bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dendritic polymers: from aesthetic macromolecules to commercially interesting materials
Authors: Voit B. I. 
Published: April 2003

AbstractDendritic polymers, perfectly branched dendrimers as well as hyperbranched materials, are discussed in some detail. The variety of the synthetic routes to perfect dendrimers and some highlights of the achieved structures document the rapid increase of activity in this field. Much information on growth, defects, dimensions, and properties of these globular macromolecules has be gained with special characterization techniques and their differences to linear polymers have become obvious. Hyperbranched polymers, which can be prepared in a one‐step synthesis, cover almost the same structures as their perfect analogs and an interesting comparison of their properties can be made. High solubility and functionality, small dimensions, globular structure, and interesting viscosity behavior qualify both types of dendritic polymers for new applications. The transition from aesthetic macromolecules to commercially interesting materials is discussed with some examples.
Sequence distribution and miscibility of SMA copolymers
Authors: Pionteck J. , Reid V. , Macknight W. J. 
Published: April 2003

AbstractWe have investigated the miscibility of poly(styrene‐co‐maleic anhydride) (SMA/SMA) blends, i.e. blends of two SMA copolymers which have different maleic anhydride (MA) contents. 33 SMA copolymers with MA contents between 2 and 29 vol.% were used. The MA contents were determined by two different techniques: FTIR using a titration technique for calibration and DEPT NMR, which was also employed to determine the triad sequence distribution of the SMA copolymers investigated. The miscibility was determined by the single Tg criterion as measured by DSC after annealing at 220°C for 2 min. After normalization of the polymerization degree to N=1000 (χcr=0.002), we found miscibility for such blends (1:1 by weight) where the difference in the MA contents Δ[MA] is less than or equal to 2.5 vol.%. At higher differences in MA content the copolymers are immiscible. The miscibility is independent of the overall MA content. The resulting interaction parameter χs, MA is equal to 3 at 220°C. A comparison of the miscibility window determined experimentally with calculated miscibility windows where special interaction energies are assigned to the different triad‐–triad combinations does not show any evidence for an influence of the sequence distribution on the miscibility of SMA/SMA blends.
Surface effects on polymer blends and block copolymer melts: Theoretical concepts of surface enrichment, surface induced phase separation and ordering
Authors: Binder K. 
Published: April 2003

AbstractSurfaces have a profound effect on the structure and related properties of multiphase polymeric materials, such as polymer mixtures and block copolymer mesophases. In particular, phase transitions in the bulk (unmixing, microphase separation, etc.) may be complemented by surface‐induced transitions (formation of wetting layers, surface‐directed spinodal decomposition, surface‐induced ordering). This review gives a brief introduction to the phenomenological theories of such phenomena, emphasizing the simplest approach based on Flory—Huggins—de Gennes free energy functionals and associated Monte Carlo simulations. More sophisticated theories and recent experiments are mentioned briefly.
Chromatographic characterization of complex polymer systems with thermal field‐flow fractionation
Authors: Antonietti M. , Briel A. , Tank C. 
Published: April 2003

AbstractThermal field‐flow fractionation (TFFF) coupled with multi‐angle laser light scattering (MALLS) is a promising quantitative method for determining the molecular‐weight distribution (MWD) of complex polymers and their aggregates. This paper describes the application of TFFF‐MALLS to linear polystyrene as well as highly cross‐linked microgel and sulfonated polystyrene samples. In addition, the chromatographic characterization of block copolymer micelles with different core chemistry is performed. The dependence of retention volume on the mass diffusion coefficient D and the thermal diffusion coefficient DT was confirmed. It is shown that DT, as predicted by theory, depends only on the solvent, being independent of both molecular weight and structure.
Morphological and thermal investigations of nylon‐6‐poly(sulfone ether)‐nylon‐6 triblock copolymers
Authors: Schnablegger H. , Kaufhold W. , Kompf R. T. , Pielartzik H. , Cohen R. E. 
Published: April 2003

AbstractThree triblock copolymers of nylon‐6 (Ny6) and aromatic poly(sulfone ether) (PSuE) were investigated relative to their morphology and their thermal properties. Generally, the nylon blocks of the three Ny6‐PSuE‐Ny6 samples were very short (between 5 and 16 monomer units). Heterogeneous, microphase‐separated morphologies could be observed for all samples, independent of the processing conditions, i.e., solvent casting or melt cooling. However, the process conditions were highly influential on the formation of the supramolecular structures (i.e., spherulites), especially when the crystallizable block was short.
Modification of properties of epoxy polymers by high hydrostatic pressure
Authors: Beloshenko V. A. , Pacter M. K. , Varyukhin V. N. 
Published: April 2003

AbstractA study was made of the changes in density, thermal resistance and mechanical and dielectric properties of a number of epoxy polymers cured at high hydrostatic pressure. The possibility of controlling characteristics under pressure is shown. The most important is the change in the glass‐transition temperature; the effect of pressure on the mechanical properties and thermal resistance is small.
Self‐consistent field theory of block copolymers and block copolymer blends
Authors: Whitmore M. D. , Vavasour J. D. 
Published: April 2003

AbstractThis paper reviews the numerical, self‐consistent field theory of block copolymers and blends in which they are a major component, and the relationship of this approach to analytic theories of the weak and strong segregation limits. The major topics of interest are microphase separation and, in blends, its interplay with macrophase separation. The paper contains a brief summary of the existing theory in a form which is generalized to include various architectures and blends, and applications to amorphous copolymers, semi‐crystallizable copolymers, copolymer/solvent mixtures, and binary and ternary copolymer/homopolymer mixtures. Phase diagrams, and the scaling of microdomains with molecular weights, temperature and concentration are analyzed and compared with experiment. The distributions of components between and within subdomains, which are calculated directly, provide the basis for understanding and identifying different segregation regimes. Of particular interest are the limitations of the theory.
Continuous fractionation of an ionene containing cycloaliphatic moieties and the dependence of the glass transition temperature on molar mass
Authors: Schultes K. , Wolf B. A. , Meyer W. H. , Wegner G. 
Published: April 2003

AbstractAbout 340 g of a cycloaliphatic ionene (see formula given in the introduction) were fractionated by a continuous counter‐current extraction method (CPF). The efficiency of the separation was checked by viscometry and gel permeation chromatography (GPC). Ten different fractions with number average molecular masses between 16 000 and 29 000 D were obtained and their glass transition temperatures Tg determined by differential scanning calorimetry (DSC) for their bromide and tetrafluoroborate salts. No molecular weight dependence of Tg was found, in contrast to recently reported results with aliphatic ionenes, where — in case of the bromide — Tg increases with rising molecular weight.
Local ac current contrast on carbon fiber surfaces imaged by scanning force microscopy
Authors: Sturm H. , Schulz E. 
Published: April 2003

AbstractAfter a delamination process in a C‐fiber reinforced polymer composite, the identification of the polymer residue of poly‐(phenylene sulphide) on carbon fiber surfaces gives important information on the composite failure mechanism. Using scanning force microscopy (SFM) in its lateral force imaging mode or with the stiffness imaging mode, it is almost impossible to distinguish the two composite components owing to a very low material‐based contrast of the local friction and compliance. The new technique using contrast based on a local AC current measurement allows a clear identification of the conducting carbon fiber and the non‐conducting polymer coverage.
New synthetic approach to oh‐functionalized poly(p‐xylylene)s by coupling of aromatic dialdehydes and diketones in the presence of smi2
Authors: Wege V. U. , Greiner A. 
Published: April 2003

Abstract1,2‐dihydroxysubstituted poly(p‐xylylene)s were synthesized in the presence of samarium(II)‐iodide. The structure and endgroups of the polymers were verified by spectroscopy and chromatography. The structure—property relationships of the poly‐1,2‐diol structures obtained were investigated. Polymer analogous transformations were carried out for poly‐(1,4‐phenylene‐1,2‐ethanediol). The reaction parameters were investigated with respect to degrees of polymerization. Although some of the polymers were soluble, precipitation was found to be the reason for limited molecular weights.
Samarium(II) iodide: A diastereoselective reagent for the synthesis of aromatic 1,2‐diol structures — model reactions
Authors: Wege V. U. , Greiner A. 
Published: April 2003

AbstractVariation of the reaction conditions for the C—C coupling reaction of aromatic carbonyl compounds to their 1,2‐diol structures in the presence of samaraium(II)‐iodide led to different diastereoselectivities. The molar ratio of the starting materials, substituents, and solvent variation had a significant influence on 1,2‐diol formation. An interpretation of the observed results is suggested. Sterical demands of the active complex and an intramolecular samarium‐oxygen interaction could lead to the diastereomer ratio obtained.
Anionic polymerization of fluorostyrenes
Authors: Sugiyama K. , Ishizone T. , Hirao A. , Nakahama S. 
Published: April 2003

AbstractAnionic polymerizations of 2‐, 3‐, and 4‐fluorostyrenes (2‐, 3‐, and 4‐FSt) were carried out at −78°C in THF with sec‐butyl‐lithium, oligo(α‐methylstyryl)lithium, ‐dipotassium, and (1,1‐diphenyl‐3‐methyl‐pentyl)lithium as initiators to give the respective polymers in quantitative yields. The propagating carbanion derived from 2‐FSt is found to survive at least for 5 min at—78°C, affording the anionic living poly(2‐FSt) with predictable molecular weight and very narrow molecular weight distribution. The addition of styrene to the anionic living poly(2‐FSt) in THF affords poly(2‐FSt)‐block‐polystyrene in quantitative efficiency, indicating the high nucleophilicity of the propagating carbanion of 2‐FSt. During the polymerization of 3‐FSt, the benzyne intermediate is formed probably due to meta‐fluoro substitution to cause polymer coupling reaction. Poly(4‐FSt) produced has narrow molecular weight distribution and slightly higher molecular weight than the calculated one. The results of the polymerizations of 2‐FSt and 4‐FSt suggest that persistency of the propagating carbanionic species of 4‐FSt is slightly lower than that of 2‐FSt at −78°C.
A novel living coordination polymerization of alkoxyallenes by a π‐allylnickel catalyst [1]
Authors: Tomita I. , Kondo Y. , Takagi K. , Endo T. 
Published: April 2003

AbstractA coordination polymerization of alkoxyallenes (2a‐2f) by the [η3‐(allyl)NiOCOCF3] (1) /PPh3 system was carried out to obtain a polymer (3) bearing exomethylenes on the main chain. The structure of the obtained polymer was confirmed by 1H‐, 13C‐NMR and IR spectra, and was revealed to consist of two units, one bearing an exomethylene side chain and the other an end ether side chain as a result of 1,2‐ and 2,3‐polymerization. In the case of methoxyallene, the ratio was estimated as 32:68. The number average molecular weight (M̄n) of the resulting polymer varied linearly with increasing ratio of monomer to initiator. The molecular weight distributions (M̄w/M̄n) of the polymers obtained here were always approximately 1.1. These results may strongly support that the present polymerization proceeds by a living mechanism. Under an inertatmosphere, the propagating end of the polymer was quite stable and could be kept without any decrease in activity for more than a week. The proportion of 1,2‐ and 2,3‐polymerization was a little affected by the substituents on the alkoxyallenes, as the steric bulkiness of the substituents increased the content of 2,3‐polymerization units.
Thermodynamics and molecular ordering of carbonate‐type dimer liquid crystals with emphasis on the geometrical characteristics of the linking group
Authors: Abe A. , Furuya H. , Nam Su Yong , Okamoto S. 
Published: April 2003

AbstractMainchain liquid crystals having a regularly alternating rigid‐flexible repeating structure often exhibit distinct odd‐even oscillation in their thermodynamic quantities with respect to the number of methylene units in the spacer. The effect has been widely observed from dimer (DLC) to polymer liquid crystals (PLC), but not in the monomer liquid crystals (MLC) which comprise a mesogenic unit carrying one or two tails. The degree of oscillation varies depending on the chemical structure of the linking group used to join the spacer with mesogenic units. In our previous work, we have suggested that such characteristics are mainly due to the geometrical arrangement of the linkage. In this work, we have prepared a series of carbonate‐type MLCs NCϕϕOCOO(CH2)n—1CH3, where ϕ is a phenyl group, as well as DLCs NCϕϕOOCO(CH2)nO‐COOϕϕCN. The thermodynamic behaviors at the nematic‐isotropic NI transition have been compared with those previously reported for the ether‐type DLCs. For the dimer series, the molecular orientation and the spacer conformation were investigated by using 2H NMR technique. The origin of the difference in the odd‐even behaviors has been traced back to the geometrical characteristics of the linking groups, which affect the relative orientation of the terminal mesogenic cores, thus leading to modification of the conformational distribution in the nematic state. The analysis has yielded the nematic conformation which satisfactorily reproduces the observed values of the dipolar and quadrupolar couplings. The bond conformation vs. bond order plots are shown for the n odd and n even systems together with the corresponding results derived previously for the ether‐type DLCs. Although the numbers of bonds of the flexible spacer are not exactly comparable with each other, the conformational ordering along the spacer tends to be pronounced in both DLC systems.
Oxidation–reduction alternating copolymerization of stannylenes with p‐benzoquinone derivatives
Authors: Kobayashi S. , Iwata S. , Shoda S. 
Published: April 2003

AbstractStannylenes, bis[bis(trimethylsilyl)amido]tin(II) (1) and bis[bis(trimethylsilyl)methyl]tin(II) (2), have been copolymerized with p‐benzoquinone derivatives to afford a novel class of tin‐containing polymers (4 and 5) having a tetravalent tin unit and a p‐hydroquinone unit alternatingly in the main chain. The oxidation state of the stannylenes changes from two to four while the p‐benzoquinone moiety is reduced to the corresponding p‐hydroquinone unit, indicating that the copolymerization proceeds via a redox process (oxidation‐reduction copolymerization). Some of the resulting copolymers are stable at room temperature and soluble in common organic solvents such as chloroform and n‐hexane. The molecular weight (Mw) of the resulting copolymers was in the range of 1.1 x 105 to 4.9 x 103.
Uniform polymer beads of micrometer size
Authors: Horák D. 
Published: April 2003

AbstractVarious methods are reviewed that have been developed in recent years to produce uniform polymer beads with diameter larger than 1 μm. Methods such as emulsifier‐free emulsion polymerization, suspension polymerization (including non‐standard polymerization devices and a method of activated swelling), dispersion polymerization, precipitation polymerization, and other techniques are covered. The discussion focuses on the mechanism of bead formation and variables influencing the properties of the beads. Potential applications of monosized beads in both industry and research are described.
Static and dynamic light scattering from multicomponent polymer mixtures PS/PDMS/PMMA/toluene
Authors: Benmouna M. , Duval M. , Strazielle C. , Hakem F.‐I. 
Published: April 2003

AbstractThe static and dynamic scattering properties of multicomponent polymer mixtures are examined starting from the theoretical formalism based on the random phase approximation (RPA) for multicomponent polymer mixtures in the presence of a low molecular weight solvent. The results are compared with the light scattering data reported recently by Strazielle and coworkers [1] for polystyrene/polydimethylsiloxane/polymethylmethacrylate/toluene mixtures. The present paper is an extension of the work published recently by these authors [2] and considers data obtained from several concentrations of PMMA. It also includes a discussion of the dynamic properties which are obtained by quasi‐elastic light scattering.
X‐ray diffraction and TGA studies on annealed PPT twaron fibers and powder
Authors: Hindeleh A. M. , Obaid A. A. Abu 
Published: April 2003

AbstractTwaron fiber is spun from the polymer poly(paraphenylene terephthalamide), PPT, and has a crystallinity of 82%. Wideangle X‐ray diffraction, combined with the multipeak resolution procedure, was applied to study the changes in the structure after annealing the fiber in the temperature range of 100–675°C. The structural parameters included crystallinity (crystalline order), microparacrystal (mPC) size, and netplane spacing. A thermogravimetric analysis (TGA) was made to determine the loss in mass of the fiber in the temperature range in which the annealing study was carried out.Crystallographically‐disordered (amorphous) powder of the PPT polymer was prepared by grinding crystalline Twaron fibers, which had a crystallinity of 87%, in a vibratory ball mill for a period of 64h. A study was then made to determine the extent to which the original crystallinity or mPC size is restored after annealing the powder in the temperature range of 100–425°C.
Polymerization of acrylonitrile with magnesiumdialkyls. Reaction conditions and stereospecificity
Authors: Opitz G. , Heller A. , Scheller D. , Berger W. 
Published: April 2003

AbstractThe stereospecificity of acrylonitrile polymerization initiated by organometallic compounds of alkali and alkaline earth metals was investigated. The triad tacticities of the polymers obtained was analyzed by 13C NMR and the molecular weights and their distributions were measured by size exclusion chromatography. A decisive influence of temperature on acrylonitrile polymerization initiated by dialkylmagnesium (di‐n‐hexyl‐ and di‐n‐butylmagnesium) in mesitylene was found. Products polymerized at temperatures above 100°C contain high molecular weight fractions with predominantly isotactic configuration (isotactic triad content 50—55%). The stereospecificity of polymerization was observed only in a medium which is a non‐solvent for the product. All the other investigated metalorganics do not initiate a stereospecific polymerization on these conditions. In order to elucidate the stereospecific polymerization mechanism we examined NMR data by model calculations. The triad tacticity of some predominant isotactic polyacrylonitrile samples is described by the enantiomorphic sites (e.m.s.) model. This means that the propagation takes place at enantiomeric catalyst sites which determine the configuration of the incoming monomer unit. Summarizing the experimental observations and the interpretation of the polymer structure, a model of the active centers involving associated dialkylmagnesium structures is proposed.
Thermal and microwave‐activate non‐aqueous free‐radical dispersion polymerization of methyl methacrylate in n‐heptane
Authors: Albert P. , Hölderle M. , Mülhaupt R. , Janda R. 
Published: April 2003

AbstractThermal and microwave‐induced free‐radical non‐aqueous dispersion polymerization of methyl methacrylate (MMA) in the presence of poly(styrene)‐block‐poly(ethene‐alt‐propene) dispersing agent were compared. For controlled polymerization in the microwave field, a new microwave polymerization reactor was built to afford uniform heating and to control temperature via microwave power variation. At identical MMA concentration and polymerization temperature of 70°C no special effect of the microwave field on conversions, molecular weights and particle sizes of PMMA was detected with respect to conventional thermal free radical dispersion polymerization.
Microwave‐treated low‐density polyethylene films
Authors: Hindeleh A. M. , Bulos B. R. 
Published: April 2003

AbstractLow‐density polyethylene films, 80 μm thick, were exposed to microwave radiation and the following parameters were characterized: (i) the monoclinic to orthorhombic phase transformation, crystallinity and crystallite size using wide‐angle X‐ray diffraction, (ii) mechanical properties, and (iii) light absorption in the wavelength range of 200—800 nm. The following effects have been detected after microwave treatment: The major orthorhombic phase component increased, the monoclinic component decreased, the orthorhombic crystallite size decreased, the crystallinity, which was taken as the ratio of the scatter from the orthorhombic phase to the total scatter under the whole diffraction scan, increased. The mechanical properties improved. No change in the absorption of light was detected.
Measurement of orientation in uniaxially drawn polyacrylonitrile
Authors: Bashir Z. 
Published: April 2003

AbstractIn the literature, an estimate of the degree of orientation in drawn polyacrylonitrile (PAN) fibers is often inferred from the arc‐width of the strongest equatorial peak at 2ϑ = 16.8° in the wide angle X‐ray diffraction pattern. The absence of sharp meridional peaks in the diffraction pattern of oriented PAN means that chain orientation‐factors cannot be directly calculated. In this work, Wilchinsky's method for calculating the degree of chain orientation from the azimuthal intensity distribution of a strong equatorial peak has been adopted.
Combined LC main chain/side chain polymers
Authors: Zentel R. , Brehmer M. 
Published: April 2003

AbstractCombined LC‐polymers possess the structural properties of both LC main chain and LC side chain polymers. Beneath this structural speciality, their broad LC‐phases and their polymorphism (different smectic phases and one nematic phase as a function of temperature) make them interesting. Crucial to an understanding of them is the fact that main chain and side chain mesogens orient parallel to each other and interact cooperatively to form the LC‐phase. Due to this synergism the temperature range of the LC‐phase is much broader than that of the corresponding LC main chain and LC side chain polymers. This interplay of main chain and side chain mesogens allows structures to be designed with preferably nematic or smectic phases. Whenever both types of mesogens can arrange in the same height, preferably smectic phases are formed. If this is not possible, the nematic phase dominates.The incorporation of chiral groups allows cholesteric and chiral smectic C* phases to be prepared. For the latter, ferroelectric modes have been observed dielectrically. By crosslinking of combined LC‐polymers, combined LC‐elastomers can be prepared, in which the LC‐phases are nearly unchanged. These elastomers allow a mechanical orientation of the LC‐phases and, in particular, an untwisting of the helical superstructure of cholesteric and chiral smectic C* phases. In the latter case ferroelectric monodomains are obtained. The piezoeffect — to be expected — for LC‐elastomers with chiral smectic C* phases was first demonstrated for this class of polymers.