bluuebunny/crossref_metadata_2025_split huggingface dataset:
Efficient epoxidation of terminal and internal alkenes using t‐butylhydroperoxide catalysed by polybenzimidazole‐supported Mo(VI).(PBI.Mo)
Authors: Olason Gunnar , Sherrington David C. 
Published: March 2011

AbstractA polybenzimidazole‐supported Mo complex (PBI.Mo) has been prepared by a method already reported. Extensive investigation of digestion procedures has shown a dry‐ashing method using NaNO3/HNO3 (conc.) at 560°C to be an optimal method for preparing samples for Mo analysis by atomic absorption spectrophotometric methodology. Mo loadings in the range 1.32–0.62 mmol Mo g−1 polymer were demonstrated. PBI.Mo has been used as a heterogeneous catalyst in the epoxidation of cyclohexene, methylene‐cyclohexane, 4‐vinyl cyclohexene, styrene, 1,3‐pentadiene and allyl chloride, bromide and alcohol using t‐butylhydroperoxide as the oxidant. The catalyst is very effective for the first four substrates, somewhat less active than soluble MoO2acac2, but providing final yields and purity of products generally better than using MoO2acac2. The 1,3‐pentadiene displays an overall conversion of ∼35% with a distribution of the four possible monoepoxide isomers similar to that obtained with MoO2acac2 as catalyst. The allylic substrates showed poor conversion probably as a result of secondary (oligomerisation) reactions involving the epoxide products. Running the epoxidations for extended periods in air allows in situ generation of alkyl hydroperoxides in the case of cyclohexene and 4‐vinylcyclohexene and these are then effective internal oxidants for further Mo catalysed epoxidation of these alkenes. When run under anaerobic conditions the reactions are very clean with no evidence of any free radical processes contributing. In all cases Mo leaching is minimal. Good activity is seen in the recycling of PBI.Mo in the case of styrene and 1,3‐pentadiene, although with cyclohexene and 4‐vinylcyclohexene steady deactivation is seen, probably as a result of catalyst fouling. Thermogravimetric analyses suggest that it might be possible to burn off the foulant without destroying the catalyst.
The propagating species in living cationic polymerization: Living nature and steric structure of polymers
Authors: Kanaoka Shokyoku , Higashimura Toshinobu , Sawamoto Mitsuo 
Published: March 2011

AbstractThis paper discusses the nature of the living growing species in cationic polymerization from the viewpoint of the steric structure of poly(isobutyl vinyl ether) [poly(IBVE)]. At −78 °C, living polymerization was induced with the HCl‐IBVE adduct (1)/ZnCl2 system in a EtNO2/CH2Cl2 mixture, whereas similar systems with EtAlCl2 led to conventional cationic polymerization. In this polar medium, both systems gave polymers with very similar and low isotacticity (meso ≈ 56%), indicating that the propagating reaction is mediated by free ions. Thus, regardless of solvent polarity, or involvement of free ions or ion pairs, living cationic polymerization requires a suitably nucleophilic counteranion. As model reactions of the growing species, 1/ZnCl2 and 1/EtAlCl2 were directly analyzed by 1H NMR spectroscopy.
Model block copolymers with complex architecture
Authors: Hadjichristidis Nikos , Poulos Yiannis , Avgeropoulos Apostolus 
Published: March 2011

AbstractThe synthesis of non linear block copolymers of the type (BA)2B (3‐miktoarm star copolymer), (BA)3B (4‐miktoarm star copolymer), (BA)3B(AB)3 (super H‐shaped), B2AB2 (H‐shaped) and (B,A)A(B,A) (π‐shaped), where A is polyisoprene 1,4 and B is polystyrene was performed using anionic polymerization techniques and suitable chlorosilane chemistry. Characterization data showed that the samples are molecularly and compositionally homogeneous. TEM, SAXS and SANS were used to study the microphase behavior of the copolymers. For all samples, the results were analyzed in the frame of the theoretical predictions given by Milner and taking into account the results from previous studies on the A2B and A3B miktoarm star copolymers.
Styrolux+ and styroflex+ ‐ from transparent high impact polystyrene to new thermoplastic elastomers: Syntheses, applications and blends with other styrene based polymers
Authors: Knoll Konrad , Nießner Norbert 
Published: March 2011

AbstractStyrolux and Styroflex are styrene and butadiene based block copolymers prepared by butyllithium initiated anionic polymerization. Styrolux is a transparent, tough and stiff thermoplastic material for high speed processing. Its specially designed molecular structure allows homogeneous mixing with general purpose polystyrene maintaining the transparency. Styroflex is a newly commercialized product with the mechanical behavior of a thermoplastic elastomer, e.g. low modulus and yield strength, high elongation and excellent recovery. High transparency and thermal stability give the competitive edge over conventional styrene‐butadiene elastomers. Styroflex, Styrolux and general purpose polystyrene form a unit construction system e.g. for transparent film materials and injection molded parts with fine‐tunable hardness and toughness.
Stereoregular polymerization of methyl methacrylate initiated by dialkylmagnesium‐quaternary ammonium salt adducts
Authors: Novakov Christo P. , Tsvetanov Christo B. 
Published: March 2011

AbstractThe anionic polymerization of methyl methacrylate was carried out in the presence of Bu2Mg/quaternary ammonium salts in toluene at 0°C. It was found that the bulkiness and shape of the salt strongly affect the polydispersity and tacticity of the resulting polymers. Molecular weight distribution is in the range 1.3 <M>w/Mn 4.7.>Tetrahexylammonium chloride causes the most drastic change in the tacticity. The structure of R4MNX, as well as the nature of the metal and the t‐BuOLi ligands produce a radical effect on the polymer properties. These initiator components perform their role by changing the microenvironment of the ligated and aggregated growing chains. The results clearly reveal the great potential of the mixed associate or mixed base as strong stereospecific initiator systems.
Ylide mediated polymerization of methacrylates and acrylates in the presence of tetraphenylphosphonium cation 3
Authors: Zagala Angela P. , Dimov Dimo , Hogen‐Esch Thieo E. 
Published: March 2011

AbstractTriphenylmethide tetraphenylphosphonium (TPM, TPP) or methylisobutyrate tetraphenylphosphonium (MIB, TPP) formed by ion exchange reactions of TPP chloride(TPPCl) with the TPM or MB potassium salts in THF, initiate the living polymerization of MMA producing PMMA's with narrow MW distributions (below 1.3) at ambient temperatures.
Optically active polymers of 3‐alkylmalic acids: Contribution of the bioconversion for diversifying the chiral precursors
Authors: Bear Marie‐Maud , Langlois Valérie , Masure Michèle , Guerin Philippe 
Published: March 2011

AbstractThe need for new optically active monomers and polymers is conducive to the setting up of stereospecific synthesis routes starting from chiral precursors. The biomass can be considered as a major source for extracting such biomolecules aimed at chemoenzymatic transformation and further polymerization. Due to its versatility, ß‐methylaspartate ammonia‐lyase, from cell‐free extracts of Clostridium tetanomorphum, has been used in the bioconversion of alkylfumarates into optically active pure 3‐alkylaspartic acids with alkyl=methyl, ethyl, isopropyl. These amino acids have been transformed in several steps into optically active benzyl 3‐alkylmalolactonates leading to semi‐crystalline polyesters. 3‐Methylaspartic acid includes two chiral centers and the racemic compound containing the four stereoisomers can be prepared by a multiple step synthesis. The ability of ß‐methylaspartase to catalyse both syn‐ and anti‐elimination of ammonia from natural 3‐methylaspartic acid has been expressed to retain one stereoisomer and this bioconversion is a preparative method for obtaining unnatural stereoisomers. Moreover, the catalytic hydrogenolysis of the benzyl α,ß‐substituted ß‐lactone yields stable 3‐alkylmalolactonic acid which can be coupled with functional alcohols and copolymerized. At last the introduction of (2S)‐3,3‐dimethyl‐2‐butanol, using Rhodotorula glutinis as microorganism in a biological synthesis step, as chiral ester pendant group, has conducted to optically active polyesters with very high melting transition temperatures. The combination of bioconversion and chemical synthesis is a very useful tool for building hydrolyzable functionalized polyesters required for temporary applications.
Copolyethers with controlled structure: Mechanism of formation and microstructure
Authors: Bednarek Melania , Kubisa Przemyslaw 
Published: March 2011

AbstractCationic copolymerization of 3‐membered cyclic ethers (oxiranes) with 5‐membered cyclic ether (tetrahydrofuran) leads to linear copolyethers containing significant amount of cyclic fraction. When the copolymerization is conducted in the presence of diols, telechelic copolymers are formed by the process in which oxirane is incorporated into copolymer irreversibly by Activated Monomer mechanism, while tetrahydrofuran is incorporated reversibly by Active Chain End mechanism. Thus both kinetic and thermodynamic factors can be used to control the rate of the incorporation of comonomers. Studies of the kinetics of the competing reactions leading to formation of copolymer, studies of copolymer microstructure by 13C‐NMR and analysis of the composition of the cyclic fraction, led to the correlation between the copolymer microstructure and the amount of cyclic fraction formed. The dependence of the cyclic fraction content on the reaction conditions was therefore explained.
Cationic polymerization of aliphatic cyclocarbonates
Authors: Kricheldorf Hans R. , Weegen‐Schulz Bettina , Jenssen Jörg 
Published: March 2011

AbstractNumerous polymerizations of trimethylene carbonate (TMC) and neo‐pentylene carbonate (NPC) were conducted in solution using methyl triflate as initiator. The polymerization mechanism was elucidated and rapid backbiting degradation along with the formation of ether groups was detected. When strong Lewis acids such as BF3, SnCl4 or SnBn4 were used as initiators, much higher molecular weights were obtained, but the resulting polycarbonates still contained ether groups. BuSnCl3 was found to be the most useful initiator yielding high molecular weight polycarbonates free of ether groups. However, in this case it is not clear, if a cationic mechanism or a coordination‐insertion mechanism is involved.
Initiation of cationic polymerization by photoinduced electron transfer
Authors: Yagci Yusuf 
Published: March 2011

AbstractThe objective of this paper is to discuss: (i) the general approaches to the initiation of cationic polymerization by photinduced electron transfer reactions (ii) the use of photoinduced electron transfer reactions for block copolymer synthesis. For the first, it is concluded that three general methods are currently available which involve reduction of onium salts by (a) photogenerated radicals, (b) photoexcited sensitizers or (c) electron donor compounds in charge transfer complexes. According to this view, a variety of initiating systems are discussed. For the second, recent developments on the application of photoinduced electron transfer reactions to the synthesis of block copolymer of monomers polymerizable with different mechanisms are presented.
Stepwise pyrolysis for recycling of plastic mixtures
Authors: Bockhorn Henning , Hornung Andreas , Hornung Ursel 
Published: March 2011

AbstractFor chemical recycling of plastic refuses a cascade of cycled‐spheres reactors has been developed combining separation and decomposition of polymer mixtures by stepwise pyrolysis at moderate temperatures. In low‐temperature pyrolysis, mixtures of poly(vinyl chloride), polystyrene and polyethylene or polystyrene, polyamide 6 and polyethylene have been separated into hydrogen chloride, styrene and polyamide 6 and aliphatic compounds from polyethylene decomposition. Compared with the low‐temperature pyrolysis of the single components, some interactions between the polymers are found when pyrolyzing mixtures. Some mechanistic aspects of these interactions are discussed.
Energy recovery
Authors: Akehata Takashi 
Published: March 2011

AbstractIncinerators in use, power‐generating incinerators and pollution‐prevention methods in energy recovery from waste incineration are briefly reviewed. Results of a recent energy recovery experiment under real operating conditions are described: The addition of waste plastic to municipal solid waste brought about more stable combustion and no increase in the concentrations of dioxins. It is remarked that energy recovery through incineration is probably the best currently available means of disposal for plastics which are too difficult to recycle.
Several hypotheses and regularities in the chemistry of highly organized substances
Authors: Aleskowskii Valentin 
Published: March 2011

AbstractIt was found that level of structural substance organization, amount of embodied information, and consequently, substance properties are determined by the degree of the substance polyatomicity. This substantiates the fact that both covalent and noncovalent supermolecular individuals, which are the matter of the chemistry of highly organized compounds, fulfil the same general chemical but different specific regularities. Among the former there is extended Prust's law, which was re‐established by the fact of production and identification of solids with the constant composition. It was also found that formation of any individuals is due to production and realization of a certain amount of information sufficient for their structural organization. Chemical modeling of biosynthesis was chosen as the common approach for developing the processes of production and realization of information. It was shown that well‐known processes of chemical buildup (CB) and molecular self‐assembling (MSA) are those chemical models. The application of announced regularities has opened up a new perspective to create chemical‐information technology (CIT), allowing us to produce material resources making no perturbations in the planet ecosystem.
Augmented cylindrical wave method in the theory of electronic structure of quantum nanowires
Authors: D'yachkov Pavel N. , Kepp Oleg M. , Nikolaev Alexander V. 
Published: March 2011

AbstractA computational method for the band structure of nanowires having approximately cylindrical symmetry is developed. The effective one‐electron potential is supposed to have spherical symmetry in the region of the atomic centres and is assumed to be constant in the interstitial region. The corresponding electronic density is supposed to be localised inside the region of cylindrical shape. The base wave functions are obtained by sewing together solutions of the Schrödinger equation for an electron in the empty cylinder (cylindrical waves) with spherically symmetrical solutions for the muffin‐tin spheres. Under the condition of the continuity of the base functions and their first derivatives overlap integrals and Hamiltonian matrix elements are obtained. Dispersion curves and electronic densities of states for chains of transition metals and those of nanowires from metals from K to Zn are calculated.
Study of the DNA packing caused by charged compounds of different nature in solution
Authors: Kasyanenko Nina A. , Zanina Anna V. , Plotnikova Ludmila V. , Simonenkov Andrei A. , Defrenne Stephanie , Nazarova Olga V. , Panarin Evgenii F. 
Published: March 2011

AbstractA comparative study of DNA interaction with different counterions in solution has been conducted by the following methods: flow birefringence (FB), low‐gradient viscometry, circular dichroism (CD), and UV‐spectroscopy. The influence of counterions on the persistence length and polyelectrolyte swelling of DNA has been investigated. The process of DNA packing during the interaction with trivalent ions in solution has been studied, as well as the influence of Mn2+ on the binding of trivalent ions with DNA.
Cluster carbonyls of Os, Fe and Fe‐Rh on oxide supports: Synthesis and properties
Authors: Kuznetsov Boris N. , Kovalchuk Vladimir I. , Chesnokov Nikolai V. , Mikova Nadezhda M. , Naimushina Lilia V. 
Published: March 2011

AbstractSurface nano‐size structures have been obtained by supporting on oxide supports (SiO2, MgO, Al2O3) some cluster carbonyls of Os, Fe, Fe‐Rh and by their following thermal conversions. Surface species were characterized by IR‐spectroscopy, high‐resolution TEM, XPS, Mössbauer spectroscopy and temperature‐programmed desorption technique. Their catalytic properties was studied in CO hydrogenation reaction.
Organized molecular assemblies: Creation and investigation of their functional properties
Authors: Repinsky Sergey M. 
Published: March 2011

AbstractOne of the most important problems of modern chemistry, both preparative and theoretical one, is the creation of organized atomic ‐ molecular assemblies i.e., atoms and molecules bound in a definite manner and interacting with each other, as a jointly, they become able to behave like an assembly, a single mechanism, to perform some functions, for example, to recognize separate molecules of environment (receptors), to transform an electromagnetic signal to electric field (photosynthetic), to memorize (memory cell), catalyze function and others.The chemistry of preceding period had been developing as the science of properties and transformations of individual compounds and substances. At present the progress in the notion of the nature of chemical bonds, a new level of understanding of the chemical reactions mechanism, the knowledge of the regularities of nonstationary states in reactive media and the data on the at processes interfaces have determined the up to day problem of organized molecular assemblies with a required functionality.Thermal oxidation of silicon crystals which is the key process in the technology of integral circuits production can be represented, in its main features, by the mechanism of semiconductor dissolving in the condensed phase. A characteristic feature of silicon oxidation is that the silicon activation energy of the limiting stage is lower than that of the formation of gas ‐ phase monoxide, difference being the energy of siloxane net reorganization in silicon dioxide. The analysis shows that within the row of possible systems semiconductor ‐ dielectric, it is silicon ‐ silicon dioxide that is distinguished by a maximum self ‐ organizing effect. This is one of the main reasons why only silicon could be chosen among large number of semiconductor substances for use in the technology of integral circuits.A molecular system of amphiphilic long ‐ chain molecules, obtained according to the Langmuir ‐ Blodgett method is an example of simplest assembly on the basis of which the elements of gas sensors can be prepared, as well as the systems of quantum dots, the objects of the low ‐ dimension physics.We have investigated assemblies constructed from multimolecular compositions using the Langmuir ‐ Blodgett technique and thin ‐ layer systems based on glassy and amorphous silica films with fragments of organic molecules introduced into the matrix.Molecular engineering is a new level of the modern preparative chemistry; moreover, it is a system of concepts introducing a new culture in technology. In this sense, it is most important to realize the evolution principle in the strategy of science research.
Optimisation of photo‐induced geometric isomerisation of azobenzene derivatives in dye‐doped polymer films for enhanced photo‐induced poling
Authors: Mitchell G. R. , King N. R. 
Published: March 2011

AbstractPhoto‐induced geometric isomerisation of azobenzene based chromophores can be utilised in a variety of molecular control procedures including photo‐induced poling. In such processes additional mobility is imparted to chromophores trapped in a glassy matrix through the photo‐induced trans‐cis‐trans cycle. We show that by using selected narrow wavelength bands of light to induce the isomerisation cycle during photo‐induced poling, enhanced levels of polar order can be obtained in comparison to those obtained with monochromatic light. We attribute this to an increase in the fraction of chromophores which undergo isomerisation via an inversion mechanism. As a result, a higher proportion of the chromophores are able to participate in the photo‐induced poling process since the free volume for isomerisation is reduced from that required for the rotation mechanism.
Complex formation through heterogeneous nucleation of thermoreversible gelation
Authors: Guenet Jean‐Michel , Lopez Daniel 
Published: March 2011

AbstractThe preparation method and the molecular structure of a composite material consisting of a ternary system polymer/bicoppercomplex/solvent are presented. The properties of each binary system are exposed first. The polymer solutions produce thermoreversible gels while the bicopper organic complex forms a randomly‐dispersed, self‐assembling structure in organic solvents. It is shown that, in a common solvent, the bicopper complex acts as a nucleation agent for the gelation of the polymer (heterogeneous nucleation). As a result, bicopper complex filaments are encapsulated in a polymer matrix.
NMR approach to kinetics of polymer ordering in polyacrylonitrile solutions and acrylonitrile‐sodium methallylsulfonate copolymer solutions: Solution‐concentration and polymer‐tacticity effect
Authors: Margulies Monique Marie , Viallat Annie , Addad Jean‐Pierre Cohen 
Published: March 2011

AbstractPartial crystallinity of polyacrylonitrile and acrylonitrile‐sodium methallylsulfonate copolymer is detected by X‐ray diffraction in dimethyl formamide and glycerol‐dimethyl formamide solutions in the range of polymer concentration (0.14, 0.325 mol/mol). Kinetics of isothermal ordering are followed by NMR for various temperatures, polymer concentration of the solutions and polymer tacticities. The rate of polymer ordering increases upon either a decrease of the temperature, an increase of the polymer concentration or an increase of the percentage of isotactic triads. Mandelkern's model of isothermal polymer crystallisation is applied to estimate the size of critical crystalline nuclei. Assuming that crystallites growth is negligible along polymer chain axis, one can deduce the maximal size of crystallites along this axis. The size of the crystallites perpendicularly to polymer chain axis is evaluated by X‐ray diffraction. It is found to be of the order of 100 Å.
Polymerisation of intercalated solvents in gels; An attempt to obtain molecular blending
Authors: Corstjens Tosca , Rastogi Sanjay , Lemstra Piet 
Published: March 2011

AbstractRecent studies performed on gels like syndiotactic polystyrene/benzylmethacrylate and poly‐benzyl‐L‐glutamate/benzylmethacrylate indicate that the solvent molecules can be intercalated between or within the helices of the polymer. The present paper describes the UV polymerisation of these intercalated solvents. It was found that for both systems the solvent stays intercalated between the helices after polymerisation. This method can therefore be used to blend two immiscible polymers on a molecular scale.
Chemical separations by nanoporous crystalline samples of syndiotactic polystyrene
Authors: Guerra Gaetano , Milano Giuseppe , Venditto Vincenzo , Loffredo Fausta , De Ballesteros Odda Ruiz , Cavallo Luigi , De Rosa Claudio 
Published: March 2011

AbstractChemical separations based on absorption phenomena into syndiotactic polystyrene samples including a nanoporous crystalline phase are described. These separation phenomena are due to the presence into the crystalline phase of cavities whose size and shape have been studied through sorption experiments relative to linear hydrocarbons and through calculation procedures relative to the available crystalline structures of different polymorphic and clathrate forms of syndiotactic polystyrene.