Nico Scharnagl

ß-D,L,-Butyrolactone was polymerized at 50°C in deuterated solvents of different polarity, and both the conversion and the formation of crotonate groups were directly determined from the reaction mixture by means of H-NMR spectroscopy. Two classes of initiators, namely nonionic ones, such as tertiary amines or triphenylphosphine, and ionic ones, such as potassium salts of alcohols, phenols, and carboxylic acids, were

ABSTRACT β-Propiolactone was reacted with triethylamine, pyridine, triphenylphosphine, potassium tert-butoxide, potassium (4-t-butylphenoxide) or potassium benzoate in CDCl3 or dimethylsulfoxide in an n.m.r. tube. The 1H n.m.r. analyses revealed in all cases formation of large amounts of acrylate groups. β-Propiolactone was polymerized at 20°C with triethylamine, pyridine or triphenylphosphine at a monomer/initiator ratio (M/I) of 50:1, and the endgroups of the isolated poly(β-propiolactone)s were characterized by 1H- and 13C-n.m.r. spectroscopy. Acrylate groups were found in all cases, even when the initiation with triphenylphosphine was conducted at −70°C. Sodium methoxide and potassium t-butoxide even attack polypropiolactone, yielding acrylate endgroups by deprotonation and elimination. In the presence of methanol, transesterification with formation of methyl ester endgroups also takes place. Only small amounts of acrylate groups were found when tributyltin methoxide served as initiator at 60–100°C. With aluminium isopropoxide acrylate endgroups were almost absent. Thus, the degree of deprotonation allows a differentiation between a true anionic polymerization and a nonionic insertion mechanism.

ß-D,L,-Butyrolactone was polymerized at 50°C in deuterated solvents of different polarity, and both the conversion and the formation of crotonate groups were directly determined from the reaction mixture by means of H-NMR spectroscopy. Two classes of initiators, namely nonionic ones, such as tertiary amines or triphenylphosphine, and ionic ones, such as potassium salts of alcohols, phenols, and carboxylic acids, were

An app. is disclosed for prepn. and sepn. of esp. biol. org. flow media (e.g., wastewaters) by liq. or gaseous membrane permeation, comprising a stack consisting of a plurality of membrane elements distanced from each other by means of a spacer. The flow medium flows around the membrane elements of the stack. The permeate delivered by the membrane elements is collected in >=1 element(s) traversing the stack and removed externally. The spacer element has a larger dimension in the flow direction of the medium to be sepd. than that which is perpendicular to the flow direction. [on SciFinder (R)]

The consumption of water and a redn. in operating costs was achieved by the use of membrane technol. in a bottle-washing plant. Ultrafiltration, nanofiltration, and reverse osmosis techniques wee used as well as various modular systems, whereby the membrane properties were tested under cross-flow conditions. The parameters cond., pH value, and COD were used to det. the water quality. The selected membrane was used in a lab.-scale test and checked in the modular system. These investigations indicated water savings of <50% and cost estns. showed an amortization time of <2 yr. [on SciFinder (R)]

ABSTRACT Polymerization via anionic mechanisms or insertion mechanisms (pseudoanionic mechanisms) are compared for β-lactones and L-lactide. The following aspects are discussed: initiation and deprotonation of β-lactones, back-biting degradation, stereosequences of poly(β-D,L-butyrolactone), racemization of L-lactide, systematic variation of endgroups including synthesis of macromers.

ABSTRACT Studies in the literature have shown that magnesium fluoride is an interesting coating for protecting magnesium and magnesium alloys from corrosion in biological environments. In this chapter, this coating formation process and its relevant properties are discussed in detail. The corrosion performance of magnesium alloys with fluoride coating in regular saline solution, simulated body fluid, and in vivo is described. The current challenges and future trends are critically discussed based on recent reports in the literature.

ABSTRACT Chemically and thermally resistant membranes suitable for the separation of low molecular weight substances from organic solvents were developed. Porous membranes from polyacrylonitrile and polyamideimide were optimized for this application. Cellulose ethers, like hydroxypropylmethylcellulose (HPMC) and polyether-block-polyamides, were used as selective coatings. Special attention was paid to the separation of edible oil/solvent mixtures. Composite membranes with 99% oil retention could be prepared with HPMC as selective layer.

ABSTRACT β-Propiolactone was reacted with triethylamine, pyridine, triphenylphosphine, potassium tert-butoxide, potassium (4-t-butylphenoxide) or potassium benzoate in CDCl3 or dimethylsulfoxide in an n.m.r. tube. The 1H n.m.r. analyses revealed in all cases formation of large amounts of acrylate groups. β-Propiolactone was polymerized at 20°C with triethylamine, pyridine or triphenylphosphine at a monomer/initiator ratio (M/I) of 50:1, and the endgroups of the isolated poly(β-propiolactone)s were characterized by 1H- and 13C-n.m.r. spectroscopy. Acrylate groups were found in all cases, even when the initiation with triphenylphosphine was conducted at −70°C. Sodium methoxide and potassium t-butoxide even attack polypropiolactone, yielding acrylate endgroups by deprotonation and elimination. In the presence of methanol, transesterification with formation of methyl ester endgroups also takes place. Only small amounts of acrylate groups were found when tributyltin methoxide served as initiator at 60–100°C. With aluminium isopropoxide acrylate endgroups were almost absent. Thus, the degree of deprotonation allows a differentiation between a true anionic polymerization and a nonionic insertion mechanism.

(11) Yasuda, H.; Stannett, V. In Polymer Handbook, 2nd ed.; ... Poly(1actones). 9. Polymerization Mechanism of Metal Alkoxide Initiated Polymerizations of Lactide and Various Lactones ... Hans R. Kricheldorf,* Martin Berl, and Nico Scharnagl Institut fur Technische und ...

ABSTRACT In daily life a large amount of water is used for the cleaning of bottles from the beverage industry. If the amount of fresh water used can be reduced by membrane technology to at least 50% of the starting values, the total costs can be reduced too. During the present work we used different types of membranes, ranging from ultrafiltration (UF) down to reverse osmosis (RO). The membrane properties were studied under cross flow conditions with varying flow rates and different transmembrane pressures. For quality assessment the chemical oxygen demand (COD), conductivity, hardness degree of water and nitrate amount of both feed and permeate solution were measured during the experiments. The most characteristic parameters for the calculation of the energy consumption were permeate flux, energy demand of the pumps and the cleaning procedures and chemicals for membrane recovery. First the experiments were performed at laboratory scale with a small membrane tes cell and different types of washing waters. With these basic results a a small pilot plant for continuous operation was built. The feed stream could be controlled from 10 up to 400 l/h and the transmembrane pressure could rise to 70 bar. During this part energy consumption and the cleaning possibilities of the membrane system were also studied. The water quality of the first part of the experiments could be confirmed, and the energy and performance data were used for designing a pilot plant to be connected directly into the water stream of the washing process where the system is to be tested under real conditions. Based on the experiments it was calculated that the amount of fresh water can be reduced by at least 55% by connecting a membrane system into the washing machine.

ABSTRACT Polyacrylonitrile (PAN) membranes for ultra- and microfiltration were developed by GKSS. They are fabricated on a non-woven by a phase inversion process. It is shown that the formation process mainly depends on the polymer concentration of the casting solution as well as on the temperature of the precipitation bath. Therefore, different membrane morphologies can be obtained. They vary from large finger-like pores to homogeneous microporous structures. The flux of the membranes can be adjusted between 100 up to nearly 2000 l/m2h bar with high rejection. PAN membranes have good chemical stabilities and can be welded by heat or ultrasound. This makes the production of membrane envelopes possible, which are used in several filtration module types like Amafilter PM and Rochem FM. Today the membranes are commercially available and used in several applications such as water treatment, concentration of whey or protein, concentration of oil/water mixtures, etc. In these applications the membrane demonstrated high stability against chemical cleaning agents. It resists sodium hypochlorite, citric acid and weak alkaline solutions.

ABSTRACT Generell sind bei der Anwendung von Membranen zwei Aspekte von besonderer Bedeutung. Zum einen werden Transporteigenschaften und Trennleistung für Einsatz und Anlagenauslegung benötigt. Zum anderen sind die Parameter wichtig, die die Transporteigenschaften und andere Grundlagen zum Transportverhalten bei der Trennung mittels Membranen beschreiben. Um Trennprozesse und deren Effizienz genauer zu definieren, sind weitere Parameter wichtig, z. B. die Rückhaltung gegenüber bestimmten Stoffen bzw. bei Gasen die Selektivität. Dieser Beitrag geht auf verschiedene Methoden zur Bestimmung von Membraneigenschaften mit dem Schwerpunkt auf porösen Systemen ein. Dabei werden Bild gebende Verfahren der Mikroskopie ebenso vorgestellt wie Methoden, die die Wechselwirkung eines Mediums mit der Membran betrachten und bewerten.

This article provides a contribution towards the mechanistic understanding of surface phenomena observed during the corrosion of Mg-based substrates particularly in the low anodic polarization range. The concept considers the recent literature explaining cathodic hydrogen evolution from noble acting areas even during global anodic polarization. Heavy metal impurities in the ppm range or intermetallics are always present even in highly pure magnesium. Their potential effect was investigated here in more detail. The experimental results contribute to understanding the role of iron impurities in dark area formation and suggest a way for linking the observed phenomena to the recent literature. The shown enhanced cathodic activity of dark areas especially at the corrosion front and the superfluous hydrogen are linked to an iron re-deposition mechanism due to iron reduction. The proposed mechanism is based on the results obtained from innovative characterisation techniques using magnetic fields, diffraction experiments and transmission electron microscopy, which show the formation of iron rich zones, especially at the corrosion front offering "in statu nascendi" metallic Fe films acting as active cathodes for hydrogen reduction.

Siloxane composite membranes are crosslinked by radiation (esp. an electron beam) to give ultrafiltration membranes which show no swelling or degrdn. by org. solvents during the sepn. of small mols. from solvents, e.g., sepn. of corn oil from hexane or isooctane or sepn. of polyethylene glycol (mol. wt. 1500) from toluene or EtOH. [on SciFinder (R)]