bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isothermal growth, thickening, and melting of poly(ethylene oxide) single crystals in the bulk
Authors: Kovacs A. J. , Gonthier A. , Straupe C. 
Published: June 2010

AbstractCharacteristic features of isothermal growth, thickening, and melting behavior of melt grown single crystals of low molecular weight poly (ethylene oxide) fractions are presented and discussed in terms of their relevance to basic concepts of polymer crystal growth. Measurements of growth (G) and thickening rates of once folded chain crystals were extended (up to the melting point) into a temperature range where usually only extended chain crystals grow. Monolayer extended and folded chain crystals melt by lateral shrinkage, the rate of which (G−) depends not only on temperature, but also on thermal history. G− increases exponentially with the degree of superheating, and the value of the temperature coefficient d log G−/dT is proportional to the lamellar thickness. In the narrow temperature interval where transition from once folded to extended chain growth occurs, the crystal morphology displays some spectacular features. These may be accounted for in terms of the crystal habit and the rate of completion, g. of a molecular layer in the particular (hk0) prism face considered. Morphological analysis shows that g is of the same order of magnitude as G(hkO), leading to the conclusion that the growth of these PEO crystals is controlled by multiple surface nucleation rather than by deposition of a single surface nucleus.
Viscoelastic behavior of polystyrene‐tricresyl phosphate solutions
Authors: Riande Evaristo , Markovitz Hershel , Plazek Donald J. , Raghupathi N. 
Published: June 2010

AbstractThe viscoelastic behavior of solutions of a narrow molecular weight distribution polystyrene in tri‐m‐toly 1 phosphate has been determined from the glassy to the terminal zones of response. The polymer concentration was varied from one to 100% thereby providing for the first time a complete picture of the influence of a solvent on the time‐dependent response of a polymer.A computer analysis, governed by human judgment, has been used to extract retardation spectra which can be used to regenerate the reduced recoverable creep compliance curves within the scatter bands of the data. With the resulting retardation spectra, dynamic compliance and moduli curves have been calculated.
Multicomponent solutions of biological macro‐molecules: Thermodynamic and conformational studies of DNA
Authors: Eisenberg Henryk 
Published: June 2010

AbstractIn this contribution we show how theoretical concepts and experimental procedures developed in the study of macromolecular solutions can be applied towards obtaining information on polymers of biological interest. Thermodynamic and conform ational studies of DNA solutions will be reviewed. Equilibrium sedimentation and density measurements under well specified conditions contribute to our understanding of preferential and, sometimes, specific interactions. Equilibrium sedimentation in a density gradient unambiguously determines the molecular weight of large DNA particles. The flexibility of DNA molecules is well described by the persistent, or worm‐like chain. The Kratky‐Porod persistence length (derived from light scattering and transport measurements) provides a unique parameter invariant over the whole molecular weight range accessible to experimentation. Angular dependence of the scattering of light has now been extended to the study of quasi‐elastic scattering which provides additional information with respect to internal motion and flexibility on DNA molecules.
The cationic dimerization of 1,1‐diphenylethylene. I. Nature of active centers in the case of protonic and lewis acids initiation, at low temperature, in dichloromethane solution
Authors: Sauvet G. , Vairon J. P. , Sigwalt P. 
Published: June 2010

AbstractThe reaction of 1,1‐diphenylethylene with titanium tetrachloride or with trifluoromethane‐sulfonic acid has been studied at −30 and −70°C in dichloromethane solution, and has given, in both cases, relatively stable diphenyl alkyl carbocations. PMR spectra show that these cationic species are mainly monomeric, i.e., (I). In the electronic spectra, a main absorption band at 435 nm is assigned to both monomeric (I) and dimeric (II) cations, whereas, a 520 nm absorption is assigned to monomer solvated forms of I and II. A third absorption at 456 nm was detected by resolution of the overlapping absorptions at 435 and 520 nm and might be assigned to the dimeric cation, autostabilized through a ß‐phenyl ring interaction. Constants of the equilibria between the different species were determined at − 30°C.
Vinyl ketone‐sec‐allyl alcohol copolymers–open chain‐hemiacetal ring tautomerism
Authors: Merle‐Aubry Liliane , Merle Yves , Selegny Eric 
Published: June 2010

AbstractThree poly(vinyl ketones) have been partially reduced to obtain different copolymers of vinyl ketones and secondary allyl alcohols. The first set of copolymers is obtained by partial reduction of poly(phenyl vinyl ketone). UV studies indicated that the Beer‐Lambert law cannot be applied to the different carbonyl bands. This is explained by a ring‐chain tautomerism between a carbonyl group and a neighboring hydroxyl group.IR and 13C NMR spectroscopy confirmed these results and proved the existence of this tautomerism.The second set of copolymers were obtained by partial reduction of poly(methyl vinyl ketone). UV showed the tautomsrism was strongly shifted toward the ring form; acetal condensation occurs in (tetrahydrofuran) THF‐methanol‐water mixture solution.The third set of copolymers obtained by partial reduction of chiral poly [(S‐2‐methyl‐butyl)vinyl ketone] were studied by UV, ORD (optical rotary dispersion), and CD (circular dichroism); all three methods giving concordant results. The tautomerism was shifted more toward the chain form than for the reduced poly(methyl vinyl ketones) but less than for reduced poly(phenyl vinyl ketones).The addition of strong acid to the polymer solution shifts the equilibrium toward the chain form; a similar shift is observed when the original polymer is in the solid state.
The formation and dissociation of networks formed by polymer‐plasticizer interactions
Authors: Makaruk L. , Retko I. 
Published: June 2010

AbstractSystems containing polycarbonate and aromatic plasticizers with nitro groups were investigated. It was found, experimentally, that in these systems the tensile strength and tensile modulus increased. These changes of mechanical properties termed as antiplasticization can be interpreted as a result of crosslinking by the van der Waals bonds between the macromolecules and molecules of plasticizer. Considerations concerning the equilibrium of formation and dissociatiation of these networks were made in order to explain the phenomenon of threshold concentration of the plasticizer, below which antiplasticization and above which plasticization occur, as well as the nonlinear dependence of the glass transition temperature on the plasticizer concentration.
Interaction of maleic acid derivatives with gelatin
Authors: Kovács G. , Hardy G. , Szimàn O. , Szücs M. 
Published: June 2010

AbstractThis work deals with the crosslinking efficiency of different maleic acid derivatives (glycol dimaleate, glycerol trimaleate, pentaerithritol tetramaleate, mannitol hexamaleate) and copolymer of vinyl maleate for a better understanding of the mechanism of crosslinking. The reactions were carried out in an aqueous gel state of the biopolymer at 50°C. The kinetics of network formation was followed by measuring the melting point of the gel in contact with water. Such factors, as the decrease of hydrogen ion concentration or the increase of water content of the gel, were found to accelerate the rate of crosslinking. Amines, which were able to block the active sites in a competitive reaction, retarded the process. Synthetic polymers were used to delimit the possibilities of the interactions which might be responsible for the crosslinking. It was assumed that primarily the free amino groups of gelatin are involved in the crosslinking reaction by forming H‐bonds with the maleates.
Inhomogeneities in epoxy resin networks
Authors: Kreibich Ursula T. , Schmid Rolf 
Published: June 2010

AbstractInhomogeneities in the crosslink density of polymer networks have been proven, e.g., by electron microscopic studies, thermomechanical measurements, swelling experiments, light scattering and mechanical investigations. Using the differential scanning calorimetry (DSC)‐method, a new effect arising from inhomogeneities could be found by annealing studies of amorphous polymers carried out well below Tg. At those temperatures, the annealing of common epoxy resin systems causes a phase separation of the higher and lower cross‐linked regions. The results are a splitting of the glass transition into one part occurring at the initial transition temperature, while another part shifts towards significantly lower temperatures. This phenomenon may be used to obtain some information about the extent of the regions of different crosslinking density which, consequently, influence the physical properties of the material. The effect is obviously not restricted to crosslinked polymers, since it could also be confirmed for thermoplastic resins like poly(methyl methacrylate) or polystyrene. With increasing annealing temperatures, the morphology of the polymer is gradually changed to a state where a pronounced short‐range orientation, depending on the chemical structure of the segments, takes place. This state produces an endothermic peak in the DSC diagram superimposed on the glass transition.
Mechanical behavior of partially hydrolyzed preswollen polyacrylonitrile networks
Authors: Janáček J. , Stoy A. , Stoy V. 
Published: June 2010

AbstractThe basic mechanical deformation and ultimate characteristics were measured for three‐dimensional polyacrylonitrile networks swollen in water to equilibrium prepared in the presence of three different concentrations of diluent during polymerization (aqueous solution of ZnCl2, volume fraction of polymer v0 = 0.474, 0.578, 0.666), and hydrolyzed to various degrees. At the same time, the time dependence of the tensile modulus Ep(t) was measured at various temperatures within the range 25–85°C, and the temperature dependence of the modulus Ep(t)(t = 300 sec) within the range 25–80°C was measured. The results of mechanical characteristics were empirically correlated with the time of hydrolysis, the modulus Ep(t) (t = 300 sec; T = 25°C) and the content of the nitrile groups. It was demonstrated that the pseudoequilibrium modulus which is the measure of the degree of crosslinking and depends on the chemical composition of hydrolyzed polymer samples, is closely connected with their ultimate characteristics.
Kinetic and thermodynamic factors in polymer chemistry
Authors: Hawthorne D. G. , Solomon D. H. 
Published: June 2010

AbstractMany polymer structures cannot be established unambiguously by the traditional methods used by organic chemists, and often it is necessary to postulate the likely manner in which the molecules are distributed and/or the detailed chemical structure of the repeat units. In many cases, polymer scientists have predicted structures based on thermodynamic factors. This approach has been fairly successful in the past, but it is now apparent that unqualified application of considerations based on thermodynamic stability can be misleading in certain cases. Specific examples of this are discussed with reference to the placement of monomers in vinyl polymerization and to the repeat units in cyclopolymerization; other examples are mentioned briefly.
Singlet energy migration down conjugated polymer chains
Authors: North A. M. , Ross D. A. 
Published: June 2010

AbstractThis paper discusses the migration of singlet energy along polymer chains. This is a process of technical importance in that it can affect the efficiency with which the energy from an absorbed photon is transferred to some acceptor molecule which may then function as a photostabilizer or photosensitizer.When the side groups or unit chromophores on a chain are connected by strong electronic interactions (as in conjugated systems), the energy migration is extremely efficient, and it is probable that the energy is delocalized as a coherent exciton. The observed migration characteristics in poly(phenyl acetylene) and poly(p‐methoxyphenyl acetylene) are explained in terms of delocalization in a distribution of conjugated sequence lengths. In fluid solutions, segmental rotation maintains the distribution in dynamic flux, providing an “intersystem” ladder for the energy to be converted to long wavelength excitons, so that the effective migration distance is large and most of the fluorescence is long wavelength. In solids the distribution is static, effective migration distances are smaller, and the fluorescence contains an appreciable emission at shorter wavelengths from short sequences.
Photosensitized and γ‐ray‐induced graft copolymerizations of monomers to cellulose
Authors: Davis Neil P. , Garnett John L. , Urquhart Rodney G. 
Published: June 2010

AbstractThe variables affecting the photosensitized copolymerization of monomers to cellulose using the simultaneous technique have been systematically investigated. Such variables include type of sensitizer, structure of monomer, and type of solvent. LOW molecular weight alcohols are particularly effective as grafting solvents, especially for styrene and methyl methacrylate. Polyfunctional acrylates predominantly homopolymerize rather than graft, as do acrylonitrile and acrylic acid. Vinyl acetate and 4‐vinylpyridine graft with little competing homopolymerization, although only the latter monomer gives reasonable yields at short conversion times. A Trommsdorff effect is observed for the styrene‐alcohol system. Novel copolymerization behavior is found when mixed alcohols are used as solvents for styrene grafting. Data from the photosensitized grafting are compared with corresponding studies using initiation by ionizing radiation. Results in both ultraviolet and ionizing radiation systems are interpreted in terms of common intermediates involving charge‐transfer bonded species.
Trityl salt‐initiated polymerization of styrene
Authors: Johnson A. F. , Pearce D. A. 
Published: June 2010

AbstractStyrene reacts with catalytic quantities (10−3 to 10−6 mole/1.) of trityl hexachloroantimonate (Ph3CSbCl6) in methylene chloride at ambient temperature to produce trace quantities of various styrene dimers and no polymer during the lifetime of the salt. Both linear and cyclic dimers have been found, some of which contained a trityl group; however, the major proportion consisted of isomeric forms of 1,3‐diphenylbutene‐1 and 1‐methyl‐3‐phenylindane. A kinetic study of the loss of Ph3CSbCl6 showed that the reaction is first‐order with respect to both [monomer] and [salt], and an initiation rate constant of 2.7 mole−1 sec−1 is obtained. With Ph3CSbCl6 concentrations greater than 10−3 mole/1., polymerization occurs. In contrast, trityl hexafluoroantimonate (Ph3CSbP6) in the same solvent at concentrations of 10−3 to 10−6 mole/1. gives rise to rapid and complete polymerization of styrene before all the salt is consumed. An apparent kp of ∼ 5.0 × 102 1./mole · sec has been obtained, but a gel‐permeation chromatography (GPC) analysis of the polymers shows the polymerization to be more complex than is apparent from the kinetic data at 0°C.
Cationic polymerization of 2‐alkenylfurans. I. General features
Authors: Gandini Alessandro , Martinez Ricardo 
Published: June 2010

AbstractThis paper reviews the major features of the cationic polymerization of 2‐vinylfuran, 2‐isopropenylfuran, 2‐vinyl‐5‐methylfuran, and 2‐isopropenyl‐5‐methylfuran, in methylene chloride using trifluoroacetic acid as initiator. Only the latter monomer gives polymers of regular structure in the temperature range −78 to 30°C. The others exhibit important side reactions leading to alkylation of the furan ring at 5C (when this is not methylated) and to polyunsaturated chains (if the carbon in the α position to the ring is tertiary). The kinetics of the polymerizations are affected by these side reactions. A brief analysis is made of the initiation, propagation, and termination reactions, and of the nature of the active species.
Synthesis of elastomers by cationic polymerization with expansion in volume
Authors: Bailey William J. , Iwama Hideaki , Tsushima Rikio 
Published: June 2010

AbstractA bifunctional bis spiro ortho ester, hydroquinone bis‐(1,4,6‐trioxaspiro[4.4]non‐2‐ylmethyl) ether, was prepared in a 30% yield by treating hydroquinone diglycidyl ether with γ‐butyrolactone in the presence of boron trifluoride etherate. Copolymerization of a mixture consisting of 90% of 1,4,6‐trioxaspiro[4.4]‐nonane and 10% of the bis spiro ortho ester produced an elastomer with essentially no change in volume. Condensation of ethylene thiocarbonate with pentaerythritol in the presence of tributyltin oxide gave a 20% yield of a bis spiro ortho carbonate, 1,4,6,10,12,15,16,19‐octaoxatrispiro[4.2.2.4.2.2]nonadecane. Copolymerization of a mixture consisting of 90% of 1,5,7,11‐tetraoxaspiro[5.5]undecane and 10% of the bis spiro ortho carbonate gave an elastomer with a 3% increase in volume.
The initiation reaction in the molecular iodine‐induced polymerization of vinyl alkyl ethers
Authors: Johnson A. F. , Young R. N. 
Published: June 2010

AbstractThe first stage in the molecular iodine‐initiated polymerization of some vinyl alkyl ethers has been investigated at ambient temperature in several solvents. An equilibrium is established between monomer and iodine, prior to polymerization, which has the stoichiometry I2 + MX. The equilibrium constants in n‐hexane, cyclohexane, and chloroform have been investigated and the heat of formation of X determined. The results indicate that X is a diiodide and not a charge‐transfer complex. In solvents of higher dielectric constant, the equilibrium is perturbed by polymerization. Conventional spectrophotometry and stopped‐flow techniques have been employed to determine the rate of equilibration. In all of the solvents examined, a first‐order dependence on [monomer] and a second‐order dependence on [iodine] was observed. A mechanism is proposed.
Beitrag zur verfolgung des abbaues von polyäthylen während der verarbeitung
Authors: Zámorský Z. 
Published: June 2010

AbstractThe degradation of low‐density polyethylene under thermal stress in a quiet state and during processing from the melt was investigated. It was found that the limiting viscosity value decreases in both cases and the gel content increases, reaching a maximum in the range of 140–160°C. The molecular weight distribution broadens mostly toward the low fractions at the expense of the middle fractions. The main factors in the destruction are temperature and oxygen. The influence of frictions is not important.
Study of the thermal oxidation of polyole‐fins. V. Volatile products in the thermal oxidation of polyethylene
Authors: Barabás K. , Iring M. , Kelen T. , Tüdös F. 
Published: June 2010

AbstractOrganic volatiles formed in the thermooxidation of polyethylene at 150 and 160°C, 760 torr oxygen pressure were investigated by gas chromatographic analysis. Aldehydes and ketones having a linear chain were identified as the major components of the organic fragments investigated. Their concentration in the gas phase was found to decrease with increasing molecular weight; the main component was acetaldehyde which was present in an amount exceeding that of any other component by nearly one order of magnitude. A considerable amount of ethylene and low molecular weight alcohols was also found in the degradation atmosphere.The evolution kinetics of the volatile products has been described by S type curves very similar to those of oxygen absorption with the period of maximum slopes coinciding with maximum hydroperoxide content in the polymer. Organic compounds are estimated to constitute only a small percent of the total amount of volatiles, in accordance with previous observations, recording that water is the dominant component.
Antioxidants and stabilizers. LX. Transformations of octadecyl 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl) propionate and properties of products
Authors: Lerchová J. , Nikiforov C. A. , Pospíšil J. 
Published: June 2010

AbstractThe oxidation of octadecyl 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl) propionate (I,R = C18H37) with tert‐butylperoxyl gives rise to a derivative of cyclohexadienone II. The mixture remaining after the isolation of the above compound contains colored compounds which are not quinonemethide III (R = C18H37); the latter was prepared by oxidation of I with Ag2O. The effect of I‐III on the oxidation of tetralin was determined at 65 and 120°C.
Antioxidants and stabilizers. LXIV. Effect of derivatives of cyclohexadienone and 1,4‐benzoquinone on the oxidation of atactic polypropylene at 120°C
Authors: Buben I. , Pospíšil J. 
Published: June 2010

AbstractThe effects of selected alkylperoxycyclohexadienones and derivatives of 1,4‐benzoquinone on the oxidation of atactic polypropylene, cetane, and tetralin at 120°C were compared. Considerable differences have been found in the ways of influencing the oxidation of the first two hydrocarbons which under certain given conditions absorb oxygen much more slowly than tetralin in previous investigations (Buben and Pospíšil, Collect. Czech. Chem. Commun., 40, 977, 987 (1975)).
Recrystallization of polymers during drawing
Authors: Čačković H. , Loboda‐Čačković J. , Hosemann R. 
Published: June 2010

AbstractIt is known that in branched polyethylene during cold‐drawing a solid state diffusion of the single chains takes place during which the branches are trapped in the amorphous phase and an equilibrium state of highest possible crystallinity is attained if ϵ ≦ 1.3%. This no longer can be achieved for larger e values and the sizes D̄002 of the microparacrystallites (mPC) in fiber direction attain a definite smallest value of 60 å. This is explained by a feedback of the lateral dimensions of the mPCs which on account of paracrystalline distortions, have sizes of 60‐100 å in a metastable state. The driving force of a minimum surface‐to‐volume ratio stabilizes therefore the D̄002 value and constraints the incorporation of more and more branches into the mPCs. Now the volume of the lattice cell increases monotonically with e > 0.013 and the melting point decreases according to Sanchez and Eby.
Study of orientation in amorphous polymers by the creep thermomechanical method
Authors: Forgács P. , Hedvig P. 
Published: June 2010

AbstractTensile creep of unplasticized and plasticized PVC and toughened polystyrene compounds were recorded as a function of the temperature with the UNIRELAX device developed in our laboratory and produced by Tetrahedron Associates, San Diego, California, U.S.A. The thermomechanical curves obtained this way were found to be governed by the creep process as well as by the recovery of the elastic deformation frozen‐in by processing. Using small stress levels (10 g/mm2) the thermomechanical curve was mainly determined by the recovery of the frozen‐in deformation. Effects of thermal history on the creep thermomechanical curves were studied and interpreted. Using a mathematical formalism derived earlier for amorphous polymers, the curves were computer‐processed in order to separate creep from the recovery of the frozen‐in deformation and to obtain isothermal kinetic curves.