bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Hydrogen Bonding on the Propagation Rate Coefficient in Free‐Radical Polymerizations of Hydroxypropyl Methacrylate
Authors: Beuermann Sabine , Nelke Dorit
Published: June 2004

The propagation rate coefficient kp was determined for hydroxypropyl methacrylate by applying pulsed laser initiated polymerizations and subsequent analysis of the polymer by size‐exclusion chromatography. kp data were derived for polymerizations in bulk and in several solvents: toluene, tetrahydrofuran (THF), benzyl alcohol, and supercritical CO2. With the exception of THF, no solvent influence on kp was observed. For polymerizations in THF kp values 40% below the corresponding bulk data were obtained. In addition, the activation energy of kp for polymerizations in THF is higher than for the other systems. The results are explained by a complexation of the OH group contained in the ester group with THF. As a consequence, H bonds between OH groups and carbonyl O atoms, which occur in the other systems, are not formed in the presence of THF. This explanation is supported by Raman spectra, which show that association of carbonyl groups does not occur for systems containing THF, whereas for all other systems the occurrence of two peaks at 1 703 cm−1 and 1 720 cm−1 is indicative of the vibrations of two different – associated vs. not associated – types of carbonyl groups. Based on the change in activation energy it is suggested that a true kinetic solvent effect occurs.

Temperature dependence of kp for HPMA polymerizations in bulk and in solution of THF. The literature data for bulk polymerizations are taken from ref. 22. Open symbols refer to νrep = 10 Hz and filled symbols to νrep = 25 Hz.

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Temperature dependence of kp for HPMA polymerizations in bulk and in solution of THF. The literature data for bulk polymerizations are taken from ref. 22. Open symbols refer to νrep = 10 Hz and filled symbols to νrep = 25 Hz.
Amination of Poly(ether imide) Membranes Using Di‐ and Multivalent Amines
Authors: Albrecht Wolfgang , Seifert Barbara , Weigel Thomas , Schossig Michael , Holländer Andreas , Groth Thomas , Hilke Roland
Published: June 2004

Covalently aminated polyimide membranes are prepared by wet chemistry using different amines as modifiers. During this synthesis process carbonyl groups of the imide ring react with amine groups forming amide groups maintaining the macromolecular structure and an additional amide group bearing free amine groups. The reaction sequence was verified by FTIR‐ATR and XPS measurements. Using poly(ethylene imine)s, highly aminated polyimide membranes with amine contents higher than 500 nmol/cm2 membrane can be produced which can be used as basic functions for further modification. As a result of amination, the hydrophobic polyimide membranes were strongly hydrophilized. Depending on the process parameters for functionalization and the applied modifier, a symmetric or an asymmetric distribution of amine functions across the membrane was observed. The distributions of amine functions were determined by SEM microscopy (EDX mode) and by AR‐XPS (take‐off angle resolved XPS). Calculations suggest that in the case of an asymmetric distribution the pores of the surface layer are almost completely filled with a swollen network of the modifier, which allows the covalent binding of second modifiers in order to obtain new types of composite membranes.

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Kinetic Studies of the Copolymerization of Ethylene with Norbornene by ansa‐Zirconocene/Methylaluminoxane Catalysts: Evidence of a Long‐Lasting “Quasi‐Living” Initial Period
Authors: Jansen Johannes Carolus , Mendichi Raniero , Sacchi Maria Carmela , Tritto Incoronata
Published: June 2004

Copolymers of ethylene (E) with norbornene (N) were synthesized using the catalysts rac‐Et(Ind)2ZrCl2/MAO (1), 90%rac/10%meso‐Et(4,7‐Me2Ind)2ZrCl2/MAO (2), and rac‐H2C(3‐t‐BuInd)2ZrCl2/MAO (3). Catalyst activity, molar mass (MM), and copolymer composition were studied as a function of time. The polymers showed an unusually narrow molar mass distribution (MMD) and a significant increase of their MM with time for up to one hour, suggesting a “quasi‐living” polymerization at 30 °C. The experimental data were fitted to kinetic equations and the propagation and transfer reactions were described in quantitative terms. Norbornene greatly depressed the propagation rate, along with the chain transfer rate. The more sterically hindered catalysts of the series showed lower propagation and chain transfer turnover frequency than 1 and yielded polymers with a low (2) to very low (3) norbornene content. The presence of norbornene in solution seemed to be one of the main factors responsible for the observed “quasi‐living” character of the copolymerization, probably due to coordination of norbornene to the active site. Time‐resolved kinetic studies also allowed for the calculation of the fraction of active metal centers, ranging from 56% (3) and 66–68% (1) to 94% (2) of the total zirconium present, depending on catalyst structure.

Left: molar mass (top) and polydispersity (bottom) as a function of the normalized polymer yield. The dashed line is the theoretical curve for ideal living polymerization. Catalysts 1 (□), 2 (▵), and 3 (○) at N/E ratio 12.5 and catalyst 1 (⋄) at N/E ratio 28.4. Right: enlargement of the low yield section.

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Left: molar mass (top) and polydispersity (bottom) as a function of the normalized polymer yield. The dashed line is the theoretical curve for ideal living polymerization. Catalysts 1 (□), 2 (▵), and 3 (○) at N/E ratio 12.5 and catalyst 1 (⋄) at N/E ratio 28.4. Right: enlargement of the low yield section.
A New Class of Cationic Organoiron Polynorbornenes Containing Azo Dyes
Authors: Abd‐El‐Aziz Alaa S. , Okasha Rawda M. , Afifi Tarek H. , Todd Erin K.
Published: June 2004

Ring‐opening metathesis polymerization of novel organoiron norbornene monomers functionalized with azobenzene chromophores using the Grubbs catalyst resulted in the production of the corresponding cationic organoiron polynorbornenes. UV‐vis analysis of the organometallic polymers in DMF showed maxima from 420–430 nm, and upon acidification a bathochromic shift to 510–520 nm was observed. Cyclic voltammetric studies showed that the iron centers underwent reversible reduction steps between −1.2 and −1.4 V. Thermogravimetric analysis of the organoiron polymers showed two weight loss steps from 225 to 255 °C and from 400 to 510 °C. Differential scanning calorimetry showed that the cationic organoiron polynorbornenes had glass transition temperatures (Tg) between 145 and 178 °C, while the Tg values of their organic analogs occurred between 99 and 104 °C.

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Stable Free‐Radical Polymerization of Styrene in Combination with 2‐Vinylnaphthalene Initiation
Authors: Lizotte Jeremy R. , Long Timothy E.
Published: June 2004

The elevated temperatures required for the stable free‐radical polymerization (SFRP) process lead to thermal initiation of styrene via the classic Mayo mechanism. Studies have shown the utility of styrene thermal initiation in controlled autopolymerization processes. In addition, the thermal polymerization of 2‐vinylnaphthalene (2VN), a styrenic derivative with an additional fused ring, was examined. An Arrhenius analysis of the 2VN thermal polymerization process using in‐situ FT‐IR spectroscopy demonstrated a greater propensity for 2VN thermal polymerization compared to styrene. A modified Mayo mechanism was proposed based on additional resonance stabilization in 2VN derived radicals compared to a single ring of resonance stabilization for styrene. The utility of 2VN as an initiator in the SFRP of styrene was investigated. 2VN initiation resulted in polymers that are end‐functionalized with a single 2VN unit or a polycyclic unit that results from Diels‐Alder reaction in the initiation mechanism. Variation of the styrene/2VN molar ratio in the presence of 2,2,6,6‐tetramethylpiperdinyl‐1‐oxyl enabled molecular weight control and narrow molecular weight distributions (ca. 1.1–1.2). The integrity of the polymer end groups was confirmed using 1H NMR and UV‐vis spectroscopy. In addition, the UV‐vis absorbance of the 2VN initiating unit was used for construction of a calibration curve for molecular weight prediction based on the intensity of the absorbance at 312 nm associated with 2VN initiation. The observed rate constant for the polymerization initiated with 2VN (1.73 × 10−5 s−1) was comparable to that of benzoyl peroxide (kobs = 1.99 × 10−5 s−1) initiation.

SFRP of styrene thermally initiated with 2VN.

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SFRP of styrene thermally initiated with 2VN.
Interconversion of Alternating Poly(ester amide)s and Cyclic Ester Amides from Adipic Anhydride and α,ω‐Amino Alcohols
Authors: Fey Thomas , Keul Helmut , Höcker Hartwig
Published: June 2004

Poly(esters amide)s from adipic anhydride and α,ω‐amino alcohols were obtained by polycondensation of α‐carboxyl‐ω‐hydroxyl amides under mild conditions in solution or by bulk polycondensation at elevated temperatures. For the polycondensation in bulk the influence of catalyst and of temperature on the number‐average molecular weight was studied. At a temperature of 170 °C the polycondensation process is followed by a ring‐closing depolymerisation and the formation of cyclic ester amides. Ten‐ to fourteen‐membered cyclic ester amides were obtained and characterized. The ring‐opening polymerisation of these cyclic ester amides leads, in a controlled mode, to poly(ester amide)s. The interconversion of poly(ester amide)s and cyclic ester amides by ring‐closing depolymerisation and ring‐opening polymerisation is possible. The poly(ester amide)s from adipic anhydride and homologous α,ω‐amino alcohols H2N(CH2)xOH (x = 2–6) are semicrystalline materials, their melting points show the odd/even effect observed for [n]‐polyamides and [n]‐polyurethanes.

Synthesis of alternating poly(ester amide)s.

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Synthesis of alternating poly(ester amide)s.
Photocontrol of Birefringence and In‐Plane Molecular Orientation in Copolymer Liquid Crystal Films with 4‐Methoxyazobenzene and Photo‐Cross‐Linkable Side Groups
Authors: Kawatsuki Nobuhiro , Uchida Emi , Yamamoto Tohei
Published: June 2004

Control of the in‐plane orientation direction in a polymethacrylate copolymer liquid crystal film substituted with 4‐methoxyazobenzene (4MAz) and 4‐methoxycinnamoyloxybiphenyl (4MCB) side groups, and control of the reversible birefringence of the resultant oriented film are described. High‐order in‐plane molecular orientation was generated by irradiating with linearly polarized (LP) 365 nm light and subsequent annealing. By adjusting the exposure dose, the reorientation direction was controlled parallel and perpendicular to the electric vector (E) of the LP light. Cooperative reversion of the orientation direction for both the 4MAz and 4MCB groups was observed, and the orientational order, S, varied from −0.79 to +0.75, without the side groups aggregating. The degree of the photoreaction and the distribution of the photoproducts from the 4MAz and 4MCB side groups through the axis‐selective photoreaction explain the reversion of the orientation direction. Optical recording, erasing, and birefringent control of the resultant oriented films were demonstrated by employing the photoisomerization of the 4MAz side groups using nonpolarised (NP) 405 nm light.

Order parameters of a P1 film after irradiating with LP 365 nm light (circles) and that following subsequent annealing (squares), as a function of exposure energy.

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Order parameters of a P1 film after irradiating with LP 365 nm light (circles) and that following subsequent annealing (squares), as a function of exposure energy.
Shear Induced Demixing and Rheological Behavior of Aqueous Solutions of Poly(N‐isopropylacrylamide)
Authors: Badiger Manohar V. , Wolf Bernhard A.
Published: June 2004

The interrelation between the phase separation behavior and the rheological performance of aqueous solutions of high molecular weight (Mw = 1 600 kg/mol) poly(N‐isopropylacrylamide) was investigated. The system demixes upon heating and the cloud point temperature, Tcp decreases steadily with rising polymer concentration up to 10 wt.‐%. The application of shear supports phase separation and reduces Tcp markedly. This observation is interpreted in terms of destruction of intersegmental clusters formed in the quiescent state owing to favorable interactions. Intrinsic viscosities and Huggins coefficients as well as the viscosities, η at higher polymer concentrations are closely connected with the thermodynamic conditions. [η] decreases by almost two orders of magnitude upon heating, whereas the corresponding increase of kH is less pronounced. The η values (constant shear rate) of the moderately concentrated solutions as function of T pass a maximum at the corresponding phase separation temperatures. The existence of clusters also manifests in terms of stress overshoot and of particularities observed with solutions that are sheared for the first time.

Transmittance (ratio of intensities of the transmitted light and the incidence light) of a 2.0 wt.‐% PNIPAm solution in water as a function of temperature at different shear rates indicated. Heating rate is 0.22 °C/min.

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Transmittance (ratio of intensities of the transmitted light and the incidence light) of a 2.0 wt.‐% PNIPAm solution in water as a function of temperature at different shear rates indicated. Heating rate is 0.22 °C/min.
A Suitable Photoinitiator for Pulsed Laser‐Induced Free‐Radical Polymerization
Authors: Buback Michael , Kuelpmann Albrecht
Published: June 2004

Detailed kinetic studies into free‐radical polymerization via pulsed laser experiments ideally require photoinitiators which almost instantaneously dissociate into primary free‐radical fragments that rapidly add to monomer molecules and thus induce macromolecular growth. 2‐Methyl‐4′‐(methylthio)‐2‐morpholinopropiophenone (MMMP) is shown to be such a suitable photoinitiator. Measurement of monomer conversion induced by a single laser pulse, within the so‐called single‐pulse pulsed laser polymerization (SP–PLP) experiment, provides direct information about the chain‐length dependence of the termination rate coefficient if MMMP is used as the photoinitiator.

Relative monomer concentration vs time trace of a methyl acrylate homopolymerization at 40 °C and 2 000 bar where MMMP was used as the initiator. The primary radical concentration from MMMP photo‐decomposition increases from curve (a) to (b) to (c) by the ratios 1:2.2:5.7.

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Relative monomer concentration vs time trace of a methyl acrylate homopolymerization at 40 °C and 2 000 bar where MMMP was used as the initiator. The primary radical concentration from MMMP photo‐decomposition increases from curve (a) to (b) to (c) by the ratios 1:2.2:5.7.
Early Stages of Propylene Bulk Phase Polymerization with Supported Metallocene Catalysts
Authors: Knoke Stefan , Korber Frank , Fink Gerhard , Tesche Bernd
Published: June 2004

For the initial steps of propylene bulk phase polymerization with a silica‐supported metallocene/MAO‐catalyst the processes of polymer growth, particle expansion and carrier fragmentation are investigated. Gravimetric analysis of the kinetics is given. Light optical examination of the particles shows a significant particle expansion during the first minutes of polymerization, which is not comparable to known observation from the slurry process. Electron microscopic investigation on cross sections of the polymer particles allows a detailed insight into the process of polymer growth, carrier fragmentation and particle expansion. The results are compared with the polymer growth and particle expansion model developed with slurry polymerizations under mild model conditions. In bulk phase polymerization particle expansion and carrier fragmentation are much faster due to more drastic reaction conditions. Nevertheless, it is still possible to observe a shell‐by‐shell degradation of the carrier material. Varying start up behaviors of single catalyst grains are observed. We are able to correlate the initial polymerization activity of individual grains with the cocatalyst loading and distribution on the catalyst carrier by means of microanalytical techniques. The results explain the varying start up behaviors of single grains. It becomes clear why different states of fragmentation are mixed up in the observed polymer samples.

Insight into catalyst grains after 0.5 min propylene bulk phase polymerization.

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Insight into catalyst grains after 0.5 min propylene bulk phase polymerization.
Cycle Formation in the Polycondensation of Potassium 3‐Bromomethyl‐5‐methylbenzoate
Authors: Sepulchre Maurice , Sepulchre Marie‐Odile , Belleney Joël
Published: June 2004

Potassium 3‐bromomethyl‐5‐methylbenzoate 2K, preformed or obtained from 3‐bromomethyl‐5‐methylbenzoic acid 2 by exchange reaction with potassium undecanoate 5K, was polymerized in bulk or in 1‐methyl‐2‐pyrrolidone (NMP), in the presence or not of a trifunctional core molecule. GPC analyses of the reaction products have shown that small cyclic oligomers (usually from C2 to C6) are formed in all the cases. MALDI‐TOF MS of polymers have shown that, in the range of masses examined, those prepared by polymerization of 2K in bulk or in NMP are almost exclusively formed of cycles. In the polymer obtained by polymerization, in NMP, of 2 in the presence of 5K linear and cyclic species coexist. In the polymer resulting from the polymerization of 2K in the presence of 2,4,6‐tris(bromomethyl)mesitylene (TBMM) the expected three‐arm stars are predominant and the content in cycles is relatively low and obviously the lowest of all the other prepared polymers. The formation of cycles (large and/or small) is an inherent component of the polycondensation of 2K. Cyclization strongly contributes to the limitation of molar masses of the reaction products.

MALDI‐TOF mass spectrum (reflector mode) of PB2 (run 3, Table 1). Symbols: •, Cn; ×, (Cp[D])LqOCH3 and +, (Cp[D])LqBr.

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MALDI‐TOF mass spectrum (reflector mode) of PB2 (run 3, Table 1). Symbols: •, Cn; ×, (Cp[D])LqOCH3 and +, (Cp[D])LqBr.
Alternating Copolymerization Reaction of Propylene Oxide and CO: Variation of Polymer Stereoregularity and Investigation into Chain Termination
Authors: Allmendinger Markus , Eberhardt Robert , Luinstra Gerrit A. , Rieger Bernhard
Published: June 2004

The cobalt‐catalyzed alternating copolymerization reaction of racemic propylene oxide and CO affords regioregular but atactic poly(hydroxybutyrates). The application of enantiomerically pure (R)‐ or (S)‐propylene oxide results in the formation of isotactic, optically active and crystalline materials. In contrast to the perfect isotactic microstructures that are available via the microbial pathway, our approach allows to tailor the stereoregularity of the polymer products, and hence their melting points by application of mixtures of the epoxide enantiomers. Investigations into the polymer stereochemistry show that the epoxide units undergo a clean regioregular incorporation into the polymer chain with retention of configuration at the stereogenic carbon centers. MALDI‐TOF and online ATR‐IR experiments give insight into the mechanism of chain termination reactions.

Sketch of regio‐ and stereoselective epoxide incorporation.

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Sketch of regio‐ and stereoselective epoxide incorporation.
Strain Rate, Temperature, and Microstructure‐Dependent Yield Stress of Poly(ethylene terephthalate)
Authors: Lim Jung Yul , Donahue Henry J. , Kim Sang Yong
Published: June 2004

Yield stress of a series of poly(ethylene terephthalate) (PET) filament samples, which differ in molecular draw ratio, was observed at a range of strain rate and temperature to reveal the relation between microstructure and yield stress behavior. Based on the observations, a novel correlation between (quasistatic) tensile yield behavior and dynamic mechanical properties was proposed. Above secondary relaxation temperature and below primary relaxation temperature, changes in yield stress with strain rate and temperature could be described successfully with one activated rate process, Eyring's model of yielding, regardless of the microstructure of PET samples. The activation enthalpy of Eyring's model increased almost linearly with crystallinity, while the activation volume decreased with crystallinity in a sigmoidal fashion. We suggest that crystalline structural development elevates the energy barrier for yield, and that the scale of molecular motion for yield decreases with microstructural development, not only because of the decrease in molecular volume. Such a scale of molecular motion as Eyring's activation volume could possibly interpret the loss tangent (tan δ), i.e., as the activation volume increases, loss tangent maxima of both primary and secondary relaxation increase almost linearly.

Relation between the activation volume of Eyring's model of (quasistatic tensile) yield and loss tangent maximum of the dynamic mechanical behavior.

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Relation between the activation volume of Eyring's model of (quasistatic tensile) yield and loss tangent maximum of the dynamic mechanical behavior.
Water‐Swollen Hydrogels with Pendant Terthiophenes
Authors: Chen Li , Gong Jian P. , Ohsedo Yutaka , Osada Yoshihito
Published: June 2004

A chemically cross‐linked and water‐swollen poly(AA3T‐co‐AA) gel having pendant terthiophenes was synthesized by radical copolymerization of [(2,2′:5′,2″‐terthiophen‐5‐yl‐)methyl acrylate] (AA3T) and acrylic acid (AA), and its swelling, dissociation, and doping behaviors were studied. The gel swells in high pH solution, which is associated with the dissociation and, hence, electrostatic repulsion of the AA units, and the pH value at which the swelling starts increases with increasing AA3T composition. The dissociation of the gels is suppressed, presumably due to the incorporation of the hydrophobic AA3T unit, and, once started, the dissociation could be promoted by AA3T in the low pH region. Poly(AA3T‐co‐AA) copolymers and gels can be easily electrochemically and chemically doped. The volume change of the gels is observed during doping/undoping and the maximum volume change reached was about 50%.

The pH dependence of the degree of swelling, q, for poly(AA3T‐co‐AA) gels with various F at 25 °C. (•) F = 0.11, DCL = 20%; (▪) F = 0.05, DCL = 20%; (▴) F = 0, DCL = 10%.

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The pH dependence of the degree of swelling, q, for poly(AA3T‐co‐AA) gels with various F at 25 °C. (•) F = 0.11, DCL = 20%; (▪) F = 0.05, DCL = 20%; (▴) F = 0, DCL = 10%.
Ring‐Opening Copolymerization of 2‐Aryl‐1‐methylenecyclopropanes with Carbon Monoxide Initiated by Pd–bpy Complexes
Authors: Kim Sunwook , Takeuchi Daisuke , Osakada Kohtaro
Published: June 2004

[PdCl(Me)(bpy)] and a mixture of the complex with cocatalysts; NaBARF (BARF = [B{C6H3(CF3)2‐3,5}4]−), NaBF4, AgBARF, AgBF4, and AgOTf, catalyze the copolymerization of 2‐phenyl‐1‐methylenecyclopropane with carbon monoxide to produce a new polyketone accompanied by ring opening of the monomer. 1H and 13C{1H} NMR spectra indicate that the polymers have two isomeric repeating units in which the phenyl substituents occupy different positions. The molecular weights of the polyketones formed by the reactions with a [Pd]/[cocatalyst]/[2‐phenyl‐1‐methyleneyclopropane] ratio of 1:3:70 are in the range of Mn = 13 100–86 000. The polymer obtained by the reaction promoted by [PdCl(Me)(bpy)]/MBARF, where M = Ag or Na, shows a narrow molecular weight distribution, Mw/Mn = 1.44 and 1.59, respectively. The catalysis is effective also for the ring‐opening copolymerization of 2‐aryl‐1‐methylenecyclopropanes bearing Me and F substituents on the phenyl ring. Isotope‐labeled experiments revealed the mechanism of the polymerization, which involves a 1,2‐insertion of the monomer into the Pd–acyl bond to produce a cyclopropylmethyl palladium intermediate, and subsequent β‐alkyl elimination to give the Pd–alkyl complex.

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Orientation of the Main Chain in Liquid‐Crystalline Side‐Chain Polyesters with Variation of Main‐Chain Spacer Length
Authors: Hempel Günter , Dimitrova Albena , Lindau Jürgen , Reichert Detlef , Schneider Horst
Published: June 2004

Previous X‐ray investigations on liquid‐crystalline side chain polyesters with variable spacer length in the side chain as well as in the main chain led to the assumption that the structure will change qualitatively if the main chain spacer length exceeds a certain value. We obtained indications supporting this assumption by applying two‐dimensional 13C NMR. It was shown that for a sample with main chain spacer shorter than the critical length, the main chain segments align perpendicular to the side chains (〈P2〉 = −0.46), and for spacer length larger than critical length, the main chain segments preferentially orient themselves parallel to the side chain (〈P2〉 = 0.28).

Visualization of the main‐chain order as revealed by the values of Table 2. The opening angle of the cones corresponds to the average angle of deviation as defined in the text.

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Visualization of the main‐chain order as revealed by the values of Table 2. The opening angle of the cones corresponds to the average angle of deviation as defined in the text.
Mechanisms of Moisture Sorption in Barrier Polymers Used in Food Packaging: Amorphous Polyamide vs. High‐Barrier Ethylene‐Vinyl Alcohol Copolymer Studied by Vibrational Spectroscopy
Authors: Lagaron Jose M. , Gimenez Enrique , Catala Ramon , Gavara Rafael
Published: June 2004

The nature of the association between sorbed water and two high‐barrier hydrophilic polymers used in oxygen‐sensitive food packaging, and exhibiting opposite oxygen barrier behavior in the presence of moisture, has been studied by FT‐Raman and FT‐Infrared spectroscopy. The polymers considered in this work were an ethylene‐vinyl alcohol copolymer with superior oxygen barrier properties (32 mol‐% of ethylene EVOH) and an amorphous polyamide (aPA). The results revealed that for the latter glassy amorphous polymer, water molecules associate with the CO and NH groups of the ca. 10% “free” amide moieties, being the excess sorbed water self‐associated in clusters; thus, moisture sorption does not appear to disrupt the originally present hydrogen‐bonded amide groups. This “unusual” behavior leads to an overall increase in the extension of the hydrogen‐bonding, which may help explain the lower oxygen permeability displayed by the aPA with increasing relative humidity on the basis of the known free‐volume competing mechanism. Differently, water sorption appears to progressively disrupt the strong polymer self‐association present in the very efficient high‐barrier semicrystalline EVOH material by hydrogen‐bonding to hydroxyl groups, hence leading to the well‐known highly plasticized rubbery structure with much lower intermolecular cohesion and oxygen barrier.

FT‐IR spectra of severely dried, dry (dotted), and water‐equilibrated (thicker line) aPA in the range 2 600–3 800 cm−1.

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FT‐IR spectra of severely dried, dry (dotted), and water‐equilibrated (thicker line) aPA in the range 2 600–3 800 cm−1.
Radical Grafting Polymerization of Vinylformamide with Functionalized Silica Particles
Authors: Meyer Torsten , Spange Stefan , Hesse Stephanie , Jäger Christian , Bellmann Cornelia
Published: June 2004

Two different radical polymerization techniques have been applied to covalently graft vinylformamide (VFA) onto silica particles. Grafting by the polymerization of VFA using an immobilized azo initiator on silica has been found less effective, because monomer conversion is limited in non‐aqueous solvents and grafting yields are low in water. Radical copolymerization of VFA with vinyltriethoxysilane (VTS)‐functionalized silica particles is suitable to produce poly(vinylformamide) (PVFA) silica hybrid particles in respectable yield. The VFA/VTS‐silica ratio determines the degree of grafting. The PVFA‐VTS‐co‐grafted silica particles can be acidically hydrolyzed into poly(vinylamine)‐grafted silica particles. Molecular structures of the surface groups and grafted polymer chains have been confirmed by means of solid state 13C{1H} cross‐polarization magic‐angle spinning (CP MAS) NMR spectroscopy. Zeta potential measurements show the altering of the former silica particles surface charges arising from the introduction of basic groups on the surface.

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Cover Picture: Macromol. Chem. Phys. 10/2004
Authors: Monaco Guglielmo , Viglione Rosario G.
Published: June 2004

Cover: According to a theoretical analysis in terms of a three‐state rotational isomeric state model, in favorable cases variations of conformational statistics can be described by a mechanism as simple as a children's game, where r‐children are unfaithful messengers, m‐children are faithful ones and the behavior of the whole sequence is determined by the number (even or odd) of unfaithful messengers. This mechanism turns out to be operative in many vinyl polymers and helps considerably in sequencing their tacticity‐spread NMR signals. The artwork has been realized by Dr. P. Vanacore.

Further details can be found in the Full Paper by G. Monaco* and R. G. Viglione on page 1327.
Equivalent conditions to the nonnegativity of a quadratic functional in discrete optimal control
Authors: Hilscher Roman , Zeidan Vera
Published: June 2004

In this paper we provide a characterization of the nonnegativity of a discrete quadratic functional ℐ with fixed right endpoint in the optimal control setting. This characterization is closely related to the kernel condition earlier introduced by M. Bohner as a part of a focal points definition for conjoined bases of the associated linear Hamiltonian difference system. When this kernel condition is satisfied only up to a certain critical index m, the traditional conditions, which are the focal points, conjugate intervals, implicit Riccati equation, and partial quadratic functionals, must be replaced by a new condition. This new condition is determined to be the nonnegativity of a block tridiagonal matrix, representing the remainder of ℐ after the index m, on a suitable subspace. Applications of our result include the discrete Jacobi condition, a unification of the nonnegativity and positivity of ℐ into one statement, and an improved result for the special case of the discrete calculus of variations. Even when both endpoints of ℐ are fixed, this paper provides a new result. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Factorization of operator valued Lp for 0 ≤ p < 1
Authors: Mezrag Lahcène
Published: June 2004

In [5], it is proved that a bounded linear operator u, from a Banach space Y into an Lp(S, ν) factors through Lp1 (S, ν) for some p1 > 1, if Y* is of finite cotype; (S, ν) is a probability space for p = 0, and any measure space for 0 < p < 1. In this paper, we generalize this result to uv, where u : Y → Lp(S, ν) and v : X → Y are linear operators such that v* is of finite Kašin cotype. This result gives also a new proof of Grothendieck's theorem. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Oscillation theorems for second order matrix differential systems
Authors: Wang Qi‐Ru
Published: June 2004

By employing the generalized Riccati technique and the integral averaging technique, new oscillation criteria are established for a class of second order matrix differential systems. These criteria extend, improve and unify a number of existing results and handle a number of cases not covered by known criteria. In particular, several interesting examples that illustrate the importance of our results are included. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Living Polymerization of α‐Amino Acid N‐Carboxyanhydrides (NCA) upon Decreasing the Reaction Temperature
Authors: Vayaboury Willy , Giani Olivia , Cottet Hervé , Deratani André , Schué François
Published: June 2004

Summary: The n‐hexylamine‐initiated polymerization of Nε‐trifluoroacetyl‐L‐lysine N‐carboxyanhydride in N,N‐dimethyformamide was studied by nonaqueous capillary electrophoresis. A polypeptide with a broad molecular weight distribution was obtained and side reactions were clearly identified for polymerization at room temperature. The possibility of living polymerization at 0 °C was demonstrated.

Synthesis of living polypeptides by primary amine initiated polymerization of NCA at low temperatures.

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Synthesis of living polypeptides by primary amine initiated polymerization of NCA at low temperatures.
Stimuli‐Responsive Semi‐Fluorinated Polymer Brushes on Porous Silica Substrates
Authors: Granville Anthony M. , Brittain William J.
Published: June 2004

Summary: A diblock copolymer brush consisting of poly(methyl acrylate)‐block‐poly(pentafluoropropyl acrylate) (Si/SiO2//PMA‐b‐PPFA) was synthesized on a porous silica substrate. The brush was exposed to selective solvents, as well as thermal treatments, to induce a surface rearrangement. The rearrangement resulted in the selective loss or creation of an ultrahydrophobic layer by location of the fluoropolymer segment. This work demonstrates that surface rearrangements observed on flat surfaces can be transferred to porous substrates.

Image of a water droplet in contact with an Si/SiO2//PMA‐b‐PPFA ultrahydrophobic polymer brush, synthesized from a porous silica substrate.

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Image of a water droplet in contact with an Si/SiO2//PMA‐b‐PPFA ultrahydrophobic polymer brush, synthesized from a porous silica substrate.
Cover Picture: Macromol. Rapid Commun. 13/2004
Authors: Rettig Hartmut , Krause Eberhard , Börner Hans G.
Published: June 2004

Cover: Integration of sequence‐defined oligopeptides into synthetic polymers opens a broad scope of possibilities for interfacing synthetic and biological systems. The cover picture features a two‐step procedure used to realize such chimera structures, with defined molecular weights and low polydispersity indices. The presented strategy includes the solid‐phase supported synthesis of an oligopeptide ATRP macroinitiator, subsequently followed by a solution‐phase atom transfer radical polymerization (ATRP).

Further details can be found in the Communication by H. Rettig, E. Krause, and H. G. Börner* on page 1251.
Structure Formation in the Crystallization and Annealing of Tetracontane Nanoparticles
Authors: Vao‐Soongnern Visit , Xu Guoqiang , Mattice Wayne L.
Published: June 2004

Summary: Crystallization, melting and annealing of nanoparticles of tetracontane were simulated via a Monte Carlo method on the second nearest neighbor diamond (2nnd) lattice by including short‐ and long‐range interactions. Nanoparticles can be obtained from an equilibrated tetracontane melt by increasing three periodic lengths to values that are effectively infinite. Nanoparticles, which contain 155 chains of C40H82, have been produced. After a deep quench from 473 K to 298 K, the crystallization process was investigated by the evolution of the density profile, fraction of bonds in the trans state, and the orientational order parameter. The vicinity of the center is less dense and less well ordered than portions of the nanoparticle located further from the center. The crystals form first in the region close to the surface. Each nanoparticle usually contains multiple crystalline domains. A melting phenomenon was observed at a temperature about 365 K when the nanoparticle crystal was heated. Annealing of the multiple domain crystal at 360 K can transform the structure to a more regular one without a grain boundary.

Snapshot of the final structure containing a single domain crystal after 20 million MCS.

image

Snapshot of the final structure containing a single domain crystal after 20 million MCS.
Today's sheet metal materials and their forming properties
Authors: Bach F.‐W. , Roßberg A. , Schäperkötter M. , Schaper M. , Walden L. , Weber J.
Published: June 2004

The production and processing of sheet metals of high‐strength steels, titanium, aluminum or magnesium alloys is investigated intensively at universities and in the industry. The main emphasis is put for example on the aluminum space frame concept as well as on the succeeding projects of the ULSAB‐study in the field of the steel sheet metals.

Within this article the qualification of the above mentioned materials for the application as deep‐drawing materials will be discussed. The aim of the development for new deep‐drawing sheet metals is to decrease the elastic part of the forming, which means to lower the yield point. A high elastic portion would cause a high resilience after the forming of the sheet metals and therefore an increased requirement of force and form error during the forming process.

Furthermore the optimized sheet metal material should have a great uniform elongation, so that it can be plastically deformed in a wide range. The beginning of the deformation should be possible at low forming forces but due to the deformation an increase of the hardening should be caused, so that the finished component has high strength. But it is not possible to realize both aims, high strength and great uniform elongation, at the same time.
Lasererwärmung zur Verbesserung des Umformergebnisses beim Kragenziehen von Aluminium‐ und Magnesiumknetlegierungen
Authors: Groche P. , Erhardt R.
Published: June 2004

Die Halbwarmblechumformung hat sich bei der Herstellung von geometrisch komplexen Bauteilen aus Magnesium‐ und Aluminiumknetlegierungen als nützlich erwiesen. In vielen Fällen, z. B. beim Tiefziehen, ist eine großfläche Erwärmung sinnvoll. Sollen aber, wie beim Kragenziehen, nur kleine Bereiche eines größeren Bauteils ausgeformt werden, ist eine lokale Erwärmung mittels Laserstrahlung vorteilhafter. Auf diese Weise lässt sich die Wärmemenge zeitlich und örtlich gut dosiert einbringen. In Versuchen konnte das Aufweitverhältnis gegenüber dem kalten Zustand bei einer lokalen Bauteiltemperatur von rd. 200 °C je nach Werkstoff um mehr als das doppelte gesteigert werden. Es zeigte sich, dass hierbei ein relativ enges Prozessfenster einzuhalten ist, da Werkstoffversagen nicht nur bei zu geringer, sondern auch bei zu hoher Umformtemperatur auftritt.
Simulation der geometrischen Oberflächen‐ wandlung beim Drücken optischer Bauteile
Authors: Groche P. , Schäfer R.
Published: June 2004

Mit Hilfe umformtechnischer Verfahren werden oftmals Bauteile mit Spezifikationen sowohl im Hinblick auf Bauteilform, als auch die Oberflächengüte hergestellt. Die Realisierung der geforderten Oberflächeneigenschaften basiert aber auch heute noch vorwiegend auf Erfahrungswerten. Am Beispiel des Drückens soll in diesem Artikel eine Methode vorgestellt werden, mit deren Hilfe die Oberflächengüte durch Finite Element Simulation vorherbestimmt werden kann.
Plumbagin induces reactive oxygen species, which mediate apoptosis in human cervical cancer cells
Authors: Srinivas Priya , Gopinath Gokul , Banerji Asoke , Dinakar Abhilash , Srinivas Gopal
Published: June 2004

There is an emerging evidence that plumbagin (5‐hydroxy‐2‐methyl‐1, 4‐naphthoquinone) may have potential as a chemotherapeutic agent. However, the growth inhibitory mechanisms of plumbagin have remained unexplored. The aim of the study was to determine whether plumbagin‐induced cell death in human cervical cancer cell line, ME‐180, exhibited biochemical characteristics of apoptosis and to check whether N‐acetyl‐l‐cysteine (NAC), which is a free radical scavenger, can reverse the cytotoxic effects of plumbagin. It can be concluded from the results that plumbagin inhibits the growth of ME‐180 cells in a concentration and time‐dependent manner. The cytotoxic effect of plumbagin induced cell death is through the generation of reactive oxygen species (ROS) and subsequent induction of apoptosis as demonstrated by the present data. Treatment of cells with plumbagin caused loss of mitochondrial membrane potential (ΔΨm), and morphological changes characteristic of apoptosis, such as the translocation of phosphatidyl serine, nuclear condensation, and DNA fragmentation. Moreover, plumbagin‐induced apoptosis involved release of mitochondrial cytochrome c and apoptosis inducing factor (AIF), thus activation of caspase‐dependent and ‐independent pathways, as shown by the plumbagin‐mediated activation of caspase‐3 and ‐9. Our results also show that pretreatment of ME‐180 cells with NAC blocks plumbagin‐induced loss of ΔΨm and subsequent release of cytochrome c, AIF, and caspase‐9 and ‐3 activation, thus inhibiting the apoptotic ability of plumbagin. © 2004 Wiley‐Liss, Inc.
Retrovirus‐mediated gene transfer and expression of EGFP in chicken
Authors: Koo Bon Chul , Kwon Mo Sun , Choi Bok Ruyl , Lee Hoon Taek , Choi Ho Jun , Kim Jin‐Hoi , Kim Nam‐Hyung , Jeon Iksoo , Chang Wonkyong , Kim Teoan
Published: June 2004

Here, we successfully demonstrate expression of the EGFP (enhanced green fluorescence protein) gene in chickens using replication‐defective MLV (murine leukemia virus)‐based retrovirus vectors encapsidated with VSV‐G (vesicular stomatitis virus G glycoprotein). The recombinant retrovirus was injected beneath the blastoderm of non‐incubated chicken embryos (stage X). After 12 days incubation, all of the eight living embryos assayed were found to express this vector‐encoded EGFP gene, which was under the control of the RSV (Rous Sarcoma Virus) promoter, in diverse organ tissues, including head, beak, neck, wing, hock, tail, toes, heart, amnion, and yolk sac. Surprisingly, despite the presumed cytotoxicity of EGFP, some embryos hatched and survived and these had prominent green fluorescent spots, both in internal organs and externally. Mol. Reprod. Dev. 68: 429–434, 2004. © 2004 Wiley‐Liss, Inc.
Evaluation of renal parenchymal disease in a rat model with magnetic resonance elastography
Authors: Shah Nihar S. , Kruse Scott A. , Lager Donna J. , Farell‐Baril Gerard , Lieske John C. , King Bernard F. , Ehman Richard L.
Published: June 2004

Alterations in the mechanical properties or “hardness” of tissues allow physicians to detect disease by palpation. Recently, attempts have been made to quantitate and image these tissue properties with the use of magnetic resonance elastography (MRE). This technique has been validated in ex vivo specimens, including kidney, breast, and prostate. In this study, in vivo MRE imaging of rat renal cortex is demonstrated and validated with a disease model that will facilitate further studies. Normal rats and rats with nephrocalcinosis induced with either 2 or 4 weeks of ethylene glycol exposure were studied with MRE. Histology in the diseased rats documented the presence of nephrocalcinosis. MRE measurements and images of shear stiffness were highly reproducible in individual rats. The shear stiffness of the renal cortex in normal rats was 3.87 kPa (95% CI 2.84–4.90 kPa). The shear stiffness increased to 5.02 kPa (95% CI 3.34–6.70 kPa) after 2 weeks of exposure, and to 6.49 kPa (95% CI 4.84–8.14 kPa) after 4 weeks of exposure (P = 0.0302, α < 0.05). MRE is capable of detecting alterations in the tissue mechanical properties of kidneys in vivo. It is a promising noninvasive technique that might have pathologic and prognostic significance. Magn Reson Med 52:56–64, 2004. © 2004 Wiley‐Liss, Inc.
High‐resolution multistation peripheral MR angiography using undersampled projection reconstruction imaging
Authors: Du J. , Korosec F.R. , Thornton F.J. , Grist T.M. , Mistretta C.A.
Published: June 2004

A novel protocol for three‐station MR angiography (MRA) of the lower extremities is described. A time‐resolved undersampled projection reconstruction (PR) acquisition was used to image the calf station during a first injection, and non‐time‐resolved PR acquisitions were used with the bolus‐chase technique to image the abdomen and thigh stations during a second injection. The streak artifacts resulting from undersampling the PR data were reduced with the use of a spatial Fermi filter based on the sensitivity of each coil element in a peripheral vascular phased‐array coil. This novel technique provided high spatial resolution and a broad range of coverage, and depicted the contrast dynamics in the most distal station of the lower extremities. Magn Reson Med 52:204–208, 2004. © 2004 Wiley‐Liss, Inc.
Fast acquisition‐weighted three‐dimensional proton MR spectroscopic imaging of the human prostate
Authors: Scheenen Tom W.J. , Klomp Dennis W.J. , Röll Stefan A. , Fütterer Jurgen J. , Barentsz Jelle O. , Heerschap Arend
Published: June 2004

The clinical application of 3D proton spectroscopic imaging (3D SI) of the human prostate requires a robust suppression of periprostatic lipid signal contamination, minimal intervoxel signal contamination, and the shortest possible measurement time. In this work, a weighted elliptical sampling of k‐space, combined with k‐space filtering and pulse repetition time (TR) reduction minimized lipid signals, intervoxel contamination, and measurement time. At 1.5 T, the MR‐visible prostate metabolites citrate, creatine, and choline can now be mapped over the entire human prostate with uncontaminated spherical voxels, with a volume down to 0.37 cm3, in measurement times of 7–15 min. Magn Reson Med 52:80–88, 2004. © 2004 Wiley‐Liss, Inc.
Quantification of the curvature and shape of the interventricular septum
Authors: Moses Daniel A. , Axel Leon
Published: June 2004

The interventricular septum (IVS) occupies a unique position within the heart, lying between the left (LV) and right (RV) ventricular cavities. Changes in its normal geometry may signify not only abnormalities of the septal myocardium, but also abnormal pressure differences between the LV and RV. Flattening of the IVS has been noted with cross‐sectional imaging in association with pulmonary hypertension, but the septal curvature and shape have not previously been measured in three dimensions. This paper describes a method to model the RV surface of the IVS from spatially registered cross‐sectional images for measurements of curvature. A smoothing 2D spline surface is constructed through the RV septal surface at regular times during the cardiac cycle, and the principal curvatures, as well as the Gaussian and mean curvatures, shape index, and curvedness, are calculated. Vector and color surface maps and graphs of average curvature and shape indices are constructed. Consistent curvature patterns were observed in four normal subjects. This method of measuring septal geometry can provide potentially useful new information on the effects of RV disease. We examine the problem of describing septal motion, and describe a simple measure of septal curvature that may be of clinical value. Magn Reson Med 52:154–163, 2004. © 2004 Wiley‐Liss, Inc.
MRI measurement of liver regeneration in mice following partial hepatectomy
Authors: Garbow J.R. , Kataoka M. , Flye M.W.
Published: June 2004

Improvements in noninvasive imaging modalities are crucial for preoperative in vivo assessments of liver condition and potential for regeneration after liver resection for removal of liver tumors. To that end, an MRI study of liver regeneration in mice following partial hepatectomy is described and validated. Hepatic volumes were accurately measured from contrast‐enhanced, gradient‐echo images of the liver. Regeneration curves were constructed for a series of mice (N = 6) from a longitudinal MR study, with images collected 1, 2, 3, 4, 5, and 9 days following surgery. We validated the MR method by correlating serial MR‐measured volumes with liver wet weight. The success of this method will enable future studies to better elucidate the factors that affect regeneration, and help to optimize the timing and dosing of chemotherapeutics to minimize their deleterious effects on liver regeneration. Magn Reson Med 52:177–180, 2004. © 2004 Wiley‐Liss, Inc.