bluuebunny/crossref_metadata_2025_split huggingface dataset:
On catalytic properties of poly‐4‐vinylpyridine and its copolymers in reactions between isocyanates and alcohols
Authors: Pshezetsky V. S. , Massouh I. , Kabanov V. A. 
Published: June 2010

AbstractThe catalytic properties of poly‐4‐vinylpyridine and its copolymers with styrene at different compositions were investigated in reactions of mono‐ and diisocyanates with alcohols and glycols. The catalytic activity of polymeric catalysts was compared with that of pyridine. It was found that the reaction rate is proportional to the concentration of polymer catalyst up to that concentration at which the reaction system becomes considerably viscous, which testifies to the accessibility of catalytic sites in the polymer for the reactants. Studies of the dependence of the reaction rate in phenyl isocyanate–methyl alcohol and toluylene diisocyanate–ethylene glycol reactions on the concentrations of the reactants indicates that the pyridine‐catalyzed reaction is first order with respect to isocyanates and alcohols. The polymer‐catalyzed reactions are characterized by higher rates in comparison with those catalyzed by pyridine in the range of low reactant concentrations. But when the concentration increases, the rates of polymer‐catalyzed reactions reach limit values and finally become less than in the case of pyridine. The catalytic activity of polymeric catalysts is higher, the higher the styrene content in the copolymer. The peculiarities of polymeric catalysts' behavior as compared with the behavior of low molecular catalyst is ascribed to an inhomogeneous distribution of reagents between the solvent and the macromolecular coils and their aggregates.
Electrolytically initiated anionic polymerization of isoprene
Authors: Funt B. Lionel , Bhadani Suraj N. 
Published: June 2010

AbstractElectrolysis of solutions of isoprene in tetrahydrofuran‐initiated living‐anionic polymerization was studied. The concentration of living ends was measured by spectrophotometry and could be maintained at any desired level by adjustment of the charge passed through the solution. An electronic feedback device, which regulated current flow to maintain constant optical absorbance, permitted kinetic studies at constant concentration of living ends. Simple first‐order kinetics could be observed in these systems at constant living anion concentration, despite a rapid attrition of living ends due to interaction with the solvent. The number of living anions could be reduced quantitatively by reversal of the impressed current. The control of the anion concentration implied a companion control over the molecular weight distribution.
Cyclo‐ and cyclized diene polymers. XIV. Structure and properties of poly(2,3‐dimethylbutadiene‐1,3)
Authors: Gaylord N. G. , Štolka M. , Štěpán V. , Kössler I. 
Published: June 2010

AbstractPolymerization of 2,3‐dimethylbutadiene‐1,3 with the Ziegler‐type catalyst Al(i‐C4H9)3‐TiCl4 yields cis‐1,4‐polydimethylbutadiene, when the Al component is in excess, and cyclic polydimethylbutadiene with reduced unsaturation and some trans‐1,4 units in the chain, when the Al/Ti ratio is 1 or less. Similar cyclic polymer is formed in polymerization initiated with acid catalysts such as AlC2H5Cl2. Polydimethylbutadiene obtained with the complex cobalt catalyst Al(i‐C4H9)2ClCoCl2·pyridine is predominantly cis‐1,4 with about 20% of 1,2 units. Radical polymerization at elevated temperature gives high 1,4‐polydimethylbutadiene with both cis and trans units. The polymer obtained by irradiation of dimethylbutadiene at low temperatures is also cyclic with some trans‐1,4 units. Irradiation of dimethylbutadiene in thiourea canal complex leads to relatively high trans‐1,4 polymer. Absorption bands in the infrared spectra at 1125, 1201, and 1251 cm.−1 are typical of cis‐1,4, and bands at 1156, 1227, and 1263 cm.−1 are typical of trans‐1,4, structures.
Hydrodynamic properties and optical anisotropy of molecules of linear and cyclolinear polyphenylsiloxanes in solution
Authors: Tsvetkov V. N. , Andrianov K. A. , Vinogradov E. L. , Shtennikova I. N. , Yakushkina S. E. , Pakhomov V. I. 
Published: June 2010

AbstractSome fractions of cyclolinear polyphenylsiloxanes (ladder polymer) were investigated by flow birefringence, diffusion, and sedimentation in solution. By the same methods were investigated some samples of linear polymethylphenylsiloxanes (MPhS), which differ one from another by degree and order of substitution of methyl groups on phenyl ones. The experimental data obtained were used for the determination of the optical anisotropy and rigidity of the polymer molecules. The negative segmental anisotropy of MPhS molecules is increasing monotonically with degree of substitution by phenyl groups. Rotational hindrance of side phenyl radicals somewhat changes with degree and order of substitution, although flexibility of the backbone remains practically unchanged. Optical anisotropy of molecules of cyclolinear polyphenylsiloxane (CLPhS) is very high, which appears to be the result of great skeletal rigidity of the main double chain. Dependence of anisotropy and hydrodynamic characteristics upon molecular weight also indicates on great rigidity of CLPhS molecular chain. Dimensions of Kuhn's statistical segment for CLPhS molecules, determined from optical and hydrodynamic data, is one order higher than the values usually obtained for chain molecules of synthetic polymers.
Specific volume, dielectric properties, and mechanical properties of cured epoxy resins in the glass‐transition region
Authors: Shito Nobuhiko 
Published: June 2010

AbstractA diglycidyl ether of bisphenol A was crosslinked with dodecenylsuccinic anhydride at various conditions. The dilatometric, dielectric, and dynamic mechanical measurements were carried out on the cured resins in the glass‐transition region. The effects of the ratio of anhydride to epoxy resin, of accelerator concentration, and of curing condition on the measured properties of the cured resins were studied. The reduction of accelerator concentration causes a marked decrease of the crosslinking density and in consequence has a great influence on the glass‐transition temperature and other properties of the cured resin system. The observed values of specific volume at the glass‐transition temperature increase with increasing ratio of anhydride to epoxy resin and also increase with increasing crosslinking density. These values can be predicted approximately as sums of the atomic volumes. The temperature dependence of the dielectric relaxation time for the α process can be represented by the universal WLF equation. The values of the WLF reference temperatureTsare 55–61°K. higher than the observed values of the glass‐transition temperatureTg.The temperatures of maximum loss tangent for Young's modulus are 3–10°K. higher than those of maximum dielectric loss tangent at the same frequency. The concentrations of the network chains effective in rubber elasticity are 20–40% of the theoretical concentrations predicted from the compositions.
Reactivity of the residual allyl group in poly(allyl methacrylate)
Authors: Kamogawa Hiroyoshi , Furuya Setsuko , Kato Masao 
Published: June 2010

AbstractCompletely soluble linear allyl methacrylate polymers with pendant allyl groups were prepared, in high conversion, by the lithium‐initiated polymerization of allyl methacrylate in tetrahydrofuran. Three reactions typical of olefinic double bonds (i.e., crosslinking with benzoyl peroxide or with azobisisobutyronitrile, vulcanization with sulfur or with sulfur monochloride, and epoxidation with perbenzoic acid) were found to proceed smoothly for the remaining allyl groups in the polymers. In its reactivities toward these reagents the allylic double bond in the polymer compares with the terminal double bond of an olefinic hydrocarbon but is inferior to an internal double bond. Effects of the separations of the pendant allyl groups with inert monomer units by copolymerization are also recognized.
Sulfurization of polyhydrazides
Authors: Frazer A. H. , Fitzgerald W. P. 
Published: June 2010

AbstractThe reaction of polyhydrazides with phosphorus pentasulfide in pyridine has yielded polyoxathiahydrazides, polydithiahydrazides, and poly‐1,3,4‐thiadiazoles. At 115°C. after 30 min. of reaction time the major product was polyoxathiahydrazide; after 24 to 48 hr. the major product was polydithiahydrazide; after 120 hr. the major product was poly‐1,3,4‐thiadiazole. 3‐Picoline and pyridine were the preferred reaction media; other picolines, lutidine, piperidine, quinoline, dimethylacetamide, and o‐dichlorobenzene were not useful. Characterization of the polymeric products was accomplished by a combination of thermal and spectroscopic analyses. Ultraviolet absorption spectra, relative fluorescence of long‐wavelength ultraviolet light, thermogravimetric analysis, differential thermal analysis, and characteristic absorption bands in the infrared were all used to elucidate structure. This reaction has been found to be general for polyhydrazides. All‐aromatic, aromatic‐aliphatic, aromatic‐heterocyclic, and aromatic‐oxalic hydrazides have yielded the corresponding polyoxathiahydrazides, polydithiahydrazides, and poly‐1,3,4‐thiadiazoles.
The reaction of nylon 66 with diisocyanates and diacid chlorides
Authors: Perry Eli , Savory John 
Published: June 2010

AbstractDiisocyanates and diacid chlorides were allowed to react with two types of nylon 66 yarn made from polymers of 14,800 and 21,000 number‐average molecular weights. The higher molecular weight yarn had a more ordered structure initially, as indicated by density measurements. Both diisocyanates and diacid chlorides crosslinked the yarn, as is shown by insolubility in 90% formic acid. Isocyanates were more efficient crosslinking reagents than diacid chlorides. Diacid chlorides caused simultaneous degradation of the yarn. The overall rate of reaction of the reagents with the yarn responded to temperature reagent concentration, and time, as would be expected of low molecular weight materials bearing the same functional groups. Catalysts had only a small effect on the rate of reaction. The reaction occurred in the less ordered regions of the yarn, as indicated by (1) a faster rate of reaction with the less ordered yarn, (2) the accelerating effect of swelling solvents on the rate, and (3) the reduction in extent of reaction with increase in molecular size of the reagent, even though the reaction was not limited by diffusion.
Polymerizations catalyzed by noble metal‐olefin complexes
Authors: Rinehart R. E. 
Published: June 2010

AbstractSeveral noble metal‐olefin complexes were prepared and studied as polymerization catalysts. Catalytic behavior of complexes toward specific monomers is invariably a property of the metal atom. Polymerization rates may depend upon ligands associated with the metal, but ligands do not alter the course of reaction. Olefin complexes of rho‐dium(I) chloride are superior catalysts for the emulsion polymerization of 1,3‐butadiene to crystalline trans‐1,4‐polybutadiene. The rates of polymerization are dependent to some extent upon the olefinic ligands. In all cases rates can be increased by addition of certain hydride donors. Chelating diolefins, such as 1,5‐cyclooctadiene and norbornadiene, can serve as stabilizing ligands in catalytically active complexes. When added as free diolefin to polymerizing recipes containing either salts or complexes of rhodium, however, chelating diolefins are effective inhibitors of polymerization. Olefin complexes of iridium(I) chloride do not polymerize butadiene, but are effective catalysts for the ring‐opening polymerization of norbornene in bulk, solution, or emulsion. Polymermerization rates are very sensitive to the nature of the ligands within the complex; the more unstable complexes give the faster rates. Specific hydride donors do not usually enhance catalytic activity of iridium complexes, and may lead instead to complete deactivation of the complexes. The selective behavior of complexes of various noble metals toward specific monomers is strikingly illustrated by polymerization of norbornadiene. Three different polymer structures are obtained from complexes of the three metals rhodium, iridium, and palladium. From rhodium polymer consists of nortricyclene units, from a 1,5‐addition. Iridium leads to ring‐opened oxygenated polymer, whereas palladium catalyzes formation of 1,2‐addition polymer.
Rapid measurement of the chemical contribution to network chain density for natural rubber
Authors: Redding R. B. , Smith Derek A. 
Published: June 2010

AbstractThe swollen compression modulus (Reticulometer) method has been used to measure the gaussian modulus factor (Gc) in compression for natural rubber vulcanizates covering a wide range of crosslink concentration. The values obtained are in good agreement with estimates from tension measurements (Gt) over the limited range of modulus accessible using tension techniques. By correlation with equilibrium swelling measurements, data for both peroxide and thiazolesulphur vulcanizates have been fitted by the Flory‐Rehner equation. Effective values of the polymer‐solvent interaction parameter (xeff) have been determined and found to be 0.42 and 0.43 for peroxide and sulphur vulcanizates respectively, these values being independent of degree of cure. A correlation between Gc and chemical contribution to network chain density, (pM−1c) chem' is reported for peroxide‐vulcanized natural rubber based on published data. To expedite the determination of (pM−1c)chem values, a commercial oscillating disk rheometer has been calibrated using Reticulometer data. A linear relationship is obtained between Gc and rheometer torque for the modulus range studied, for both 1° and 3° rotor displacement. Use of the relationship between modulus factor and chemical crosslinking now enables direct estimation of chemical contribution to network chain density from rheometer torque values.
Structure of semi crystalline fibers from interpretation of anelastic effects
Authors: Prevorsek D. C. 
Published: June 2010

AbstractA theory of fiber strength is reviewed which assumes that the rupture of fibers is a result of the formation and propagation of cracks across the fiber. The derived equations which include three parameters related to molecular structure, modulus, energy of the weakest bond and fracture surface energy are used to estimate the strength of flawless ensembles of perfectly oriented molecules. A method is discussed to estimate the fracture surface energy of such systems as function of molecular weight and degree of random chain folding. A comparison of theoretical data with the strength of a series of highly oriented poly‐(ethylene terephthalate) fibers having approximately the same morphological characteristics but different molecular weight leads to the following conclusions. First, the strength determining phase of these fibers has a lower density than the fibers, and second, this low density phase consists of highly extended molecules whose average length between the folds exceeds 1500Å.The characteristics of the two phase system of these fibers, the phase of the matrix and the aspect ratio of crystallites are determined by analyzing the intensity of viscoelastic transitions and by treating the data by means of Halpin‐Tsai equations. A structural model is proposed which is consistent with the results of this analysis and with the small‐ and wideangle X‐ray diffraction data.
Quantitive kinetic study of vinyl chloride polymerization in suspension
Authors: Hauss A. F. 
Published: June 2010

AbstractAnalysis of various time‐conversion curves obtained with different AIBN‐concentrations at 65°C led to relative rate constants of conversion in the liquid and precipitated phase. Due to the density difference between the two phases, the time‐ and conversion‐dependent volume concentration of the initiator and the conversion‐dependent volume concentration of the free liquid and polymer‐dissolved monomer could be calculated per unit volume of suspended reaction mixture. By this calculation, the molar concentrations of all reactants were given for each point on the time‐conversion curves. On the basis of known kinetic equations a correlation could be achieved between conversion in the range up to 70% conversion and time by using the time integral of the effective initiator concentration. Exact correlation revealed a side reaction of the initiator AIBN, which was supposed to be due to small traces of oxygen. The desactivated initiator amount is nearly constant over all polymerization runs with different initial initiator concentrations. Taking this into account, the experimentally determined time‐conversion curves coincide with the calculated ones.
Polymerization of vinyl chloride in the presence of crosslinking agents
Authors: Itoh I. , Itoh S. , Matsumura I. , Maruyama H. 
Published: June 2010

AbstractVinyl chloride was polymerized in the presence of a small quantity of such crosslinking agents as diallyl esters and divinyl ethers in a suspension and an emulsion system, in order to prepare poly(vinyl chloride) having very high polymerization degree.In the case of suspension polymerization, the average polymerization degree increased at first and decreased thereafter, via the maximum with the formation of gel, as the amount of crosslinking agent was increased.In the case of emulsion, however, when diallyl esters were used, the average polymerization degree changed in the same manner as in suspension without formation of gel. But divinyl ethers showed no effect on polymerization degree or gel formation.The difference of the effect of crosslinking agents on average polymerization degree and gel formation was discussed in both suspension and emulsion polymerization systems.
Amorphous surface layers in polyethylene single crystals
Authors: Peterlin A. , Zachmann H. G. 
Published: June 2010

AbstractDensity, heat of fusion and melting temperature data of annealed polyethylene single crystals suggest the existence of a temperature‐dependent pseudo‐amorphous surface layer which contains chain folds and free chain ends. In the ideal two‐phase model, one assumes two such amorphous layers of thickness ℓ/2 each on the two (001) surfaces of the crystalline core of thickness D = L ‐ℓ, where L is the total thickness of the single crystal. The thickness of such a layer was calculated under the assumption of random length loops and cilia (free chain ends) for the case of adjacent reentry and of a Maxwellian distribution of loop width. The excess energy requirement of the shortest loops with the high concentration of gauche conformations favors longer loops and hence increases the surface layer thickness. The reduction of entropy by the restrictions imposed by finite loop width and the availability of a half space only acts in the opposite direction. The calculated thickness depends on the true supercooling ΔT = Tm° ‐ T if L is kept constant and on relative supercooling ΔTrel = Tm‐T, where Tm is the actual melting point of the crystal, if the crystal core thickness D is kept constant. A qualitative agreement between theory and experiment on this basis seems possible by proper consideration of the contribution of loops and cilia.
Empirical equations for representing viscoelastic functions and for deriving spectra
Authors: Smith Thor L. 
Published: June 2010

AbstractSeveral equations containing two empirical constants are considered for representing G(t), G′(ω), J′(ω), and J(t) in the glass‐to‐rubber dispersion zone. With these equations, data on the NBS polyisobutylene can be closely represented. The relaxation spectrum H(τ) and the retardation spectrum L(τ) were derived exactly from the equations for G′(ω) and J′(ω), respectively. The derived equations have the same functional form, and thus H(τ) and L(τ) can be interconverted, under certain conditions, by employing an auxiliary equation that interrelates the relaxation and retardation times at which the spectra maximize. An exact transformation of an equation for G(t) gave a second equation for H(τ); from the constants in this equation, L(τ) was calculated. The methods for obtaining and interconverting H(τ) and L(τ) for polyisobutylene gave results that agree satisfactorily with literature data obtained by the usual approximation methods.
The behavior of cotton cellulose and beech wood in ammonia atmosphere
Authors: Bariska Mihaly , Popper Rudolf 
Published: June 2010

AbstractIn order to learn more about the plasticization of wood, sorption measurements on cellulose rich specimen, cotton fibers, and bending tests on beech wood were performed in ammonia atmosphere. The results showed that the sorption of NH3 on cotton was substantially hindered at low relative vapor pressure, presumably due to interaction of NH3 with hydrate water. Near the saturation pressure a reduction of the sorption capacity was observed because of developing collapse in the capillary system. In the middle relative vapor pressure range the equilibria were retarded while the active surface area was extended to more than double. Observations at different temperatures‐15, 25, 35°C, revealed that the extension of the sorptive area took place consistently at the same ammonia content of the specimen. The other mentioned diverging sorption features, however, were intensified variously by raising the temperature. No difference was found between the ammonia sorption properties of cellulose I and III.Bending tests on beech wood laths in ammonia environment displayed a dynamic progression of the plasticization. At the beginning of the exposition to ammonia the bending ability of the specimen was increasingly enhanced. When in course of the plasticization the modulus of elasticity of the laths dropped below 1/3 of the starting value, bendability changed by levelling off progressively. The conclusion thereof that the plasticization of wood can be forced only to given limits was confirmed by destructive bending tests and by porosimetric measurements. To reach a sufficiently softened state of the beech laths with dimensions 25×1×0.6 cm, 15 min appeared to be enough while further alterations could be observed even on the smallest specimen size for considerably longer periods.
Fibrillar lignin or fibrillar pectin?
Authors: Leppard Gary G. , Colvin J. Ross 
Published: June 2010

AbstractPrevious work had demonstrated that an ultraviolet absorbing, fibriliar substance is present on the outer wall surface of suspension‐cultured cells and between adjacent cells. The fibrils were called lignofibrils on the basis of their resistance to enzyme attack, ultraviolet absorption, alkaline nitrobenzene degradation, and extraction by aqueous dioxane. However, more complete chemical analysis of the fibrils demonstrates that their major component is a linear polygalacturonic acid to which an ultraviolet absorbing compound(s) is attached. The term lignofibril for this material is therefore withdrawn. Extended fibrils exhibit no detectable close‐range order by X‐ray diffraction. Similar fibrils have now been observed in native tissues, but their biological function is still problematical.
Mechanical behavior of cellulose in relation to cell wall theories
Authors: Mark R. E. 
Published: June 2010

AbstractOne of the goals of research in wood and fiber mechanics is to provide evidence on the microfibrillar constitution of the cell wall. The mechanical evidence must be reconciled with the spectroscopic, radiological, and chemical evidence; and with the results of microscopic observations at all levels, to arrive at an understanding of molecular and supermolecular organization in plant cells. Certain mechanical criteria (e.g., strength and elastic properties) must be satisfied for any theory of cellulose structure to be compatible. In this paper, the current theories of molecular organization in the cell wall are considered, with particular emphasis given to the question of elastic moduli for the composite fiber wall.