bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ring‐chain competition in a branched polycondensate system
Authors: Ross‐Murphy Simon B. 
Published: June 2010

AbstractIn this paper, the kinetics of copolyesterification of the well studied branching system formed by the reaction of 1,3,5‐tri(carboxymethyl)benzene, (BTA), and decane‐1, 10‐diol, (DMG) are described with special reference to the relative rates of inter‐ and intramolecular reactions (ring‐chain competition). The conversion β at time t, and the gel point βc were measured by continuously monitoring the pressure of steam evolved in a closed system at 175°C. during the course of polycondensation, using a pressure transducer.Experiments were carried out using 1,3,5‐tri(diphenylmethylcarboxymethyl)benzene as a diluent to further encourage intramolecular reaction. The experimental ratecurves passed smoothly through the gel point, and agreed well with those rate curves calculated using the “spanning tree” model of cascade theory, until substantially after the gel point. The overall reaction order was very close to the third order (acid self‐catalyzed) kinetics expected from studies of simple esterification.The amount of cyclization in the BTA/DMG system was confirmed to be small. Less than 1.2% of links are formed intramolecularly, at the gel point, βcβc was found to be 0.718 ± 0.006, compared to 0.707 i.e., 2−1/2 for a random 2:3 functional alternating copolycondensation. The small difference indicates that the BTA/DMG system is the closest approach yet to a random tree‐like network.
Cyclization in crosslinking polymerization. II. Chain polymerization of a bis unsaturated monomer (polydisperse case)
Authors: Dušek K. , Ilavský M. 
Published: June 2010

AbstractThe procedure suggested for the description of ring‐chain competition in the polymerization of a bis unsaturated monomer derived in Part I for monodisperse primary chains was extended to include the case of polydisperse primary chains. The cyclization probability and differential fractions of units in the chain are regarded as different for each group of r‐mers. The composition of primary chains remains practically unchanged at r > 100, and the summations were therefore truncated at r = 100. Model calculations show that trends in the composition change of the polymer and of the gel point as a function of the degree of polymerization of primary chains, of the distribution width, and of dilution are in accord with experimental findings. Comparison with the data published on the polymerization of dialiyl phthalate (with a marked cyclization and short primary chains) has revealed that the model is generally satisfactory, but that it somewhat underestimates cyclization because of the neglected effect of cycles on the conformational statistics of chains, or the neglected effect of excluded volume. This is particularly reflected in a lower calculated conversion at the gel point. This underestimation may partially be compensated for by assuming a higher chain flexibility.
Curing kinetics of epoxy resins
Authors: Olcese Tito , Spelta Osvaldo , Vargiu Silvio 
Published: June 2010

AbstractCuring kinetics of some epoxy systems was studied by means of differential scanning calorimetry. We examined the influence of a few nitrogenous curing agents with different chemical structures on the rate of curing; different levels of the accelerator were tested. We also investigated the influence of two different resins on the rate of curing. The calorimetric measurements were performed in isothermal conditions and at different scanning rates. The experimental plot of the curing rate was checked by comparison with some theoretical equations, and information was collected on activation energies, reaction orders, and temperature influence.
Diffusion and sedimentation of serum albumin in concentrated solutions
Authors: Kitchen Robert G. , Preston Barry N. , Wells John D. 
Published: June 2010

AbstractWe have measured the self‐diffusion coefficient, D, of serum albumin (by the open‐ended capillary method) and the mutual diffusion coefficient, Dm, for serum albumin solutions (by the capillary method, and in the ultracentrifuge) at concentrations up to 0.2 g°Cm−3. Our self‐diffusion data follow those of Keller et al. [J. Phys. Chem., 75, 379 (1971)], but we can find no experimental support for their contention that Dm = D at high concentrations. Indeed, our results closely follow the theoretical relation Dm = D (1 – cv)(1 + 2A2 Me +…).Where c, v, A2, and M are, respectively, the concentration, partial specific volume, second virial coefficient, and molar mass of serum albumin.We have also studied the concentration dependence of the frictional coefficients in diffusion and sedimentation. The two frictional coefficients are equal only in very dilute solutions of serum albumin.
Improved thermoplastic elastomers through cationic polymerization
Authors: Sigwalt P. , Polton A. , Miskovic M. 
Published: June 2010

AbstractCationic grafting has been realized on three types of elastomers that contain either reactive allylic or alkyl chlorides (acting as cocatalysts) or double bonds (“direct grafting”) or both (e.g., chlorobutyl rubber). In the case of chlorobutyl rubber, polymerization yields were always 100%, and grafting efficiencies (percentage of grafted indene over total indene) were often near 100%. The best results were obtained when grafting a copolymer of indene and α‐methylstyrene around −50°C. (The polymer obtained has a tensile strength of 130 kg/cm2 at 20°C and 50 kg/cm2 at 100°C.) Grafting of indene on chlorinated ethylene‐propylene copolymers could be made with grafting efficiencies of about 70%. Direct grafting of indene on nonchlorinated unsaturated elastomers, such as EPDM rubbers, has been made with grafting efficiencies higher than 50%. In this case, grafting could be realized around 0°C. The various reactions that influence the grafting efficiencies are discussed: initiation involving the polymer chain, grafting through termination on double bonds, transfer to monomer, and transfer to polymer.
The nature of propagating species in cationic polymerization of vinyl compounds
Authors: Higashimura Toshinobu 
Published: June 2010

AbstractA suitable combination of the stability of propagating carbocation and the nucleophilicity of counterion is necessary in general for the formation of polymers with a bimodal molecular weight distribution: for styrene or p‐chlorostyrene, less nucleophilic counterions (ClO4−, CF3SO3−) are suitable; for p‐methyl‐or p‐methoxystryene, highly nucleophilic I3− or I− is required. In the styrene polymerization with ClO4− or CF3SO3− as counterion, the common‐ion salt effect on the molecular weight distribution and the steric structure of the polymer suggest that two kinds of ion pairs as well as free ions are involved in the cationic polymerization. These species have been found to be different not only in reactivity in homopolymerization but also in monomer selectivity in copolymerization.
Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. IV. Structural changes occurring in different types of high‐density polyethylene
Authors: Holmström Arne , Sörvik Erling M. 
Published: June 2010

AbstractThe thermal and thermo‐oxidative degradation of reprecipitated and “as received” samples of different types of high‐density polyethylene (HDPE) have been studied. Two of the samples were of conventional Phillips type, being essentially linear and having one vinyl group per molecule. The other two HDPE's were also produced by chromium catalysts, but according to Union Carbide's fluidized bed process. In one of these resins the molecules had vinyl end groups while the other resin was fully saturated.Contrary to earlier statements concerning the thermal degradation of polyethylene it was found that HDPE is not degraded according to a random scission type of mechanism. Instead both molecular diminishing and enlargement are found to occur simultaneously. This is, however, in accordance with our recent findings on low‐density polyethylene (LDPE).The samples were heated at temperatures between 284 and 355°C under high purity grade nitrogen during thermal degradation and under nitrogen containing up to 1.14% oxygen during thermo‐oxidative degradation. Changes in molecular weight distribution and degree of long chain branching (LCB) were followed by gel chromatography and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry. Both reprecipitated and “as‐received” samples gave identical results.For all the HDPE's an increase in heating time and temperature and oxygen content was found to increase the formation of low molecular weight material, long chain branches, volatile products, carbonyl‐, ether‐, and olefinic groups, discoloration, and insoluble material. Although there was much in common between LDPE and HDPE there were also certain noticeable differences, even within the HDPE group. These differences are suggested to be due to different catalyst residues in the HDPE's causing, e.g., the fully saturated material to degrade at 100°C lower temperature than expected.
The effect of the chemical and physical properties of carbon black on the thermal and photooxidation of polyethylene
Authors: Kovács E. , Wolkober Z. 
Published: June 2010

AbstractThe antioxidant and UV stabilizing effect of different carbon blacks on parafin oil model compound with and without additional stabilizers was investigated. The thermal and photooxistabilities of the samples were characterized by the induction period of the oxygen consumption which was measured volumetrically in a closed system filled with oxygen. A relationship was established between the induction periods of the thermal oxistability curves and the distributions of oxygen content within the active groups of the blacks.Determining the stabilities of the polymer‐black‐antioxidant systems, synergistic and antagonistic phenomena were observed. These effects were explained by taking nto account the quality and amount of the active sites of the blacks.The photooxidation experiments corroborated the double role of the black as UV stabilizer. Primarily it acts as a UV screen, its effectiveness being proportional to its specific surface. In addition to this, the synergism and antagonism observed in the ternary systems suggested that the carbon was also involved in the photooxidation as a chain terminating and peroxide decomposing agent.
A new concept for understanding the plastoelasticity of polymers
Authors: Hosemann R. , Loboda‐Čačković J. 
Published: June 2010

AbstractChain molecules of partially crystalline polymers are built up as a three‐dimensional network using one part of their chain segments. The other parts of segments of each molecule are embedded in microparacrystals (mPCs). It is pointed out that the random coil concept is nevertheless a good first approximation for the real conformation of a chain molecule. Its straight segments build up the mPCs. They act as the knots of a three‐dimensional network and explain the phenomenon of the affine transformation and retransformation properties of these structures. On this basis, one can develop a rheology which is in accord with the molecular structure. Mechanical models can be applied, which, contrary to those of conventional methods, substantially contribute Kelvin and Maxwell elements to microdomains and not to volume elements. One microdomain contains at least 106 mPCs, including their surrounding network. The positions of the centers of the microdomains obey the rules of affine transformation. They consist of a large number of mPCs. Stretching experiments with linear polyethylene Lupolen 6001H (BASF) are discussed as an example. In the pseudo‐Hooke's law range until elongations of γ ∼ 30%, statistically distributed mPCs in suitable positions are plastically deformed. At longer γ‐values cooperative deformations of layers of mPCs set in and give rise to a necking process. Stretching is thermoreversible under a natural draw ratio because the relaxation time of the Maxwell elements is long enough compared with the time taken for the microdomains to travel through the neck. Their retardation time is calculated and has a minimum value of 2 min, 6 mm behind the beginning of the neck.
Interpretation of light scattering in moderately concentrated polymer solutions
Authors: Dautzenberg H. 
Published: June 2010

AbstractLight scattering curves of moderately concentrated polymer solution in good solvents show increasing curvature at higher concentrations in the range of small scattering angles. An attempt was made to separate the scattering curves into their intra‐ and intermolecular contributions and draw conclusions concerning the radial distribution function of the molecular centers of gravity in solution. The results obtained suggest the formation of a network of overlapping coils as the structure model for such systems. Model calculations on rotational ellipsoids showed that preferential parallel orientation of coils having no spherical symmetry may offer an explanation for the peculiar behavior of the intra‐ and interparticular scattering functions, which was derived from experimental data.
Theory of light scattering from a system of interacting spherical macromolecules
Authors: Hess W. , Klein R. 
Published: June 2010

AbstractA nonlinear stochastic transport equation for the concentration fluctuations of interacting macromolecules is derived. This dynamic equation is transformed into a pair of linear equations, and the connection of the solutions to these equations with the light scattering spectrum and an effective diffusion constant are established.
Phase equilibria of polystyrene solutions
Authors: Tager A. A. , Andreeva V. M. , Vshivkov S. A. , Tjukova I. S. 
Published: June 2010

AbstractThe cloud‐point curves for polystyrene (PS) solutions in ethylbenzene, decalin, and cyclohexane have been studied. Investigations of the spinodal for these systems were carried out using the light scattering method proposed by Chu and Scholte. The existence of the upper critical solution temperature polystyrene–for the system ethylbenzene has been demonstrated. For the sample of PS with a narrow molecular mass distribution the cloud‐point curves are binodal. The tops of binodals and spinodals coincide.From the temperature and angle dependences of light scattering the radius of gyration were calculated using the theory of Debye and of Vrij and Esker.
On the theory of stabilization of dispersions with adsorbed polymer
Authors: Hesselink F. Th. 
Published: June 2010

AbstractSome aspects of the development of the theory of stabilization of dispersions with adsorbed (anchored) polymer molecules are reviewed. Approximate analytic expressions are derived for the repulsion between both flat particles and spheres. It is shown that the HVO theory (developed by Hesselink, Vrij, and Overbeek) predicts the behavior observed by Napper et al. for latex systems stabilized with anchored polymer. Napper's opposing contention is based on a comparison of experimental observations with theoretical curves, calculated for different experimental conditions. Napper's theoretical and experimental arguments for the omission of the volume restriction term from the interaction equation for particles covered by adsorbed polymers are shown to be invalid. The effect of the size distribution of the adsorbed tails on the steepness of the repulsion curve is demonstrated.Dolan and Edwards' recently developed theory, which does not involve an artificial split of the free energy into a configurational and a mixing term, is shown to yield results similar to those obtained with the HVO theory.
Crystallization‐induced reactions of copolymers. V. Important reaction variables in the reorganization of random to block copolyesters
Authors: Lenz Robert W. , Schuler Alan N. 
Published: June 2010

AbstractThe effects of reaction parameters including copolyester composition, catalyst type and amount, temperature, time, endgroup concentration (molecular weight), and degree of crystallinity were determined for the reorganization of random to block poly(ethylene terephthalate‐co‐succinate). The crystallization‐induced reactions, which were the basis of these ordering processes, were carried out at temperatures at or below the terephethalate unit melting points of the initial copolyester. All samples so treated showed increased melting points, recrystallization temperatures, and degrees of crystallinity which correlated with increased blockiness of the terephthalate units, as determined by nuclear magnetic resonance spectroscopy. At reaction temperatures greater than 15°C below the initial copolyester melting point, those parameters which controlled the rate of the ester interchange reaction also controlled the extent of the reorganization. Within approximately 15°C of the melting point, the reaction rate was apparently less important than physical factors related to the crystalline properties of the initial copolyester.
Polymerization of vinylpyridinium salts. X. Copolymerization studies of cationicanionic monomer pairs
Authors: Salamone J. C. , Watterson A. C. , Hsu T. D. , Tsai C. C. , Mahmud M. U. , Wisniewski A. W. , Israel S. C. 
Published: June 2010

AbstractThe mechanism of the spontaneous polymerization of vinylpyridinium salts in aqueous and acidic solution has been actively investigated in recent years. Recent reports have suggested that these reactions are free radical in nature. In order to investigate the involvement of free radical initiation in the spontaneous polymerization reactions, an investigation of ion pair copolymers between the cationic 4‐vinylpyridinium moiety and the anionic vinylsulfonate, 2‐acrylamido‐2‐methylpro‐panesulfonate, and p‐styrenesulfonate has been undertaken. The results of spontaneous polymerization suggest that for 4‐vinylpyridinium vinylsulfonate, only the cationic moiety is polymerized, whereas for 4‐vinylpyridinium 2‐acrylamido‐2‐methylpropanesulfonate, two homopolymers or a block copolymer apparently result, and for 4‐vinylpyridinium p‐styrenesulfonate, an alternating copolymer appears to be obtained.
Depolarized rayleigh spectroscopy of rigid macromolecules
Authors: Pecora R. 
Published: June 2010

AbstractSome applications of depolarized light‐scattering spectroscopy to the study of rigid macromol‐ ecules in solution are described. The depolarized light‐scattering method can be used to obtain ro‐ tational diffusion coefficients and static and dynamic correlation factors of rigid macromolecules. In molecules exhibiting some flexibility, intramolecular conformational relaxation times may also be obtained. Dynamic polarized light‐scattering measurements give the orientation averaged translational diffusion coefficient. With the Perrin relations for spheroids, the rotational and translational diffusion coefficients may be combined to yield the macromolecular solution dimensions. In addition, changes in rigidity and shape of rigid macromolecules may be observed by measuring changes in the depolarized spectrum. For instance, the total depolarized intensity and relaxation time usually decrease when a helical molecule is denatured to a flexible form. The rotational diffusion coefficients obtained by light scattering may also be combined with relaxation times obtained by other techniques such as nuclear magnetic relaxation to draw inferences about molecular rigidity and local motions.
Modification of fibrin by synthetic polymers
Authors: Kovács G. , Fedorova N. , Kiss L. , Killy T. 
Published: June 2010

AbstractFibrin‐based resorbable surgical implant material is applied in clinical practice with success. However, its good swelling is a disadvantage in using it for fixing broken bones. To alter the swelling properties of fibrin, chemical modifications were carried out on it by synthetic polymers and polymer reactions. The following modified fibrins were prepared and served as models to study the swelling and enzymatic digestion under in vitro conditions: fibrin with pendant semimaleate groups, with poly(ethylene oxide) and poly(N‐vinyl‐2‐pyrrolidinone) side chains, fibrin‐copoly(ethylene maleic anhydride), and fibrin‐copoly(ethylene maleic acid) polymer substances.
Some chemical aspects of the behavior of synthetic polymers in a living organism
Authors: Lipatova T. E. 
Published: June 2010

AbstractThe problems engendered in the use of polymers for endoprostheses and in glues for tissues are considered. An approach to the solution to the problem through the use of polymers with controllable rates of “resorption” (biodestruction) in the organism and glues for soft tissue is demonstrated.
Anticoagulation activity of some sulfate‐containing polymers of the methacrylate type
Authors: Šorm M. , Nešpurek S. , Mrkvičková L. , Kálal J. , Vorlová Z. 
Published: June 2010

AbstractA number of synthetic polymers and copolymers of the methacrylate type with a different content of sulfate, sulfamide, and carboxylic groups have been prepared. The anticoagulation activity of polymers thus obtained was compared with that of heparin. The highest anticoagulation activity was found with copolymer II containing 86 mol % of sulfate and 14 mol % of carboxylic groups. A surprisingly weak activity was observed with polymers containing sulfamide groups.
Dissociation and recombination reactions in solid polymers
Authors: Smets G. , Nijst G. , Schmitz‐Smets M. , Somers A. 
Published: June 2010

AbstractPhotochemical and thermal dissociation of labile molecules in the solid state or dissolved in solid polymer matrix affords reaction products which differ in composition and relative amounts from those obtained in solution. These differences are interpreted on the basis of limited rotation and diffusion possibilities. When the dissociation produces reactive species which can recombine thermally or photochemically, the kinetics do not follow a bimolecular reaction mechanism, as in solution experiments. On the contrary, they show a stepwise process, that has been described by Waite, Lebedev, and Butyagin. As a first step, rapid “cage recombination” occurs, followed by a second very slow step corresponding to the diffusion‐controlled recombination of isolated species (radicals or monomers). These stepwise reaction kinetics are illustrated by three different dissociation–recombination equilibria.a. thermal dissociation of benzpinacol and its derivatives and radical recombination.b. photochemical dissociation of hexaphenyl‐1.2′‐bisimidazole into triphenyl‐imidazolyl radicals and their recombination.c. photochemical dissociation of substituted anthracene‐ and (benz)acridizinium dimers and photochemical recombination of monomers In (b), radical pairs and isolated radicals can easily be distinguished by ESR. On the basis of Waite's rate equations, the diffusion coefficient of the radical and the “cage” dimension can be calculated. The cage dimensions agree with these determined by Butyagin for radical decay on γ‐irradiated polymers. Experiments at different temperatures (below and above Tg) stress the influence of the segmental mobility of the polymers, as well as of the molar volume of the labile molecules.