bluuebunny/crossref_metadata_2025_split huggingface dataset:
Absolute size exclusion chromatography. Part 2. Calculation of molecular weight averages
Authors: Sorokin Isidoro H. , Andreetta Héctor A. , Figini Rubén V. 
Published: March 2011

AbstractAn absolute method to obtain molecular weight averages is theoretically proved and experimentally applied to size exclusion chromatographic data. The method is based on stoichiometric relationships and uses labelled polymer molecules.
Optimization of continuous polymerization reactors: Start‐up and change of specification
Authors: Farber Jorge N. , Laurence Robert L. 
Published: March 2011

AbstractOptimal policies for the control of large disturbances (start up and change of specification problems) in continuous polymerization reactors are determined numerically and compared. Several algorithms are implemented for the solution of two‐point boundary value problems characterized by stiff systems and singular controls. The performance of different policies and solution methods is evaluated.
Complexes of Lewis acids in the cationic polymerization of olefins
Authors: Halaška V. , Marek M. , Pecka J. 
Published: March 2011

AbstractFindings concerning the origin of electron donor‐acceptor complexes between olefinic hydrocarbons and chosen Lewis acids supplemented by new results are summarized. The important characteristics reported here are stoichiometric ratios of complex formation determined by the variation and titration methods, equilibrium constants and the thermodynamic parameters AG, AH and AS derived from them. Attention has been devoted to the characterization of frontier orbitals of olefins and Lewis acids using ionization potentials, half‐wave polarographic oxidation potentials, electron affinities and half‐wave polarographic reduction potentials. The aim consists in a quantitative characterization of redox processes which occur in elemental initiation reactions. The final evaluation of the data obtained has confirmed that the complexes involved in this case are weak and behave in accordance with the Mulliken theory.
Living cationic polymerization of vinyl monomers: Mechanism and synthesis of new polymers
Authors: Sawamoto Mitsuo , Higashimura Toshinobu 
Published: March 2011

AbstractThis paper reviews the recent progress in our research on the living cationic polymerization of vinyl compounds by the hydrogen iodide/iodine (HI/I2) initiating system, with emphasis on its scope, mechanism, and applications to new polymer synthesis. The scope of the living cationic polymerization has been expanded to include vinyl ethers, propenyl ethers, unsaturated cyclic ethers, and styrene derivatives as monomers. The initiation/propagation mechanism was discussed on the basis of recent direct analysis on the living system by NMR and UV/visible spectroscopy. The proposed mechanism involves a quantitative formation of Hl‐vinyl ether adduct [CH3‐CH(OR)‐I; l] that is by itself incapable of initiating polymerization. In the presence of iodine, however, the CH‐I bond of l is electrophilically activated by iodine and living propagation occurs via the insertion of vinyl ether to the activated CH‐I bond. Such living polymerizations were found to proceed in not only nonpolar but polar solvents (CH2Cl2) as well. Quenching the living end with amines gave polymers capped with an amino group that in turn enabled us to determine the living end concentration. Applications of the HI/I2‐initiated living process to the synthesis of new bifunctional and block polymers were also described.
Cationic polymerization of vinyl ethers as synthetic path to diphylic polymers and potential complexants
Authors: Skorokhodov Sergei S. 
Published: March 2011

AbstractThe polymers of universal solubility like dimethyl ether of ethylene glycol and dioxane are synthesised by cationic polymerization of cis‐1,2‐dimethoxyethylene and p‐dioxene. Some specific features of polymerization, going on long‐lived active centers, are observed. In the case of polymerization of cis‐1,2‐dimethoxyethylene, conducted under usual conditions, the possibility of obtaining polymers with molecular weights as high as 106 and M̄w/M̄N<1.5 is shown. Improved procedures of cyclopolymerization of divinyl ethers of mono‐, di‐, and triethylene glycols are described. Some solution properties of polymers obtained, including conformational transitions and metal ion complexing, are discussed.
Coordination polymerization of ω‐alkenoates and ω‐epoxyalkanoates
Authors: Liping Hu , Vogl Otto 
Published: March 2011

AbstractAs functional polymers have become more and more used, the need for a general synthesis of addition polymers with functional groups became greatly important. We have achieved the polymerization of ω‐alkenoates with coordination initiators of the Ziegler‐Natta initiation type using titanium trichloride‐based transition metal initiators modified with dialkylaluminum chloride. To accomplish this polymerization required that the ω‐alkenoates be precomplexed with dialkylaluminum chloride. High molecular weight homopolymers and copolymers with olefins have been obtained. The polymerization of ω‐epoxyalkanoates with coordinative anionic polymerization systems based on triethylaluminum/water/acetylacetone (1.0/0.5/1.0) has also been accomplished. Homo‐ and copolymers of high molecular weight and of relatively narrow molecular weight distribution have been prepared. All polymers and copolymers of functional olefins and epoxides have been characterized and the study of the reactivity of the functional groups attached via a flexible spacer to the polymer main chain has been started. Special attention was given to the classical cationic copolymerization of trioxane with derivatives of ω‐epoxyundecanoate to prepare novel functional polyoxymethylenes of potential commercial interest.
Olefinpolymerization with highly active soluble zirconium compounds using aluminoxane as co‐catalyst
Authors: Kaminsky Walter , Külper Klaus , Niedoba Stefan 
Published: March 2011

AbstractThe homogeneous Ziegler‐Natta–catalysts, consisting of a zirconocene compound and methyl‐aluminoxane, lead to extremely high polymerization activities. With bis(cyclopentadienyl)zirconium dichloride pure atactic polypropylene and polyethylene with activities up to 30.106 g PE/g Zr·h are formed. The higher the degree of oligomerization of the aluminoxane the more active are the catalysts. The density of polyethylene (LLDPE) can be lowered by using 1‐butene or 1‐hexene as comonomers. Incorporation of dienes gives EPDM‐elastomers. Highly isotactic polypropylene can be prepared by using chiral rac‐ethylene bis–(tetrahydroindenyl) zirconium dichloride together with methylaluminoxane as cocatalyst. The toluene soluble part here consists of less than 0.2 weight percent. After resolution of this racemate it is also possible to produce optically active polypropylene and polybutene.
Advances in the field of organo‐element polymers
Authors: Korshak V. V. , Kozyreva N. M. 
Published: March 2011

AbstractOrgano‐element polymers are a rapidly developing field of high molecular weight compounds. As A.N. Nesmeyanov points out, the organo‐element polymer chemistry is the science lying between inorganic and organic chemistry, that is undoubtedly its positive factor, because this allows to prepare polymeric compounds combining positive properties of the compounds of these two fields. Due to this, many elements of the Periodic System capable of forming various polymeric compounds are widely investigated, and a number of organo‐element polymers have already found practical application in many fields of modern engineering and national economy. It should be noted that at present already more than 75 elements have been used in synthesis of various high molecular weight organo‐element compounds. Besides carbon, among these compounds hydrogen, oxygen and silicon are remarkable. Other elements only begin their way to the polymer field. The concept of raznozvennost (different‐units structure) is of great importance for studying the synthesis and the properties of these polymers. This concept made it possible to clarify distinguishing role of anomalous units in determining the complex of physico‐chemical properties of high molecular weight organo‐element compounds. It is especially important to emphasize that among factors giving rise to anomalous units causing polymer raznozvennost the presence of stable isotope atoms arranged statistically in polymer macromolecules plays an essential role. The lecture is a general review of polymers by the groups of the Periodic System. It discusses the methods for synthesis of organo‐element polymers used at the present time as well as perspective development of this field in the future.
Electrical conductivity of partly oxidized aromatic and heteroaromatic polymers
Authors: Koßmehl Gerhard 
Published: March 2011

AbstractThe electrical conductivity of aromatic and heteroaromatic polymers as well as polymers with aromatic, heteroaromatic and vinylene units in the main chain, can be enhanced by oxidation. In a single electron transfer reaction, a polymer with a salt structure (“doped polymer”) can be formed. Such polymers can also be prepared in a one‐step reaction from low‐molecular weight compounds by oxidants, as well as by electrochemical reaction. Electrochemically produced samples have higher electrical conductivities (as high as 6298K = 0,5 Ω−1 · cm−1) than samples made by chemical oxidation from the same starting material.
Microphase separation transition in block copolymer melts
Authors: Hewel M. , Ruland W. 
Published: March 2011

AbstractThe microphase separation transition (MST) in block copolymer melts has been studied using synchrotron SAXS. The results indicate that the MST occurs in the range of molecular weights and Flory‐Huggins interaction parameters x predicted by the theory of Leibler (Ref. 5). Studies of the MST as a function of molecular weight for constant composition can be used to determine the temperature dependence of x. The observed change of macrolattice constants with temperature is somewhat different from theoretically predicted values.
Solvent modified unperturbed dimensions of macromolecules ‐ their determination via NMR ‐ data and their relevance ‐
Authors: Cantow Hans‐Joachim , Pfannemüller Beate 
Published: March 2011

AbstractTemperature dependent unperturbed and solvent modified unperturbed dimensions of macromolecules are derived, in a first order approximation, from NMR‐data determined on low‐molecular‐weight analogs in the respective milieu. Because the long range interactions ‐ excluded volume and polymer ‐ polymer interaction ‐ are absent in the conformational balance of those models, the macrodimensions derived in this way are the unperturbed ones, with and without the influence of specific solvent action. Studies on head‐to‐head vinyl polymers are reported. It is demonstrated that the unperturbed dimensions in virtually non‐interacting solvents,<r2>o, may exceed those in thermodynamically good ones, <r2>s, as a consequence of differing conformational balance at segmental level.It is pointed out that those temperature and solvent dependent unperturbed dimensions are effective also in polymer solutions, as long as the molecular weight of the polymer is not exceeding the critical length necessary for occurrence of long range interactions.Capabilities in analyzing the conformational balance in plasticized systems and in compatible polymer blends are discussed. Here the conformation of the second component may be studied in parallel, as a consequence of similar concentrations of both partners in the system.θ‐dimensions depend on the type of the pseudoideal solvent. This effect is discussed on the base of NMR studies on the unperturbed conformations at segmental level in the respective θ‐ milieu.
Spectral quality enhancement as an aid to polymer characterisation
Authors: Maddams William F. 
Published: March 2011

AbstractThe limit to the information on the microstructure of polymers that may be obtained from their vibrational spectra is often set by overlapping bands, markedly broader than the spectrometer resolution. Following the initial pioneering work of Pohl and Hummel, using a simple curve fitting technique, mathematical methods of spectral quality enhancement have progressed very considerably. These methods are reviewed critically and new results are presented. The desirability of imposing some parameter constraints in curve fitting is demonstrated, and this has led to the development of methods for peak narrowing, as an aid to peak finding. The two important approaches, derivative spectroscopy and Fourier selfdeconvolution (FSD), are discussed in terms of their application to the complex of overlapping bands in the v(C‐Cl) region of the infrared spectrum of poly(vinyl chloride). A development of the FSD method termed Fourier band isolation, is described and preliminary results indicate that it has considerable promise. The maximum entropy method is discussed briefly.
Polymer coatings on steel substrates: An infrared spectroscopic study of temperature effects
Authors: Barbour R. L. , Mooney J. R. , Mehicic M. , Weinert R. J. , Benton K. C. , Grasselli J. G. 
Published: March 2011

AbstractPolymer coatings on steel substrates were analyzed by reflectance/absorbance infrared spectroscopy. Initial studies were performed ex‐situ on samples which had been cured at a variety of temperatures on two different substrates. Further studies were done in‐situ under both air and nitrogen atmospheres. The two substrates studied were untreated cold‐rolled steel and cold‐rolled steel with a conversion coating of zinc phosphate. Changes in the spectra of the phosphate conversion layer correlated well with anti‐corrosion properties. Mechanisms of degradation and cure could be determined from the in‐situ studies (1).
Über die spektroskopische bestimmung der spezifischen volumina von amorphem (va) und kristallinem (vc) polyethylenterephthalat
Authors: Simak P. 
Published: March 2011

AbstractThe intensity of the IR‐absorption bands of PET, which depends on the chain conformation (crystallinity), has been correlated with the specific volume of the samples produced under different conditions. It has been found that the absorption data of the ‐0‐CH2‐CH2‐0‐groups, discussed in the literature, leads to wrong vc‐ and va‐values. From our FTIR measurements of PET we obtained the spec. volume vc=ca. 0,66 cm3/g and va=0, 747 cm3/g. The amount of the trans‐conformation in the amorphous (for a well quenched sample) PET is about 12 ‐ 15%. The absorption band at 990cm−1 is not due to the sharp folds in PET.
Infrarot‐mikrospektroskopie an polymeren
Authors: Peitscher Günter W. 
Published: March 2011

AbstractIR microspectroscopy allows the identification and even quantitative analysis of tiny objects down to nanograms. A typical example is the investigation of specks or fish eyes in plastics. Other applications include the determination of local concentration changes of plasticizer or the oxygen uptake during aging. Such microinvestigations require sophisticated preparation techniques and specially equipped high‐performance spectrometers. Some practical examples and results are presented; they demonstrate the use of micro‐KBr, microtome, microsheet, and micropyrolysis techniques.
Molecular analysis of the interface of poly(ether‐ether‐ketone) and the basal plane of graphite single crystals
Authors: Nguyen Huy X. , Ishida Hatsuo 
Published: March 2011

AbstractThe interfacial interaction of the basal plane of graphite single crystals and poly(aryl‐ether‐etherketone) (PEEK) was investigated using Fourier transform infrared reflection‐absorption spectroscopy (FT‐IR‐RAS). PEEK melt‐quenched on the basal plane of a graphite single crystal does not show preferential orientation. However, upon annealing, the polymer chains crystallize perpendicularly to the basal plane of the graphite single crystal. The rate of this surface‐induced orientation during crystallization is found to be dependent on the film thickness. These results were verified by using model compounds of PEEK and by calculations based on optical theories.
Rheo‐optical fourier‐transform infrared spectroscopy of polymers 12. Variable temperature studies of strain‐induced crystallization in sulfur‐crosslinked natural rubber
Authors: Siesler Heinz W. 
Published: March 2011

AbstractRheo‐optical Fourier‐Transform infrared (FTIR) spectroscopy has been applied to investigate the onset, progress and decay of strain‐induced crystallization during loading‐unloading cycles of sulfur‐crosslinked natural rubber in the temperature range from 300 K to 423 K. The technique allows to detect crystallization online to the mechanical treatment upto 383 K.
Solid state 13‐C NMR spectroscopy with special reference to proteins and their derivatives. A comparison with vibrational spectroscopic methods
Authors: Martinmaa Jukka , Lindberg J. Johan , Maunu Sirkka‐Liisa 
Published: March 2011

AbstractPossible applications of solid‐state NMR in studies on polypeptides and proteins are presented. Several examples of 13‐C CP/MAS NMR spectra are discussed in relation to model compounds and polypeptides from various sources. A comparison is made with vibrational spectroscopic methods. It is concluded that the CP/MAS NMR method is especially useful in elucidating secondary structures in the unperturbed state, and, thus, may also be useful in the study of various conditions involving the disturbance of biochemical equilibria (e.g. the skin disease psoriasis and β‐fibrilloses). In these cases the NMR method is more elucidative than vibrational spectroscopy. However, owing to the fact that multiple spectral scans must be performed, it is very time consuming. It therefore appears that high resolution Fourier transform infra‐red spectroscopy is a complementary method, but not as informative regarding structural details in secondary structures. Combining both methods together provides a powerful tool for structure analysis.
500 MHz 1H NMR studies on the configuration and conformation in the piezoelectric copolymer of vinylidene cyanide and vinyl acetate
Authors: Jo Yong Sung , Inoue Yoshio , Chūjô Riichirô , Miyata Seizo 
Published: March 2011

AbstractThe 500‐MHz 1H NMR spectrum of vinylidene cyanide‐vinyl acetate copolymer, P(VDCN/VAc), provided detailed information concerning the configuration (ϵ‐tacticity) and conformations. The 1H NMR data also demonstrated that P(VDCN/VAc) is an equimolar and highly alternating copolymer without the regioirregular defects (complete head‐to‐tail arrangement), which is in good agreement with the previous C‐13 NMR result. The calculated ϵ‐isotacticity σ(ϵ) is equal to 0.5, suggesting that P(VDCN/VAc) is completely atactic. Due to this nonstereoregular structure, P(VDCN/VAc) in the bulk shows the amorphous phase by X‐ray and DSC measurements. Making use of 1H‐homodecoupling, the splittings due to ϵ‐tacticity as well as proton‐proton spin coupling could be separately assigned. From the vicinal coupling constants, J(AX) and J(BX), obtained in methylene proton resonance, conformer populations around H(A)H(B)C‐CH(X)‐CH(A ‘)H(B’ ), were calculated. The conformation of P(VDCN/VAc) in DMF solution consists of only TG and TT, forming not a random coil structure but a helical structure with a large radius of curvature.
Polarized fluorescence spectra of poly(ethylene terephthalate) films
Authors: Hennecke Manfred , Fuhrmann Jürgen 
Published: March 2011

AbstractThe polarized excitation and fluorescence spectra of lowcrystalline, isotropic poly(ethylene terephthalate) (PET) film samples were measured in the glassy state at room temperature. Whereas the emission anisotropy r0 of the excitation spectrum, recorded at the fluorescence maximum, changes sharply from 0.35 to 0 with decreasing wavelength in the region around 317 nm, the polarization of the fluorescence spectrum of PET is independent of wavelength. The fluorescence polarization of PET remains constant, if the temperature is increased up to 22 °C above Tg until the light scattering due to the crystallization causes complete depolarization.The photophysical behaviour supports the existence of a dilute solution of groundstate ‐ stable sandwich dimers in the non‐crystalline regions of PET.
The composition of an antioxidant obtained by styrylation of phenol
Authors: Milina R. , Laufenberg G. , Budzikiewicz H. 
Published: March 2011

AbstractThe composition of an antioxidant obtained by styrylation of phenol under the catalysis of oxalic acid has been determined by gas chromatography/mass spectrometry and other mass spectroscopic techniques as well as by comparison with authentic samples. It is shown that in addition to the products obtained by styrene addition to the ortho and/or para position of phenol, mentioned in the literature, oligostyrenes, compounds containing more than three styrene units per phenol molecule, and reaction products with urotropin (hexamethylenetetramine) ‐ added as a quencher ‐ are contained in the mixture.
Plasma treatment of the inner surface of polymer tubes for the improvement of their anticoagulant properties
Authors: Jansen B. , Steinhauser H. , Prohaska W. 
Published: March 2011

AbstractSmall‐diameter tubings from chlorinated polyethylene, polyetherurethane and silicone rubber were treated in a special plasma reactor using 1 kHz audiofrequency with rectangular characteristics with the aim to modify the inner surface of the tubings. Non‐polymerizable gases like air, N2, NH3 and CO2 were used as plasma gases to create suitable functional groups on the surfaces; hydrophilic monomers like N‐methyl‐N‐vinylacetamide and vinyl acetate were used to obtain thin grafted homogeneous surface layers. Surface analysis of the modified tubings was generally conducted by contact angle measurements, and ATR‐spectroscopy in the case of grafted materials. As a first test of the blood‐compatibility the activated and non‐activated partial thromboplastin time of human plasma exposed to the modified polymer tubings was determined.
Molecular level approach to the origin of the steric control in organozinc catalyst for oxirane polymerization
Authors: Tsuruta Teiji 
Published: March 2011

AbstractA new type of single crystals was formed by a reaction between diethylzinc and DL‐1‐methoxy‐2‐propanol. The constituent unit of this single crystal was shown to be a two to two complex of zinc dialkoxide and ethylzinc alkoxide, [MeOCH2 CH(Me)OZnOCH(Me)CH2 OMe]2 · [EtZnOCH(Me)CH2 OMe]2, which has a chair type structure. The two to two complex was found to exhibit higher activity and stereospecificity in the PO polymerization compared with those of the one to six complex which were reported previously. Molecular level elucidation was made on the basis of NMR studies for polymerization system with a partly deuterated two to two complex as initiator. The excellent stereospecificity in isotactic propagation was ascribed to the highly chiral hole around the active site of the chair type complex. Another series of study revealed chemical behavior of cyclohexene oxide (CHO), which is different from that of PO, toward several organozinc compounds. The two to two complex was the only catalyst which showed high activity for both MO and CHO polymerizations. Three samples (I), (II) and (III) of poly‐(CHO) were prepared with Et2Zn, EtZnOR and the two to two complex, respectively. After careful examinations of each of the three samples, it was concluded that most parts of the main chain of polymer (III) molecule were composed of syndiotactic triad, SS‐RR‐SS(or RR‐SS‐RR), while polymer (I) and (II) molecules contained syndiotactic and heterotactic triads in comparative amounts. In the CHO polymerization, the chiral hole of the two to two complex cannot recognize the mode of orientation of the achiral monomer, and the complex seems to serve as a simple bulky group which facilitates syndiotactic addition of CHO monomer molecule to the active site, strong steric effects being exerted from the penultimate unit of the growing chain during the propagation stage.