bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the activity of some sulfur compounds in the modification of vulcanizates by vinyl monomers
Authors: Beniska J. , Štaudner E.
Published: June 2010

The kinetics of the bulk polymerization of styrene in the presence of tetramethylthiu‐ramdisulfide ([TMTD]; 2.11 × 10−4‐1.67 × 10−1 mole/1., and some other sulfur compounds at 80, 95, 115, 130, and 140°C, were studied. The rate of polymerization has been measured as a function of the concentration of the studied compound. The formal order of reaction (n) was determined with respect to the concentration of TMTD, which varies with the increase of the concentration of TMTD and temperature of polymerization in the range 0 < n < 0.5 and it is possible to express by the relation: n = d In Rp/d In [I] = n0(1 − C[I]2)/(1 + B[I] + C[I]2). The decrease of the polymerization rate compared with the rate arising from the simple reaction scheme is caused by the participation of radicals on the termination reactions: (P' + RS', RS' + RS'), which permits us to solve this type of polymerization as a retardation polymerization: Rp − A[I]1/2 /(I + B[I] + C[I]2)1/2. (A, B, and C are complex constants dependent on temperature.) The calculated values of the fraction of primary radicals taking part in the termination reaction (assuming the neglect of the reaction (RS' + RS') grow with the increase of the concentration TMTD and temperature. The relatively high values of complex transfer constants Ci'‐(0.57–0.98) and the observed decrease of values of effective activation energies with an increasing concentration of TMTD are in accordance with the given reaction scheme. The observation of other sulfur compounds (zincdiethyldithiocarbamate, dibenzothiazolyldisulfide, dipentamethylenthiuramtetrasulfide, and N‐cyclohexyl‐2‐benz‐thiazylsulfenamide) showed that they had a considerably smaller influence on the polymerization of styrene than did TMTD.
Über Vernetzte Makromolekulare Stoffe mit Inhomogener Netzwerkdichte
Authors: Funke Werner
Published: June 2010

Visual swelling characteristics of crosslinked polyester resins in good swelling agents lead one to suppose that in these resins the crosslinks are not equally distributed. When polyester resins are cured by heat without added peroxide, the maximum conversion and therefore also the maximum crosslink density have been shown to depend on the initial radical concentration in the reaction medium. After the gelling point the conversion could not be enhanced by increasing the polymerization temperature. Obviously the primary network, which arises at the gelling point, predetermines the structure of the fully cured resin. Because of the relatively high functionality of the polyester molecules, the large degree of polymerization of the arising copolymer chains and their predominantly alternating structure, growing chain radicals are rapidly attached to the network. It must be assumed that after the gelling point the polymerization proceeds mainly at certain centers, the final number and extent of which depend on the special conditions of the polymerization reaction. The change of the reactivity ratios of the monomers, normally to be observed at high conversions, is explained by the restricted mobility of the still‐unsaturated polyester chains. The conversion at which this restriction appears depends on the structure of the primary network. Under special conditions popcorn formation takes place during polymerization of polyester resins. These popcorn polymers may be considered as an extreme case of a network with an unequal distribution of crosslinks. The composition of these popcorn‐containing polyester resins indicates that their existence is due to the reduction of the mobility and reactivity of the polyester chains at a very low conversion.
New class of film‐forming electrically conducting polymers
Authors: Lupinski J. H. , Kopple K. D. , Hertz J. J.
Published: June 2010

Conducting polymers consisting of a polycation, 7,7,8,8‐tetracyanoquinodimethan anions (TCNQ−) and neutral TCNQ are described. Polycations employed were derived from poly‐4‐vinylpyridine, atactic and isotactic poly‐2‐vinylpyridine, poly‐N‐vinyl‐imidazole, polyethyleneimine, poly‐4‐dimethylaminostyrene, and a copolymer of 4‐vinyl‐pyridine and styrene. These materials have an unusual combination of properties, not reported before for organic semiconductors, in that they are of high molecular weight, are soluble in organic solvents, and have conductivity controllable over several orders of magnitude by varying their content of neutral TCNQ. The highest conductivity observed so far for these materials is 10−3 Ω−1 cm.−1. In the solid‐state conduction proceeds through an electronic mechanism.
Determination of critical points in multicomponent polymer solutions
Authors: Koningsveld R. , Staverman A. J.
Published: June 2010

As a rule, critical temperatures of liquid‐liquid phase separations in polymer solutions do not coincide with the maximum separation temperatures. It can be shown that the critical point is situated on the right‐hand branch of the cloud‐point curve, which is a quasibinary section of the multidimensional temperature–composition diagram. Determination of the exact position of the critical point is possible by measuring phase–volume ratios as a function of concentration at temperatures close to the cloud‐point. This is demonstrated by measurements on the systems polyethylene‐diphenyl ether and polystyrene‐cyclohexane. Determination of the critical circumstances appears to be a sensitive means of testing the relation for the free enthalpy of mixing.
The role of the homogenous and heterogeneous components of ziegler catalysts in the development of polymerization activity
Authors: Váradi J. , Czájlik I. , Baán A. , Chirkov N. M. , Tsvetkova V. I.
Published: June 2010

The eomposition and polymerization activity of a given catalyst system (TiCI4‐Et2AlCl) were determined. The solid particles formed by the reaction of the catalyst components were separated at two given times, which were characteristic of the polymerization kinetics. The polymerization activities of the catalyst precipitates were determined in the presence of Et2AlCl and other cocatalysts. It was established that the measured polymerization activities of the catalyst precipitates are higher in the initial system than in the presence of other cocatalysts. The composition of the liquid phase of the catalyst was studied and it was found to contain certain dissolved Ti compounds, the titanium content of which could be determined after hydrolysis as trivalent Ti. The concentration of this titanium compound depends on the solvent used. The polymerization kinetic studies provided evidence that the maximum polymerization rate, i.e., the process of polymerization as a whole, depends on the kind of the solvent used and thus on the quantity of dissolved titanium compounds in the liquid phase.
Intermolecular forces in the process of heat aggregation of globular proteins and the problem of correlation between aggregation and denaturation phenomena
Authors: Jaenicke R.
Published: June 2010

The heat aggregation of globular proteins depends on a coupled coagulation and exchange reaction which may be differentiated with respect to its relative proportions by specific inhibition of aggregation and by degradation analysis. In general, the coagulation by weak intermolecular forces exceeds the covalent exchange reaction (disulfide and lanthionine bonds). Decreasing net charge further diminishes the covalent aggregation and at the same time the rate of denaturation, so that under isoelectric conditions as the limiting case, the particles agglomerate with conservation of their native state. At high electrostatic potential denaturation is the precursor of aggregation. Inhibition of aggregation is produced by formaldehyde, weak protic solvents, ionic detergents, and urea, etc.; only formaldehyde seems to react without denaturation, leading to the conclusion that hydrogen bonds cause the coagulation of the native particles while aggregation by hydrophobic interactions presupposes (partial) denaturation. Ion‐pair bonds may participate in the aggregation at extreme pH values. As regards the tertiary and quaternary structure, one may conclude that in the native state polar groups must be situated in the periphery of the molecule while the nonpolar side chains cluster together in the center of the globular molecule. This result verifies Kendrew's principle of tertiary structure formation derived from solid‐state x‐ray analysis for the molecule in solution and is also compatible with the specific dissociation‐association phenomena observed in the case of the quaternary structure.
A review of the electrical properties of monomeric and polymeric charge‐transfer complexes
Authors: Labes M. M.
Published: June 2010

The electrical properties of a large number of monomeric charge‐transfer (CT) complexes have been studied; a range of 20 decades is observed in their conductivity. We have learned that there is a structurally related anisotropy of the conductivity, that powder measurements can be very misleading, and that the conductivity is high in CT complexes having a large radical‐ion component in the ground state. Further progress requires learning how to achieve purity and measure carrier mobility in single crystals, and attempts made thus far in these directions are reviewed. A major problem in achieving high conductivity in polymers is to increase chain‐chain interaction; CT complexing is an effective way of accomplishing this and a number of donor polymer‐monomeric acceptor systems have been examined. There has been very little work on carrier mobility. The emphasis in the future must be to achieve and study pure, well‐understood structures.
Crystal nucleation in polyethylene: The droplet experiment
Authors: Gornick F. , Ross G. S. , Frolen L. J.
Published: June 2010

The droplet technique was utilized to obtain estimates of the isothermal rate of homogeneous crystal nucleation in highly supercooled melts of unfractionated linear polyethylene. In a typical experiment a cell containing a suspension of several hundred micron‐size spherical droplets of the polymer was placed on a microscope hot stage and quenched from a temperature well above the melting point of polyethylene to the desired crystallization temperature. When viewed between crossed polarizers, the droplets were initially invisible but, upon freezing, they appeared as visible birefringent spheres. The time dependence of the process was followed by time‐lapse photography. Half times (T1/2) for the freezing of those droplets remaining unfrozen by the time the crystallization temperature was attained were thus obtained at a series of undercoolings and related to the desired nucleation rate constant I (nuclei cm.−1 sec.−1) by the equation I = In 2/T1/2/v, where v is the droplet volume. The temperature dependence of I, as obtained by the above procedure, was analyzed in accord with current theories of homogeneous nucleation of chain‐folded polymer crystals. From this analysis, an estimate, 14,960 ergs3 cm.−6 was made of the quantity (%sG2%sGe), where %sG and %sGe are, respectively, the lateral and end‐surface free energies of the crystal.
The effects of structural modifications on the critical properties of PBI fiber
Authors: Singleton R. W. , Noether H. D. , Tracy J. F.
Published: June 2010

The only improvement seen in increasing the molecular orientation of PBI fiber over that exhibited by presently defined target property material is the improvement seen in the strength and stiffness of the material at high strain rates. This improvement, however, cannot be extrapolated to a good impact performance. No advantage of fiber crystallization was detected in the properties measured in this evaluation conducted in accordance with the current state of the art of testing of high temperature fibers. However, as the testing of high temperature performance fibers becomes more sophisticated, advantages of crystallization undetectable in this investigation may appear. Should this occur, it would then be advisable to explore the crystallization of PBI further in an attempt to induce a higher degree of crystallinity than accomplished in this work while maintaining adequate tensile properties.
High‐strength, high‐modulus glass fibers
Authors: Lewis Albert , Robbins David L.
Published: June 2010

This paper describes work that was conducted to develop high‐strength, high‐modulus glass fibers. Statistical experimental design and data analysis were used to determine some of the sampling, testing, and fiberizing variables that affect the dispersion of mechanical property data of glass fiber specimens. The simplex lattice experimental design was used in glass compounding studies. The experimental method is described. Three glass compositions with high mechanical properties are described. One of these glasses is composed of MgOAl2O3SiO2. The other two are 4‐component glasses and contain MgOAl2O3SiO2 and BeO, or La2O3.
Translation of fiber properties into composites
Authors: Schwartz H. S.
Published: June 2010

The strength and modulus of elasticity of fiber‐reinforced plastic composites are a function of the strength, modulus, volume content, and directional orientation of the fibers used in the composites. Continuous fibers are generally preferable to noncontinuous fibers because the continuous types are easier to align, impregnate with resin, and fabricate into large structures by filament‐winding techniques. The principal function of the matrix in a composite is the transfer of loads between and among fibers. For plastic matrices both chemical adhesion of the matrix to the fibers and shrinkage of the matrix around the fibers are important factors in this load transfer. The structural efficiency of fibers in composites is usually determined by measuring mechanical properties of simple composite specimens containing known volume per cents of the fibers, and comparing the measured mechanical properties of the composites with those predicted analytically.
Polymer crystallization
Authors: Geil P. H.
Published: June 2010

A review of the mechanism of polymer crystallization has recently been published. That review will not be repeated here. In this brief written report we wish only to emphasize several aspects of polymer crystallization and discuss several new results from our laboratories which will be described in more detail elsewhere.
The relationship of fibers structure to diffusion of dyes
Authors: Sprague B. Sheldon
Published: June 2010

A series of cellulose acetate yarns representing wide ranges of orientation and molecular aggregation were dyed with several disperse (non‐ionic) dyes at various temperatures, and the average diffusion coefficient of dye in fiber was determined. The activation energy for diffusion is determined, and the transition phenomena noted with cellulose acetate are discussed. The role of water and temperature in modifying fiber structure, as related to dye diffusion, is discussed, and dye diffusion is shown to be a most sensitive tool for the examination of small structural differences in fibers.
Fractionation of linear polyethylene with gel permeation chromatography. Part II
Authors: Nakajima Nobuyuki
Published: June 2010

Several commercial samples of linear polyethylene were fractionated by gel permeation chromatorgraphy (GPC); they had four columns of maximum nominal capacity of 107 A. The molecular weight distribution thus obtained revealed delicate variations: none of the results could be perfectly represented by a log‐normal distribution. With selected samples the performances were compared among four GPC units, all having four columns. With columns of similar capacity satisfactory reproducibility could be achieved from different units, if sufficient care were taken in calibration and operation. The results with the two‐column unit were significantly different from those with the four‐column units. The difference in concentration of sample solutions appeared to be a part of the cause. The different elution times of two columns and four columns seemed also to have contributed. Among the four‐column units slightly variant results were obtained in the high molecular weight tail, when the maximum capacity of the column was different. Two solvents, o‐dichlorobenzene and 1,2,4‐trichlorobenzene, were used for this work. Solvent effects were found in neither GPC nor dilute‐solution viscosity.
Über synthetische Matrizenreaktionen
Authors: Kämmerer H. , Shukla J. , Oender N. , Scheuermann G.
Published: June 2010

Molecularly homogeneous, polynuclear phenolic compounds were esterified with acrylic acid and methacrylic acid chlorides. The pcresyl esters of acrylic and methacrylic acid react in high dilution in boiling benzene with a large excess of radicals derived from AIBN in such manner that the growth step of the free‐radical polymerization is prevented; this may be denoted a “suppressed” polymerization. The application of these conditions to the previously mentioned poly‐nuclear esters results in the formation of molecularly homogeneous cyclooligomers (ladder oligomers). Alkaline hydrolysis of these oligomers permits recovery of the polynuclear phenols and yields molecularly homogeneous oligoacrylic acid and oligomethacrylic acid, the structures of which were proved by the preparation of a variety of ester derivatives. The presented reaction path seems to be a very simple model of the biosynthesis of proteins. Finally, evidence is presented for the consideration of this reaction sequence as a synthetic matrix reaction.
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

The 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

Electrolysis 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

Polymerization 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

Some 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

A 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

Completely 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

The 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

Diisocyanates 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

Several 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

The 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

A 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

Analysis 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

Vinyl 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

Density, 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

Several 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

In 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

Previous 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

One 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.
The interpretation of high resolution electron micrographs of the cellulose elementary fibril
Authors: Hanna Robert B.
Published: June 2010

Some of the present evidence for the structure of the celluiose elementary fibril may be attributed to artifacts. The factors involved in the production of these artifacts may include the phenomenon of phase image granularity, the thickness of the ultrathin section, the structure of the negative stain, and the nature of the substrate. Interpretation of high resolution electron micrographs requires an intimate knowledge of these factors.
Some problems in radiation grafting to cellulose fibers
Authors: Sakurada I. , Okada T. , Kaji K.
Published: June 2010

In the case of grafting by preirradiation method, the presence of air during preirradiation by gamma rays has practically no influence on the percent grafting, whereas the presence of water decreases the activity to a great extent. ESR studies of preirradiated cotton and rayon show that the active species for the grafting are not peroxides but free radicals even when the irradiation is carried out in air. The number of scissions of chemical bonds of the cellulose molecule by the irradiation is found to be practically independent of the degree of polymerization and microstructure of the initial cellulosic fiber; the presence of air also has no effect on the degradation. In the case of styrene grafting, breaking strength of single fibers remains substantially unchanged by the grafting, but the increase of denier by the grafting results in a drop of tenacity (g/den) of the single fibers. It is true that cellulosic fibers become hydrophobic by the grafting of styrene, but the tendency to absorb water calculated on the cellulose basis increases by the increasing percent graft. This may be the reason for the rather low wet tenacity of the styrene grafted cellulosic fibers.
Chromatographic and ion exchange properties of radiation copolymerized celluloses
Authors: Dilli S. , Garnett J. L. , Martin E. C.
Published: June 2010

The potential of radiation copolymerized celluloses in chromatography, particularly in the reversedphase technique is discussed. A range of styrenated celluloses has been prepared from copolymerizing styrene with Whatman 40, 41, and 42 papers. The effect of percent styrene on the separation characteristics of a number of dyestuffs on these grafted papers has been studied. Significant differences in chromatographic behavior of the dyes is observed between the grafted and nongrafted papers. Similar changes in RF values between the two types of papers are also observed for the separation of a range of 19 typical cations. Detailed studies have been performed particularly with Zn+2, NI+2 and Cd+2. In the separation of the fatty acids, stearic, myristic and lauric, the grafted celluloses are shown to possess advantages over the untreated Whatman equivalent. For column chromatography, a methylmethacrylate‐cellulose radiation copolymer has been used to quantitatively separate a mixture of oil soluble dyes. This same mixture could not be separated on a column of untreated cellulose powder. Finally the ion exchange properties of grafted copolymers where the monomer contains a functional group such as −NH2, −SO3H or even a heterocyclic nitrogen (the vinyl pyridines) are discussed.
Deformation behavior of amorphous film of nylon 11 and some other polyamides above and below the glass transition temperature
Authors: Northolt M. G.
Published: June 2010

The deformation behavior of initially amorphous films of nylons 11, 66, and 12 has been studied at drawing temperatures above and below the glass transition temperature. Evidence has been found that the glass transition temperature in polyamides is connected with a disruption of the hydrogen‐bonded network. In addition these experiments indicate that the kind of hydrogen‐bonded network present in the crystalline state determines whether the orientation of the crystallites in film specimens drawn below the glass transition temperature is uniaxial or biaxial.
Influence of thermal history on the melting behavior of isotactic polystyrene
Authors: Overbergh N. , Berghmans H. , Smets G.
Published: June 2010

Multiple melting transitions of thermally crystallized isotactic polystyrene were studied. This behavior was attributed to a very rapid reorganization during the melting of the crystalline structure originally formed. From differential scanning calorimetry and optical microscopy it was shown that the rate of reorganization decreases with increasing reorganization temperature TR. This reorganization will only occur if its rate is larger or equal to the scanning rate. A TR value can be defined for each scanning rate and the resulting melting temperature TRM increases when the scanning rate decreases. This increase of TRM is also examined by annealing at different temperatures. A linear relationship between TRM and TR is observed and gives an extrapolated equilibrium melting point of 240°C; moreover the slope is smaller than for isothermal crystallization (TM versus TC). These phenomena are confirmed by optical microscopic observations.
Morphological changes during annealing of doubly oriented polycaprolactam
Authors: Baldrian J. , Pelzbauer Z.
Published: June 2010

Doubly oriented polycaprolactam films were annealed with the ends free at temperatures between 145 and 200°C for 30 min. As the annealing temperature rose the long period increased, the transverse dimensions of fibrils grew anisotropically, and the low‐angle diffraction intensity and density also increased. On the other hand, there was a decrease in the breadth of crystalline reflections. During annealing the film shrank in the direction of the fibril axis (M) and expanded in the direction (N) in which the pressure was acting during the production process. No changes could be observed in the direction normal to the MN plane. The supermolecular structure was also investigated by means of electron microscopy. The phenomena observed are explained in terms of the Peterlin two‐stage model of plastic deformation of the crystalline polymers, which assumes the formation of strongly extended fibrils, connected by interfibrillar “tie” molecules.