bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystallite structure of cellulose
Authors: Chang Martin M. Y. 
Published: April 2003

AbstractThe crystallite structure of cellulose has been elucidated through analyses of the degradations of model compounds by gel‐permeation chromatography. These compounds include single crystals of cellulose triacetate, regenerated cellulose from single crystals, precipitated celluloses from solutions, and commercial regenerated cellulose. The corresponding distribution profiles are found to follow the Keller transformation, which is a characteristic behavior of the folded crystals of synthetic polymers. It is also found that the leveling‐off DP of cellulose is a first‐order approximation of the corresponding fold length. A detailed folding chain model for the regenerated cellulose was constructed, and the various aspects of the structure are discussed. The kinetic data and the degradation products of native celluloses were also analyzed and found to obey the ruling of the chain fold model but not the conventional fringe‐micellar model. In addition, an iodine‐staining experiment pinpoints a minimum of 1.5% of true amorphous material; this is in quantitative agreement with the conformation analysis for the six‐fold helical β‐loop bonds. It is therefore suggested that the same chain‐fold conformation is applicable to the native polymer. The hydrolysis of cellulose is found to be composed of a triple mode of degradation, i.e., a first‐order random scission at the folds, a zero‐order peeling reaction at the ends of the crystallites, and a first‐order random scission on the lateral surfaces of the cellulose.
Investigation of physical state and phase behavior of polyester‐imides
Authors: Sidorovich A. V. , Koton M. M. , Kuvshinsky E. V. , Nikitin V. N. , Adrova N. A. , Baklagina Yu. G. , Mikhailova N. V. 
Published: April 2003

AbstractChanges in properties of linear aromatic heterocyclic polymers of the polyimide class after introduction of ester linkages into their dianhydride component and of the oxygen and sulfur atoms into their diamine component have been studied. Thermomechanical, dilatometric, thermographic characteristics and x‐ray diffraction patterns of poly(ester amic acids) and polyester‐imides have been investigated. On heating, poly(ester amic acids) and amorphous polyesterimides exhibited a peculiar effect of self‐orientation of macromolecules. The x‐ray diffraction patterns of unoriented films indicate that they exhibit axial‐planar texture with the c axis of macromolecules in the film plane. The formation of the texture is preceded by mutual arrangement of macromolecules, i.e., by a precrystallization process beginning in the amorphous state. Because of this, on heating at temperatures ranging from 200 to 380°C, polyester‐imides yield highly crystalline products. Crystallographic parameters of the polymer lattices on x‐ray diffraction patterns and dichroism of absorption bands in polarized infrared spectra, the most probable conformations of macromolecules of some polyesterimides are proposed.
Radiation‐induced homogeneous polymerization of ethylene in cyclohexane
Authors: Watanabe Terutaka , Wada Takeshi , Takehisa Masaaki , Machi Sueo 
Published: April 2003

AbstractThe radiation‐induced polymerization of ethylene in cyclohexane was carried out in a reactor of 100 ml capacity under a range of temperature of 25–150°C, dose rate of 4.1 × 104–2.9 × 105 rad/hr, pressure of 200 kg/cm2, and amount of cyclohexane of 20–90 ml. The polymerization was found to proceed at a steady state from the beginning. The polymerization rate is maximum at ca. 50 ml of cyclohexane. The dose rate exponent of the polymerization rate was 0.6 at every temperature from 25 to 150°C. The polymer molecular weight is in the range of 103–104, independent of dose rate, and decreases with increasing amount of cyclohexane. The molecular weight distribution is unimodal and narrow. Kinetic analysis of these results indicates that the polymerization proceeds via a simple scheme of homogeneous polymerization and the polymer molecular weight was determined by the chain transfer reaction which takes place mostly with cyclohexane. The unimodal and narrow molecular weight distribution is also consistent with the homogeneous polymerization scheme.
Effect of ultraviolet irradiation on terpolymerization of sulfur dioxide with two unsaturated compounds
Authors: Furukawa Junji , Kobayashi Eiichi , Nakamura Morio 
Published: April 2003

AbstractThe terpolymerization of sulfur dioxide, butene‐1 and acrylonitrile affords terpolymers containing equimolar amounts of sulfur dioxide and butene‐1 with various acrylonitrile contents. Ultraviolet irradiation was found to accelerate the polymerization and decrease the acrylonitrile content in the polymer. This fact is interpreted by a mechanism through a copolymerization of sulfur dioxide–butene‐1 complex and acrylonitrile, whereby the polymerizability of sulfur dioxide–butene‐1 complexed monomer may be accelerated by ultraviolet light. In fact, a binary system of sulfur dioxide and butene‐1 was found to be accelerated by ultraviolet irradiation, and it affords a maximum rate at a 1:1 composition of feed monomer. Ultraviolet light of 250–300 mμ wavelength is effective for the initiation and the propagation. This may be ascribed to the ultraviolet absorption of the sulfur dioxide–butene‐1 complex. The temperature coefficient was measured in both dark and ultraviolet irradiation reactions. The ultraviolet irradiation enhances the reactivity of sulfur dioxide–butene‐1 complexed monomer at low temperature. In the terpolymerization with sulfur dioxide, isoprene, and butadiene, the ratio of isoprene and butadiene in the terpolymer was not altered by ultraviolet irradiation because both monomers from complexes with sulfur dioxide, perhaps having the same temperature coefficient for the polymerization.
Photostabilization of polypropylene. II. Stabilizers and hydroperoxides
Authors: Carlsson D. J. , Wiles D. M. 
Published: April 2003

AbstractThe effects of various polyolefin photostabilizers on the thermal and photodecomposition of model and polymeric hydroperoxides have been investigated, both in the liquid and solid phases. Several extremely effective ultraviolet stabilizers belonging to the metal chelate class can cause the rapid thermal decomposition of model and polymeric hydroperoxides. Although stabilizers did not reduce the quantum yield for polypropylene hydroperoxide photolysis, several additives can scavenge hydroxyl and macroalkoxy radical products which result from hydroperoxide photolytic cleavage. Ultraviolet stabilizers which were found to trap radicals were able to prevent the photodegradation of polypropylene which already contained a significant concentration of hydroperoxide groups. Highly effective polypropylene ultraviolet stabilizers probably operate by a range of mechanisms including hydroperoxide decomposition, radical scavenging and singlet oxygen quenching.
ESR and chemical study of p‐polyphenylene formed by using an AlCl3–CuCl2 catalyst
Authors: Lerner N. R. 
Published: April 2003

AbstractThe free radicals in p‐polyphenylene and the formation of free radicals in this polymer upon pyrolysis in vacuum have been studied by means of electron spin resonance. For an unpyrolyzed series of polymer samples, a linear relationship was observed between free radical concentration and increasing carbon content. The free radicals observed in the unpyrolyzed samples did not react with NO. When samples of polyphenylene were pyrolyzed, additional free radicals were produced which did react with NO. The growth of free radical concentration upon pyrolysis was observed to be closely related to the production of volatile products from the polymer. In the temperature range 250–600°C, HCl was the principal volatile species produced. Two mechanisms were involved in HCl production: a process with an activation energy of 7.1 kcal/mole which led to the production of stable free radicals; and a process involving 75 kcal/mole which was unconnected with the production of free radicals. From 600 to 700°C, H2 was the principal volatile degradation product. The rate at which H2 was evolved showed a second‐order dependence on phenyl units bearing two or three substituents; this process had an activation energy of 79 kcal/mole. Electron spin resonance spectra indicated that this process led to the production of free radicals, and infrared spectra showed that a highly crosslinked product resulted.
Polymerization of σ‐bonded organo‐transition metal derivatives of styrene
Authors: Fujita N. , Sonogashira K. 
Published: April 2003

AbstractFive new monomers of transition metal complexes containing a styryl group, trans‐\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Pd}({\rm PBu}_{\rm 3})_2 \rlap{--} ({\rm C}_6 {\rm H}_4 {\rm CH} \hbox{=\hskip-2pt=} {\rm CH}_2 ){\rm X\ X \hbox{=\hskip-2pt=} Cl(Ia),\ X \hbox{=\hskip-2pt=} Br(Ib)},\ {\rm X \hbox{=\hskip-2pt=} CN(Ic),\ X \hbox{=\hskip-2pt=} Ph(Id)} $\end{document} and trans‐\documentclass{article}\pagestyle{empty}\begin{document}${\rm Pt(PBu}_{\rm 3} {\rm )}_{\rm 2} \rlap{--} ({\rm C}_{\rm 6} {\rm H}_{\rm 4} {\rm CH} \hbox{=\hskip-2pt=} {\rm CH}_2 ){\rm Cl}({\rm II})$\end{document}, were synthesized. The monomers were readily homopolymerized in benzene with the use of AIBN or BBu3–oxygen as the initiator. Copolymerization of Ia with styrene was carried out by using AIBN. From the Cl content of the copolymers by analysis, monomer reactivity ratios and Q–e values were obtained as follows: r1 = 1.49, r2 = 0.45; Q2 = 0.41, e2 = −1.4 (M1 = styrene, M2 = Ia). Based on the above data, the σ‐bonded palladium moiety at para position of styrene acts as a strongly electron‐donating group to the phenyl ring. This is also supported by the olefinic β‐carbon chemical shift of 13C NMR for Ia.
Thermal stability of graft modifications of PVC and related materials
Authors: Abbås K. B. , Thame N. G. 
Published: April 2003

AbstractThe grafting of polyisobutylene and polybutadiene onto PVC by use of alkylaluminum compounds gives graft copolymers which are superior in thermal stability to unmodified PVC as determined by dehydrochlorination measurements at a low degree of decomposition. The alkylation of toluene with PVC also exhibits high heat stability. The improved thermal stability observed for the modified samples is ascribed to the existence of an induction period and/or lower dehydrochlorination rates. PVC grafted with polybutadiene in the absence of cobalt cocatalyst exhibits autocatalytic behavior and is less stable than the unmodified PVC.
Initiation and propagation steps in the equibinary polymerization of butadiene by bis(h3‐allylnickel trifluoroacetate)
Authors: Thomassin J. M. , Walckiers E. , Warin R. , Teyssié Ph. 
Published: April 2003

AbstractPolymerization of butadiene by bis(h3‐allylnickel trifluoroacetate) in benzene and o‐dichlorobenzene solvents yields an equibinary 1,4‐polybutadiene, containing equal amounts of cis and trans isomers. Initiation proceeds by addition of the allylic moiety of the initiator to a butadiene molecule. The rate of initiation is high enough to ensure complete consumption of the catalyst for a monomer/catalyst molar ratio of about 10 at 5°C. The propagation exhibits the characteristics of a “living” polymerization: the molecular weight is proportional to the conversion, and at the end of the reaction, the average degree of polymerization is equal to the monomer/catalyst molar ratio. Living polybutadienyl‐nickel trifluoroacetate is able to reinitiate not only butadiene polymerization but also allene polymerization. However, for high [monomer]/[catalyst] ratios, conversion‐dependent transfer reactions limit the molecular weight to 7000 in benzene and to 70,000 in bulk polymerization in the presence of small amounts of o‐dichlorobenzene.
Starch xanthate–polyethylenimine reaction mechanisms
Authors: Carr M. E. , Hofreiter B. T. , Russell C. R. 
Published: April 2003

AbstractThe chemical nature of starch xanthate (SX)–polyethylenimine (PEI) reaction products has been studied because of their effectiveness as wet‐end additives for improving strength properties of paper. Model compounds, in conjunction with ultraviolet, infrared, and chemical analyses, served to elucidate SX–PEI reaction mechanisms. Aqueous solutions of SX (degrees of substitution 0.1–0.5) were titrated with PEI at pH 5–7 (25–30°C) to form SX–PEI flocculent precipitates that were determined to be polyelectrolyte complexes. However, when solutions of SX–PEI were kept at pH 10–12, products were formed that included dithiocarbamic acid salts in major quantities, PEI thioureas, and minor quantities of O‐starch PEI thinocarbamate. Acid precipitation of these SX–PEI polymeric reaction products from their alkaline solutions, which contained residual xanthate and PEI, also yielded polyelectrolyte complexes. Model systems suggest that PEI thiuram disulfide and starch xanthide, possible products of air oxidation, could be present in minor amounts and would react rapidly with PEI to yield thioureas and thioncarbamates, respectively. Apparently, mixtures of xanthate and amine gave (1) dithiocarbamic acid salts from both xanthate groups and CS2 (decomposition from xanthate), (2) thioureas from both dithiocarbamic acid salts and thiuram disulfide, and (3) thioncarbamates, principally from xanthate as opposed to xanthide.
Poly(alkyl α‐chloroacrylates). IV. Tacticity analysis from 300 MHz proton magnetic resonance spectra
Authors: Dever G. R. , Karasz F. E. , Macknight W. J. , Lenz R. W. 
Published: April 2003

Abstract300 MHz proton magnetic resonance spectroscopy was applied to the determination of triad structures of three poly(alkyl α‐chloroacrylates) of widely varying stereoregularities. Assignments and quantitative analyses were made for all of the tetrad peaks in the backbone methylene resonance of poly(methyl α‐chloroacrylate), poly(ethyl α‐chloroacrylate), and poly(isopropyl α‐chloroacrylate). In addition the methyl singlet peaks of poly(methyl α‐chloroacrylate), the methyl triplet peaks of poly(ethyl α‐chloroacrylate) which had not been amenable previously to resolution at 220 MHz, and the methyl doublet peaks of poly(isopropyl α‐chloroacrylate) were resolved, and the triad values which were obtained from these pendant ester group resonances compared favorably with triad values calculated from experimental tetrad values. As a demonstration of the internal agreement of the triad and tetrad peaks assignments, statistical calculations of the stereochemical structures of the actic and syndiotactic polymers were generally described well or to a first approximation by random selection statistics (Bernoullian) while the stereochemical statistics of the moderately to highly isotactic polymers were consistent with a nonrandom statistical process (first‐order Markovian), as expected.
Polymérisation anionique de l'isoprène: Nature de la paire d'ions et stéréospécificité. II. Influence de la nature du solvant
Authors: Essel Alain , Salle Robert , Golé Jean , Pham Quang‐Tho 
Published: April 2003

AbstractThe present work reports some new results on the dependence between the stereospecificity of the anionic propagation of isoprene and the nature of the active centers. The stereospecificity of the propagation of macroheterobicylce separated ion pairs does not depend on the nature of the alkali counterions, and the microstructure of the polyisoprenes obtained does not differ from that of those produced by free ions. Variations in the microstructure were observed in the propagation of contact ion pairs, depending on the nature of the cation and the solvent used. These variations are likely to be related to the degree of intimacy of the contact ion pairs. There are two main factors which affect the stereospecificity of the propagations in different ways: the size of the cation and the donating power of the solvent. Finally, the external solvation of the propagation ions pairs was confirmed by the microstructure of polyisoprenes synthesized in mixed (inert + donor) solvents.
ESCA studies of polymers. VII. Shake‐up phenomena in some alkane–styrene copolymers
Authors: Clark D. T. , Dilks A. 
Published: April 2003

AbstractShake‐up satellites corresponding to π* → π transitions accompanying C1s core ionizations have been studied for polystyrene and a series of alkane–styrene copolymers. It is shown that the shake‐up intensities are additive in nature and give a direct measure of copolymer compositions.
Studies on the photooxidation mechanism of polymers. IV. Effect of ultraviolet light (2537 Å) on solid PVC particles suspended in different liquids
Authors: Rabek Jan F. , Canbäck Göran , Lucky Julia , Rånby Bengt 
Published: April 2003

AbstractThe photolysis of virgin PVC powder suspended in water, methanol, n‐hexane, aqueous NH4OH (30 wt‐%), and 0.1 wt‐% iodine in methanol and also as dry powder was studied. The mechanism of photolysis of PVC powder has been investigated by using ESR spectroscopy, conductivity titration, gel‐permeation chromatography (GPC), and absorption spectroscopy. Photolysis of PVC has been found to occur by a free‐radical mechanism. ESR spectroscopy permits a partial identification of several different types of free radicals in PVC such as alkyl, polyenyl, and peroxy radicals. An interpretation is proposed of the mechanism of formation of conjugated polyene structures, and also a new explanation of the crosslinking mechanism, in which transfer of unpaired electrons to double bonds occurs, is suggested. It has also been found that conjugated double bonds can photosensitize free‐radical formation as a result of increased ultraviolet absorption due to polyene structures.
Effect of surface swelling on diffusion in polymers. I. Infrared spectroscopy
Authors: Sefton M. V. , Merrill E. W. 
Published: April 2003

AbstractThe effect of stress transfer‐limited swelling in the surface region on the hydroxylation of styrene–butadiene–styrene block copolymers in the bulk state was investigated. Films of the copolymer were allowed to react with peracetic acid to effect epoxidation and simultaneously with acetic acid and water to cleave the epoxy rings. By infrared spectroscopy it was observed that the hydroxyl content of the films decreased with increasing film thickness and the epoxy content increased commensurately. This was attributed to the presence of a lag between the advancing diffusion fronts for the epoxide groups and for the cleavage agents. This lag increases with increasing thickness due to the presence of stress‐transfer mechanisms which act to reduce the degree of swelling in the surface region and which are more effective in thicker films. The hydroxyl content increased exponentially with time, giving rise to the observation of significant induction time before there was any infrared evidence of hydroxyl formation. This resulted from the relief of part of the compressive stress in the surface region by the reaction process, which in turn increased the permeation rate of peracid.
Synthesis of polyesters by using divalent metal salts of monohydroxyethyl phthalate: Metal‐containing polyesters from such metal salts, anhydride, and epoxide
Authors: Matsuda Hideaki 
Published: April 2003

AbstractSynthesis of metal‐containing polyesters by reactions of the divalent metal salts of monohydroxyethyl phthalate with phthalic anhydride and epoxide were investigated. It was found that the metal carboxylate groups of these metal salts catalyze the above reactions. These reactions were further studied in model reactions with the use of the Ca salt of monoethyl phthalate. Products obtained were linear metal‐containing polyesters containing ionic links in the main chain; they were yellow or slightly yellow glassy materials; yields were generally high. Molecular weights obtained by the end‐group analyses were generally low; with increase in content of the metal salts in the feed the molecular weight of the polyesters decreased. Inherent viscosities (in DMF at 30°C) of the metal‐containing polyesters were low, ranging from 0.033 to 0.052. Elemental analyses are generally in good agreement with the calculated values. Thermogravimetric analyses of the polyesters were also discussed.
Physicomechanical properties of grafted polymers obtained by radiation‐induced polymerization by radical and ionic mechanisms
Authors: Kabanov V. Ya. , Aliev R. E. , Sidorova L. P. 
Published: April 2003

AbstractThe radiation‐induced grafting of acrylonitrile, 4‐vinylpyridine, and styrene was carried out by both radical and ionic mechanisms. Grafted polymers with equal percentages of graft were obtained by the radical and ionic propagation of the grafted chains. The molecular weight of homopolymers has been determined. The thermomechanical properties of the graft polymers were investigated. The yield temperatures for the graft polymers obtained by ionic propagation of the grafted chains is higher than that of graft polymers obtained by a radical mechanism. This is attributed to the higher molecular weight of the grafted chains obtained by the radiation‐induced grafting by the ionic mechanism. The radiation‐induced grafting of polyacrylonitrile increases significantly the thermal stability of polyethylene. The differential thermal analysis shows no marked differences in properties of the polymers.
Supported catalysts for stereospecific polymerization of propylene
Authors: Chien James C. W. , Hsieh J. T. T. 
Published: April 2003

AbstractTetrabenzyltitanium (B4Ti), tribenzyltitanium chloride (B3TiCl), tetra(p‐methylbenzyl)titanium (R4Ti) and tri(p‐methylbenzyl)titanium chloride (R3TiCl) have been used as catalysts for ethylene and propylene polymerization activated by AlEt2Cl. B4Ti‐AIEt2Cl in solution polymerizes ethylene readily but its activity decays rapidly. B4Ti was also supported on Cab‐O‐Sil, Alon C, and Mg(OH)Cl. The last support was found to give catalyst with longest lifetime with a rate of polymerization, Rp = 7.0 g/hr‐mmole Ti‐atm ethylene. 14CO counting techniques gave 1.13 × 10−3 mole of propagating center per mole of B4Ti; the rate constant of propagation, kp = 540 l./mole‐sec. None of the tetravalent titanium compounds polymerize propylene in solution. However, when supported on Mg(OH)Cl, Cab‐O‐Sil, Alon C, Cab‐O‐Ti, and charcoal, they all polymerize propylene. In this work the supports were characterized by various techniques, including the paramagnetic probe method, to determine the concentration and nature of surface hydroxyls. Those factors controlling the rate and stereospecificity of propylene polymerization were investigated. The system B3TiCl–Mg(OH)Cl–AlEt2Cl is the most active with Rp = 2.89 g/hr‐mmole Ti‐atm propylene. The concentration of propagation center is 0.9 × 10−3 mole per mole of B3TiCl; kp = 32 l./mole‐sec. This catalyst gave only about 70% stereoregular polymer. Diethyl ether is found to raise stereospecificity to 100%, but there is a concommittent tenfold decrease of activity. Other interesting catalyst systems are: (π‐C5H5)TiMe3–Mg(OH)Cl–AlEt2Cl (1.56, 89.5); (π‐C5H5)TiMe2–Mg(OH)Cl–AlEt2Cl (0.075, 94.5); and (π‐C5H5)TiMe3–Alon C–Al‐Et2Cl (0.08,97.2), where the first number in the parenthesis is Rp in g/mmole Ti‐hr‐atm and the second entry corresponds to percentage yield of stereoregular polypropylene. Hafnocene and titanocene supported on Mg(OH)Cl produce only oligomers of propylene.
Quantitative estimation of trans‐1,4 and cis‐1,4 isomers in polychloroprene by high‐resolution NMR
Authors: Okada Tadashi , Ikushige Testuo 
Published: April 2003

AbstractIn the 1H‐NMR spectrum of polychloroprene dissolved in C6D6, the CH proton signal was separated into two triplet peaks. These triplet signals were assigned to the CH proton in the trans‐1,4 and cis‐1,4 isomers by measurement of 1H‐NMR spectra of 3‐chloro‐1‐butene and a mixture of trans‐ and cis‐2‐chloro‐2‐butene as model compounds for the 1,2, trans‐1,4 and cis‐1,4 isomers. In 1H‐NMR spectra (220 Mcps) of polychloroprene dissolved in C6D6, two triplet signals were separated completely from which the relative concentrations of trans‐1,4 and cis‐1,4 isomers could be obtained quantitatively.