bluuebunny/crossref_metadata_2025_split huggingface dataset:
Copolymerization of methacryloyl‐terminated PMMA macromonomers with methyl methacrylate
Authors: Radke Wolfgang , Müller Axel H. E. 
Published: March 2011

AbstractMethacryloyl‐terminated macromonomers (MM) of polymethylmethacrylate (PMMA) of two different molecular weights were prepared by group transfer polymerization (GTP). They were copolymerized with methyl methacrylate (MMA) by radical polymerization using toluene as the solvent. The relative reactivity of the MM, 1/r1, decreases with increasing initial MM concentration. This is interpreted as a consequence of the increasing viscosity of the reaction medium leading to an increasing diffusion control of the MM addition. At a constant weight ratio of MMA to MM the reactivity of the longer macromonomer is higher than of the shorter one. Increasing the molar ratio [MMA]/[MM], i.e. increasing the average distance between two grafts in the resulting comb polymer, increases the reactivity of the MM. These results are interpreted on the basis of a model describing the segment density in the vicinity of the radical chain end of the comb polymer.
The mechanism of plasma‐induced polymerization
Authors: Simionescu Cristofor I. , Simionescu Bogdan C. 
Published: March 2011

AbstractThe paper is concerned with the discussion of the different mechanisms proposed for plasma‐induced (initiated) polymerization. This new approach to polymer synthesis proceeds through a free radical mechanism, but presents some peculiar characteristics. The initiation reaction is practically instantaneous and the activity of the propagating chains appears to be unusually high and very stable in time.
Mechanism and microstructure in the free‐radical polymerization of vinyl chloride: Head‐to‐head addition revisited
Authors: Starnes W. H. , Wojciechowski B. J. 
Published: March 2011

AbstractThe recent realization that 1,2‐dichloroethyl branches occur in poly(vinyl chloride) (PVC) has now led to a full description of the chemical consequences of head‐to‐head addition during the free‐radical polymerization of vinyl chloride (VC). A kinetic analysis of the relevant reaction scheme is developed here and then verified with the aid of literature values for the branch concentrations of PVC samples prepared by polymerization at subsaturation VC pressures. The analysis allows the following conclusions to be drawn: (1) Kinetically free chlorine atoms are not formed from polymeric ‐CHCl‐CH‐CH2Cl or ‐CH2‐CH‐CHCl‐CH2Cl radicals. Loss of chlorine from these radicals results exclusively, instead, from β scission reactions that transfer chlorine directly to the monomer and are kinetically second‐order, overall. (2) The monomer transfer constant that pertains to the transfer occurring after head‐to‐head addition is, indeed, a true constant that is independent of the concentration of VC. (3) In conventional bulk or suspension VC polymerizations, the rates of the propagation reactions are not controlled by diffusion, even at conversions of ca. 90%. (4) A second type of monomer transfer process probably is responsible for the reductions in polymer molecular weight that result from polymerization at subsaturation VC pressures. This transfer pathway involves the inter‐ and/or intramolecular abstraction of methylene hydrogen from the polymer by the ordinary head‐to‐tail macroradicals. The resultant β‐chloroalkyl radicals then transfer chlorine to VC by β scission.
Cooperativity and chirality in a wormlike helical macromolecule
Authors: Green Mark M. , Peterson Norman C. , Lifson Shneior , Sato Takahiro , Teramoto Akio 
Published: March 2011

AbstractA question about broken rods and worms concerning the dimensional characteristics of poly(alkyl isocyanates) led to the discovery of an extreme sensitivity of this polymer class to tiny chiral perturbations. There is a cooperative source of this phenomenon and statistical thermodynamic methods allow quantitative expression to the forces at work. From this effort we could answer the original question and also extend these ideas into the area of lyotropic liquid crystals where the interplay of macromolecular and supramolecular helicity seems to play by the same rules.
Synthesis and characterization of thermotropic polyester‐block‐polyethers
Authors: Thuillier Pascal , Tessier Martine , Maréchal Ernest 
Published: March 2011

AbstractPolyester‐block‐polyethers with rigid thermotropic polyarylate blocks are prepared and studied. Rigid polyarylates are poly(1,5‐pentanediyl 4,4′‐biphenyl‐dicarboxylate) or poly(1,5‐pentanediyl 4,4′‐trans‐stilbenedicarboxylate). Flexible blocks are oligo(oxytetramethylene)s (M̄n = 620 or 2030). The block copolymers are characterized by 1H and 13C NMR spectroscopies. The use of 500 MHz 1H NMR permits their complete structural analysis showing that they contain a cyclic oligomer. SEC, polarizing microscopy and X‐ray studies show that their mesophase is smectic. Their viscoelastic properties are compared to those of some aromatic polyester‐block‐polyethers.
Novel organoboron polymers hydroboration polymerization and haloboration polymerization
Authors: Chujo Y. , Tomita I. , Saegusa T. 
Published: March 2011

AbstractAs a novel methodology for the preparation of organoboron polymers, this paper describes “hydroboration polymerization” and “haloboration polymerization”. A polyaddition between diene and tert‐hexylborane (thexylborane) produced a polymer consisting of C‐B bonds in the main chain. The resulting organoboron polymers can be regarded as a polymer homologue of trialkylborane and can be expected as a novel type of reactive polymers. For example, the reaction of organoboron polymer with carbon monoxide followed by the oxidative treatment produced a polyalcohol by the migration of C‐B bonds. Similarly, the reaction with potassium cyanide produced a polyketone. On the other hand, hydroboration polymerization of dicyano compounds such as isophthalonitrile with t‐butylborane produced an air‐stable boron‐containing polymer (polycyclodiborazane) having B‐N four‐membered rings via dimerization of iminoborane species. In haloboration polymerization, i.e., a polyaddition between diacetylene and boron tribromide, a linear poly(organoboron halide) was obtained. This polymer still has B‐Br bonds in its structure and was used not only as a novel reactive polymer but also as a polymeric Lewis acid.
Stereospecific living polymerization and copolymerization of methacrylate and their use for construction of stereoregular chain architecture
Authors: Hatada Koichi , Kitayama Tatsuki , Ute Koichi 
Published: March 2011

AbstractHighly isotactic and highly syndiotactic living polymerizations of alkyl methacrylates were carried out in toluene at low temperatures by t‐C4H9MgBr and t‐C4H9Li‐R3A1, respectively. These living polymerizations enabled us to prepare highly stereoregular block and random copolymers of methacrylates with narrow molecular weight distributions. Reaction of ethylene glycol dimethacrylate with isotactic PMMA anion gave a highly branched star polymer. Syndiotactic PMMA star polymer was prepared by similar method. Stereoregular PMMA macromonomers with styrene and methacryloyl functions were prepared by using the stereospecific living polymerizations and polymerized by radical and anionic mechanisms. It was found that isotactic PMMA formed stereocomplexes with various types of syndiotactic polymethacrylates when treated under certain conditions. The complexes showed melting points which differ in a wide range of temperature. Isotactic and syndiotactic MMA oligomers without molecular weight distribution were isolated by supercritical fluid chromatography up to 29‐mer and characterized.
Molecular architecture control in acrylic polymers by group transfer polymerization
Authors: Webster Owen W. 
Published: March 2011

AbstractGroup transfer polymerization (GTP)a of acrylic monomers is mediated by a trialkylsilyl‐capped growing chain end. It operates at room temperature and above and permits a high degree of molecular architecture control. Block, comb, graft, star, and loop polymers are readily synthesized. It appears that GTP is an associative process under mild nucleophilic catalysis and a dissociative process under strong nucleophilic catalysis.
Folded chain crystallization of thermotropic, random terpolymer, main chain liquid crystal polymers
Authors: Kent S. L. , Geil P. H. 
Published: March 2011

AbstractSingle crystals, suitable for electron microscopy and diffraction, have been grown from the quiescent and sheared “liquid crystal” state and solution for several random terpolymer polyesters having a nearly equimolar amount of a flexible segment dicarboxylate (4–7 CH2), oxybenzoate and dioxyphenyl. In all cases, in thin films and on free surfaces, folded chain lamellae are observed. High temperature electron diffraction has permitted characterization of the transition behavior and structure of the liquid crystal state. Permanganate etching permitted characterization of the interior of molded, extruded or spun samples; in these cases extended chain lamellae are observed. The results suggest chain folding in the nematic state at least in the thin films and on surfaces, with chain folding also possible in the bulk followed by chain extension by “sliding” diffusion.
Phase separation in bulk statistical copolymers and their mixtures with homopolymers. I. Theory
Authors: šolc K. 
Published: March 2011

AbstractA method based on the Flory‐Huggins thermodynamics is presented for modeling phase equilibria in bulk statistical copolymers of two monomers. For a given phase separation, a component's preference for one of the phases depends only on its composition, and there always exists a balanced composition which shows no preference at all and assumes equal concentrations in both phases. In contrast, the degree of enrichment depends exponentially on the component's chain length and the magnitude of the deviation of its composition from the balanced one. A fast two‐loop iteration scheme is devised for numerical computation of phase equilibria for any distribution of chain length and composition. Critical state formulas can be cast succintly in terms of averages of deviations from the balanced composition (which here equals the z‐average composition). At the critical composition, the (z+1)‐average of cubed deviations has to be zero, whereas the critical value of the interaction parameter is inversely proportional to the z‐average of squared deviations and to the w‐average chain length. Thus, e.g., a copolymer with a symmetrical distribution always constitutes a critical mixture.
Polymer microspheres as carriers of the immobilized enzymes
Authors: Hayashi Toshio 
Published: March 2011

AbstractIn this paper, after an outline of the nature and methods of the immobilization of enzymes, some properties of covalently immobilized enzyme, such as enzymic activity, stability and specificity, will be discussed with experimental results obtained by us. Papain is selected as a model of hydrolytic enzymes, and polymer supports employed are polyacrolein microspheres, porous beads of chitosan, and poly(γ‐methyl‐L‐glutamate). The effect of spacer on the activity and stability of covalently immobilized enzyme is also considered.
Polymeric drugs as immunomodulatory vaccines against multiple sclerosis
Authors: Sela Michael 
Published: March 2011

AbstractCOP‐1, a synthetic basic random amino acid copolymer, is effective in suppression of experimental allergic encephalomyelitis in guinea pigs, rabbits, mice, rhesus monkeys and baboons, and of the exacerbating‐remitting type of multiple sclerosis in humans. COP‐1 is cross‐reactive at the monoclonal antibody level with the basic protein of the myelin sheath of the brain (BP), and the suppressive effect may be related to this immunological cross‐reaction. Indeed, competition for the major histocompatibility complex (MHC) class II antigen, between BP and COP‐1, may be one explanation for its beneficial effect in the disease. This polymeric drug, COP‐1, may, therefore, be considered also an immunomodulatory vaccine, and may serve as a prototype to vaccines against autoimmune diseases.
Development of N‐(2‐hydroxypropyl)methacrylamide copolymer conjugates for delivery of cancer chemotherapy
Authors: Duncan Ruth , Ulbrich Karel 
Published: March 2011

AbstractIn recent years a series of N‐(2‐hydroxypropyl)methacrylamide (HPMA) copolymers have been synthesised containing antitumour agents, particularly doxorubicin (Dox) bound to the polymer carrier by peptidyl spacers designed for cleavage by lysosomal thiol‐dependent proteases, enzymes known to show increased activity in metastatic tumours. Such conjugates display a broad range of antitumour activities against leukaemic, solid tumour and metastatic models, and recent experimentation has focussed on investigating further their mechanism of action. It is believed that drug conjugation leads to reduced toxicity, passive accumulation within solid tumours due to the enhanced permeability and retention effect and subsequent controlled drug release. All these factors contribute to the improved antitumour activity seen.
Nonlinear dielectric and conductive spectra of polymers
Authors: Furukawa Takeo 
Published: March 2011

AbstractNonlinear complex permittivities have been measured as a function of frequency for various polar polymers by applying a sinusoidal electric field and detecting higher harmonic dielectric responses. It is shown that the Debye relaxation of the linear permittivity accompanies the third‐order nonlinear relaxation represented by ϵ3*=δϵ3/(1+iωϵ3)3 in accord with phenomenological prediction. Combinations of relaxation strengths, δϵ1 and δϵ3, allow estimates of the saturation polarization as well as the moment and density of equivalent dipoles comprising the relaxation process. Analogous measurements and analysis have been extended to examine the nonlinear conductive spectra of ion‐conducting polymers.
Controlling the mechanical performance of composites
Authors: Vu‐Khanh T. 
Published: March 2011

AbstractThere are presently several models based on different assumptions out of which one may find one to predict the elastic properties of a given type of composite. However, there is not a single theory which can be used to model all systems. One of the difficulties encountered in verifying the proposed models is the non‐uniformity of the dimension, distribution, shape, and orientation of the reinforcement, resulting from the processing conditions of the composite in practice. Much work has been carried out in an effort to express theoretically the strength and stiffness of composites. In spite of extensive investigation efforts, prediction is still a controversial subject. Unlike the elastic properties, which involve only small deformations without irreversible processes, fracture performance depends on many parameters. Besides the reinforcement dimension, shape and orientation, the interfacial adhesion and the microscopic failure mechanisms also play major roles in both strength and toughness.
Elastomers and thermoplastics as modifiers for thermosetting resins
Authors: Bucknall C. B. , Maïstros G. , Gomez C. M. , Partridge I. K. 
Published: March 2011

AbstractFactors affecting mixing and demixing from solutions of thermoplastics and elastomers in epoxy resin are discussed, and related to morphology; dielectric monitoring is used to follow phase separation in curing elastomer blends. Mechanisms of toughening are related to morphology.
Polymer grafted on porous silica as supports for catalysts and reagents
Authors: Guyot A. , Revillon A. , Carlier E. , Leroux D. , Le Deore C. 
Published: March 2011

AbstractThe main part of the paper is dealing with 4 routes used to anchor chloromethyl groups to polymer grafted onto porous silica. The most efficient route involves first, grafting of a coupling agent bearing one function active in radical polymerization as initiator, comonomer or transfer agent, and then polymerization of vinylbenzyl chloride. The grafting efficiency, the homogeneity of the grafting process and the conformation of the grafted polymer are discussed, depending on the experimental conditions. Other grafted polymers are 1,2‐polybutadiene and poly(phenylsiloxane). For catalytic applications, chloromethyl groups are reacted with ephedrin and the resulting solid is used for benzaldehyde alkylation with diethylzinc. On the other hand, grafted poly(phenylsiloxane) is sulfonated and used for esterification and phenol alkylation by dodecene.
Synthesis and characterisation of porous polymers
Authors: Sherrington D. C. 
Published: March 2011

AbstractState‐of‐the‐art electron microscopic studies have been made of the ultrastructure of a matrix of specifically prepared styrene‐divinylbenzene resin sorbents. Image analysis methods have been applied to quantify the porous morphology of these resins in the “dry”, “freeze‐dried” and “frozen” states. Significant swelling has been demonstrated in the wet state. Highly porous Polyhipe® monoliths have been prepared and used to produce a polyamide‐impregnated composite support for use in solid phase synthesis of peptides. The composite shows good pressure resistance and allows high yields of pure peptides to be achieved. Polyhipe® polymers with very high surface areas (up to 350 m2g−1) have been prepared by applying the methodologies of porous particulate resin production to achieve highly porous walls in the Polyhipe® structures. Finally, novel procedures are described for the preparation of porous particulate polyimides and polybenzimidazoles involving a paraffin oil dispersion methodology. These thermooxidatively stable resins have been prepared with modest surface areas of ∼30 m2g−1 and offer good prospects for use as supports for alkene transition metal complex oxidation catalysts.
Application of ion‐exchange membranes in industrial processes
Authors: Strathmann H. 
Published: March 2011

AbstractIon‐exchange membranes are used on a large scale in many commercially relevant processes such as in electrolytical and electrodialytical procedures as well as in energy conversion or storage systems. The discussion in this paper, however, is concentrated on processes using ion‐exchange membranes in mass separation. The basic concept of the processes and their advantages as well as intrinsic limitations are discussed. Processes using ion‐exchange membranes in water treatment as well as in the chemical and food industry are described in selected examples and recent improvements in membrane products and process performance are discussed.
Transport of gases through polymeric membranes
Authors: Wessling M. , Boomgaard T.v.d. , Mulder M.H.V. , Smolders C. A. 
Published: March 2011

AbstractIn this paper tailor‐made polymers like polyoxadiazoles, polytriazoles and polyimides are compared with conventional polymers as gas separation membrane materials. Because their permeation characteristics as a function of the free volume does not compare too well with that of the conventional ones the term free volume was reconsidered. Based on a unique relation between the diffusion coefficient and the jump of the heat capacity at the glass transition temperature Tg, the transport mechanism in the polymer matrix is considered to occur in jump motions from one cavity to an adjacent one. This mechanism was reconfirmed by a molecular dynamics study. It is shown that mass transport at high penetrant concentrations is not time‐independent but a phenomenon with transient characteristics. This transient character is also found in the volumetric behaviour during sorption. The polymer matrix is described as a network with topological constraints which changes its state upon high swelling stresses induced by the sorbed penetrant.
New trends of membrane separation technology
Authors: Kimura Shoji 
Published: March 2011

AbstractFor separation of various organic ‐ aqueous mixtures and organic‐organic mixtures, there are three possible membrane separation technologies, namely, reverse osmosis(RO), pervaporation(PV) and vapor permeation(VP). A theoretical comparison is introduced. Using various membranes experimental data are demonstrated for varieties of such systems. Finally one example method to design a suitable membrane for a particular system is demonstrated.
High‐molecular‐weight ultraviolet stabilizers for plastics
Authors: Minagawa Motonobu , Kikkawa Kazumi 
Published: March 2011

AbstractThe effect of molecular weight (MW) of ultraviolet (UV) stabilizers (hindered amine light stabilizers and ultraviolet absorbers) on performance in plastics are discussed. There exists an optimum MW for them, which may change with test conditions, applications and so forth. Recent new trends in plastics used in automobile (higher temperature processing, the use of easily recyclable plastics and upgrading their durability) seem to move the optimum MW for UV stabilizers to higher ones. The future of high‐molecular‐weight UV stabilizers (oligomeric and polymer‐bound) are surveyed in connection with their higher performance due to lower volatility and higher retention in plastics.
Thermal and photooxidative studies of polyethylene
Authors: Bigger Stephen W. , Scheirs John , Delatycki Oskar 
Published: March 2011

AbstractThe technique of oxygen uptake measurement for assessing the photo‐ and thermal stability of polyethylene is reviewed. An oxygen uptake apparatus is described which was used to determine the thermooxidative stabilities of nascent, high‐density polyethylenes produced by Ziegler‐Natta, and silica‐supported “silyl chromate” and “chromocene” catalyst systems. The oxygen uptake results are compared with those obtained from the thermochemical technique of differential scanning calorimetry.
Effect of treated filler on the compatibility of poly(methyl methacrylate) / polystyrene blends
Authors: Scherbakoff Natalia , Ishida Hatsuo 
Published: March 2011

AbstractThis work describes a new approach for compatibilizing immiscible polymer blends by fillers. The polystyrene ‐ poly(methyl methacrylate) ‐ glass beads is the studied system. The role of the silane‐treated and non‐treated filler surface on the compatibilization process of this immiscible blend has been evaluated by dynamic mechanical spectrometry, scanning electron microscopy and size exclusion chromatography. The observed changes in morphology are correlated with the enhancement of the interfacial adhesion between polymer/filler and polymer/polymer.
On the relationship between seed‐based and ICA‐based measures of functional connectivity
Authors: Joel Suresh E. , Caffo Brian S. , van Zijl Peter C. M. , Pekar James J. 
Published: March 2011

AbstractBrain functional connectivity (FC) refers to inter‐regional synchrony of low frequency fluctuations in blood oxygenation level dependent functional magnetic resonance imaging. FC has been evaluated both during task performance and in the “resting” state, yielding reports of FC differences correlated with behavior and diagnosis. Two methodologies are widely used for evaluating FC from blood oxygenation level dependent functional magnetic resonance imaging data: Temporal correlation with a specified seed voxel or small region of interest; and spatial independent component analysis. While results from seed‐based and independent component analysis methodologies are generally similar, they are conceptually different. This study is intended to elucidate and illustrate, qualitatively and quantitatively, the relationship between seed and independent component analysis derived measures of FC. Seed‐based FC measures are shown to be the sum of independent component analysis‐derived within network connectivities and between network connectivities. We present a simple simulation and an experiment on visuomotor activity that highlight this relationship between the two methods. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.