bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methodology in studying improvement of polyacrylates biodegradability
Authors: Gancet Christian , Pirri Rosangela , Dalens Jean Marc , Boutevin Bernard , Guyot Bernard , Loubat Cédric , Le Petit Jean , Farnet Anne Marie , Tagger Simone 
Published: March 2011

AbstractThe biodegradability of polyacrylic acid derivatives may be improved through introduction of some fragility points within the main carbon chains. These weakness points can be either hydrolizable bonds or oxidizable sites. Enzymatic hydrolysis and oxydative biomimetic degradation tests have been set up in order to quickly evaluate new polymeric structures, before their possible evaluation through microbial degradation by Candida tropicalis.
Novel lipase‐catalyzed ring‐opening copolymerization of oxiranes and dicarboxylic anhydride forming polyesters bearing carboxyl groups and their physicochemical properties and biodegradability
Authors: Matsumura Shuichi , Okamoto Takeshi , Tsukada Keisuke , Mizutani Noriyuki , Toshima Kazunobu 
Published: March 2011

AbstractOxiranes, such as benzyl glycidate and glycidyl phenyl ether, were copolymerized with dicarboxylic anhydride by lipase at a temperature between 60 and 80 °C to yield the corresponding polyesters bearing carboxyl or phenyl groups. Bulk polymerization, especially at 80 °C, and preferably using porcine pancreatic lipase, gave biodegradable polyesters with a molecular weight of greater than 10000. Poly(sodium carboxylate)s containing ester linkages in the backbone prepared in this study were readily biodegradable by the activated sludge and exhibited a calcium ion sequestration capacity.
Characterization of nanoparticles
Authors: Lechner M. D. , Mächtle W. 
Published: March 2011

AbstractNanoparticles with diameters from 1–100 nm are used in large quantities for very different applications. A precise determination of the important physical quantities (which are responsible for the application properties) such as diameter, particle size distribution, and surface is therefore very essential. The most common methods for the determination of these quantities are analytical ultracentrifugation (AUC) and dynamic light scattering (DLS). The paper demonstrates the techniques of getting a precise characterization of nanoparticles and suggests a new method for the correction of the sedimentation coefficient and its distribution with respect to the diffusion coefficient.
Phenomena of counterion binding, polyion complexation and polyion condensation
Authors: Nordmeier Eckhard 
Published: March 2011

AbstractThe article handles some aspects of polyelectrolyte research investigated during the last ten years at the university of Osnabrück. They are: counterion binding, polyion complexation, and polyion condensation. Fundamental features are presented that are common to the behaviour of most polyions. Another intention is to bridge a gap between synthetic and biological polyelectrolyte research. For this purpose, DNA condensation is reviewed in some detail.
Temperature and pH sensitive polymers in water ‐ from solution to thin films
Authors: Kuckling Dirk , Adler Hans‐Juergen P. , Arndt Karl‐Friedrich , Ling Long , Habicher Wolf Dieter 
Published: March 2011

AbstractA series of temperature and pH sensitive polymers which contain both temperature and pH sensitive components were synthesised by copolymerization of N‐isopropylacrylamide (NIPAAm) and acrylamide derivatives containing a spacer and a sensitive headgroup. The cloud point and heat of transition (ΔHPT) of aqueous solutions of polymers with various compositions were measured by means of DSC. The observed cloud points and ΔHPT values strongly depend on the polymer composition and the pH value. The irradiation of dimethylmaleinimide groups (DMIAAm) bearing copolymers with UV light resulted in crosslinking of the polymers. The prepared thin layers showed fast temperature dependent swelling with transition temperatures similar to the uncrosslinked polymers.
Theory of relaxation spectra of polymer networks with interchain friction and long‐range hydrodynamic interactions
Authors: Gotlib Yuli YA. 
Published: March 2011

AbstractThe dynamic network model taken into account the friction relative to incompressible effective viscous medium (EVM), the hydrodynamic interactions of a network with the EVM, and the interchain friction is considered. Two collective network relaxation spectra (RS) arise. The first RS corresponds to the network motion relative to immobile EVM, the EVM does not take part in this motion. The second RS includes the combined viscous motion of the network and EVM because of long‐range hydrodynamic interactions. This RS is finite and narrow for infinitely large network. The symmetry of this motion is in concordance with that of incompressible EVM. The existence of interchain friction leads to the narrowing of both types of relaxation spectra.
Dynamics of macromolecules and nuclear magnetic relaxation: Application of mode‐coupling diffusion theory to DNA, proteins and their complexes
Authors: Fausti Simone , La Penna Giovanni , Perico Angelo , Pratolongo Roberto 
Published: March 2011

AbstractA mode‐coupling approach has been used to solve the Smoluchowski diffusion equation describing the correlation functions relevant in nuclear magnetic relaxation experiments on biological molecules like protein and DNA. A good reproduction of relaxation patterns for molecules that are fluctuating about three‐dimensional structures imposed by secondary motives has been found. Important differences can be explained with the poor statistics collected by numerical simulations that do not contain fluctuations contributing to rates in the ns time‐scale, therefore comparable with rotational rates.
Electron crystallography and organic materials with non‐linear optical properties
Authors: Voigt‐Martin Ingrid G. , Kolb Ute , Kothe Hans , Yakimanski Alexander V. , Yu Ri‐Cheng , Matveeva Galina N. , Tenkovtsev Andrey V. 
Published: March 2011

AbstractResults of electron microscopic studies of crystal structures of a number of bis‐benzylidene cyclohexanones are presented. It is shown that some of these compounds are efficient crystalline non‐linear optically active (NLO) chromophores with second harmonic generation (SHG) properties. Appropriately functionalized chromophores of this type can be used as a polycondensation comonomer to produce partly crystalline main‐chain NLO‐active polymers. Electron diffraction crystal structural data, obtained for very small crystals, allowed us to get reasonable estimations of macroscopic crystal NLO‐coefficients, relating quantum‐chemically calculated molecular first hyperpolarizability components to crystal axes.
Influence of salts on hydrophobically end‐capped polyethylene oxides in aqueous solution
Authors: Beaudoin Emmanuel , Gourier Christine , Lapp Alain , François Jeanne 
Published: March 2011

AbstractThe influence of four different salts (NaCl, KBr, CaCl2 and MgCl2) on the associative behaviour of poly(ethylene oxide) (POE with M=32000g/mol) hydrophobically end‐capped with hexadecyl groups in aqueous solutions was investigated. Phase diagrams were obtained, structural properties were established by small angle neutron scattering (SANS) measurements and studies on the viscoelastic properties of the solutions were performed by low‐shear viscosity and dynamic stress experiments. The influence of the four salts is compared as well as the difference of the interactions obtained with and without salts.
Comparative study of the poly‐dimethylsiloxane monolayer with styrene and polystyrene
Authors: Marchenko Svetlana B. , Gritskova Inessa A. , Zaitsev Sergei Yu. 
Published: March 2011

AbstractPolydimethylsiloxane (PDS) and it mixtures with styrene and polystyrene (PSt) are able to form stable monolayers at the liquid‐gas interfaces in contrast to pure styrene or PSt. The surface pressure — molecular area isotherms of PDS monolayers have two regions at low and high pressures with pronounced transition plateau in between. The area per PDS molecule in the liquid‐expanded state is about 1.60 nm2 (at 5 mN/m) that can be explained by twisting of polymer chain into the helical conformation. The area per PDS molecule in the liquid‐condensed state is about 0.48 nm2 (at 20 mN/m) that can be explained by PDS reorientation in the helical conformation from the horizontal to the vertical position with respect to the air‐water interface. The addition of styrene in the PDS monolayer drastically changes the π‐A isotherms (no transition plateau) with area increase from 0.47 till 2.70 nm2 per PDS with the increasing of polymer concentration from 1 to 10 mass %. In contrast, there are only small quantitative changes in the isotherms in the presence of PSt in the PDS monolayer. Thus, the formation of the polymer adsorption layers at the interface has been studied, modeling the initial and final step of the styrene polymerization in emulsion.
Simulation of intermediate order in polymeric glasses
Authors: Ludovice Peter J. , Ahmed Savant , van Order Jon , Jenkins Jerry 
Published: March 2011

AbstractThe glass phase of most polymers is typically considered amorphous. However, many commercially important polymer glasses do contain a subtle level of structural order intermediate between the crystalline and truly amorphous phases. These include a number of commercially important polymers. This “Intermediate Order” is distributed homogeneously throughout the glass phase and is therefore quite different than the morphology of semi‐crystalline materials. Typical computer simulation methods can fail to accurately reproduce the structure of polymers with intermediate order, because they are often based on the assumption that the polymer structure is truly amorphous. Given the subtle nature of this order, computer simulation is important in understanding this structural order and the unique material properties commonly associated with it. We outline the critical issues required for the successful simulation of polymer glasses with intermediate order, and discuss the results of some continuing research designed to improve the accuracy of such simulations.
Morphology and mechanical properties of low‐molecular ‐ weight polyethylene and ultrahigh‐molecular‐weight polyethylene films drawn up to 200‐fold
Authors: Bin Yuezhen , Fukuda Miwako , Kurosu Hiromichi , Matsuo Masaru 
Published: March 2011

AbstractUltrahigh‐molecular‐weight polyethylene (UHMWPE) and low‐molecular‐weight polyethylene (LMWPE) blend films were prepared by gelation/crystallization from solutions. UHMWPE with the viscosity‐average molecular weight (Mv) of 6×106 and three kinds of LMWPE with (Mv) <5×104 were used. The LMWPE/ UHMWPE compositions chosen were 1/1, 2/1, 4/1 and 9/1. The resulting blend gels with the 9/1 composition (10% UHMWPE content) became films by evaporating the solvents, although LMWPE homopolymer gels have no ability to form films. The films with the above compositions could be readily elongated up to 200‐fold in a hot oven. Such high elongation is assumed to be due to the existence of a suitable level of entanglements between UHMWPE and LMWPE chains. The orientational degree of LMWPE crystallites became poorer as the LMWPE content in the blend film increased, indicating a decrease in the number of entanglements. The storage modulus of the blend films at the same draw ratio decreased as the LMWPE content increased. The storage modulus of the 1/1 blend film with λ = 200 reached about 50 GPa at 20°C but the storage modulus decreased drastically with further increase in the LMWPE content: The value of the 9/1 blend film with λ = 200 was less than 10 GPa. This means that a suitable level of entanglements between LMWPE and UHMWPE chains plays an important role in transmitting the drawing force effectively and promoting the orientational degree of the c‐axis, owing to the crystal transformation from a folded to a fibrous type.
Relationship of hierarchical structure to mechanical properties
Authors: Baer E. , Hiltner A. , Jarus D. 
Published: March 2011

AbstractThe mechanical properties in complex systems are explained based on the hierarchical structures present in the system. Hierarchical structures designed for specific mechanical responses are best exemplified by examples from biology. Collagen, a main component in soft connective tissues, is organized into hierarchical structures in the form of tendons or intervertebral discs as examples. Understanding these structures is vital in relating the structures to the intended properties. This approach is also used to characterize organic/inorganic natural composites such as human bone, reindeer antler and nacre. Another example of a hierarchical structure in biology with excellent mechanical properties is that of cellulose, when organized into wood. The importance of hierarchical structures also applies to synthetic polymers for a clearer understanding of the structure‐property relationships. Solid‐state biaxially oriented polypropylene has excellent tensile and impact properties, which are explained by the hierarchical structure induced during the processing. Thermotropic liquid crystalline polymers develop a hierarchical structure during injection molding that influence the final properties. Furthermore, the impact modification of polycarbonate is more easily understood when the system is explained in a hierarchical manner. It is also now possible to create or force hierarchical structures in synthetic polymers by microlayering technology. Several systems are outlined in which a hierarchical structure is created to enhance specific properties. SAN, a brittle polymer, can be microlayered with PC to create tough materials due to the scale, interaction and architecture of the microlayered composite. Another example is the effect of microlayered composite of PC/SAN on the interfacial adhesion mechanisms. Furthermore, toughening mechanisms in filled microlayers are examined based on the hierarchical structure.
Application of the crack resistance concept to the toughness characterization of high‐impact thermoplastics
Authors: Seidler Sabine , Grellmann Wolfgang 
Published: March 2011

AbstractHeterophasic reactor‐grade polypropylene‐ethylene copolymers were diluted with a propylene‐ethylene random copolymer to obtain materials with a constant EPR/PE‐particle diameter but various interparticle distances. In addition to these copolymers, PP/EPR blends were investigated. According to the results of instrumented impact tests, brittle‐to‐tough transitions were found at different temperatures. In the materials with PP matrix, two transitions in the load‐deflection behaviour were seen. The first transition occurs from the elastic to the elastic‐plastic material behaviour, the second from the unstable to stable crack growth. “Critical” interparticle distances could be determined in the region of predominantly unstable crack growth as well as in the region of predominantly stable crack growth. With increasing test temperature, both transitions shift to higher interparticle distances. From this theoretically similar behaviour of fracture mechanical values quantifying different proportions of the crack growth process, one can conclude that different processes must be occurring.
Mechanical properties of crosslinked polyolefin‐based materials
Authors: Chodák Ivan , Nógellová Zuzana , Kokta Bohuslav V. 
Published: March 2011

AbstractThe effect of crosslinking on mechanical properties of various polyethylene‐based materials is compared. In virgin polyethylene, higher strength results from formation of spatial network, especially at increased temperatures. On the other hand, decreased crystalline portion leads to lower Young's modulus values compared with the uncrosslinked polymer. Crosslinking of LDPE/PP blends leads to a dramatic increase in elongation at break and impact resistance. The reason is seen in an in situ formation of very efficient compatibilizers via co‐crosslinking on the phase boundary. In LDPE filled with silica, the main effect consists in higher elongation at break and increased toughness, although the effect is lower than that in LDPE/PP blends. Increased resistance to the crack growth rate was demonstrated to be a reason for the observed behaviour. In LDPE filled with organic fillers, formation of direct covalent bonds on the interface and a significant increase in adhesion is suggested to be the reason for the enormous increase in Young's modulus and tensile strength observed.
Deformation behavior and mechanical properties of hard elastic and porous films of polyethylene
Authors: Elyashevich Galina , Karpov Evgenii , Kozlov Alexandr 
Published: March 2011

AbstractHard elastic samples of linear polyethylene were prepared by melt extrusion at a high velocity of the melt flow and by subsequent annealing of crystallized samples. The deformation behavior of hard elastic samples obtained by annealing of as‐spun samples at different temperatures has been analyzed at uniaxial extension resulting in formation of porous structure. Mechanical properties of microporous films in the longitudinal and transverse directions have been investigated. Composite systems consisting of a microporous polyethylene film and a thin layer of an electroconducting polymer have been prepared. Mechanical properties of composite systems, such as elastic modulus, tensile strength, and break elongation, have been compared with the properties of polyethylene substrates.
From dynamic mechanical properties to plastic strain behavior of epoxy networks. Effect of the network architecture
Authors: Pierre A. , Sindt O. , Thorne N. , Perez J. , Gérard J. F. 
Published: March 2011

AbstractClosed epoxy networks with various architectures, i.e., crosslink density and chain flexibility between crosslinks, were considered in this study. The crosslink density can be varied by preparing epoxy‐amine networks from a mixture of primary amines having different functionalities using mixtures of poly(oxypropylene)amines or a monofunctional amine having the same chemical structure acting as a chain extender. The chain flexibility is modified by considering aliphatic epoxy prepolymers instead of aromatic. The influence of the architecture of the epoxy networks on the low‐ and high‐stress mechanical properties is discussed. The dynamic mechanical spectroscopy conducted in wide ranges of frequency and temperature gives insight into the molecular level analyzing the data in both the glass transition region (α‐relaxation) and sub‐Tg relaxation zones. A model described by Perez and based on the existence of nanofluctuations of density or quasi‐point defects and the concept of hierarchically correlated molecular motions are also used to describe the low‐stress mechanical behaviour. The same theory is extended by taking into account the large‐stress effects and used to analyze the stress‐strain curves recorded in compression at various temperatures and strain rates. This modeling can describe variation of the flow stress with temperature and gives a unique description of the yielding of all the epoxy networks. From this model, the main physical parameter determining the flow stress is the cohesion of the solid state resulting from intermolecular interactions; the loss of cohesion, as temperature increases, corresponds to the α‐process which depends on the network architecture. Finally, the strain and stress at break (sr and ϵr) recorded in tension at various temperatures and strain rates for epoxy networks having various crosslink densities are correlated with the low‐stress behavior from the shift factors, aT, determined in the glass transition region.
Short predicting the strength and toughness of fiber composites
Authors: Kardos J. L. , Halpin J. C. 
Published: March 2011

AbstractPredictions of strength and toughness for short‐fiber‐reinforced plastic systems are complex but industrially crucial problems. In this contribution, we utilize a new approach which accounts for the large stress concentration penalties in a perfectly aligned short‐fiber composite. Although empirical, the approach permits calculation of a strength reduction factor which can then be utilized with an appropriate failure criterion to calculate the strength of a wide range of short‐fiber composite systems. A similar approach is used for the toughness problem, with the fracture toughness of an isotropic, random‐in‐a‐plane, short‐fiber composite being expressed in terms of the fracture toughness of single unidirectionally oriented plies with cracks oriented along the two orthotropic axes. For both strength and toughness, a laminate analogy approach is used. The short‐fiber system is thought of as being composed of several plies or layers, each containing uniaxially aligned short fibers. The plies are oriented in the laminate to replicate the actual system fiber orientation distribution, and the linear stress‐strain or fracture toughness properties are calculated by analyzing the individual ply responses to the overall applied stress. Comparison with experimental data for random‐in‐a‐plane fiber orientation and for biased in‐plane orientations at practical fiber volume loadings shows good agreement. In the case of fracture toughness, there was qualitative agreement between theory and experiment, but the data scatter precluded a rigorous comparison.
Comparative study of mechanical and dielectric properties of glassy acrylic polymers containing 1,3‐dioxane rings in their structures
Authors: Díaz‐Calleja Ricardo , Riande Evaristo 
Published: March 2011

AbstractA comparative study of mechanical and dielectric relaxation behaviour in the glassy region of some acrylic polymers containing 1,3‐dioxane rings in the side chain is reported. Earlier results for similar polymers containing cycloaliphatic rings are used to interpret the results obtained. This study suggests that simple mechanisms based on chair‐to‐chair inverse conformational transitions are not able to explain in a unified way the responses of these polymers in the glassy region to mechanical and electric perturbation fields.
Yielding and fracture in crosslinked epoxies
Authors: Tcharkhtchi Abbas , Trotignon Jean‐Pierre , Verdu Jacques 
Published: March 2011

AbstractFrom a comparison of tensile properties of two epoxy networks crosslinked, respectively, with an aromatic diamine or an anhydride and from the available literature data on the fracture properties of thermosets, it has been tried to establish structure‐property relationships in this field. Attention was focused on possible specific aspects of the crosslinked polymers. Surprisingly, the crosslink density does not seem to play a crucial direct role in fracture. In contrast, there is a relation between toughness and Tg: Aliphatic networks of low Tg are generally tougher than aromatic ones. The local mobility plays a very important role because it partly controls the value of Poisson's ratio (which determines the relative importance of dilatant stresses and shear stresses responsible, respectively, for brittle rupture and yielding) and, presumably, the activation volume of yielding (which partly determines the broadness of the temperature interval of ductility).