bluuebunny/crossref_metadata_2025_split huggingface dataset:
Competitive reactions in solutions of DNA‐containing polyelecrtolyte complexes
Authors: Izumrudov Vladimir A. , Zhiryakova Marina V. , Kargov Sergei I. , Zezin Aleksandr B. , Kabanov Victor A. 
Published: March 2011

AbstractThe reaction of competitive binding of two polyanions ‐ DNA and synthetic fluorescence‐tagged poly(methacrylate) (PMA*) ‐ with the quencher polycation poly(N‐ethyl‐4‐vinylpyridinium) (PEVP) was studied by fluorescence quenching technique. It is found that ability of DNA to displace PMA* from water‐soluble nonstoichiometric interpolyelectrolyte complex (NPEC) formed by PMA* and PEVP ‐ NPEC(PMA*‐PEVP) ‐ and to form water‐soluble NPEC(DNA‐PEVP)magnified image can be determined by both a parameter Ψ = PPMA+/Ppevp, where Ppma+ and Ppevp are the degrees of polymerization of PMA* and PEVP, respectively, and by the nature and concentration of alkali and alkali earth metal cations. According to their ability to shift the equilibrium to the right the cations can be arranged in the series Ca2+ > Mg2+ >> Na+ > K+ > Li+. The data obtained are in accordance with the differences in the selectivity of alkali and alkali earth cations binding with competitive polyanions.
Polymer ultrathin films with immobilized photosynthetic reaction center proteins
Authors: Kalabina N. A. , Zaitsev S. Yu. , Zubov V. P. , Lukashev E. P. , Kononenko A. A. 
Published: March 2011

AbstractProperties of mixed monolayers of lipid‐photosynthetic reaction center proteins (RC) were studied and the optimum conditions for stable films fabrication were determined. The following synthetic: N‐acryloylphosphatidylethanolamine (ACPE), tetracosa‐11, 13‐diinoic acid (TDA), pentacosa‐10, 12‐diinoic acid (PDA), dioctadecyldienoylphosphatidylcholine (DODL) and natural lipids: L‐α‐phosphatidylethanolamine (PE), L‐α‐phosphatidylcholine (PC) were used. The rate of polymerization of the mixed ACPE‐RC and TDA‐RC monolayers is lower in comparison with corresponding values for pure lipid‐like monomers on air/water interface. The optical and photoelectrical measurements provide evidence for an orientation of RCs on interface. Hydrophilic H‐subunit in monomeric and polymeric ACPE‐RCs, and monomeric DODL‐RCs monolayers is preferentially oriented towards water as in the pure RC monolayers. Opposite orientation was found with TDA‐RCs and PDA‐RCs films. No preferential orientation for lipid‐RCs from C. aurantiacus monolayers was found because of the RCs having low assymmetry of hydrophobic subunits (M and L).
Novel method to form giant liposome entrapping DNA
Authors: Kumazawa Noriyuki , Mel'Nikova Yulia S. , Yoshikawa Kenichi 
Published: March 2011

AbstractWe report a new method to prepare giant liposome with the size of several tens micrometers, entrapping DNA molecule within the closed phospholipid membrane. The formation of such liposomes has been confirmed through the observation with fluorescence microscopy.
A control of primary structure in the products of macromolecular reactions
Authors: Litmanovich Arkady D. , Platé Nicolai A. 
Published: March 2011

AbstractBasing on the theory of macromolecular reactions, an influence of various factors on a units' distribution (UD) of the forming macromolecules is considered. In diluted solutions UD is determined by a competition between external reagent and intrachain interaction of reacted and unreacted units, first by neighbor effect. Should accelerating action of remote units is commensurable with that of nearest neighbors, such a conformational effect enlarges the formation of alternating sequences. In a melt, interchain effect shifts UD to a random one. In a polymer blend consisting of reacting and non‐reacting but influencing the reactivity components, UD of transforming macromolecules is formed under concerted action of the reaction and interdiffusion. Thus modern achievements of the theory permit to analyze peculiarities of a wide set of reaction systems and facilitate a choice of optimal conditions for the preparation of tailor‐made macromolecules.
Chiral crystallization of helical polymers
Authors: Meille Stefano V. , Allegra Giuseppe 
Published: March 2011

AbstractCrystallization of achiral or racemic helical polymers in chiral crystals is quite frequent and while in some cases it may relate to the thermodynamic stability of the chiral polymorph, in others it must be associated with kinetic factors. Analysis of the available literature data suggests that in the second instance a key role must be played by the nucleation step, i.e. specifically by the formation of precrystalline entities. Furthermore a survey of the chiral crystal structures for helical polymers evidences that they are frequently characterized by a quasi‐hexagonal packing. The hexagonality index H, defined as the ratio of the largest to the smallest distance between the axis of the reference helix and its six nearest neighbors, appears to be a reliable indicator of the presence of helices of a single handedness or, respectively, of both in a given crystal structure. A detailed analysis of the general energetic and entropic factors favouring chiral crystallization of helical polymers is carried out. It is shown that a hexagonal or pseudo‐hexagonal arrangement (i.e. the six‐fold coordination) in either the crystalline or in a precrystalline state, promotes chiral crystallization and is in its own turn favoured by clustering of isochiral helices.
The polyurethaneisocyanurate morphology
Authors: Zenitova Lubov A. , Bakirova Indira N. , Kirpichnikov Petr A. 
Published: March 2011

AbstractBy catalytic trimerization polyurethaneisocyanurates (PUIC) with varying content of isocyanate and oligoester fragments were obtained. The number of triisocyanurate fragments in the PUIC network was determined with infrared spectroscopy and by using the multiple disrupted complete internal reflection technique. It was also shown that the PUIC resistance to high temperatures improves as the content of triisocyanurate fragments increases.
Coil‐globule transition: Self‐assembly of a single polymer chain
Authors: Chu Benjamin , Wu Chi 
Published: March 2011

AbstractThe coil collapse problem is of interest not only because it represents the simplest model of protein folding, but also because of its fundamental importance as related to polymer nanostructures and fractionation. It is extremely difficult to observe the coil‐to‐globule transition experimentally because at finite concentrations in a poor solvent, the macromolecules tend to aggregate due to phase separation when the collapsed state is being achieved. In the mid‐1980s, two‐stage kinetics of a single‐chain collapse was proposed theoretically.1,2 The first successful experimental observation of a two‐stage coil‐to‐globule transition was achieved by quenching a dilute solution of polystyrene (PS) in cyclohexane.3By using a thinnest capillary tube cell with a wall thickness of 0.01 mm and a diameter of 5 mm for dynamic light scattering, two relaxation times, τcrum for the crumpled globule state and τeq for the compact globule state, were determined4 for the first time. The relaxation times were much slower than expected. From the size of the crumpled globule and that of the compact globule and by assuming the intraglobular density to be uniform, the volume fraction of the PS chain in the crumpled globule state, ϕcrum, and that in the compact globule state, ϕcomp, can be estimated, with ϕcrum = 0.02 and ϕcomp ∼ 0.24‐0.4 at 28°C for polystyrene in cyclohexane. The results imply that a single‐chain globule contains a large amount of solvent. It should also be noted that ϕcomp is temperature dependent, i.e., one would have to go to hypothetically low temperatures in order to squeeze out all the solvent (cyclohexane) in the compact PS globule.The single‐chain coil collapse state could be achieved under equilibrium conditions by using a high molecular weight, Mw ∼ 1.08 × 107 g/mol; Mw/Mn < 1.06) poly(N‐isopropylacrylamide) (PNIPAM) in water,<5 even though the ten million molecular weight for PNIPAM was substantially lower than that for polystyrene (Mw ∼ 50 × 106 g/mole).6 Under equilibrium conditions, it was feasible to determine both the hydrodynamic radius Rh and the radius of gyration Rg. The ratio of Rg/Rh changed from 1.45 to 0.77, clearly demonstrating the transition from the theta coil state to the compact globule state. At the maximum value of the scaled expansion factor αs3 |τ| Mw1/2, Rg/Rh = 1.33 where αs = Rg/Rg (θ) and τ = |T‐θ| / θ with θ being the theta temperature. In the compact globule, Rg/Rh was of the order of 0.7, implying that the PNIPAM compact globule in water still contained ∼80% water, of the same order of magnitude as the PS compact globule in cyclohexane at 7° below its theta temperature (35°C).
Molecular recognition phenomena in polyelectrolyte systems
Authors: Kabanov V. A. 
Published: March 2011

AbstractThe term “molecular recognition” is commonly used to describe various specific interactions, sometimes being not well defined. Let's assume that some species A can separately interact with either species B1, or B2, (or B3, B4 etc.) forming A·B1, or A·B2, (or A·B3, or A·B4 etc.) complexes. Here we say “recognition” assuming selective complexation of A with B1 in the mixture containing also B2 (B3, B4… etc.). At the same time it means discrimination of all other B species except B1.
Block polyelectrolytes in aqueous environments
Authors: Khougaz Karine , Moffitt Matthew , Zhang Lifeng , Eisenberg Adi 
Published: March 2011

AbstractAnalogous to the self‐assembly of low‐molecular‐weight amphiphiles in aqueous solutions, the formation of spherical micelle‐like aggregates has been observed in systems of amphiphilic block copolymers in water. The aggregates, often called micelles due to structural similarities with surfactant associates, are found to exist above the critical micelle concentration (cmc). The micellization of amphiphilic block copolymers has been investigated using a wide range of techniques, such as size‐exclusion chromatography (SEC), static and dynamic light scattering (SLS and DLS), small‐angle x‐ray scattering (SAXS), small‐angle neutron scattering (SANS), transmission electron microscopy (TEM), viscometry, and steady‐state fluorescence spectroscopy.The present lecture is a review of recent work in our laboratory concerning the micellization of ionic block copolymers. These high‐molecular‐weight amphiphiles may contain one or more of a variety of ionic blocks, such as poly(4‐vinylpyridinium alkyl halides), poly(metal acrylates), poly(metal methacrylates) and sulfonated polystyrene. In water, such polymers are referred to as block polyelectrolytes, as they combine the colloidal behavior of block copolymers with the long‐range electrostatic interactions of polyelectrolytes. Early work in this field has been reviewed by Selb and Gallot.1
Anionic polymerization of spiro monomers derived from germylene
Authors: Shoda Shin‐Ichiro , Ohnishi Yasuharu , Yagi Katsuhiko , Kamo Hiroki , Kobayashi Shiro 
Published: March 2011

AbstractThe ring‐opening polymerization of a spiro germanium enolate proceeds smoothly catalyzed by an anionic initiator, giving rise to a poly(germanium acyclic enolate), an organometallic polymer having a germanium enolate structure. The resulting polymers have an O‐germanium enolate unit and a C‐germanium enolate unit in the main chain. Various anionic catalysts including neutral alkali metal salts, methanol, and water initiate the polymerization effectively. The monomer of the spiro germanium enolate is easily prepared in situ by the reaction of a cyclic germylene with methyl vinyl ketone.
Oxetane photopolymerization—A system with low volume shrinkage
Authors: Nuyken Oskar , Böhner Ralf , Erdmann Christoph 
Published: March 2011

AbstractSeveral mono‐, bi‐ and trifunctional oxetanes were synthesized and polymerized in bulk and in solution cationically. Selected photoinitiators have been applied. It was found that sulfonium salts are very efficient due to good solubility, almost no discolouration of the product and storage stability in the monomer in the absence of light. The conversion was determined by quantitative IR‐spectroscopy. Conversion between 75% and 85% was found in all cases. The shrinkage during polymerization was much lower than for vinyl monomers. No inhibition by oxygen was recognized. Monomer layers thicker than 5.5 mm could be polymerized. The products are transparent and almost colourless. The glass transition temperature of the crosslinked polymers was above the temperature of a human body.
Synthetic and mechanistic aspects of metal‐free polymerizations of acrylates
Authors: Reetz Manfred T. , Hütte Stephan , Herzog H. Martin , Goddard Richard 
Published: March 2011

AbstractMetal‐free initiators are easily prepared from neutral CH‐ and NH‐acidic compounds such as malonic acid esters, nitriles, sulfones, nitro‐alkanes, cyclopentadiene, fluorene derivatives, carbazoles and succinimide. These anions have tetrabutylammonium ions as cationic counterions, but they are not completely free “naked” anions as traditionally assumed. Rather, anion and cation are intimately connected to each other via H‐bonds. These salts initiate the polymerization of acrylates, methacrylates and acrylonitrile, forming polymers in the MW range of 1500 to 20000 with narrow molecular weight distributions (D = 1.1–1.4) in optimized cases. A completely different approach involves initiators of the type α‐iodo malonic acid esters CH3C(I)(CO2R)2 and α‐ iodo isobutyric acid esters (CH3)2C(I)CO2R in combination with (nBu)4N+I− at 60°C. This novel initiator system is specific for metharcylates, i. e., acrylates are not polymerized.
Highly heterotactic polymerization of methacrylates — Higher order stereoregulation and stereochemical significance
Authors: Kitayama Tatsuki , Hirano Tomohiro , Zhang Yajun , Hatada Koichi 
Published: March 2011

AbstractA combination of tert‐butyllithium (t‐BuLi) and bis(2,6‐di‐t‐butylphenoxy)methylaluminium (MeAI(ODBP)2) was found to be an efficient initiator for heterotactic living polymerization of certain alkyl methacrylates in toluene at low temperatures. The polymerization of methyl methacrylate (MMA) with t‐BuLi/MeAI(ODBP)2 (AI/Li=5 mol/mol) in toluene at −78°C gave heterotactic‐rich poly(methyl methacrylate) (PMMA) with narrow molecular weight distributions (MWDs) (heterotactic triad fraction mr = 68%, ratio of weight‐ to number‐average molecular weights M̄w/M̄n = 1.06‐1.17). Other alkyl methacrylates also gave heterotactic polymers under the same conditions; in particular, ethyl and butyl methacrylates gave polymers with heterotactic triad fractions of 87%. The highest triad heterotacticity of 91.6% was obtained for the polymerization of ethyl methacrylate at −95°C. Some characteristic features of this stereospecific polymerization were discussed based on the polymerization results combined with other structural information of the polymer such as chain‐end stereostructure and stereosequence distribution in the main chain.
Multi‐arm star polyisobutylenes: 3. New insight into the chemistry of star formation: Star‐star coupling and core contraction
Authors: Kennedy J. P. , Marsalkó T. M. , Majoros I. 
Published: March 2011

AbstractDetails of the chemistry of linking living polyisobutylene (PIB⊕) pre‐arms with divinylbenzene (DVB) to multi‐arm PIB stars have been studied by triple‐detector size‐exclusion chromatography (SEC). Computer‐aided deconvolution of multimodal differential refractive index (RI), laser light scattering (LLS), and ultraviolet (UV) traces obtained by SEC indicates the formation of complex product mixtures. The observations were interpreted in terms of inter‐and intramolecular reactions of initially‐formed active stars. Thus intermolecular or star‐star couplings are proposed to lead to higher order (secondary, tertiary, etc.) stars, whereas intramolecular reactions result in core‐contraction. The mechanism of these reactions has been outlined. The effect of PIB⊕ pre‐arm length on star‐star coupling was analyzed.
A review on the structure and characterization techniques of silane/matrix interphases
Authors: Suzuki Noriyuki , Ishida Hatsuo 
Published: March 2011

AbstractRecent studies regarding the interphase of silane coupling agents and organic polymer matrices are reviewed with emphasis on its structure and property, and characterization techniques for the interphase. Chemical, physical and physicochemical effects on the formation of silane/matrix interphase and resultant properties are discussed. Improvements of the performance of composite materials are also discussed in relation to the interphase structure. Several representative characterization techniques for interphase are also described.
Introduction of tailored interphases in composite materials based on a thermoset or on a semi‐crystalline polymer matrix
Authors: Gerard Jean‐François , Chabert Bernard 
Published: March 2011

AbstractInterphases having different structures can be created in composite materials based on a thermoset or semi‐crystalline matrices. The mechanical behavior of the reinforced or filled polymers is dependent on the characteristics of these interfacial zones. The microstructures of the interphases result from the interactions occuring at the filler surface. For the thermoset matrices, the structure of the interphases (continuous, distinct) is dependent on the chemical reactions between the surface or the sizing and the reactive mixture during the processing. In the case of the presence of a sizing, the miscibility with the polymer matrix can be also involved. For the semi‐crystalline matrices, the melting and cooling conditions are the main conditions but the occurence of a shearing in the supercooled melt can create transcrystalline regions. Another way consists in the introduction of tailored interphases with controlled properties. Coatings or surface treatments based on functionalized polymers can be made on the fillers or fibers before introduction in the polymer matrix. For the thermoset systems, a soft interlayer with a controlled thickness is introduced at the filler surface, whereas for the semi‐crystalline matrices, polymer chains having the same structure than the matrix are grafted on the surface.
Electrical properties of filled polymers and some examples of their applications
Authors: Klason Carl , Mcqueen Douglas H. , Kubát Josef 
Published: March 2011

AbstractPolymers containing electrically conductive fillers show interesting electrical properties like semiconductors and metals without losing the processability of polymers. Typical applications are as antistatic (electrostatic dissipation) materials, electro‐magnetic interference shielding materials, heaters and sensors. The selection of filler and polymer governs the properties obtained in such composites.
High swelling gels for sensing applications
Authors: Ranucci Elisabetta , Ferruti Paolo , Ferrari Vittorio , Marioli Daniele , Taroni Andrea 
Published: March 2011

AbstractCrosslinked hydrophilic polymers of different chemical structures can be used as sensor coatings for the detection of gaseous analytes. If their crosslink density is low, these materials behave in aqueous media as soft hydrogels with high swelling capacity. From a physico‐mechanical standpoint, they are amorphous rubber‐like materials, with high flexibility of their macromolecular chains. This property is particularly significant in view of applications in the sensors field, because it favours diffusion of the analyte molecules through the coating layer. This paper deals with the application of poly(ethylene glycols) (PEG)‐ and poly(N‐vinylpyrrolidinone) (PVP)‐based crosslinked resins as relative humidity (RH) sorbing materials, and of a poly(amidoamine)(PAA)‐based resin as SO2‐sorbing material. The electronic devices used for evaluating the sorption capability of these polymeric coatings were gravimetric resonant sensors. Resins of various crosslink density, and therefore of various swelling ratios in water, were purposely prepared and characterized. Thin coating, layers, prepared by casting from dilute aqueous suspensions of the resins, previously micronized in water, were used for sorption experiments. All experiments were performed in controlled RH and temperature environments.
Liquid chromatography techniques for characterizing poly(Vinyl Alcohol)
Authors: Meehan Elizabeth , Reid Simon P. , Samios Eleftherios , Dawkins John V. 
Published: March 2011

AbstractPoly(vinyl alcohol) (PVOH) samples may contain several heterogeneities requiring the development of chromatographic techniques for characterization. Size exclusion separations have been carried out using a number of aqueous eluents, incorporating electrolyte, or electrolyte/organic modifier, or surfactant. The most favourable molecular size separation was obtained using 0.25% w/v sodium lauryl sulfate as eluent. Reasonable values for molecular weights of PVOH samples have been determined. Compositional distributions in copolymer systems can be assessed using high‐performance liquid chromatography employing a reversed‐phase separation mechanism. For poly(vinyl alcohol), gradient elution with water/tetrahydrofuran (THF) with a wide pore polystyrene‐based packing produced separations dependent on degree of hydrolysis and sequence length distribution. The elution results were verified with a column packed with non‐porous beads. Partially hydrolysed PVOH samples appeared to have a broad distribution of composition.
Some emerging techniques in polymer mwd characterization
Authors: Nguyen Tuan Q. , Yu G. , Kausch H. H. 
Published: March 2011

AbstractRoutine MW analysis of polymers is generally performed in solution by Gel Permeation Chromatography. The technique, however, presents increasing difficulties in the ultra‐high and ultra‐low MW range. Moreover, GPC is not applicable to most fluorinated and»high performance«thermoplastics which require dissolution temperatures close to the polymer melting point. In response to these challenges, polymer scientists have developed new methods of MWD determination. Although these methods have not yet reached the versatility of GPC, they present potential for further development and are interesting as complementary techniques to GPC. For sparingly soluble polymers, melt viscoelastic properties have been used to obtain information on polymer MWD. Flow birefringence, based on the orientation and extension of long flexible molecular chains in a shear field, has been applied to the characterization of ultra‐high MW polymers. For low MW polymers and oligomers, the MALDI mass spectrometry technique, with its unique capabilities to resolve individual oligomers within a MWD, proves to be an interesting alternative to conventional GPC characterization.
Liquid chromatography at the critical point of adsorption — A new technique for polymer characterization
Authors: Pasch Harald 
Published: March 2011

AbstractLiquid chromatography at the critical point of adsorption (CC) is a versatile method for the determination of different types of molecular heterogeneity in polymers. Operating at the transition point of size‐exclusion and adsorption modes of liquid chromatography, this method is capable of separating polymers according to their functionality. At the critical point of adsorption the polymer chain behaves like an invisible part of the macromolecule and only the heterogeneities (functional groups, blocks, grafts) manifest themselves chromatographically.The application of this method to the determination of the chemical heterogeneity of block copolymers and the composition of polymer blends is demonstrated. Block copolymers can be analysed with respect to the block lengths of the individual blocks. A complete description of their molecular heterogeneity is possible using two‐dimensional chromatography CC vs. SEC. Binary polymer blends are separated with respect to the components regardless of their individual molar masses under experimental conditions, where one component elutes at the critical point of adsorption.