bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physical aging phenomena in silica and glass beads filled elastomers (EPDM)
Authors: Haidar B. , Salah Deradji H. , Vidal A. , Papirer E. 
Published: March 2011

AbstractThe physical aging concept is generally used to explain the typical behavior of amorphous glassy materials such as amorphous polymers. It can be easily evidenced by measuring the effect of a static deformation on the dynamic mechanical properties. In this paper, an attempt is made to determine the “glassy” behavior of elastomeric EPDM chains when they are confined in the vicinity of the filler (glass beads, silicas) surface. It is demonstrated that glassy behavior and physical aging phenomena are detected even with a filled elastomer. Furthermore, the influence of the filler volume fraction, the filler nature and of filler surface treatments with silanes were studied. Finally, an original attempt is made to explain filler‐rubber reinforcement by a kind of bimodal network created from linkages between a densely packed interfacial region and the outer loose matrix.
Failure mechanics in thermoplastics filled with inorganic filler and elastomer inclusions: Experiments and modeling
Authors: Jancar J. 
Published: March 2011

AbstractElastic and viscoelastic moduli, yielding and failure of ternary composites of thermoplastic matrix filled with particulate fillers and elastomer inclusions are discussed. Modeling of the role of elastomer interphase in elastic response and in failure processes, based on the combination of numerical method (Finite Element Analysis) and percolation concept, is presented for PP/EPR/filler systems. Proposed expressions for Young modulus, yield strength and critical strain energy release rate are used to predict the lower and upper limiting values of these properties in the case of the two limiting morphologies. Good agreement is found between theoretical predictions and experimental data.
The application of hydrated mineral fillers as fire retardant and smoke suppressing additives for polymers
Authors: Hornsby Peter R. 
Published: March 2011

AbstractThe characteristics of hydrated mineral fillers are discussed with reference to their use as fire retardant additives for polymers. Particular consideration is given to their mode of action and criteria which influence their performance, both in reducing polymer flammability and in suppressing smoke evolution during combustion. Methods for reducing their adverse effect on mechanical properties of the host polymer are also highlighted.
Production of carbonates and hydrates and their use as flame retardant fillers
Authors: Rothon Roger N. 
Published: March 2011

AbstractFlame retardant fillers are of growing importance as they do not give the high smoke and corrosive gas emissions associated with some other flame retardants The basic characteristics of a flame retardant filler are described, together with the manufacture of the principal commercial types. Experimental results are presented to demonstrate that their flame retardant effect is more complex than predicted by a simple endothermic decomposition model.
Fatigue behaviour of filled polymers
Authors: Trotignon Jean Pierre , Tcharkhtchi Abbas 
Published: March 2011

AbstractThe fatigue resistance of any material is the combined resistance to crack initiation and then to crack propagation.1) In most of the cases, fillers act as strong cracks initiators. The Fatigue Crack Propagation can, under certain conditions, be improved (glass beads in epoxy) and this can be attributed to the crack front pinning mechanism. This mechanism is mainly governed by interparticle distances.2) The number of particles per volume unit and thus the interparticles distance seems to be a key factor for endurance resistance. Thus, for a given number of particles per volume unit, the fatigue lifetimes are in good correlation with the FCP data.3) A very rigid bounding between fillers and matrix is not necessarily good in terms of fatigue lifetime. A rubbery interphase can accommodate the deformation around the particle and thus can avoid a crack nucleation.
Hydrophobized polysaccharide macrogel formed by addition of surfactants
Authors: Deguchi Shigeru , Akiyoshi Kazunari , Lindman Björn , Sunamoto Junzo 
Published: March 2011

AbstractSolution properties of an aqueous mixture of cholesterol‐bearing pullulan (CHP) and an ionic surfactant, sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DoTAC), were studied. The mixture forms gel or sol depending on the polymer‐surfactant composition. Because the unmodified pullulan/surfactant/water mixture does not show any gel formation at all over the composition range studied, the hydrophobic cholesterol moieties play an essential and important role in the gel formation. The phase behavior could be interpreted by formation of mixed micelles between cholesterol moieties of CHP and the surfactants. This was supported also by SAXS studies in the sol region. Rheological measurements of the gel showed that viscoelastic response of the CHP/SDS gel was controlled by at least two different processes with shorter and longer relaxation times. This was different from previously reported results for a system such as hydrophobically modified (hydroxyethyl)cellulose (HMHEC) and SDS.
Amphoteric poly(vinyl alcohol) gel as a force generator: Observation of microporous gel formation with cryo‐SEM
Authors: Suzuki Makoto , Tateishi Tetsuya , Matsuzawa Masahiko , Saito Masakatsu 
Published: March 2011

AbstractAmphoteric PVA hydrogels were made from mixed aqueous solutions of poly(acrylic acid), poly(allylamine) hydrochloride and poly(vinyl alcohol) by repetitive freezing and thawing. The hydrogen bond induced gelation produced an elastic and tough microporous hydrogel which generated tension as high as 0.3MPa corresponding to the solvent exchange from water to acetone. In this paper we show the microscopic structure of hydrogels determined by means of cryo‐SEM technique and X‐ray analysis.
Polysaccharide gels for colon targeting
Authors: Brøndsted Helle , Hovgaard Lars 
Published: March 2011

AbstractPolysaccharides appear to have a potential as drug carriers for site‐specific drug delivery to the colon due to the well‐known fermentation of polysaccharides by the anaerobic microflora in the colon. This paper gives a short presentation of the rationale of colon‐specific drug delivery and briefly describes various in vitro and in vivo methods for testing of polysaccharide gels for colonic drug delivery. The application of dextran hydrogels is used as an illustrative example of a polysaccharide based colonic drug delivery system.
Gelation and aggregation of mucin in relation to the stomach's protective barrier
Authors: Bansil Rama , Cao Xingxiang , Bhaskar K. Ramakrishnan , Lamont J. Thomas 
Published: March 2011

AbstractDynamic light scattering was applied to study the effects of pH and concentration on pig gastric mucin. At low concentration (C = 2.0 mg/ml), the distribution of diffusion constants is independent of pH, with an average diffusion constant D = 4 × 10−8 cm2/s. At pH2, very large aggregates with 100‐time slower D (2 × 10−8cm2/s) are seen. Depolarized DLS can be observed at pH2 even at low concentration (C = 5.0 mg/ml). The rotational and translational diffusion constants were analyzed using the Kirkwood‐Riseman model for rods and show that at pH2 mucin is a rod‐like molecule of length 390 nm, diameter 55 nm, with an axial ratio (length/diameter) of 7. However, at pH7, no significant depolarized signals could be detected at any of the concentrations examined in the study. These results suggest that the mucin monomer undergoes a conformational change from a flexible to a rod‐like conformation upon lowering pH from 7 (neutral) to 2 (acidic). Such conformational change and aggregation of the gastric mucin molecule at acidic pH may provide a mechanism by which the gastric mucin layer prevents the stomach from digesting itself, since the back diffusion of acid from the lumen to the gastric epithelium is retarded by the gel layer.
Hydrogels and vascular grafts‐state of the art and beyond
Authors: Zdrahala Richard J. 
Published: March 2011

AbstractVascular grafts represent significant part of implantable medical devices. While the autologous grafts utilizing saphenous veins are used exclusively in cardiac artery bypass graft (CABG) procedures and in peripheral indications, polymer‐based grafts are widely used to replace diseased vasculature with internal diameter above 6 mm. The PET yarn is either knitted or woven into tubes of controlled patterns and porosity. The PTFE tubes are expanded into porous conduits (ePTFE) and the polyurethanes are spun, wound, dipped and foamed to produce porosities most suited for the healing. This porosity causes the blood to leak through the graft wall or at anastomosis through the suture holes. Both the wall leakage and suture hole bleeding remain rather serious drawbacks. Currently, collagen, gelatin, albumin and their derivatives are used as sealants. Various modes of application and degree of crosslinking are utilized to control in vivo degradation and graft healing. Enhancement of graft patency via improvement of initial hemocompatibility could be achieved by application of bioactive coatings. Heparinized systems seem to dominate in this field but many new concepts are being investigated. Intraluminal endothelization via endothelial cells seeding and mediating biologicals will open significant potential for synthetic grafts with ID well below 6 mm. Porous biodegradable tubes could be used as temporary scaffold to attract and promote cell propagation and ingrowth, the true angiogenesis. High‐swelling hydrogels could play a significant role both as sealants and modifiers of graft bioperformance. This paper discusses concepts and potentials needed for patent “small caliber” graft.
Interaction of cells with polymers
Authors: Smetana Karel , Vacík Jiří , Dvořánková Barbora 
Published: March 2011

AbstractThis paper summarizes the results of our experiments studying the effect of functional chemical groups of synthetic hydrophilic polymers on the recognition of these materials by macrophages in in vivo experiments. The interaction of keratinocytes with synthetic hydrophilic polymers in vitro is also demonstrated. The implants containing anionic groups (carboxylates) were shown to be better tolerated by nonspecific immunity. The keratinocytes are able to grow on hydrophilic polymer supports and migrate to surfaces with improved adhesivity (in vitro). The clinical applications of these experiments are demonstrated.
Thermally reversible polymer gels for biohybrid artificial pancreas
Authors: Vernon Brent , Gutowska Anna , Wan Kim Sung , Han Bae You 
Published: March 2011

AbstractAs an approach to replacing islets of Langerhans in an implanted biohybrid artificial pancreas, thermally reversible polymers based on N‐isopropylacrylamide were synthesized and then evaluated as an extracellular matrix for islets in an immunoprotecting membrane pouch. A high molecular weight poly(N‐isopropylacrylamide‐co‐acrylic acid (2 mole % in feed)) demonstrated gelation at 37°C and became a solution below 30°C. This polymer exhibited minimum syneresis (water separation) upon gelation from a solution state when the temperature was raised from room temperature to 37°C, while poly(N‐isopropylacrylamide) exhibited considerable syneresis under the same conditions. These properties influence the efficiency of islet entrapment. The copolymer was able to entrap rat islets almost 100%, but the homopolymer entrapped less than 50%. The static insulin secretion of the islets in the copolymer matrix at high glucose concentration (16.5 mM) was comparable to that of control islets, however, the entrapped islets showed prolonged viability in vitro. These results indicate the potential of developing a rechargeable biohybrid pancreas using thermally reversible polymer gels.
Collapse in responsive hydrogels
Authors: ilavský Michal 
Published: March 2011

AbstractThe swelling and mechanical behaviour of ionic poly(acrylamide) networks formed using both positively and negatively charged crosslinkers or acrylamide quaternary ammonium salt of various alkyl lengths as comonomers is reviewed. The effect of the charge concentration, its polarity, crosslinking density and the strength of hydrophobic interactions (proportional to the alkyl length) on the occurrence and the extent of the first‐order phase transition is discussed. The results are compared with the theory describing the swelling equilibria in polyelectrolyte networks.
Surface reorientation of hydrogels based on methacrylate copolymers
Authors: Lukáš Jaromír , Sodhi Rana N.S. , Sefton Michael V. 
Published: March 2011

AbstractSurface molecular structures of two statistical copolymers, poly(2‐hydroxyethyl methacrylate‐co‐butyl methacrylate) (HEMA‐co‐BMA) and poly[2‐(2‐ethoxyethoxy)ethyl methacrylate‐co‐butyl methacrylate] (EOEOEMA‐co‐BMA), were studied by X‐ray photoelectron spectroscopy (XPS). Besides the classical “dry” XPS technique, where the polymer samples were air‐dried, also “deep‐freezing” technique was used, where the samples were investigated in deep‐frozen hydrated state. The differences in results obtained by the two techniques are discussed from the point of view of the polymer surface chain reorientation in response to various environment. The reverse polymer chain reorientation from the hydrated towards dry state was also followed.
Liquid chromatography of macromolecules at the point of exclusion — Adsorption transition. Principle, experimental procedures and queries concerning feasibility of method
Authors: Berek D. 
Published: March 2011

AbstractLiquid Chromatography of macromolecules at the Point of Exclusion‐Adsorption Transition (LC PEAT) called also liquid chromatography under critical conditions of adsorption or liquid chromatography at the critical point of adsorption is a new and rapidly developing technique that ‐ in combination with some other LC separation procedures ‐ allows separation and molecular characterization of many complex polymer systems as polymer blends, interpolymers or functionalized oligomers. In this critical discussion review, the principles of LC PEAT are briefly elucidated and the nomenclature of some terms connected with the technique is proposed. The most important experimental procedures as eluent and column packing selection are described in detail. The weakpoints of method are discussed in terms of the sensitivity of results towards minute eluent composition, temperature and pressure changes, as well as towards both chemical and physical structure of separated macromolecules and column packing used. The peak broadening, skewing and splitting that often accompany the LC PEAT experiments are also outlined. Above ‐ mentioned, so far mostly overlooked problems may lead to limited repeatability of results and to low sample recovery, especially at higher polymer molar mass values, thus causing queries concerning the broader applicability and experimental feasibility of method, on the other hand these problems can also be regarded as a challenge to both theoreticians and experimentalists who can substantially contribute to the improvement of this powerful method ‐ and thus to its widespread application.
Compositional characterization of styrene copolymers by non‐exclusion liquid chromatography
Authors: Mori Sadao 
Published: March 2011

AbstractRecent advances in high‐performance liquid chromatography enable us to separate synthetic copolymers according to composition. Several techniques for non‐exclusion liquid chromatography (NELC) for polymers and copolymers are reviewed, focusing on the technique developed in our laboratory. Size exclusion chromatography in combination with NELC makes possible the accurate determination of both molecular weight distribution and chemical composition distribution of copolymers at the same time.
Separation of copolymers by adsorption liquid chromatography
Authors: Sato Hisaya , Ogino Kenji , Darwint Tri , Kiyokawa Iwao 
Published: March 2011

AbstractBinary random copolymers of styrene with butadiene, methyl methacrylate, and t‐butyl methacrylate, and styrene‐methyl methacrylate‐acrylonitrile random terpolymers were separated by adsorption chromatography. The HPLC conditions required for the sample to adsorb to the stationary phase are discussed. Sequence length as well as composition affected the elution volume of block and graft copolymers of styrene and butadiene. A mixture of terpolymers having different composition was separated to each component by cross‐fractionation using two types of adsorption chromatography.
Control of polymer structure by chain transfer processes
Authors: Rizzardo Ezio , Chong Y. K. , Evans Richard A. , And Graeme Moad , Thang San H. 
Published: March 2011

AbstractChain transfer can be performed effectively by a mechanism of addition‐fragmentation with appropriately substituted allylic compounds, vinyl ethers and thionoesters. Selection of substituents allows the optimization of chain transfer activity and the preparation of macromonomers and other end‐functional polymers from acrylates, methacrylates, styrene and vinyl acetate. The addition‐fragmentation concept has been extended to the free radical ring‐opening polymerization of cyclic allylic sulfides.
The importance of exchange reactions in controlled/living radical polymerization in the presence of alkoxyamines and transition metals
Authors: Matyjaszewski Krzysztof 
Published: March 2011

AbstractThe role of exchange reactions in controlled/living radical polymerizations is analyzed. Styrene polymerization in the presence TEMPO and atom transfer radical polymerization (ATRP) catalyzed by transition metals (CuIIX2/2Bipy complex) are compared. ATRP proceeds approximately one order of magnitude faster than TEMPO‐moderated polymerization due to a higher stationary concentration of radicals and an equilibrium more shifted to the side of radicals. ATRP can provide better defined polymers with polydispersities down to Mw/Mn≈1.05. This fact can be ascribed to a faster deactivation process and a smaller contribution of side reactions. The polydispersities in both systems are defined by the relative rates of the deactivation and propagation processes. The rate constant of deactivation of growing polystyryl radicals by TEMPO is in the range of kd≈108 mol−1·L·s−1, which is substantially higher than the previously reported value.
Initiation of free radical polymerization by thermal cleavage of carbon‐carbon bonds
Authors: Braun Dietrich 
Published: March 2011

AbstractFree carbon radicals for initiation of polymerization processes can be generated either by light‐induced fragmentation or by homolytic thermal dissociation of suitable compounds. For thermal initiation of polymerization processes beside azo, peroxy and some other thermolabile compounds also alkanes with highly substituted carbon‐carbon bonds are capable. The reason why this interesting class of initiators, even more than 100 years after their discovery, has found only limited applications in radical polymerization is caused by their special mechanism of chain reaction initiation. The formed and in most cases highly resonance‐stabilized substituted alkyl radicals are not very reactive against monomers like methyl methacrylate or styrene but more against growing macroradicals. Therefore, during the initiation step at rather high primary radical concentrations only low‐molecular oligomers with two alkane end groups are formed. Under special conditions this process is reversible, whereas in some other cases the reaction can be described as a “dead end” polymerization. The oligomers which were formed e.g. in the case of methyl methacrylate polymerization with tetraaryl butane dinitriles are able to re‐initiate the polymerization process similar as in a living polymerization which can be used for the synthesis of block copolymers. Mechanism, kinetics and possible applications of such alkane‐initiated polymerizations are discussed.
Free‐radical polymerization in micellar media: Effect of microenvironment
Authors: Candau Françoise , Volpert Edgar , Lacik Igor , Selb Joseph 
Published: March 2011

AbstractA micellar polymerization process has been used to prepare polyacrylamide or poly(acrylic acid) hydrophobically modified with low amounts (1–5 mol%) of an N‐alkyl‐ or N‐alkylarylacrylamide. The effect of the initial monomer segregation on the copolymer microstructure and the copolymerization mechanism has been investigated. This method leads generally to multiblock copolymers in which the number and length of the hydrophobic blocks vary with the initial number of hydrophobes per micelle. Interestingly, the copolymerization of acrylamide with disubstituted acrylamides leads to homogeneous samples with an average copolymer composition independent of the degree of conversion, in contrast to what is observed with monosubstituted acrylamides for which a drift in composition is observed. The difference in polarity between the bulk phase and the micellar phase is responsible for this behavior. This microenvironment effect modifies the reactivity ratios of those hydrophobes capable of forming hydrogen bonds, whereas the reactivity of the other hydrophobes remains unaffected.
Polymerization of water soluble cationic vinyl monomers
Authors: Jaeger Werner , Hahn Mathias , Lieske Antje , Zimmermann Arvid , Brand Fabien 
Published: March 2011

AbstractThis paper summarizes investigations on the radical polymerization of cationic vinyl monomers with respect to the peculiarities of the reaction in aqueous solution, the synthesis of model polymers and polyelectrolytes with regular structure as well as to a new process of stabilized precipitation polymerization. The rate of polymerization depends on the ionic strength of the solution. Random copolymers of diallyldimethylammonium chloride and acrylamide with variable charge density but equal molecular weight were synthesized by a feeding technique. Block copolymers consisting of charged and uncharged monomelic units with different hydrophilicity are available using macroazoinitiators. The novel polymers are powerful stabilizers in the precipitation polymerization of water soluble cationic vinyl monomers in aqueous salt solution leading to a dispersion of fine polymer particles. Polyampholytes with alternating positively and negatively charged monomelic units in the backbone were obtained by cyclocopolymerization of diallylanmine compounds and derivatives of maleic acid.
Recent developments in miniemulsion polymerization
Authors: Aizpurua Imanol , Amalvy Javier , Barandiaran Maria J. , De La Cal José C. , Asua José M. 
Published: March 2011

AbstractSome developments in miniemulsion polymerization aiming at taking advantage of its unique mechanisms minimizing the drawbacks of this technique are discussed. The discussion includes preparation of highly concentrated latexes, miniemulsion polymerization in continuous stirred tank reactors (CSTRs), and elimination of the low‐molecular‐weight hydrophobe.
Reactivity in radical polymerisation: An improved method for the prediction of monomer reactivity ratios and transfer constants
Authors: Jenkins Aubrey D. , Jenkins Jitka 
Published: March 2011

AbstractHalf a century after the Q‐e scheme was promulgated, a substantially improved method for predicting monomer reactivity ratios and transfer constants has been developed from the Patterns of Reactivity scheme. It is based on the same premise as its predecessors, that reactivity is controlled partly by thermodynamic and partly by polar factors, but the new treatment yields values much closer, on average, to the reported experimental data.