bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of thermo‐reversible gels by means of sedimentation equilibria
Authors: Borchard Werner , Cölfen Helmut
Published: March 2011

This paper describes the deformation of gels in a centrifugal field leading to a continuous equilibrium. A gel is considered to be a binary mixture of cross‐linked polymer and solvent and is assumed to remain isotropic during the deformation. From the equation for the osmotically effective pressure, called swelling pressure, the thermodynamic properties of a gel can be calculated. For highly swollen gels the expression of Svedberg and Pedersen is obtained. It is shown that the complete concentration dependence of the swelling pressure in the concentration range of the maximally swollen gel up to that at the cell bottom can be measured in a single equilibrium experiment. The homogeneity of weakly cross‐linked gels can be examined by means of the method described. Soluble parts which are not incorporated into the polymer network can also be detected if they are present. From the swelling pressure‐concentration curves it is possible to derive the thermodynamic properties of the physically crosslinked gelatin/water gels that were investigated. These gels can be described by means of a slightly modified Flory‐Huggins equation with an interaction parameter χw in the weight fraction scale, which depends linearly on concentration. The interaction parameters show a dependence on concentration which is explained by an increased branching and crosslinking of the polymer with increasing initial polymer concentration of the gels. At low initial polymer concentration, the primary chains have to aggregate to build up relatively long chains between the network junctions. The static shear modulus G which can be calculated from the network term has the same order of magnitude as the real part of the complex shear modulus which is measured at low frequency.
Characterization of polysaccharide solutions by means of chromatography‐multidetection
Authors: Huber Anton
Published: March 2011

Size exclusion chromatography (SEC) combined with double detection, utilizing a differential refractive index (DRI)‐ and a low angle laser light scattering (LALLS) ‐ detector represents a powerful experimental set‐up in the field of chromatography‐multidetection (C‐MD). By means of these techniques high‐quality information for profound polymer characterization is provided in a fast and semi‐automatical (autosampler/PC‐controlled) way. Molecular characteristics such as molecular weight distributions, molecular weight averages, tendencies for intermolecular interactions, can be obtained by these techniques. Successful handling of data from C‐MD‐techniques within reasonable time ranges requires adequate hardware and software. This is especially true if advanced data processing is applied, e.g. to yield polymer particle size/shape characteristics in terms of Staudinger/Mark/Houwink constants (K,a), distributions of sphere equivalent particle radii (RcD)‐, sphere equivalent mass density of solved polymer coils (ρcD)‐ and intrinsic viscosity ([η]D). For aqueous solutions of polysaccharide samples (waxy maize starch hydrolyzate, hydroxyethyl‐amylopectin from waxy maize hydrolyzate, dextran) data from SEC‐DRI/LALLS and universal calibration experiments are utilized for a comprehensive physico‐chemical characterization of these polymers.
Determination of molar mass and molar mass distribution of blood plasma substitutes (plasma expanders)
Authors: Lemmes R. , Schwengers D. , Weimann B.
Published: March 2011

Blood plasma substitutes, such as dextran and hydroxyethyl starch, cause an expansion of the liquid volume in blood vessels due to their high colloid‐osmotic pressure and water‐binding potential, and are therefore applied clinically as so‐called plasma expanders for rapidly increasing the liquid volume. This potentially life‐saving effect only applies while the plasma substitute is present in the bloodstream. For this reason knowledge of the retention time is of great importance. As the retention time is directly related to the molecular weight distribution of polydisperse hydrocolloids, an estimation of the parameters of this distribution is therefore of crucial significance in the quality control of plasma expanders.

Besides absolute methods (e.g. GPC/LALLS), there is special interest in GPC as a relative method with calibration against narrow molecular weight standards. This is because of its wide distribution, the speed at which it can be carried out, and the low expenditure on apparatus. Furthermore, there are advantages if commonly accepted pharmacopoeial methods can be performed in a manner that allows the results to be compared easily. In order to implement the molecular weight determination method in Pharmacopoeia Nordica's (Ph.Nord, or Svensk Läkemedelsstandard “SLS”) dextran monograph, a suitable software for VAX computers was developed at the Max Planck Institut für Kohlenforschung in Mülheim/Ruhr.
Evaluation of K⊖ from [η]‐M‐data of binary and ternary polymer systems
Authors: Zisenis Mathias , Springer Jürgen
Published: March 2011

Unperturbed dimensions of flexible linear macromolecules can be obtained from [η]‐M‐data in any solvent, good or poor, single or mixed. Usually Kθ is estimated by a relationship between [η]/MW0.5 and Mw0.5 first proposed by Burchard and by Stockmayer and Fixman. But, it is well‐known that the Burchard‐Stockmayer‐Fixman‐plot shows downward curvature, especially for good solvent systems. Various efforts have been made to achieve relations with better linearity. One of the first was the semi‐empirical relation between ([η]/Mw0.5)0.5 and Mw/[η] by Berry. Predicting a relationship of the excluded volume parameter z to the viscosity expansion factor by α5η instead of α5η Tanaka obtains that ([η]/Mw0.5)5/3 is linear in Mw0.5. By allowing for the dependence of the viscometric interaction parameter B, which is correlated to the second virial coefficient A2, on molar mass, Gavara, Campos and Figueruelo predict a linear dependence of [η]/Mw0.5 against A2.Mw0.5. It is not our intention here to discuss the validity of these theories, but to compare them with experimental data.
Molecular characterization of starch polysaccharides
Authors: Vorwerg W. , Burchard W.
Published: March 2011

Light scattering and rheologic measurements have been carried out with native starch in DMSO and with degraded amylopectin of a starch hydrolysate in water at different temperatures. The measurements of dilute solutions in DMSO were made to get a reference for the molecularly dispersed state. In water association take place which under certain conditions leads to gelation. An aqueous solution of about 11.5% (w/w) degraded amylopectin was investigated in detail. Structural change was observed during cooling the solution below 20°C with both techniques. A fractal dimensions of about 2.5 was found at temperatures above 20°C indicating non‐swollen random aggregates. Light scattering proved to be the more sensitive method than rheology, but in both experiments a structural collapse was detectable. A fractal dimension of about 1 was now obtained which is characteristic for rigid, elongated supra‐structures. A certain time after this collapse an increase of loss and storage module and particle growth in light scattering were obtained. The crossing of the G' and G” was taken as point of gelation and the same gelling time was estimated from light scattering. Hence, the combination of oscillatory rheology with light scattering is an appropriate procedure for a thorough investigation of such complex, structure forming systems.
Preparation and characterization of latices with hydrophobic core and hydrophilic shell
Authors: Hashemzadeh A.
Published: March 2011

Anionic and non‐ionic copolymer latices with a hydrophobic core and hydrophilic shell were prepared using emulsifier‐free emulsion polymerization. Styrene was used as the hydrophobic monomer; acrylic acid, acrylamide, and methacrylamide were employed as the hydrophilic monomers. The amount of chemically bound hydrophilic monomers in latex and unbound homopolymers in water were determined. The salt stability and redispersability of latices in water after spray‐drying were also investigated.
Aggregation of flexible‐rigid‐flexible triblock copolymers
Authors: Raphael E. , de Gennes P. G.
Published: March 2011

We discuss the aggregation behavior of flexible‐rigidflexible triblock copolymers in a selective solvent of low molecular weight. Aggregation may lead either to plates of (R) covered by brushes of (F), or to large “needles” (as a consequence of the Skoulios effect). In the absence of anisotropic bonding between adjacent rods, the “fence” morphology is not expected.
Comments on fluctuations of cross‐links in gels
Authors: Rubinstein M. , Ajdari A. , Bastide J. , Leibler L.
Published: March 2011

Localization of cross‐links is an important issue in the theory of rubber elasticity. We consider freely‐hinged rigid rod networks and show that in some cases they behave like critical objects: junctions fluctuate on all length scales. Such networks exhibit anomalously low shear modulus and cannot resist shear deformations. These conclusions are very different from the classical picture and might be of some significance for gels near the critical point of volume transition. We comment on the reasons for the different behavior of gels under more usual conditions and raise questions concerning the ability of cross‐links to rearrange on scales larger than the mesh size.
Exploring the domain validity of the equations relating the intrinsic viscosity to the molecular weight by using the characteristic numbers of polymers
Authors: Dondos Anastasios
Published: March 2011

Plotting log[η] versus logM (Mark‐Houwink‐Sakurada equation) we observe a crossover region in which a continuous variation of the exponent of this equation takes place. This crossover region is delimited by two characteristic numbers: Nc (or Mc), the number of statistical segments (or the molecular weight) in the onset of excluded volume behavior and Nc' (or Mc') the number of statistical segments (or the molecular weight) in the onset of the complete excluded volume behavior. Relations are given in order to obtain these numbers. The Stockmayer‐Fixman‐Burchard equation is valid for the flexible and wormlike polymers in the molecular weight region which lies above the crossover region while the Dondos‐Benoit equation is valid in the medium and low‐molecular‐weight region including the crossover region.
Structure of iPP‐PS composites with specific dispersion of PS component
Authors: Kryszewski M. , Pluta M. , Trznadel M. , Milczarek P.
Published: March 2011

The results of structure investigations of two‐component iPP‐PSa) systems obtained by UV‐initiated polymerization of liquid styrene diffused into unoriented and oriented iPP matrices have been presented. Initial structure of iPP matrices was modified by different preparation and various conditions of orientation. Presented results show that the final structure of the composites strongly depends on the initial structure of the matrices and employed conditions of styrene polymerization process.
Model macromolecules
Authors: Rempp Paul , Lutz Pierre
Published: March 2011

The interest for tailor ‐ made macromolecules arises from their use as calibration samples for characterization techniques, and from their prominent role in the investigations of structure/properties relationships. The conditions most appropriate for the synthesis of model macromolecules of various kinds are reviewed. Two cases of controlled polymer synthesis are considered in greater detail: Cyclic macromolecules and star shaped polymers
Unusual synthesis of vinyl monomers and polymers
Authors: Heitz W.
Published: March 2011

Metal catalyzed reactions enable an easier synthesis of monomers and a new approach to many polymers.
A challenge to novel fluoropolymers
Authors: Yamabe Masaaki
Published: March 2011

Perfluoro(vinyl ether) derivatives are extremely versatile monomers in preparing a variety of functional fluoropolymers. In this paper, two challenging topics in the development of novel fluoropolymers will be introduced. Carboxylated perfluoro(vinyl ether) can be copolymerized with tetrafluoroethylene to afford perfluorinated ion‐exchange membranes, which realize the innovative process for pollution‐free and energy‐saving chlor‐alkali production. Another topic includes the discovery of selective cyclo‐polymerization of specially designed difunctional perfluoromonomers such as perfluoro(allyl vinyl ether) which is readily derived from the carboxylated perfluoro(vinyl ether). The novel perfluoropolymer with a cyclic structure in the main chain is characterized by an exceptional transparency, and has been commercialized with expectation of major applications in electronics industries.
Dedicated polymers for future progress in microelectronics
Authors: Rubner Roland , Ahne Hellmut , Sebald Michael , Sezi Recai
Published: March 2011

The continuous miniaturization in microelectronics requires advanced materials and processes. Novel specifically functionalized anhydride‐containing filmforming polymers which spontaneously react with bisaminoalkylsiloxanes were synthesized for use in photolithographic processes. This allows the modelling of photoresist patterns and thus enhancement of practical resolution. In addition, efficient polymeric dielectrics with improved solubility in environmentally safe solvents were developed. The latter can be patterned using the above mentioned photolithographic process.
Water‐soluble polymers for hostile environment enhanced oil recovery applications
Authors: Hsieh H. L. , Moradi‐Araghi A. , Stahl G. A. , Westerman I. J.
Published: March 2011

This paper describes polymerization and properties of a number of water‐soluble polymers suitable for enhanced oil recovery applications. The polymers described here can tolerate long‐term exposure to hostile environment conditions of elevated temperatures and high salinity and hardness levels encountered in deeper petroleum reservoirs. The stable polymers reported here, in principle contain two or more of the following monomers: acrylamide, N‐vinyl‐2‐pyrrolidone, sodium 2‐acrylamido‐2‐methylpropanesulfonate and N,N‐dimethylacrylamide in proper ratios. The polymers reported here can be used directly to increase the viscosity of the injected water and consequently reducing its mobility to recover additional oil from petroleum reservoirs. Alternatively, these polymers can be used in combination with a suitable crosslinker to produce gels in‐situ to block high permeability channels or fractures under hostile environment applications.
Oligomers of stereoregular polymers
Authors: Garner Charles M. , Bartus Jan , Simonsick William J. , Ute Koichi , Hatada Koichi , Vogl Otto
Published: March 2011

The embryonic state of the ionic methyl methacrylate (MMA) and of trihaloacetaldehyde polymerization was studied. The composition of the oligomer mixtures, the end groups and the stereochemistry of individual compounds of the oligomers was investigated. Depending upon the initiating systems the oligomerization of methyl methacrylate can give either isotactic or syndiotactic oligomers. Trihaloacetaldehye oligomerization is highly dependent on the ceiling temperature of polymerization. The oligomerization of fluoral and chloral is compared with a more detailed study of the bromal polymerization and even more interestingly with the cooligomerization of chloral and bromal.
Constant pressure molecular dynamics: Instantaneous external stress tensor in systems with periodic boundary conditions
Authors: Winkler Roland Georg
Published: March 2011

A stress tensor for systems with periodic boundary conditions is presented, which is different from the wellknown Irving‐Kirkwood expression. It is shown that it represents the external stress for particles initially in one of the cells of the periodic system. The statistical properties of the pressure, derived from the stress tensor, are discussed. It is demonstrated that this pressure can be used to simulate a constant pressure ‐ constant enthalpy ensemble. Constant pressure computer simulations on the basis of the proposed stress tensor are free of artificial parameters and the internal pressure is not constrained, in contrast to previously existing constant pressure simulation schemes.
Simulation of first‐ and second‐order transitions in asymmetric polymer mixtures
Authors: Deutsch H.‐P. , Binder K.
Published: March 2011

The critical properties of dense asymmetric binary polymer mixtures are studied by grand canonical simulations within the framework of the 3‐dimensional bond fluctuation lattice model. The monomers interact with each other via a potential ranging over the entire first peak of the pair distribution. An asymmetry is realized by giving the ratio of interactions λ = ∈AA/∈BB between monomers of the A‐species and of the B‐species a value different from 1. Using multiple histogram extrapolation techniques for the data analysis, the two phase region, which is a line of first‐order transitions driven by the chemical potential difference, and the critical point are determined for a mixture of chains with 32 monomers each. At a critical potential difference Δμc unmixing occurs below a critical temperature Tc. It is found that Δμc is proportional to the asymmetry (1 ‐ λ) and that the quantity 4kBTc/(3 + λ)∈ is independent of the asymmetry, consistent with the prediction of the Flory theory.
Relation between amorphous structure of polymers and penetrant diffusion: A molecular dynamics simulation
Authors: Takeuchi Hisao , Okazaki Keiji
Published: March 2011

Molecular dynamics simulation has been performed for studying the relation between amorphous structure of polymers and penetrant diffusion. The self‐diffusion coefficients of O2 and He in various polymer models, which differ from each other in view of the amorphous structure, were calculated above their glass transition temperatures. The amorphous structure was characterized by considering the percolation of the unoccupied volume. A good correlation was found between the self‐diffusion coefficients and the number of clusters in the unoccupied volume at the critical point of the percolation. Based on the simulated cluster size distribution at the critical point, we defined a parameter into which effects of both the amorphous structure and the penetrant size are well incorporated. It was confirmed that the penetrant diffusion is intimately associated with the amorphous structure of polymers.
Modeling plasticizer diffusion in rubbery PVC
Authors: Vaz Roy J. , von Meerwall Ernst D.
Published: March 2011

In recent work4, the trace diffusion, Do of 14 plasticizers dissolved in rubbery PVC, CCl4 and neat, was determined and well correlated with estimated static minimal molecular diameter further reduced to account for cooperation between sidegroups and host chain segments. Here numerical molecular modeling has been used in an effort to put this correlation on a firmer basis. The modeling accounts for plasticizer major and minor axis bond flexibility, plasticizer shape in terms of steric and electrostatic fields surrounding the diffusants and the van der Waals volume. The correlation with experimental results of the diffusants is found to be good except for a single molecule with disk‐like geometry in PVC for which a different geometry may be operative.
Modeling the conformations and motions of isolated polymer chains in the narrow channels of their crystalline inclusion compounds with small‐molecule, host clathrates
Authors: Tonelli Alan E.
Published: March 2011

The narrow channels occupied by polymer chains in their crystalline inclusion compounds(IC) with small‐molecule, host clathrates, such as urea and perhydrotriphenylene(PHTP), provide a unique, solid state environment. Single polymer chains are confined to occupy narrow cylindrical channels whose walls consist of a crystalline matrix of the small‐molecule, host clathrate. Because the IC channels are well‐separated, each included polymer chain is isolated from its neighbors, and is therefore free from cooperative, interpolymer interactions which often dominate and complicate the behavior of bulk polymers. We have modeled polymer chains included in their IC channels by restricting the conformations accessible to small chain fragments(9–20 backbone bonds) to those which fit into a cylinder whose diameter(5.5Å) mimics the observed channel cross‐section. After establishing the population of channel conformers, a test is performed to determine the possibility of interconverting between them without any portion of the polymer chain fragment leaving the channel during any step in the interconversion process. The results of our modeling are compared to observations made on a variety of polymer‐IC's formed with either or both of the host clathrates, urea and PHTP. General agreement is found between the modeled conformations and mobilities of cylindrical polymer chain fragments and those observed directly from the crystalline polymer‐IC's, principally by solid state NMR, DSC, and X‐ray diffraction.
Twiston vs. random fluctuation as the source of the rapid motion of polyethylene in the inclusion complex with perhydrotriphenylene
Authors: Zhan Yongjian , Mattice Wayne L.
Published: March 2011

Recently molecular dynamics simulations were performed for polyethylene in the inclusion complex with perhydrotriphenylene. The system contained ninety molecules of perhydrotriphenylene, arranged in six stacks of fifteen molecules each, and one molecule of n‐tetracontane, C40H82. The internal CH2‐CH2 bonds in n‐tetracontane have a very strong preference for the trans state. Nevertheless, the chain exhibits a high degree of internal flexibility. This motion produces a characteristic pattern in δ|ψ N + i ψi| vs. N, where ψi describes the instantaneous angle of a C‐H bond vector at carbon atom i about the axis defined by the channel, and δ denotes the fluctuation. The pattern expected for δ|ψ N + i ψi| vs. N is derived for the case where the rapid internal motion is produced by a twiston. It is compared with the results from the simulation and from the expectation for the case where the rapid motion arises from uncorrelated internal fluctuations within the trans state at each CH2‐CH2 bond.
Polyelectrolyte brushes
Authors: Borisov O.V. , Birshtein T.M. , Zhulina E.B.
Published: March 2011

The simple scaling theory of weakly‐charged polyelectrolyte brush (the layer of polyelectrolyte chains grafted at one end onto an impermeable surface) immersed into a good solvent has been developed.The asymptotic scaling dependences of the free layer thickness on charge density and solvent strength are obtained.

The behavior of polyelectrolyte brush subjected to normal and tangential external forces is considered. New “polyelectrolyte effect” is predicted: shear of a free polyelectrolyte brush leads to a decrease in brush thickness in contrast to the case of a free neutral brush. Such behavior is equivalent to that of a neutral brush subjected to external normal stretching force. This force in the case of polyelectrolyte brush is created by the osmotic pressure of mobile counterions neutralizing grafted chain charges.
Docking of a polymer chain on a surface with Monte Carlo methods illustrated by polyimide on silicon
Authors: Hädicke Erich , Brode Stefan
Published: March 2011

A computer simulation technique for docking small molecules in the cavities of zeolites has been used for modelling the arrangements of a single polymer chain on a crystalline solid substrate in atomistic detail. This Monte Carlo procedure calculates a large number of polymer/solid arrangements and eliminates identical aggregates. We model only the physicosorption between the two phases by taking only the nonbonding van der Waals interactions into account. The interface of a single polyimide chain and the Si (100) plane is used as a test case. We found, that the aromatic rings of the deposited polyimide prefer a coplanar arrangement to the Si surface. In this arrangement the polymer chain is distorted compared with the conformation in vacuum.
Structure, conformation and dynamics of polymer chains at solid melt interfaces
Authors: Pan Chongmin , Bitsanis Ioannis
Published: March 2011

We have performed molecular dynamics, and lattice Monte Carlo simulations of polymeric melts in the vicinity of solid surfaces. The structural features of the solid‐melt interface were very simple. The interfacial width was comparable to the segment size. Inside this narrow interface the segment density profile was oscillatory. The density oscillations were much less pronounced than those present at solid‐atomic liquid interfaces. On a scale much larger than the segment size, chain conformations were found to be identical with those of ideal chains next to a reflective barrier. In particular, the number of surface‐segment contacts scaled like the square root of the molecular weight. Extensive molecular dynamics simulations showed that chain desorption times increase with molecular weight but at a rate much slower than the longest relaxation time of Rouse chains. Therefore, sufficiently long chains desorbed almost freely from the surface despite the presence of attractive surface‐segment interactions. A study of chain relaxation dynamics confirmed that the Rouse modes constitute an appropriate set of normal coordinates for chains in the melt interacting with a solid surface. The effect of the surface on mode relaxation was significant. All relaxation processes of chains located within a couple of radii of gyration from the surface were slowed down considerably. This effect, however was approximately the same for fast and slow modes and independent of molecular weight for sufficiently long chains.
Anionic polymerization of butadiene: A MNDO study of the potential energy surface of the propagation reaction in polar and non‐polar media
Authors: Siggel Lorenz , Knoll Konrad , Hädicke Erich , Brode Stefan
Published: March 2011

The anionic polymerization of butadiene, to both the 1,2‐ and 1,4‐addition products, is an important industrial process. It is known that the reaction can be steered to either the 1,2‐ or 1,4‐product by the addition, or absence, of a complexing solvent such as ether. The goals of the current study were to map the MNDO Potential Energy Surfaces (PES) of the propagation reactions both in the presence and absence of dimethyl ether to gain insight into the factors influencing the reaction's selectivity. Single point ab initio calculations at the DZP level were run on all reactants, products and transition states as a cross check on the MNDO results.
A few considerations on some catalysts for olefin polymerization
Authors: Luciani Luciano , Milani Federico , Zannetti Roberto , Di Noto Vito
Published: March 2011

Among many precursors and catalysts for alpha‐olefins polymerization, one seems to be particularly interesting, because it has not been completely clarified yet.

We refer especially to precursors obtained via reaction between Mg‐alkyls and SiCl4.

The products of this reaction are not well known; in fact, under some operating conditions, a special form of MgCl2 is obtained, showing x‐ray diffraction peaks in the angular region lower than 15° (2 theta), which corresponds to the 5.9 A interplanar spacing, characteristic of alpha‐MgCl2.

Under other conditions, MgCl2 is obtained in the well known and strongly disordered delta structure.

By employing these precursors, some catalytic systems for alpha‐olefins polymerization have been prepared.

In this paper, the peculiar aspects of these precursors and catalysts are described, particularly focusing on the correlation between structure and performances in ethylene and propylene polymerization.
Ethylene polymerization kinetics with heterogeneous Ziegler‐Natta catalysts
Authors: Kissin Y. V.
Published: March 2011

Ethylene polymerization kinetics was examined using a supported Ti‐based catalyst activated by AlEt3. A computer‐based technique for deconvoluting the GPC curves into constituent Flory components was developed. The kinetic analysis showed that the catalyst contains five populations of active centers. Each population has different formation and deactivation rates, produces polymers of different molecular weights and is differently affected by hydrogen.
Structure‐activity and structure‐selectivity correlations in metallocene‐based catalysts for α‐olefin polymerization
Authors: Burger Peter , Hortmann Kai , Brintzinger Hans‐Herbert
Published: March 2011

Zirconocene complexes carrying substituents at various positions of their ring‐bridged ligand frameworks were studied as catalysts for methylalumoxane‐activated propene polymerization. Effects of different substitution patterns on catalyst activities and on chain lengths and stereo‐ and regio‐regularities of the polymers produced are correlated with geometrical features of the complexes, e.g. with parameters describing their structural rigidity or the aperture and obliquity of their coordination gaps.
Hemiisotactic poly(propylene) through propene polymerization with the ipr[3‐mecpflu]zrcl2/mao catalyst system: A kinetic and microstructural analysis
Authors: Herfert Norbert , Fink Gerhard
Published: March 2011

Through polymerizing propene by means of the catalyst system iPr[3‐MeCpFlu]ZrCl2/MAO it was possible for the first time to generate hemiisotactic poly(propylene); the microstructure of this polymer is characterized by an alternating sequence of monomer units with equal and statistical configuration. iPr[3‐MeCpFlu]ZrCl2 is one of the new developed stereorigid ansa‐metallocene catalysts which by means of the structure of the bridged η‐ligand system are considered to give access to the description and calculation of the behaviour of the stereospecifity. In the present paper the α‐olefin polymerization was investigated with the iPr[3‐MeCpFlu]ZrCl2/MAO catalyst system by means of kinetics and product analytics; parameter were the [Al]:[Zr] ratio, the monomer concentration, the polymerization temperature, the polarity of the solvent as well as the chain length of the starting α‐olefin. The order of the polymerization reaction concerning the propene concentration was found to be 1,3; this broken order indicates a complex reaction. Concerning the dependency of the polymerization rate on the [Al]:[Zr] ratio a bell‐shaped curve was found; obviously, at very high [Al]:[Zr] ratios the complex MAO compound inhibits the active zirconocene centre. The microstructure of the poly(propylene)s generated in toluene at 25°C corresponds with the expected hemiisotactic structure. On the contrary, the microstructure of the poly(propylene)s generated in toluene at higher polymerization temperatures and in the polar solvents o‐dichlorobenzene and methylene chloride at 25°C shows considerable deviations from a hemiisotactic structure. Under these polymerization conditions the stereospecifity of the iPr[3‐MeCpFlu]ZrCl2/MAO catalyst can only be satisfyingly explained with isomerization reactions of the active zirconocene species between two insertion steps. These isomerization reactions without monomer coordination occur preferably starting from the unstereospecific state of the catalyst. This interpretation is confirmed by 1‐butene and 1‐hexene polymerization experiments.
The role of non‐coordinating anions in homogeneous olefin polymerization
Authors: Siedle A. R. , Lamanna W. M. , Newmark R. A. , Stevens J. , Richardson D. E. , Ryan M.
Published: March 2011

We present an overview of homogeneous olefin polymerization catalysts in which chain initiation and propagation involves a metallocenium ion (e.g. Cp2ZrMe+) that can be produced by equilibrium or irreversible CH3− transfer. The Kaminsky catalyst is an example of the former. Complexes of (C6F5)3B with water, alcohols, mercaptans, silanols and oximes are strong acids which can protonate dialkylmetallocenes to produce weakly‐coordinated metallocenium salts that are hydrocarbon soluble and which produce high molecular weight poly‐1‐olefins. Polymer molecular weight is correlated with the steric and electronic effects of the ligands attached to the metal.
A new mechanism for the transition metal catalyzed copolymerization of conjugated dienes with olefins: The double coordination mechanism
Authors: Robert P. , Spitz R.
Published: March 2011

We have focused our interest on the ethylene‐ butadiene copolymerizations catalyzed with Ziegler‐Natta type catalysts. The catalysts used are MgCl2 supported titanium catalysts. The main features of these copolymerizations (stereospecificity of the butadiene enchainments, multiblock structure, gel formation) cannot be rationalized on the basis of the Cossee mechanism. We propose a new model: The double coordination mechanism. It explains all the phenomena observed. Experimental confirmations will be presented in this paper.
Recent advances in the neodymium catalysed polymerisation of 1,3‐dienes
Authors: Wilson David J.
Published: March 2011

The benefits of using a homogeneous neodymium‐based catalyst for the industrial “high cis” polymerisation of 1,3‐butadiene are underlined.

Preformed homogeneous catalysts for the “high cis” polymerisation of 1,3‐butadiene based on Nd(carboxylate)3/diisobutylaluminium hydride/tbutyl chloride have been examined. The effects of changing (a) the order of catalyst component addition, (b) the carboxylate component and (c) the halogen component, on catalyst homogeneity, activity and polymer characteristics have been examined.
Kinetics and mechanisms in anionic ring‐opening polymerization
Authors: Penczek Stanislaw , Duda Andrzej
Published: March 2011

Recent advances in the anionic ring‐opening polymerization (AROP), including covalent (pseudoanionic) polymerization, are reviewed. Thermodynamics, kinetics, and mechanisms of AROP are discussed, covering mostly polymerization of oxiranes, lactones and cyclic siloxanes as monomers. The following general problems of AROP are discussed: anionic polymerizability, thermodynamics ‐ particularly of the monomers exhibiting low ring strain, chemistry of initiation, structures and reactivity of active species. New phenomena, particularly polymerization with reversibly aggregating species are analyzed in more detail. Chain transfer to polymer ‐ the major side reaction ‐ is analyzed quantitatively, by introducing the selectivity parameter β, expressed by the ratio kp/ktr. This parameter has been determined for the anionic and pseudoanionic polymerization of ϵ‐caprolactone.
Tailoring of polyacrylates with combined initiators
Authors: Vlček Petr , Lochmann Lubomíar
Published: March 2011

This article summarizes possibilities of tailoring polyacrylates and polymethacrylates prepared by anionic polymerization initiated with combined (mixed) initiators especially those containing alkali metal tert‐alkoxides as stabilizing additives. First part gives a short overview of side reactions in anionic polymerization of polar vinyl monomers and the ways of solving the problem. Second part is devoted to the anionic polymerization of acrylic and methacrylic esters initiated with mixed initiators. Examples of synthetic methods are given for the preparation of special polymeric products based on acrylates, and the necessity of using different polymerization conditions for individual acrylic esters is demonstrated with respect to branching of the ester alkyl group.
Highly stereospecific protonation of stereoregular living PMMA anions with several alcohols
Authors: Ute Koichi , Asada Takeshi , Miyatake Nobuo , Hatada Koichi
Published: March 2011

Living and highly isotactic poly(methyl methacrylate) (PMMA) anion (M̄n = 2.5 × 103) prepared with t‐C4H9MgBr as an initiator was protonated with phenol in toluene at −78°C. The reaction was stereospecific toward meso addition, and the meso/racemo ratio at the chain‐end of the resultant polymer was 89/11. Addition of 1,4‐dioxane to the living isotactic PMMA anion in toluene at −78°C remarkably reduced the viscosity of the system, and protonation of the PMMA anion with phenol in the presence of 1,4‐dioxane enhanced the meso‐specificity to 94%. On the other hand, the protonation reaction of the living syndiotactic PMMA anion (M̄n = 2.5 × 103), which was generated by t‐C4H9Li/(n‐C4H9)3Al in toluene at −93°C, with t‐butanol was found to be 97% racemo‐specific. These highly stereospecific protonation reactions of the stereoregular PMMA anions were in contrast to the protonation of the anions with methanol or benzyl alcohol which was almost non‐stereospecific.
Novel synthesis of high molecular weight polymers with extremely low polydispersity by the unique initiation properties of organo‐lanthanide complexes
Authors: Yasuda Hajime , Yamamoto Hitoshi , Takemoto Yasunori , Yamashita Masahiro , Yokota Kiyohiko , Miyake Shigenobu , Nakamura Akira
Published: March 2011

Organolanthanide(III) complexes such as |(C5Me55)2SmH|2 and (C5Me5)2SmMe(THF) were found to initiate the living polymerizations of methyl methacrylate (MMA) to give high molecular weight polymers (M n > 500 × 103) with extremely low polydispersity (M w/Mn = 1.04). The syndiotacticity increased up to 95.2% by lowering the temperature to −95°C. The molecular structure of the 1:2 adduct of (C5Me5)2SmH with MMA determined by X‐ray method indicates that this intermediate assumes the 8 membered ring conformation where the Sm atom is bound to MMA in an enolate form and the ester of penultimate MMA is coordinated to the metal. Based upon these results, an anionic coordination mechanism has been proposed for the present reaction. Organolanthanide(II) complexes also exhibit high activity and proceed the living polymerizations. Organolanthanide(III) complexes also initiate the living polymerizations of lactones such as ϵ‐caprolactone and δ‐valerolactone. The stoichiometric reactions indicate that real active species assumes the alkoxylanthanide(III) form.
Well‐defined polyisocyanates via organotitanium(IV) catalyzed living polymerizations of isocyanates
Authors: Patten Timothy E. , Novak Bruce M.
Published: March 2011

The development of living organotitanium(IV) catalyzed polymerizations is presented. A living polymerization of alkyl isocyanates was developed using TiCl3OCH2CF3, I, as a catalyst, through which large quantities of well‐defined (in terms of molecular weight and polydispersity) polyisocyanates are obtainable under ambient conditions. η5‐CpTiCl2OCH2CF3 (Cp = cyclopentadienyl), II, is also an excellent catalyst for the polymerization of isocyanates and, unlike I, will polymerize monomers containing Lewis basic functional groups in the side chain. Compound II was used to synthesize poly(allyl isocyanate) and poly(2‐isocyanatoethyl methacrylate). Both polymers were found to be soluble, in contrast to previous reports, and spectroscopic characterization showed that no crosslinking of the side chains had occurred.
Recent developments in the field of star‐shaped polymers
Authors: Rein David , Rempp Paul , Lutz Pierre Joseph
Published: March 2011

The interest for star‐shaped polymers arises from their unique structure and enhanced segment density. This paper will review the different methods of preparation for star‐shaped polymers. Two cases of special interest will be considered in greater detail: the core‐first method which gives access to end‐functionalized star‐shaped polymers and the three‐step method which leads to the so called hetero‐star copolymers with rather specific properties.
Near‐ and supercritical fluid solvents for living anionic polymerizations
Authors: Desimone J.M. , Maury E.E. , Lemert R.M. , Combes J. R.
Published: March 2011

Near‐ and supercritical fluids are investigated as solvents for anionic polymerizations of 1,3‐dienes. Solvent strength (solubility parameter) of mixtures of light hydrocarbons containing cyclohexane is shown to be adjustable using solvatochromic probe methods. The results indicate that these mixtures have solubility parameter values that are lower than conventional liquid solvents and represent a regime of solvent strength that has remained unexplored for ionic polymerizations. The anionic initiator 3‐methyl‐1,1‐diphenyl‐pentyllithium (MDPPL) was shown to be soluble in supercritical ethane and that its ultraviolet/visible absorption maximum was sensitive to systematic density changes of the supercritical fluid induced by pressure profiling. These results were extended to the anionic polymerization of isoprene in butane/cyclohexane mixtures.
New consideration of the mechanism of chain transfer to monomer in anionic polymerization
Authors: Arest‐Yakubovich Alexander A. , Litvinenko Galina I.
Published: March 2011

A new kinetic scheme for chain transfer to monomer in the anionic polymerization of hydrocarbon monomers is presented. The scheme agrees with generally accepted views on the chemical mechanism of carbanionic reactions better than the one used previously. It is suggested that the most probable path of the transfer reaction is the proton abstraction from the side group of the monomer, the terminal double bond of the monomer molecule remains unchanged, and therefore the intermediate species can participate in succeeding reactions as a macromonomer. The discrepancy between the predictions of the proposed scheme and of the previous one concerning the molar characteristics of polymers are discussed and the ways to establish the true mechanism of transfer in particular systems are suggested.
Principles and design of living cationic polymerization of vinyl monomers: The nature of the growing species based on in‐situ 1H NMR analysis
Authors: Sawamoto Mitsuo , Higashimura Toshinobu
Published: March 2011

This paper focuses on in‐situ 1H NMR analysis of model reactions that are directed to clarify the nature of the growing species in the following three classes of living cationic polymerization based on the stabilization of the growing carbocations with nucleophilic counteranions and added salts:

(a) Vinyl ethers/HCl/SnCl4/added nBu4N+Y‐;

(b) Vinyl ethers/HX/ZnCl2 (salt free);

(c) Styrene/HX/SnCl4/added nBu4N+Y‐ (X and Y: halogen) Through the NMR analysis, system (a) provides evidence for the generation of carbocations from adducts [CH3CH(OR)Cl] of vinyl ethers and hydrogen chloride and also for the suppression of such ionic species by the added salts. For systems (b) and (c) the spectroscopic observation demonstrated rapid counteranion exchanges in the growing species, indicating that upon reacting with a monomer the living end assumes an ionic character.
A survey of kinetic and mechanistic similarities in living polymerization systems
Authors: Iván Béla
Published: March 2011

In the light of recent discoveries in the field of living polymerizations it seems inevitable to reconsider our views on these polymerization systems. This paper surveys the kinetic and mechanistic similarities in living polymerizations, and analyses and compares chain transfer dominated nonliving polymerizations and living systems to conclude on the nature of propagating species, shelflife and livingness. Some recently raised specific problems are also summarized and discussed. It has been found that most of the living polymerizations known to date, such as living anionic, cationic ring opening, group transfer, carbocationic, ring opening metathesis, Ziegler‐Natta, free radical and immortal polymerizations, exhibit the characteristics of quasiliving polymerization, i.e., an equilibrium exists between propagating (active) and inactive (dormant) species. On the basis of this finding and a comparison between mechanistic and kinetic models of quasiliving and ideal living polymerizations, it is suggested that the former is the general phenomenon, and ideal living polymerization is a subclass of quasiliving polymerizations.
Group transfer polymerization — A critical overview
Authors: Bywater Stanley
Published: March 2011

Available evidence on the mechanism of group transfer polymerization is presented. The data are discussed in terms of the possibility that the chain carriers are enolate anions rather than the originally suggested pentacoordinate silicon complexes.
Termination processes in group transfer polymerization
Authors: Brittain William J. , Dicker Ira B.
Published: March 2011

Two major termination processes in the GTP of methacrylates and acrylates have been studied. For methacrylates, intramolecular cyclization is the dominant, if not sole, termination reaction. Both cyclization and O/C‐silyl isomerization of the chain end are observed for acrylates. Oligomerization experiments were used to study the relative rates of cyclization and propagation and the influence of temperature, catalyst and dp. Under typical GTP conditions for methacrylates, cyclization is at least two orders of magnitude slower than monomer addition.
The effect of hydrostatic pressure on the flow properties of various polymers
Authors: Baker F. S. , Thomas M.
Published: March 2011

A novel device to fit on the exit of the ACER capillary extrusion rheometer has been designed to allow the controlled application of hydrostatic pressure to the body of the fluid under test. The rheological properties of the fluid can be examined over a wide range, ambient to 200MPa. This paper will describe the equipment and the effect of hydrostatic pressure and temperature on the flow properties to the various polymer melts, PC, ABS, PP and HDPE.
The correlation between residual stresses and delamination behavior of polymer coatings
Authors: Farris RICHARD J. , Goldfarb JAY , Maden MICHELE A.
Published: March 2011

The determination of residual stresses in thin polymer coatings is important for the prediction of failure due to delamination and cracking. If the internal tensile stresses exceed the cohesive strength of the solid coating, cracking may occur which can result in coating ‐ substrate delamination. This is especially important in the coatings and electronics industries in which coating reliability is central to the performance of a product. There are three primary causes of residual stresses in coatings, 1.) Chemical reactions in which a condensation molecule is evolved and given off during processing, 2.) Evaporation of solvent or carrier solution during drying, and 3.) Mismatch in coefficients of thermal expansion between the substate and the coating.
Impregnation, flow and deformation during processing of advanced thermoplastic composites
Authors: Savadori A. , Cutolo D.
Published: March 2011

Thermoplastic matrix composites are of increasing technical interest. This new generation of materials is not only comparable to conventional thermosetting systems in terms of performance and durability, but also affords considerable incentive in weight reduction and cost‐effective manufacturing. A careful description of the different intermediate material forms is presented in this paper along with their advantages and inherent drawbacks in processing and the manufacturing steps which follow. The micro‐mechanics of flow and deformation which, however, have to occur are partly different from that known from thermosetting composites and metallic materials. Therefore, the flow and micro‐deformation mechanisms, such as resin percolation, transverse flow and inter as well as intra‐ply slip will be discussed in detail along with their importance to get optimum consolidation of the final components.
Low band‐gap oligomers and polymers
Authors: Müllen Klaus , Scherf Ullrich
Published: March 2011

The relationship between electronic structure and chemical stability is discussed for three different classes of low band‐gap oligomers and polymers. In oligo‐ and poly[n]acenes as well as in poly‐(arylenemethide)s, the low band‐gap character is connected with a high chemical reactivity due to an energetically favored rearomatization of olefinic or quinonoid substructures, respectively. For double‐stranded oligo‐ and poly(rylene)s, the stability is dramatically increased. Therefore, rylenes appear especially promising in the field of low band‐gap materials.
Liquid‐crystalline polymers for fibres
Authors: McIntyre J.E.
Published: March 2011

Recent advances in the development of liquid‐crystalline polymers for fibres are reviewed. The discussion of lyotropic systems concentrates upon poly(p‐phenylene terephthalamide) and its copolymer with 3,4′‐oxydiphenylene terephalamide units. The discussion of thermotropic systems identifies specific problems restricting the development of fibres and suggests some possible means of improvement.