bluuebunny/crossref_metadata_2025_split huggingface dataset:
Equilibrium nano‐structures in poor solvent polymer solutions near glass transition temperature
Authors: Dormidontova Elena , Erukhimovich Igor , Khokhlov Alexei R. 
Published: March 2011

AbstractPoor solvent polymer solutions near the glass transition temperature are considered on the basis of the nonlocal entropy model which allows the possibility of microphase separation transition. The dependence of the magnitude of nonlocal entropy and nonlocality radius on the temperature are explicitly taken into account. It is shown that accounting for nonlocal entropy can lead to i) the solubility enhancement in the vicinity of glass transition temperature, ii) microphase separation transition. Microphase separation transition is studied in the weak segregation limit. Phase diagrams containing the regions of stability of different microdomain structures, as well as the regions of macroscopic phase separation, are obtained.
Interface effects in nematic liquid‐crystalline structures of polymer solutions
Authors: Kuznetsov Dmitri V. 
Published: March 2011

AbstractA solution of long semirigid linear macromolecules was considered. The liquid‐crystalline nematic ordering in the solution was analyzed theoretically using an Onsager‐type approach. The orientation entropy was calculated in the frameworks of Lifshits' approach, successfully developed for this system originally by Khokhlov and Semenov. For homogeneous liquid‐crystalline phase using the third virial approximation for intersegmental steric interaction the orientation distribution function, the free energy density, the isotropic‐nematic coexistence and the spinodal conditions were computed numerically for two types of polymer flexibility mechanism: persistent chains and chains of freely joint segments. For the asymptotically exact second virial approximation the applicability region was analyzed. We considered the general equations, which describe the concentration and orientational segment distribution for a semirigid persistent polymer chain at a surface (or interface) of any shape and orientation. These equations were numerically solved for the case when the nematic director axis was perpendicular to a planar interface boundary between the real coexisting nematic and isotropic phases. The coordinate‐dependencies of the polymer concentration and of the order‐parameter take the smooth two‐steps form in the interface region.
Interfacial tension of a demixed A/B polymer blend with A‐B diblock copolymer near the critical point
Authors: Nose Takuhei 
Published: March 2011

AbstractEffects of A‐B diblock copolymers on the interfacial tension of a demixed homopolymer A/B blend near the critical point has been studied theoretically and experimentally. A simple theory developed here predicts that a crossover from weak to strong reduction of interfacial tension with addition of a small amount of diblock copolymers can be observed upon going away from the critical temperature, where the interfacial tension exhibits a maximum in its temperature dependence, if polymeric index of the diblock copolymer is much larger than that of the homopolymers. The temperature of the maximum approaches the critical point with increasing copolymer concentration. These predictions have experimentally been confirmed for a demixed oligo(styrene)/oligo(dimethylsiloxane) blend with poly(styrene)‐block‐poly(dimethylsiloxane).
Effect of molecular architecture on DBS‐induced block copolymer gels: A rheological study
Authors: Nuñez Carlos M. , Whitfield J. Kaye , Mercurio Debra J. , Ilzhoefer John R. , Spontak Richard J. , Khan Saad A. 
Published: March 2011

AbstractDibenzylidene sorbitol (DBS) is capable of gelling a variety of organic solvents and polymeric materials by forming a rigid, 3‐D hydrogen‐bonded network. In this work, two poly(siloxane)/poly(propylene oxide) segmented copolymers of equal composition and molecular weight, but different architectures (endblocked vs. pendant), as well as a pure poly(propylene oxide), have been gelled with DBS. We have investigated the dynamic rheological properties of these gels to ascertain the effect of copolymer architecture, PDMS comonomer and DBS concentration on network formation.
Comparison of the association process in physical gels and in polymers with small amounts of stickers
Authors: Rogovina L. Z. , Vasil'Ev V. G. 
Published: March 2011

AbstractThe association processes in physical gels and physical networks with smal amount of stickers are compared on the basis of the generalization of literature data and our own results on the gels of gelatine, PVA and olygocarbodiimides as well as on the physical network formation in poly(dimethylcarbosiloxane) with side COOH groups. The measurement of the rheological properties is used as a main method of the association evaluation. The role of the rearrangement of the intra‐ to intermolecular bonds and of the thermodynamic quality of the solvent in the process of physical network formation is emphasized.
Nanosize metal clusters in polymer systems
Authors: Sergeev Gleb B. , Gromchenko Irina A. , Petrukhina Marina A. , Prusov Andrey N. , Sergeev Boris M. , Zagorsky Vyacheslav V. 
Published: March 2011

AbstractThree synthetic methods have been developed for embedding nanosize metal clusters into polymers: (i) in situ synthesis of silver nanoparticles in cross‐linked poly‐acrylamide gels, (ii) implantation of cryochemically produced silver nanoparticles into poly‐acrylamide gels, and (iii) encapsulation of metal nanoparticles in poly‐p‐xylylene films. All methods allow one to produce 3–20 nm stable metal clusters embedded into bulk materials, thin films or fine particles dispersed in organic solvents or water. Results on some physical properties of the metal‐polymer systems thus obtained are presented.
Microscopic inhomogeneities in weakly‐charged temperature sensitive polymer gels and solutions
Authors: Shibayama Mitsuhiro 
Published: March 2011

AbstractA comparison of small‐angle neutron scattering (SANS) intensity functions, I(q), was made between gels and solutions of poly(N‐isopropyl acrylamide‐co‐acrylic acid) (NIPA/AAc), where q is the magnitude of the scattering vector. I(q)'s were strongly dependent on polymer concentration as well as temperature. At low temperatures, I(q)'s for both gels and solutions were similar to each other and were monotonous decreasing functions. However, at high temperatures above θ, the so‐called theta temperature of poly‐NIPA in aqueous solution, both had a distinct peak and a significant difference appeared in I(q) due to the presence or absence of crosslinks. Origins of the peak and the differences in I(q) are discussed.
Molecular dynamics simulation study of the dynamics of fluids at solid‐liquid interfaces
Authors: Winkler Roland G. , Schmid Rolf H. , Reineker Peter 
Published: March 2011

AbstractThe dynamics of fluids at solid‐liquid interfaces is investigated. In particular, we consider a simple Lennard‐Jones fluid as well as a melt of hexadecane chains. For the Lennard‐Jones fluid, the numerical results are compared with analytical calculations based on the diffusion equation, which shows that the numerical results can very well by described by the solution of the diffusion equation for reflecting surfaces. The diffusion coefficient is practically independent of the position within the film, although the fluid is inhomogeneous perpendicular to the surface. In contrast, the dynamics of the centers of mass of hexadecane molecules perpendicular to repulsive surfaces is severely slowed down due to their extended and anisotropic nature and cannot be described by a single particle diffusion equation.
Kinetics of collapse and decollapse of a single double‐stranded DNA chain
Authors: Yoshikawa K. 
Published: March 2011

AbstractTransition of a single duplex DNA between elongated coil and condensed globule has been studied by the technique of single molecular observation with fluorescence microscopy. It has become clear that individual DNA chains undergo first‐order phase transition. We have observed the time‐dependent change of the DNA structure accompanied with the phase transition from coil to globule. The speed of the compaction was found to be almost constant along the DNA chain. It is indicated that the coil‐globule transition exhibits the phenomenon of “nucleation and growth”. The process of the decollapse of a single DNA has also been observed, the time dependence of the long axis length being described as l ∼ t1.8.
Polymerization and molecular recognition in the monolayers of the surface‐active derivatives of crown‐ethers
Authors: Zaitsev Sergei Yu. , Vereschetin Vadim P. , Zubov Vitalj P. 
Published: March 2011

AbstractThe four surface‐active derivatives of crown‐ethers with a variety of fatty alkyl chains were synthesized and studied in monolayers at various conditions. The areas per crown‐ether molecule in monolayers are increasing significantly in the presence of various alkali metal cations in the aqueous subphase. These effects can be explained as complex formation between crown‐ethers in the monolayers and cations from aqueous subphase, causing a change in the conformation of the polyether ring of the molecule at the interface. This is accompanied with the change in the cation selectivity (Na+ > Li+ > K+ > Cs+) as compared with the series in volume (K+ > Cs+ > Na+ > Li+). Polymerization of the crown‐ether monolayer allows to stabilize the conformation of the molecule at the interface as if tuned to the definite cation.
Self‐assembly phenomena in multicomponent systems composed of polyelectrolytes and ionic surfactants
Authors: Zezin Alexander B. , Izumrudov Vladimir A. , Kabanov Victor A. 
Published: March 2011

AbstractThe ability of anionic surfactants to expel fluorescencetagged poly(methacrylate) polyanion (PMA*) from nonstoichiometric water‐soluble interpolyelectrolyte complex (NIPEC) formed by PMA* and polycation‐quencher poly(N‐alkyl‐4‐vinylpyridinium) (PAlkVP) and to form polyelectrolyte‐surfactant complex (PESC): NIPEC(PMA*‐PAlkVP)+surfactant ⇔ PESC(PAlkVP‐surfactant)+PMA* was revealed and studied by fluorescence quenching technique and high‐speed sedimentation. It was found that the transfer of poly(N‐ethyl‐4‐vinylpyridinium) from NIPEC to PESC proceeded up to complete conversion providing a self‐assembly of both PESC and NIPEC particles in the course of the reaction. The concentration of the surfactant and the “tail” length of the surfactant molecule, as well as the structure of Alk groups, temperature, pH, ionic strength, and the nature of added low‐molecular‐weight electrolyte proved to be the factors of the reaction equilibrium control.
Hierarchical structures in natural and synthetic polymer science
Authors: Baer Eric , Hiltner Anne 
Published: March 2011

AbstractThe founders of our dynamic field uncovered the wonders of both natural and synthetic polymers by using relatively primitive instruments and techniques. They developed the foundations on which we now build complex materials systems. By using the lessons from macromolecular systems in biology, our scientific community is now designing synthetic polymers that mimic natural materials (1, 2). This paper is divided into two parts.1. Hierarchical structure‐property relationships in connective tissues‐lessons from biology2. Micro‐ and nano‐ layered polymeric systems
Self‐assembling with formation of mesogenic polymer structures in non‐mesogenic species
Authors: Plate' N. A. , Talroze R. V. 
Published: March 2011

AbstractThe trivial statement that liquid crystals are formed on the base of either mesogenic organic molecules or molecules with amphiphilic structure may be applied to polymers as well. But at the same time it became clear that polymer LC world in certain sense is richer than the low‐molecular one and more and more one finds mesophase and LC polymers based on non‐mesogenic macromolecules. Linear polyphosphazenes, polysiloxanes, some ladder polymers etc. exhibit mesophase behavior in absence of any mesogenic groups in their structure.
Selectivity as a measure of “livingness” of the polymerization of cyclic esters
Authors: Penczek Stanislaw , Duda Andrzej 
Published: March 2011

AbstractThe selectivity parameter, defined as the ratio of the rate constant of desired elementary reaction (i.e. initiation or propagation) to the rate constant of the competing side reaction, should be used as a quantitative measure of the livingness of polymerization. The most important side reactions in the anionic and pseudoanionic polymerization of cyclic esters are presented and the importance of selectivity in initiation and propagation is discussed, taking into account the relation between selectivity and the structure of monomers, initiators, and active species. Reasons for the low selectivity of ions and the high selectivity of aluminium‐based initiators, namely dialkylaluminium alkoxides (R2AlOR') and aluminium trialkoxides (Al(OR)3) are given. The relatively low reactivity and steric hindrance, created by the presence of bulky substituents at the Al atom, are responsible for the enhanced selectivity. Thus, Al(OR)3 found recently to carry three chains, provides particularly crowded and therefore selective active species. The structure of the aluminium alkoxide active species is described, as established on the basis of 1H NMR, 27Al NMR, and molecular weight measurements by Multi Angle Laser Light Scattering (MALLS) of the living polymers.
Cationic polymerization with titanium(iv) compounds: Living polymerization and possibility of stereoregulation
Authors: Sawamoto Mitsuo , Kamigaito Masami 
Published: March 2011

AbstractThis paper deals with the development of living cationic polymerizations and the possibility of stereoregulation therein based on the modulation of the Lewis acid activators by their ligands. For this, titanium(IV) chlorides [TiCl4‐n(OR)n] with various alkoxy or aryloxy groups were synthesized and employed for the cationic polymerizations of isobutyl vinyl ether (IBVE) in conjunction with HCl‐IBVE adduct. Living polymerizations were feasible with the titanium chlorides [TiCl2(OR)2] disubstituted with isopropoxy or phenoxy groups in CH2Cl2 at −15°C. The meso (isotactic) contents of the polymers obtained with TiCl2(OR)2 at −78°C became larger (up to 86%) with bulkier o‐substituents of phenoxy groups on the titanium compounds.
Synthetic applications of non‐polymerizable monomers in living carbocationic polymerization; recent developments
Authors: Hadjikyriacou S. , Li D. , Bae Y. C. , Faust R. 
Published: March 2011

AbstractRecent developments using non‐(homo)polymerizable monomers, for the synthesis of functional polymers and block copolymers by living cationic polymerization are discussed. The preparation of block copolymers based on IB and αMeSt or IBVE are reported using DPE capping followed by Lewis acidity moderation. The use of non‐polymerizable diolefins such as bis (diphenylethylenes) for in situ coupling of living chains is also discussed. Depending on the structure of the diolefin mono‐ or diaddition is observed.
Liquid crystalline block copolymers by sequential cationic or promoted cationic and free‐radical polymerizations
Authors: Galli Giancarlo , Chiellini Emo , Yagci Yusuf , Serhatli Ersin I. , Laus Michele , Angeloni Annino Sante 
Published: March 2011

AbstractThe scope for the study of the synthesis and properties of liquid crystalline (LC) block copolymers is briefly outlined. While there are many approaches to the synthesis of LC block copolymers, the use of azo macroinitiators is very versatile and allows one to produce diverse block copolymer architectures. Azo macroinitiators are prepared by cationic or promoted cationic polymerization of tetrahydrofuran (1) or cyclohexene oxide (2), and are then used to initiate the free‐radical polymerization of various methacrylates 3,4 or acrylates 5–9 containing mesogenic azobenzene or biphenyl units thereby yielding block copolymers. The AB or ABA block copolymers are microphase‐separated and form smectic and/or nematic mesophases similar to the respective LC homopolymers.
New materials from telechelic polyacetals
Authors: Goethals Eric J. , Walraedt Saskia R. , Han Xinghua , Trossaert Geert G. , Hartmann Patrick J. 
Published: March 2011

AbstractTelechelic polyacetals, obtained by cationic ring‐opening polymerization of 1,3‐dioxolane (DXL) and 1,3‐dioxepane (DXP), have been used as building blocks for polymer materials. In the first part of this paper, the synthesis and the properties of networks based on polyDXL α,ω‐bis(methacrylates) are discussed. The second part deals with the synthesis and the properties of polyacetal polyurethanes. A thermoplastic polyurethane was prepared with poly(DXL‐co‐DXP) α,ω‐diol as soft segment and the combination butane‐1,4‐diol and hexamethylene diisocyanate as hard segment. Polyurethane networks were obtained from polyacetal polyols and diphenylmethane diisocyanate (MDI). Some physical properties of these new materials are reported.
Kinetic and thermodynamic control in the cationic copolymerization of cyclic ethers
Authors: Bednarek Melania , Kubisa PrzemysłAw , Penczek StanisłAw 
Published: March 2011

AbstractCationic copolymerization of tetrahydrofuran with ethylene oxide in the presence of diols proceeds, at the properly chosen conditions, with complete conversion of both comonomers and leads to telechelic oligodiols. These conditions are based on the simultaneous kinetic and thermodynamic control for two operating mechanisms namely active chain end and activated monomer mechanism. Kinetics of copolymerization and model reactions were studied. The ratios of rate constants of competing reactions, governing the copolymer composition, were determined and it was found, that the microstructure of the copolymer can be controlled at low conversion while at higher conversion the kinetics of the competing parallel reactions is not favourable for the formation of a regular copolymer, in contrast to the previously studied copolymerization of tetrahydrofuran with epichlorohydrin.
Anionic and coordination polymerization of 3‐butyrolactone
Authors: Lenz Robert W. , Jedlinski Zbigniew 
Published: March 2011

AbstractAluminoxane catalysts and anionic initiators can polymerize 3‐butyrolactone, 3‐BL, to high molecular weight stereoregular polymers. With the racemic monomer, [R,S]‐3‐BL, anionic polymerization with alkali metal complexes can form syndiotactic polymers and aluminoxane catalysts can form either highly isotactic, syndiotactic, or atactic poly‐3‐butyrolactone, P‐3‐BL, depending on the composition and method of preparation of the aluminoxane and the conditions of polymerization.
Effect of bulkiness and lewis acidity of aluminium compounds on the anionic polymerization of methyl methacrylate in toluene
Authors: Schlaad Helmut , Müller Axel H. E. 
Published: March 2011

AbstractThe bulkiness and the Lewis acidity of added aluminium compounds strongly affect the polymerization of methyl methacrylate in toluene at −78°C. The polymerization strongly deviates from ‘ideal’ first‐order kinetics, i.e. the first‐order time‐conversion plots are kinked at low monomer conversions. Additionally, for the more bulky and more Lewis‐acid aluminium alkyls, the time‐conversion plots show a further downward curvature. This curvature is not the result of a termination reaction because the polymers are free of side products like β‐ketoesters or vinyl ketone units. The molecular weight distributions and tacticities of the resulting polymers are also affected. Dependent on the aluminium compound used, molecular weight distributions are in the range of 1.2 < Mw/Mn < 7, and the triad tacticity of the polymer can change from highly syndiotactic over atactic or heterotactic to highly isotactic.
Synthetic approaches towards new polymer systems by the combination of living carbocationic and anionic polymerizations
Authors: Feldthusen Jesper , Iván Béla , Müller Axel H. E. , Kops Jørgen 
Published: March 2011

AbstractThis study summarizes recent efforts to obtain by combination of living carbocationic and anionic polymerizations block copolymers which are potential precursors for building new well‐defined polymeric architectures with microphase separated morphology. Living carbocationic polymerization (LCCP) yields telechelic polyisobutylene (PIB) chains with a variety of useful endgroups, such as tert‐chlorine, isopropenyl, primary hydroxyl, tolyl etc. When tolyl‐ended PIB was used as precursor for macroinitiator of living anionic polymerization of 2‐(tert‐butyldimethylsilyloxy)ethyl methacrylate (tBuMe2SiOEMA), mixtures of homopolymers and block copolymers were formed due to incomplete lithiation of this chain end. In another approach a new functionalization method was developed by end‐quenching living PIB chains with 1,1‐diphenylethylene (DPE). In the presence of BCl3 a new telechelic PIB with 2,2‐diphenylvinyl (DPV) endgroups was formed. A corresponding DPV model compound was synthesized from 2‐chloro‐2,4,4‐trimethylpentane (TMPCl). Because of steric hindrance less than quantitative lithiation of this material occurred. Controlled deprotection of PtBuMe2SiOEMA obtained by living anionic polymerization (LAP) was utilized to prepare a precursor network composed of partially deprotected PtBuM2SiOEMA and hydroxyl‐telechelic PIB by using a diisocyanate crosslinker. After network formation deprotection with HCl was completed and a new amphiphilic network (APN) containing PIB and poly(2‐hydroxyethyl) methacrylate) (PHEMA) segments crosslinked by urethane linkages was obtained.
Synthesis of triblock copolymers made of a fluorinated central block and two outside poly(1,3‐dioxolane) blocks
Authors: Djebar Abdelkader , Reibel Léonard , Franta Emile 
Published: March 2011

AbstractConditions are given that allow the preparation of highly amphiphilic triblock copolymers where the central block is a perfluoropolyether (number average molar mass equal to 2000) only soluble in freon‐type solvents, and the outside blocks are made of water soluble poly(1,3‐dioxolane) whose molar mass can be controled by the amount of 1,3‐dioxolane consumed. Two methods are described: it is possible either to use CH2Cl2 as a solvent (but only one of the two phases yields the expected product) or to recourse to a Fomblin‐rich fraction prepared previously as the initial diol (but the product of the reaction can be heterogeneous and separation has to be performed).
Stopped‐flow investigation of the cationic oligomerization of trans‐1,3‐diphenyl‐1‐butene initiated by trifluoromethanesulfonic acid in dichloromethane
Authors: Vairon Jean‐Pierre , Charleux Bernadette , Rives Alain 
Published: March 2011

AbstractReaction of trans 1,3‐diphenyl‐1‐butene (D), the trans ethylenic dimer of styrene, with trifluoromethanesulfonic acid in dichloromethane has been performed at temperatures lower than room temperature using a stopped‐flow technique with real time UV‐visible spectroscopic detection. The main product of the reaction was the indanic dimer of D. A transient absorption at 340 nm has een assigned to 1,3‐diphenylbutylium, a model for the polystyryl cation. Other absorptions at 349 nm and 505 nm have also been observed and were assigned to an allylic cation, 1,3‐diphenyl‐1‐buten‐3‐ylium, resulting from hydride abstraction from D. This species was very stable at temperatures lower than −30°C. A general mechanism was proposed based on a kinetic study of the involved reactions.