bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computer simulation of the liquid crystal formation in a semi‐flexible polymer system
Authors: Darinskii Anatoly A. , Neelov Igor M. , Zarembo Anna , Balabaev Nikolai K. , Sundholm Franciska , Binder Kurt 
Published: April 2003

AbstractMolecular dynamic simulations are reported for system of semi‐flexible linear rod‐like molecules. The molecules are composed of Nc tangent soft spheres, connected by elastic springs. Rigidity is introduced by additional springs between all pairs of spheres along the molecule. The formation of only a nematic LC phase is shown for all systems with Nc = 8 and different flexibility. The effect of flexibility on the order parameter and the volume fraction at the LC phase transition is compared with theoretical predictions by Khokhlov‐Semenov and with available simulation data. The dependence of the anisotropy of diffusion on chain flexibility in LC phase was studied. The polymer brushes consisting of flexible and semi‐flexible (composed of linear rod‐like segments) chains were simulated at different grafting densities. Height of brush, order parameter, distribution of density and chain ends in brush were obtained in both cases and compared with theoretical predictions.
Computer simulations of stretching and collapse of polymer molecules in solution
Authors: Neelov Igor M. , Adolf D.B. , Davies G.R. , Darinskii F Anatoly A. , Niemela Satu , Skrifvars M. , Sundholm Franciska 
Published: April 2003

AbstractComputer simulations are reported for system of linear polymer molecules, diblock copolymer and dendrimer in dilute solution without and with elongational flow. The effect of fluctuating hydrodynamics interactions (HI) on the coil‐stretch transition of linear polymers and dendrimers in elongational flow is studied. The process of coiling of homo‐ and blockcopolymer from completely extended state is also simulated.
Microphase coexistence in polymeric brushes
Authors: Birshtein Tatiana M. , Amoskov Victor M. , Klushin Leonid I. , Mercurieva Anna A. , Polotsky Alexey A. , Iakovlev Petr A. 
Published: April 2003

AbstractA collapse of polymeric brushes in a solvent can be induced by a change in external conditions, for example, solvent quality or its temperature. The systems with following specific interactions are considered in this paper, namely, polyelectrolyte brushes, amphiphilic brushes in a mixture of incompatible solvents, and brushes with possibility of liquid‐crystalline ordering of polymer segments. For all the systems it is shown that the brush collapse can be observed under certain conditions, and it occurs through a microphase segregation. There are two microphases of different densities that coexist in the brush. The effect is caused by general properties of the swollen phase of polymeric brush and hence appears at all types of the interactions that can induce a phase transition of the brush into collapsed state.
Adsorption of flexible polymers on small colloids: complexes and gels
Authors: Diez Orrite S. , Bonet Avalos J. , Johner A. , Joanny J.F. 
Published: April 2003

AbstractWe describe adsorption of neutral flexible polymer chains onto small colloids that can be covered by one chain. We discuss the structure of star‐shaped complexes and their abundance in dilute solution. In semi‐dilute solution similar complexes form crosslinks between chains and cause gelation.
Conducting polymers electromechanical actuators and strain sensors
Authors: Spinks Geoffrey M. , Wallace Gordon G. , Liu Lu , Zhou Dezhi 
Published: April 2003

AbstractElectromechanical actuators are being investigated for a wide range of applications in medical, electronics and industrial areas. One attractive application is to incorporate conducting polymer fibre actuators into fabrics for use in prosthetic applications. In this paper, the design of polypyrrole fibre actuators for use in a glove to open and close the human hand (for assisting those with paralysis or hand injuries) is described. The key requirements for this application are the simultaneous generation of 16 mm of contractile movement and 2.9 N of force. Although not critical in the first prototypes, eventually it will also be necessary to produce a rate of movement of around 10 mm sec−1. The effect of the geometry of polypyrrole actuators is examined in this paper and it is shown that a tubular geometry is superior to conventional flat films. Another aspect of the practical use of actuator materials is their control. Fabric strain gauges with polymer actuators is a convenient means for providing feedback control to the actuating element. The fabric strain gauges ideally articulate with fibre actuators to give both the actuating and sensing function in the same fabric structure.
Synthesis of novel architectures by radical polymerization with reversible addition fragmentation chain transfer (RAFT polymerization)
Authors: Moad Graeme , Mayadunne Roshan T.A. , Rizzardo Ezio , Skidmore Mellissa , Thang San H. 
Published: April 2003

AbstractRadical polymerization with Reversible Addition‐Fragmentation chain Transfer ‐ RAFT polymerization can be adapted to produce a wide variety of block copolymers and other polymers of complex architecture. Such polymerizations require use of a suitable compound [Z‐(C=X)X‐R], which is selected to have a very high transfer constants in radical polymerization of the desired monomers, and appropriate choice of reaction conditions. Block and multiblock polymers, stars and grafts are available through use of precursors containing multiple thiocarbonylthio groups. Stars and microgels are also available through self assembly and crosslinking of RAFT synthesized block copolymer micelles and by a varient of the ‘arm‐first’ approach wherein of a diene monomer is (co)polymerized in the presence of a preformed RAFT‐made polymer. This paper briefly reviews RAFT polymerization then examines the scope for utilizing the technology in the construction of novel architectures.
Nematic conformation of oxyethylene spacers involved in main‐chain liquid crystals
Authors: Furuya Hidemine , Iwanaga Hiroshi , Nakajima Takeshi , Abe Akihiro 
Published: April 2003

Abstract2HNMR measurements were performed on main‐chain dimer and polymer liquid crystals (LC) having oxyethylene (OE) spacers ‐(OCH2CH2)xO‐(x=2, 3). The orientational as well as conformational characteristics of these molecules have been investigated in bulk and in a nematic solution. The OE spacer was found to take spatial arrangements characteristics of the nematic phase. The nematic conformation of the spacer remains nearly invariant over a wide range of temperature and concentration. In these analyses, the ratio of the deuterium quadrupolar splittings Δν/ΔνR (Δν: spacer and ΔνR: mesogenic unit) provided an important information regarding the spatial configuration of molecules in the LC state. The results obtained in this study are consistent with our previous conclusion drawn on a series of main‐chain LC oligomers and polymers comprising n‐alkane spacers ‐O(CH2)nO‐ (n=9, 10).
Synthesis, properties and molecular modeling of functional hyperbranched polymers and dendrimers
Authors: Fomine S. , Fomina L. , Guadarrama P. 
Published: April 2003

AbstractThe design, synthesis, properties and molecular modeling of fully conjugated dendritic molecules and conjugated hyperbranched polymers are described. It has been shown that conjugated hyperbranched molecules are much more soluble than their linear analogues while maintaining all the properties characteristic of conjugated polymers. It was found that the use of polymeric solid support in hyperbranched polymerization allows to control molecular weight and degree of branching (DB). The molecular modeling of hyperbranched conjugated molecules reveals that hyperbranched structure of conjugated molecules affects significantly neither their stability nor the conjugation. On the other hand the terminal groups affect appreciably the electronic structure of conjugated hyperbranched molecules.
Matrix‐assisted laser desorption/ionization mass spectrometry of synthetic polymers. 7. analysis of fatty alcohol ethoxylates by coupled liquid chromatography at the critical point of adsorption and MALDI‐TOF mass spectrometry
Authors: Spriestersbach Karl‐Heinz , Rode Karsten , Pasch Harald 
Published: April 2003

AbstractFatty alcohol ethoxylates can be analyzed efficiently with respect to functionality and molar mass by coupled liquid chromatography and MALDI‐TOF mass spectrometry. Both techniques are coupled via a robotic interface, where the matrix is coaxially added to the eluate and spotted dropwise onto the MALDI target. It is shown that liquid chromatography at critical conditions of adsorption coupled to MALDI‐TOF yield useful structural information on oligomer masses and chemical composition. In particular, the analysis of technical fatty alcohol ethoxylates by LC‐CC/MALDI‐TOF reveals the presence of different functionality fractions in one sample. The oligomer distributions of all functionality fractions are determined.
Ultraviolet (UV) curing of phosphated polyurethane‐acrylic dispersions
Authors: Mequanint Kibret , Sanderson Ronald D. 
Published: April 2003

AbstractPhosphate‐containing polyurethane‐acrylic dispersions were synthesised for UV curing studies. The effects of light intensity, substrate‐dependent temperature increase, soft‐segment content and water on conversion were investigated. The effect of the light intensity on conversion was twofold. At first, conversion increased with light intensity. This was attributed to the inability of shrinkage to keep pace with the polymerisation and crosslinking, resulting in the creation of free volume, thereby facilitating reaction and enhanced conversion. At higher intensities, conversion was found to be reversed or, at least, it remained constant, owing to increasing radical‐radical termination reactions. Phosphated‐polyurethane coatings with high soft‐segment content show improved conversion with exposure time. This was found to be related to the chain mobility, caused by the low glass transition temperature of the soft segment. The effect of water on conversion was also twofold. On the one hand, water had a plasticising effect on the UV curing and the polymerisation rate was fast. On the other hand, the gel content was found to be lower when films were cured before the evaporation of water.
Investigation into the interactions between filler and elastomers used for tyre production
Authors: Costa Giovanna , Dondero Giovanni , Falqui Luciano , Castellano Maila , Turturro Antonio , Valenti Barbara 
Published: April 2003

AbstractAn investigation in the interactions between silica and elastomers used in the production of tyre treads was carried out. To achieve some knowledge on the interactions between reinforcing agent and elastomers, which are fundamental in determining the rubber reinforcement, inverse gas chromatography (IGC) at infinite dilution was used to evaluate surface properties of both unmodified and modified silica and to calculate the adsorption free energy and enthalpy of low molecular weight analogues of elastomers. The predictions derived from the thermodynamic study were compared with some of the results obtained by a morphological analysis of silica‐filled compounds carried out by transmission electron microscopy (TEM) and automated image analysis (AIA).
Water‐soluble polymeric materials with the ability to bind metal ions
Authors: Rivas Bernabé L. , Pereira Eduardo 
Published: April 2003

AbstractWater‐soluble polymers containing carboxylic acid, phosphonic acid, and sulfonic acid groups were investigated as polychelatogens by means of the liquid phase polymer‐based retention technique, LPR, under different experimental conditions. The retention profiles were determined and the maximum retention capacity (MRC) of these polymers was determined at different pH and polymer‐metal ion ratio. The metal ions investigated were: Ag(I), Cu(II), Co(II), Ni(II), and Cr(III). An important effect of the pH and the ligand type was observed on the metal ion retention. The MRC values of the divalent metal ions were very similar and higher than that for the trivalent cation, indicating that the polymer‐metal ion interaction was basically of an electrostatic type.
Electron spin resonance studies of reversible addition‐fragmentation transfer polymerisation
Authors: Calitz F.M. , Tonge M.P. , Sanderson R.D. 
Published: April 2003

AbstractThe polymerisation of styrene in the presence of cumyl dithiobenzoate (RAFT agent) was studied. Electron spin resonance spectroscopy was used to determine the time‐dependence of the concentrations of the intermediate radical species, as a function of temperature and relative initial amounts of reactants. The intermediate radical concentration was found to be much lower than predicted by the studies of Barner‐Kowollik et al.[Barner‐Kowollik, C.; Quinn, J. F.; Morsley, D. R.; Davis, T. P. J. Polym. Sci. Part A: Polym. Chem. 2001, 39, 1353], but consistent with that observed by Hawthorne et al.[Hawthorne, D. G.; Moad, G.; Rizzardo, E.; Thang, S. H. Macromolecules 1999, 32, 5457] and Kwak et al.[Kwak, Y.; Goto, A.; Tsujii, Y.; Murata, Y.; Komatsu, K.; Fukuda, T. Macromolecules 2002, 35, 3026] Several observations that are not consistent with the current RAFT model were made. Intermediate radical signals were observed long after a significant amount of initiator remained and an extra signal appeared in the ESR spectrum at longer reaction times.
RAFT polymerisation in water‐borne organic dispersions
Authors: Tonge M.P. , McLeary J.B. , Vosloo J.J. , Sanderson R.D. 
Published: April 2003

AbstractTwo different approaches to achieving controlled reversible addition‐fragmentation chain transfer polymerisation in water‐borne dispersions have been attempted, both giving reasonable control over molar mass evolution. Molar mass increased linearly with conversion, and the colloidal instability that has sometimes been observed in similar systems (e.g. [de Brouwer, H.; Monteiro, M. J.; Tsavalas, J. G.; Schork, F. J. Macromolecules 2000, 33, 9239]) was avoided. The similarity of results for the two quite different approaches can largely be reconciled utilising the theory of Luo et al.[Luo, Y.; Tsavalas, J.; Schork, F. J. Macromolecules 2001, 34, 5501]The average number of radicals per particle, in terms of both propagating and RAFT intermediate radicals were compared, using two current models in the literature for the ratio of propagating to intermediate species. [Barner‐Kowollik, C.; Quinn, J. F.; Morsley, D. R.; Davis, T. P. J. Polym. Sci. Part A: Polym. Chem. 2001, 39, 1353; Monteiro, M. J.; de Brouwer, H. Macromolecules 2001, 34, 349; Kwak, Y.; Goto, A.; Tsujii, Y.; Murata, Y.; Komatsu, K.; Fukuda, T. Macromolecules 2002, 35, 3026] Possible implications for water‐borne dispersions under such conditions are that the maximum value of the average number of propagating radicals per particle may be significantly lower than 0.5, depending on the dominant mechanism for radical loss.
Propene copolymers: an overview of recent research
Authors: van Reenen Albert J. 
Published: April 2003

AbstractIn recent years, some of the focus in our laboratories has been on the use of metallocene catalysts, mostly in conjunction with methylalumoxane as cocatalyst, in the polymerisation of, inter alia, propylene. This paper reviews the main areas of research either already published or about to be published. In particular, the area of propylene copolymers is addressed. The copolymers of propylene with the linear α‐olefins C4 ‐ C10 and C12, C14 and C18; the branched olefins 4‐methyl‐1‐pentene, 4,4 dimethyl‐1‐pentene, 3‐methyl‐1‐butene and 3‐methyl‐1‐hexene; and other olefins (3‐(1‐adamantyl)propene and 1,5 hexadiene) are briefly discussed and relevant results highlighted. The effect of comonomer on the reaction mechanism with both syndiospecific and isospecific metallocene catalysts is also discussed.
Theory of static scattering from weakly charged copolymers in solution
Authors: Benmouna Mustapha , Vilgis Thomas A. , François Jeanne 
Published: April 2003

AbstractThe static scattering properties of weakly charged copolymers in solution are investigated. The cases of symmetrical and nonsymmetrical diblocks are considered and various structure factors calculated. The electrostatic interaction is introduced via a combination of the random‐phase approximation and the Debye‐Hückel approximation. Several cases of charge distributions are considered. In particular, diblock copolymers made of neutral and charged monomers and oppositely charged monomers are considered. All the cases deal with systems in the homogeneous disordered phase where no mesophase structures or micelle formations can be observed.
Statics and dynamics of single chains in polymer blends and copolymer melts — results beyond the random phase approximation
Authors: Vilgis Thomas A. , Benmouna Mustapha 
Published: April 2003

AbstractWe present new results on the behaviour of single chains in homo‐and copolymer blends which are beyond the rendom phase approximation (RPA). The radius of gyration of a chain in the blend was found to depend strongly on the interactions as well as the effective diffusion constant of a single chain in the blend or copolymer melt. Note that these results cannot be obtained in the original formulation of the RPA. They are based on the effective Hamiltonian of the chain in the medium. In the equation found for the self diffusion constant of a single chain, Ds, the second term is directly the value of the effective potential at zero wave vector. Thus the measurement of Ds would detect the screened potential at q = 0. Experimental verification of these results is in progress.
Wetting transitions of asymmetric binary polymer mixtures
Authors: Chen Zheng Yu , Noolandi Jaan 
Published: April 2003

AbstractWe examine the effect on surface‐wetting phase transitions in polymer mixtures when the degrees of polymerization of the two components are different. It has been demonstrated by Schmidt and Binder (J. Phys. (Paris) 46, 1631 (1985)) that in a symmetric polymer mixture a second‐order wetting transition occurs if the wall‐polymer interaction f(ϕ0) has a negative curvature f″(ϕ0), where ϕ0 is the surface volume fraction of the polymer component preferred by the wall. We found that in an asymmetric mixture this is not necessarily the case.
A kinetic tree‐like model of non‐linear alternating copolymerization of monomers with non‐equal reactivities of functional groups and substitution effect
Authors: Galina Henryk , Kaczmarski Krzysztof , Para Beata , Sanecka Bożena 
Published: April 2003

AbstractA kinetic model is presented that can be used to predict moments of size distribution of polymer species in the system where a tri‐functional monomer with groups of different reactivity (such as glycerol) reacts irreversibly with a bi‐functional monomer with no cycle formation. A Smoluchowski‐like equation is used to follow the time evolution of the size distribution of polymer molecules up to the gel point. The results are confronted with calculations made by using the statistical cascade theory. The two methods of calculations give slightly different results. The reasons for the differences are discussed.
Chain linear dimensions in the surface‐enriched layer of polymer mixtures
Authors: Wang Jian‐Sheng , Binder Kurt 
Published: April 2003

AbstractWe calculate the mean‐square end‐to‐end distances and mean‐square gyration radii using the bond fluctuation model for a binary polymer blend in the presence of a wall by Monte Carlo simulation. In the bulk, the size of the minority, low‐concentration polymer species is compressed compared to the majority one. In the vicinity of the wall, where the minority polymer concentration is enriched due to attraction from the wall, the dimensions of the two types of polymers are approximately equal and are essentially the same as in an athermal polymer melt. Thus, the geometric constraint is more important to the structure of the polymers than the polymer‐polymer and polymer‐wall interactions.
Collapse of polyelectrolyte networks induced by their interaction with an oppositely charged surfactant. Theory
Authors: Khokhlov Alexei R. , Kramarenko Elena Yu. , Makhaeva Elena E. , Starodubtzev Sergei G. 
Published: April 2003

AbstractA very simple theory of swelling and collapse of weakly charged polyelectrolyte networks in the solution of an oppositely charged surfactant has been developed. The following contributions to the free energy were taken into account: free energy of volume interaction and of elastic deformation of the network chains, free energy connected with micelle formation and free energy of translational motion of all mobile ions in the system (translational entropy). Both the cases of a solution of charged surfactant and that of a mixed solution of charged and neutral surfactant components have been taken into account. It has been shown that the behaviour of the network depends on the total surfactant concentration in the system and corresponds to one of the three following regimes: At low concentration, micelles inside the network are not formed and the behaviour of the polymer network is similar to that of a network swelling in the solution of a lowmolecular‐weight salt (regime 1). In the second regime, surfactant concentration inside the network exceeds the critical micelle concentration and micelles are formed; in this regime the network collapses because surfactant molecules, aggregated in micelles, cease to create “exerting” osmotic pressure in the network sample. In the third regime, at very high surfactant concentration, formation of additional micelles inside the network ceases, and the network dimensions coincide with those of the corresponding neutral network.
Kinetics of polymer analogous reactions
Authors: Szymanski Ryszard 
Published: April 2003

AbstractThe kinetics of reactions of polymer units depending on the closest vicinity is analyzed. The derived equation can be applied to transformations of homopolymers into copolymers. It directly allows (by fitting of the calculated kinetic curve to experimental data) to determine the corresponding rate constants, provided the analyzed reaction is zero or pseudo‐zero order with respect to the transformation reagent (and first order with respect to the polymer units). The Proposed procedure of numerical calculations allows to adopt the derived equation to other systems. It is shown in the Appendix that the distribution of blocks in the resulting copolymer is not Bernoullian, contrary to previous claims or assumptions.
Kinetics theory of anionic copolymerization with constant monomer ratio, 1. Sequence distribution
Authors: Hu Xiaodong , Yan Deyue 
Published: April 2003

AbstractThe chain microstructure of copolymers generated via anionic copolymerization with constant monomer ratio is studied theoretically by using the linear operator technique to solve the kinetic differential equations. The microstructural parameters for copolymers, such as the functions of sequence distributions, average length of the sequence and fractions of dyads and triads, are derived and further connected with initial conditions and reaction time so that one can predict the chain microstructure for copolymers from the polymerization conditions.
Fractal dimensions of polymeric phthalocynines
Authors: Knothe Gerhard 
Published: April 2003

AbstractAs a result of their structure, polymeric phthalocyanines have four fractal dimensions for every size/shape/dilation combination. The construction of polymeric phthalocyanines resembles known fractals. A structure model of the polymer is extended. For infinitely large polymeric phthalocyanines, the same limiting value for the fractal dimensions (D = 2) was found to be valid for all structures.