bluuebunny/crossref_metadata_2025 huggingface dataset:
Pairwise Comparisons in Each of Several Groups with Heterogenous Group Variances
Authors: Cheung S.H. , Wu K.H. , Quek A.L.
Published: April 2003

Pairwise comparison procedures are frequently applied to analyze experimental results. In particular, practitioners in the area of medical researches often encounter situations which require these statistical techniques to compare various treatments. In this article, we focus on pairwise comparison procedures in a two‐factor design, where comparisons of one factor are made simultaneously for each level of another factor. For example, several new drugs to treat a certain cancer are being compared for both male and female patients. Previous research efforts were mainly devoted to models with homogeneous variances. The current paper is to address more common scenario where group variances are heterogeneous.
Simple circuit to improve electric field homogeneity in contour‐clamped homogeneous electric field chambers
Authors: Herrera José A. , Canino Carlos A. , López‐Cánovas Lilia , Gigato Regnar , Riverón Ana Maria
Published: April 2003

We redesigned contour‐clamped homogeneous electric field (CHEF) circuitry to eliminate crossover distortion, to set identical potentials at electrodes of each equipotential pair and to drive pairs with transistors in emitter follower stages. An equipotential pair comprised the two electrodes set at the same potential to provide electric field homogeneity inside of the hexagonal array. The new circuitry consisted of two identical circuits, each having a resistor ladder, diodes and transistors. Both circuits were interconnected by diodes that controlled the current flow to electrodes when the array was energized in the ‘A’ or ‘B’ direction of the electric field. The total number of transistors was two‐thirds of the total number of electrodes. Average voltage deviation from potentials expected at electrodes to achieve a homogeneous electric field was 0.06 V, whereas 0.44 V was obtained with another circuit that used transistors in push‐pull stages. The new voltage clamp unit is cheap, generated homogeneous electric field, and gave reproducible and undistorted DNA band patterns.
High levels of mitochondrial DNA heteroplasmy in single hair roots: Reanalysis and revision
Authors: Grzybowski Tomasz , Malyarchuk Boris A. , Czarny Jakub , Miścicka‐Śliwka Danuta , Kotzbach Roman
Published: April 2003

The present study demonstrates a reinvestigation of the mitochondrial DNA sequence heteroplasmy, which was previously found by the use of nested polymerase chain reaction (PCR) technique in single hairs of 13 individuals. The direct PCR approach was used for the amplification of mitochondrial DNA and a phylogenetic analysis was applied to both data sets for the verification of the authenticity of sequences. The comparative analysis of the sequencing results obtained from the same hair DNA extracts – but using two different techniques – shows that direct mitochondrial DNA amplification results in a considerably lower number of mixed positions. The majority of the confirmed heteroplasmic variants preferentially occurs in mitochondrial DNA hypervariable sites (mutational hotspots). However, the pattern of heteroplasmic mutations observed in four extracts after nested PCR significantly differs from the pattern of natural mutations. Some of these rare polymorphisms should be revised as inconsistent with phylogenetic expectations. The results of the present study contribute to the earlier reports by indicating that phylogenetic analysis is an effective tool in a posteriori quality check of mitochondrial DNA data.
Formation of a resistive region at the anode end in DNA capillary electrophoresis
Authors: Bilenko Olga , Gavrilov Dmitri , Gorbovitski Boris , Gorfinkel Vera , Gouzman Michael , Gudkov Georgy , Khozikov Vyacheslav , Khozikov Olga , Kosobokova Olga , Lifshitz Nadia , Luryi Serge , Stepoukhovitch Andrew , Tcherevishinick Marina , Tyshko Georgy
Published: April 2003

We have studied the formation of a resistive region in the capillary during DNA separation. This effect is caused by an unequal change in the mobilities of cations and anions at the interface between the running buffer solution and the capillary. We studied the motion of the resistive region boundary by sequential removal of portions of the affected capillary end. We found that in the process of developing the resistive region the distribution of the electric fields in the capillary changes from uniform to extremely nonuniform, with a very high field (above 1 MV/cm) in the resistive region and a reduced field (80 V/cm) in the rest of the capillary. Though theoretically a resistive region may appear either at the anode (detection) or the cathode (injection) end of the capillary, all previous publications report the formation of the resistive region at the cathode side. In our experiments, however, the anomalous region is formed at the anode. Thus, the separated DNA peaks move towards the slowly progressing resistive region. Our results indicate that the DNA is stopped at the boundary and does not enter the region. When the resistive region is clipped off the peak motion resumes. This suggests that there exists a potential barrier at the resistive layer boundary that prevents the drift of the peaks towards the anode. The formation of the resistive region interferes with a normal separation process causing a gradual decrease of the capillary current and the deceleration and eventual quenching of the peak motion. For the ABI chemistry, we experimented with adding polymers to the electrode buffer to equate the transference numbers for anions and cations, and found the conditions at which this effect is completely eliminated.
Dynamic range of fluorescence detection and base‐calling accuracy in DNA sequencer based on single‐photon counting
Authors: Gavrilov Dmitri N. , Gorbovitski Boris , Gouzman Mikhail , Gudkov Georgiy , Stepoukhovitch Andrei , Ruskovoloshin Victor , Tsuprik Andrei , Tyshko Georgiy , Bilenko Olga , Kosobokova Olga , Luryi Serge , Gorfinkel Vera
Published: April 2003

Recently, we developed a family of high‐performance automated capillary DNA sequencing instruments based on a single‐photon detection of fluorescently labeled DNA fragments. Our machines employ digital and broadband techniques, essential for achieving superior instrument sensitivity and dynamic range. In the present paper, we discuss limitations of the instrument's performance caused by the nonlinearity of single‐photon detectors as well as methods for nonlinearity compensation which increase the detection dynamic range and base‐calling accuracy.
A high‐throughput on‐line microdialysis‐capillary assay for D‐serine
Authors: O'Brien Kylie B. , Esguerra Manuel , Klug Christina T. , Miller Robert F. , Bowser Michael T.
Published: April 2003

A high‐throughput method is described for the analysis of D‐serine and other neurotransmitters in tissue homogenates. Analysis is performed by microdialysis‐capillary electrophoresis (CE) with laser‐induced fluorescence (LIF) detection in a sheath flow detection cell. Sample pretreatment is not required as microdialysis sampling excludes proteins and cell fragments. Primary amines are derivatized on‐line with o‐phthaldialdehyde (OPA) in the presence of β‐mercaptoethanol followed by on‐line CE‐LIF analysis. Under the separation conditions described here, D‐serine is resolved from L‐serine and other primary amines commonly found in biological samples. Each separation requires less than 22 s. Eliminating the need for sample pretreatment and performing the high‐speed CE analysis on‐line significantly reduces the time required for D‐serine analysis when compared with traditional methods. This method has been used to quantify D‐serine levels in larval tiger salamander retinal homogenates, as well as dopamine, γ‐amino‐n‐butyric acid (GABA), glutamate and L‐aspartate. D‐serine release from an intact retina was also detected.
Plasticity of protein expression during culture of fetal skin cells
Authors: Vuadens Françoise , Crettaz David , Scelatta Corinne , Servis Catherine , Quadroni Manfredo , Bienvenut Willy‐Vincent , Schneider Philippe , Hohlfeld Patrick , Applegate Lee A. , Tissot Jean‐Daniel
Published: April 2003

In order to gain insight into the biology of fetal skin during culture, cellular proteins were studied during four culture passages (P00, P01, P04 as well as P10) using high‐resolution two‐dimensional (2‐D) gel electrophoresis and mass spectrometry (MS). Bioinformatic analyses were focused on a region of each gel corresponding to pI between 4 and 8 and Mr from 8000 to 35 000. In this area, 373 ± 42 spots were detected (N = 18). Twenty‐six spots presented an integrated intensity that increased in the higher passages, whereas five spots showed a progressively lower intensity in subsequent passaging. MS analysis was performed on spots that were unambiguously identified on preparative 2‐D gels. Among the 26 spots showing an increased size between P00 and P10, 9 were identified, and corresponded to 3 proteins: (i) peptidyl‐prolyl cis‐trans isomerase A (P05092; cyclophilin A or cyclosporin A‐binding protein), (ii) triosephosphate isomerase (P00938), and (iii) enoyl‐CoA hydratase (P30084). Among these nine identified spots, three were absent at P00, but were present at P10. They corresponded to isoforms of peptidyl‐prolyl cis‐trans isomerase and triosephosphate isomerase, respectively. Liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) analyses of the acidic isoforms of triosephosphate isomerase showed modifications of cysteine residues to cysteic acid. All these isoforms were clearly present in the skin cells of a 4‐year‐old child, as well as in skin cells from a 80‐year‐old man, at P00. These observations probably reflect either an oxidative stress related to cell culture, or, alternatively, maturation, differentiation and the aging of the cells.
Kommentar: Auftrieb für Ingenieure und Informatiker
Authors: Nehmer Jürgen
Published: April 2003

Neue Qualifizierungswege für den akademischen Nachwuchs — Frühe Selbständigkeit und internationale Vernetzung werden gefördert
Vom Aufstieg und Fall der Stadt Xkipché
Authors: Prem Hanns J. , Vallo Michael , Paap Iken
Published: April 2003

Mexiko ist reich an steinernen Zeugnissen der Maya‐Kultur. Wie das Beispiel Xkipch� zeigt, haben die Maya ihre Häuser und Paläste offenbar vor dem Untergang verlassen. Archäologen untersuchen die Hintergründe
Ähnlich und doch verschieden?
Authors: Wolf Heike , Spinath Frank M. , Angleitner Alois
Published: April 2003

Prägen die Anlagen unserer Gene oder die Einflüsse der Umwelt das Verhalten des Menschen? Eine Studie an Zwillingen gibt neue Aufschlüsse
Kolloidchemische Systematik der Polymerisationsprozesse
Authors: von Wenning H.
Published: April 2003

Die Mannigfaltigkeit der Bedingungen, unter welchen Polymerisationsprozesse ablaufen können, macht eine rationelle Gliederung notwendig. Hier wird der Versuch unternommen, eine Klassifizierung der Polymerisationsprozesse unter kolloidchemischen Gesichtspunkten zu geben.

Die bei der Polymerisation zur Anwendung kommenden Emulgatoren und Initiatoren können öllöslich, wasserlöslich oder unlöslich sein. Durch die Eigenschaften dieser Molekül‐, Mizell‐ und Phasenkolloide werden die kolloidchemischen Polymerisationsbedingungen bestimmt.

Polymerisationsprozesse in Lösung ohne Emulgator sind einphasig. Polymerisationsprozesse mit löslichen Emulgatoren vollziehen sich in zweiphasiger Emulsion.

Unlösliche, feste Emulgatoren lassen Polymerisationsprozesse dreiphasig ablaufen.

Im Gegensatz zu molekulargelösten (öllöslichen und wasserlöslichen) Polymerisationsinitiatoren, die die Zahl der Phasen nicht verändern, wird durch feste Polymerisationsinitiatoren die Zahl der Phasen erhöht und der Polymerisationsprozeß selbst in die Grenzflächen der Phasen verlegt, unter welchen die Grenzschichten Fest‐Flüssing, Fest‐Gas und Flüssig‐Flüssig von besonderer Bedeutung sind.

Die kolloidchemische Bedeutung der Phasengrenzfläche Fest‐Flüssig für die stereochemische Polymerisation wird eingehend diskutiert.

Die Systematik scheint auch eine rationelle Verschlüsselung für Hollerith‐ oder Randlochkarten zu gestatten.
Über natürliche und synthetische amylose VII. Die gestalt der amylosemoleküle1
Authors: Husemann Von E. , Bartl H.
Published: April 2003

Durch viskosimetrische Untersuchungen an Amyloseacetaten verschiedenen Substitutionsgrades sowie an Amylosen, die in wäßriger Lösung oder in festem Zustand „gealtert”︁ waren, wird festgestellt, daß die Moleküle unter Ausbildung von sehr festen innermolekularen Wasserstoffbindungen ihre Gestalt kontinuierlich ändern (Kontraktion). Partielle Substitution führt zu einer Stabilisierung der Gestalt, vollständige Substitution bewirkt maximale Streckung. Es besteht weder bei Amylosen noch bei teilweise substituierten Derivaten eine eindeutige Beziehung zwischen Polymerisationsgrad und Viskositätszahl.
Zur anionischen ε‐caprolactam‐polymerisation. Versuche über die viskositätsstabilisierung
Authors: Griehl Wolfgang , Schaaf Siegfried
Published: April 2003

Zur Erzielung eines gleichmäßigeren Verlaufs der anionischen Caprolactam‐Polymerisation wurden GRIGNARD‐Verbindungen eingesetzt. Es gelang damit Polymerisationen auszulösen, die den bekannten Gesetzmäßigkeiten folgten. Ein Zusatz von Essigsäureestern langkettiger Alkohole zum Polymerisationsansatz erbrachte dagegen eine deutlich stabilisierende Wirkung. Noch besser wirkt Acetylcaprolactam, das bezüglich des verwendeten Initiators und des Caprolactams in verschiedenen Konzentrationsverhältnissen eingesetzt wurde. Die dabei auftretenden Gesetzmäßigkeiten über die Abhängigkeit des Zahlenmittels des Gleichgewichtspolymerisationsgrades von der Acetylcaprolactam‐ bzw. Natriumcaprolactamkonzentration und von der Polymerisationstemperatur stimmen mit denen der beschleunigten Radikalkettenpolymerisation überein.
Über die autoxydation ungesättigter verbindungen XI. Mitteilung. Die katalyse der autoxydation von linolsäuremethylester mit linolsäuremethylesterhydroperoxyd
Authors: Kern Von W. , Dulog L. , Selz G.
Published: April 2003

Aus oxydiertem Linolsäuremethylester wurde das Linolsäuremethylesterhydroperoxyd durch Gegenstromverteilung isoliert und reinem Linolsäuremethylester als Katalysator für die Autoxydation zugesetzt. Kinetische Versuche zeigen die identische Wirkung des zugesetzten Linolsäuremethylesterhydroperoxydes und des Autokatalysators der Spontanreaktion.
Die co‐vernetzung von polyvinylpyrollidon und polyacrylamid in wässriger lösung durch co‐60‐gamma‐strahlen
Authors: Henglein Von Arnim
Published: April 2003

Polyvinylpyrollidon und Polyacrylamid, die in wäßriger Lösung einzeln unter Gamma‐Bestrahlung vernetzen, bilden in derselben Lösung ein gemeinsames Netzwerk. Allgemein sind für die Netzwerke aus zwei Polymeren diejenigen Grenzstrukturen denkbar, in denen zwei Homo‐Netzwerke der beiden Polymeren nur physikalisch miteinander verflochten sind (Misch‐Netzwerk) oder aber echte chemische Bindungen zwischen den polymeren Komponenten bestehen (Co‐Netzwerk). Co‐Vernetzung läßt sich durch die Bildung eines Pfropf‐Mischpolymeren bei geringen Vernetzungsgraden und durch kinetische Messungen über die Konzentrations‐Abhängigkeit der Vernetzungsgeschwindigkeit in verdünnten Lösungen erkennen. Im System Polyvinylpyrollidon‐Polyacrylamid findet Co‐Vernetzung statt.

Während dieser Versuche wurde beobachtet, daß die Viskosität verdünnter Lösungen des Polyacrylamids oft anormalerweise ansteigt um bei höheren Dosen wieder abzufallen. Es wird vorläufig angenommen, daß sich in verdünnten Lösungen zunächst Mikro‐Netzwerke über kleine Bereiche des gelösten Polymeren bilden. Diese Mikro‐Gele vernetzen bei höheren Dosen immer mehr in sich; ihre reduzierte Viskosität wird zunächst durch die Erhöhung des Molekulargewichts und später durch die Veränderungen ihrer Form und Quellfähigkeit bestimmt.
Zum flockungsverhalten makromolekularer polyelektrolyte I. Die flockungswirkung von polystyrolsulfonat gegenüber eisenhydroxydsolen
Authors: Gärtner Von Klaus , Efer Klaus
Published: April 2003

Die Flockungswirkung von Natriumpolystyrolsulfonat gegenüber Eisenhydroxydsol wurde mit Hilfe von Trübungsmessungen untersucht. Koagulation findet nur bei optimalen Konzentrationen an Koagulator statt, bei weiterer Erhöhung des Koagulatorzusatzes tritt eine Stabilisierung ein, die durch Vorstellungen über den Mechanismus der Flockung erklärt werden kann. Eine Abhängigkeit der Wirksamkeit vom Molekulargewicht des Polyelektrolyten kann nicht beobachtet werden.
Dilatometric and nuclear magnetic resonance studies of polyethylene with different branching and crystallinity
Authors: Peterlin A. , Kras̆ovec F. , Pirkmajer E. , Levstek I.
Published: April 2003

Highly branched (DUPONT) and nearly unbranched (Marlex 50) polyethylenes were investigated. The samples were partly crystallized. Marlex was also prepared in pure crystalline form. Dilatometric investigations revealed a sharp melting point and practically no relaxation phenomena in pure crystals. Nuclear magnetic resonance absorption spectra of branched samples definitely show remains of narrow line even at – 170°C., but it disappears completely with Marlex. In pure crystals the narrow line is extremely weak below 70°C. and changes reversibly with temperature. After heating over 70°C. irreversible changes occur, the samples approaches the structure of Marlex crystallized from melt.
Schmelz‐ und kristallisationserscheinungen bei makromolekularen substanzen. II. Haupt‐ und nachkristallisation aus der unterkühlten schmelze von 4,6‐polyurethan
Authors: Rohleder Von J. , Stuart H. A.
Published: April 2003

Mit einer Dichtewaage werden Kristallisationsisothermen von 4,6‐Polyurethan aufgenommen. Nach einer Beschreibung der Apparatur werden die Meßergebnisse im Temperaturbereich oberhalb 163°C und über Kristallisationszeiten von zehn Minuten bis zu zwei Tagen mitgeteilt.

Zur Deutung der Kristallisationsisothermen wird zwischen Haupt‐ und Nachkristallisation unterschieden. Die Hauptkristallisation wird als Wachstum morphologischer Strukturen verstanden und die Nachkristallisation als langsame Verbesserung des mäßigen mittleren Ordnungsgrades innerhalb dieser Strukturen. Die Hauptkristallisation wird im Sinne von AVRAMI, EVANS und MORGAN ausgewertet. Für die systematischen Abweichungen von der AVRAMI‐Gleichung wird eine mögliche Deutung diskutiert. Die Nachkristallisation wird durch eine einfache, sinngemäße Gleichung beschrieben.
Irradiation of phosphonitrilic chlorides. Part I. Irradiation of lower homologues
Authors: Spindler M. W. , Vale R. L.
Published: April 2003

The irradiation of trimeric and higher molecular weight linear and cyclic phosphonitrilic chlorides is described using 4 MeV electrons from a linear accelerator. The yields of polymer obtained under a variety of conditions, in the presence and absence of oxygen, are given. The changes in the infrared spectrum following irradiation indicate the presence of phosphorus‐oxygen‐phosphorus bonds in the polymers. It is found that the cyclic polymers are radiation stable in accordance with their aromatic character whereas the linear polymers and phosphonitrilic chloride gel are more sensitive to ionizing radiation.
Prüfung der gültigkeit der copolymerisationsparameter zur berechnung der zusammensetzung von copolymerisaten vernetzter polyesterharze bei hohen umsätzen
Authors: Funke Von Werner , Knödler Siegfried , Feinauer Roland
Published: April 2003

Für Polyesterharze aus reinem Fumarsäurepolyester und verschiedenen Mengen Styrol wurde nach der Copolymerisation der Umsatz an beiden Monomeren experimentell bestimmt. Aus dem gefundenen Umsatz wurde die Zusammensetzung der Copolymerketten mittels der integrierten Copolymerisationsgleichung berechnet. Als r‐Parameter wurden die von der linearen Copolymerisation von Fumarsäurediäthylester und Styrol bekannten Werte verwendet.

Die experimentell erhaltenen Werte für die Zusammensetzung stimmten relativ gut mit den berechneten überein. Man kann daher den Schluß ziehen, daß die bekannten Reaktivitäten beider Monomeren durch Einbau der Fumarsäureeinheiten in Polyester und Copolymerisation mit Styrol zu hohem Umsatz nicht wesentlich verändert werden. Möglicherweise ist eine geringfügige Abweichung der Zusammensetzung in Richtung höheren Styrolgehaltes auf die allgemeine Diffusionskontrolle am Ende der Härtungsreaktion zurückzuführen.
Copolymerization of 3,3‐bis(chloromethyl) oxacyclobutane and tetrahydrofuran
Authors: Saegusa Takeo , Imai Hirosuke , Furukawa Junji
Published: April 2003

The copolymerization of 3,3‐bis(chloromethyl)oxacyclobutane (BCMO) and tetrahydrofuran (THF) was performed by using various FRIEDEL‐CRAFTS catalysts. The molecular complex compounds of BF3, SnCl4 and AlBr3 were found to give amorphous polymers of considerably high molecular weight. Other FRIEDEL‐CRAFTS catalysts such as FeCl3, AlCl3, TiCl4, SbCl5, SbF3 and PCl5 gave no polymeric products. Most polymers were soluble in chloroform and insoluble in methanol. This solubility characteristic was taken to indicate that the polymeric products were real copolymers and not mixtures of two homopolymers of BCMO and of THF. The monomer reactivity ratios of BCMO and THF were determined in the BF3·(C2H5)2O catalyzed copolymerization at 0°C., which were r1 (BCMO) = 0.82 ± 0.05 and r2 (THF) = 1.00 ± 0.05. The infrared spectrum of the copolymer was shown to be composed of the two homopolymers except for the adsorption at 1000 cm−1 which is absent in the copolymer. The band at 1000 cm−1 is a crystalline band of homopoly‐THF, and this finding also supports the random copolymerization.
Eine neue Methode zur Bestimmung von Verteilungen der 3,4‐ (bzw. 1,2‐)Addition oder der Cyclisierung auf die Moleküle von Polyisopren und Polybutadien
Authors: Hoffmann Von M.
Published: April 2003

Durch Umsetzung mit Perbenzoesäure wird die Löslichkeit von Molekülen des 1,4‐Polyisoprens in Tetrachlorkohlenstoff‐Methanol‐Gemischen so stark vergrößert, daß sich Moleküle, die überwiegend nach dem Prinzip der 3,4‐ (bzw. 1,2‐)Addition aufgebaut sind, oder solche, die einen starken Verlust an Doppelbindungen (z.B. durch Cyclisierung) erlitten haben, leicht abtrennen lassen. Mit Hilfe der Trübungstitration können Bruchteile eines Prozentes von ihnen in cis‐1,4‐Polyisopren nachgewiesen werden. Die Löslichkeit von cis‐1,4‐Polybutadien wird durch die Reaktion mit Perbenzoesäure weniger vergrößert als die von cis‐1,4‐Polyisopren.
Sauerstoffbestimmung in polymerisationsansätzen und metallorganischen katalysatoren
Authors: Sinn Von Hansjörg , Aumann Dieter
Published: April 2003

Bei der aktivierungsanalytischen Sauerstoffbestimmung durch Zählung des nach 6Li(n,α)t; 16O(t,n) 18F entstehenden 18F kann vorteilhaft Lithiumbutyl als Tritonenquelle verwendet werden.

In 500 mg Lithiumbutyl können 1 γ Sauerstoff leicht bestimmt werden.

Wegen der Mischbarkeit des Lithiumbutyls mit anderen metallorganischen Katalysatoren, Lösungsmitteln und Monomeren ist auch in solchen Systemen entsprechende Sauerstoffbestimmung möglich.
Über die stabilität der konfiguration von taktischen polystyrolen
Authors: Braun Von Dietrich , Hintz Hans , Kern Werner
Published: April 2003

Es wurde die Möglichkeit der Veränderung der Taktizität von isotaktischem Polystyrol geprüft. Weder durch mechanischen Abbau in der Kugelmühle noch durch chemischen Abbau mit Aluminiumtrichlorid in Lösung wird die taktische Struktur der Polystyrole beEinflußt.

Durch Einwirkung von K/Na2O auf isotaktisches Polystyrol erhält man Poly‐α‐Kaliumstyrol, dessen Taktizität ebenfalls unverändert ist, da nach der Hydrolyse wieder kristallisierbares Polystyrol zurückgewonnen wird.

Somit zeigt taktisches Polystyrol gegenüber „racemisierenden”︁ Agentien wesentlich größere Stabilität als vergleichbare niedermolekulare Modellverbindungen.
Determination of the molecular weight of polymethyl methacrylate by end‐group analysis
Authors: Misra G. S. , Gupta V. P.
Published: April 2003

The polymerization of methyl methacrylate, using γ,γ′‐azo‐(γ‐cyano‐n‐valeric acid) as initiator has been studied at 90 and 100°C. in dimethyl formamide solution. Several samples of polymethyl methacrylate of low molecular weight (below the osmotic pressure range) have been prepared under a variety of conditions in the presence of the above initiator. The molecular weights of the samples have been determined by viscosity and end‐group titrations, both for fractionated and unfractionated samples. The results are then compared with those obtained by other authors. It was found that for unfractionated polymer samples equation: M̄n = 1.99·105·[η]1.46 of EVANS et al. seems to hold good. For sharp fractions, the relationship: M̄n = 2.81·105[η]1.32 of the same authors appears to give reasonably good correspondence.
Zur kenntnis von acrylsäure enthaltenden copolymerdispersionen. I. Über die auswertung von streulichtmessungen
Authors: Wesslau Von Hermann
Published: April 2003

Streulichtmessungen an Polymerdispersionen kann man auswerten, indem man den Logarithmus der reziproken Streuintensität bzw. log magnified image gegen sin2 ν/2. darstellt. In dieser Darstellung liefern Streufunktionen monodisperser und auch mäßig heterodisperser Dispersionen Geraden, aus deren Neigung die Teilchengröße berechnet werden kann. Als Grundlage für die Rechnung genügt die RAYLEIGH‐GANS‐DEBYEsche Theorie. Die Grenzen der Anwendbarkeit werden experimentell ermittelt: sie liegen für Polystyrol bei ca. 400 mμ und für Polyacrylester bei ca. 800 mμ.
Kinetische ergebnisse bei der polymerisation von äthylen und propylen. Zur polymerisation mit metallorganischen mischkatalysatoren, 2. Mitteilung
Authors: Schnecko Von H. , Reinmöller M. , Weirauch K. , Bednjagin V. , Kern W.
Published: April 2003

Es wird über kinetische Ergebnisse bei der Polymerisation von äthylen und Propylen mit ZIEGLER‐NATTA‐Katalysatoren berichtet. Für die Abhängigkeit der Reaktionsgeschwindigkeit von Monomerdruck und von der Gesamtkatalysatorkonzentration werden lineare Beziehungen gefunden. Die Messung der Temperaturabhängigkeit erlaubt eine Berechnung der Aktivierungsenergie nur bei Anwendung von TiCl3, nicht von TiCl4. Bei der Variation der Konzentration der angewandten Al‐organischen Komponenten erhält man mit TiCl3 stets Kurven in Form von Adsorptionsisothermen, mit TiCl4 dagegen Maximumskurven und in einem Fall ebenfalls eine Adsorptionsisotherme. Die experimentellen Ergebnisse werden diskutiert und können teilweise durch Gleichungen beschrieben werden.
Polymerization of propylene with vanadium halides and aluminum alkyls
Authors: Natta G. , Mazzanti G. , De Luca D. , Giannini U. , Bandini F.
Published: April 2003

The polymerization of propylene with VCl3 and aluminum alkyls has been studied. The decrease of the polymerization rate with the increase of the polymerization temperature, in the presence of the catalytic system VCl3‐Al(C2H5)3, is connected with the surface reduction of VCl3 to VCl2. When using Al(C2H5)2Cl at temperatures below 90°C. no reduction of VCl3 is detectable, and the rate of polymerization regularly increases with increasing temperature.

Using VCl3 in combination with Al(C2H5)3 the stereospecificity is higher than in the case of Al(C2H5)2Cl, in contrast to catalytic systems based on violet TiCl3.
Polybenzimidazoles. III. Polyamides containing benzimidazole rings
Authors: Iwakura Yoshio , Uno Keikichi , Imai Yoshio , Fukui Motoo
Published: April 2003

A new aromatic diamine containing benzimidazole rings, 2,2′‐di‐p‐aminophenyl‐5,5′‐bibenzimidazole, was prepared by the condensation of 3,3′‐diaminobenzidine tetrahydrochloride with p‐aminobenzoic acid in polyphosphoric acid. The diamine was subjected to polycondensation with dicarboxylic acid chlorides in dimethylacetamide to form polyamides.

These polyamides showed excellent thermal stability.
A study of the fine structure of regenerated cellulose fibers
Authors: Bingham B. E. M.
Published: April 2003

The examination of a series of high wet modulus fibers by methods commonly employed in studying fiber structure has shown that these methods measure overall molecular accessibility rather than truly crystalline material. The only unequivocal measure of lattice structure is obtained from X‐ray measurements. The amount of such material within the molecular structure appears to be governed by probability and in consequence such measurements would seem to have little significance in terms of fiber properties.

In as much as marked changes in one dimensional order, as measured by birefringence, can be directly correlated with changes in fiber structure, as determined by other methods, birefringence measurements appear to be a tool of considerable value in structural studies.

Using such correlations, it has been shown that an ideally oriented regenerated cellulose fiber has a conditioned birefringence of 0.056 and an accessibility of 27%.
Reactive polymers. II. Syntheses and copolymerizations of some new monomers via DIELS‐ALDER‐reaction
Authors: Iwakura Yoshio , Nakabayashi Nobuo , Lee Ming Hsing
Published: April 2003

A number of monomers containing reactive groups such as epoxide and isocyanate were prepared through DIELS‐ALDER reaction. Butadiene, cyclopentadiene, glycidyl sorbate, and isoprene were used as dienes; glycidyl methacrylate, glycidyl methyl itaconate, glycidyl ethyl maleate, glycidyl acrylate, vinyl isocyanate, glycidyl vinyl sulfonate, methyl methacrylate, and acrylonitrile as dienophiles. The adducts obtained generally had high boiling points, and the yields were 40 to 80%, based on the dienophile charged. The monomer reactivity ratios of some typical monomers were determined.
Über den thermischen abbau von poly‐α‐methylstyrolen unterschiedlicher taktizität
Authors: Braun Von Dietrich , Heufer Gert
Published: April 2003

Es wurde der thermische Abbau von Poly‐α‐methylstyrolen verschiedener Taktizität in Substanz unter Stickstoff bei Temperaturen zwischen 220 und 240°C untersucht. Dabei wurde gefunden, daß die kationisch hergestellten, hochgradig syndiotaktischen Polymeren wesentlich langsamer depolymerisieren als die fast ataktischen, anionisch hergestellten Poly‐α‐methylstyrole. Die Ergebnisse beim Abbau von Poly‐α‐methylstyrolen mit verschiedenen Endgruppen machen neben dem hauptsächlich durch statistische Kettenspaltung erfolgenden Abbau auch einen teilweise am Kettenende einsetzenden Abbau wahrscheinlich.
Initation mechanism of acetaldehyde polymerization by alkyl aluminum catalyst
Authors: Fujii H. , Tsukuma I. , Saegusa T. , Furukawa J.
Published: April 2003

The initiation of the acctaldehyde polymerizations with

catalysts were studied by gasometry and gas chromatography. It was found that Al(C2H5)3 first reacted with acetaldehyde to give (I) under the polymerization condition. Then the polymerization was initiated by the sec‐butoxyl group, but not by the ethyl group; 2 ethyl groups of (I) remained unreacted during the following polymerization. Therefore, the active species of these two catalysts seem to be similar. However, they were found to differ in stereospecificity which was ascribed to the degree of aggregation of species (I).
p‐Vinylbenzoic acid: A convenient preparation, copolymerization, and examination as dye receptive modifier for acrylic fibers and as ion exchange resin component
Authors: Ōsawa E. , Wang K. , Kurihara O.
Published: April 2003

A convenient preparation of p‐vinylbenzoic acid from β‐haloethylbenzene with 67% overall yield was described. Monomer reactivity ratio of p‐vinylbenzoic acid (1) to acrylonitrile (2) was determined:

p‐Vinylbenzoic acid increased the affinity of acrylic fibre toward cationic dye when copolymerized with acrylonitrile, but was less effective than sulfonic acids as dye receptive site. Acid ion exchange resins based on p‐vinylbenzoic acid possessed a high selection factor of Ca2+ over Mg2+.
Über die bildung und struktur von polymeren des α‐cyanstyrols und des p‐phenylendiacrylnitrils. II
Authors: Funke Von W.
Published: April 2003

Bei der Reaktion von p‐Phenylendiacetonitril (p‐Xylylendicyanid) mit Formaldehyd in Gegenwart von Alkaliverbindungen bilden sich vernetzte Polymere. Versuche mit Phenylacetonitril (Benzylcyanid) und Formaldehyd sowie mit monofunktionellen Modellverbindungen weisen darauf hin, daß diese vernetzten Polymerendurch anionische Polymerisation intermediär entstehender Phenylenacrylsäurenitrileinheiten gebildet werden. Als Endgruppen konnten Methoxyl‐, Hydroxymethyl‐, und Imidoestergruppen nachgewiesen werden. Die Bildung von Hydroxymethyl‐ und Imidoestergruppen stellt eine Gleichgewichtsreaktion dar. Imidoestergruppen entstanden nur aus solchen Nitrilgruppen, deren benachbarte C‐Atome noch H‐Atome besitzen.
Zur charakterisierung der copolymerketten und der netzwerkdichte in polyesterharzen
Authors: Nollen Von K. , Funke W. , Hamann K.
Published: April 2003

Es wurden die Molekulargewichts‐ und die Konstitutionsverteilungen der Copolymerketten verschiedener Polyesterharze bestimmt. Hierbei zeigte sich eine systematische Änderung der Molekulargewichts‐ und der Konstitutionsverteilung mit der Zusammensetzung der Polyesterharze. Das Molekulargewicht der Copolymer ketten ist im allgemeinen so groß, daß die Netzwerkdichte der Polyesterharze durch die endliche Länge der Copolymerketten nicht wesentlich beeinflußt wird.
Infrared studies of polymer chain folding I. Linear polyethylene
Authors: Koenig J. L. , Witenhafer D. E.
Published: April 2003

An infrared method has been developed for studying folding in linear polyethylene utilizing the assignment of the 1350 cm−1 and 1304 cm−1 bands to gauche methylene units. Gauche methylenes can occur in the disordered regions or as a part of the fold; their absorption coefficients are different in the two regions and allow one to determine their contribution to each region by simultaneous solution of the absorbance equations.

The results indicate the fold structure of slow‐cooled bulk polyethylene is essentially the same as the folds of solution crystallized polyethylene and no disordered regions containing gauche methylenes exist. Rapidly cooled samples contain gauche methylenes in anomalous structures which tend to disappear during annealing. Annealing at 120°C. produces no change in the fold structure of single crystals.
Activation of poly[N‐(2‐hydroxypropyl)methacrylamide] for the binding of bioactive molecules, 2. Activation with cyanogen bromide
Authors: Chytrý Vladimír , Kopeček Jindřich
Published: April 2003

The amount of chymotrypsinogen linked to poly[N‐(2‐hydroxypropyl)methacrylamide], which was activated by cyanogen bromide, under various conditions was determined. The optimal activation time was found to be indicated by the beginning of an invariable base consumption during the reaction of the polymer with cyanogen bromide. The degree of activation increased with the concentration of cyanogen bromide and with the pH, and the yield of coupling can be increased by variation of the temperature, concentration of the reaction components, and pH. At room temperature and pH 9,3, the coupling reaction was completed in less than 24 h. The stability of the activated polymer depends strongly on temperature and pH. The analysis of the active moieties on the polymer carrier revealed that the application of the generally accepted mechanism for cyanogen bromide activation of polysaccharide carriers to the activation of poly[N‐(2‐hydroxypropyl)methacrylamide] remains to be proved.
A general method for the determination of “monomolecular property versus molar mass relationships” from measurements on polymolecular polymers
Authors: Bareiss Rolf E.
Published: April 2003

“Monomolecular property (p) versus molar mass (M) relationships” of the type p = Kp · Map as would result from an experimental determination of p and M of a polymer‐homologous series of strictly monomolecular polymers can also be obtained from a polymer‐homologous series of polymolecular samples or fractions, provided their correct corresponding averages p and M are determined (Principle of Corresponding Averages). In order to obtain the monomolecular intrinsic viscosity [η] vs. M relationship (Mark‐Houwink relationship), the corresponding averages weight‐average intrinsic viscosity ([η]w ≡ [η]) and viscosity‐average molar mass (M[η]) of a series of polymer‐homologous, polymolecular polymer samples or fractions have to be determined experimentally. Accordingly, the corresponding monomolecular relationships sedimentation coefficient s vs. M, diffusion coefficient D vs. M, and mean‐square radius of gyration 〈r2〉 vs. M are obtained by the determination of a series of couples of the corresponding averages s vs. M, D vs. M, and 〈r2〉 vs. M, respectively. The experimental determination of the corresponding averages presented is possible by different methods, including the determination of the molar mass distribution.
Oligo(thiophénylènes‐1,4) α,ω‐difonctionnalisés, 3. Oligomères α,ω‐diaminés et copolyamides qui en dérivent
Authors: Daccord Gérard , Sillion Bernard
Published: April 2003

Polyamides 7a and 7b were prepared from α‐(4‐aminophenyl)‐ω‐aminopoly(thio‐1,4‐phenylene)s (3a) by reaction with 1,12‐dodecanedioic acid (6), tribloc copolymers 9 from 3a and 11 aminoundecanoic acid (8), and multibloc copolymers 10 from 3a, 6, and 8. The properties of these copolymers were studied by DSC and compared with those of N, N'‐lauroyl derivatives of 3a as model compounds. Phase separations were observed with products containing at least four phenylene units in the thiophenylene blocs. However, the Tg was found to increase with increasing number of phenylene units.
Studies on the CHCL3‐soluble fraction of polythiophene and its conductivity on doping with iodine
Authors: Cao Young , Wu Quihui , Guo Kezhen , Qian Renyuan
Published: April 2003

The CHCl3‐soluble fraction of polythiophene, prepared by catalytic coupling of thienyl Grignard reagent, was characterized by VPO, GPC, TLC, 1 H NMR, and WAXS measurements. Iodine doping of this polymer shows a maximum conductivity of the order of 5 Ω−1· cm−1, much higher than that of I2‐doped compact powder pellets of the insoluble polymer. IR spectra of slightly I2‐doped polythiophene show two new strong absorption bands, one at 1360–1380 cm−1 and the other at 1140 cm−1. XPS results indicate that the C 1st peak does not change after doping while the profile of the S 2p peak changes markedly. This suggests that in I2‐doped polythiophene the positive charge is localized on the S atom. Combined results of the change of the I 3d XPS peak profile and the Raman spectrum in the low frequency region suggest that iodine in doped polythiophene is present in the form of the I2 moleculre and the I‐ion, in contrast to polyacetylene where iodine exists in the form of I3− and I5− anions.
Thermisch und UV‐photochemisch initiierte hochdruckpolymerisation des ethylens, 1. Molmassen‐mittelwerte
Authors: Buback Michael , Choe Chul‐Rim , Franck Ernst‐Ulrich
Published: April 2003

Ethylene is polymerized with thermal and with UV‐photochemical initiation at temperatures between 130°C and 255°C up to pressures of 2500 bar. The conversions are between two and five percent. The degrees of polymerization as obtained from viscosity experiments are dependent on reaction temperature and pressure, but are insensitive to the kind of initiation, thermal or photochemical. These observations are explained by an equation which relates the degree of polymerization to kinetic parameters of the system which have partly been determined by independent experiments. From this equation, the activation energy and the activation volume of the transfer constant with the monomer, cm, are determined to be Ea(cm) = 43,9 ± 4 kJ · mol−1 and ΔV≠ (cm)=20,1 ± 3 cm3 · mol−1, respectively.
Photoinitiators and photoinitiation, 5. Photodecomposition of some α‐hydroxymethylbenzion derivatives: Sulfonic esters
Authors: Gaur Hardew Angad , Groenenboom Cornelis J. , Hageman Hendrik J. , Hakvoort Gerard T. M. , Oosterhoff Pieter , Overeem Ton , Polman Romkina J. , van der Werf Sake
Published: April 2003

The photodecomposition of several sulfonic esters of α‐hydroxymethylbenzion (1a) was studied by means of ESR and 1H NMR‐CIDNP techniques. An exclusive α‐cleavage into benzoyl and α‐hydroxy‐α‐sulfonyloxymethylbenzyl radicals (6 and 7) through a triplet excited state was observed. Radicals (7) were found to undergo elimination of sulfonic acid to give benzoylmethyl radicals (9) in an extremely fast process. Chemical confirmation was provided by naphthalene quenching and radical‐trapping experiments using 1‐dodecanethiol and 2,2,6,6‐tetramethylpiperidin‐1‐oxyl, respectively. Photodecomposition of the sulfonic esters in the presence of 1,1‐diphenylethylene as a model substrate for vinyl monomers indicated that both benzoyl and benzoylmethyl radicals are highly reactive towards the carbon‐carbon double bond.
Precursors of hydrophilic polymers, 3. The potentiometric behaviour of isotactic and atactic poly(2‐dimethylaminoethyl methacrylate) in water/ethanol solutions
Authors: Přádný Martin , Ševčík Stanislav
Published: April 2003

The dissociation constants of partially ionized isotactic and atactic poly(2‐dimethylaminoethyl methacrylate) in water/ethanol solutions were measured. The strong dependence of the apparent dissociation constant on the degree of ionization of the macromolecule is discussed using viscometric data and compared with the properties of low‐molecular‐weight model compounds. The values of the internal dissociation constants at various ionic strength in various water/ethanol solutions were obtained by extrapolation of the apparent dissociation constants to zero ionization degree of the macromolecule. The conformational structures of macromolecules in solution are discussed.
Precursors of hydrophilic polymers, 5. Activation parameters of quaternization of poly(2‐dimethylaminoethyl methacrylate) with methyl iodide
Authors: Přádný Martin , Ševčík Stanislav
Published: April 2003

The paper deals with the quaternization reaction of isotactic and atactic poly(2‐dimethylaminoethyl methacrylate) with methyl iodide in three water‐ethanol solutions at different temperatures. Using the temperature dependence of the rate constants extrapolated to zero conversion, the activation quantities at the beginning of the reaction were calculated (activation energy, enthalpy, entropy, free enthalpy, and the frequency factor). The reactivities of the two polymers are compared with each other and then also with that of a low‐molecular weight model compound, 2‐dimethylaminoethyl pivalate (DAEP). Reactivity of all compounds under investigation increases with increasing water content in the solvent: that of DAEP due to the decreasing negative activation entropy, that of the two polymers as a result of decreasing activation energy. Using the measured activation energies and entropies, polarity of the transient state of the polymers is discussed in comparison with the low‐molecular weight model, along with polymeric effects which may become operative in the quaternization reaction.
DSC studies of linear low density polyethylene. Insights into the disrupting effect of different comonomers and the minimum fold chain length of the polyethylene lamallae
Authors: Burfield David R. , Kashiwa Norio
Published: April 2003

This paper reports a DSC examination of a series of linear low density polyethylenes (LLDPE) prepared variously with propylene, 1‐butene or 4‐methyl‐1‐pentene comonomers. The enthalpy of fusion of the crystalline regions of the LLDPE decreases progressively with increasing comonomer content and is effectively independent of the comonomer type. Disruption of polymer crystallinity is thus determined principally by the number and distribution of the chain irregularities. A sequence length of n = 14 was calculated as the critical chain dimension below which polyethylene segments cannot be readily packed into a stable crystal lattice.
Formation of large cyclic amides by catalytic depolymerization of polyamides
Authors: Langhammer Monika , Lüderwald Ingo , Weingärtner Michaela
Published: April 2003

Nylon 8, nylon 12, nylon 6.6, nylon 11.6 and nylon 12.12 were thermally converted into cyclic oligomers at 280 to 330°C within one to three hours. The reaction is catalyzed by small amounts of salts of different carboxylic acids and is supposed to take place by an anionic depolymerization mechanism.
Conformational analysis of higher poly(oxyalkylenes) using empirical force field calculations
Authors: Miyasaka Taira , Yoshida Takaichi , Imamura Yoshio
Published: April 2003

The conformational energies for the various rotational isomers of model compounds for poly(oxytrimethylene), POM3, and poly(oxytetramethylene), POM4, were calculated by means of the empirical force field method, and statistical mechanics calculations were made for the configuration‐dependent properties of POM3 and POM4. Although the dipole moment ratios of these polymers directly calculated from the results of the force field calculations agreed well with the observed ones, the estimated characteristic ratios did not agree with the observed ones. When the two geometric parameters of POM3 were changed, excellent agreement between the experimental values and the estimated ones was obtained. In case of POM4, when only geometric parameters were changed, the agreement was less satisfactory. The value for the interaction energy Eσ, which is directly derived from the result of the force field calculation for the model compound of POM4, seems to be overestimated because of a fault minimum. The value for the interaction energy Eσ is estimated to be the same as for POM3. Moreover, when the four geometric parameters were changed, the estimated values agreed well with the experimental ones. The direct use of the results of the force field calculations is not always satisfactory, but the parameters obtained are a good initial set of parameters to reproduce the observed configuration‐dependent properties.
Precursors of hydrophilic polymers, 7. Potentiometric properties and structure of copolymers of 2‐dimethylaminoethyl methacrylate
Authors: Přádný Martin , Ševčík Stanislav
Published: April 2003

The study concerns the potentiometric behaviour of statistical copolymers of 2‐dimethylaminoethyl methacrylate with 2‐hydroxyethyl methacrylate, acrylamide, methacrylamide, 2‐methacryloyloxyethyltrimethylammonium methylsulfate, and of copolymers arising by the partial quaternization of poly(2‐dimethylaminoethyl methacrylate) with methyl iodide in various water‐ethanolic solutions. The potentiometric properties of poly(4‐dimethylaminobutyl methacrylate) and poly(6‐dimethylaminohexyl methacrylate) are also reported. The course of modified titration curves and the differences between pK0 values of copolymers and pK values of low‐molecular weight model compounds are discussed. Side chains of copolymers of 2‐dimethylaminoethyl methacrylate have a cyclic conformation (similarly to the homopolymer); the carbonyl and amine group interact with each other. Copolymers formed by the partial quaternization of poly(2‐dimethylaminoethyl methacrylate) with methyl iodide in a water‐ethanolic medium (Menshutkin's reaction) have a block structure, which suggests a zip mechanism of the quaternization reaction.
Metathesis degradation of poly(butadiene‐alt‐propene)
Authors: Hummel Klaus , Lechner Hildegard , Zekoll Haimo , Chemelli Ronald
Published: April 2003

Poly(butadiene‐alt‐propene) (1) was degraded by metathesis reaction using symmetric olefins (3‐hexene and 4‐octene) in chlorobenzene solution in the presence of WCl6/(CH3)4Sn as catalyst. Identification of the degradation products by means of a combination of gas chromatography (GC) and mass spectrometry (MS) revealed small amounts of “defects” in the almost ideally alternating copolymer 1. These were non‐alternating sequences of 2‐butenylene and methylethylene units, vinylethylene units and branching points. In addition, the metathesis degradation of 1 with 4‐octene was investigated kinetically between 15 and 40°C. The measurements confirm that the thermodynamically stable 4‐methylcyclohexene is the final product. This can be formed directly from the polymer and via oligomeric products. The formation of these intermediates is preceded by an induction period. Their concentrations pass maxima, the positions of which depend on the size of the molecules and on the temperature.