bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plastic deformation of polypropylene VII. Long period as function of temperature and rate of drawing
Authors: Baltà‐Calleja F. J. , Peterlin A. , Crist B. 
Published: April 2003

AbstractPolypropylene fibers prepared by quenching in ice‐water were drawn at 25, 80, 120, and 140°C to a draw ratio between 6 and 8 at draw rates 0.05, 0.5, 5, and 50 cm/min. The long period increases almost linearly with the draw rate for drawing at 25°C and decreases for drawing at higher temperatures. The effect in the latter cases is an annealing effect. As a consequence of the shorter exposure of the drawn fibers to the high temperature at higher draw rate, the long‐period growth proceeds for a shorter time and hence results in a smaller increase of long period. At 25°C, however, the long‐period growth is negligible. The increase of long period with draw rate is the consequence of higher adiabatic heating as calculated from the energy input during the plastic deformation which transforms the spherulitic into the fibrous structure. One concludes that the long period established during this transformation depends on the maximum temperature reached in the micronecking zone and not on the macroscopically observed temperature of the sample in the neck.
High‐pressure phase of polytetrafluoroethylene
Authors: Flack H. D. 
Published: April 2003

AbstractThe effect of hydrostatic pressure on the crystal structure of PTFE has been studied up to pressures of ca. 25 kbar by x‐ray diffraction. The experimental method uses opposed diamond anvils of small surface area as transmitters of pressure with MoKα x‐radiation propagating through these anvils. A small specimen of oriented polymer is held in place with a molybdenum gasket. Pressures are measured by change in lattice spacing of sodium chloride included with some specimens. It is found that above 4.5 kbar the PTFE changes to a high‐pressure phase in which the molecules have transformed from their normal helical arrangement to that of a planar zigzag and that the planes of the molecules all lie parallel to one another. Further changes in the diffraction pattern on increase in pressure are attributed to slip and twinning in the high‐pressure phase rather than to another phase change.
Crystallization of polyethylene at high pressure: A kinetic view
Authors: Calvert P. D. , Uhlmann D. R. 
Published: April 2003

AbstractA model for the crystallization kinetics of polymers is outlined and is used to interpret observations of the crystallization of polyethylene at high pressures. This model introduces a distinction between σe the lamellar surface energy which controls the lamellar thickness, and σe′, the surface nucleus surface energy which controls the growth rate. Differential scanning calorimetry and electron microscopy data for several polyethylenes crystallized at pressures of up to 8 kb are presented. From the dependence of lamellar thickness on the crystallization undercooling at 5 kb, it is found that σe increases markedly with pressure leading to the formation of very thick crystals at high pressures. The magnitude of the increase in σe is in agreement with σe values calculated from the dependence of melting temperatures on pressure. The nucleus surface energy σe′ is not expected to vary significantly with pressure, and estimates of growth rates of 5 kb which indicate that the growth rate does not vary significantly with pressure at constant under‐cooling confirm this. Fractionation effects and the differences in behavior between different polyethylenes are also discussed.
Polymer particle formation in suspension polymerization of vinyl chloride and vinyl acetate
Authors: Ueda Tsutomu , Takeuchi Katsuyuki , Kato Michiaki 
Published: April 2003

AbstractEquipment has been designed and assembled in such a way that direct microscopic observation of polymer particle formation in suspension polymerization of vinyl chloride and vinyl acetate is possible. The apparent mode of transformation from monomer droplets into polymer particles has thus been studied under two sets of conditions: (1) with agitation and (2) without agitation. In both cases, as the initial vinyl acetate/vinyl chloride ratio was raised, the apparent change in the shape and transparency of particles occurring during the course of polymerization became less evident. In vinyl chloride homopolymerization and vinyl acetate–vinyl chloride copolymerization with relatively high vinyl chloride concentrations, the polymer particles burst during the course of polymerization. Some factors which affect the change in the size of particles are also discussed.
Long branching in poly(vinyl acetate) and poly(vinyl alcohol). IV. Polymerization of vinyl trimethylacetate in the presence of crosslinked poly(vinyl acetate)
Authors: Nozakura Shun‐Ichi , Morishima Yotaro , Murahashi Shunsuke 
Published: April 2003

AbstractIn order to clarify the grafting behavior of vinyl trimethylacetate (VTMAc) onto poly‐(vinyl acetate) (PVAc), the polymerization of a radioactive VTMAc in the presence of a crosslinked PVAc gel was studied in accordance with the experimental technique described in the previous papers. It was found that, at 60°C, the grafting onto the main chain of PVAc takes place about 2.8 times as readily as that onto the acetyl side group on PVAc.
Base cleavage of epichlorohydrin polymers
Authors: Vandenberg E. J. 
Published: April 2003

AbstractEpichlorohydrin polymers cleave much more readily with organolithium compounds than do other poly(alkylene oxides). In dilute toluene solution (1–2%) at −78°C, the cleavage of polyepichlorohydrin occurs as rapidly as BuLi is added. The end‐groups formed are about equimolar amounts of hydroxyl and carbonyl with small amounts of acetylene ends. This same cleavage reaction but without acetylene ends can be obtained with NaOH or NaOCH3 in dimethyl sulfoxide at 65°C. The carbonyl groups can be reduced with LiAlH4 in tetrahydrofuran to give hydroxyl‐ended polymers. A mechanism is presented for this unusual cleavage reaction.
Complexation du chlorure de vinyle par le tetrahydrofuranne et le n‐butyraldéhyde: Étude par résonance magnétique nucléaire haute résolution
Authors: Tho Pham Quang , Taieb Maurice 
Published: April 2003

AbstractExamination of the HR‐NMR spectra of vinyl chloride in the presence of tetrahydrofuran and n‐butyraldehyde suggests the formation of donor‐acceptor type complexes. The equilibrium quotients and NMR constants were estimated by using the Benesi‐Hildebrand method. The existence of these complexes would explain the anomalies observed: first, in the anionic polymerization of vinyl chloride initiated by tert‐butylmagnesium chloride is tetrahydrofuran. The initiation step seems to be governed by this complexation phenomenon; second, in the radical polymerization of the same monomer in n‐butylaldehyde the obtained poly(vinyl chloride) is more syndiotactic than the radical polymer prepared in bulk by the usual methods.
Kinetic study of amination of chloromethylated polystyrene with hydroxyalkylic tertiary amines
Authors: Drăgan Stela , Petrariu I. , Dima M. 
Published: April 2003

AbstractThe kinetics of the amination of chloromethylated polystyrene with two hydroxyalkylic tertiary amines (1‐dimethyl‐amino‐3‐propanol and 1‐dimethylamino‐2‐propanol) in dimethylacetamide and dioxane was studied. The amination of benzyl chloride with the two amines in dimethylacetamide was followed. It was found that the amination of chloromethylated polystyrene is a two‐step reaction taking place with different rates. The rate constants k1 and k2 were calculated for the two stages, and a self‐accelerating effect of the reaction was noticed. Also, the influence of the position of the hydroxyl group versus the tertiary nitrogen was investigated. The increase of the dielectric constant of the solvent favorably influences the reaction rate.
Copolyesters of glycols and bisphenols: A new preparative process
Authors: Hamb F. Lynn 
Published: April 2003

AbstractA new process for the preparation of copolyesters of glycols and bisphenols is described. Employing a preformed polyester, an acid, and a bisphenol diacetate, the procedure is useful for a variety of copolyesters. It is illustrated with the preparation of copolyterephthalates of ethylene glycol and 4,4′‐isopropylidenediphenol. The reaction is proposed to proceed by an initial cleavage of the polyester, followed by polymerization of the acid‐ and acetate‐terminated products. Intermediate heterogeneous structures then equilibrate.
Production of organometallic polymers by the interfacial technique. XXVII. Reaction variables in the synthesis of poly[oxy(dicyclopentadienylzirconium)oxycarbonylferrocenylcarbonyl]
Authors: Carraher Charles E. , Reimer James T. 
Published: April 2003

AbstractThe synthesis of poly[oxy(dicyclopentadienylzirconium)oxycarbonylferrocenylcarbonyl] was studied as a function of several reaction variables. Yield varied greatly with pH, reaching a maximum around pH = 7.5; yield was greater for systems employing a saturated aqueous solution of the disodium 1,1′‐ferrocene dicarboxylate falling rapidly to a plateau; yield attained a maximum as the aqueous volume was varied but decreases throughout the range studied as the volume of CHCl3 increases; a plateau in yield was reached at around a stirring rate of 20,700 rpm. For more dilute solutions (6.7 × 10−3M) yield is dependent on the concentration of both reactants and seeks a maximum around a stirring time of 30 sec.
Polymerization of β‐carbomethoxypropionaldehyde
Authors: Sumitomo Hiroshi , Kobayashi Kazukiyo , Saji Toshihiro 
Published: April 2003

AbstractHigh molecular weight crystalline poly(carbomethoxyethyl)oxymethylene was prepared from β‐carbomethoxypropionaldehyde with the use of organometallic compounds. The characterization, fractionation, x‐ray analysis, and viscosity measurement were carried out. Degradation by hydrochloric acid gave a highly crystalline but soluble polymer of a lower molecular weight. It was interesting to note the high solubility character of the polymer in organic solvents in contrast to the poor solubility of the isomeric poly(acetoxyethyl)oxymethylene. From the relationship among the intrinsic viscosity, Huggins' constant, and the solubility parameter of solvent, the solubility parameter of the polymer was determined to be 9.3 (cal/ml)1/2.
Dielectric relaxation of acrylonitrile–butadiene copolymers
Authors: Ikada Eiji , Watanabe Teizo 
Published: April 2003

AbstractDielectric constants and losses of four kinds of acrylonitrile–butadiene copolymers of different degrees of polymerization were measured in the glass–rubber transition region. Curves of the dielectric losses against frequency showed asymmetric loss curves as often seen in α‐relaxations of polar polymers. The loci of Cole‐Cole plots of the complex dielectric constants of these copolymers fitted well the loci of Havriliak‐Negami's equation,

The distribution parameters (1 − α) and β of the relaxation times were calculated. It is suggested that the mechanism of relaxation of the long chains is governed by a cooperative mechanism consisting of two concurrent motions: the first motion is the segmental relaxation of the polar chains, and the second is the induced motion of the neighboring segments successive to the first one.
Application of mass spectrometry to the study of fluoropolymers. II. The copolymer from trifluoronitrosomethane (CF3NO) and tetrafluoroethylene (C2F4)
Authors: Flowers W. T. , Haszeldine R. N. , Henderson E. , Lee A. K. , Sedgwick R. D. 
Published: April 2003

AbstractThe techniques of mass spectrometry have been applied to the copolymer from tri‐fluoronitrosomethane (CF3NO) and tetrafluoroethylene (C2F4). The copolymer yields spectra of a repetitive nature, typical of the repeating units in the polymer chain. Molecules with masses up to m/e 6400 can be distilled from the unfractionated polymer which is stable up to 220°C. Interpretation of the mass spectrum suggests a linear structure for the regular polymer.
Block copolymer formation from copolymers of phenylvinylene carbonate
Authors: Mulvaney J. E. , Sasaki Y. 
Published: April 2003

AbstractCopolymers of phenylvinylene carbonate with styrene and p‐chlorostyrene are readily prepared with radical initiators. The carbonate portion of the copolymers has been hydrolyzed to a 1,2‐glycol which was then oxididatively cleaved with periodate–perman‐ganate to produce a polymer with carboxyl and keto endgroups. Block copolymers were then prepared by conversion of the carboxyl groups to an acid chloride, followed by coupling with diols or a diamine.
Preparation and polymerization of methylenecyclobutene and 1‐methyl‐3‐methylenecyclobutene
Authors: Wu Chester C. , Lenz Robert W. 
Published: April 2003

AbstractMethylenecyclobutene (MCB) and 1‐methyl‐3‐methylenecyclobutene (MMCB) were synthesized, characterized, and polymerized by anionic and cationic initiators. Structural analyses of the polymers were carried out by infrared and NMR spectros‐copy. The cationic polymerization of MCB appeared to proceed entirely by a 1,5‐propagation mechanism to form low molecular weight polymers in low yields. Anionic polymerization of this monomer, on the other hand, proceeded primarily through a 1,2‐propagation path, again forming only low molecular weight polymeric products in low yield. In contrast to MCB, the methyl‐substituted monomer, MMCB, polymerized readily with cationic initiators to produce unusually high molecular weight polymers in high conversions. On the basis of both infrared and NMR spectroscopic analyses, it was concluded that the polymers also contained essentially only 1,5‐addition repeating units. Anionic initiators such as n‐BuLi were unable to induce polymerization of this monomer, but polymerization by Ziegler‐Natta catalysts proceeded readily to yield polymers virtually identical in structure and molecular weight to those obtained with cationic initiators.
Asymmetric interaction of optically active polymers with asymmetric small molecules. IV. Effect of hydrophobic groups on asymmetric interaction
Authors: Ihara Y. , Nakano H. , Koga J. , Kuroki N. 
Published: April 2003

AbstractIn order to investigate the mechanism of the asymmetric interaction between optically active polymers and small molecules, optically active copolymers of N‐acrylyl L‐amino acids(N‐acrylyl‐L‐phenylalanine, N‐acrylyl‐L‐tryptophan, and N‐acrylyl‐L‐leucine, respectively) and N,N′‐hexamethylene diacrylylamide were synthesized, and interaction of these polymers with the optical isomers of phenylalanine and tryptophan was investigated. In the interaction of these acidic polymers with amino acids performed at pH 5.0, significant difference in amount of adsorption between the D and L isomers of amino acids were observed, and the L form of amino acids was adsorbed preferentially. The interaction between optically active small molecules was also investigated: these results showed a similarity to the results for interaction between optically active polymers and amino acids. In some instances of asymmetric interaction the influence of hydrophobic interaction between a polymer and substrate was clearly perceived. The stereoselective effects on the asymmetric interaction are discussed.
Statistical nonstationarity of the composition of styrene with methyl methacrylate in the cooligomer
Authors: Tsuchida Eishun , Mishima Kunio , Kitamura Kiwamu , Shinohara Isao 
Published: April 2003

AbstractIt was found that the composition of cooligomer produced in the styrene(A)–methyl methacrylate(B)–CCl4(S) system deviates from the statistical steady‐state composition predicted from the Mayo‐Lewis equation on the low molecular weight side when the molar ratio of [A]/[B] is large. When the molar ratio of [A]/[B] is small, however, it is not obvious whether or not this phenomenon is observed, because the cooligomer of low molecular weight cannot be obtained easily since the chain transfer constant of the poly(methyl methacrylate) radical to CCl4 is very small in comparison, with that of the polystyryl radical. This behavior is shown to be attributable mainly to the preferential consumption of styrene monomer in the initiation step, based on the structure of the cooligomer, as inferred from the mechanism of the initiation, transfer, and termination, and the stochastic approach in which the cooligomerization process is regarded as a Markov process.
Polymerizations with homogeneous chromium catalysts
Authors: Zuech E. A 
Published: April 2003

AbstractHomogeneous catalysts derived from chromium complexes and organo‐aluminum compounds have been discovered which effect the polymerization of ethylene and the oligomerization of simple olefins. The applicable chromium derivatives are halide complexes of the type CrX2L2, CrX2L2(NO)2, CrX3L3, and [CrX3L2]2, wherein the ligands L are pyridine, tri‐n‐butylphosphine, and the like. The nature of the systems with regard to polymerization or oligomerization has been demonstrated to be primarily a function of the organoaluminum halide cocatalyst and of the reaction conditions. In general, systems containing ethylaluminum dichloride cocatalyst afford simple oligomerization products at reaction temperatures above 50°C, while at lower temperatures those containing organoaluminums of the type R3Al2X3 or R2AlX effect the polymerization of ethylene as the principal reaction.
Phonon green's function for polymer chains. I. Treatment of conformational defects
Authors: Hölzl Klaus , Schmid Christhard 
Published: April 2003

AbstractIt is shown that the Green's function (GF) method of Lifshitz can be applied to conformational defects in polymers by taking correctly into account the actual geometrical configuration of the molecules. In contrast with methods currently in use in polymer dynamics, this method is not restricted to the calculation of the density of states, allows the treatment of infinitely long chains, and provides a direct assignment of typical frequencies to certain defect types. Furthermore, arbitrary frequency accuracy can be obtained with computer time drastically reduced from that required by other methods. A short review is given of the computation of experimental quantities which are related to phonons (in harmonic approximation, but in the presence of defects) and which can be obtained from the GF. Expressions are derived for the matrix elements of the harmonic GF of zigzag chains, valid for a general force field. The symmetry of the defects is taken advantages of by introducing symmetry coordinates.
Phonon green's function for polymer chains. II. a semianalytical method for the exact computation of the green's function for regular polymers
Authors: Schmid Christhard , Hölzl Klaus 
Published: April 2003

AbstractAn exact method is presented for calculating the density of states and any complex matrix element of the harmonic phonon Green's function of single polymer chains of infinite length. The method takes advantage of the one dimensionality of the Brillouin zone. In comparison to the standard root sampling method, the method presented here has all the advantages of a fully analytic procedure (in particular, smooth curves instead of histograms) and offers and enormous increase in accuracy while at the same time drastically decreasing the computer time. For illustrational purposes, the method is applied to the defect model of Opaskar and Krimm and to the diatomic linear chain. In addition to the reproduction of the results obtained by Opaskar and Krimm, explicit expressions for the resonance and localized modes are derived.
Crystallization during polymerization of poly‐p‐xylylene
Authors: Kubo Shigeo , Wunderlich Bernhard 
Published: April 2003

AbstractCrystallization during polymerization of p‐xylylene from the gas phase has been studied between 200 and −196°C. From room temperature to −17°C the polymer crystal morphology changes in that the crystallinity decreases. In this range the process is thought to be of the successive polymerization and crystallization type. The morphology is in agreement with this mechanism, of the folded‐chain β‐polymorph type with proper epitactic orientation of the chains with respect to the support surface. At −78°C an intermediate, poorly crystallized polymer results. At 196°C the reaction is most likely of the simultaneous polymerization and crystallization type. The morphology is, in agreement with the changed mechanism, of a metastable, irregularly folded β‐polymorph type with no orientation of the chains relative to the support surface. No significant changes in molecular weight were observed in the polymers produced between 26 and −196°C.
Kinetics of strain‐induced crystallization of a trans‐polypentenamer
Authors: Kraus Gerard , Gruver J. T. 
Published: April 2003

AbstractThe kinetics of the strain‐induced crystallization of a crosslinked 89% trans‐polypentenamer was studied as a function of temperature and strain by using a combined birefringence—stress relaxation technique. The crystallization rate was found to be extremely sensitive to both variables and was, within experimental error, a function of the degree of undercooling alone, the increase in crystallization rate with strain being a direct consequence of the melting point elevation. From the isothermal, isometric crystallization rates, the development of crystallinity in constant‐rate‐of‐strain experiments was calculated and related to characteristics of the stress‐‐strain curve and of the temperature‐strain rate dependence of tensile strength. These calculations allow one to estimate under what conditions sufficient crystallinity may be expected for the attainment of high strength in absence of reinforcing fillers. Crystallinities measured in this work were of the order of 10% or less. A limited x‐ray diffraction study confirmed the low order of crystallinity indicated by the stress‐birefringence measurements. The relatively high precision of the latter makes this technique attractive for the estimation of small straininduced crystallinities in rubbers.
Determination of the coefficients of selective sorption in polymer solutions in multicomponent solvents from density increments
Authors: Kratochvíl Pavel , Pouchlý Julius , Sedláček Blahoslav 
Published: April 2003

AbstractThe density increment method has been used to measure the selective sorption coefficient of 2,2,3,3‐tetrafluoropropanol (TFP) onto poly(methyl methacrylate) from the solvent mixture benzene‐TFP (80:20 by volume). The results are in good agreement with the data obtained by the established refractive index increment method. The density increment method seems to be a promising tool for the characterization of polymer solutions in multicomponent solvents.
Conformations of branched poly(α‐amino acids) in solution and at the air—water interface
Authors: Williot J. P. , Ruysschaert J. M. , Jaffé J. 
Published: April 2003

AbstractThe validity of Silberberg's hypothesis concerning the conformation of branched polypeptides was tested by studies on solutions and on monolayers. The poly(α‐amino acids) investigated consisted of poly‐L‐lysine backbones with side chains of poly(gamma;‐benzyl L‐gutamate) and poly(β‐benzyl L‐aspartate). In solution, the conformation was studied in the mixed solvent chloroform–dichloroacetic acid. Optical rotatory dispersion measurements demonstrated the existence of a helix–coil transition which is a function of the length of the side chain. A significant “transition curve” appeared between 9 and 15 residues. From the results, it may be assumed that the poly‐L‐lysine backbone is extended in a coiled conformation and the side chains are coiled or helical, depending on the number of glutamate residues. At the air–water interface, a discontinuity in the surface‐pressure curve appears between 9 and 15 residues per side chain. The similarity with the results obtained in solution appears significant; however, this has to be confirmed with methods more specific for structural modifications.