bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric characterization of latex suspensions by microwave spectrometry using mixture laws
Authors: David R. , Henry F. , Pichot C. 
Published: March 2011

AbstractMixtures of latexes and aqueous solutions of CaCl2, NaCl and KCl have been characterized by dielectric spectrometry in the microwave domain (at 5 GHz and at room temperature). The interpretation of the data was based on the concept of mixture laws applied for low concentrations of latex (< 10% in weight) and salt (concentration < 1 mol.1−1). The additivity of dielectric properties was in good agreement with that predicted using classical mixture laws.
Polymeric surfactants in emulsion polymerization
Authors: Piirma I. 
Published: March 2011

AbstractThe stabilizing efficiency of a variety of amphipathic copolymers was studied in aqueous emulsion polymerizations of styrene, methyl methacrylate and acrylonitrile. Using the number, and size of the particles as the criterion of stability, it was found that the availability for anchoring of the backbone in the amphipathic graft copolymers was crucial for stability. Within a system, a change in the backbone chain length with the same percent hydrophilic grafts had no effect on the outcome of the reaction: the latices stabilized to the same number of particles of the same size.The results with the polystyrene‐block‐poly(ethylene oxide) copolymers as stabilizers in styrene polymerization gave indication that for efficient anchoring the block length need not be more than 10 monomeric units, and that a poly(ethylene oxide) (PEO) with weight‐average molecular weight Mw = 3000 is just as effective stabilizer as is a block with PEO of Mn = 9000.
Batch emulsion copolymerization of 50/50 vinyl acetate/ n‐butyl acrylate using poly(vinyl alcohol) emulsifier
Authors: Vanderhoff J. W. , Earhart N. J. , Dimonie V. L. , El‐Aasser M. S. 
Published: March 2011

AbstractIn the batch emulsion copolymerization of 50/50 vinyl acetate/n‐butyl acrylate mixture, no emulsifier or sodium lauryl sulfate emulsifier gave a n‐butyl acrylate‐rich copolymer until the n‐butyl acrylate became depleted, and a vinyl acetate‐rich copolymer and poly(vinyl acetate) thereafter, as expected from the disparate copolymerization reactivity ratios (r1 0.05; r2 5). In contrast, poly(vinyl alcohol) emulsifier gave an initial polymerization of vinyl acetate at a rate equal to or greater than that of the n‐butyl acrylate up to 7–37% conversion; then, the n‐butyl acrylate polymerized preferentially until it became depleted, followed by the remaining vinyl acetate, to give a vinyl acetate‐rich copolymer and poly(vinyl acetate), as expected from the copolymerization reactivity ratios. The mechanism proposed for this process comprised the grafting of vinyl acetate on the poly(vinyl alcohol) in solution to give a water‐insoluble graft copolymer, which precipitated and served as the locus for nucleation of poly(n‐butyl acrylate)‐rich particles. Fully hydrolyzed poly(vinyl alcohol) required a higher degree of grafting to give a water‐insoluble graft copolymer than partially hydrolyzed poly(vinyl alcohol).
Stereospecific and anionic ring‐opening polymerization
Authors: Spassky Nicolas 
Published: March 2011

AbstractThe polymerization features of the polymerization of heterocyclic monomers using anionic or coordinated anionic type initiators are examined. The chemical and configurational structure of initiating species depends on the regiospecificity of the ring‐opening reaction. Propagating rate constants, solvation and macrocyclisation phenomena are discussed. The structure and the chemical composition of stereospecific initiators are described. Different types of mechanisms (enantiomorphic sites and end‐chain) are illustrated. The dependence of selectivity on different parameters is discussed. Various aspects of chiral catalysis leading to stereoelective and enantiogenic processes are presented. Some examples of recent trends in anionic and stereospecific ring‐opening polymerization are given.
Use of cyclic carbonate oligomers in the synthesis of bisphenol‐a polycarbonate‐polydimethylsiloxane copolymers
Authors: Evans Thomas L. , Carpenter John C. 
Published: March 2011

AbstractPolydimethylsiloxane‐polycarbonate block copolymers were prepared by sequential anionic polymerizations of cyclic carbonate oligomers and octamethylcyclotetrasiloxane, or by reaction of hydroxy‐terminated polydimethylsiloxane oligomers with cyclic carbonates or by reaction of hydroxy‐terminated polycarbonate oligomers (derived from cyclic carbonates) with chlorine‐terminated polydimethylsiloxane oligomers. The use of cyclic carbonates for making the copolymers afforded a synthetic flexibility not available through conventional methods involving phosgene.
Ring‐opening polymerization of cyclic ketene acetals and unsaturated cyclic spiro ortho esters
Authors: Bailey William J. , Gu Jia‐Ming , Lin Yin‐Nian , Zheng Zhi‐Feng , Zhou Lin‐Lin 
Published: March 2011

AbstractThree new substituted cyclic ketene acetals and two unsaturated spiro ortho esters were synthesized. The free radical polymerization of cyclic ketene acetals gave zero or very low yields because of steric hindrance effects. However, cationic polymerization gave relatively high yields of polymers with predominant ring opening. Although the cationic polymerization of the spiro ortho esters produced mostly double ring‐opened polymers, their free radical polymerization yielded non‐ring‐opened polymers.
Functional oligomers of norbornene, 2 ‐ kinetics and mechanism of the oligomerization reaction
Authors: Cramail Henri , Fontanille Michel , Soum Alain 
Published: March 2011

AbstractA comprehensive study of initiation and propagation steps of norbornene oligomerization initiated by WC16/Me4Sn in the presence of unsaturated diesters, was carried out. Kinetic orders, apparent rate constants and thermodynamic parameters were determined. Given the experimental results, a mechanism of both initiation and propagation reactions is proposed.
Ring‐opening metathesis polymerization and cyclic organoborane monomer
Authors: Chung T. C. 
Published: March 2011

AbstractThis paper summarizes our research result in the preparation of functional groups containing polyolefins, including linear and cyclic polymers, by using ring‐opening metathesis polymerization (ROMP) and cyclic organoborane monomers. Most organoborane moieties are very stable to metathesis catalysts. In turn, the borane containing polymers can be converted to a broad range of functional polymers with various functional groups, such as ‐OH, ‐NH2, ‐NHR, under mild conditions. With some pre‐designed monomers, several unique polymer structures, such as alternating copolymers have been prepared. In addition, the conformation of the polymer chain, from high cis double bonds to high trans ones, can be controlled by using various catalyst systems and reactions conditions. In this paper, we will also discuss some physical properties of the resulting polymers including thermal stability and chain conformations in selective solvents and at air‐water interfaces.
Synthesis, mechanisms. Kinetics and characterization of polyamic acid and polyetherimides
Authors: Grenier‐Loustalot Marie‐Florence , Joubert Frédéric , Grenier Philippe 
Published: March 2011

AbstractWe have synthesized a series of model compounds to study the polymerization mechanisms of polyamic acids prepared from a dianhydride and an aromatic diamine. Structural information (FTIR, liquid and solid (CPMAS) 13C NMR spectroscopy) obtained with model compounds has enabled the precise determination of the endchains (anhydride/amine acid ratios) in the polymers synthesized. In terms of reaction mechanisms, it was snown that the reaction path of dianhydride ring opening is such that the carbon atom bearing the carbonyl group on the benzene ring (meta from the bridge) preferentially undergoes nucleophilic attack and that the anhydride rings on the initial monomer can be considered to be independant. It was also shown that the reaction solvent has a very pronounced effect on the stereoselectivity of the reaction.
Aluminium‐27 NMR studies of aluminiumporphyrins
Authors: Desimone J. M. , Stangle M. , Riffle J. S. , McGrath J. E. 
Published: March 2011

AbstractAluminium‐27 NMR has been employed to study several different aluminiumporphyrins based on (5, 10, 15, 20‐tetraphenyl)porphyrin (TPPH2). The aluminiumporphyrins were formed by reacting a stoichiometric amount of trialkylaluminium with TPPH2to yield TPPAl‐R. The resulting aluminiumporphyrin was modified by adding a stoichiometric amount of various carboxylic acids to form aluminiumporphyrin carboxylates that had varying steric and electronic effects on the macrocycle.
Synthesis of rodlike polyhydrocarbons
Authors: Heitz W. 
Published: March 2011

AbstractStiff macromolecules are obtained by combining two aromatic units, either directly or by vinylene or ethynylene. The palladium‐catalyzed synthesis of poly(1,4‐phenylenevinylene), poly(1,4‐phenyleneethynylene), and poly‐p‐phenylene is described. Side reactions influencing the rodlike structure are investigated by model reactions.Phenyl‐substituted poly‐p‐phenylene is obtained starting from phenyl‐1,4‐dibromobenzene. This is a solution and melt processable polymer that is stable up to 600°C. By anionic polymerization of 2‐phenyl‐1,3‐cyclohexadiene a precursor polymer with Mw/Mn = 1,1 can be obtained with molecular weights up to 30 000. By aromatization, poly(phenyl‐1,4‐phenylene) with a narrow molecular weight distribution is obtained. All of these polymers show thermotropic behaviour.Poly(1,4‐pyridinium salts) are a new class of polymers. They are rodlike polycations. With large gegenions they are soluble in organic solvents.
Rotational barriers and chain dynamics
Authors: Allegra Giuseppe , Ganazzoli Fabio 
Published: March 2011

AbstractInternal viscosity, or the high‐frequency viscous dissipation in polymer dynamics originating from the rotational energy barriers around skeletal bonds, is basically attributed to hindrance against the motion of conformational changes along the chain contour. The non‐equilibrium statistical‐mechanical background of the theory is discussed. Comparison between calculations and experimental results of the complex modulus and of the optical flow birefringence from polystyrene solutions under alternating shear stress is discussed. The best‐fitting value of the characteristic time for bond rotation τ0, i.e., the only parameter required for internal viscosity, is in good agreement with the results of NMR, ESR and dielectric relaxation experiments.
Degradable polyethylene‐starch complex
Authors: Albertsson Ann‐Christine , Karlsson Sigbritt 
Published: March 2011

AbstractA biodegradable additive is often included in otherwise inert polymers in order to get a degradable material. Low density polyethylene (LDPE) containing starch in a masterbatch (MB) was degraded by photooxidation (UV). LDPE samples containing MB were more degraded than LDPE samples containing only starch. The MB contains a transition metal and an antioxidant thereby improving the total environmental degradation.
Shaping molecules and molecular architectures for linear and non‐linear optical properties
Authors: Wegner Gerhard 
Published: March 2011

AbstractThe linear and non‐linear optical (NLO) properties of novel macromolecular materials are described. Solid polyelectrolyte glasses exhibit high refractive indeces and excellent transmission at low dispersion. Polyconjugated macromolecules provide for materials with NLO‐properties interesting for χ(3)‐processes. The scaling behaviour of χ(3)∼λmax is demonstrated. Ultrathin layers of hairy‐rod type polymers are excellent objects to study wave‐guide related processes in organic systems.
Mesomorphic poly(diethylsiloxane) elastomers
Authors: Godovsky Yu. K. , Valetskaya L. A. , Papkov V. S. 
Published: March 2011

AbstractThe prediction of the long‐term behaviour of polymeric materials ageing outdoors can be based on the so‐called “mechanistic” approach, i.e. the recognition of the mechanisms of the chemical evolution in artificial photoageing and in weathering. As far as no physical ageing is involved, the variations through weathering of the physical properties are only due to the chemical evolution. In such conditions, the expansion scale for experiment time can be based on the acceleration of the ongoing chemistry in artificial photoageing.To recognize the mechanisms previously observed in laboratory conditions, it is of main importance to identify the intermediate and final photoproducts in the first layers of the polymeric materials exposed outdoors. This detailed analysis can be carried out, at present time, by means of micro‐FTIR‐spectrophotometry, a recent development of FTIR spectroscopy, which allows measurements on 5–10 μm layers. Examples of determinations on polyamides, PVC and dienic elastomers will be presented and the origin of various photoproduct profiles will be discussed.
Thermolysis of diaryl disulfides: A new route to poly(arylene sulfide)s
Authors: Wang Zhi Yuan , Hay Allan S. 
Published: March 2011

AbstractThermolysis of diphenyl disulfide in the presence of iodoarenes yielded the corresponding unsymmetric diaryl sulfides. This new reaction has been utilized for the synthesis of high molecular weight poly(phenylene sulfide) and poly(naphthylene sulfide)s, starting from bis(4‐iodophenyl) disulfide and bis(iodonaphthyl) disulfides. Poly(phenylene sulfide) with a melting temperature above 250 °C was also obtained from bis(4‐bromophenyl) disulfide in the presence of a suitable reducing agent (e.g. potassium iodide). Heating bis(4‐chlorophenyl) disulfide afforded only a low molecular weight polymer. Bis(4‐fluorophenyl) disulfide remained stable under the same thermolysis conditions.
New synthesis of polyamides and related condensation polymers by using N‐trimethylsilyl‐substituted diamine monomers
Authors: Inai Yoshio 
Published: March 2011

AbstractThis article reviews our current work on the synthesis using N‐trimethylsilyl‐substituted diamines for polyamides and related condensation polymers. The polycondensations of N‐silylated aromatic diamines with aromatic dicarboxylic acid chlorides proceeded much more rapidly and yielded higher molecular weight aramids, compared with the polymerizations using the parent diamines. Thus, this method is efficient and versatile over the conventional diamine route for the synthesis of aramids, as well as other diamine‐based condensation polymers including polybenzoxazoles and polyimides having high molecular weights.
Polyrotaxanes: Synthetic methodologies & characterization
Authors: Gibson Harry W. , Engen Paul T. , Shen Xi Ya , Sze Jean , Lim Christina , Bheda Mukesh , Wu Charles 
Published: March 2011

AbstractThe synthesis of polyrotaxanes, comprised of linear macromolecules threaded through cyclic species, may be accomplished by either of two strategies: (1) statistical threading, in which the macrocycle is used as solvent and threading is predominantly entropically driven, or (2) template threading, involving an enthalpic driving force such as charge transfer or metal complexation. This paper summarizes our efforts in this field by describing syntheses by both step and chain growth methodologies and the characterization of the resultant polyrotaxanes. Examples include polyesters, polyethers, polyurethanes, polystyrene and polyacrylonitrile. The polyrotaxanes possess properties (thermal, solubility, mechanical, etc.) that differ from the corresponding linear polymers. In some systems phase separation occurs, producing morphologies that consist of crystalline macrocycles and either amorphous or crystalline linear backbones; these results demonstrate the ability of the macrocycles to move along the linear backbone in the melt without dethreading.
Benzocyclobutenes in polymer synthesis
Authors: Kirchhoff R. A. , Bruza K. , Carriere C. , Rondan N. 
Published: March 2011

AbstractBenzocyclobutenes constitute the basis of a new and versatile approach to the synthesis of high performance polymers for applications in the electronics and aerospace industries. The basic technology involves a family of thermally polymerizable monomers which contains one or more benzocyclobutene groups per molecule. The benzocyclobutene when heated to 200°C undergoes a retrocyclic opening of the aliphatic four membered ring to afford the highly reactive o‐xylylene, which can either react with itself, or react with other sites of unsaturation leading to the formation of thermally stable polymers. Depending upon their functionality, these monomers can be polymerized to yield either thermoset or thermoplastic materials. The polymers typically exhibit good thermal stability and retention of mechanical properties at elevated temperature. The monomers are processable from the melt and are useful in the preparation of high temperature coatings, advanced composites and adhesives.
Interfacial interactions in particulate filled thermoplastics: Mechanism, strength, properties
Authors: Pukánszky Béla 
Published: March 2011

AbstractUsing the results of stress analysis the factors influencing the micromechanical deformations in particulate filled composites were studied. It was shown that interfacial interactions influence slightly shear yielding and crazing, but have a significant effect on dewetting. Interactions can be modified by surface treatment. Types and mechanisms of surface treatment are discussed. A model describing the composition dependence of tensile properties makes possible the quantitative evaluation of interaction. Attention is called to the importance of composite structure; aggregation, orientation of anisotropic particles, nucleating effect of the filler, all can change the properties of the composite.
Monosized polymer particles in biochemical and biomedical separations
Authors: Ellingsen Turid , Aune Oddvar , Berge Arvid , Kilaas Lars , Schmid Ruth , Stenstad Per , Ugelstad John , Hagen Steinar , Weng Ellen , Johansen Liv 
Published: March 2011

AbstractThe method of activated swelling allows production of highly monodisperse polymer particles in the range of 1 to 100μm, with identical bead‐to‐bead morphology. Monosized particles with a wide variety in content of crosslinker, pore size and pore size distribution have been evaluated in different areas of biotechnology. Underivatized macroporous particles have been developed for reversed phase and size exclusion chromatography in organic solvents. Supports for aqueous phase ion exchange have been produced by covalent coupling of a hydrophilic layer to the particle surface. These media give excellent characteristics with regard to selectivity, capacity and recoveries of biomolecules. In this paper proteins and peptides are used to illustrate chromatographic performance. Monosized polymer particles have been magnetized by a process where magnetic iron oxides are formed inside preformed monodisperse particles. These particles are used extensively in selective isolation of cells and bacteria and in DNA technology. This paper reviews some new results in the field of cell separation.
Use of micro‐FTIR spectrophotometry in the determination of polymer photoageing mechanisms
Authors: Lemaire Jacques , Gardette Jean‐Luc , Lacoste Jacques 
Published: March 2011

AbstractThe mechanisms of artificial accelerated photoageing, in the meaning of the “mechanistic” approach recently developed, have been determined for many classes of polymeric materials. The mechanism accounts for the formation and conversion of the main intermediate photoproducts and for the accumulation of final photoproducts. Based on the observed kinetics of the chemical evolution, described through the variations of a single critical photoproduct in artificial conditions and in the early stages of weathering, the lifetimes of polymeric materials can be predicted in many circumstances. Moreover, in the mechanistic approach, the influence of each photostabilizer (anti‐UV, conventional antioxidant, redox antioxidant, hydroperoxide reducer) is evaluated and rationalized from the rate of formation of the critical photoproducts. The recognition of the on‐going mechanism which controls the weathering of unstabilized and stabilized polymers is therefore of major importance to allow the conversion of data collected in laboratory to data corresponding to the real use. Fourier Transform Infrared (FTIR) microspectrophotometric determinations of profiles of final critical photoproducts and of residual photostabilizers afford a direct control of the relevancy of laboratory experiments. This recent technique which couples the FTIR technique and IR microscopy allows a full chemical analysis of 100 μm2‐microzones or of 5 μm‐elementary layers at the surface of the sample. Profiles could be determined up to 200–300 μm from the surface. Examples of polymers whose photoageing is completely controlled by chemical defects like pigmented poly(vinyl chloride) (PVC) and poly(methyl methacrylate) (PMMA) will be presented. Photooxidation, thermooxidation and ozonization of dienic elastomers will be compared to actual weathering to demonstrate the irrelevancy of the ozone test for the prediction of longterm behaviour of elastomers in the presence of light.
Comparison of living polymerization systems
Authors: Iván Béla 
Published: March 2011

AbstractRecent developments in the field of living polymerization are surveyed. Comparison of the available mechanistic and kinetic information is made for living anionic, cationic, free radical, group transfer, ring‐opening metathesis, Ziegler‐Natta and immortal polymerizations. This evaluation indicates that the majority of living polymerizations involve quasiliving equilibrium between active (propagating) and dormant (nonpropagating) polymer chains. On the basis of the kinetics of a general model for quasiliving and ideal living polymerizations it is concluded that ideal living polymerization is a special subclass of quasiliving polymerizations. Classification of living polymerization systems is also attempted.
Polymer chains in good solvent within attracting walls
Authors: Allegra G. 
Published: March 2011

AbstractIt is known that a polymer chain in an ideal solvent confined within parallel attracting walls undergoes a second‐order transition at the temperature T* satisfying the equation exp[‐ε/(kBT*)]=6/5; here the model consists of a chain placed on a cubic lattice, and ε (<0) is the attractive energy experienced by a chain segment contacting a wall.We then investigate the effect induced by a good solvent upon the chain behavior. A single chain is considered; within the Gaussian approximation, we assume that its partition function may be factorized in two terms, one across the wall planes and another parallel to them. For an interplanar distance L significantly smaller than the average radius of gyration the compressed chain is assumed to reach a uniform density, so that the free energy contribution due to the intrachain atomic contacts is a function of the density alone. It may be shown that the effective value of ε/(kBT*)(=σ) is the difference between the value to be expected “in vacuo” and β/(z‐2), where z is the degree of coordination of the lattice and β is the excluded‐volume parameter. As a result, for large values of L we may have an attractive effect exerted by the chain on the walls whereas at small L's we invariably have a repulsion. For the cubic lattice we have a repulsion and an attraction for large L approximatively for σ < ln(6/5)+β/(z‐2) and for σ > (ln(6/5)+β/(z‐2), respectively, whereas we have inversion between the two regimes at some distance L for intermediate values of σ. In the limit of an infinite molecular weight the inversion translates into a thermodynamic transition.We believe the present model may explain some important features seen in polymer adhesion.