bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel synthesis of electroconducting polymers from simple monomers with transition metal complex catalysts
Authors: Toshima Naoki
Published: March 2011

Electroconductive polyaromatics or polyarylenes have been successfully prepared by the oxidative polymerization of the corresponding simple monomers over the transition metal complex catalyst. For example, poly(1,4‐phenylene) was prepared from benzene by using oxygen as an oxidant and a copper(I) chloride‐aluminum chloride double complex as the catalyst. The same catalytic system was applied to the preparation of poly(2,5‐pyrrolylene) and poly(2,5‐thienylene) from pyrrole and 2,2′‐bithiophen, respectively. The electrochemical oxidative polymerization was also carried out for the preparation of the poly(1,4‐phenylene) and poly(1,4‐naphthylene) films in the presence of copper(I) chloride and aluminum chloride.
Kinetics of metal exchange reaction of Cu(II)‐poly(vinyl alcohol) complex with Ca(II)‐ethylenediamine‐N,N,N′,N′‐tetraacetic acid in aqueous solution
Authors: Suzuki Tuneo , Shirai Hirofusa , Hojo Nobumasa
Published: March 2011

The kinetics of the metal exchange reaction between the Cu(II)‐poly(vinyl alcohol) complex (Cu(II)‐PVA) and Ca(II)‐ethylenediamine‐N,N,N′,N′‐tetraacetic acid (Ca(II)‐EDTA) were studied by mixing both solutions in a spectrophotometer at pH 9.7–11.0, at μ = 0.10(KNO3) and at 25°C. The reaction is initiated by the formation of unstable Cu(II)‐H‐PVA by the attack of H+ to Cu(II)‐PVA, and while both ligand exchange and metal exchange steps occur, the latter may be rate‐determining. The kinetic expression of this reaction was determined as ‐d[Cu(II)‐PVA]/dt = k[Cu(II)‐PVA] [H+] [PVA]/[Ca(II)‐EDTA], where k = k1 + k′2[H+], k1 = 3.85 × 10−2 sec−1, k2 = k′2 · K−HCu(II)‐H‐PVA 9.59 × 105 1 mol−1 sec−1.
Functionalization of silica (II) ‐ oxidation of cyclohexanes in the presence of functionalized silica complexed by iron and copper
Authors: Kurusu Yasuhiko
Published: March 2011

Silica gel was modified with (N,N‐dimethyl‐3‐ aminopropyl)trimethoxysilane and the functionalized silica catalysts thus prepared complexed with iron and copper to produce FS‐1{Fe},FS‐1{Cu}. 11.2% of methylcyclohexane was oxidized in the presence of oxygen with FS‐1(Fe) at 60°C. 2‐Hydroxymethylcyclohexane was obtained in 59% yield. The structural differences between FS‐1 (Fe)and FS‐1 {Cu} are discussed.
Evidence of polyphenols nitrosation by computer aided ESR spectroscopy
Authors: Marchettini Nadia , Pogni Rebecca , Basosi Riccardo
Published: March 2011

Polyphenols play an important role as model systems in transition metal derivatives for the preparation of macromolecular systems. Among the metal ions ironnitrosyl coordination chemistry has received much attention in the past because of its important role in inorganic and biological processes. In the case of Fe(I)(NO)2 complexes with polyphenols ligands in solution, difficulties in the interpretation of the ESR spectra arise from complicated patterns due to simultaneous presence of different nitrogen nuclei directly bound to the metal ion or due to the presence of equilibria between species under slow exchange conditions. In order to overcome these difficulties the investigations reported here were carried out using computer simulation of ESR spectra combined with selective isotopic substitution of 14NO with 15NO. Resorcinol displays an unexpected nine lines ESR pattern at g=2.018 which can be explained only by considering more than two nitrogen atoms interacting with the unpaired electron delocalized over the metal complex.
Polymers with indane units by cationic polymerization
Authors: Nuyken Oskar , Maier Gerhard , Yang Dazhong , Leitner Michael B.
Published: March 2011

In spite of the difunctionality of the monomers, cationic polymerization of 1,3‐ and 1,4‐diisopropenylbenzene does not lead to branched or cross‐linked products. Instead, soluble polymers are obtained, containing the 1,1,3‐trimethylindane system as repetitive unit along the backbone. These polymers are interesting materials because of their high glass transition temperature (200°C‐250°C) and good thermal stability in air (2% weight loss at 450°C). Although the molar mass of the polyindanes seems to be limited due to a side reaction, it is possible to produce telechelic polyindanes. Substitution of an alkyl side chain onto the isopropenyl groups of 1,4‐diisopropenylbenzene leads to monomers which yield substituted polyindanes with glass transition temperatures as low as 26°C. Such polymers still exhibit good thermal stability: at 340°C a weight loss of only 2% occurs. 1,4‐Diisopropenylbenzene can even be anionically polymerized to linear polymers. In this case, the resulting polymer possesses isopropenyl phenyl side groups, which can be used as initiators for cationic polymerization of isobutene to obtain grafted copolymers.
Carbenium ions, onium ions, and covalent species in the cationic polymerization of alkenes
Authors: Matyjaszewski Krzysztof
Published: March 2011

The importance of exchange reactions between various types of active species present in the cationic polymerization of alkenes is addressed. Reactivities of carbocations, corresponding ion pairs, onium ions, and covalent species are discussed for model systems and in real polymerization. The influence of various parameters on the equilibria between carbenium ions, onium ions, and covalent species is described. Rate constants of the isomerization of active sites are estimated and correlated with polydispersities. General ways to improve control of cationic polymerization of alkenes are discussed.
The role of N‐acyllactam in polymerizations of lactams
Authors: Puffr Rudolf , Stehlíček Jaroslav , Šebenda Jan
Published: March 2011

In anionic, cationic and non‐catalyzed polymerizations of lactams, highlyreactive N‐acyllactams are formed in slow initiation steps. These imides enter then the propagation and termination reactions. All types of lactam polymerizations can be accelerated by an intentional addition of N‐acyllactams or other acylating agents, including the polymerizations where N‐acyllactams are not spontaneously formed. The rate data of the initiation, propagation, transacylation and side reactions and of N‐acyllactam hydrolyses, alcoholyses, acidolyses and aminolyses are surveyed.
Determination of highly resolved particle size distributions in the submicron range by ultracentrifugation
Authors: Mächtle Walter
Published: March 2011

Two methods, the H2O/D2O‐analysis and the Coupling‐Particle‐Size‐Distribution(PSD)‐Technique, to determine the distribution of the density and the sire of sub‐micron particles by means of an ultracentrifuge, are outlined. Either of them base only on Stokes' equations and on Mie's light scattering theory. Because of the possibility to measure seven samples simultaneously and to raise the rotor speed exponentially from 0 to 40,000 rpm, particle diameters from 10 to 3000 nm can be measured at high resolution. The H2O/D2O‐analysis supplies a density distribution and also a size distribution, provided the sample is chemically homogeneous. The Coupling‐PSD‐Technique allows to determine highly resolved size distributions of extremely broad distributed dispersions by only one single run. Several examples applying either method are given.
Size exclusion chromatography of polyelectrolytes with aqueous elution solvents
Authors: Bruessau Rudolf J.
Published: March 2011

Size exclusion chromatography (=SEC) is a widly used method for determining the molecular weight distribution of polymer samples. But using aqueous elution solvents, this method is even today combined with numerous problems, mostly caused by the polyelectrolyte structure of water soluble polymers. Therefore we will firstly give a survey of this special features and discuss preventive measures. From this view then some working rules will be derived with special regard to the devices, columns and calibration standards available today. Finally we will give some remarks about the specific experimental conditions for ultrahigh molecular weight samples.
Characterization of copolymers by high performance liquid chromatography
Authors: Glöckner Gottfried
Published: March 2011

Size exclusion chromatography (SEC) is capable of evaluating the molecular weight distribution (MWD) of a sample. Information about the chemical composition distribution can be gained by gradient high performance liquid chromatography (gradient HPLC), where a poor starting eluent is, in the course of the separation, substituted by another one of increasing elution strength. Both normal‐phase and reversed‐phase systems can be employed. The combination of SEC and gradient HPLC enables chromatographic cross‐fractionation to be performed efficiently.
Determination of persistence lengths and mark‐houwink constants of aromatic polyesters from GPC‐differential viscometric coupling
Authors: Schmitt R. , Bolle B. , Greiner A. , Heitz W.
Published: March 2011

The introduction of lateral substituents and/or twisted biphenylylene units increase the solubility of aromatic para‐linked polyesters. Two polyesters of this type of structure were characterized by gel permeation chromatography (GPC), low angle laser light scattering (LALLS) and viscometry. From the molecular weights and limiting viscosity numbers obtained by universal calibration and LALLS/viscometry the Mark‐Houwink constants and persistence lengths were determined. The values of these parameters indicated that the polyesters can be described as wormlike chains in dilute solution.
Molar mass determination of macromolecular compounds by matrix‐assisted laser desorption ionization mass spectrometry
Authors: Karas Michael , Bahr Ute , Deppe Andreas , Stahl Bernd , Gießmann Ulrich
Published: March 2011

Matrix‐assisted laser desorption ionization is a recently developed new ionization technique which enables macromolecular compounds to be investigated by mass spectrometry. The general features of the technique are described, they have so far mainly been worked out for biopolymers such as proteins. Fast and precise molecular weight determination is possible up to 400,000 Dalton. First examples described in this paper indicate that the technique also holds great promise for the investigation of synthetic polymers.
Molar mass determination by end group analysis ‐ amino group determination in aliphatic and partially aromatic polyamides with 1‐fluoro‐2,4‐dinitrobenzene in benzyl alcohol
Authors: Rossbach Volker , Leumer Gerhard , Böhme Sigrid
Published: March 2011

End group analysis is the most important absolute method of obtaining number‐average molar mass values for polymers of the step‐growth polymerization type. A great number of methods are available which primarily differ in the detection of the end group concerned. Special chemical methods based on the formation of covalent derivatives of the end groups (e.g. introduction of UV/VIS chromophores) are important if there is a need to demonstrate, with the aid of gel permeation chromatography, that damage to the polymer (e.g. onset of cross‐linking) has occurred.

In the case of fibre‐forming polycondensation products, the applicability of end group analysis is often restricted by the lack of suitable reagents and solvents. This is also true of the determination of amino end groups in polyamides by means of 1‐fluoro‐2,4‐dinitrobenzene, as is already contained in the German Standards specification (DIN 54 274) ‐ albeit only for polyamide 6 and 6,6. This contribution describes a modified version of the 1‐fluoro‐2,4‐dinitrobenzene method. The analytical principle and practical procedure correspond to those of DIN 54 274, but the solvent used for the reaction with the reagent is benzyl alcohol, and that for the photometric evaluation is 1,1,1,3,3,3‐hexafluoro‐2‐propanol. The scope of the method is thus increased. Examples of applications for this method are commercial products based on aliphatic polyamides (6; 11; 12; 6,6; 6, 12), partially aromatic polyamides (2,4,4‐trimethylhexamethylenediamine, terephthalic acid; copolyamides with bis‐(4‐aminocyclohexyl)propane(2), isophthalic acid, ω‐aminododecanoic acid) and multicomponent systems with the abovementioned polyamides (bicomponent fibres, blends). It is shown that large differences may arise between the value determined by titration and the actual amino end group content. In addition, the presence of secondary amino groups can be demonstrated in polyamides of the Trogamid T type.
Neutron reflection studies at polymer‐polymer interfaces
Authors: Fernandez M. L. , Higgins J. S. , Penfold J.
Published: March 2011

The application of the neutron reflectivity technique to the study of polymer‐polymer interfaces is described and several examples given. The high resolution of the technique allows the details of the interface during early stages of mixing to be resolved for a partially miscible blend. The results are discussed in terms of recent theories.
Thin film order of symmetric diblock copolymers
Authors: Russell Thomas P. , Menelle Alain , Anastasiadis Spiros H. , Satija Sushil K. , Majkrzak Charles F.
Published: March 2011

The ordering in thin films of symmetric diblock copolymers of polystyrene and poly(methyl methacrylate) has been investigated by neutron reflectivity as a function of film thickness and temperature. The order‐disorder transition in the thin films was found to lose its first order character in that the transition occurs in a continuous manner without the correlation length becoming infinite. In addition, a transition from a partially to fully ordered state was observed which was fully reversible. This transition depended in a power law manner on the film thickness and extrapolates to the bulk order‐disorder transition temperature for thick films.
Surface modification of polymers by photoinitiated graft polymerization
Authors: Rånby Bengt
Published: March 2011

Two methods for modification of polymer surfaces by photoinitiated grafting have been developed and applied to films and fibers of synthetic polymers, e.g. polyethylene and polypropylene with acrylic monomers. In the batch process the substrate is enclosed in a cell containing initiator and monomer vapor. UV light through a quartz window initiates the grafting reaction by exciting the initiator (e.g. benzophenone). The grafting reaction is slow (1 to 3 min) due to the inefficient transfer of initiator and monomer through vapor phase. In the continuous process the substrate is presoaked in a solution of initiator and monomer and then drawn into a reactor “on line” where the substrate is irradiated by UV light through a quartz window. The grafting takes place in the very thin surface layer of solution on the substrate. The grafting efficiency is high (70–80% of the polymer formed is grafted) and the process is rapid (5–15 s due to the efficient transfer of initiator and monomer through the liquid phase. The continuous surface grafting process is promising for industrial applications.
Kinetic behavior of propagating radical in bulk polymerization of styrene
Authors: Shen Jia‐Cong , Wang Guo‐Bin , Zheng Ying‐Guang , Yang Mei‐Lin
Published: March 2011

High resolution ESR spectra of polystyrene radical at various conversion in the bulk polymerization have been determined. The propagation and termination rate coefficients during the whole process of polymerization were evaluated from the conversion and the propagating radical concentration determined by ESR. It was found that the propagating radical has two stable conformations. The reduction of the radical activity with the conversion is partly resulting from the wrapping effect which is due to the far slower segment relaxation and the very rapid propagation.
Some newer concepts on ethylene/α‐olefin copolymerization on heterogeneous Ziegler‐Natta catalysts
Authors: Wang Jian‐Guo , Zhang Wen‐Bin , Huang Bao‐Tong
Published: March 2011

Unsteady diffusion kinetics, recently advanced by this laboratory, is applied to the examination of some polymerization and molecular chain structure problems. Hitherto deemed “anomalous” phenomena, such as the faster rate of copolymerization of ethylene/α‐olefin than the homopolymerization of ethylene and the enrichment in the incorporation of a higher α‐olefin in its copolymerization with ethylene by a lower α‐olefin, are reasonably explained by unsteady diffusion of monomers. Molecular chain structure of copolymers, such as compositional heterogeneity and its dependence on comonomer incorporation originates from the difference in diffusion coefficients of the monomers. A copolymer composition equation taking into consideration the unsteady diffusion was developed. In cases where simulated curves were compared with experimental curves, good agreements were found.
Ring‐opening metathesis polymerization of exo‐dicyclopentadiene: Reversible crosslinking by a metathesis catalyst
Authors: Fisher Richard A. , Grubbs Robert H.
Published: March 2011

exo‐Dicyclopentadiene has been polymerized by several well characterized, single‐component metathesis catalysts to provide soluble, linear, poly exo‐dicyclopentadiene. Under the best circumstances the polymerizations proceed in a living manner. The crosslinking of polymer chains which can occur under high monomer concentration has been investigated and determined to result from the secondary metathesis of the cyclopentene substituent.
Molecular engineering of discotic liquid crystals
Authors: Bauer Stefan , Plesnivy Thomas , Ringsdorf Helmut , Schuhmacher Peter
Published: March 2011

The game of molecular engineering of LC systems via combination of molecular architecture and functionalization of mesogens has opened interesting perspectives in the field of liquid crystals. This contribution summarizes different examples of this interplay using discotic liquid crystals as its basis.
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

Polymers 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

Semi‐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

A 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

Polymer 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

Previously, 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

Molecular 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

Polymer 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

We 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

Classical 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

This 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

The 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

Incompletely‐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

Stereospecific, 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

The 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

The 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

Some 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

Living 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

Several 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

Six 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

Initiators 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

The 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

A 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

Uniaxial 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

Experimental 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

Non‐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

The 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.
Mass transport and mechanical properties of solid polymers
Authors: Doghieri Ferruccio , Sarti Giulio C.
Published: March 2011

A general mathematical formulation is proposed for the description of the diffusion of low molecular weight species into a polymer matrix, in the presence of significant stress and deformation fields. The model is based on the usual momentum and mass balance equations; a crucial point is that it makes use of constitutive equations for the stress and for the diffusive mass flux which are not chosen independently of each other since they must obey precise thermodynamic restrictions; the latter are found in rather general terms.
Chemical transformations and phase transitions in polymer rheology and technology
Authors: Malkin A. Ya. , Kulichikhin S.G
Published: March 2011

Fundamental rheokinetic effects observed in processes of linear polymerization and three‐dimensional oligomer curing are discussed. It was shown that changes in rheological properties during linear polymerization can be described by relationships based on treating a reactive mass as a polymer solution, if a newly formed polymer is soluble in reactive medium. Phase separation limits this approach and leads to some new rheological consequences such as change in the rate of viscosity growth (in some cases viscosity can even decrease in the course of polymerization). Shearing influences temperature of a phase transition and kinetics of chemical reaction if it proceeds in heterogeneous conditions. The same phenomena were also observed for oligomer curing which can occur in heterogeneous manner with microgelation and formation of colloid particles of a new phase before the gelation of a system as a whole.
Phase behavior and structure in mesogen containing polyurethanes
Authors: Macknight W.J. , Papadimitrakopoulos F.
Published: March 2011

The mesophase to crystal phase transition observed upon heating the monotropic liquid crystal polyurethane (2,6‐LCPU‐6), based on the mesogenic biphenol 4,4′‐bis(6‐hydroxyhexoxy)biphenyl (BHHBP) and 2,6‐toluenediisocyanate (2,6‐TDI), has been investigated by differential scanning calorimetry (DSC), wide angle x‐ray scattering (WAXS) and infrared (IR) spectroscopy. Hexafluoroisopropanol (HFIP) fast solvent‐evaporation casting resulted in 2,6‐LCPU‐6 thin films with a glassy mesophase morphology. The mesophase to crystal exothermic transition has been observed by DSC between 130 and 140°C, depending on sample preparation. It is accompanied by a substantial increase of H‐bonding between urethane C=O and N‐H, as observed by IR. Curve fitting analysis of the conformationally sensitive amide I region revealed three bands; ordered H‐bonded carbonyl groups, disordered H‐bonded carbonyl groups, and “free” carbonyl groups. The prime feature of the 130°C transition is the substantial increase of ordered H‐bonded carbonyl groups at the expense of disordered H‐bonded carbonyl groups. Crystal melting occurs between 180 and 210°C and is accompanied by the complete disappearance of the ordered H‐bonded peak along with substantial changes in the frequency and width at half‐height of the disordered H‐bonded peak
Relaxation processes in oriented liquid crystalline polymers
Authors: Ward I.M.
Published: March 2011

A review is presented of research on oriented thermotropic liquid crystalline polymers undertaken at Leeds University. A range of main‐chain polyesters has been studied based on 1,4‐hydroxybenzoic acid and 2,6‐hydroxynaphthoic acid as the primary monomers. By using a combination of dynamic mechanical, dielectric and NMR measurements insight has been gained into the molecular motions associated with the three principal relaxation processes. The behaviour in tension, for stresses parallel and perpendicular to the principal orientation direction, has been related to that in shear by use of mechanical models.
Fast switching ferroelectric liquid‐crystalline polymers
Authors: Scherowsky Günter
Published: March 2011

The principles of ferroelectricity, especially in liquid crystals (FLC) and polymers, are briefly presented. In a liquid‐crystalline side chain polyacrylate electro‐optical switching with response times of 200–400 μs was measured. Besides the ferroelectric switching an even shorter electroclinic switching process was detected.

The influence of the spacer length and the molecular weight on the ferroelectric properties is discussed. The kind and number of chiral centers and their location in the side group strongly affects the electrooptical properties. In one polymer a change of the optical contrast caused by a sign reversal of the spontaneous polarization was found. In another FLC polymer three switching states (antiferroelectric behaviour) were detected. With coloured and fluorescent FLC polymers, obtained by mixing or by copolymerization new promising applications in electrooptical devices are expected.
Morphology control in polymeric multiphase systems with block copolymers and structured latexes
Authors: Riess Gérard
Published: March 2011

Some application possibilities of block copolymers for the morphology control in polymeric multiphase systems are reviewed. The microdomain formation of block copolymers in the solid state is illustrated in the case of functionalized block copolymers and for interpolymer complexes. The preparation of “hairy latex” by emulsion polymerization in the presence of hydrophilic‐hydrophobic block copolymers is shown in connection with their applications in the controlled agglomeration process of latexes and for the preparation of polymer particles having microvoids. The surface activity of block copolymers in polymeric oil‐in‐oil systems is illustrated for silicone oil filled polymers. These materials have a low kinetic friction coefficient and act as reservoir systems with the lubricant incorporated in the polymer matrix.
Microscopic structures in phase inversion membranes: The use of polymer blends for membrane formation by immersion precipitation
Authors: Boom R.M. , Rolevink H.W.W. , Boomgaard Th. van den , Smolders C.A.
Published: March 2011

Membrane formation by immersion precipitation has been investigated for two different polymer blends: poly(ether sulfone) / poly(vinyl pyrrolidone), a common blend for obtaining high performance UF or MF membranes, and poly(ether sulfone) / poly(styrene). The latter blend contains a polymer as additive that is not soluble in the precipitant used. It yields structures that confirm the fundamental basis of a model describing the formation of membranes from polymer blends. It appears that the membrane formation is dominated by the diffusional behaviour of the polymers relative to each other.

A general classification of membrane structures from a polymer blend is presented; it is established that spinodal decomposition may well be responsible for the open porous structures usually found when using a polymer blend such as poly(ether sulfone) and poly(vinyl pyrrolidone).