bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polyion interchange reactions of interpolyelectrolyte complexes in aqueous solutions and gels
Authors: Kabanov V. A. 
Published: March 2011

AbstractCooperative coupling reaction between two opposite charged polyelectrolytes results in formation of polyelectrolyte complexes (IPEC). This reaction is very fast and diffusion controlled.Whether IPECs formed by linear polyions are soluble or limitary swellable in aqueous media is decided by their composition, namely, by a ratio of oppositely charged polyions as well as by a water phase composition (the nature and the concentration of a simple salt, pH, the presence and the concentration of organic additives etc.).The most important intrinsic property of IPECs is their ability to participate in interchange (exchange and substitution) reactions with competing polyions. The kinetics and the position of equilibria in these reactions are controlled by the low molecular salt concentration, the nature of small counterions, DP of interaction polyelectrolytes, as well as by their linear charge density.IPECs can be formed also by interacting linear and opposite charged networks. It is shown that linear polyelectrolytes dissolved in aqueous solution can penetrate unexpectedly fast into oppositely charged cross‐linked polyelectrolyte gels to form “snake‐in‐cage” composites representing IPECs of corresponding polyion segments. It is proved that the mechanism consists in “relay‐race” transfer of linear polyion segments from one segment of the polyelectrolyte network to the other via interpolyelectrolyte exchange reaction. The driving force for the fast transport of linear polyions into the gel is produced by coupling reaction between two polyelectrolytes proceeding on solution/gel interface.
Poly(ether amide) triblock and star block copolymers
Authors: Clark R. J. , Henkee C. S. 
Published: March 2011

AbstractTriblock and three arm, poly(ether amide) star block copolymers have been synthesized and characterized. Di‐ and tri‐functional amine terminated polyethers were reacted with caprolactam at elevated temperatures to produce the block copolymers. The polyether amines were incorporated at levels ranging from 5%‐40%. Differential scanning calorimetry(DSC) evaluation reveals no reduction in the crystalline melting point of the polycaprolactam end blocks up to 40% polyether incorporation. Dynamic mechanical spectroscopy and FTIR were used to confirm the incorporation of the polyether. A comparison is made between triblock and star block copolymers, and between poly(propylene glycol) and poly(ethylene glycol) polyether midblocks. These block copolymers have improved impact performance as well as a flexural modulus that first increases and then decreases as the amount of polyether is increased in the block copolymer.
Synthesis of homopolymers and block copolymers of methacrylates using a mixed Al/Li alkyl initiator
Authors: Haddleton David M , Muir Andrew V G , O'Donnell John P , Richards Stuart N , Twose David L 
Published: March 2011

AbstractWe report the use of a triisobutylaluminium/tert‐butyllithium initiator in the preparation of living methacrylate homopoloymers and a wide range of methacrylic block copolymers. The system, which we have referred to as Screened Anionic Polymerisation (SAP), is very tolerant of impurities and is effective in hydrocarbon solution with reaction rates such that high molecular weight polymers can be produced at temperatures readily accessible for large scale industrial use. A mechanism for the reaction is proposed based on preliminary spectroscopic evidence.
Polyethylene diblock copolymers: Direct synthesis and morphological analysis
Authors: Drzewinski Michael A. 
Published: March 2011

AbstractPolystyrene and polybutadiene were block copolymerized with high density polyethylene using a transformation reaction from an anionic to a Ziegler‐Natta type polymerization. Various reaction parameters were investigated and optimized. Efficiencies of conversion of the anionic block to diblock were as high as 33% (100% normalized) consistent with the known 3/1 Li‐R/Ti relationship in the active catalyst species. The activity of the polymeric Li‐R/Ti catalyst with regards to ethylene polymerization was as high as 40 000 grams of polymer/mole Ti. Characterization of the resultant polymers is consistent with diblock copolymer structures but transmission electron microscopy shows distinct differences between the morphological behavior of these materials and the now well established morphological behavior of amorphous‐amorphous diblock copolymers. These differences are readily explained by consideration of the interactions between the competing thermodynamic processes of microphase separation and crystallization.
Network structure of inorganic/organic hybrid gels
Authors: Kajiwara Kanji , Krakovský Ivan , Urakawa Hiroshi , Kohjiya Shinzo 
Published: March 2011

AbstractTwo series of inorganic/organic hybrid gels were prepared by the sol‐gel reaction of triethoxysilyl‐terminated poly(tetramethylene oxide) and tetraethoxysilane. The structure of hybrid gels was observed by small‐angle X‐ray scattering, and the scattered profiles were analysed by assuming a priori the density correlation functions. The results suggest that the hybrid gel is composed of organic‐rich, inorganic‐rich and organic/inorganic mixed regions. The size and structure of respective regions were discussed in terms of the correlation lengths evaluated from the scattering profiles.
Water swelling of polyester networks
Authors: Belan F. , Bellenger V. , Mortaigne B. , Verdu J. 
Published: March 2011

AbstractThe water equilibrium concentration in styrene crosslinked polyesters increases with the temperature; this behaviour has been interpreted in terms of material expansion induced by temperature. We have verified this hypothesis by swelling measurements in water and gravimetric experiments at various temperatures between 30°C and 90°C. Samples were propylene glycol/neopentyl glycol ‐ maleate / isophthalate copolymers crosslinked by styrene.
Synthesis and study of poly(ethylene oxide) membranes obtained from homopolymerization of peo macromonomers
Authors: Schmitt Bertrand , Alexandre Eliane , Boudjema Karim , Lutz Pierre J. 
Published: March 2011

AbstractHydrogels were obtained by free‐radical polymerization of bifunctional macromonomers. This reaction can be conducted in water solution or in organic solvent. The kp value is yet strongly depending on the solvent used. The properties of these networks will be compared to those of networks obtained by end‐linking procedures. These materials were also used as a semi‐permeable membrane in the conception of an artificial pancreas.
The peculiarities of physical network formation in carboxyl‐containing poly(dimethylcarbosiloxane)
Authors: Rogovina Lidiya Z. , Vasilev Viktor G. , S. Papkov Vladimir , Shchegolikhina Olga I. , Slonimskii Grigorii L. , Zhdanov Alexandr A. 
Published: March 2011

AbstractAn unusual effect of physical network formation during heating or at room temperature alter previous heating was found for originally liquid poly(dimethylcarbosiloxane) containing 0.5 – 2.5 mol% of side carboxyl groups by means of the measurement of its Theological properties. The reason for this behaviour is supposed to be the predominance of intramolecular hydrogen bonding of COOH groups in original polymer and the intra– to Intermolecular bonds rearrangement during heating. The alternative reason can be the microphase separation with domains of COOH groups. The reversibility of the network is confirmed by the decrease in the elasticity modulus, development of irreversible deformation on further heating and by break‐up of Junctions on the addition of small amounts of polar liquids.
Anisotropic light scattering and rheological study of the physical gelation of atactic polystyrene in carbon disulfide
Authors: Lehsaini Nourdinne , Weill Gilbert , François Jeanne 
Published: March 2011

AbstractThe physical gelation of the solutions of atactic polystyrene (aPS) in carbon disulfide (CS2) is studied by the excess of anisotropic light scattering δHv and by the Theological properties. An abrupt jump of δHv at gelation temperature shows that a part of the chains are stiffened upon gelation. This effect which is independent of aPS molecular weight strongly decreases with concentration. It is well correlated with an abrupt change of the plateau modulus GN which indicates the formation of additional entanglements in the gel phase with respect to the sol. The compatibility of these abrupt jumps with the thermodynamic theories used to interpret the concentration and molecular‐weight dependence of the gelation temperature is discussed.
Microphase separation during the concurrent formation of two polymer networks
Authors: Widmaier Jean‐Michel 
Published: March 2011

AbstractAs a rule, interpenetrating polymer networks (IPNs) are multiphase systems, and the degree of microphase separation is determined by the competition between the chemical kinetics of reaction and the physical kinetics of phase separation. For semi‐IPNs of crosslinked polyurethane and linear polystyrene obtained by a one‐step process, the development of the morphology has been followed by light transmission measurements and by optical microscopy, and finally examined by scanning electron microscopy. When phase separation takes place after gelation, the rather short elastic chains of polyurethane limit the growth of the styrenic phase at a submicroscopic level and the materials thus formed are transparent. On the contrary, when the reaction medium can phase‐separate before gelation of polyurethane, the final morphology results from a superposition of two levels of phase separation: i) a fine dispersion of the components and ii) a gross phase separation of polystyrene noduli surrounded by a polyurethane‐rich shell.
Application of network models to physical gels
Authors: Clark Allan H. , Nishinari Katsuyoshi , Ross‐Murphy Simon B. , Watase Mineo 
Published: March 2011

AbstractThere are a number of physical models which describe properties of physical gels, such as the time dependence of viscoelastic properties, stress‐strain dependence, and the concentration dependence of gel(ation) time and of gel modulus. One of the latter, due to ourselves, has been useful for fitting data for a number of systems including PVC and gelatin gels. However one of its limitations is that it has three “molecular” parameters, and only infrequently can these be estimated from independent experiment. In some cases a better way of testing the model's viability is to compare data concurrently for different concentrations and molecular weights in a surface fit. This paper reviews earlier work and illustrates the extended technique applied to new data for agarose and PVA gels.
Swelling and fractal heterogeneities in networks
Authors: Vilgis T. A. , Sommer J.‐U. , Heinrich G. 
Published: March 2011

AbstractIn this paper we revisit old swelling data on polymer networks that have not been interpreted theoretically on a closed molecular basis. If the osmotic pressure of the swollen network is compared to the osmotic pressure of the corresponding uncrosslinked solution unsolved problems appear, when the relative osmotic pressure is plotted against the degree of swelling, i.e. the deformation due to swelling. A significant maximum appears which cannot be explained by any of the recently derived elastic models, such as junction constraint or other entanglement models. It is suggested in this paper that the maximum is a consequence of structural heterogeneities of fractal nature. If such fractal heterogeneities are assumed a strong maximum in the relative osmotic pressure can be reproduced. The physical reason is the different thermodynamic behavior of uncrosslinked linear chains and crosslinked self‐similar (non‐linear) polymers. The conclusion is supported by numerical (Monte Carlo) simulations.
Microgels ‐ colloidal models for the cross‐linked state
Authors: Antonietti Markus 
Published: March 2011

AbstractThis article describes the synthesis of various types of microgels with different cross‐linking topologies. The swelling data of the standard systems can be fitted with non‐affine theories of rubber elasticity. Light scattering shows the existence of long‐range swelling heterogeneities. The dynamic mechanical behaviour shows some peculiarities, e.g. small spherical microgels show viscous flow.Besides statistically cross‐linked systems, critically cross‐linked as well as macroporous systems can be made. The critical systems exhibit a fractal structure scaling which depends on synthetic conditions. This dependence agrees well with the different dynamic percolation theories. On the other hand, no clear relation between structure scaling and the observed dynamic behaviour can be found.A qualitative scheme which explains various effects observed during cross‐linking of microgels is presented.
Dynamics of junction point motions in model network polymers
Authors: Shi Jiefeng , Dickinson L. Charles , MacKnight William J. , Chien James C.W. 
Published: March 2011

Abstract31P solid‐state exchange 2D NMR and spin‐lattice relaxation times (T1P) have been used to investigate the motion of a crosslink unit in model networks. The networks were formed from tris(4‐isocyanatophenyl) thiophosphate with telechelic poly(propylene glycol) or poly(tetrahydrofuran). From the variation of the 2D NMR pattern with temperature and mix time, the motion of the crosslink is identified as Brownian reorientational diffusion. Good simulations of the spectra were obtained using the Williams‐Watts distribution of correlation times. The temperature dependence of the crosslink motion follows the WLF equation. The parameters derived from the NMR data are sufficient to describe the temperature dependence and breadth of both the dielectric and mechanical loss associated with the glass transition. The T1P relaxation data fitted equally well to the Cole‐Cole or the Williams‐Watts relaxation functions. The motion of the crosslinks can be described quantitatively by the activation energies and the coupling parameters.
Comparison of irreversible and reversible cluster formation
Authors: Weißmüller Max , Merkle Gerhard , Burchard Walther 
Published: March 2011

AbstractCovalent and reversible cluster molecules were synthesized by an A3B2 type gelation. Crosslinking of three‐arm hydroxyl‐terminated star polymers with 2,4‐toluenediisocyanate gave branched polymers, while the reversible analogue was made by crosslinking of tertiary amine‐terminated star polymers with bis(4‐hydroxy‐3,5‐dinitrophenyl) adipate. Gelation process was followed by static and dynamic light scattering. The extent of reacted groups was measured with UV spectroscopy. Growth of the covalent clusters could be described in terms of percolation scaling laws. The experimental gel point (POH, cr = 0.70) was shifted significantly from the theoretical predicted gel point (POH, cr = 0.50), indicating extensive ring formation during the gelation. The reversible endlinking reaction gave no macroscopic gelation, though increase of the cluster dimensions was observed. Ring formation proved to be an important side reaction in both cases; however, the ring formation ability seems to change in a different manner during the course of a gelation.
The influence of network structure on the macroscopic mechanical properties of crosslinked polymers
Authors: Kausch H. H. , Fan LU A. , Cantwell W. J. , Szöcs F. 
Published: March 2011

AbstractNeat and rubber‐toughened epoxy resin systems EPN/BA and EPN/DDS with significantly different crosslink densities and glass transition temperatures were tested under widely different experimental conditions ranging from impact to long‐term loading. The resulting deformation mechanisms were examined in order to ascertain the effects of network structure and toughening modifiers. Different toughening mechanisms were observed in low‐ and high‐crosslink‐density epoxy systems, modified with the same core‐shell rubber particles.
Polymer networks in dentistry
Authors: Lindén L.Å. , Rabek J. F. , Adamczak E. , Morge S. , Kaczmarek H. , Wrzyszczynski A. 
Published: March 2011

AbstractPolymer networks applied in clinical dentistry can be divided into two groups: (i) hard, solid two‐and threedimensional crosslinked structures formed during photo‐curing of dental polymeric filling compositions, and (ii) soft, hydrogel‐type of networks based on polymeric ionic complexes, used for the tightening of microchannels in teeth.The first group is based on crosslinked di‐ and trifunctional monomers, and on solid poly(acrylic acid) ‐ inorganic glasses (“glass ‐ ionomer cements”) This group has found wide clinical applications, in spite of many disadvantages such as susceptibility towards hydrolytic, mechanical. bio‐ and enzymatic degradations, and contents of toxic, allergenic and mutagenic components.The second group, the soft‐hydrogel type of networks, has been investigated and developed at our institute in order to tighten channels in teeth. The microchannels, with a diameter of 30–200Å in enamel and 1–3 μm in dentine, are filled with a loose, native bio‐hydrogel of protein origin. Hydrogels have the ability to swell in water of biological fluids present in the oral cavity, and can retain a significant fraction of fluid within the structure. Decreasing pH below 5.5 causes a slow dissolution of the hydroxyapatite crystals in the walls of the microchannels with a consequent widening of their lumens. Metabolites and toxins from microorganisms, which are always present in the oral cavity, can penetrate into these enlarged channels and cause inflammatory reactions in the underlying pulp tissue. In order to decrease fluid flow and inhibit penetration of microorganisms, but still allow diffusion of ions and water, we have developed and tested polymeric hydrogels based on poly(acrylic acid) and metal salts, and chitosan, which can be formed directly in the micro‐channels of dental hard tissues.
FT‐NIR Spectroscopy of some long‐chain fatty acids and alcohols
Authors: Ozaki Yukihiro , Liu Yongliang , Czarnecki MirosłAw A. , Noda Isao 
Published: March 2011

AbstractFourier‐transform (FT) near‐infrared (NIR) spectroscopy has proved to be a powerful technique in investigating structure and thermodynamic properties of long‐chain fatty acids and alcohols. In order to extract useful information from the NIR spectra, bands due to the second as well as first overtones of OH‐stretching modes of the monomeric forms were employed. It has been also found that two‐dimensional (2D) NIR correlation spectroscopy can accentuate useful information often obscured in the complicated NIR spectral data set.
Dynamic ft‐ir spectroscopy of polymer films and liquid crystals
Authors: Gregoriou Vasilis G. , Palmer Richard A. 
Published: March 2011

AbstractThe use of continuous‐scan and step‐scan Fourier transform infrared (FT‐IR) spectroscopic techniques to study the dynamics of the response of polymer films and liquid crystals to external perturbations is described here. The first application of dynamic stepscan FT‐IR deals with the response of various polymer films to sinusoidally modulated tensile strain. In these experiments, a small amplitude sinusoidal stress is applied to a polymeric film and the transition dipole responses are monitored as a phase lag with respect to the external perturbation. The degree of deformation is small enough to cause only linear reversible responses to the sample. The main advantage of the technique is that it can provide valuable information at the molecular level that can be used to interpret the macroscopic properties of the polymeric material under investigation. Results for heterogeneous polymers include semicrystalline high density/low density polyethylene blends and the micro‐phase separated copolymer Kratonr̀ are presented. In addition, continuous‐scan stroboscopic FT‐IR was used to explore the submolecular (functional group) contributions to the reorientation dynamics of the liquid crystal director in response to pulsed (DC) electric fields. For the nematic liquid crystal molecules, 4‐pentyl‐4'‐cyanobiphenyl (5CB) and 4‐pentyl‐4'‐cyanophenylcyclohexane (5PCH), the individual response of the rigid and floppy parts was examined.
The dynamics of glass‐forming polymers in the microscopic‐mesoscopic time scale. A quasielastic neutron scattering phenomenological approach
Authors: Colmenero J. 
Published: March 2011

AbstractThe dynamics of three glass‐forming polymers, PVC, PB and PI, has been investigated by time of flight (TOF) neutron scattering in a time scale from 10−13s to 1011s looking for the crossover from microscopic dynamics to segmental dynamics (α relaxation). A new analysis procedure has been applied to TOF data in order to separate harmonic vibrational and relaxational contributions. Due to the involved assumptions, this procedure can be considered only as a first approximation adequate for the case of “fragile” systems (in the Angell's meaning) like the polymers here investigated. The behaviour obtained was the same for the three polymers studied. The intermediate scattering function corresponding to the relaxational dynamics, Io(Q,t), shows two different dynamical regimes separated by a crossover time tc (≈ 2 ps), which hardly depends on Q (momentum transfer) and temperature. At t < t<c, Io(Q,t) displays a Debye‐like behaviour (exponential decay). The activation energy found for the relaxation time corresponding to this regime was in the range of 2–5 Kcal/mol, i.e., in the range of the activation energy for local conformational transitions in isolated macromolecular chains. At t > tc and, at least at high temperature, Io(Q,t) shows a Kohlrausch‐Williams‐Watts (KWW) behaviour similar to the obtained one by means of backscattering neutron techniques in the mesoscopic time scale (10−11s to 10−7s) and dielectric measurements in the macroscopic time scale (10−7s to 10°s). This KWW regime can be associated to the segmental dynamics involved in the α relaxation. A phenomenological interpretation is outlined. In this framework, the Debye‐like regime is interpreted to be the segmental dynamics free from intermolecular hindrances. Therefore, tc should be the time at which intermolecular interactions start to play a significant role concerning to the segmental dynamics. This interpretation recalls some of the basic ideas of the so called “Coupling‐Model” proposed a long time ago by Ngai.
A comparison between PA‐FTTR and FT‐Raman spectroscopies in the structural analysis of annealed injected‐moulded poly (ethylene terephthalate)
Authors: Quintanilla Luis , Rodríguez‐Cabello José Carlos , Merino Juan Carlos , Pastor Jose María 
Published: March 2011

AbstractWith the introduction of the Fourier Transform technique in Raman spectroscopy (FT‐Raman) and the development of new methods in FTIR, such as FTIR with photoacoustic detection (PA‐FTTR), vibrational spectroscopy has been launched into a new era of application in polymer chemistry and physics. This work provides a comparative study between PA‐FTIR and FT‐Raman techniques in which the potentials and limitations of these two methods are investigated by following and analyzing structural variations that take place in annealed injected‐moulded poly(ethylene terephthalate) (PET). Both spectroscopic techniques appear to be suitable to detect structural changes that occur in PET submitted to different annealing temperatures. We suggest that these variations are directly related to conformational rather than crystallinity changes. The main drawbacks of PA‐FTIR are the lengthy adquisition time of spectra and the photoacoustic saturation that can appear in regions with quite high optical absorption coefficient. Conversely, FT‐Raman technique does not suffer from neither of these problems. However, the sensitivity to structural changes of certain infrared bands seems to be higher than that of analogous Raman bands and small structural details such as the regularity of chain folding, can only be detected in the infrared spectra.