bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design, synthesis, and surface activity of amphiphilic perfluorinated oxazoline polymers
Authors: Sogah Dotsevi Y. , Kaku Mureo , Shinohara Ken‐ichi , Rodriguez‐Parada Jose M. , Levy Moshe 
Published: March 2011

AbstractPolymers derived from 2‐[2‐(perfluoroalkyl)ethyl]‐2‐oxazolines have been prepared in very good yields with molecular weights up to 50000. The polymers are crystalline with melting temperatures (Tm's) varying from 180 to 232°C depending on the length and type of the perfluorinated side chain, have good thermal stability and are soluble in fluorinated solvents. They are effective as modifiers of surfaces of hydrophilic polymers, such as nylon‐6,6, and give acceptable complement activation parameters. Factor C3a (μg/ml) released is 5.3 in contrast to positive control value of 45.2 (activated sepharose) and negative control = 4.8. A 1:1 mixture of 2‐octyl‐2‐oxazoline and 2‐[2‐(perfluorohexyl)ethyl]‐2‐oxazoline copolymerize to give a block copolymer that exhibits two separate Tm's. The partially perfluorinated polymers also form stable monolayers at air‐water interface.
Structure‐property relationships in high‐performance thermoset‐thermoplastic blends
Authors: McGrail P T , Street A C 
Published: March 2011

AbstractSemi‐crystalline and amorphous aromatic polymers have become well established as high‐performance engineering polymers and composite matrices. Such polymers with functional groups introduced, may be used to toughen, and modify the processing properties of, a range of thermosetting resins, in addition to being copolymerisable, crosslinkable and/or chain‐extendable.This paper describes structure/property relationships which have been established for functionalised polyaromatics and systems which utilise them.
High‐speed living polymerization with a new catalyst system based on metalloporphyrin
Authors: Inoue Shohei , Aida Takuzo , Kuroki Masakatsu , Sugimoto Hiroshi 
Published: March 2011

AbstractA novel catalyst system composed of aluminium porphyrin and an organoaluminium compound with bulky substituents brings about high‐speed living polymerizations of epoxide, lactone, and methacrylic ester to give the polymers with controlled molecular weight.
Applications of polymer rism theory to blends
Authors: Honeycutt J. D. 
Published: March 2011

AbstractPolymer RISM (reference interaction site model) theory is a theory of polymer systems in the liquid phase in which account for chemical realism can be made. Results are reported here of phase diagrams (spinodals) for blend systems calculated by means of this theory, using the mean spherical approximation as a closure. The systems investigated are an isotopic blend, a set of homopolymer/copolymer blends, and a model blend containing specific interactions.
Structure as a function of relaxation in glassy polymers
Authors: Ludovice Peter J. , Qian Caibao 
Published: March 2011

AbstractPreviously, amorphous glasses were simulated by carrying out energy minimization on initial conformations generated by growing polymer chains in a periodic cube. It was not known what degree of relaxation these simulated glasses possessed. The degree relaxation is determined by the thermal history of the bulk polymer and in turn determines numerous important properties. Constant stress molecular dynamics (CSMD) followed by energy minimization was used to simulate different thermal histories of an isotactic poly(propylene) glass. This simulation approach produced glasses in which the degree of energetic relaxation was a function of the thermal history. Based on the simulated cohesive energy density, the simulation using minimization alone produced a glass that was energetically annealed. However, the local geometry and x‐ray structure factor indicate that it has a different structure than those obtained using CSMD followed by energy minimization and may not be structurally relaxed.
Computer simulation of stress relaxation
Authors: Blonski Slawomir , Brostow Witold , Kubát Josef 
Published: March 2011

AbstractMolecular dynamics simulations of stress relaxation have been performed for models of metals and polymers. The method which employs coupling between the simulation cell and an external thermal bath as well as an applied stress has been used. Two‐dimensional models of the materials are defined with interactions described by the Lennard‐Jones (Mie 6–12) and harmonic potentials. A special method is employed to generate chains in dense polymeric systems. Simulated stress relaxation curves are similar for metals and polymers, while there exist essential differences in the stress‐strain behavior of the models. During the relaxation, trajectories of the particles in different materials display a common feature: there exist domains in which movement of the particles is highly correlated. This observation supports the cooperative theory of stress relaxation developed by one of us. The results of the simulations do not significantly depend on the number of particles in the system nor on other simulation details.
Grafted polymer layers under variable solvent conditions: A Monte Carlo simulation
Authors: Lai Pik‐Yin , Binder Kurt 
Published: March 2011

AbstractPolymer chains anchored with one end at a hard wall under variable solvent conditions are investigated by Monte Carlo simulations using the bond‐ fluctuation model. Detail information on the structural properties are obtained above, at, and below the Θ‐point and discussed in terms of the appropriate theories. In particular, the scaling of the brush thickness is formulated and verified by the simulation data. For the dynamics at the Θ‐point, both the relaxation time of the chain configuration and the mean‐square time displacement are studied. At temperatures distinctly below the Θ‐point, we find that the layer develops considerable lateral inhomogeneity in its density, which has not been predicted by previous theories.
Analytical methods vs. numerical results for reacting layered systems
Authors: Sokolov I.M. , Blumen A. 
Published: March 2011

AbstractWe consider here reactions in layered systems. We model a situation in which the mixing of the reactants precedes the chemical reaction and show that the overall decay kinetics is determined by the initial striation thickness distribution. Thus the kinetics is controlled by the diffusive motion of the spatial inhomogeneities (clusters). Different numerical approaches to the problem are discussed and the results of the numerical modeling are compared with the analytical considerations.
Classical and metallocene catalytic systems: Comparison between the stereochemical mechanisms of α‐olefin polymerization
Authors: Zambelli Adolfo , Pellecchia Claudio 
Published: March 2011

AbstractClassical Ziegler‐Natta and Kaminsky‐Ewen catalysts promoting polymerization of hydrocarbon monomers are compared considering the reactivity and the stereochemical mechanisms of polymerization. It is suggested that also the “active sites” of heterogeneous catalysts could be cationic.
Recent progress in heterogeneous Ziegler‐Natta catalysts
Authors: Soga Kazuo 
Published: March 2011

AbstractThis paper summarizes the results on regio‐ and stereochemical control of heterogeneous Ziegler‐Natta catalysts which we have obtained for the last several years. Convenient converting methods of active species from aspecific into isospecific are first shown with the use of a completely aspecific catalyst. Effects of catalyst isospecificity on the polymerization of various olefins as well as olefin copolymerizations are then described in some detail. Finnaly, the preparation method of Ti‐based regioirregular catalyst and its application to ethylene‐propene copolymerization are reported in brief.
Predictions from the trigger mechanism for Ziegler‐Natta polymerization of α‐olefins
Authors: Ystenes Martin 
Published: March 2011

AbstractThe trigger mechanism is a new concept for understanding the polymerization of α‐olefins with Ziegler‐Natta catalysts. The mechanism is based on the interaction of two monomers in the transition state, where an incoming monomer triggers the insertion of a complexated monomer. The monomer site is never a free site, and is thus protected from attack by Lewis bases in the reaction medium. The stereochemical discrimination is due to the interaction of the two monomers. This interaction determines the orientation of the incoming monomer, and the stereochemistry of the insertion is given when the monomer is complexated. The model predicts a reaction rate order vs. monomer concentration between 1.0 and 2.0, a reduced overall polymerization rate above a given temperature, very complex kinetics for copolymerization, a lower stereochemical discrimination for the first inserted monomer, and a high stereochemical discrimination.
Polyhedral oligometallasilsesquioxanes as models for silica‐supported catalysts
Authors: Feher Frank J. , Blanski Rusty L. 
Published: March 2011

AbstractIncompletely‐condensed silsesquioxanes offer excellent potential as ligands in homogeneous models for silica‐supported catalysts. This paper focuses on the chemistry of Cr and V‐containing silsesquioxanes, which are proposed as models for silica‐supported chromates and vanadates. It has been shown that the reactivities of these transition‐metal‐containing silsesquioxanes can be very different than that observed for stoichiometrically similar alkoxide or siloxide complexes. In particular, two new catalysts for the polymerization of olefins have been prepared by reacting structurally well‐defined Cr and V‐containing Si/O frameworks with trialkylaluminum reagents. Mechanistic studies on the vanadium system implicate high‐valent V(V) complexes as the active catalytic species.
Syntheses and models for stereospecific metallocenes
Authors: Ewen John A. , Elder M. J. 
Published: March 2011

AbstractStereospecific, bridged [LL']M(R)+ catalysts (L, L' = substituted‐cp, ind, or flu; R = hydrocarbyl) have been prepared by three new synthetic procedures. Propylene polymerizations with our new catalyst synthetic reagents, tris(pentafluorophenyl)boron (F15), magnesium dichloride, and trityl tetrakis(pentafluorophenyl)borate (trityl‐F20) are compared with results obtained with the N, N‐dimethyl‐anilinium‐F20 salt and with methylaluminoxane (MAO). Trimethylaluminium (TMA) or triethylaluminium(TEAL) scavenged poisons in the MAO free polymerizations. The site‐control mechanism is discussed.
New mechanistic aspects and structure activity relationships in the allyl nickel complex catalysed butadiene polymerization
Authors: Taube R. , Schmidt U. , Gehrke J.‐P. , Böhme P. , Langlotz J. , Wache S. 
Published: March 2011

AbstractThe present state of knowledge of the mechanism of the allyl nickel complex catalysed stereoselective butadiene polymerization is outlined. On the basis of the reaction model, which has been worked out more thoroughly and comprehensively by our systematic experimental investigations during the last years, the thermodynamic and kinetic control of the catalytic activity and selectivity in dependence on the structure of the allylnickel complexes will be discussed. Finally, it will be shown how the structure of the technical nickel catalyst could be elucidated for the first time and how its catalytic properties can be explained in the framework of the derived structure‐activity relationships.
Stereochemistry of anionic vinyl polymerization
Authors: Hogen‐Esch T.E. 
Published: March 2011

AbstractThe stereochemistry of anionic polymerization of vinyl monomers: CH2=C(R)C(Y)=X where X and Y are O, N or C and R = H or alkyl is discussed in terms of a: the geometry of the ‐CH2C‐(R)C(Y)=X intermediate existing as E‐ or Z‐isomers; b: the interactions of cation (Li, Na, etc.) with the anion and coordinating groups on the penultimate or antepenultimate asymmetric carbon. The E/Z ratio appears to be determined directly by the s‐trans/s‐cis approach of the monomer. The nature of the coordination of the counter ion is considerably more complicated and is discussed in detail.
Critical examination of some basic concepts of ionic polymerization
Authors: Szwarc Michael 
Published: March 2011

AbstractSome problems in ionic polymerization are reviewed. The existence of a variety of species participating in ionic polymerizations is stressed and the distinction between the growing, dormant, and dead polymers emphasized. An example of a kind of polymer that does not fit any of these three classes is given suggesting that still other examples might be discovered in the future.
Lewis acid ‐ assisted high speed living anionic polymerization by the aluminum porphyrin ‐ Lewis acid systems
Authors: Aida Takuzo , Kuroki Masakatsu , Sugimoto Hiroshi , Watanabe Tsuyoshi , Adachi Takato , Kawamura Chikara , Inoue Shohei 
Published: March 2011

AbstractLiving anionic polymerization of methacrylic esters initiated with aluminum porphyrins (1) was found to be dramatically accelerated (e.g., 46 000 times) upon addition of bulky Lewis acids such as alkylaluminum diphenolates (3). Under appropriate conditions, a narrow MWD poly(methyl methacrylate) with Mn exceeding a million could be synthesized. The key conception of this high speed living polymerization is the coexistence of nucleophile (2) and Lewis acid (3) realized by steric repulsion.
Organocuprates as initiators for the polymerization of methyl methacrylate in THF
Authors: Dimonie Mihai , Mardare Daniela , Coca Simion , Hogen‐Esch Thieo E. , Zöller Joachim 
Published: March 2011

AbstractSeveral types of lithium organocuprates (I) e.g. R2CuLi, RR'CuLi, R3CuLi2, R2CuLi2X (X‐ CN, SCN), were prepared and used as polymerization initiators for methyl methacrylate in THF at temperatures ranging from −30 to +20 *C. Polymerization initiated by a mixed homocuprate, e.g. lithium n‐butyl (thien‐2‐yl)cuprate was studied in more detail. Kinetic measurements indicated an overall large (−4 to −14 kcal) apparent negative activation energy of polymerization in the −30 + +20 *C temperature range. The reaction was shown to have a kinetic order of about 1.5 with respect to initiator concentration. Conductance measurements indicate that the equivalent conductance increases with initiator concentration in the 10−2 + 10−1 M range indicating the formation of multiple ions formed by intermolecular association. The data are consistent with a polymerization involving aggregated ion pairs of as yet undetermined composition. The negative activation energy is tentatively interpreted as due to the exothermic formation of aggregates existing as highly solvated ion pairs.
Anionic living polymerization of styrenes containing electron‐withdrawing groups
Authors: Nakahama Seiichi , Ishizone Takashi , Hirao Akira 
Published: March 2011

AbstractSix styrene derivatives containing electron‐withdrawing groups were synthesized and polymerized with anionic initiators in THF to afford stable anionic living polymers. The electron‐withdrawing substituents are N,N‐dialkylamide(1), N‐alkylimino(2), oxazoline(3), tert‐butyl ester(4), N,N‐dialkylsulfonamide(5) and cyano(6) moieties. The polymers obtained have predictable molecular weights and narrow molecular weight distributions. The respective postpolymerizations proceeded with quantitative efficiency indicating that each polymer chain end retained the propagating reactivity. However, the resulting living polymers could not initiate the polymerizations of styrene and isoprene. On the other hand, the styrene derivatives(5 and 6) were polymerized with weak nucleophilic initiators, such as living polymer of tert‐butyl methacrylate. These results suggest that the electron‐withdrawing groups stabilize the living ends and also activate the respective monomers for anionic polymerization. The substitution effect reflects on the 13C NMR chemical shift of β‐carbon of each vinyl group. The signal of the β‐carbon appeared at lower magnetic field than that of styrene indicating electron deficiency on the carbon‐carbon double bond of these monomers.
Preparation of polymers with polycarbonate sequences and their depolymerization; an example of thermodynamic recycling
Authors: Keul Helmut , Müller Achim J. , Höcker Hartwig 
Published: March 2011

AbstractInitiators based on hydroxytelechelic polyethylene oxide, polytetrahydrofuran and polydimethylsiloxane were used for the anionic ring‐opening polymerization of 2.2‐dimethyltrimethylene carbonate (DTC). Under suitable conditions high yields of block copolymers of the AB and ABA types were obtained, depending on the initiator used. Ring‐closing depolymerization of poly(2.2‐dimethyltrimethylene carbonate) [poly(DTC)] and of copolymers containing poly(DTC) blocks with catalysts based on potassium or tin results under suitable conditions in DTC.
Some aspects of the living isobutylene polymerization
Authors: Kelen Tibor , Kelen Tibor , Balogh Lajos , Majoros Istvan , Deak Gyorgy 
Published: March 2011

AbstractThe possibilities of increasing the livingness in cationic isobutylene polymerizations has been investigated. It has been assumed that the living chain‐end is polarized but non‐dissociated and relatively stable, therefore, i) shifting of the dissociation equilibrium by adding salts with common or non‐common anion in excess, and ii) increasing of the stability of the chain‐end by complexing it with electrondonors, may increase the livingness of the system. Indeed, the addition of n‐Bu4NCl or n‐Bu4NI to systems with BCl3 or TiCl4 coinitiators, as well as the addition of dimethyl sulphoxide as electrondonor in a broad concentration range, improved the living character. The possibility of complexation of the chain‐end by the monomer has also been supported
Similarity of the relaxation modulus of polydisperse polymers
Authors: Caswell Bruce , Paboojian Stephen J. 
Published: March 2011

AbstractA similarity rule due to Markovitz is used for the correlation of the relaxation modulus for different polymeric materials. This rule has long been employed implicitly in the empirical shifting rules for the reduction to common curves of viscoelastic data measured on the same polymer over a range of temperatures and concentrations. It is shown here for the rubbery regime of polydisperse polymers that when relaxation moduli are scaled with the steady‐state compliance and the time with the mean relaxation time, data for a variety of amorphous polymeric materials tend to plot on a common curve. This suggests that the dimensionless rubber modulus is, to first order, a common function of dimensionless time for materials which include whole polymers and polymer solutions, the effects of temperature and concentration being automatically incorporated into the two scaling parameters. For materials with sufficient polydispersity the correlation appears to be valid over a wide range of the available experimental data. These amorphous materials appear to share only one feature, flexible molecules with broadly distributed molecular weights. For narrowly dispersed polymers the modulus in the terminal zone is also correlated according to the above rule, but the influence of other parameters appears as the transition to the glassy regime is approached. An additional application of the similarity rule allows the relaxation modulus computed from molecular dynamics simulations of idealized polymers to be compared with experimental moduli for real materials even though the characteristic times for these systems differ by more than ten orders of magnitude.
The nonlinear strain measure of polymer melts and rubbers: A unifying approach
Authors: Wagner M. H. 
Published: March 2011

AbstractUniaxial elongation and compression data of linear and branched polymer melts as well as of rubbers are analyzed with respect to their nonlinear strain measure. This is found to be the result of two contributions: (1) affine orientation of network strands, and (2) isotropic strand extension. Network strand extension is caused by an increasing restriction of lateral movement of polymer chains due to deformation, and is modelled by a molecular stress function f, which in the tube concept of Doi and Edwards is the inverse of the relative tube diameter. At small strains, f2 is found to be linear in the average stretch for melts as well as for rubbers, which corresponds to an affine deformation of the tube. At large strains, melts show maximum molecular tension depending on the degree of long‐chain branching, while rubbers show maximum extensibility.
Experimental methods in polymer melt rheology
Authors: Meissner Joachin 
Published: March 2011

AbstractExperimental developments in different areas of polymer melt rheology and recent results are reviewed: Shear oscillations were performed with mixtures of polyisobutylenes (PIB) of relatively small molecular mass distributions and with blends of polystyrene (PS) and polymethylmethacrylate (PMMA). For the latter, the interfacial tension between the melts of PS and PMMA can be derived from the results. ‐ In constant shear rate flow, the measurement of the first normal stress difference N1 in a commercial cone‐and‐plate rotational rheometer is simple if the test temperature is kept extremely constant. By a further modification a partial integral of the pressure distribution is measured from which the second normal stress difference N2 can be determined. ‐ The molecular orientation in shear flow results in a rheological anisotropy that can be studied in a parallel‐plate shear rheometer in which the polymer melt sample can arbitrarily be sheared in two perpendicular directions. ‐ For melt elongation by rotary clamps constant, arbitrary ratios of the strain rate components can be applied. Planar elongations of the PIB samples indicate an influence of the width of the molecular mass distribution. More general elongations with a change of the strain rate ratio during the test are of especial interest as is documented by the comparison of the resulting stresses with predictions from different network theories. ‐ In a rheometer for simple elongation at 170°C, recovery after melt extension of the PS/PMMA blends reveals a value of the interfacial tension equal to the one obtained from shear oscillations.
Volume relaxation and related dynamic mechanical property changes during physical aging of poly‐ether‐ether‐ketone (peek)
Authors: D'Amore A. , Pompo A. , Nicolais L. 
Published: March 2011

AbstractNon‐equilibrium glasses, including polymer glasses, spontaneously tend to approach the equilibrium state. The time‐dependent phenomena occurring in glassy polymers below the glass transition are commonly referred to as physical aging. Since the physical aging results primarily in a volume relaxation (or densification), our efforts have been focused on the measurements of the time‐dependent behavior of the specific volume. The dependence of the storage and loss moduli upon aging have been related to the progressive loss of mobility associated with the volume relaxation. A Williams‐Watts type equation has been adopted to model the volume relaxation data at different temperatures, and a numerical procedure has been developed in order to predict the kinetics of volume relaxation subjected to complex thermal histories.
Effect of filler morphology and surface chemistry on the rheological properties of filled polypropylenes
Authors: Adams J. M. , Walters K. 
Published: March 2011

AbstractThe effect of filler size, shape and surface chemistry is investigated for mineral‐filled polypropylene. Viscosity, first normal stress difference and dynamic properties are all considered. It is shown that, other things being equal, viscosity decreases as filler size increases, the filler surface is made hydrophobic or the shape of the filler is changed from ‘blocky’ to ‘platey’. The first normal stress difference is found to be relatively insensitive to such changes.