bluuebunny/crossref_metadata_2025_split huggingface dataset:
New catalytic systems for acetylene polymerization
Authors: Catellani Marinella , Destri Silvia , Bolognesi Alberto , Albizzati Enrico 
Published: April 2003

AbstractThe synthesis of polyacetylene (PA) films, having interesting mechanical properties and improved air stability, was performed by means of catalytic systems with Ti(OBu)4 and aluminoxanes as cocatalysts (i.e. R2AlOAlR2, R2AlSAlR2, R2AlN(n‐Bu)AlR2). Scanning electron microscopic characterizations, density and specific surface area measurements are indicative of films more dense than the ones polymerized by means of the classic Shirakawa and Luttinger methods. Draw ratios up to 3,5 were observed.
Hydrophilic silicone rubber materials containing dimethylsiloxane and urethane moieties in the main chain
Authors: Koßmehl Gerhard , Neumann Walter , Schäfer Horst 
Published: April 2003

AbstractBy addition of various diisocyanates (5a, b) to oligomeric organosiloxanes, oily viscous polymers with urethane and siloxane moieties were obtained, which were crosslinked by reaction with 1–10 weight‐% of a peroxide. The resulting silicon rubber material is stable to hydrolysis. Films (F1 – F21) of these materials were characterized by their FMIR‐IR‐spectra. Some films (F3, F8, F10 – F12 and F17) show oxygen permeation values and contact angles which qualify these materials for contact lenses. The other films may be useful as materials for contact lenses after hydrophilizing.
Polymeric and oligomeric dimethylsiloxanes with alcoholic groups and their conversions into polymers with dimethylsiloxane and urethane moieties
Authors: Koßmehl Gerhard , Neumann Walter , Schäfer Horst 
Published: April 2003

AbstractAddition of allyloxytrimethylsilane (2a) or allyl 2,3‐epoxypropyl ether (2c) to dihydrosiloxanes (1a and 1b) leads to the protected organoalkylsiloxanes 3a, 4a, 5a, 3c and 4c, which can be hydrolyzed to the corresponding hydroxyl compounds 3b, 4b, 5b and 4d. Addition of isocyanates 6a—c to these hydroxyl compounds results the model compounds 7a—c and 8a—c. Polymers 10a, b and 11a, b were prepared under similar conditions by addition of diisocyanates 9a, b to the hydroxyl compounds.
Syntheses of telechelic oligo‐ and poly(carboxypiperazine)s
Authors: Schwalm Reinhold , Heitz Walter 
Published: April 2003

AbstractPoly(carboxypiperazine) is only accessible via low temperature polycondensation methods. The melting point of the polymer is higher than the temperature of its decomposition. Oligomers with piperidine end groups were prepared to determine the melting points of the pure polymer by extrapolation from the melting points of the oligomers. The decomposition temperatures were determined by thermogravimetry. These studies led to the design of meltable telechelics.
Functional polymers and sequential copolymers by phase transfer catalysis, 21. Thermotropic aromatic poly(ether sulfone)s: A new class of thermotropic aromatic main‐chain liquid crystalline polymers
Authors: Shaffer Timothy D. , Percec Virgil 
Published: April 2003

AbstractThermotropic aromatic poly(ether sulfone)s (3a — e) were prepared by phase transfer catalyzed (PTC) polyetherification of bis(4‐chloro‐3‐nitrophenyl) sulfone (1) with mesogenic aromatic diols. The synthesized polymers were characterized by differential scanning calorimetry and optical polarization microscopy to determine their phase behavior. All polymers appear to be amorphous. Only the polyethers based on 2,6‐dihydroxyanthraquinone (2a) and 1 exhibit enantiotropic liquid crystalline behavior. This demonstrates that fully aromatic polyethers can be prepared as thermotropic liquid crystalline polymers.
Equilibria in the anionic polymerization of methyl methacrylate, 1. Chain‐length dependence of the rate and equilibrium constants
Authors: Müller Axel H. E. , Lochmann Lubomír , Trekoval Jiři 
Published: April 2003

AbstractThe rate constants of polymerization and cyclization and the equilibrium constants of polymerization are calculated from kinetic data of the anionic oligomerization of methyl methacrylate initiated by methyl α‐lithioisobutyrate in THF at 25°C, and of the “disproportionation” of living oligomers. The numeric method reported earlier was improved. The rate constants of cyclization decrease with chain‐length, due to increasing steric hindrance. The rate constants of polymerization depend on the concentration of active centres, due to the formation of associates. Rate and equilibrium constants of polymerization decrease with chain‐length. This is discussed in terms of intramolecular coordination of the counterion with ester groups of the chain.
Compatibility of polymers in polymer blends investigated by gas chromatography
Authors: Klotz Stephan , Schuster Robert H. , Cantow Hans‐Joachim 
Published: April 2003

AbstractPolymer‐polymer and polymer‐solvent Flory‐Huggins interaction parameters are given for the systems polystyrene/poly(methyl vinyl ether), polystyrene/solvent, and poly(methyl vinyl ether)/solvent. In principle polymer‐polymer interaction should be independent of the solvent probes used. In this study it was found that polymer‐polymer interaction is influenced by the solvent probe. These influences are discussed as a function of the chemical nature of the interacting vapour phase. However, these effects are not decisive for the phase behaviour of polymer blends. Phase separation was observed at high temperature. Gas chromatography measurements facilitated a quantitative thermodynamic description of the system polystyrene/poly(methyl vinyl ether) over a wide range of temperature and composition.
Die gitterstatistik des gaußschen parakristalls
Authors: Blöchl Georg , Bonart Richard 
Published: April 2003

AbstractHosemann's ideal paracrystal is characterized by the Gaussian error propagation of shortrange lattice distortions along the edges of the lattice cells. In a Gaussian paracrystal, however, the short‐range distortions propagate radially throughout space. In contrast to Hosemann's model there is no need for the lattice cells to be parallelepipeds in Gaussian paracrystals. Based on distance and directional fluctuations, a lattice‐independent description of long‐range distortions is introduced by its so‐called characteristics. Thus, the lattice factor describing the interference effect is found by a two‐fold Fourier transform similar to the approach of Warren and Averbach. This will be explained in detail in a following paper.
Der gitterfaktor des gaußschen parakristalls
Authors: Blöchl Georg , Bonart Richard 
Published: April 2003

AbstractBy using so‐called “characteristics”, the long‐range distortion in Gaussian paracrystals may be described in a way which is independent of the lattice, provided distance and directional fluctuations between neighbouring lattice points are used. By a two‐fold Fourier transform — similar to the approach of Warren and Averbach — the lattice factor, describing the interference effect of the Gaussian paracrystal, is found from the convolution of an ideal reciprocal lattice with a lattice‐independent profile function. Threadlike “one‐dimensional” Gaussian and ideal paracrystals are identical with each other. Making use of the two‐fold Fourier transform, Hosemann's K‐factor splits into isolated discs (“Scheibchen”) showing Lorentzian profiles. The profile function of two‐and three‐dimensional Gaussian paracrystals shows a Lorentzian‐2/3 or a Lorentzian‐2 profile, respectively. The different profiles are experimentally distinguishable when using a position‐sensitive detector. Thus, based on experimental results, paracrystalline lattice distortions with Gaussian characteristics are detectable.
Chain packing in two aromatic heterocyclic polymers, one of which has a ladder structure
Authors: Nayak Kasmath , Mark James E. 
Published: April 2003

AbstractA semiempirical method was used to calculate the interaction energies in the ladder polymer poly(3,6‐dioxo‐1H‐2,3,6,6a‐tetrahydro‐2,6a,11‐triazaindeno[1,2‐b]pyrene‐2,8,9‐triyl‐1‐ylidene‐1‐nitrilo) (BBL, 1) and the single‐strand polymer poly(5,8‐dioxo‐4b,5,8,8a‐tetrahydro‐4b,8a,13,16‐tetraazadiindeno[1,2‐a:1,2‐i]pyrene‐3,10‐diyl) (BBB, 2), in order to elucidate their chain packing. The van der Waals contribution to the total intermolecular interaction energies was found to be more significant than the Coulombic one. The prediction of short‐range interplanar spacings in the neighborhood of 3,3 Å along the z axis (chains above one another) and 8,8 Å along the y axis (chains alongside one another) is in good agreement with X‐ray diffraction results.
Phase structure and compatibility studies in poly(ethylene oxide)/poly(methyl methacrylate) blends
Authors: Martuscelli Ezio , Silvestre Clara , Addonizio M. Luisa , Amelino Luciano 
Published: April 2003

AbstractMorphology, crystallinity, and melting behaviour of solution‐cast films of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends were investigated as a function of composition, using optical and scanning electron microscopy, differential scanning calorimetry, and dilatometry. Up to a content of about 40 wt.‐% of PMMA the blend films are completely filled with PEO spherulites, no separated domains of PMMA being observed. This observation suggests, in agreement with small angle X‐ray scattering analysis, that for such compositions the PMMA molecules are incorporated in interlamellar regions of PEO spherulites. Blends with higher content of PMMA show islands of crystalline PEO within a matrix of PMMA; large amorphous regions coexist with not well developed PEO spherulites. Addition of PMMA strongly increases the nucleation density for PEO crystals. The solubility parameters δ of PEO and PMMA were calculated from specific volume values as a function of temperature. It was found that at temperatures higher than that of PEO melting the difference δ(PEO) ‐ δ(PMMA) is very low suggesting that the two polymers are compatible in the melt. Compatibility of PEO and PMMA was also predicted by using a theoretical approach which allows to calculate the free energy of mixing as a function of composition and temperature.
Anionic polymerization of 4‐methyl‐2‐oxetanone
Authors: Jedliński Zbigniew , Kurcok Piotr , Kowalczuk Marek , Kasperczyk Janusz 
Published: April 2003

AbstractPotassium solutions, obtained by contacting the metal mirror with a THF solution of a crown ether were found to initiate the anionic polymerization of 4‐methyl‐2‐oxetanone (1) (β‐butyrolactone). The tacticity of the resulting polymer 2 was established by means of 13C NMR spectroscopy. The results indicate that living polymers of 1 were formed, and the polymerization proceeds without abstraction of hydrogen from the monomer and no termination and transfer reactions take place.
Kinetics of the free radical copolymerization of diethyl maleate with methyl methacrylate
Authors: Braun Dietrich , Cei Gustavo 
Published: April 2003

AbstractThe kinetics of the free radical copolymerization of diethyl maleate (M1) with methyl methacrylate (M2) was studied in bulk at 60°C with azoisobutyronitrile (AIBN) as initiator. The reactivity ratios of the system were determined by means of 1H NMR spectroscopy. The obtained values show that diethyl maleate is not only unable to homopolymerize (r12 = 0) but also display a very low tendency to incorporate in the polymer chain (r21 = 370) under the present conditions. Molecular weight measurements showed that a normal, although very slow growth reaction involving diethyl maleate takes place. Therefore, chain transfer could be neglected in the kinetic analysis. The dependence of the initiation rate constant on the monomer feed was analysed by means of the inhibition method. An equation for describing the observed dependence of polymerization rate on feed composition was derived taking into account the influence of solution viscosity on the termination rate constant (diffusion theory).
The effect of TiBr4 on ethylene polymerization catalyzed by tetrabenzyltitanium
Authors: Giesemann Jürgen , Ernst Eberhard , Ernst Angela , Ulbricht Joachim 
Published: April 2003

AbstractThe kinetics of the ethylene polymerization catalyzed by Ti(CH2C6H5)4/TiBr4 in toluene at 0°C was studied. The effects of the mole ratio of the catalyst components and of the quantity of catalyst on the polymerization were investigated. Using the number of active centres, the rate constant of the propagation reaction was evaluated. The number of active centres was determined by quenching the polymerization with 1‐butanol tritiated at the hydroxyl group. Compared with the kinetic data of the catalyst system Ti(CH2C6H5)4/AlBr3, the present results indicate that the nature of the cocatalyst mainly affects the conditions for the formation of active centres, but has no essential influence on their reactivity. These results support the concept of monometallic structure of the active centres in Ziegler‐Natta catalysts.
Epitaxial polymerization of acetylene
Authors: Yamashita Yuhiko , Nishimura Setsuro , Shimamura Kaoru , Monobe Kazuo 
Published: April 2003

AbstractEpitaxial polymerization of acetylene was studied using systematic series of homologous isomorphic compounds as substrates for the purpose of establishing techniques for preparing well oriented polyacetylenes. From electron microscopy, it was confirmed that polyacetylenes grow on the substrate in the form of fibrils whose orientation is strongly dependent on the lattice matching between polyacetylene and substrate crystals: e.g. with naphthalene and anthracene as substrates the fibrils assume zigzag orientation in three specific directions on the crystal but with biphenyl and terphenyl the zigzag fibrils assume predominantly two specific directions. The mechanism of epitaxial growth during polymerization on the various substrates is discussed on the basis of the features of the epitaxial fibrils.
Photochimie des polyamides aliphatiques, 5. Oxydation du polydodécanamide (PA12) photocatalysée par TiO2 et ZnO
Authors: Roger Agnès , Sallet Daniel , Lacoste Jacques , Lemaire Jacques 
Published: April 2003

AbstractThe influence of two photoactive pigments (ZnO and TiO2 in the rutile form) on the dual photochemistry occurring in polydodecanamide was analyzed, on analytical and kinetics grounds. Variations in the concentration of amino, hydroperoxide and imido groups as function of the photoactive pigment content were studied. At wavelengths longer than 300 nm, zinc oxide exhibits an inner filter effect at low content; an antagonist photocatalytic influence is observed at high content (5–10%). The inner filter effect and the photocatalytic activity of titanium dioxide are observed simultaneously even at low content of titanium dioxide (1–10%). At 254 nm and 25°C, the filter effect of ZnO is prevalent on the formation of amino and acidic groups. Titanium dioxide acts as a filter and a photocatalyst: the formation of amino groups is inhibited, whereas the rate of formation of acidic groups is apparently not modified.
Preparation and thermolysis of N‐ammonioamidates as model precursors of new type of segmented poly(ether‐urethane)s
Authors: Masuyama Araki , Iwasaki Tadashi , Okahara Mitsuo 
Published: April 2003

AbstractN‐Ammonioamidates 2 (aminimides) containing a hydroxyl group, oxyalkylene units, and an alkylene chain or a phenylene group in an acyl moiety were prepared in satisfactory yields from the corresponding esters 1. By thermolyses in diglyme, cyclic urethanes (type of crown ethers) 3 and oligo(ether‐urethane)s 4 were formed, depending on the structure of the N‐ammonioamidates. The latter are applicable to the syntheses of new model compounds of segmented poly‐(ether‐urethane)s.
Réaction époxide amine: Réactivité du sulfonyl‐4,4′ dianiline vis‐à‐vis du groupement époxy
Authors: Grenier‐Loustalot Marie‐Florence , Cazaux Frédéric , Grenier Philippe 
Published: April 2003

AbstractMechanism and kinetics of the polycondensation of 4,4′‐sulfonyldianiline (2) with 2,3‐epoxy‐1‐phenoxypropane (1) were analysed in the absence or presence of a catalyst [N,N‐(dimethyl)‐benzylamine or BF3 complex]. Chemical data obtained by 13C NMR and HPLC show that secondary reactions (homopolymerisation, reaction of hydroxyl groups with the epoxy groups) take a prominent part.
A facile synthesis of monodisperse carboxylated polystyrene and derivatives
Authors: Argyropoulos Dimitris S. , Bolker Henry I. 
Published: April 2003

AbstractA method is presented for the synthesis of monodisperse carboxylated polystyrene (3) and derivatives by a Friedel‐Crafts acylation of monodisperse polystyrene with ethyl oxalyl chloride (1). Saponification of the resulting α‐keto ester yields the randomly carboxylated copolymer, whose structure was confirmed by NMR and infrared spectra. Viscosity measurements and gel permeation chromatography showed that no chain cleavage operated during the process of functionalization. The value of the technique lies in its simplicity of execution and the availability of starting materials.
Synthesis and characterization of polyamine graft copolymers with a poly(2‐hydroxyethyl methacrylate) backbone
Authors: Maruyama Atsushi , Senda Eiichi , Tsuruta Teiji , Kataoka Kazunori 
Published: April 2003

AbstractRadical copolymerizations were carried out with 2‐hydroxyethyl methacrylate (HEMA) and a polyamine macromonomer (1). 1H NMR, IR, liquid chromatography and turbidity measurements showed the polymer obtained to be poly[(HEMA)‐graft‐polyamine]. The monomer reactivity ratio for the polyamine macromonomer was found to be similar to that of a low‐molecular‐weight analogous monomer. Microphase separated structure was observed on thin films of the copolymer by means of transmission electron microscopy. Using the column method, the biomedical behavior of the copolymer was estimated in terms of its interaction with rat lymphocytes. Strikingly, the copolymer surface was found to differentiate the lymphocyte subpopulations without any added adjuvant protein.
Block copolymers with controlled interphase width. Effects of interphase and composition on domain dimensions
Authors: Bühler Fritz , Gronski Wolfram 
Published: April 2003

AbstractUltrathin osmium tetroxid stained sections of solution cast block copolymer films were studied by electron microscopy. Two morphological systems were prepared from diblock copolymers containing 80 wt.‐% styrene and 20 wt.‐% isoprene: Systems with asymmetric lamellar morphology cast from cyclohexane, a preferential solvent for PI; and spherical morphology of rubber spheres in a continuous PS matrix, cast from tetrachloromethane, a non‐selective solvent. For the two morphologies the variation of domain dimensions was studied in dependence of molecular weight in the range from 70 000 to 600 000 g/mol. Two types of block copolymers were investigated: Unmodified block copolymers and block copolymers containing 10 wt.‐% of a random interblock between the pure polystyrene and polyisoprene blocks. For both kinds of morphologies the domain dimensions of the unmodified systems vary with Mn2/3 as predicted by Helfand's theory. In the modified block copolymers a much weaker increase with Mn is found for both morphological systems. The results can be understood in terms of equilibrium domain dimensions controlled by an interfacial tension depending on both composition and sequence structure of the block copolymers.
Transformation of oligodimethylsiloxanols in the presence of a strong base. Reactivity enhancement of the siloxane bond by the adjacent hydroxyl group
Authors: Chojnowski Julian , Kaźmierski Krzysztof , Rubinsztajn Stawomir , Stańczyk Wlodzimierz 
Published: April 2003

AbstractThe kinetics of the base catalysed disproportionation of polydimethylsiloxanes having silanol end groups was studied using the model systems 1,1,3,3,3‐pentamethyldisiloxane‐1‐ol (1) and 1,1,3,3,5,5,7,7,9,9,9‐undecamethylpentasiloxane‐1‐ol (5) in 2‐propanol in the presence of alkali metal 2‐propanolates and in THF containing 2 vol.‐% of water in the presence of NaOH. The results did not confirm our earlier mechanistic proposition. Silanone is not formed intermediately. The process proceeds according to the kinetic law for a bimolecular process and shows a high negative value of activation entropy. However, the reaction exhibits some features better explained by an elimination‐addition than by an SN2 mechanism. The hydroxyl group exerts a specific role making the cleavage of the adjacent siloxane bond much easier. The reaction is also accelerated by the assistance of the alkali metal counter ion and its rate seems to be little dependent on the basicity of the nucleophile. A mechanism combining elements of both the SN2 and the elimination‐addition pathways is proposed.
Thermal dehydrochlorination of poly(vinyl chloride), 2. Transiently and permanently acting structural defects
Authors: Lukáš Rudolf , Přádová Olga 
Published: April 2003

AbstractSamples with an increased content of chloroallyl structures were prepared by chemical degradation of poly(vinyl chloride) (PVC) using potassium tert‐butoxide. The samples were thermally dehydrochlorinated in an inert atmosphere, and their dehydrochlorination curves were determined by the continuous potentiometric method. The results show that the chloroallyl structures affect the dehydrochlorination of PVC only transiently. The same conclusion is obtained by an analysis of experimental data of the dehydrochlorination of PVC samples enriched in structures with the chlorine atom bound to the branching site (structures with the chlorine atom at the tertiary carbon atom). A general conclusion is that all structural defects, which facilitate the elimination of hydrogen chloride along the polymer chain and exist in the polymer before its heat stress, play only a transient role in the thermal dehydrochlorination of PVC. These structural defects initiate the splitting‐off of hydrogen chloride during the induction period of dehydrochlorination and form conditions for a gradually increasing effect of the basic initiation mechanism, which in the course of dehydrochlorination gives rise to chloroallyl structures. The formation of chloroallyl structures is brought about by a reaction between regular structural PVC units and s‐cis‐enone, dienone, or polyenone structures. A possible mechanism of this reaction, consisting in an interchain syn‐elimination of hydrogen chloride, is suggested.
Kinetics and mechanism of formation and properties of polymers composed of paired macromolecules
Authors: Korshak Vasili V. , Suprun Anna P. , Slonimskii Grigorii L. , Askadskii Andrei A. , Birshtein Tatyana M. , Vointseva Irina I. , Mustafayeva Balakhanum B. , Nikolskii Oleg G. 
Published: April 2003

AbstractThe influence of formation conditions on structure and properties of reaction products from two different macromolecules (paired polymers) such as polystyrene and poly(1,1,2‐trichlorobutadiene) or polystyrene and poly(vinyl chloride) is investigated. Mechanical properties, molecular mobility, heat resistance, thermostability, and fire resistance are shown to be regulated over a wide range by changing the molecular weight of the initial polymers, their ratio in the reaction mixture, etc. The interaction of different macromolecules in solution to form paired polymers is analyzed theoretically and experimentally. An analysis of structure and properties of the resulting products by refractometry, viscometry, sedimentation velocity, statistical analysis, and others shows that paired polymers are systems of the “coil‐in‐coil” type held together by chemical bonds in the zones of mutual penetration.
13C and 1H NMR study of polymers obtained by polymerization of styrene oxide using diethylzinc/water system as initiator
Authors: Kasperczyk Janusz , Jedliński Zbigniew J. 
Published: April 2003

AbstractStyrene oxide was polymerized by the initiator ZnEt2/H2O and the structure of the resulting polymers was determined by means of 1H and 13C NMR spectroscopy. Both the crystalline and the amorphous fraction have regular head‐to‐tail structure indicating that the oxirane ring opens exclusively at the β position. The stereochemistry of the growth of the crystalline, highly isotactic fraction follows first order Markov statistics, while that of the amorphous fraction follows Bernoulli statistics.