bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hindered interdiffusion in asymmetric polymer‐polymer junctions
Authors: Brochard‐Wyart F. , De Gennes P. G. 
Published: March 2011

AbstractWe discuss theoretically the diffuse interface formed when a long (L) polymer is put into contact with shorter chains (S) of the same material (all chains being entangled). At time t shorter than the reptation time TL of the long chains, the L chains behave like a gel swollen by the S chains. The “penetration factor” ψ (i.e. the volume fraction of S near the gel surface) is controled by a balance between the osmotic pressure of the swollen L chains, and the elastic tension ψ due to swelling. If t is larger than TS (the reptation time of the short chains), ψ is of order Ne/NS (where Ne is the number of monomers between entanglement points, and NS is the degree of polymerisation of the short chains). On the other hand, if t < TS, NS must be replaced by the average number s (t) of monomers of an S chain which have entered the L region, and ψ ∼ Ne/ s (t) ∼t−1/2. The width of the mixed region e(t) increases like s 1/2(t) at TS, and like (DSt)1/2 (where DS is the reptation diffusion constant of the S chains) at t>TS.
Deformation in networks: The role of the chain length distribution
Authors: Kilian H. G. 
Published: March 2011

AbstractIf strain energy in “chain length dispersed networks” is equipartitioned, chains of different lengths must be strained to different degrees. A van der Waals network considered as a “conformational gas network with weak interactions”, the stress‐strain behaviour of networks with a chain length distribution can be represented by an equivalent monomodal network. The mean maximum strain is uniquely related to the real structure. Global interactions should not depend on the chain‐length distribution. Within the framework of the approach presented, the relative stress‐strain curves of bimodal networks of different composition can be interpreted. It is deduced that it may be difficult to identify the individual “deformation” of the radii of gyration of short and long chains by neutron scattering experiments. It is possible to derive a parameter which characterizes the width of the chain length distribution in networks.
The preparation and characterisation of novel polyether gels
Authors: Knowles P. R. , Stubbersfield R. B. , Price C. 
Published: March 2011

AbstractPoly(ethylene oxide)s end‐capped with n‐alkane chains (C16‐C21) have been found to form stable gels in aqueous media. The crosslinks are believed to occur through association of the n‐alkane chains. The dependence of the degree of swelling of the gels on the lengths of the alkane and poly(ethylene oxide)(Mn= 10000, 20000 and 30000) chains were studied. Degrees of swelling have been compared with results predicted by simple network theory.
Small angle neutron scattering from interpenetrating networks
Authors: Richards R. W. 
Published: March 2011

AbstractThe basic principles of small angle neutron scattering are set out in precise form together with the interpretation of scattering data using both the model approach and the statistical interpretation. These methods have been applied to interpenetrating networks of polydimethylsiloxane and deuteropolystyrene and polydimethylsiloxane and polymethacrylic acid. Discrete regions appear to exist in the first of these IPN systems and to some extent the mechanical properties can be evaluated from small angle neutron scattering data. For the second IPN, the statistical approach had to be used, results of which indicated that the polymethacrylic acid regions are continuous. This conclusion was confirmed by a separate permeation study.
Contribution of crazing to the toughness of amorphous and semicrystalline polymers
Authors: Michler Goerg H. 
Published: March 2011

AbstractCrazes or craze‐like deformation bands occur in many different polymers. Mechanisms of initiation and growth of the crazes have been studied using different techniques of electron microscopy. Examples of modifying amorphous and semi‐crystalline polymers are given to demonstrate to which extent the macroscopic toughness of the polymers is affected by changes in the microscopic structure and by the amount of crazes.
Plastic flow and multiple fracture of semicrystalline polymers
Authors: Prut E. V. 
Published: March 2011

AbstractThe mechanism of plastic flow of isotactic polypropylene is considered in terms of Eyring's equation. It is demonstrated that to explain the dependence of the yield point on temperature a dependence of activation volume on overcooling (Tm‐T) must be admitted. The effects of drawing rate and temperature on the ultimate elongation of polypropylene are discussed in the case of two‐step drawing. The critical conditions of extrusion in solid state are considered. Criteria of transformation of a steady flow into unsteady state are suggested. Multiple fracture of semicrystalline polymers under critical conditions of plastic is described.
Kinetics of polymer failure at moderate and low temperatures
Authors: Slutsker A. I. , Veliev T. M. , Alieva I. K. , Abasov S. A. 
Published: March 2011

AbstractThe time of expectation for breakdown (life‐time, τ) was measured as a function of temperature (T) and tensile stress (σ) for a variety of polymers, including nylon‐6, polyethylene, poly(ethylene terephthalate) and poly(tetrafluoroethylene). At moderate temperatures (above ∼200 K), the τ(1/T)σ dependences are exponential (of the Boltzmann‐Frenkel type). The elementary acts of polymer fracture occur at these temperatures through the thermal‐fluctuation above‐barrier transitions. At low temperatures (below ∼200 K), τ is T‐independent (an athermic plateau) and, therefore, the above‐barrier mechanism is ruled out. It is concluded that the elementary acts of fracture proceed at low temperatures via the tunnel below‐barrier mechanism. Possible types of tunnel processes (tunneling of atoms or electrons) are discussed.
Influence of electron beam irradiation on the impact properties of polystyrene/EPDM rubber blends
Authors: van Gisbergen J. G. M. , van Der Sanden M. C. M. , De Haan J. W. , van De Ven L. J. M. , Lemstra P. J. 
Published: March 2011

AbstractThe influence of electron beam (EB) irradiation on the impact properties of compatibilized polystyrene/ethylene‐propylene‐diene‐monomer (PS/EPDM) blends was studied. The change in impact value upon irradiation proved to be strongly dependent on the type of compatibilizer used. Using a polystyrene/polybutadiene (SB) diblock copolymer as a compatibilizer, a twofold increase in Izod value could be achieved upon irradiation. Irradiation of a blend using a polystyrene/ethylene‐propylene (SEP) copolymer as a compatibilizer resulted in a decrease in impact strength. These observations can be related to a radiation induced increase in interfacial adhesion in case of the SB copolymer, which does not occur for the SEP copolymer. Due to the abundance of double bonds in the SB copolymer, this copolymer reacts very fast upon irradiation and may co‐crosslink with, or graft onto the EPDM phase. For the SEP copolymer crosslinking occurs only at much higher doses and is (partly) overruled by chain scission and consequently the adhesion between matrix and dispersed phase will hardly change. This view is supported by analytical methods as FT‐IR and NMR as well as from Tg measurements.
Toughness of epoxies modified by preformed acrylic rubber particles
Authors: Levita Giovanni , Marchetti Augusto , Lazzeri Andrea 
Published: March 2011

AbstractA bisphenol‐A diglycidyl ether resin, cured with isophorone‐diamine at 60°C, was modified by means of preformed core‐shell acrylic rubber particles. Blends with rubber contents up to 30 phr by wt were tested. The fracture toughness depended linearly on the amount of rubber and significant improvement was found. No deterioration of temperature resistance was also observed. The viscosity of resin/modifier mixtures was controlled by means of antifoaming agents. A comparison with liquid acrylonitrile‐butadiene copolymers showed that core‐shell particles are efficacious tougheners. The effect of a bimodal particle size distribution was considered. In the size range investigated (0.2+5μm) no synergic effect was observed.
Heterogeneity of structure and mechanical properties of polymers
Authors: Marikhin V. A. , Myasnikova L. P. 
Published: March 2011

AbstractSpecific features of development of micro‐ and macrofibrils as well as the structure of their interfaces are considered for oriented filaments of high‐density polyethylene with different initial supermolecular structures. As evidenced by SAXS, WAXS, EPR, Raman spectroscopy and electron microscopy, the melt‐crystallized samples contain a greater amount of tie molecules connecting macro‐ and microfibrils than the samples crystallized from solution. This hampers slippage of fibrils past each other and does not allow high draw ratios to be achieved. It was found that the density of macrofibrillar ends in the drawn melt‐crystallized samples is nearly an order of magnitude greater than that in the drawn samples crystallized from solution. This leads to generation of kink bands (dangerous large‐scale defects) and, as a result, the sample, being oriented, fractures long before high draw ratios and a perfect fibrillar structure are reached. The ultraoriented samples produced from solution have a more perfect intrafibrillar structure, and the density of intrabrillar disordered regions is close to that of crystalline ones. Nevertheless, they do contain clusters of defects which limit their mechanical properties. The analysis of the Raman and X‐ray data shows that these defects are localized at crystallite boundaries in the long periods. Possible routes for improvement of the parameters of the fibrillar structure and their relation with mechanical properties are discussed.
Energetics of stress relaxation in glassy polymers at high pressures
Authors: Ya. Goldman A. , Kestelman V. N. , Maksimov V. L. 
Published: March 2011

AbstractKinetics of relaxation of the shear stress in glassy poly(methyl methacrylate) were studied in isobaric, isothermal and isochoric conditions. In isochoric conditions the relaxation rate depends only on temperature and polymer volume is the main parameter for the rate of stress relaxation. Isobaric and isochoric activation energies and activation volume of the stress relaxation were determined. The results are shown to satisfy the thermodynamic relation of activation parameters of the relaxation process. The size of the area in which the elementary stress relaxation process occurs in glassy poly(methyl methacrylate) was evaluated.
The effect of structural organization on the mechanical strength of poly(vinyl alcohol) gels
Authors: Hnát Vladimír , prokopová Eva , Raab Miroslav 
Published: March 2011

AbstractUltimate mechanical properties of poly(vinyl alcohol) adhesive layers prepared from fresh aqueous solution, aged solution and water‐swollen PVA particles are compared. Tensile strength and toughness of dry adhesive layers significantly increase in the cited order. These differences may be attributed to the formation of heterogeneous thermoreversible network upon ageing and to the presence of heterogeneities in PVA gel which act as barriers against crack propagation.
A new model of inhomogeneous deformation used for craze formation
Authors: Kreitmeier S. , Göritz D. 
Published: March 2011

AbstractThe coil‐strand (CS) model is described. After a phase of elastic deformation of an isotropic coil a highly oriented strand and a still isotropic rest coil are formed. Entropy and several energy contributions are calculated and compared with experimental data. The constant tensile stress acting on the craze surface, the inverse relationship between fibril extension ratio and fibril volume fraction and the temperature dependence of the product of tensile stress and fibril diameter can be calculated directly from the model. Some other properties are discussed.
Optical and electro‐optical switching processes in polymeric liquid crystals
Authors: Anderle Klaus , Birenheide Richard , Wendorff Joachim H. 
Published: March 2011

AbstractLow‐molar‐mass and polymeric liquid crystals exhibit large nonlinear optical responses, due to a combination of orientational order and fluidity. Polymeric liquid crystals have the disadvantage of longer response times but offer the advantage that the liquid‐crystalline state and any modulation imposed on it can be frozen‐in in the anisotropic glassy state. This holds in particular for light‐induced reorientations of the director and thus of the optical axes based on a photoselection process of photostationary mesogens.
Nondestructive evaluation of polymer materials by solid state NMR imaging
Authors: Blümich B. , Blümler P. , Günther E. , Schauss G. , Spiess H. W. 
Published: March 2011

AbstractMany polymer products are heterogeneous. Examples of heterogeneities are the chemical composition, distributions of mechanical stress, and variations in flexibility or molecular orientation. Applications of NMR imaging to polymers are summarized and investigations of the aging of rubber are reported as well as novel deuteron NMR techniques to image molecular order and mobility of polymers below the glass transition temperature.
Polymer compatibility ‐ a consequence of repulsive groups within monomer units
Authors: Siol Werner 
Published: March 2011

AbstractThe majority of compatible polymer mixtures known so far has been rationalized by assuming special interactions between the different polymers or by specific repellent forces within certain types of copolymers. Thus, the compatibility of PMMA with special copolymers of styrene and acrylonitrile is explained by an intramolecular repulsion within the copolymer between the two comonomers styrene and acrylonitrile. In our opinion this phenomenon is not limited to copolymers, but also holds for explaining the compatibility of various homopolymers such as PVDF/PMMA. To this end we simply regard the homopolymer PVDF (‐CH2‐CF2‐) as a copolymer of ‐CH2‐ and ‐CF2‐ “monomers”. By the same token it is possible to assume repellent forces within the PMMA monomer units (i.e. repulsion between the CH2‐C(CH3) and the polar carbonyl group). Those strong repellent forces within the PVDF and PMMA homopolymers can be reduced by mixing the two species. This concept of repulsive forces within monomers as a driving force for polymer‐polymer compatibility can be used to search for new classes of compatible polymers. This will be demonstrated with the polystyrene/polyalkylmethacrylate blends. Thus, with comparable geometry in the side chains, polystyrene and polymethacrylic esters will form compatible blends, as born out in the systems polystyrene/polycyclohexyl methacrylate or poly‐tert‐butyl styrene/poly‐3,3,5‐trimethylcyclohexylmethacrylate which are compatible in all proportions. Taking into account certain steric prerequisites, one can even obtain compatible blends lacking exothermic interaction.
One‐ and two‐dimensional order in multilayered structures of liquid‐crystalline polymers
Authors: Tsukruk Vladimir 
Published: March 2011

AbstractThe parameters of the multilayered ordering in liquid‐crystalline polymers have been analysed in the terms of longitudinal and transversal correlation lengths. The perfection of one‐ and two‐dimensional order in the multilayered structures of smectic comb‐like liquid‐crystalline polymers, low‐molecular‐weight liquid crystals and Langmuir films has been compared.
Functionalized liquid‐crystalline polymers towards NLO‐applications and piezo‐sensors
Authors: Kapitza Heinrich , Poths Holger , Zentel Rudolf 
Published: March 2011

AbstractA systematic synthesis of functionalized 1c polymers is possible starting from precursor polymers with phenolic groups. The esterification of these precursor polymers with chiral acids proceeds nearly quantitatively and produces polymers with cholesteric and chiral smectic C* phases. A further functionalization of these polymers with “NLO‐chromophores” produces polymers, which are suitable for second harmonic generation; a functionalization with crosslinkable groups leads to polymers, which act as piezoelements.
X‐ray diffusive scattering and the mesomorphic states in polymers
Authors: Kuzmin N. N. , Matukhina E. V. , Makarova N. N. , Polycarpov B. M. , Antipov E. M. 
Published: March 2011

AbstractThe structural peculiarites of a number of polymers have been investigated by using the analysis of the X‐Ray amorphous scattering curves. These polymers were studied in three different (amorphous, semi‐crystalline and mesomorphic) phase states. By means of such type of analysis, it was shown that: 1) for the amorphous ethylene‐propylene random copolymer (PP‐PE) and for semicrystalline polyethylene (PE), the glass transition temperature can be determined with a high accuracy; 2) the mesomorphic state and the two structural transitions can be found in noncrystallized polydimethylsilmethylene (PDMSM); 3) besides the crystalline phase, two structural components having pure liquid and mesomorphic nature, may be determined in PE; 4) the mesomorphic state is revealed in poly‐4‐methyl‐pentene‐1 (P4MP1) in the temperature range both below and above the melting point; 5) the structural transition is realized within the mesomorphic state in poly‐deoamethyloyolohexasiloxanes (PDMCHSs); 6) a new meso‐phase 1‐ mesophase 2 transition is registered in poly‐diethylsiloxane (PDES).
Novel alicyclic dianhydrides and polyheterocycles on their basis
Authors: Zhubanov B. A. , Shpilman N.Y U. , Almabekov O. A. , Solomin V. A. , Kozybaev K. O. 
Published: March 2011

AbstractDianhydrides of alicyclic tetracarboxylic acids were synthesized by chemical modification of tri‐cyclodecenetetracarboxylic dianhydride and its chloro‐containing derivatives. By polycondensation of these di‐anhydrides with diamines polyimides were obtained. Thermal and thermooxidative degradation of these polyimides are discussed. By the interaction of polyamic acid carboxylic groups with diamines in presence of phosphorus pentoxide a number of polyimidoamidines have been synthesized, some physico‐chemical properties of them are studied.
Evolutional kinetics of metal‐polymer complexes formation
Authors: Lishinsky V. , Travin S. , Rakhnianskaja A. , Psheshetsky V. 
Published: March 2011

AbstractUnder the conditions of polydental binding, metal ions couple azacrown ether links of the polymer, limiting segmental chain mobility and decreasing statistical weight of the states available for complex formation. According to the rate constant dependence on conversion extent two different regimes of the complex formation reaction may be given: 1) retardation resulting from decreasing reactivity, the measured rate constant decreases by a few orders of magnitude in the course of time; 2) retardation followed by increasing reactivity, the observed rate constant remains unchangeable. The process covering conformational nonequilibrium states of macromolecular coil makes it dependent on the system prehistory which violates the law of mass action. The couplings being labile, the instantaneous value of pseudomonomolecular rate constant of the reaction is a function of conversion extent on metal and is not dependent on absolute polymer uptake by metal. The reaction rate in each point does not depend only on reagents concentration ratio but also on the character of metal ion distribution along the polymer chain obtained to the given moment. At complex formation with “hard” couplings the increase of metal concentration makes the effective retardation of the process change, whereas initial parts of the kinetic curves remain practically the same. In this system pseudomonomolecular rate constant does not seem to be a function of conversion extent, but is defined by absolute quantity of the formerly bound metal. Formal application of the law of mass action in this case is useless, it is necessary to apply distribution function on reactivity. Unlike solid phase systems nonequivalent character of reaction sites in the polymer is of evolution character, i.e.it arises in the course of the reaction on the account of polymer coil conformation change.
Modification of polymer surface properties by inert and reactive surface‐active compounds
Authors: Rudoy V. M. , Ogarev V. A. 
Published: March 2011

AbstractGeneral conditions of formation and dynamics of adsorption layer of inert surface‐active compounds at the polymer/gas interface were investigated. A quantitative model describing the behavior of surface‐active additive in polymer film during evaporation into gaseous phase was developed. The correctness of the model was demonstrated on the specific example of studying the behavior of fluoro‐organic compounds in polyethylene. The possibility of modifying surface properties of thermoreactive polymers by reactive surface‐active compounds was elucidated. It was found that the degree of epoxy polymer surface modification in systems made up of epoxy resin/monoepoxy ester of fatty acid is controlled by the ratio between the additive's rate of diffusion and the rate of its chemical reaction.
Surface composition of siloxane‐containing polymers
Authors: Gorelova Marianna , Levin Victor , Pertsin Alexander 
Published: March 2011

AbstractX‐ray photoelectron spectroscopy was used to study relationships between the surface and bulk composition in block copolymers and blends of poly(dimethyl‐siloxane), poly(bisphenol A sulfone) and poly(bisphenol A carbonate). In all cases the polymer surfaces were highly enriched in siloxane. At a fixed siloxane concentration in the bulk the highest enrichment was observed in the blends of homopolymers and the lowest in the copolymers. It was found that the addition of small quantities of a siloxane‐rich copolymer to another copolymer having a lower siloxane content may reduce the surface siloxane concentration of the latter. This unusual surface behavior was explained by the formation of an over‐layer in which the macromolecules of the siloxane‐rich copolymer are oriented nearly parallel to the sample surface.
The reversible network formation in polydimethyl‐siloxanes with side carboxyl groups
Authors: Rogovina L. Z. , Tchegolihina O. A. , Vasiliev V. G. , Levin V. Yu. , Zhdanov A. A. 
Published: March 2011

AbstractThe peculiarities of the structurisation of polydimethylsiloxane with carboxyl side groups are investigated by studying its viscosity, elasticity and thermomechanical behaviour over a large temperature interval. The structurisation exhibited in the transition from initial liquid to elastomeric state is shown to be thermoreversible. It occurs more intensively as temperature increases. The cooling of the polymer to room temperature leads to the liquefaction of the elastomer proceeding over a long time; this time depending on the temperature and the length of time of heating. The reasons for these peculiarities lie in the relation between intra‐ and intermolecular interactions between COOH‐groups and the specific changes of polydimethylsiloxane conformations with temperature.