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This report presents a study about the morphology of a cross-linked aromatic polyamide (PA) film in its dry and wet state using small-angle neutron scattering (SANS), positron annihilation lifetime spectroscopy (PALS), and scanning electron microscopy (SEM). PA is used as active skin layer for reverse osmosis membranes and determines the selectivity of the membrane with respect to water and salt molecules. This selectivity of PA is largely determined from its morphology. The PA film scatters the neutrons much stronger and shows a different profile as expected from randomly distributed nanoscopic large pores. SANS contrast variation, using supercritical CO2 as contrast medium, confirms that pores are the only scattering centers. The analysis shows that interconnected pores of an average radius of about 16 A determine the scattering. The pores are formed as a network of channels showing a fractal structure. PALS determines pores of ∼6 A diameter representing the diameter of such channels. The volume fraction of the pores is estimated as ∼10% which after water up-take increases by ∼30% due to slightly swelling of the pores.

Rapid population growth and the associated rise in industrialization and food production have resulted in a tremendously increased demand for clean water.

In this work cross-linked hybrid organic-inorganic membranes consisting of polymeric matrix functionalized with sulfonic groups and uniformly distributed silica domains have been successfully synthesized through in situ polymerization strategy via photo-initiated copolymerization of acrylic monomers (acrylonitrile AN, acrylamide AAm, 3-sulfopropyl acrylate potassium salt SPAK) and simultaneous formation of silica counterpart using TEOS-based sol-gel system. N,N′-methylenebis(acrylamide) (MBA) was used as a cross-linker. The ratio between monomers was maintained stable, whereas the amount of added sol-gel system was varied. The influence of inorganic component content on properties of hybrid polymer-inorganic membranes was investigated. Chemical composition, thermal properties, structure and morphology of the obtained hybrid membranes were investigated by ATR-FTIR, TGA, DSC, SEM and EFTEM. Proton conductivity of the synthesized membranes was high (7.6 to 13.5 mS/cm) and increases with an increase of silica content. The prepared membranes were thermally stable up to 90 °C, and exhibited proton conductivity and swelling coefficients sufficient for possible use as proton-conducting membranes.

Hydrogen production using water electrolysers equipped with an anion exchange membrane (AEM), a pure water feed and cheap components such as platinum group metal-free catalysts and stainless steel bipolar plates (BPP) can challenge proton exchange membrane (PEM) electrolysis systems as the state of the art. For this to happen the performance of the AEM electrolyzer must match the compact design, stability, H2 purity and high current densities of PEM systems. Current research aims at bringing AEM water electrolysis technology to an advanced level in terms of electrolysis cell performance. Such technological advances must be accompanied by demonstration of the cost advantages of AEM systems. The current state of the art in AEM water electrolysis is defined by sporadic reports in the academic literature mostly dealing with catalyst or membrane development. The development of this technology requires a future roadmap for systematic development and commercialization of AEM systems and components. This will include basic and applied research, technology development & integration, and testing at a laboratory scale of small demonstration units (AEM electrolyzer shortstacks) that can be used to validate the technology (from TRL 2-3 currently to TRL 4-5). This review paper gathers together recent important research in critical materials development (catalysts, membranes and MEAs) and operating conditions (electrolyte composition, cell temperature, performance achievements). The aim of this review is to identify the current level of materials development and where improvements are required in order to demonstrate the feasibility of the technology. Once the challenges of materials development are overcome, AEM water electrolysis can drive the future use of hydrogen as an energy storage vector on a large scale (GW) especially in developing countries.

Free-standing polyelectrolyte multilayer membranes have been formed by the layer-by-layer technique using a dip-coating apparatus. The polymer-chain mobility has been studied by 1H relaxation in the rotating frame T 1rho NMR with 13C chemical shift resolution. For each of the individual polymers a single relaxation component has been observed for all resolved signals. In the multilayer a significantly different relaxation time T 1rho has been observed with a minor second component. The interaction between the oppositely charged polyelectrolytes influences the molecular mobility.

The preparation of quaternary ammonium salts containing allyl and methallyl groups from dimethylamine and pyrrolidine, and the free-radical initiated cyclopolymerization of these salts is described. It is shown by NMR analysis that poly(ammonium salts) are formed consisting of pyrrolidinium and azoniaspiro[4.4]nonane containing repeating units respectively with one or even two adjacent quaternary carbon centers along the chain. The ability to polymerize decreased from diallyl over allylmethallyl to dimethallyl monomers. Already polymers from diallylammonium salts showed sufficient stability in alkaline medium at 80 °C over a period of 168 h and for additional 18 h at 120 °C.

Papillary glioneuronal tumor (PGNT) is a WHO-defined brain tumor entity that poses a major diagnostic challenge. Recently, SLC44A1-PRKCA fusions have been described in PGNT. We subjected 28 brain tumors from different institutions histologically diagnosed as PGNT to molecular and morphological analysis. Array-based methylation analysis revealed that 17/28 tumors exhibited methylation profiles typical for other tumor entities, mostly dysembryoplastic neuroepithelial tumor and hemispheric pilocytic astrocytoma. Conversely, 11/28 tumors exhibited a unique profile, thus constituting a distinct methylation class PGNT. By screening the extended Heidelberg cohort containing over 25,000 CNS tumors, we identified three additional tumors belonging to this methylation cluster but originally histologically diagnosed otherwise. RNA sequencing for the detection of SLC44A1-PRKCA fusions could be performed on 19 of the tumors, 10 of them belonging to the methylation class PGNT. In two additional cases, SLC44A1-PRKCA fusions were confirmed by FISH. We detected fusions involving PRKCA in all cases of this methylation class with material available for analyses: the canonical SLC44A1-PRKCA fusion was observed in 11/12 tumors, while the remaining case exhibited a NOTCH1-PRKCA fusion. Neither of the fusions was found in the tumors belonging to other methylation classes. Our results point towards a high misclassification rate of the morphological diagnosis PGNT and clearly demonstrate the necessity of molecular analyses. PRKCA fusions are highly diagnostic for PGNT, and detection by RNA sequencing enables the identification of rare fusion partners. Methylation analysis recognizes a unique methylation class PGNT irrespective of the nature of the PRKCA fusion.

A hydrophilic hyperbranched poly(amido amine) (PAMAM) was successfully bonded onto the active PA-layer of a RO-membrane by chemical coupling. The coating is accomplished by spraying a 10 wt% solution of PAMAM directly after the interfacial polymerisation onto the surface. The chemical structure and performance of both unmodified and modified membranes were evaluated. Results from XPS, SEM and zeta-potential measurements confirmed a successful and stable modification. A model reaction of trimesoyl chloride with butylamine in aqueous and alcoholic solution approved a high possibility for covalent PAMAM bonding to the surface. Application of an aqueous PAMAM solution resulted in an almost complete surface coverage with PAMAM, while the use of a methanolic solution led to an inhomogeneous coverage with PAMAM clusters. The permeability increased by 20–25% upon modification with PAMAM. While the modification with the aqueous solution has no negative effect on salt retention, modification with the methanolic solution resulted in lower salt retention. Furthermore, membranes modified with aqueous PAMAM solution showed very low protein adsorption compared to unmodified samples or samples modified with methanolic PAMAM solution.

In this study the effects of cation exchange polymer coatings on activated carbon electrodes for capacitive deionization (CDI) were investigated. Electrodes were fabricated from activated carbon, graphite and PVDF, then coated with sulfonated poly(arylene ether sulfone) random copolymers. Additional resistance was created by the coating layer, however compared with the uncoated electrodes the coatings did not significantly affect the rate of charge build up. Electrochemical impedance spectroscopy (EIS) results indicated that both capacitance and charging resistance are influenced by polymer conductivity, water uptake and the thickness of the coating layer. The results also indicated that in addition to functioning as a superficial charge barrier, copolymer that penetrates into the carbon substrate might offset the loss in capacitance caused by PVDF binder pore blockage.

Electro-membrane processes are successfully applied in desalination of sea and brackish water, waste water treatment, chemical process industry, and food and pharmaceutical industry. Key compound is the ion-exchange membrane, which enables the selective transport of ions. The intention of this paper is to briefly review synthetic aspects in the development of new ion-exchange materials for both anion-exchange and cation-exchange purposes.

Kinetic studies on the reaction of decafluorobiphenyl and di- and tetra(phenylthio)-substituted perfluorobiphenyl with thiophenol in the presence of triethylamine were performed by in situ 19 F NMR spectroscopy to determine rate constants. In well-defined consecutive reactions, the even-numbered phenylthio derivatives are main products whereas the odd-numbered derivatives are much more reactive and were observed only in low concentrations. Very pronounced differences in rate constants and reactivity were obtained.

Cation exchange membranes prepared from random and multiblock side-chain sulfonated poly(ether sulfone)s have been characterised to evaluate their suitability for electrodialysis and membrane capacitive deionization applications. The side chain sulfonation of the copolymers resulted in membranes with a high degree of sulfonation and ion exchange capacities (IEC) in the range of 1.44–2.05 mmol/g, which is comparable to commercially available membranes. The multiblock copolymer, which can be considered as having a microheterogeneous structure, exhibited a high IEC and water uptake due to large, hydrophilic domains, while the random copolymers had lower swelling rates. Membrane conductivity in the Na+ form reached as high as 15.13 mS/cm for the random copolymers and 16.74 mS/cm for the block copolymer. Transport numbers were found to be as high as 0.99 for random copolymers, but as low as 0.84 for the block copolymer. Based on these results, these side-chain sulfonated random copolymers are potential candidates for use in electro-driven desalination systems.

Catalytic amounts of cesium carbonate are sufficient to initiate the “silyl method”-type step-growth polymerization of phenylene-bis-TMS-ethers and -thioethers with activated aryl fluoride monomers, and can thus be used instead of ce-sium fluoride or potassium carbonate. Cesium fluoride is very hygroscopic and potassium carbonate is generally used in equimolar amounts. The efficiency of catalytic amounts of cesium carbonate is demonstrated by the synthesis of poly(phenylene ether ether ketone) and poly(phenylene sulfide sulfone) examples.

Copoly(arylene ether sulfone)s from 4,4′-difluorodiphenyl sulfone, 4,4′-dihydroxydiphenyl sulfone bis-trimethylsilylether, and 2,5-diphenylhydroquinone bis-trimethylsilylether were obtained by nucleophilic displacement polycondensation with high molecular weights. While the random copolymers were obtained with narrow molecular weight distributions, the molecular weight distributions of the multiblock copolymers were much broader, probably indicating branching reactions. Random as well as multiblock copolymers showed a single glass transition temperature ( T g ) at around 230 °C. Upon sulfonation with concentrated sulfuric acid, the T g s (from samples in the protonated form) were shifted to higher temperatures. NMR spectra and the determined ion-exchange capacities, which were close to the theoretical values, indicated that the pendant phenyl rings of the 2,5-diphenylhydroquinone moieties in the polymer backbone were sulfonated selectively. Membranes prepared from N-methyl-2-pyrrolidone solutions were transparent and soft. The water uptake at room temperature increased from 30% to 80% with increasing IEC. Samples with an IEC ⩾1.8 mmol/g swell to a high extend (sMBC) or even dissolve in water (sRC) at elevated temperatures. While the proton conductivities of the low IEC samples were lower than or close to that of Nafion®, the conductivities of the high IEC samples were superior to that of Nafion®. In general membranes from block copolymers showed similar water uptake and similar dimensional changes but higher proton conductivities as compared to samples from random copolymers with similar monomer composition and ion-exchange capacities.

Flat sheet polypropylene microfiltration membranes were successfully graft‐modified with acrylic acid using the macroinitiator method. The surface modification induced a change in the course of fouling. Unmodified membranes showed the strong form of critical flux during filtration of protein solution, while for the surface modified membranes the weak form of critical flux was determined. Although the critical flux could be shifted towards higher values (from ca. 20 l/m2h to>40 l/h2m) by the surface modification, the permeability decreased by a factor of 6.

Poly(arylene ether sulfone)s of high molecular weight and narrow molecular weight distribution were obtained by melt polycondensation of 4,4' -difluorodiphenyl-sulfone and trimethylsilylethers of 4,4'-dihydroxydiphenylsulfone and phenylhydroquinone using CsF as catalyst. Although a block-like structure of the polymers could be expected from the course of reaction, only a single T g ranging from 190 °C to 230 °C could be detected by DSC and which depended on the copolymer composition. Contrary to the sulfonation of similar poly(ether ether ketone)s the poly(arylene ether sulfone)s here reported were sulfonated both in the side chain and the main chain. Nonetheless the sulfonated poly(arylene ether sulfone)s showed high hydrolytic stability in water at 130 °C.

Poly(ether sulfone)s from 4,4'-difluorodiphenylsulfone (DFDPhS), 4,4'-bis-trimethylsiloxy-diphenylsulfone, and 2,5-bis-trimethylsiloxy-biphenyl were obtained by melt polycondensation with high molecular weights (ηinh > 0.4 dl/g). The nonsulfonated samples showed a single glass-transition temperature (T g) in the range from 180 to 230 °C depending on the monomer composition in the polymer backbone. The T g of sulfonated samples could not be detected by differential scanning calorimetry (DSC). Membranes with a theoretical ion-exchange capacity (IEC) ranging from 0 to 2.08 mmol/g should be obtained, assuming only a sulfonation of the pendant phenyl ring. However, the sulfonation with concentrated sulfuric acid always led to the introduction of two sulfonic acid groups into the phenylhydroquinone (PhHQ) moieties in the polymer backbone; one at the desired position at the pendant phenyl ring and one at the phenyl ring in the polymer backbone. Membranes prepared from N-methyl-2-pyrrolidone (NMP) solutions of nonsulfonated and sulfonated samples were transparent and soft to slightly brittle. The water uptake at room temperature increased with increasing IEC from 4 to 50 % (IEC ~ 1.50 mmol/g). On further increase of the IEC, a strong water uptake until dissolution was observed. Methanol diffusion coefficients for samples with an IEC up to 1.10 mmol/g were one order of magnitude lower than that reported for Nafion®.

Activated carbon electrodes for capacitive deionization (CDI) have been prepared using poly(arylene ether sulfone) random copolymers as binders. Due to the reduced mechanical strength and enhanced swelling of the polymers compared with PVDF binder, a 15 wt.% composition was found to be required to adequately bind the carbon particles. The hydrophilic nature of the polymers increased the wettability of the electrodes, however CV and EIS testing revealed a loss in capacitance compared with electrodes prepared with PVDF. This is thought to have been a result of polymer swelling, which reduced particle contact and hence charge transfer pathways within the carbon electrodes. As a result, poor micropore double layer formation was observed. Promisingly, EIS testing showed low charging resistance compared with electrodes prepared with PVDF, indicating the potential for hydrophilic polymers to be used as binders in CDI electrodes if charge transfer pathways between carbon particles can be maintained.

Novel sulphonated poly(ether ether sulphone) copolymers were synthesised by polycondensation reaction of stoichiometric amounts of silylated hydroquinone sulphonic acid, 4,4′-difluorodiphenyl sulphone and bisphenols, i.e., bisphenol-A, 4,4′-dihydroxybiphenyl, hydroquinone, phenolphthalein and 2,6-dihydroxynaphthalene. The structure of the copolymers was confirmed by using ATR-FTIR, 1 H NMR and 13 C NMR techniques. Number average molecular weight (GPC) of the polymers was in the range of 7900–18,000 g/mol. The water uptake of polymer films prepared by casting technique depended on the backbone structure and degree of sulphonation. The proton conductivity of these membranes at room temperature was in the range of 3.3 × 10 −3 –6.1 × 10 −6 S/cm.

Novel sulphonated poly(ether ether ketone) (PEEK) copolymers with controlled degree of sulphonation were synthesized by polycondensation reaction of varying ratios of silylated phenolphthalein, silylated biphenol, 5,5′-carbonyl-bis(2-fluoro benzene sulphonate) (sulphonated 4,4′-difluorobenzophenone) and 4,4′-difluorobenzophenone. The structure of the copolymers was confirmed by using ATR and 1 H NMR techniques. Molecular mass of these samples was determined by GPC. Thermal stability of the samples was evaluated using TGA technique. Methanol diffusion coefficients were in the range of 6.57 × 10 −8 to 2.5 × 10 −6 cm 2 /s. The proton conductivity of the membranes in the temperature range of 25–75 °C was found to be 10 −5 to 10 −3 S/cm.

This paper reviews recent progress in the development of alternative membrane materials to perfluorinated ionomers for fuel cell applications focusing DMFC. Special attention is paid to sulfonated block copolymers, which have advantageous properties such as lower methanol crossover and swelling as compared to that of analogous random copolymers of the same overall composition.

A number of low molecular weight sulfonated aromatic compounds: carboxamides, imides, sulfonamides, as well as sulfonated polymers; aramides and poly(styrene-p-sulfonic acid), were tested for their stability on heating in water and dilute acid to temperatures ranging from 130–200 °C. Desulfonation was observed with some compounds. Sulfonamide linkages were found to be stable, while carboxamide linkages and phthalimides were not.

An alternative method using established polymer processing and membrane formation processes to prepare hydrophilic membranes based on acid modified polyolefins is introduced. This process includes blend formation by reactive extrusion of functionalized polyolefins (polypropylene; PP) and a hydrophilic polyamide (PA). In a first step the pore formation is realized by extracting non-covalently bound polyamide. The resulting membranes are tested by pure water as well as protein filtration. The properties are discussed in terms of permeate flux, retention capability and fouling behavior.

Homo- and both random and block copolyaramides of high molecular weights, with sulfonated moieties in the backbone, were obtained by low temperature polycondensation technique in a dipolar aprotic solvent (NMP) using (a) free aromatic diamines in the presence of pyridine as acid acceptor and (b) N,N′-bis-trimethylsilyl derivatives of the diamines without additional acid acceptor. The addition of low molecular weight electrolytes (LiCl or CaCl2) and in some cases trimesoyl chloride to the reaction mixture was found to be favorable for the synthesis of high molecular weight polyamides. The materials had a theoretical ion exchange capacity of up to 3.14 meq/g. The membranes were characterized in terms of morphology, thermal stability, water-uptake, and ion exchange capacities.

Membranes with designed surface and filtration properties were prepared by the adsorption of polyelectrolyte multilayer systems on membrane surfaces using the layer-by-layer electrostatic self assembly (ESA) technique. Microfiltration membranes with a first polyelectrolyte layer grafted onto the surface showed excellent stability during filtration process. Although a twofold higher permeate flux was observed for a three-layer polyelectrolyte complex membrane compared to a just grafted one the protein retention did not change remarkably. Additionally, a reduced protein adsorption was detected for repulsive electrostatic forces between the substrate and the protein under applied conditions. Pervaporation membranes with an anionically functionalized polyamide-6 support or Nafion®- 117 support and a dense separating layer consisting of poly(acrylic acid) and poly(ethylenimine) were prepared. Those membranes were used to separate aqueous organic mixtures. Six double layers were sufficient to obtain membranes with high water permselectivity. Membranes with similar properties but a lower number of deposited layers were obtained, when the adsorption process was carried out at 80°C.

Composite membranes for pervaporation of water/alcohol mixtures were prepared by consecutive alternating adsorption of poly(acrylic acid) (polyanion) and poly(ethylenimine) (polycation) on a polyamide-6 substrate. The influence of preparation conditions on the pervaporation separation properties of polyelectrolyte multilayer composite membranes was studied. Variation of polyelectrolyte concentration of the dipping solution and adsorption time had only a minor effect on the membrane performance. On the other hand, high molecular weight polyelectrolytes had a high impact on membrane performance. A separation factor α of 2500 was observed for a membrane having four double layers. Best results were obtained when the adsorption temperature was raised from 25°C to 80°C A membrane with two double layers showed a separation factor α of 900.

Synaptic communication requires constant adjustments of pre- and postsynaptic efficacies. In addition to synaptic long term plasticity, the presynaptic machinery underlies homeostatic regulations which prevent out of range transmitter release. In this minireview we will discuss the relevance of selected presynaptic mechanisms to epilepsy including voltage- and ligand-gated ion channels as well as cannabinoid and adenosine receptor signaling.

Composite pervaporation membranes composed of an asymmetric polyamide-6 membrane and an ultrathin self-assembled polyelectrolyte separating layer are described. The supporting membrane was prepared from both an unmodified polyamide-6 and a comb-like polymer with carboxyl terminated polyamide-6 side chains. A high end group concentration was found to be advantageous for sufficient adhesion of the multilayer systems on the supports. Up to 20 layers were deposited onto the membrane surface by dipping the membranes in aqueous solutions containing oppositely charged polyelectrolytes. The polyanions used were poly(acrylic acid), poly(styrene sulfonic acid) and alginic acid. The polycations used were poly(diallyldimethylammoniumchloride), chitosan and poly(ethylenimine). Performance of these membranes depends strongly on the layer number and on the type of polyelectrolytes. In general, membranes modified with two weak polyelectrolytes of high charge density gave the best separation properties while those modified with strong polyelectrolytes of low charge density led to poorer separation properties. However, the highest separation factor (≥10,000) for a water/2-propanol mixture (12/88 w/w) at permeate flux of 300 g/m 2 h was obtained with six double layers consisting of poly(ethylenimine) and alginic acid. These composite membranes were stable over an operating period of at least 400 h.

Integrally-skinned asymmetric polyamide-6 membranes were prepared by casting 15 wt.% solution of polymer in 85 wt.% formic acid onto a glass plate and precipitation in water at 4°C. The obtained membranes were dried for 1 h at different temperatures ranging from 25 to 140°C in air and from 25 to 200°C in vacuum, respectively. The pervaporation separation properties of such treated membranes were studied with binary water-2-propanol mixtures consisting of 5 to 95 wt.% water. The membranes showed water permselectivity over a wide range of the feed composition. Thereby the water permselectivity reached a maximum at low water contents in the feed mixture. The selectivity was improved by thermal treatment of the membranes at temperatures above the glass transition temperature T g of polyamide-6 (≈60°C). However, the permeate flux decreased with increasing drying temperature due to the removal of entrapped water from amorphous domains, the formation of new crystalline domains and the decrease of the pore size and of the specific surface area during the thermal treatment. These effects were confirmed by dsc measurements, X-ray scattering experiments and BET measurements.

Die Bestrahlung von Polyaramid-Ultrafiltrationsmembranen (PA-UF-Membranen; NADIR® UF-PA-5) mit energiereichen Elektronen ergab im Energiedosisbereich von D≈150 bis 200 kGy eine Erhohung des Ruckhaltevermogens R von 93 auf 98%. Entgegen der ublichen Erfahrung trat dabei keine Reduzierung des Permeatfluswertes JPVP auf. Durch ζ-Potentialmessungen und IR-spektroskopische Untersuchungen konnte der Einbau von zusatzlichen Carboxygruppen durch die Bestrahlung nachgewiesen werden, die diesen Effekt im wesentlichen verursachen. Electron beam irradition of polyaramide ultrafiltration membranes (PA-UF membranes; NADIR® UF-PA-5) led to an increase of retention R from 93% to 98% in the applied dose range between 150 and 200 kGy. Contrary to common findings, no reduction of permeate flux JPVP was observed. The formation of carboxy groups caused by electron beam irradiation was confirmed by ζ-potential measurements and ATR-FTIR spectroscopic investigations.

In-situ attenuated total reflection (ATR)-FTIR spectroscopy was used to monitor the consecutively alternating adsorption of polyethylenimine (PEI) and poly(acrylic acid) (PAC) onto both Si crystals (SiO) and CO2 plasma-treated polypropylene (PP) films. The vibration band vas(COO−) and v(CO) of PAC are diagnostic for the polyelectrolyte layer build-up and sensitive to protonation changes. Human serum albumine (HSA) adsorption experiments revealed a strong decrease of fouling for the PP films, which were modified with polyelectrolyte multilayers, in comparison to the unmodified ones.

Flat sheet polypropylene microfiltration membranes were successfully graft‐modified with acrylic acid using the macroinitiator method. The surface modification induced a change in the course of fou...

Despite great effort that has been made to reduce and understand fouling, this phenomenon is still a major problem in membrane applications. Numerous methods, both from a chemical and engineering point of view, have been introduced to overcome this problem. In this contribution, we report on the modification of membranes with polyelectrolytes and polyelectrolyte multilayers utilizing two of the mentioned strategies. The effect of surface modification on the fouling behavior as well as on the critical flux will be discussed on two examples, microfiltration membranes and RO membranes.

Triblock copolymers were prepared from L-lactide and a poly(ethylene glycol) of Mn = 1020. With GeO2 and SnO2 only low conversions were obtained, regardless of the reaction temperature. Sb2O3 caused partial racemization, and only SnO gave satisfactory results. When other samples of poly(ethylene glycol) were used (e.g., with Mn = 600 or 3250), partial racemization occurred even with SnO. However, with Sn(II) 2-ethylhexanoate, racemization-free triblock copolymers were obtained under the reaction conditions used. The results of the characterization indicate that the triblock copolymers possess unimodal molecular weight distribution. The lactide blocks crystallize in the α-modification and suppress in most, but not all, cases the crystallization of the poly(ethylene glycol) blocks. The crystallization of long poly(ethylene glycol) blocks observed in several cases indicates a triphasic character of these samples.

Linear polybiurets can be synthesized by polycondensation of chloroformyl isocyanate and N,N′-bis(trimethylsilyl)-α,ω-diaminoalkanes or silylated aromatic diamines. The polybiurets were characterized by elemental analyses, inherent viscosity measurements, IR spectroscopy, 1H, 13C, 15N NMR spectroscopy in solution, differential scanning calorimetry (DSC) measurements, wide-angle X-ray scattering (WAXS) and thermogravimetric analyses. All polybiurets are semicrystalline materials with a low rate of crystallization and unexpectedly low melting points. 13C and 15N NMR cross-polarization/magic angle spinning (CP/MAS) spectra of the solid polybiurets indicate different conformations for the amorphous and crystalline phase. All polybiurets gradually decompose upon heating above 200°C. Synthetic methods and properties of linear biurets were also checked by synthesis and characterization of N,N′-dioctylbiuret.

Membrane-based processes have found wide acceptance and are used as powerful alternatives for conventional techniques such as distillation, extraction, or energy production. Frequently, membranes prepared from commodity polymers do not have the desired properties for the various applications. For example, fouling is still an unsolved problem in membrane applications, which is closely related to surface properties of both the membrane and the foulant. To meet the requirements for the various tasks, membranes with tailor-made properties are needed. In this contribution on the one hand surface modification techniques are described, which are used to (a) obtain microfiltration membranes with low-fouling tendency and (b) to prepare membranes with required properties in pervaporation separation applications. On the other hand modification/functionalization of polymers for use as ion-exchange membranes in energy-producing systems (fuel cells) are discussed. The focus is set on surface modification with polyelectrolytes and polyelectrolyte multilayer systems. This versatile technique enables the preparation of porous membranes with adjustable surface charge and low-fouling tendency without interference of permeate quality. Dense pervaporation membranes based on polyelectrolyte multilayer systems, with high selectivities and moderately high flux were obtained. The performance of such membranes can be controlled by the polyelectrolytes used (charge density) and the preparation conditions (e.g. temperature). Finally, a short introduction of new membrane materials based on fully aromatic polymers as alternatives to perfluoroalkylsulfonic acids, such as Nafion, is given.

A series of aliphatic polyallophanates was prepared by polyaddition of N,N′-bistrimethylsilyl-α,ω-diaminoalkanes onto butane- 1,4-bis(alkoxycarbonylisocyanate). A partially aromatic polymer was obtained by polyaddition of N,N′-bistrimethylsilyl-4,4′-diaminodiphenylmethane. The linear polyallophanates isolated after methanolysis of the trimethylsilyl groups were characterized by elemental analyses, inherent viscosities, DSC measurements, i.r.-, 1H-NMR, 13C-NMR- and 15N-NMR-spectroscopy and in some cases by WAXS powder patterns. All polyallophanates were semicrystalline materials which gradually decomposed in the molten state.