bluuebunny/crossref_metadata_2025_split huggingface dataset:
Degradation behaviour of polyurethane studied by linear temperature programmed pyrolysis FTIR spectroscopy
Authors: Herzog Klaus 
Published: March 2011

AbstractFTIR spectrometers with two measurement beams offer the possibility to record and process spectra from 4000 to 400 cm−1 taken every 30 seconds in situ from a polyurethane film which is subjected to a programmed linear rise of temperature from ambient to 400°C and to take quasi simultaneously the spectra of the gaseous pyrolysis products. As an example, polyurethane (PUR) prepared from diphenylmethane diisocyanate (MDI) with polyesteralcohol from adipic acid was thermally degraded to isocyanate and polyester alcohol. Carbodiimid was found in the pyrolysis products and carbon dioxide was detected in the pyrolysis gas. The isocyanate evaporation and the thermal degradation of polyester alcohol were studied.
Polyolefin blends
Authors: Kresge E. N. , Lohse D. J. , Datta S. 
Published: March 2011

AbstractPolyolefin blends of proper morphology exhibit physical properties from high‐extension, low‐modulus elastomers to high‐modulus tough resins. The morphology is controlled by rheology of the polymers, blending conditions and the use of graft polymer compatibilizers. The graft polymers were synthesized by polymerizing isotactic polypropylene with unsaturation in an ethylene‐propylene‐diene terpolymer. Graft copolymers result in smaller phase sizes and a more stable morphology for the blends. The development of polyolefin blends is reviewed with emphasis on materials with high concentration of elastomer phase.
Anionic synthesis of polystyrene and polybutadiene heteroarm star polymers
Authors: Quirk Roderic P. , Lee Bumjae 
Published: March 2011

AbstractThe use of living linking reactions of poly(styryl)lithium with 1,3‐bis(1‐phenylvinyl)benzene followed by crossover reactions with styrene or butadiene monomers has been used to prepare four‐armed heteroarm, star‐branched polymers. Bimodal molecular weight distributions have been observed for crossover reactions with both styrene and butadiene. Addition of THF ([THF]/[Li]=14–32) for crossover to styrene and lithium sec‐butoxide for crossover to butadiene produces monomodal molecular weight distributions. Symmetrical, four‐armed star polystyrenes have been synthesized; properties have been compared with a corresponding polymer prepared via a silicon tetrachloride linking reaction. Heteroarm, star‐branched polymers with two polystyrene arms and two polybutadiene arms with high 1,4‐microstructure have been prepared.
Effect of composition and structure on rheological properties of styrene‐butadiene block copolymers
Authors: Horák Zdenêk , Kruliš Zdenêk , Večerka František , Kováf Josef 
Published: March 2011

AbstractStyrene‐butadiene copolymers of the S‐B‐S and S‐B‐S‐B‐S types, both unmodified and extended with paraffinic‐naphthenic oil, were studied by dynamic mechanical spectroscopy and capillary rheometry. In the triblocks at low deformation rates, an increase in 1‐vinylethylene unit content leads to an increase in complex dynamic viscosity |η*|. This may be explained by their different supermolecular structure with a higher proportion of long relaxation times. The pentablocks show a considerable effect of molecular parameters on their flow behaviour at low deformation rates. In all the systems, steady viscosity η shows no significant differences at higher shear rates. Obviously the supermolecular structure is disintegrated in these conditions and the effect of chemical structure is negligible. An expected decrease in viscosity in the whole range of deformation rates was observed with the oil‐extended copolymer. The dependences of complex dynamic viscosity on angular frequency were compared with those of steady viscosity on shear rate but no unequivocal conclusion as regards the validity of the Cox‐Merz rule could be reached.
Recovery of photodegraded polymers by surface treatment
Authors: Decker Christian 
Published: March 2011

AbstractA two‐step process has been developed in order to renovate highly photodegraded polymers. It was applied to clear and pigmented commercial PVC plates, which were exposed to accelerated weathering. The brown highly degraded top layer was first removed by sandpapering, which makes the color disappear and restores the original impact resistance of PVC. In a second step, a thin film of a UV‐curable acrylic resin was sprayed onto the PVC plate, which thus recovered its initial transparency. After a 1s UV exposure, the coated PVC was found to exhibit an excellent resistance to chemicals, weathering and scratching. One of the distinct advantages of this new low‐cost recycling process is that it is based on existing technologies and can be carried out directly on the plastic structures to be renovated.
Effect of chain aggregation and ionic interactions on the proton dissociation equilibria of weak polyacids
Authors: Cesàro Attilio , Sagui Maria Celeste 
Published: March 2011

AbstractA theoretical interpretation of the dissociation behavior of weak polyacids is given. Incorporation of conformational variability in the free energy of a polyelectrolyte system extends the validity of the counterion condensation theory to cases in which cooperative transitions and/or aggregation phenomena take place. Comparison of the theoretical predictions with experimental data on ionic polysaccharides, either natural or derivatives, is presented.
Biomimetic oxidation of thiol and application to odor‐removing fiber
Authors: Shirai Hirofusa , Hanabusa Kenji , Koyama Toshiki , Tsuiki Hisanaga , Masuda Etsuko 
Published: March 2011

AbstractThe oxidation of HO‐CH2‐CH2‐SH (RSH) by molecular oxygen and Fe(III)‐ as well as Co(II)‐multicarboxyphthalocyanine and the mechanism in homogeneous aqueous system were investigated. As application to enzyme‐like heterogeneous catalysts, Fe(III)‐as well as Co(II)‐octacarboxyphthalocyanine were supported on amorphous enriched rayon staple fiber and their enzyme‐like activities were estimated. These fibers were applicated to new odor‐removers acting as artificial enzyme systems.
Polymer networks containing polyether, polyamine or polysulfide chains
Authors: Goethals Eric J. 
Published: March 2011

AbstractAn overview of newer or less‐known synthetic methods for the synthesis of polymer networks containing ether, amine or sulfide functions or a combination of these functional groups with other functional groups, is presented. Emphasis is given on new methods starting from well ‐ defined telechelic prepolymers. A number of these prepolymers are obtained by living cationic systems, more particularly cationic ring‐opening and cationic vinyl ether polymerizations.
Preparation and photoluminescence characteristics of polysiloxane pendant tris(2,2′‐bipyridine)ruthenium (II) complex
Authors: Nagai Keiji , Nemoto Nobukatsu , Ueno Yukihiko , Ikeda Koji , Takamiya Nobuo , Kaneko Masao 
Published: March 2011

AbstractPolysiloxanes containing pendant tris(2,2′‐bipyridine)ruthenium(II) complex (Ru(bpy)32+) were prepared by reaction of polysiloxane‐pendant 2,2′‐bipyridine (PSiO‐bpy) with cis‐Ru(bpy)2Cl2. In methanol solution, the polymer pendant Ru(bpy)32+ showed absorption maximum at 456nm and emission maximum at around 609nm, both of which are shifted to longer wavelength than the monomeric Ru(bpy)32+. The lifetime τ0 of the excited polymer complex with low Ru(bpy)32+ content was almost the same as that of the monomeric one in methanol (830ns), but τ0 of the polymer with higher complex content was shorter because of a concentration quenching. In a solid state, τ0 was much shorter (306–503ns) than that in a methanol solution contrary to the conventional polymeric system. Higher complex content in the polymer film caused higher glass transition temperature (Tg), but shorter τ0. These results indicate concentration quenching in the polymer film. The excited polymer pendant Ru(bpy)32+ was quenched by oxygen, and the relative emission intensity followed the Stern‐Volmer equation. In a methanol solution the quenching rate constant (kq) was the same order of magnitude as the monomeric complex, and independent of the complex content in the polymer. In a film, kq was higher for the polymer with higher complex content.
Cationoid living polymerisations
Authors: Plesch Peter H. 
Published: March 2011

AbstractThe cationoid living polymerisations have many of the characteristics of pseudo‐cationic (φ‐cat) polymerisations and none of those of cationic polymerisations. In contrast to the φ‐cat polymerisations by protonic acids, which are transfer‐dominated, those giving living polymerisations are propagated by esters which are part of a donor‐acceptor complex involving a “third reagent”. There are three types: The first is exemplified by an ester which is activated by a metal halide, e.g. HMI (from monomer M + HI) + ZnBr2, or oligoisobutyl acetate + BCl3. The second type is exemplified by a polymer triflate complexed by a dialkyl sulphide. The reagents which change the reactivity of the ester are termed “modifiers”. The acceptors, e.g. ZnBr2, which co‐ordinate to a donor group on the polymer, are positive modifiers (or activators). The donors, such as R2S, which coordinate onto an acceptor group at the end of the polymer, e.g. the acidic β‐H, are negative modifiers (or moderators).The propagation by both types of modified ester probably involves a 6‐centred cyclic transition state. The same applies to a third type of φ‐cat propagation, in which a polymeric ester reacts with a D‐A complex formed from M + I2.The formation of unwanted non‐living polymers of high DP and/or broad DPD, together with those resulting from living polymerisations, happens because the metal halides used in these reactions not only form the φ‐cat propagating centres, but also react with ionogenic impurities to initiate concurrent, short‐lived cationic polymerisations. These parasitic reactions can be suppressed by an excess of base, e.g. an ester or halide ions, which scavenge protons and carbenium ions. This phenomenon indicates that, whatever else is propagating the living polymerisations, it is unlikely to be carbenium ions.The kinetic equations for the living polymerisations, developed here, make it possible to calculate propagation rate‐constants from rate and DP data; such calculations are shown for a variety of published results.
Cationic polymerization of cyclocarbonates
Authors: Kricheldorf Hans R. , Weegen‐Schulz Bettina , Jenssen Jörg 
Published: March 2011

AbstractTrimethylenecarbonate (TMC) and neopentane diol carbonate (NPC) were polymerized with two groups of initiators, proton and carbenium ion donors or Lewis acids. Initiation with methyltriflate, triflic acid or triethyloxonium tetrafluoroborate in solution gave satisfactory yields (up to 90%) but only low molecular weights (Mn < 5000), due to rapid back‐biting degradation. IR‐ and NMR‐spectroscopy demonstrate that the propagation steps involve alkylation of the carbonyl oxygen and cleavage of the alkyl‐0 bond by analogy with lactones. Whereas borontribromide and trichloride form solid complexes with NPC or TMC, but do not initiate a polymerization, boron trifluoride is a good initiator. High yields (up to 99,5%) and high molecular weights (Mw > 105) were obtained. However, in analogy to triflic acid initiated polymerizations all polycarbonates contain ether groups. The molar fraction of the ether groups increases with the reaction temperature. High molecular‐weight polycarbonates containing ether groups were also obtained with other strong Lewis acids such as SnCl4, SnBr4 and TiCl4. In contrast, weak Lewis acids such as Bu2SnBr2 Bu3SnOMe and Sn(II)2‐ethylhexanoate yield polycarbonates free of ether groups. This finding and the NMR‐spectroscopically identified endgroups suggest that these weak Lewis acids initiate an insertion mechanism.
New aspects on the photoinitiated free radical promoted cationic polymerization
Authors: Yagci Yusuf , Schnabel Wolfram 
Published: March 2011

AbstractGeneral aspects of the photoinitiated free radical promoted cationic polymerization are discussed. The applicability of pyridinium salts, a new class of photoinitiators, of appropriate redox potential Ered1/2 in oxidizing carbon‐centered free radicals to carbocations capable of initiating the polymerization of various compounds is demonstrated. Moreover, the use of polysilanes as source for readily oxidizable free radicals is described. Furthermore, possibilities for preparing block copolymers by free radical promoted cationic polymerization are pointed out.
Stereochemistry of oligomers in stereospecific and conformational specific ionic polymerizations
Authors: Vogl Otto , Garner Charles , Simonsick William J. , Kratky Christoph , Ute Koichi , Hatada Koichi 
Published: March 2011

AbstractLow molecular weight oligomers of methyl methacrylate (MMA) and perhaloacetaldehyde were studied as to their composition, end groups and stereochemistry. The oligomerization of methyl methacrylate can be directed toward almost pure isotactic or toward almost syndiotactic oligomers depending upon the intitiating system used. Perhaloacetaldehydes showed a stereospecificity which depended upon the size and bulkiness of the side group in the polymer chain. There is no dependence of the sterospecificity based on the initiating system and only isotactic polymers could be obtained which are not only stereospecific but also conformationally specific giving conformational specific isotactic 4/1 helices.
The role of association/complexation equilibria in the anionic polymerization of (meth)acrylates
Authors: Kunkel Dietmar , Müller Axel H. E. , Janata Miroslav , Lochmann Lubomír 
Published: March 2011

AbstractThe kinetics of the anionic polymerization of methacrylates and acrylates in THF as well as the MWD of the polymers formed depend on the concentration of active centres and of additives, such as lithium halides and lithium alkoxides. These results are discussed on basis of multiple equilibria between non‐associated, associated, and complexed ion pairs which are supported by viscosity measurements. The position of these equilibria determines the rate of polymerization, whereas the dynamics of interconversion determine the polydispersity. In the absence of additives the rate of monomer addition to non‐associated ion pairs competes with the rate of association. Addition of lithium chloride mainly affects the rate of interconversion between dormant and active species, whereas lithium tert‐butoxide forms adducts which stabilize the active centre.
Recent development in stereochemical control of heterogeneous Ziegler‐Natta catalysts
Authors: Soga Kazuo , Uozumi Toshiya , Park Joon Ryeo , Shiono Takeshi 
Published: March 2011

AbstractA completely aspecific catalyst was prepared by supporting TiCl3 on MgCl2. The catalyst isospecificity could be drastically converted from aspecific into isospecific either by adding ethyl benzoate or by changing the cocatalyst from Al(C2H5)3 to Cp2Ti(CH3)2. On the other hand, the catalyst system composed of SiO2‐supported CpTiCl3 and methylaluminoxane (MAO) gave atactic polypropylene as well as a random copolymer of ethylene and propylene with frequent chemical inversion of propylene units. It was also found that the CpTiCl3/SiO2‐MAO catalyst system can afford poly(ethylene‐co‐1‐hexadecene) containing a large amount of 1‐hexadecene. The mechanisms of stereochemical control(isospecificity and regiospecificity) are discussed from these results.
Polyolefin based gas separation membranes
Authors: Lin Shangan , Lin Shaokun , Chen Xuexin 
Published: March 2011

AbstractThree kinds of membrane material were prepared by means of modification or functionalization of polyolefin. They are terpolymer of ehtylene, propene and butene‐1 (EPB), poly (butadiene‐ block‐ dimethylsiloxane) copolymer (PB‐ b‐ PDMS), and sulfonated EPDM metallic salt ionomer (S‐ EPDM‐ Me). These materials are used as oxygen enrichment membranes. Some interesting results were obtained from the separation of oxygen and nitrogen, e. g. the permeation coefficients of oxygen (P) for EPB, PB‐b‐PDMS and S‐EPDM‐Me are 23.5 × 10−10, 59.7 × 10−10 and 12.1 × 10−10 cm3(STP) · cm/cm2 · s · cmHg, and the separation factors (P/P) are 3. 8, 4. 5 and 4. 5, respectively.
Monte Carlo modelling of the polymer glass transition
Authors: Paul W. , Binder K. , Batoulis J. , Pittel B. , Sommer K. H. 
Published: March 2011

AbstractWe are proposing a lattice model with chemical input for the computer modelling of the polymer glass transition. The chemical input information is obtained by a coarse graining procedure applied to a microscopic model with full chemical detail. We use this information on Bisphenol‐A‐Polycarbonate to predict it's Vogel‐Fulcher temperature out of a dynamic Monte Carlo Simulation. The microscopic structure of the lattice model is that of a genuine amorphous material, and the structural relaxation obeys the time temperature superposition.
A QSPR for the Tg of polymers: The Koehler‐Hopfinger approach using the tripos 5.2 force field
Authors: Vaz Roy J. 
Published: March 2011

AbstractThe Koehler Hopfinger model1,2 has been modified. The modification has worked fairly well with the Tripos 5.2 Force Field together with charges calculated using the Gasteiger Marsili method. This modification has been checked using the same monomers as those used in the original reference. The table, with monomers from a few chemical functionalities such as acrylates, ethers etc. was subjected to a Hierarchical Cluster Analysis which provided justification for creating “designer” equations for each class of chemical functionality. The “designer” equations for acrylates and olefins are described. The scheme utilized the Partial Least Squares (PLS) method as available within Sybyl 5.41 in order to draw the correlations.
Donor‐ and acceptor‐modified metallocene‐based homogeneous Ziegler‐Natta catalysts
Authors: Fischer David , Jüngling Stephan , Mülhaupt Rolf 
Published: March 2011

AbstractThe polymerization kinetics of propene polymerization using metallocene/methylaluminoxane (MAO) homogeneous catalysts have been investigated to explore the role of donor/acceptor interactions and to enhance the catalyst productivities. In the case of the non‐stereospecific Cp2ZrCl2/MAO model system it has been demonstrated that, in addition to the well known irreversible deactivation, reversible deactivations, which are second order relative to the zirconium active site concentration, account for the decay of the polymerization rate. While MAO injection during polymerization enhances the polymerization rate, zirconocene addition deactivates the catalyst which can be reactivated by injecting additional MAO. A sequence of dynamic equilibria involving the formation of active cationic metallocene intermediates as well as inactive zirconocene species, e.g., zirconocene dimers, is proposed. Lewis base and Lewis acid additives have been added as probes to examine the role of such equilibria in the case of metallocene‐based catalyst systems such as MAO‐activated Cp2ZrCl2, racemic ethylenebisindenyl zirconium dichloride (EBIZrCl2), and racemic ethylenebis (4,5,6,7‐tetrahydroindenyl) zirconium dichloride (EBTHIZrCl2). While the conventional donors such as 2,6‐ditert.butyl‐4‐methylphenol (BHT) and 2,2,6,6‐tetramethylpiperidine (TMP) reduce catalyst productivities, even at very low donor/Al molar ratios, increasing propene concentration and addition of trimethylboroxine (TMB) substantially enhance catalyst productivities and affect molecular weights of the polypropylene produced with metallocene/MAO catalysts.
Synthesis and properties of stereoregular fluoro‐polymers via ring‐opening metathesis polymerization of fluorinated norbornenes and norbornadienes. An overview and progress report
Authors: Davies Geoffrey R. , James Feast W. , Gibson Vernon C. , Hubbard Hugh V. ST. A. , Ivin Kenneth J. , Kenwright Alan M. , Khosravi Ezat , Marshall Edward L. , Mitchell Jonathan P. , Ward Ian M. , Wilson Brian 
Published: March 2011

AbstractSince the first report of the ring‐opening metathesis polymerization of fluorinated monomers in 1979 considerable advances in precision and control of such syntheses have been achieved through the introduction of well defined initiators. It is now possible to carry out well controlled living and stereoregular polymerizations. The products of such syntheses can display unusually high relaxed dielectric constants, an observation which is crucial to the assignment of their tacticities and probably significant with regard to possible applications of this type of material.
Alkylidenic polymerization of alkynes from w‐based initiators: Kinetics and mechanism of activation by lewis acids
Authors: Lucas Christine , Soum Alain , Fontanille Michel 
Published: March 2011

AbstractThe polymerization of alkynes initiated by metathesis catalysts proceeds via a mechanism similar to that of the ring‐opening metathesis polymerization of cycloalkenes. Various polymerizing systems have been claimed by several authors as bringing about living character; they point out the strong influence of the substituents carried by the monomer which have been shown to hinder transfer and termination processes. Whatever the initiator used, the activity of the polymerizing system is low; this paper deals with the activation of Rudler type initiator by Lewis acids. The effect of AlR3, AlR2Cl, AlRCl2, BR3 and B(OR)3 is presented and discussed.
General principles of polymer processing modeling
Authors: Agassant J.F. , Vergnes B. , Vincent M. 
Published: March 2011

AbstractSpecific rheological and thermal properties of molten polymers and their consequences on the numerical simulation of forming processes are first reviewed. The strong coupling between flow kinematics and material temperature is pointed out. According to geometrical specificities, to the type of deformation the material is submitted to and to thermal conditions, continuum mechanics and energy balance equations can be simplified and more or less sophisticated rheological equations can be used. Finally, these considerations are applied to the modeling of steady extrusion and fiber spinning and of unsteady molding processes.
Reactive blending of polymers by interfacial free‐radical grafting
Authors: Lambla Morand , Seadan Manus 
Published: March 2011

AbstractIn blends of immiscible polymers, amphiphilic species are needed for both morphological stabilization and improvement of the mechanical properties throughout successive processing steps. In order to obtain the required concentration of amphiphilic copolymer at the interface, it seemed of interest to test the possibility of creating these species by in situ reactivity at the interface, for instance by condensation reactions occurring between functionalized polymers. There is another possibility based on the fact that most of the polymers are hydrocarbon compounds, so they are subjected to free‐radical reactivity by hydrogen abstraction on the different hydrocarbon sites. The created free‐radical polymeric species may react together leading to the well known reactions of crosslinking, grafting and/or chain degradation. Therefore, this work deals with reciprocal free‐radical reactivity of two kinds of semi‐crystalline polymers, namely one polyolefin (LDPE, HDPE, PP or EPR) associated with a polyamide (PA‐11 or PA‐6). The reaction has to occur mainly at the interface, where the resulting grafted copolymers have to be anchored for final stabilization of the biphasic system. The level of interfacial grafting and the resulting properties of the reacted blends were characterized carefully, confirming the efficiency of the interpolymeric grafting.