bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the number of active centers in Ziegler‐Natta polymerizations of olefins
Authors: Mejzlík Jiří
Published: March 2011

The methods employed for determination of the number of active centers are classified according to their principles into the following categories: (i) labelling of an organometal component as an initiating species; (ii) labelling of growing chains based on the number of macromolecules, on the number of metal‐polymer bonds, and on selective tagging of the growing chain; (iii) inhibition (retardation) of polymerization by effective catalyst poisons and calculation of the number of active centers on the basis of the poison consumption data. Typical features of the above categories are presented and advantages, as well as shortcomings of the methods are discussed.
Oh the mechanism of stereoregulation in the allylnickel complex catalyzed butadiene polymerization
Authors: Taube Rudolf , Gehrke Jörg‐Peter , Schmidt Udo
Published: March 2011

After a brief account of the present knowledge on the mechanism of the allylnickel complex catalyzed stereospecific butadiene polymerization, synthesis and catalytic properties of the cationic allylnickel(II) complexes, [C3H5NiL2]PF6 (L = P(OAlk)3, P(OAr)3, PPh3, AsPh3, SbPh3, MeCN, Me3CNC, 1,5–COD), are described. From kinetic and 31P‐NMR spectroscopic investigations, especially with [C3H5Ni(P(OPh)3)2]PF6 as a typical trans‐catalyst, the definite course of the catalytic stereoregulation has been elucidated.
Synthesis of polyheterocycles on the basis of poly‐functional monomers and study of their characteristics
Authors: Zhubanov B. A.
Published: March 2011

Application of polyfunctional monomers in the course of polycondensation allows to synthesize different types of polymers using different activity of functional groups. It is possible in this case to vary to a large extent the characteristics of the obtained polymers. The presence of functional groups of different activity in one monomer also allows to modify it by introduction of new fragments for subsequent use in polycondensation or polymerization reactions.

The abovementioned is confirmed by the example of using trimellitic anhydride and a number of alicyclic tetracarbonic dianhydrides.

Trimellitic anhydride is directly used for synthesis of polymers and also modified for preparation of new derivatives.

The perspective of using alicyclic tetracarbonic dianhydrides for synthesis of heterocycles has been shown.

Varying the monomer nature and conditions of a polycondensation reaction, polymers with different specific characteristics have been obtained: heat‐resistant, high‐ and low‐fusible, soluble, incombustible, film‐forming, fiber‐forming, binding for glass‐plastics.
Model reactions for crosslinking of poly(diolefin)s by cations
Authors: Hallensleben Manfred L. , Nimtz Fritz
Published: March 2011

In order to study the reactivity of polymer chain segments of different chemical structure, which are generated either by the chain propagation mechanisms or by isomerization reactions of the preformed polymer chain as a consequence of chemical or temperature influences, low‐molecular‐weight model reactions are of growing interest (1–3). With respect to cationically initiated crosslinking reactions of poly(diolefin)s, linear as well as cycloolefins may serve as model compounds to elucidate initiation and propagation steps in regard to network formation. Of particular interest are the number of individual polymer chains which are interconnected in the crosslink section.

1‐Methylcyclohexene, a model for cis‐1,4‐poly(isoprene), reacts with protons as well as classical carbenium ions to yield the addition products and dimers only, which show structural varieties. Some of the isomers were separated by preparative HPLC and were identified by NMR and mass spectroscopy.
Topological aspects of structure and properties of highly crosslinked networks
Authors: Topolkaraev V. A. , Berlin A. A. , Oshmyan V. G. , Prut E. V.
Published: March 2011

Statistical model approach which allows to set the quantitative interrelation between the chemical structure of initial reagents, formation mechanism, topology and in the final analysis mechanical properties of highly crosslinked networks, is considered. The role of network topology in the formation of the main physico‐mechanical properties of polymer network is singled out. The analysis is carried out on the important class of highly crosslinked networks, formed by polyaddition reaction of diepoxides with aromatic diamines.
Thermal oxidation of polyorganosiloxanes
Authors: Zhdanov A. A. , Papkov V. S.
Published: March 2011

The kinetics of noninhibited and inhibited oxidation of poly[(diethyl)siloxane] oligomers (PDES) has been investigated. Phenyl‐ β ‐naphthylamine (PNA) and tris(triethylsiloxy)vanadate (TTESV) were used as antioxidants. It is shown that in the presence of PNA the oxidation of PDES proceeds with distinct induction periods. The activation energy of the initiation stage, estimated from temperature dependence of the induction periods, is about 230 kJ/mol. TTESV can act as inhibitor and catalyst in the oxidation of PDES, depending on temperature and content of oxygen in oxidizing mixture.
Role of metal ions in development of specific properties of polymer metal complexes
Authors: Rashidova S.S H. , Urinov E. U. , Khodjaev S. G.
Published: March 2011

The character of changing the hydrodynamic and conformational characteristics of vinylpyrrolidone copolymers with acrylic acid depending on solvent nature was studied. Peculiarities in changing the hydrodynamic, molecular characteristics and complex forming properties of equimolar vinylpyrrolidone copolymer with metal ions are revealed. Metal ions introduction in copolymer macromolecules gives rise to polymer‐specific, physiologically active properties.
High‐pressure absorption spectroscopy in polymerizing systems
Authors: Buback Michael , Vögele Hans‐Peter , Winkels Hermann‐Josef
Published: March 2011

Quantitative high‐pressure absorption spectroscopy in the mid infrared, near infrared, and ultraviolet region enables direct and precise investigation of high‐pressure ethylene polymerizations with thermal, chemical, and laser‐photochemical initiation. The special advantages of kinetic studies via quantitative near infrared spectroscopy in an extended wavenumber range are outlined. Extensions of the method on copolymer systems are indicated. The spectroscopic technique is of general applicability in studies on reactions and equilibria in dense fluid states including liquids and compressed gases.
Fourier transform infrared study of orientation and relaxation in poly(methyl methacrylate)
Authors: Zhao Y. , Jasse B. , Monnerie L.
Published: March 2011

Infrared measurements of the dicroic ratio of poly‐(methyl methacrylate) absorption bands provide a valuable method for determining the orientation as well as the relaxation of chains during stretching. Different strain rates and temperatures of stretching were used. Orientation relaxation was determined and a master curve was obtained at a reference temperature TO = 135°C. The master curve shows that orientation relaxation behaves similarly to mechanical relaxation.
Annealing of the β‐modification of polypropylene
Authors: Varga József , Tóth Ferenc , Hummel D.O.
Published: March 2011

Expressive memory effect has been proven in the course of the annealing of the β‐modification of polypropylene (β‐PP). The character of the structural changes taking place in β‐PP during annealing strongly depends on the thermal history. In dependence on the thermal history βα or ββ‐recrystallization takes place during thermal treatment. In case the annealing starts from the crystallization temperature β‐PP is recrystallized into a more perfect structure with higher melting point ‐ similarly to thermodynamically stable modifications. The samples cooled below a certain temperature before subjected to annealing transform partly or fully into the α‐modification. The βα‐recrystallization tendency prevalent on the effect of recooling can be reduced or eliminated with the aid of stepwise annealing with decreasing temperature steps.
Reactivity of lactams in anionic polymerization
Authors: Sebenda Jan
Published: March 2011

The rate of anionic lactam polymerization is greatly affected by variation of the permittivity of lactams with ring size and substitution, as well as by changes of permittivity during polymerization. Therefore, an estimation of reactivities under comparable conditions is possible in solution only. The lack of any solvent permitting anionic lactam polymerization at low temperatures was circumvented by using living polymers soluble in aprotic solvents as carriers. Such polymers are able to remain in solution even after the addition of a few monomer units of a lactam, the polymer of which is insoluble. In this way, relative reactivities of a series of four‐membered lactams, as well as that of the five‐membered one were established.
Cyclic polysiloxanes
Authors: Semlyen J. A.
Published: March 2011

The preparation, fractionation and characterisation of synthetic cyclic polysiloxanes (R(CH3)SiO)x are reviewed. Particular emphasis is given to the cyclic poly(dimethylsiloxanes) (PDMS) (R is CH3) cyclic poly(phenylmethylsiloxanes)(PPMS) (R is C6H5) and cyclic poly(vinylmethylsiloxanes) (PVMS) (R is CH2=CH).

The application of high performance liquid chromatography (HPLC) and analytical and preparative gel permeation chromatography (GPC) to the preparation and characterisation of cyclic polysiloxanes is discussed. The methods include preparation of sharp fractions of relatively high molar mass cyclic polymers (with heterogeneity indices typically ca. 1.05) and comparison of the GPC and retention volumes of cyclics with the corresponding linear polymers.

Investigations of the cyclic polymers prepared have been made using a number of experimental methods and techniques. These include dilute solution viscometry and low angle neutron scattering. Comparisons are drawn between cyclic PDMS and other cyclic polysiloxanes and also between cyclic polysiloxanes and the corresponding commercially‐important linear polymers.
‘Immortal’ polymerization of epoxide with metalloporphyrin catalyst
Authors: Inoue Shohei , Aida Takuzo
Published: March 2011

Aluminum porphyrin is an excellent initiator for the polymerization of epoxides to give polyethers with narrow molecular weight distribution, even in the presence of protic compounds such as alcohols, carboxylic acids, and hydrogen chloride. The number of polymer molecules is higher than that of initiator molecules. By taking advantage of the “immortal” nature of this polymerization, a novel, efficient procedure for the synthesis of block copolymers and end‐reactive polymers with narrow molecular weight distribution is developed.
Synthesis of polyoxiranes and polythiiranes bearing a potential aldehyde group in the side chain
Authors: Goutte P. , Sepulchre M. , Spassky N.
Published: March 2011

Polyoxiranes and polythiiranes with acetal group in the side chain are prepared by polymerization of 1,1‐diethoxy‐2,3‐epoxy‐propane (DEO) and of the corresponding thiirane (DET) using different chiral and achiral initiators. In the case of poly(DET) acetal groups can be removed leading to a polymer with an aldehyde content up to 64 %. In similar experimental conditions the extent of acetal hydrolysis does not exceed 23 % for poly(DEO).
Gas phase polymerization of cyclopentene
Authors: Ismail F. , Léonard J.
Published: March 2011

Pure gaseous cyclopentene is found to polymerize on a glass surface when the polymerization is initiated with tungsten hexachloride. The polymer thus formed is colourless and has a high molar mass with a narrow molecular mass distribution. Polymerizations are carried out in the 10 to 60° C temperature range. From kinetic measurements, an overall activation energy of 69,0 kJ is obtained for the conversion of gaseous monomer to condensed polymer. NMR analyses show a distribution of cis‐and trans‐configurations of the double bonds in the polymer and the absence of any detectable branching.
Synthesis of poly‐β‐(α‐benzyl‐L‐aspartate) from L‐aspartic β‐lactam benzyl ester (3(R)‐benzoxycarbonyl‐2‐azetidinone)
Authors: Rodriguez‐Galan A. , Muñoz‐Guerra S. , Subirana J.A. , Chuong Bui , Sekiguchi H.
Published: March 2011

A study on the anionic‐assisted polymerization of L‐aspartic β‐lactam benzyl ester in solution has been carried out in order to prepare an improved poly‐β‐(α‐benzyl‐L‐aspartate). We have found that both imide formation (with appreciable racemization) and size of the resulting polymers are highly dependent on the nature of reaction medium. A high molecular weight poly‐β‐aspartate without detectable branching could thus be obtained by using solvents with low polarity. The mechanism of side reactions is discussed.
Ab‐initio electrostatic molecular potential contour maps for initiation step and Ab‐Initio MRD‐CI calculations for propagation step of cationic polymerization of oxetanes
Authors: Kaufman Joyce J. , Hariharan P. C. , Roszak S. , Keegstra P. B.
Published: March 2011

The initiation step in the cationic polymerization of cyclic ethers is influenced by basicity and ring strain. We carried out ab‐initio MODPOT/VRDDO/MERGE calculations on a variety of substituted oxetanes and generated electrostatic molecular potential contour (EMPC) maps in three‐dimensions around the molecules. The size of the negative EMPC map region around the oxygen enabled us to predict the propensity to polymerize prior to the syntheses of the actual monomers themselves. We carried out ab‐initio MODPOT/VRDDO/MERGE MRD‐CI calculations for the propagation step of oxetane reacting with protonated oxetanes to cause ring opening of protonated oxetane. Similar MRD‐CI calculations on variously substituted oxetanes will shed insight into relative copolymerization preferences.
Formation and properties of thermosetting and high tg polymeric materials
Authors: Gillham John K.
Published: March 2011

Interrelationships between reaction conditions and material properties of thermosetting and high Tg polymers are discussed from the point of view of a generalized time‐temperature‐transformation (TTT) diagram.
On several aspects of network formation and plastic deformation of tightly crosslinked epoxies
Authors: Oleinik E. P. , Bulatov V. V.
Published: March 2011

The article considers several features of the epoxy polymer network glassy state. Attention is paid to the “liquid‐glass” transition during cure, influence of the transition on the properties of network polymer, theoretical description of joint kinetics of network formation reaction and structural relaxation in tightly crosslinked polymer networks, and mechanism of plastic deformation of crosslinked epoxies in the glassy state.
Graphite intercalation compounds electrochemistry as a model for synthetic metals
Authors: Métrot André
Published: March 2011

After an introductory description of the chemical and crystallographic properties of Graphite Intercalation Compounds, their general electrochemical behavior is examined. The reversible intercalation/de‐intercalation process leading to graphite salts is more specifically described based on the author's view of interlayer capacitive electroadsorption.
Preparation and electrochemistry of modified polypyrrole films by anodic copolymerization techniques
Authors: Merz A. , Baumann R. , Haimerl A.
Published: March 2011

The anodic copolymerization of pyrrole and N‐(ω‐ferrocenylalkyl)pyrroles, FcPy‐n, at platinum electrodes in an electrolyte consisting of tributylammonium benzenesulfonate in moist acetonitrile is optimized with respect to the absolute and relative concentrations of the monomers and the spacer length of FcPy‐n. The copolymer composition is estimated from cyclic voltammograms of the polymer films. Only films with less than 20% FcPy‐n content show the typical polypyrrole voltammograms. Free standing copolymer films with a conductivity of ca. 10 S cm−1 can be prepared.
Soluble conducting polymers: The poly(3–alkylthienylene)s
Authors: Rughooputh S.D.D.V. , Nowak M. , Hotta S. , Heeger A. J. , Wudl F.
Published: March 2011

The conjugated poly(3‐alkylthienylene)s, P3ATs, can be processed from solution and subsequently used as semiconducting and metallic polymers. Both as‐synthesized and solution‐cast films can be readily doped with resulting electrical conductivities which are quite high, σ‐30–100 S/cm.
Modification of carbon electrodes by vitamin B12‐polymers
Authors: Ruhe Annette , Walder Lorenz , Scheffold Rolf
Published: March 2011

New types of electroactive polymers consisting of derivatives of vitamin B12 and epoxy resins have been synthesized. Surface modification of carbon (carbon felt or basal plane pyrolytic graphite) has been achieved by thermal curing of the monomers on the electrodes. Electrochemical response from the Co (II)/Co (I) redox couple has been observed from sub‐mono to multilayer coverages. The influence of the size of the epoxy spacer on charge propagation in the polymer has been studied. The B12‐modified electrodes have been applied to electrosynthesis and electroanalysis: They catalyze the reductive cross‐coupling of alkyl halides and activated olefins and they are efficient sensors for alkylating agents.
Electrolytically initiated vinyl polymerization
Authors: Olaj Oskar Friedrich
Published: March 2011

After a short outline of the historic development of electroinitiated vinyl polymerization and a description of the early work in this field a survey is given on the most important initiation systems. The difficulties and problems which arise, in addition to conventional initiation of vinyl polymerization, are analyzed. Among others, these comprise the spatial heterogeneity of active particle production, the necessity of dissolving the electrolyte in the polymerization system, which preferably also should be a solvent for the polymer formed, the susceptibility of the electrode process to impurities, the eventual termination of the growing chains by the products of the process taking place at the counter‐electrode, and the possibility of simultaneous initiation of anionic and free radical polymerization at the cathode and of cationic and free radical polymerization at the anode. Some examples show that in spite of these numerous difficulties precise kinetic measurements are possible in some free radical as well as in some ionic initiation systems. While the initiation of free radical polymerization processes suffers from disappointingly low current yields (≈︁10−3), throughout which makes this initiation much inferior to any conventional one, there are some positive features inherent in the electroinitiation of ionic polymerization. Especially, it is the possibility to carry out cationic polymerization exclusively in presence and under control of such counterions which are known to have favorable polymerization characteristics (this is to lead to high rates and molecular weights), however, the corresponding anhydrous acids of which do not exist, by merely oxidizing the monomer in presence of salts of these counterions (e.g. AgSbF6). Due to the non‐availability of the corresponding anhydrous acid HSbF6 this cannot be accomplished in a direct manner by conventional techniques.
Phenol electropolymerization in acid medium
Authors: Mengoli Giuliano , M. Musiani Marco
Published: March 2011

An overview is given of phenol electro‐polymerization in oxalic acid media, as a method of corrosion protection for Fe substrates. The work focuses on the electrical and/or chemical parameters of the system which mainly determine the growth and/or corrosion resistance of the organic‐inorganic films thus obtained. Quantitative evaluation of the barrier to corrosion provided by the coatings was carried out by the ac impedance technique.
Neutron scattering studies of the structure of amorphous and crystalline polymers and of polymer blends
Authors: Fischer E. W.
Published: March 2011

The technique of neutron scattering for studying both the structure and dynamics of polymer systems is now well established. In the case of amorphous flexible polymers in most cases the bulk chain dimensions agree rather well with those of the unperturbed coil. Some newer results concerning for example side‐chain liquid‐crystal polymers and segmented polyurethane elastomers are described. Neutron small‐angle scattering can also be used for the investigation of the molecular deformation mechanism during the drawing process of polymers.

In the case of semicrystalline polymers the way in which a single macromolecule traverses the crystalline and amorphous phases can also be evaluated by neutron scattering. A method has been proposed for the evaluation of the neutron scattering data without introducing detailed structural models. The only assumption made is that the molecular structure can be described as consisting of “clusters” of crystalline stems which belong to the same molecule. It is shown that this cluster model can be verified experimentally for the cases of poly(ethylene oxide), polypropylene and polyethylene.

The structure factor S(q) in compatible polymer blends is usually treated by the random phase approximation according to de Gennes. The temperature dependence of S(q) displayed by some systems, however, appears to be anomalous within this approximation. A new method is presented for evaluating the neutron scattering data which takes into account that the Flory‐Huggins interaction parameter χ is not a point‐function χδ(τ), but can be interpreted in terms of a structure model χ(τ) which consists of spatially separated positive and negative contributions within a 1–10 å range.

Finally the application of neutron scattering to diblock copolymers is discussed and it is shown that the results for the case of polystyrene‐poly (p‐methylstyrene) are in good agreement with the theoretically expected behaviour.
Reactive oligomers and polymers: Synthesis and application for polymer modification
Authors: Fedtke Manfred
Published: March 2011

The classification of reactive oligomers and some aspects of their reactivity in crosslinking systems is discussed, and related to three experimental attemps to contribute to a better understanding of epoxy network modification by reactive oligomers and polymers.

The synthesis and modification of telechelic oligomers with functional groups at the chain end as starting materials for modified epoxies proved to be successful only when all the mechanisms occurring below gel point had been investigated by model reactions on the one hand and, on the other, when the actual determination of their influence on the network structure had been established.

Ethylene‐vinylalcohol copolymers with a controllable amount of hydroxylic groups are a convenient model system. The reaction of OH‐groups with acid anhydrides produces carboxylic groups attached onto the polymer chain which are useful as hardeners for epoxy resins. The mechanisms of the synthesis and of the crosslinking reactions are more complex than might be expected.

More information is now available about the amount of oligoether sequences in epoxies prepared by anionically and cationically induced crosslinking of glycidyl ethers. Using model compounds, several different types of oligomers have been found which depend on the initiating agent.
Instruments and methods for small‐angle scattering with synchrotron radiation
Authors: Koch M. H. J.
Published: March 2011

Some aspects of small‐angle X‐ray scattering (SAXS) instrumentation for synchrotron radiation (SR) are considered below. The basic layout of instruments as well as some of the problems arising from the nature of the source and of the type of experiments are discussed. Further, a survey of the instruments available at major SR facilities is given.
Elastic light scattering from nonspherical and polydisperse particles in the size range from 100 to 2000 NM
Authors: Glatter Otto , Hofer Michael
Published: March 2011

In the case of monodisperse dilute systems it is possible to calculate the distance distribution function for homogeneous and inhomogeneous particles of arbitrary shape. The distance distribution function enables one to find a rough classification of the shape and to determine the size of the particle. This function can be deconvoluted to the radial polarization density profile for particles with spherical symmetry.

A number, mass or intensity distribution can be calculated from the light scattering data from polydisperse systems if the distribution can be described by a single parameter and if it is possible to calculate the shape factor of the particles, as it is the case for spheres and spheroids. The range of applicability of the method depends on the experimental set‐up, but is in most cases in the size range from 100 nm to several micrometers.
Polymer blends
Authors: Higgins Julia S.
Published: March 2011

Small angle neutron scattering may be used to provide information on the thermodynamic basis of polymer‐polymer miscibility via the temperature and concentration dependences of the observed interaction parameters. The kinetics of the phase separation process may also be followed and this in turn gives further information about the blend compatibility as well as providing tests of current theories of spinodal decomposition in binary mixtures.
Structure studies of langmuir‐blodgett films
Authors: Feigin Lev A. , Lvov Yurii M.
Published: March 2011

A method of small‐angle X‐ray investigation of the structure of Langmuir‐Blodgett (L‐B) films on substrates is developed. Experiments were carried out using a small‐angle X‐ray diffractometer with a position‐sensitive detector. X‐ray patterns contain 10–15 reflections with spacings from 50 Å up to 250 A and a number of ripples in the inner parts of the curves. An analysis of these ripples revealed integral parameters of L‐B films (thickness 100 ‐ 2000 A, a number of monolayers: 1–50). The Fourier‐synthesis of the structural amplitudes gave electron density profiles across the films. These profiles demonstrated the successive realization of pre‐programmed sequences of alternating bilayers in L‐B superlattices.
Small‐angle scattering as a tool for the study of microemulsion structure
Authors: Kaler Eric W.
Published: March 2011

Microemulsions are equilibrium dispersions of oil and water stabilized by a surfactant‐rich sheet at the internal oil‐water interfaces. The domains of oil and water have characteristic dimensions of a few hundred Ångstroms, and so are appropriate for study with small‐angle scattering. The scattering from droplets of oil in water or water in oil may be modelled well with modern representations of the structure of colloidal suspensions, but the structure of microemulsions containing comparable amounts of oil and water is likely bicontinuous and is well represented as a disordered lamellar structure. Recent theoretical and experimental results are reviewed and extended.
In‐situ small‐angle studies of microstructural changes in polymers
Authors: Schultz Jerold M.
Published: March 2011

A series of experiments in which small‐angle x‐ray scattering (SAXS) is used to follow microstructural changes in situ is reviewed. The work relates to primary and secondary crystallization, to melting and to physical aging. SAXS curve shapes are used to define whether primary crystallization occurs through the growth of “skeletal” or of “dense” spherulites. The integrated intensity is used to establish whether primary and secondary crystallization occur simultaneously. The ratio of second‐ to first‐order peak intensities, the absolute intensity, and reversible peak shifts are used to study the nature of secondary crystallization in polyethylene, poly(vinylidene fluoride) and a polysiloxane. The last two of these exhibit reversible peak shifts which are not consistent with simple models and it is concluded that thorough replacement of existing structures occurs during this process. SAXS peak shape changes in PE indicate that melting occurs by the random loss of crystals throughout the material. Finally, it is shown that SAXS can be a useful tool for monitoring physical aging in semicrystalline polymers.
Small angle neutron scattering (SANS) studies of diffusion in bulk polystyrene near the glass transition temperature (Tg)
Authors: Anderson James E. , Jou J.H.
Published: March 2011

Ultraslow diffusion in bulk polymers has been measured by SANS. The experiment begins by measuring scattering from heterogeneous specimens containing domains of protonated‐and deuterated‐polymers at temperatures far below Tg. The samples are subsequently held [annealed] above Tg for a known time‐interval, then cooled below Tg where SANS is measured again. Scattering changes, from before to after annealing, are analysed to obtain diffusion coefficients. The recent Summerfield ‐ Ullman procedure is used to deconvolute portions of the scattering curve that decrease and increase with annealing time. Because of SANS sensitivity to small distances, the method yields D ≈ 10−18 to 10−15 cm2/s after annealing times of 1–24 h. Data analysis is complicated by “smearing effects” which produce apparent Q‐dependent diffusion coefficients. Representative experimental results on polystyrene at 108°–130°C are discussed.
Small‐angle X‐ray scattering characterization of inorganic glasses
Authors: Walter G. , Kranold R. , Lembke U.
Published: March 2011

Small‐angle X‐ray scattering is a powerful tool in glass science. The present paper reviews the characterization of inorganic glasses by means of this technique, with specific concern for four areas; (A) the correlations between structure and properties; (B) the middle‐range order; (C) the kinetics of phase separation; and (D) the techniques of glass preparation. SAXS studies on various glass systems, e.g. vitreous silica, phosphate glasses, colour glasses, photochromic glasses, and glass‐ceramic‐forming systems, are described in terms of this approach.
Development of polymer blend phase morphology during processing
Authors: White James L. , Min Kyonsuku
Published: March 2011

We investigate the mechanics of formation of polymer blends both from the view of (i) the technology and flow characteristics in batch and continuous compounding machinery as well as from (ii) the mechanistic perspective of the formation and evolution of dispersed phases. Special attention is given to internal mixers and to intermeshing co‐rotating twin screw extruders. The role of interfacial tension and viscosity ratio in affecting phase morphology is described. We also discuss the development of polymer chain orientation in the different components of an immiscible polymer blend during processing.
Study and control of polymer blends morphology and related properties
Authors: Teyssié Ph. , Fayt R. , Jérôme R.
Published: March 2011

It will be shown how a combination of techniques allows to gain a rather precise idea of the (un)miscibility situation in polymer blends at different size scales (i.e. from ca.20 A up to lμ); typical examples include simultaneous use of TEM, SEM, NRET and ss. NMR.

On these bases, interesting blends have been studied and tailored, in which both morphology and interfacial adhesion have been controlled (in particular by the use of diblock copolymers) to provide for a better spectrum of properties. A number of situations will be described, implying commodity and engineering polymers, but also different types of fillers; their optimization has led to interesting applications in the field of better emulsion dispersions, very high impact resins, economical engineering plastics, controlled migration, filled materials,.
Digital image analysis of polymer blends morphology
Authors: Nishi Toshio , Hayashi Takafumi , Tanaka Hajime
Published: March 2011

Application of digital image analysis (DIA) to polymer blends morphology is discussed with examples. Various operations in DIA including two‐dimensional Fourier transformation (2DFT), intensity distribution, recursive region extraction, etc. are applied to morphology of polymer blends due to spinodal decomposition (SD), nucleation 6 growth (NG), and eutectic solidification (ES). Merits and drawbacks of DIA to study polymer blends morphology are discussed and the possibility of future development is presented.
Crystallization, morphology, structure and miscibility of poly(ethylene oxide) based blends
Authors: Cimmino S. , Martuscelli E. , Silvestre C.
Published: March 2011

Results of an investigation on the morphology, structure, isothermal crystallization, thermal behaviour and miscibility of poly(ethylene oxide) (PEO) based binary blends are reported. In particular poly(vinyl acetate)(PVAc), poly(methyl methacrylate) (PMMA) at different tacticity and poly(ethyl methacrylate) (PEMA) were added to PEO.

It was found that with the only exception of isotactic poly(methyl methacrylate) (IPMMA), the addition of the above cited components causes a depression in both the spherulite growth rate and the overall kinetic rate constant. The experimental G and Kn were analyzed by means of the latest kinetic theory in order to determine the influence of composition on the process of surface secondary nucleation. The optical microscopy of thin films of the sample revealed that the blends crystallized with volume filling crystals at least up to 50/50 blend composition. The small angle X‐ray scattering curves were analyzed using a recently developed methodology. The structural properties of the blends were attributed to the presence of the non crystallizable material in the interlamellar or interfibrillar regions of PEO. From the glass transition temperature it has been deduced that an homogeneous amorphous phase is present for all the blends except for the PEO/IPMMA amorphous system. For the system PEO/atactic poly(methyl methacrylate) (APMMA) the miscibility was also predicted by theoretical approaches.
Brittle‐tough transition temperatures in impact tests on rubber‐toughened plastics
Authors: Bucknall Clive B.
Published: March 2011

— In notched impact tests, rubber‐toughened plastics show abrupt transitions in toughness with increasing temperature. Typically, there are two such transitions, one just above the Tg of the rubber phase, and the second some tens of degrees higher. The factors affecting the positions of these transitions are discussed. The relaxation behaviour of the rubber phase is a key factor, but rubber content and particle size are also important. Examples of impact transitions in high‐impact polystyrene (HIPS) and toughened nylon are discussed.
Solvent effect on the miscibility of polymer blends
Authors: Bui Van Tam , Baril Daniel , Vu Thanh Long
Published: March 2011

Starting from the Flory‐Huggins theory applied to a polymer/polymer/solvent solution, an expression has been derived showing the overall effect of solvent on the composition of the polymer blend in the final solid state. This expression has been experimentally verified by investigating the miscibility of two polymer blends: polystyrene/poly(α‐methylstyrene) cast from tetrahydrofuran and cyclohexane, and polystyrene/poly (methyl methacrylate) obtained from tetrahydrofuran and chloroform. Besides the usual differential scanning calorimetry technique, thermogravimetric analysis might be helpful for detecting the miscibility of polymer blends.
Small‐angle neutron scattering study of homopolymer blends and blockcopolymers of polystyrene/polyparamethylstyrene
Authors: Jung W. G. , Fischer E. W.
Published: March 2011

Small angle neutron scattering (SANS) experiments were carried out at one mixture and two block copolymers of polystrene (PS) and poly(p‐methylstyrene)(PpMS) at different temperatures ranging from 107 to 295°C. Both block copolymers show a maximum in scattering intensity, which increases with decreasing temperature approaching the spinodal point. Theoretical curves from Leibler's mean field theory agree very well with the experimental points with (XN) as the only fitting parameter, where χ is the Flory‐Huggins interaction parameter and N is the degree of polymerization. The reciprocal value of I(qm)−1 of the maximum intensity for the block copolymers as well as the reciprocal intensity at zero scattering vector (I(q=0)−1) for the mixture obey well the ansatz I = A + B/T within the experimental temperature range. The spinodal values of (XN)S are in good agreement with the theoretical values from Leibler.
Block copolymer‐homopolymer blends in the disordered state: Determination of the interaction parameter using small angle neutron scattering
Authors: Marie Pascal , Selb Joseph , Rameau Alain , Gallot Yves
Published: March 2011

The aim of this study was to determine the interaction parameter xAB and its variation with temperature from the intensity scattered By pure block copolymer (A‐B) and block copolymer‐homopolymer (B) blends where A is polydeuteratedstyrene and B polybutadiene. SANS experiments on pure copolymers of low molecular weight have shown that the scattering curve exhibits a peak of intensity related to the correlation hole effect. χAB was determined by fitting the experimental curves using Leibler's theory and the law of variation of χAB versus temperature was established. In the case of copolymer‐homopolymer blends, the scattering spectrum is modified because of a new and additional long range correlation effect (mixing effect) which dominates in the low q range and leads to strong forward scattering. We have not found any significant variation of χ with blend composition.
Microstructure of miscible polymer blends
Authors: Vesely D. , Finch D. S.
Published: March 2011

The purpose of this work is to describe the application of new electron microscopy techniques to the study of polymer blends with very fine dispersion of phases (miscible blends). Blends of PVC with PMMA, PCL, POM and SAN were prepared by high temperature mixing on a two roll mill, or by solvent casting. Thin sections (or cast films) were investigated in the scanning transmission electron microscope and small phases were identified in most blends. The contrast was enhanced by electronic combination of bright and dark field signals, by an irradiation and staining technique and by differential mass loss. The specimens were further characterized by measurement of mass loss, resulting from electron beam damage. The non linear changes in the mass loss rate with concentration were interpreted as being influenced by partial solubility and molecular interactions.
Relaxation behaviour of stretched polymer melts
Authors: Verbraak C. L .J. A. , Te Nijenhuis K. , van Der Vegt A. K.
Published: March 2011

The relaxation behaviour of stretched polymer melts is described with the aid of the Lodge‐model, in which a finite deformation time is incorporated. The theoretical predictions, based on this model, are in fair agreement with experimental results, at least for relatively small deformations. A simple shift factor is introduced to fit the theoretical and experimental curves in the case of larger deformations.
Recognition hysteresis of the acetylcholine receptor of torpedo Californica
Authors: Neumann Eberhard , Boldt Elvira , Rauer Barbara , Wolf Hendrik , Chang Hai Won
Published: March 2011

The nicotinic acetylcholine receptor (nAcChR) of the electric organ of Torpedo californica fish exhibits a pronounced hysteresis loop in the high affinity binding of the neurotransmitter acetylcholine (AcCh). When increasing amounts of AcCh are added (pulse mode) an extremely long‐lived, metastable conformer distribution is obtained (lower hysteresis branch) between low affinity AcCh binding states (Rl) and high (Rh) and very high (Rvh) affinity states. Dialysis conditions always lead to the equilibrium binding curve (upper hysteresis branch; K̄A = 5 × 10−9M, 4°C; one A bound to the R‐monomer of Mr ≈ 290 000). Cyclic, pulse mode addition and dilution of AcCh results in scanning loops within the main hysteresis.

The kinetic analysis of the changes in free and bound AcCh during the open‐system conditions of dialysis, that releases the metastability, shows that the AcCh (A) binding proceeds along an induced‐fit pathway according to A+Rh ⇋ ARn ⇋ ARvh. The rate constant of the step ARh → ARvh is k2 = 6 × 10−3s−1 and that of the reverse step is k−2 = 3 × 10−4s−1. Direct binding of A to free Rvh can be excluded. Therefore, the state Rvh does not preexist, it is induced and only stable, as ARvh, by bound AcCh. The metastability can be described in terms of long‐lived ARvh ·R1 hybrid dimers.

Physiologically, the metastable hybrid may be viewed as a saving device: the functionally important, channel‐active R1 conformer is, at low AcCh‐concentrations [A] < 1μM, prevented to convert to the desensitized states Rh and ARvh. Furtheron, AcCh enhances the phosphorylation of phosphatidyl inositol and the auto‐phosphorylation of the receptor. If the AcCh binding hysteresis causes a phosphorylation hysteresis the desensitized nAcChR may serve as a memory molecule of the transsynaptic information signalling of the neurotransmission.
General aspects of protein adsorption
Authors: Jennissen Herbert P.
Published: March 2011

The study of protein adsorption on a mechanistic and quantitative basis is still a relatively young science and a general theory encompassing all aspects cannot be given. Till now the possibility of synthesizing surfaces in a controlled way, to elucidate the mechanism of protein adsorption ‐ a possibility existing since the advent of affinity chromatography nearly two decades ago ‐ has only been utilized to a small extent. Since this technique, however, has allowed the derivation of some general principles of protein adsorption and protein adsorption kinetics, which would otherwise not have been amenable for study, these results will be mainly referred to here.
The adsorption of lysozymes: A model system
Authors: Hansen J. , Ely K. , Horsley D. , Herron J. , Hlady V. , Andrade J. D.
Published: March 2011

Hen egg white lysozyme was adsorbed onto clean borosilicate glass and n‐pentyl silane‐treated glass surfaces. Both modified (reductively methylated) and native lysozyme were studied. Variable angle X‐ray photoelectron spectroscopy (VA‐XPS) suggested differences in the nature of the adsorbed layer depending on substrate properties, as well as on degree of methylation of the protein. Adsorbed film thickness (as measured in the dehydrated state by XPS) ranged from 14 Å on hydrophilic glass to 25 Å on the hydrophobic surface. Degree of surface coverage ranged from 45% on the hydrophobic to 69% on the hydrophilic surface. The results suggest that lysozyme unfolds to a greater extent and covers more surface on the hydrophilic glass, possibly due to strong electrostatic interactions at the pH 7.4 conditions used in the study. An analysis of the surface structure of native hen lysozyme by molecular graphics has also been performed, suggesting that adsorption on hydrophobic surfaces should occur via the hydrophobic patch opposite the enzyme active site cleft.

A comparison with human lysozyme has also been made using total internal reflection fluorescence (TIRF) spectroscopy to measure protein adsorption on model surfaces. The two proteins have significantly different interfacial properties.
Surface diffusion as a rate‐enhancing mechanism in macromolecular association: The effectiveness of one‐ and two‐dimensional surface sliding
Authors: Berg Otto G.
Published: March 2011

The effective rate for a macromolecular association can be increased if the molecules can be held together loosely by nonspecific surface forces while they search for the specific reactive sites. In this way steric constraints can be relieved. In extreme cases, a specific interaction site can be surrounded by extensive surfaces either essentially linear (e.g. a DNA site) or two‐dimensional (e.g. a membrane‐bound receptor). If ligands can bind nonspecifically and search these surfaces in a lower‐dimensional diffusion process, very substantial rate enhancements can be achieved under suitable conditions. The ranges of concentration and affinity of such nonspecific surfaces that can produce rate enhancements are derived and discussed. It is found that under the expected conditions in the living cell, such rate enhancements will be fairly modest. Nonetheless, nonspecific surface diffusion may play an important role.
Procedure for activating polymers with primary and/or secondary hydroxyl groups
Authors: Ngo That T.
Published: March 2011

A new facile method using 2‐fluoro‐1‐methylpyridinium toluene‐4‐sulfonate (FMP) for activating polymeric hydroxyl groups has recently been developed (Refs. 1–2). Such activated polymers are useful for immobilization of enzymes, antibodies and other biomolecules and for affinity matrix development. The activation method involves reacting, at room temperature, the polymer with FMP in the presence of a tertiary amine for 0.5 to 1 hour. The activated hydroxyls react readily with nucleophiles, such as amino or thiol ligands at pH 5–10. The resulting linkages between the ligand and the polymer are respectively stable secondary amine and thioether bonds. The activated polymer remains active and usable for several months when stored at 4°C in either an acidic aqueous solution or an inert anhydrous organic solvent. The “half‐life” of the activated groups in non‐nucleophilic buffer solution varies from 10 to 300 hours in the pH range of 10 to 6, being most stable at low pH. Both primary and secondary hydroxyl groups of different polymers were facilely activated and shown to react readily with nucleophilic groups of biomolecules. Furthermore, FMP provides a convenient handle for the synthesis of unique conjugates consisting of FMP and a guiding molecule. These conjugates function as an activator of the hydroxyl group of a solid support as well as a molecular guide which orients the position of the ligand to be immobilized. The conjugates make it possible to immobilize ligands in an affinity‐directed way.
Exposure of hydrophobic sites in CA2+‐binding proteins: Influence on chromatographic properties and structure‐function relationships
Authors: Krebs Joachim , Buerkler Jacqueline , Guerini Danilo
Published: March 2011

Calmodulin and related Ca2+ ‐binding proteins were characterized using different labeling, chromatographic and spectroscopic techniques. Ca2+‐binding to members of the so‐called “EF‐hand”‐ or “helix‐loop‐helix”‐model protein family induced conformational changes, thereby exposing hydrophobic sites in some of them. These sites were identified using the photoreactive, carbene‐generating, radioactive probe 3‐(trifluoromethyl)‐3‐(m‐[1251]iodophenyl)diazirine, and characterized using different high performance liquid chromatography techniques. The influence of chemical modification of some of the amino acid residues on the properties of calmodulin were characterized using circular dichroism. A correlation between an increase of oxidized methionine residues of calmodulin and a decrease of Ca2+‐induced helical content was observed.
Immunoaffinity separations of cells in two polymer aqueous phase systems
Authors: Brooks Donald E. , Sharp K. A. , Stocks S. J.
Published: March 2011

Two phase systems based on aqueous mixtures of polymers such as dextran and poly(ethylene glycol) have proven to be useful in the separation of cells via partition. By suitably modifying antibodies raised against cell surface antigens so that they partition strongly in favour of one of the phases it is possible to produce selective isolations of antigenically specified cells. Derivatization of a secondary antibody which recognizes the constant region of a class of primary antibodies provides a more generally useful immunoaffinity reagent. The theory of affinity partitioning of ideal species predicts extremely large increases in partition as the result of binding of affinity ligands. Results to date indicate effects smaller than predicted by theory, however, suggesting that the polymers and other modifying agents used to change the partition behaviour of the antibodies behave non‐ideally.