Die Analyse der verschiedenen Tetraden ergab, daß die hochmolekularen Polymere eine ataktische Struktur aufweisen. 13C-NMR Untersuchungen zeigten die Gegenwart von Kopf-Kopf und Schwanz-Schwanz Verknüpfungen. Der Anteil dieser Verknüpfungen wurde mit 23.5 % durch eine detallierte Analyse der 1H-NMR Spektren bestimmt. Die Analyse der Polymeren ergab ferner, daß es sich um eine Zyklopolymerisation des Vinylphosphonsäureanhydrids als Zwischenprodukt handelt. Mittels Titrimetrie wurde bestimmt, daß sich hochmolekulare PVPA wie eine monoprotische Säure verhält. Protonenleiter mit Phosphonsäuregruppen sind vielversprechend, weil sie eine hohe Konzentration an Ladungsträgern besitzen, thermische Stabilität aufweisen und oxidationsstabil sind. Mischungen und Copolymeren von PVPA sind in der Literatur bekannt, jedoch wurde PVPA bisher nicht ausreichend charakterisiert. Deswegen haben wir das protonenleitende Verhalten einer gut charakterisierten PVPA-Probe erforscht. Grundsätzlich ist PVPA leitend, wobei allerdings der Wassergehalt der Probe eine wesentliche Rolle spielt. Die Phosphonsäuregruppe neigt bei höheren Temperatur zur Kondensation. Es enstehen Phosphonsäureanhydride. Die Bildung dieser Gruppen wurde mittels Festkörper-NMR detektiert. Die Bildung der Anhydride beeinflußt die Protonenleitfähigkeit der PVPA erheblich, da nicht nur Ladungsträger verloren gehen, sondern wahrscheinlich auch deren Mobilität reduziert wird

SAR-based Wind Resource Statistics in the Baltic Sea

Ocean winds in the Baltic Sea are expected to power many wind farms in the coming years. This study examines satellite Synthetic Aperture Radar (SAR) images from Envisat ASAR for mapping wind resources with high spatial resolution. Around 900 collocated pairs of wind speed from SAR wind maps and from 10 meteorological masts, established specifically for wind energy in the study area, are compared. The statistical results comparing in situ wind speed and SAR-based wind speed show a root mean square error of 1.17 m s−1, bias of −0.25 m s−1, standard deviation of 1.88 m s−1 and correlation coefficient of R2 0.783. Wind directions from a global atmospheric model, interpolated in time and space, are used as input to the geophysical model function CMOD-5 for SAR wind retrieval. Wind directions compared to mast observations show a root mean square error of 6.29° with a bias of 7.75°, standard deviation of 20.11° and R2 of 0.950. The scale and shape parameters, A and k, respectively, from the Weibull probability density function are compared at only one available mast and the results deviate ~2% for A but ~16% for k. Maps of A and k, and wind power density based on more than 1000 satellite images show wind power density values to range from 300 to 800 W m−2 for the 14 existing and 42 planned wind farms

Overview of diagnosis and management of paediatric headache. Part I: diagnosis

Headache is the most common somatic complaint in children and adolescents. The evaluation should include detailed history of children and adolescents completed by detailed general and neurological examinations. Moreover, the possible role of psychological factors, life events and excessively stressful lifestyle in influencing recurrent headache need to be checked. The choice of laboratory tests rests on the differential diagnosis suggested by the history, the character and temporal pattern of the headache, and the physical and neurological examinations. Subjects who have any signs or symptoms of focal/progressive neurological disturbances should be investigated by neuroimaging techniques. The electroencephalogram and other neurophysiological examinations are of limited value in the routine evaluation of headaches. In a primary headache disorder, headache itself is the illness and headache is not attributed to any other disorder (e.g. migraine, tension-type headache, cluster headache and other trigeminal autonomic cephalgias). In secondary headache disorders, headache is the symptom of identifiable structural, metabolic or other abnormality. Red flags include the first or worst headache ever in the life, recent headache onset, increasing severity or frequency, occipital location, awakening from sleep because of headache, headache occurring exclusively in the morning associated with severe vomiting and headache associated with straining. Thus, the differential diagnosis between primary and secondary headaches rests mainly on clinical criteria. A thorough evaluation of headache in children and adolescents is necessary to make the correct diagnosis and initiate treatment, bearing in mind that children with headache are more likely to experience psychosocial adversity and to grow up with an excess of both headache and other physical and psychiatric symptoms and this creates an important healthcare problem for their future life

Synthesis of phosphonate-functionalized polystyrene and poly(methyl methacrylate) particles and their kinetic behavior in miniemulsion polymerization

Phosphonate-functionalized polymer nanoparticles were synthesized by free-radical copolymerization of vinylphosphonic acid (VPA) with styrene or methyl methacrylate (MMA) using the miniemulsion technique. The influence of different parameters such as monomer and surfactant type, amount of vinylphosphonic acid on the average particle size, and size distribution was studied using dynamic light scattering and transmission electron microscopy. Depending on the amount and type of the surfactant used (ionic or non-ionic), phosphonate-functionalized particles in a size range from 102 to 312 nm can be obtained. The density of the phosphonate groups on the particle surface was higher in the case of using MMA as a basis monomer than polystyrene. The kinetic behavior of VPA copolymerization with styrene or MMA using a hydrophobic initiator was investigated by reaction calorimetry. Different kinetic curves were observed for miniemulsion (co)polymerization of styrene- and MMA-based nanoparticles indicating different nucleation mechanisms

The tendency of otherization in the Turkish proverbs [Türk atasözleri̇ndeki̇ "öteki̇"leşti̇rme eǧi̇li̇mi̇]

In the last decades, particularly in the field of social sciences the notion of "otherization" has been highly discussed. It has been seen that the tendency to "otherize" is a phenomenon highly common in the field of folklore, most particularly in the Turkish proverbs. In this context it is possible to see that "the other" has different qualities in different contexts. Ethnic, religious and geographic factors are the most dominant ones which forms the identity of "the other". Especially in the Turkish proverbs the foreigner is qualifed as "the other" and has generally negative implications. Most commonly "non-muslims" and the people who are not Turkish are called "the others". In another context it is seen that "the other" is thougt as the "enemy". In the international relations this rhetoric still influences the determination of "the other". In the last years it is witnessed that the belief of "the old enemy would never be a friend" has been used by the Turkish mass media as a reflection of the public opinion and the proverbs commonly used. It is seen that there are times when this tendency loses its validty. Especially in the rural places to define "the other" is more characteristic but in the urban places to otherize seems to be affected by the individualism. This study aims at analyzing the reflection of folkloric factors to the general stances of the folks and vice versa. It is possible to see the validity of the proverbs in the two parallel and at the same time opposite tendancies that the world is passing through during the last decades, globalization and the east-west tension provoked by the "clash of civilisations" thesis of Samuel Huntington