bluuebunny/crossref_metadata_2025 huggingface dataset:
The industrial interest in blends
Authors: Capaccio G. , Gardner A. J. , Hope P. S. , Wilkinson K.
Published: March 2011

Selected examples of industrial blends have been reviewed. In each case specific reference has been made to their functional/economic justification. The area of incompatible blends is identified as the one with significant growth potential and providing the greatest scientific and technological challenge. Key to meeting this challenge is a concerted effort in three distinct areas, i.e. thermodynamics, processing and new compatibilisers.
Rigidity of segments of poly (ethyl methacrylate) in CCl14 solutions
Authors: Huyskens P. L. , Vael C. , Vandevyvere P.
Published: March 2011

Collegial dispersion forces originate from a coordination of the temporary electronic dipoles of a series of molecules. To insure this coordination the nuclei on a row have to replace their individual vibrations by coupled ones. Such row is then rigid. For polymers collegial forces can already be temporarily active in given parts of a solution but are regularly annihilated by intrusion of the solvent. However the regular passage through the rigid state modifies the distribution of the dipole moments during the interval that solvent or ligand molecules are in contact with the segment. In a rigid domain the correlation parameter of Kirkwood g is zero. The existence of such rigidity in solution is demonstrated by the low experimental value of gmA for the dipoles of the complexes between poly(ethyl methacrylate) and phenols. Due to the large number of segments that separate the complexes the classical explanation of stiffness of the chain due to individual interactions between neighbours does not hold.
Structures in polystyrene solutions: Their origins and their implications on physical gelation
Authors: Guenet Jean‐Michel , Klein Marc
Published: March 2011

From studies on dilute and semi‐dilute solutions it will be shown that gelation in atactic polystyrene proceeds via the creation of a nematic‐like order (formation of a polymer‐solvent intercalate with the highly syndiotactic sequences). A similar mechanism holds for isotactic polystyrene (intercalate wherein the chain adopts a near‐31 helical form). It will be emphasized that the gelation phenomenon depends upon both the solvent size and the volume of the cavities created by the phenyl groups along the chain. Finally, diffraction experiments on well‐organized structures (giant spherolites of 150–200/μm diameter) grown from isotactic polystyrene solutions and possessing the same melting point as the gel show the absence of 121 helices. Therefore, gel formation is not due to the growth of this helical form.
A definition of the concepts “gelation temperature” and “gelation curve” by means of relaxation time spectra
Authors: Visscher K. , Mijnlieff P. F.
Published: March 2011

With the aid of the Boltzmann superposition principle, the infinitesimal flow behaviour of a substance can be described in terms of a memory integral. The memory function in this integral can be expanded in a set of relaxation times and relaxation strengths: the relaxation spectrum. On basis of a specific form of the fluctuation‐dissipation theorem, a physical meaning is proposed for the relaxation spectrum. The theory of complex functions enables one to show that the relaxation spectrum, determined from dynamic mechanical measurements, has a unique meaning. The infinitesimal flow behaviour, expressed in terms of the relaxation spectrum, is used to develop a general description of the phenomenon of thermoreversible gelation. This description method was applied to a styrene‐isoprene‐styrene triblock copolymer solution.
Formation and properties of physical gels from saturated poly(ester‐urethane) in styrene
Authors: Wang Fu‐Cai , Fève Michel , Pascault Jean‐Pierre
Published: March 2011

A gel was obtained from reacting a α, ω–hydroxy‐terminated polyester oligomer and a diisocyanate in styrene. Two types of morphologies were possible which are dependent on the quantity of catalyst. The rheological experiments led to the discovery that the “gel point” was not well defined and that the gel formation was a gradual process. A certain chain length was necessary for the appearance of the gel properties. The physical cross‐links could be destroyed and re‐formed.
Structure formation and gelation phenomena in solutions of ternary interpolyelectrolyte complexes
Authors: Kabanov V. A. , Zezin A. B. , Izumrudov V. A. , Bronitch T. K. , Kabanov N. M. , Listova O. V.
Published: March 2011

The representative of the new family of mechanically reversible gels is described. The gel is formed by mixing of an aqueous solution of non‐stoichiometric interpolyelectrolyte complex of poly (sodium methacrylate) and poly(N‐ethyl‐4‐vinylpyridinium bromide) containing a certain amount of covalent links between oppositely charged polyions, with aqueous solution of poly(potassium vinylsulfate). The gelation mechanism arises to the partial replacement of the electrostatic contacts between the polycation and poly(methacrylate) anion in the original polycomplex with those between the polycation and poly(vinylsulfate) polyanion. The network of the gel is most probably formed by the nodes consisting of covalent links and interpolyelectrolyte double‐strand electrostatic clusters, united by poly(sodium methacrylate) tie‐chains.
Light scattering from reacting polymer systems. Associating polymers in a good solvent
Authors: Burchard Walther
Published: March 2011

The forward scattering of light allows determination of the osmotic modulus (=inverse osmotic compressibility), which in good solvents is a measure of repulsive forces among the particles in solution but also depends on the molar mass of the particle. The osmotic modulus increases with concentration if the particle weight remains constant. The increase differs for particles of different architecture and can for c < 3c* be described by structure specific g‐factors, where g is defined through A3=gA22 Mw with A2 and A3 being the 2nd and 3rd virial coefficients. For associating systems in a good solvent also the particle weight increases with c. A procedure is suggested which allows within limits a correction of the measured apparent molar mass M̄app (c) for the true molar mass M̄w (c) at the concentration c. Three examples are discussed in detail.
A novel molecular association of poly (acrylic acid) in dilute solution under high shear flow
Authors: Kim Oh‐Kil , Choi Ling‐Siu
Published: March 2011

A novel association of poly(acrylic acid) in dilute solution is induced by high shear flow, producing a rigid chain morphology via interchain H‐bonding; the association is destroyed upon adding salt to the shearing solution. Such macromolecular changes in conformation are reflected in drag reduction changes as a result of flow‐polymer interaction.
Elasticity and flow properties of actin gels
Authors: Hvidt Søren , Janmey Paul A.
Published: March 2011

Actin gels formed by polymerizing monomeric actin have been studied by use of small amplitude oscillatory deformations and steady shear flow. The length of actin filaments within the gel was varied by copolymerization in the presence of the filament‐capping protein gelsolin. The results for short filaments are in qualitative agreement with a model for semi‐dilute solutions of inter‐penetrating rods. Long filaments give rise to additional motions, believed to be flexing of rods. Steady shear viscosities, at high shear rates, are independent of initial filament length. Results are explained as due to breaking of filaments in shear flows.
Diffusion and phase separation in polymer solution during asymmetric membrane formation
Authors: van Den Boomgaard Th. , Boom R. M. , Smolders C. A.
Published: March 2011

Most of the commercially available polymeric membranes are prepared by the phase inversion process. In this process a thermodynamically stable polymer solution is brought to phase separation by immersing the solution in a surplus of nonsolvent, followed by an exchange of solvent and nonsolvent. The ultimate membrane structure is the result of an interplay of mass transfer and phase separation. Asymmetric membranes as well as symmetrical porous membranes can be obtained. Two types of demixing processes (l‐l phase separation and formation of aggregates) can be distinguished by the kinetics of phase separation, as the formation of aggregates is supposed to be a slower process than l‐l demixing. Because it is impossible to measure the composition changes during the demixing processes experimentally, a theoretical analysis has to be applied. A suitable formalism to calculate the diffusion induced composition changes in the immersed casting solution, as a function of thermodynamic and hydrodynamic interaction parameters will be described. With this theory it can be shown that two distinctly different mechanisms of membrane formation may occur resulting in two different types of membranes. One type has a relatively thick toplayer and mostly exhibits reverse osmosis, gas separation and pervaporation properties; the other type results in a porous type of membrane, which will exhibit ultra‐ and microfiltration properties.

Model calculations are in agreement with light transmission experiments on membrane forming systems. Therefore, it could be concluded that the elucidation of the diffusion behavior in the immersed polymer film is the key to better understanding of membrane formation by means of immersion precipitation.
Structure of single and double stranded dna solutions as studied by ultracentrifugation
Authors: Frisch H. L. , Trohalaki S.
Published: March 2011

The osmotic pressure of dense solutions of DNA fragments in aqueous 0.2‐2 M salt (NaCl, etc.) solutions were easily obtained from equilibrium ultracentrifugation data. Short, helical double stranded DNA fragment solutions showed a well defined ordering transition. The osmotic pressure of these helical solutions could be explained by the scaled particle theory of rigid sphero‐cylinders. On the other hand, dense solutions of (single stranded) etheno‐DNA derivatives (of about 100 nucleotides) showed no ordering phase transition. The osmotic pressure as a function of the ε‐DNA concentration verifies a scaling prediction for random coils in the semi‐dilute regime. Good fits to the reduced osmotic pressure are obtained by using the Kleintjens and Koningsveld modified mean field lattice gas equations of state. As inferred from the Zimm clustering function, essentially all intermolecular interactions at high ionic strength are purely repulsive.
Interaction between oppositely charged polyelectrolytes in aqueous solution
Authors: Oppermann W. , Schulz Th.
Published: March 2011

Oppositely charged polyelectrolytes interact in solution, forming polyelectrolyte complexes, which often appear as gel‐like precipitates. This kind of complex formation was studied by means of calorimetric and rheological measurements. The enthalpy effects, though being fairly small, give some information about the binding strength of counterions to the macroion. We studied the system poly(p‐styrene sulfonate)/poly(trimethylammonium‐2‐ethyl methacrylate) (PSS‐PTMA), varying systematically the low molar mass counterions of PSS. In every case, the maximum of enthalpy was found around a 1:1 (mol:mol monomer units) composition of the complexes, with the shape of enthalpy versus composition‐curve indicating a stoichiometric interaction. The maximum enthalpy decreased with increasing atomic mass of the counterion when the alkaline metal salts of PSS were used and no change was made on the side of the cationic polyelectrolyte. The salts of the alkaline earth metals gave a distinctly higher enthalpy.

On the contrary, viscosity measurements showed a very broad minimum as a function of composition, indicating that the formation of non‐stoichiometric complexes is also occurring. The conclusion of these observations is that the complex formation is stoichiometric with respect to the monomeric units, but not necessarily stoichiometric with respect to the entire macromolecules.
Structure formation in systems involving poly(ethylene oxide) and small molecules
Authors: Point Jean‐Jacques , Damman Pascal
Published: March 2011

The structure of the intercalates in which poly(ethylene oxide), PEO, is the host component and para‐disubstituted benzenes are the guest molecules is completely elucidated by X‐ray diffractometry, polarized FTIR spectrography, and calorimetry. It is shown that the association of these molecules results from the adaptation of the shape of their external surfaces. On this basis the possibility of formation of structure involving PEO and small molecules is discussed.
Solvent‐induced crystallization of syndiotactic polystyrene in toluene
Authors: Vittoria V. , Russo R. , De Candia F.
Published: March 2011

The diffusion of toluene in glassy syndiotactic polystyrene was analyzed for films with different thickness. It was found that the reduced sorption curves superimpose, denoting that the diffusion follows a Fickian behaviour. The intensity of transmitted light in a polarizing microscope was followed during swelling, and it was found that there is development of order and it is strongly diffusion‐controlled.

Films dried after immersion in toluene show a crystalline wide angle X‐ray pattern, while in the swollen state the possibility of a liquid‐crystalline‐like state can be suggested.
A kinetics approach to non‐linear polymerization
Authors: Galina Henryk
Published: March 2011

Three formal equations are presented that describe the time dependence of the size distribution of polymer species in the tree‐like homopolymerization of f‐functional monomer, the copolymerization of 3‐ and 2‐functional monomers and the homo‐polymerization of 3‐functional monomer with cyclization taken into account. The equations have the form of the Smoluchowski coagulation equation extended to take into account substitution effects that may alter the reactivities of functional groups. Average degrees of polymerization up to gel point can relatively easily be extracted from the proposed equations. The results, illustrating applications of the kinetics approach, confirm that statistical theories are inadequate to model kinetically‐controlled polymerization reactions if substitution effects are present.
Hindered interdiffusion in asymmetric polymer‐polymer junctions
Authors: Brochard‐Wyart F. , De Gennes P. G.
Published: March 2011

We 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.
The dynamics of melts and networks
Authors: Edwards S. F.
Published: March 2011

The free energy of a network is not enough to give the dynamic properties. To obtain these one must approach the network in a similar way to the approach to polymer melts. It is shown what problems arise when this is attempted, and the difficulties of the general equations are assessed.
Deformation in networks: The role of the chain length distribution
Authors: Kilian H. G.
Published: March 2011

If 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

Poly(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

The 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

Crazes 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

The 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

The 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

The 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

A 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

Specific 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

Kinetics 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

Ultimate 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

The 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

Low‐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

Many 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

The 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

The 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

A 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

The 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

Dianhydrides 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

Under 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

General 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

X‐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

The 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.
Branching kinetics of epoxy polymerization of 1, 4‐butanediol diglycidyl ether with cis‐1, 2‐cyclohexanedicarboxylic anhydride
Authors: Wu Chi , Chu Benjamin , Stell George
Published: March 2011

The copolymerization of an epoxy resin [1, 4‐butanediol diglycidyl ether (DGEB) (Note a)] with an anhydride [cis‐1, 2‐cyclohexanedicarboxylic anhydride (CH)] in the presence of N, N‐benzyldimethylamine (CA) as a catalyst produces a branched epoxy polymer. We show that the branching kinetics of the copolymerization reaction and the molecular weight distribution of the branched polymers can be approximated by using Smoluchowski's coagulation equation. In the simplest relevant application of this equation to our problem, the overall rate kernel w(u, v) that describes the branching probability in the equation turns out to be proportional to the sum of active sites on the two polymers with a time dependent coefficient. The molecular weight distribution (MWD) and the weight average molecular weight of the branched copolymers at different reaction stages before the gelation threshold are calculated theoretically. The calculated values are then compared with the experimental results obtained by using small angle X‐ray scattering (SAXS), laser light scattering (LLS), and chemical analysis. Satisfactory agreement between experimental results and the use of the coagulation equation is attained when it is assumed that the distribution of epoxy polymer molecules is exponential in the number of branching points or, equivalently, active sites, at an early stage of the polymerization reaction.
Networks from dicyanate of bisphenol a and diphenols
Authors: Bauer M. , Bauer J. , Jährig S.
Published: March 2011

Networks were prepared by copolycyclotrimerization of aromatic dicyanates with diphenols in bulk. The main reactions and structural elements were found and the network building process was modelled by cascade theory combined with a model of the reaction kinetics. Good agreement between theory and experiment is shown.
Synthesis and characterization of polymers based on the cyanate functional group
Authors: Gupta Anshu M. , Macosko Christopher W.
Published: March 2011

The chemistry and growth of polymer structures based on the cyanate linkage has been studied. The monofunctional model compound 2‐(4‐cyanatophenyl)‐2‐phenylpropane was used to study the reaction products. The synthesis was performed with four different transition metal catalysts and also without a catalyst. The quenched products were analyzed using Size Exclusion Chromatography(SEC) and 13C NMR. It was found that the reaction is relatively clean, with trimerization being the major product. A few side products were also detected, which included dimers and higher oligomeric species. Crosslinked polymers were synthesized without catalyst based on the bifunctional monomer 2, 2‐bis(4‐cyanatophenyl)propane. The structure was analyzed using 13C NMR. The conversion and number‐average degree of polymerization based on 13C NMR is reported. Conversion at the gel point was found to be higher than 60%. On this basis it was concluded that polymerization based on cyanate linkages at the conditions studied is diffusion controlled and therefore not described by Flory's mean‐field theory.
The role of mechanical phenomena during the formation of network polymers
Authors: Rozenberg B. A. , Irzhak V. I.
Published: March 2011

A review of new results concerning the role of mechanical phenomena during cure of epoxy matrices has been made. The influences of various factors (temperature, nature and concentration of components, the character of adhesion interaction of matrix and filler, etc.) on the rate of structural relaxation of polymer have been examined. The problem of the mechanical degradation of network chains under the action of internal stresses has been discussed.
Rheological studies of the gelation kinetics of Cr+3‐polyacrylamide solutions
Authors: Gallino Germana , Molinari Mario , Lockhart Thomas P.
Published: March 2011

A new rheological approach for the study of the gelation kinetics of aqueous Cr+3 polyacrylamide solutions has been investigated which relies on the assumption that at the gel point, GP, a constant amount of Cr+3 will have reacted, independent of the initial Cr+3 concentration. From this, a kinetic expression relating GP to the initial concentrations of Cr+3 and reactive groups on the polymer has been derived for the case of a crosslinking reaction first order in Cr+3 and polymer. Experimental evidence that the amount of Cr+3 reacted at the GP is constant for a given polymer and solution pH has been obtained. The good fit of the kinetic expression to the rheological data provides new evidence that the gelation reaction is first order in Cr+3 rather than second order as claimed previously.
Segmental orientation and infrared dichroism of model bimodal elastomeric networks
Authors: Hanyu Aiko , Stein Richard S.
Published: March 2011

Model bimodal networks of polytetrahydrofuran (PTHF) were prepared by end‐linking reactions. They consist of two different molecular‐weight species designated L (long) and S (short). With the S, the hydrogen atoms were replaced by deuterium, so that C‐H and C‐D infrared bands could be associated with the L and S species, respectively. Infrared dichroism could then be used to determine the second‐order orientation function, P2, for each species. Kuhn and Grün's (K‐G) rubber elasticity theory permits a calculation of P2 as a function of the elongation ratio, λ. For the unimodal system, the P2 was found to become greater with decreasing molecular weight between crosslinks, Mc, and is consistent with the theory. For the bimodal network system, the P2 for the L species was found to be almost equal to the P2 for the S species, suggesting a heterogeneous (or non‐affine) deformation of the S and L chain segments at molecular level. In another way, the equality of (P2)L and (P2)S allows us to assume that the bimodal network can be treated as the “unimodal” network consisting of the chain segments with the weight‐averaged length between the long and short chains. Under the assumption of affine deformation for such an “averaged unimodal” system, the number of statistical segments, N, was evaluated using the K‐G theory; the value of N is linearly proportional to the averaged molecular weight between the L and S species and one statistical segment was found to consist of three tetrahydrofuran (THF) monomeric units.
On the elastic and swelling behaviour of swollen poly(vinyl alcohol) networks filled with anisometric colloidal iron(III) hydroxide sol particles
Authors: Zrinyl M. , Kilian H.‐G. , Dierksen K. , Horkay F.
Published: March 2011

A new method of preparing filled networks has been developed. Well‐characterized, colloidal iron(III) hydroxide particles are incorporated into chemically cross‐linked poly(vinyl alcohol) gels. Evidence for the random distribution of individual particles is provided by transmission electron microscopy. A filler‐induced gel collapse was observed when the strength of repulsion forces between filler particles is decreased by the screening of Coulombic interactions with electrolytes.
Diffusion in microstructured block copolymer solutions
Authors: Balsara N. P. , Eastman C. E. , Foster M. D. , Lodge T. P. , Tirrell M.
Published: March 2011

This work explores the effect of heterogeneity of chemical composition on tracer diffusion, when the characteristic size of the heterogeneities approaches that of the diffusing molecule. A heterogeneous environment is created by the self‐assembly of diblock copolymers in solution. The system chosen for this study is polystyrene‐polyisoprene diblock copolymers in toluene, which is a common solvent for the two blocks. Above a certain critical concentration, these systems are known to microphase separate into swollen domains of polystyrene and polyisoprene. Diffusion of homopolystyrene through the microstructure is measured in this work. The characteristics of the microstructure are varied by studying block copolymers of different molecular weights and compositions. The tracer diffusion coefficients of the labelled polystyrenes are measured by forced Rayleigh scattering, while the microstructure of the matrix is inferred from small angle X‐ray scattering measurements.

In this paper, we report results for the diffusion of polystyrenes (molecular weights 3.2 × 104 and 9.0 × 104) in microstructured solutions of three copolymers. Two copolymer samples forming lamellae of alternating polystyrene and polyisoprene microphases and one sample forming polystyrene cylinders embedded in a polyisoprene matrix have been examined. The data indicate that the tracer diffusion coefficient of 3.2 × 104 molecular weight polystyrene in lamellar and cylindrical solutions is comparable to that of the homopolymer in a homogeneous solution of the same concentration. In contrast, the diffusion of 9.0 × 104 molecular weight polystyrene is substantially slower in the structured solutions than in unstructured solutions of the same concentration. For example, the diffusion coefficient of 9.0 × 104 molecular weight polystyrene in a 47% block copolymer solution with cylindrical microstructure is lower than its value in a homogeneous solution of the same concentration by a factor of 30.
The effect of polymer network structure on diffusive transport across chemically controlled membranes
Authors: Adler K. P. , Weiss A. M. , Grodzinsky A. J. , Yarmush M. L.
Published: March 2011

This paper focuses on the relationship between diffusive transport and membrane composition (crosslinker content and relaxed polymer volume fraction) in membranes whose permeability can be actively controlled by chemical or electrical stimuli. First, pH induced changes in permeability to uncharged fluorescent solutes were measured. Then, by correlating bath pH with membrane hydration, the transport properties of membranes of different crosslinker content and/or relaxed polymer volume fraction were compared at constant hydration.

The membrane permeability was found to decrease as the amount of crosslinker added to the membrane formulation at the time of polymerization increased, while the permeability increased as the solvent content during polymerization increased. A free volume theory which was fit to the data shows good agreement, and predicts a monotonically decreasing porosity factor with increased crosslinker content.