bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics and mechanisms of the seeded emulsion copolymerization of styrene and acrylonitrile
Authors: Nomura Mamoru , Liu Xiang , Mizutani Fumihiko , Sato Syuzaemon , Fujita Kazumi 
Published: March 2011

AbstractEffects of various operating variables on the kinetic behavior of the seeded emulsion copolymerization of styrene and acrylonitrile and on the monomer concentration in the copolymer particles were examined. Applicability of high‐performance liquid adsorption chromatography to determination of the average composition and composition distribution of the resulting copolymer was also examined.
Main chemical engineering parameters affecting radical polymerization processes in heterogeneous media
Authors: Pla Fernand 
Published: March 2011

AbstractThe main parameters which may affect both reactor performance and polymerization processes in heterogeneous media are described. Viscosity and its influence on heat and mass transfer, residence time distribution in tubular reactor, as well as, influence of agitation on coagulum formation and of monomer feed rate on polymerization rate in semi‐batch processes are examined.
Effect of filler networking on the dynamic mechanical properties of crosslinked polymer solids
Authors: Heinrich Gert , Vilgis Thomas A. 
Published: March 2011

AbstractThe strain amplitude dependence of the viscoelastic properties of eight different carbon blacks dispersed in two different rubbery networks is investigated and evaluated within the Cole‐Cole approach for the complex elastic modulus at fixed temperature and frequency. This approach is based on the Kraus model of strain‐dependent filler agglomeration‐deagglomeration rates. We find a non‐integer universal shape exponent of the Cole‐Cole process that obviously depends only on the surrounding polymer matrix but is independent of the filler grade. The exponent can be related to the fractal dimension of the carbon black surface.
Microstructural evolution in polymerizations of tetrafunctional monomers
Authors: Bowman Christopher N. , Anseth Kristi S. 
Published: March 2011

AbstractTo characterize the network structural evolution during polymerizations of multifunctional monomers and predict the relationship between reaction conditions and polymer structure, a balanced approach between experimental characterization and simulation is used. A novel method for characterizing the free volume distribution and network structure throughout the polymerization is presented. This technique involves the use of photochromic probes that require a certain local, critical volume to isomerize. By incorporating probes that require different isomerization volumes, a distribution of local volume in the network is determined. Since this technique allows in situ monitoring of the volume distribution, the effects of conversion, rates of polymerization, and monomer structure on the free volume distribution can be elucidated. Volume distributions are presented for diethylene glycol dimethacrylate. Information from the photochromic technique is further supported by kinetic gelation model predictions and transmission electron microscopy pictures of the evolving polymer structure.
The bole of vibrational spectroscopy‐microscopy techniques in polymer characterisation
Authors: Chalmers John M. , Everall Neil J. 
Published: March 2011

AbstractDetailed spectroscopic studies at the sub‐millimetre level of the chemical composition and morphology of materials can provide insights into the constitution, performance and properties of polymeric products. Infrared and Raman microscopy/microprobe spectroscopic techniques are invaluable tools for the spatially‐resolved identification, study and characterisation of polymers, their products and composites. The two vibrational spectroscopy techniques provide both complementary information and attributes to such investigations, which are discussed and exampled in this paper.
In situ vibrational spectroscopy of conducting polymer electrodes
Authors: Neugebauer Helmut 
Published: March 2011

AbstractThe application of in situ Fourier transform infrared spectroscopy for the study of electrochemical redox reactions of conducting polymers is described. The experimental setup of two different methods, external reflection absorption spectroscopy and attenuated total reflection spectroscopy, is shown. The results of spectroelectrochemical investigations of the reactions of polyaniline in different electrolyte solutions are discussed.
Structural polymorphism of crystalline polymers: Electron and atomic force microscopy contributions
Authors: Lotz Bernard 
Published: March 2011

AbstractThe contribution of electron microscopy, electron diffraction and atomic force microscopy to the elucidation of the structure of polymers ‐in particular helical polyolefins‐ is briefly presented. Particular emphasis is put on the elucidation of rather subtle aspects of the structure, such as disorders introduced by packing of up and down, or left and right handed helices in the lattice. The spectroscopic and diffraction informations are evaluated and compared.
The influence of substituents on the orientational behaviour of novel azobenzene side‐chain polyesters
Authors: Zebger Ingo , Kulinna Christian , Siesler Heinz W. , Andruzzi Fulvio , Pedersen Marianne , Ramanujam P. S. , Hvilsted SØRen 
Published: March 2011

AbstractA series of new mesogenic azobenzene propanediols with nitro, methoxy, cyano and no substituent have been synthesized and their mesomorphic behaviour mapped. The diols are employed in a melt transesterification with diphenyl tetradecanedioate to produce side‐chain polyesters with high molar masses. Diols and polyesters have similar UV‐visible spectra reflecting the acceptor character of the substituent. Polarization FTIR spectroscopy has been used to determine the mesogenic order parameter for the polyesters with different substituents at four laser irradiation wavelengths (413, 458, 488 and 515 nm). Diffraction gratings in thin polyester films have been recorded through polarization holography. Cyano and unsubstituted azobenzene polyesters are shown to exhibit the highest diffraction efficiencies on the order of 13%.
Mechanism of anionic polymerization of methyl methacrylate in the presence of aluminium alkyls
Authors: Schlaad Helmut , Müller Axel H. E. 
Published: March 2011

AbstractA bimetallic aluminate complex (‘ate’ complex) is regarded to be the active species in the anionic polymerization of MMA in the presence of aluminium alkyls in toluene. The aluminate end group is supposed to be able to coordinate to the penultimate end group of the polymer chain. As a result, the rate of polymerization is significantly slower than for aluminium‐free polymerization. Excess aluminium alkyl (Al/Li > 1) coordinates to the ester carbonyl groups of monomer and polymer, but there is no evidence for an activated monomer mechanism. To a small extent, the polymerization at −78°C is accompanied by side reactions (e.g. formation of vinyl ketones) but nevertheless it has a certain living character.
Cationic photopolymerization of ambifunctional monomers
Authors: Crivello James V. , Bi Daoshen , Lu Yijun 
Published: March 2011

AbstractCertain metal‐catalyzed hydrosilations have been found to occur in a highly regioselective manner which makes them useful for the preparation of unique classes of ambifunctional monomers. These monomers bear two chemically different functional groups within the same molecule. By selection of the appropriate functional groups it is possible to design monomers in which the functional groups react independently, copolymerize, or polymerize by different mechanisms. This article describes some recent results of the synthesis and polymerization of several novel types of ambifunctional monomers.
Living cationic polymerization of vinyl ethers in the presence of added bases: Recent advances
Authors: Aoshima Sadahito , Kobayashi Eiichi 
Published: March 2011

AbstractThe living cationic polymerization of vinyl ethers was carried out with organoaluminum compounds in the presence of various types of esters and ethers (cyclic and acyclic), to find out the suitable added bases available for the living polymerization. The effects of the basicity and steric hindrance of added bases were investigated in detail. On the basis of these results, a fast living polymerization system was realized. To synthesize water‐soluble polymers such as thermally‐induced phase separating polymers and polyalcohols with well‐defined polymer structure, the living polymerization of various vinyl ethers was examined. The aqueous solution of living poly(vinyl ethers) having oxyethylene units exhibited a quite sensitive (ΔTps=0.3–0.5°C) and reversible phase separation on heating and cooling. The effects of polymer structures (pendant substituent, polymer sequence, molecular weight, and MWD) on the phase separation behavior were investigated. PVA and block copolymers containing PVA units with a narrow MWD were also prepared via living cationic polymerization of vinyl ethers and a deprotection reaction.
From star‐shaped to dendritic poly(ethylene oxide)s: Toward increasingly branched architectures by anionic polymerization
Authors: Six Jean‐Luc , Gnanou Yves 
Published: March 2011

AbstractPolymers with dendritic structure are a category of macromolecular architectures that has received considerable attention in the last decade. These polymers, also referred to as dendrimers, exhibit a degree of branching equal to unity. Interest in dendrimers whose branching points are linked to each other by generations of macromolecular size is in contrast quite new. This paper describes a new synthetic strategy which allows access to poly(ethylene oxide) (PEO) with dendritic structure. PEO dendrimers with different degree of compactness have been synthesized upon modifying the size of successive generations.
Ring‐opening metathesis polymerization of ω‐norbornenyl polystyrene macromonomers and characterization of the corresponding structures
Authors: Breunig S. , Héroguez V. , Gnanou Y. , Fontanille M. 
Published: March 2011

Abstractω‐Norbornenyl polystyrene (PS) macromonomers whose molar masses range from 2700 to 11000 g/mole have been polymerized under living conditions by ring‐opening metathesis, with a Schrock complex as initiator. The samples obtained have been characterized by a multiangle laser light scattering (MLLS) detector connected to the outlet of a size exclusion chromatography (SEC) instrument. The experimental values of the degree of polymerization (D̄Pn) lie in close agreement with the expected ones. The compactness of the various branched species formed, which covers a wide range of segment densities (ρS), is found to depend on two factors that are their degree of polymerization and the size of the initial macromonomer. The ratio (g) of the mean‐square radii gyration (<R2b) of polymacromonomers to those (<R21) of linear PS homologues of same molar mass was also determined. Plotting the variation of g vs. the D̄Pn's of polymacromonomers gives an idea of the conformation adopted by these branched structures.
New developments in bond‐forming initiation: Lewis acids accelerate spontaneous initiation of copolymerizations of olefins and dienes
Authors: Hall H.K. , Padias Anne Buyle , Srisiri Warunee , Mikhael Michael G. , Wang Hua , Chu Guobei 
Published: March 2011

AbstractLewis acids have long been known to influence the free radical propagation of donor‐acceptor olefin monomer pairs, changing random copolymers into strictly alternating ones, by complexing to the lone pair electrons of the acceptor monomer, and enhancing its electron‐poor character. This work reports that this same interaction enhances the rates of the spontaneous initiation in these systems. In agreement with earlier literature, we found that styrene‐acrylonitrile copolymerizations proceed readily in the presence of ZnCl2 at 40° where no copolymerization occurs in the absence of the Lewis acid. p‐Methoxystyrene and isobutyl vinyl ether with AN gave more complicated results, due to competitive complexation of oxygen lone pairs with ZnCl2. Reaction of more electrophilic olefins with these donor monomers gave steadily increasing rates and a shift in product from spontaneous copolymer to inverse Diels‐Alder adduct (in the case of ester substituents) to cyclobutane. As for substituted diene monomers as the donor component, reactions of isoprene and 2,3‐dimethylbutadiene with AN are accelerated in the presence of ZnCl2 and the Lewis acid affects the competition between the [4+2] cycloaddition and the copolymerization. All of these results are interpreted in the context of formation of Lewis‐acid complexed initiating diradicals by bond‐formation.
A new understanding of the co‐catalytic activity of alumoxanes: The opening of a black box!
Authors: Barron Andrew R. 
Published: March 2011

AbstractThe isolation of non‐fluxional alumoxane compounds, [(tBu)2Al{OAl(tBu)2}]2 and [(tBu)AlO]n (n = 6, 7, 8, 9), has allowed for an investigation of the mode of activity observed for alumoxanes as co‐catalysts for the zirconocene polymerization of olefins. [(tBu)2Al{OAl(tBu)2}]2, which contains two three‐coordinate aluminum centers, shows no reaction with Cp2ZrMe2, and no catalytic activity towards ethylene polymerization. In contrast, the closed cage compound [(tBu)AlO]6 reacts reversibly to give the ion pair complex, [Cp2ZrMe][(rBu)6Al6O6Me], which is active as a catalyst for the polymerization of ethylene. Polymerization is also observed for mixtures of Cp2ZrMe2 with [(tBu)AlO]n (n = 7, 9). A new concept, “latent Lewis acidity”, is proposed to account for the reactivity of the cage alumoxanes, [(tBu)AlO]n.
Stereospecific polymerization with metallocenes: Macromolecular design via catalysis
Authors: Waymouth Robert M. , Coates Geoff , Mogstad Anne‐Lise , Stein Kevin , Fischer David , Borkowsky Sam 
Published: March 2011

AbstractForty years after Natta's discoveries of stereospecific olefin polymerization with Ziegler catalysts, new catalysts are causing a renaissance in stereospecific olefin polymerization. Metallocene Ziegler‐Natta catalysts are unprecedented in their ability to polymerize α‐olefins to a variety of polymer microstructures.1 Isotactic, syndiotactic, atactic and stereoblock poly(α‐olefins) have been produced using catalysts derived from group 4 metallocene catalyst precursors.
New polyimides using hydrazine as the diamine
Authors: Ghassemi Hossein , Hay Allan S. 
Published: March 2011

AbstractHydrazine reacts with 1, 8‐naphthalic anhydride to give, exclusively, the N‐aminoimide which reacts further with cyclic anhydrides to yield stable bisimides containing an N‐N linkage. Various bisanhydrides which contain the naphthalic anhydride moiety have been converted to the corresponding bis‐N‐aminoimides from which high molecular weight polyimides have been synthesized. The polyimides have very high glass transition temperatures but remain soluble. Polyimides derived from 3, 4, 9, 10‐perylene tetracarboxylic dianhydride are intensely red in color and are fluorescent.
Transition metal catalyzed cationic polymerizations
Authors: Crivello James V. , Fan Mingxin 
Published: March 2011

AbstractCertain complexes of platinum, rhodium, iridium and cobalt are capable of initiating cationic vinyl and ring‐opening polymerizations in the presence of a Si‐H containing cocatalyst. An investigation has shown that two distinctly different mechanisms are involved, however, in both cases cationic polymerization can be explained by the formal attack of an electrophilic silicon species on the monomers. Since the transition metal complexes listed above also are catalysts for hydrosilation reactions, it is possible to carry out simultaneous cationic polymerizations and hydrosilation reactions to prepare novel and interesting polymers and oligomers.
Genealogically directed syntheses (polymerizations): Direct evidence by electrospray mass spectroscopy
Authors: Dvornic Petar R. , Tomalia Donald A. 
Published: March 2011

AbstractFrom a synthetic perspective, divergent dendrimer syntheses are often presented as idealized hyperbranched growth processes leading to perfect dendritic structures. Experimentally it has been found that in addition to ideal structures, varying amounts of structural errors are produced at each growth stage (generation). These defects (mutants) are created as a function of processing conditions and generation specific steric effects. This investigation focused on the divergent synthesis of Starburstr̀ polyamidoamine dendrimers** and the use of electrospray mass spectroscopy for appraising ideal structure/defect ratios as a function of generation. With this methodology, initial defect types and so called “defect propagation chains” have been identified and characterized. These hyperbranched mutation (defect) patterns provide ample evidence for the “genealogically directed” character of this divergent polymerization strategy.
New materials with novel topologies. Synthesis and characterisation of telomers and polymers with ribbon topology
Authors: Feast W. James , Mitra Manju , Davies Frank P. 
Published: March 2011

AbstractThe five, seven and nine ring analogues of thianthrene have been made as model compounds for ribbon polymers based on the structural motif shown below.The smaller molecules are soluble and readily characterised but the nine ring model compound and polymers based on this structural motif are insoluble and intractable. Analogues of the model compounds and polymers which carry decyl substituents are soluble upto species having about seventy rings.
Recent advances in the design of polymers for contact lenses
Authors: Friends Gary D. , Kunzler Jay F. , Ozark Richard M. 
Published: March 2011

AbstractThree approaches for the design of polymers for extended wear contact lenses possessing high oxygen permeability are described. These approaches include the design of high strength, high water content hydrogels, the design of low water content fluorosilicone based materials and the design of hydrogels based on methacrylate end capped hydrophilic side chain siloxanes.
Biorecognizable polymers: Structure‐properties relationship
Authors: Kopeček J. , Kopečková P. , Omelyanenko V. G. , Rathi R. C. 
Published: March 2011

AbstractThe biocompatibility of polymers depends on their chemical composition, as well as physical and physico‐chemical structure. However, biocompatibility is not an intrinsic polymer property since it relates to a particular localization of the polymer in the living organism. Any foreign macromolecule may be recognized by the living organism as “non‐self”. The degree of recognition can be altered by modification of the structure of macromolecules or biomaterial surfaces. Modification of biomacromolecules (e.g., enzymes1) or biomaterial surfaces with hydrophilic polymers, e.g., poly(ethylene oxide2) or other semitelechelic hydrophilic macromolecules3 has been shown to minimize biorecognition. On the other hand, to achieve specific recognition by cell receptors and/or antigens, complementary structures have to be incorporated as a part of the polymer structure4, 5. The biorecognition of fluorescently labeled N‐(2‐hydroxypropyl)‐methacrylamide copolymers containing side‐chains terminated in acylated galactosamine by Hep G2 cells on the cellular and subcellular levels can be visualized by confocal fluorescence microscopy. The recognition of modified water soluble macromolecules strongly depends on their solution properties6. Incorporation of stimuli sensitive moieties into copolymer side‐chains permits to control recognition by external stimuli, e.g., irradiation7, 8, resulting in the change of the copolymer conformation. On the other hand, the biorecognition of unsoluble (crosslinked) copolymers depends mainly on their surface structure. The rationale for the structure modification of synthetic copolymers to regulate biorecognition will be reviewed. The principles will be described for the interaction of synthetic polymers with enzymes9, cell surface receptors and/or antigens10, 11, lectins of the gastrointestinal tract12, 13, and immobilized lectins14.
Homogeneous and heterogeneous free radical polymerizations in environmentally responsible supercritical carbon dioxide
Authors: Desimone Joseph 
Published: March 2011

AbstractFluoropolymers are used in many technologically demanding applications because of their balance of high‐performance properties. A significant impediment to the synthesis of variants of commercially available amorphous fluoropolymers is their general insolubility in most solvents except chlorofluorocarbons (CFCs). The environmental concerns about CFCs can be circumvented by preparing these technologically important materials in supercritical fluids (SCFs). The homogeneous solution homo‐ and copolymerization of highly fluorinated acrylic, styrenic and olefinic monomers in supercritical carbon dioxide using free radical methods will be discussed [Science, 257, 945 (1992)]. Detailed decomposition rates and efficiency factors will be presented for azobisisobutyronitrile (AIBN) in supercritical carbon dioxide and will be compared to conventional liquid solvents [Macromolecules, 26, 2663 (1993)]. Additionally, viscosities of polymer solutions in supercritical CO2 have been measured using a high pressure, falling cylinder viscometer. The results show that the polymer solution viscosities in supercritical CO2 are an order of magnitude lower than with the same polymers in conventional organic solvents.The results from these homogeneous solution polymerization studies has allowed us to also consider heterogeneous polymerizations in a carbon dioxide continuous phase. Conventional emulsion polymerizations of unsaturated monomers are performed in either aqueous or organic dispersion media with addition of surface active agents (surfactants) to stabilize the colloidal dispersion that forms. With free radical initiators that are preferentially soluble in the continuous phase, high rates of polymerization and high molar mass polymers can be obtained simultaneously. Herein we describe an environmentally responsible alternative to aqueous and organic dispersing media for emulsion polymerizations which utilizes supercritical carbon dioxide, in conjunction with molecularly engineered free radical initiators and amphiphilic molecules that are specifically designed to be interfacially active in CO2. Conventional lipophilic monomers, exemplified by methyl methacrylate and styrene, can be polymerized heterogeneously using a fluorinated azo‐initiator in supercritical CO2 in the presence of added surfactant to form stable emulsions that result in submicron size particles. Detailed surfactant and initiator syntheses and phase behavior will also be discussed.
New tools for analysing degradation
Authors: Albertsson Ann‐Christine , Karlsson Sigbritt 
Published: March 2011

AbstractNew tools for analysing degradability are presented. The degradation product patterns and morphology changes are proved to be means to differentiate on the one hand physical/chemical (abiotic) and on the other hand biological (biotic) ageing of polymers. In the biotic environment an assimilation of carboxylic acids occurs and a series of longer n‐alkanes (C21–C26) is present. In the abiotic samples carboxylic acids are identified but no n‐alkanes. This is in agreement with the biodegradation mechanism of LDPE proposed by us 1987. Morphology changes as manifested by crystallinity (wc) and lamella thickness (l) revealed a slow decrease of wc and (l) in biotically aged samples while the corresponding abiotically aged ones show constant or increasing values. Chromatography of low molecular weight compounds and x‐ray diffraction analysis of crystallinity and lamellae thickness creates an opportunity for a deeper insight into the degradation mechanisms.