bluuebunny/crossref_metadata_2025_split huggingface dataset:
Configurational statistics of polysaccharides. VI. Linear (1→4)‐linked galactan
Authors: Yathindra N. , Rao V. S. R. 
Published: April 2003

AbstractThe conformational energies for (1→4)‐linked α‐D‐ and β‐D‐galactans have been computed by considering nonbonded, torsional, and electrostatic interactions. The electrostatic interactions are estimated by assigning the charges to various atoms in the molecule by the method of Del Re. The characteristic ratios CN = 〈r2〉0/Nlv2 are computed for α‐D‐ and β‐D‐galactans as a function of the degree of polymerization N and the angle τ at the bridge oxygen atom. These values of characteristic ratios obtained for α‐D‐galactan are very much higher than for β‐D‐galactan, indicating that the former assumes a highly extended conformation compared to the latter. The values of characteristic ratios of both these polysaccharides show a decrease with increase in τ similar to that observed for other (1→4)‐linked polysaccharides. The calculated values of C∞ of (1→4)‐linked polysaccharides show no correlation with the number of allowed conformations but are affected both by the orientation of the interunit glycosidic bonds and the hindered potential associated with chain units. It has also been shown that the magnitude of the steric factor σ may not be used as an index of flexibility for polysaccharides which differ in type of linkage.
Mechanism of submicrocrack generation in stressed polymers
Authors: Zhurkov S. N. , Zakrevskyi V. A. , Korsukov V. E. , Kuksenko V. S. 
Published: April 2003

AbstractSubmicrocracks, free radicals, and endgroups of scissioned molecules formed in polyethylene, polypropylene, and polycaprolactam under uniaxial tension have been investigated. Measurements were carried out by small‐angle x‐ray scattering, electron paramagnetic resonance, and infrared spectroscopy. The concentration of submicrocracks is almost the same as that of free radicals but is smaller than the concentration of scissioned macromolecules by approximately three orders of magnitude. The number of scissions per crack proved to be close to the number of macromolecules passing through the cross section of a submicrocrack calculated on the assumption of close packing. It is concluded that submicrocracks in stressed polymers are formed as a result of chain reactions of macromolecular decomposition initiated by the active end primary free radicals.
Crystallization of poly(ethylene oxide) fractions: Crystallization isotherms
Authors: Beech D. R. , Booth C. , Dodgson D. V. , Hillier I. H. 
Published: April 2003

AbstractThe crystallization kinetics of a range of fractions of poly(ethylene oxide) are presented and analyzed. It is concluded that deviations from the Avrami equation with exponent of 3 are mainly due to rejection of low molecular weight molecules for the low molecular weight fractions (M̄n < 6,000) and to a process of crystal perfecting for the high molecular weight fractions (M̄n > 6,000).
Effect of solvents on the cryogenic dynamic mechanical properties of polystyrene
Authors: Morgan R. J. , Nielsen L. E. 
Published: April 2003

AbstractYoung's modulus and mechanical damping of 15 organic liquids in polystyrene have been measured from 4°K to 250°K. The concentration was generally in the range from 10 to 15%, but the polystyrene–toluene system was investigated over the range from 0 to 16%. Some liquids cause the 40°K damping peak of polystyrene to disappear, other liquids do not. Seven of the liquids which cause the disappearance of the 40°K peak give rise to new large damping peaks at the temperature expected for the secondary glass transition temperatures of the liquids, that is, at 0.77 Tg of the liquids. Some of the liquids produced large unexplained damping peaks at temperatures above the expected glass transition temperatures Tg of the liquids. It is suggested that the γ peak in polystyrene is caused by styrene monomer.
Rheological properties of poly(2,6‐dimethylphenylene oxide)—polystyrene blends
Authors: Prest W. M. , Porter Roger S. 
Published: April 2003

AbstractThe viscoelastic (VE) response of freeze‐dried blends of polystyrene (PS) and poly‐(2,6‐dimethyl phenylene oxide) (PPO) has been studied as a function of composition, frequency, and temperature to examine the degree of rheological compatibility. When blended together, the relaxation processes of both molecular species exhibit the same temperature dependence. However, the temperature dependence of the VE response is a function of composition. It is shown that this behavior can be predicted from the measured glass transition temperatures by assuming the additivity of the free volumes of the components. The properties of the blends are compared at equal free volumes. The effective segmental friction factor is found to be independent of composition while the modulus of the rubbery plateau increases with PPO concentration. This result is interpreted as a change in the entanglement molecular weight Me of the blends. When the changes in Me are considered, the relationship between the zero‐shear viscosity η0 and the 3.4 power of the weight‐average molecular weight, commonly found for high molecular weight homopolymers, predicts the compositional dependence of η0 for the PPO–PS blends. It is concluded that the PPO–PS system forms a rheologically compatible blend.
Change in infrared dichroism during and following high‐speed elongation of polyethylene
Authors: Uemura Y. , Stein R. S. 
Published: April 2003

AbstractUse of a new apparatus is described which enables infrared dichroism to be followed as a function of time following the rapid stretching of a sample. The apparatus is double beam in dichroism, in that the infrared beam is alternately polarized parallel and perpendicular to the stretching direction and the transmitted intensity is observed on an oscilloscope. Results are presented for the stretching of a low‐density polyethylene sample by approximately 28% in a time of approximately 0.1 sec. The infrared dichroism is observed to change in times of the order of 50 to 100 msec after stretching, confirming the observation made by other techniques that crystal orientation changes during this time.
Crazing of glassy polymers in alcohols and hydrocarbons
Authors: Narisawa I. 
Published: April 2003

AbstractIn the crazing of glassy amorphous polymers, wetting ability and penetration of the fluid are the important practical parameters governing the activity of the fluid. Higher molecular weight and the presence of polar groups in the fluids result in an increase in the critical stress for craze initiation in polystyrene and polycarbonate. The Eyring treatment of the craze process can describe fairly well the temperature and strain rate dependence of the critical stress. The parameters involved in the Eyring theory suggest that the crazing takes place by a molecular motion of lower energy than does macroscopic yielding.
Alternating copolymerization of isoprene and butadiene with acrylonitrile
Authors: Koma Yasuo , Iimura Kazuyoshi , Takeda Masatami 
Published: April 2003

AbstractCopolymerizations of acrylonitrile and isoprene or butadiene were carried out in the presence of a new catalytic system containing Cr(O‐tert‐Bu)4 and AlEtCl2. It was found that the copolymer compositions have a highly alternating structure, even with varying feed ratios of monomer. The nuclear magnetic resonance spectra of the copolymers obtained with this catalytic system were observed and are discussed in terms of the alternation.
Aminolysis of n‐butyl methacrylate–styrene copolymer with Di‐ and trifunctional amines
Authors: Gibson Harry W. , Bailey F. C. 
Published: April 2003

AbstractAminolysis of a random copolymer of styrene and n‐butyl methacrylate (2.54:1.00 mole ratio) with 6‐aminohexanol has been studied. Kinetics were determined by covalently dyeing the functional polymer and spectrally measuring dye content. In the presence of 1,4‐diaza[2,2,2]bicyclooctane (DABCO), an activation energy of 22.2 ± 1.0 kcal/mole was calculated from the temperature dependence of the overall rate of reaction. The rate is independent of solvent polarity. The rate at 189°C is 2.1‐fold slower than that of poly(n‐butyl methacrylate). The phenyl group of the styryl moiety inhibits the reaction, apparently via a steric effect. This aminolysis technique affords noncrosslinked (similar M̄n and M̄w) functional polymers. By a similar process an aminediol and an alcohol which contained a secondary and a primary amino group also yielded noncrosslinked functionalized polymers.
Polymerization of propadiene. III. Catalyst systems based on various rhodium (I) complexes
Authors: Scholten J. P. , van der Ploeg H. J. 
Published: April 2003

AbstractThe polymerization of propadiene to 1,2‐polyallene by various Rh(I) based catalysts is described and discussed. Also the interrelations between these Rh(I) complexes are discussed and an overall reaction scheme is given. A mechanism is put forward in which the formation of a common intermediate from propadiene and different Rh(I) complexes is the rate determining step. It is found that the activity decreases in the order: cis‐Rh(CO)2P(C6H5)3Cl > [Rh(CO)2Cl]2 > Rh(CO)3Cl. The complexes Rh[P(C6H5)3]2(CO)Cl and Rh[P(C6H5)3]3Cl proved to be inactive in the polymerization of propadiene.
Anionic polymerization of propylene oxide
Authors: Blanchard L. P. , Hornof V. , Moinard J. , Tahiani F. 
Published: April 2003

AbstractThe anionic polymerization of propylene oxide with the use of potassium tert‐butoxide and naphthalene sodium as initiator and dimethylsulfoxide, tetrahydrofuran and mixtures of both as solvent was investigated. The reactions were carried out in vacuum‐sealed dilatometers over the temperature range 20−60°C. The products were analyzed by gelpermeation chromatography and infrared spectroscopy. The object of the investigation was to obtain information on the mechanism of the reaction and elucidate some of its kinetic aspects. It is shown that the polymerization occurs by two different processes depending on the experimental conditions: one involving free ions and ion‐pairs, the other, ion‐pairs alone. In the first case, where DMSO was used as solvent, the order of the reaction with respect to the initiator is greater than unity (∼1.7), while in the second case, involving the mixture of DMSO and THF and ion‐pairs alone, the reaction order is only one. Transfer to monomer is believed to take place only in the strongly dissociating DMSO medium, where free ions are present.
Polyesters containing the norbornane structure
Authors: Wilson John C. , Hamb F. Lynn 
Published: April 2003

AbstractSeveral norbornane and norbornane condensed diesters and dimethanols have been synthesized. Varying the points of substitution in the norbornane moiety has been found to have little effect on the glass transition temperatures of polyesters prepared from these compounds. Increasing the number of norbornane residues as polymer side chains results in a linear increase in the Tg. The increase is an apparent function of the size of the norbornane moiety relative to the polymer repeating unit.
Application of mass spectrometry to the study of fluoropolymers. III. Polyperfluorobut‐2‐yne
Authors: Flowers W. T. , Haszeldine R. N. , Janik A. , Lee A. K. , Marshall P. G. , Sedgwick R. D. 
Published: April 2003

AbstractMass spectra of the volatile fractions from polyperfluorobut‐2‐yne have been obtained. The polymer appears to be thermally stable up to 300°C and molecules containing up to 12 monomer units have been identified. A regular structure is indicated by the mass spectrum which is characterized by unusually intense doubly charged ions. The endgroups are readily identified, and a conjugated polyolefin structure is indicated.
Polyorthocarbonates
Authors: Takekoshi Tohru 
Published: April 2003

AbstractHitherto unreported aromatic polyorthocarbonates have been synthesized by the reaction of dichlorodiphenoxymethane and various aromatic dihydroxy compounds.
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The polymers possess the structure of a methanetetra‐ol ether (carbonic acid orthoester) in the main chain. The direct structural evidence was obtained by 13C NMR. High molecular weight, linear polyorthocarbonates were derived from sterically unhindered bisphenols. The polymers were noncrystalline, and clear, flexible films were obtained by casting from solution. Aromatic polyorthocarbonates decomposed above 360°C under nitrogen. The polymers were extremely stable under basic conditions but were unstable in strongly acidic media, particularly at elevated temperatures.
Closed‐form solution of the finite torsion problem by use of the λ form of the strain‐energy function
Authors: Valanis K. C. 
Published: April 2003

AbstractA closed‐form solution for the stress distribution in a cylindrical elastic rod under finite torsion is given involving use of the logarithmic λ form of the strain‐energy function proposed by Valanis and Landel. Experimental torque data on natural rubber which give support to the present solution over a large range of angles of twist are shown. It is also shown how torsion data may be used to determine the λ form for deformations that lie outside the range of applicability of the logarithmic function if certain conditions apply. A solution, also in closed form, is given by using another λ form proposed by Dickie and Smith on the basis of experiments on styrene—butadiene rubber.
X‐ray measurement of cellulose crystallite orientation in cotton fibers
Authors: Seitsonen Sulo , Inkinen Pentti 
Published: April 2003

AbstractThe orientation of crystallites in a bundle of parallel cotton fibers was studied by x‐ray diffraction. The intensity distributions of the 101 and 002 diffraction rings showed the distributions of (101) and (002) planes to be identical within the limits of accuracy. Therefore, the crystallites in the cotton fibers very likely had random orientation about their long axes. The orientation distribution of these axes was calculated by using the intensity distribution of the 002 diffraction ring. The cylindrically symmetrical density distribution J(β) thus obtained was multiplied by sin β to obtain the distribution of relative numbers of crystallites at given angles β to the long axis of the fiber. The average 〈β〉 was found to be in agreement with the value of 〈sin2β〉 measured from the 002 diffraction ring. The intensity distributions on the 101 and 002 diffraction rings showed small fluctuations. These fluctuations appeared much stronger in the J(β) and sin β J(β) distributions, indicating clear discontinuities in the pitch angle distribution.
Infrared study of out‐of‐plane deformation vibrations of linear and cyclized 1,2‐ and 3,4‐polyisoprenes
Authors: Vodehnal J. , Drahorádová E. 
Published: April 2003

AbstractThis study concerns the influence of 3,4 and 1,2 addition in cyclic polyisoprenes on the extinction coefficients of the absorption bands at 890 and 910 cm−1 due to out‐of‐plane vibrations of CH2 of the isopropenyl and vinyl groups (correspoding, respectively, to 3,4 or 1,2 addition). In contrast to analogous bands characteristic of 1,4 addition (especially in the case of cis‐1,4 units of polybutadiene), the shape, position, and intensity of these bands are not influenced by changes in the structure of the macromolecular chain. The extinction coefficients of both bands did not change substantially, although the overall presence of both linear and cyclic forms varied over a wide range. It can be assumed, therefore, that the influence of configurational changes upon the intensity of the absorption bands of out‐of‐plane vibrations for double bonds is not a general phenomenon.
Annealing during polymerization of crystalline poly(ethylene terephthalate)
Authors: Miyagi Arata , Wunderlich Bernhard 
Published: April 2003

AbstractMelt‐crystallized poly(ethylene terephthalate) and etched oligomer lamellae from the same polymer have been annealed under vacuum at temperatures between 200 and 260°C and times between 3 and 48 hr. The annealed samples were analyzed through determination of viscosity‐average molecular weight, x‐ray low‐angle spacing, density, heat of fusion, and variation of melting point with heating rate. In all cases it could be shown that the crystal lamellar surfaces remained chemically reactive. Chain folds and chain ends in the surface were converted by chemical reaction to tie molecules between different crystals or different locations on the same lamella.
Influence of crystallization temperature, molecular weight, and additives on the crystallization kinetics of poly(ethylene terephthalate)
Authors: Van Antwerpen F. , Van Krevelen D. W. 
Published: April 2003

AbstractThe spherulite growth rate, the maximum spherulite radius, and the overall rate of crystallization of poly(ethylene terephthalate) (PETP) were measured by means of scattering and transmission of depolarized light. The influence of crystallization temperature, molecular weight, and additives on the above‐mentioned quantities was investigated. An expression has been derived for the spherulite growth rate of PETP as a function of crystallization temperature and the number‐average molecular weight for M̄n in the range of 19,000 to 39,000.
A model for the spherulite‐to‐fibril transformation
Authors: Robertson Richard E. 
Published: April 2003

AbstractBased on an analogy with the growth of kink bands in oriented and annealed crystalline polymers, a mechanism is suggested for the deformation‐induced spherulite‐to‐fibril transformation. Oriented and annealed material was employed as a model because it has roughly the same structure as the lamellar bundle of the spherulite. Under conditions that minimize the fibrillar quality and maximize the lamellar bundle quality, oriented and annealed crystalline polymers deform with the formation and growth of kink bands. The characteristics of kink bands are the sharpness of the kinks, occurring within zones ca. 100 Å wide, and mirror symmetry of the fibrils about the kink‐zone planes. The spherulite‐fibril transformation is suggested by analogy, then, to occur in the narrow zones that indeed are often found and to result in mirror symmetry of the chain axes about the transformation‐zone planes, which may not exactly occur because of a tendency for the tie molecules to be pulled from the lamellae during drawing. The implications for the transformation are (a) that the microfibril backbones are derived from the tie molecules between lamellae and (b) though some unfolding occurs as blocks that were adjacent within the lamellae become separated, the crystals remain mostly intact during the transformation. The analog is supported by or at least is consistent with various other results, including those from morphological and small‐ and wide‐angle x‐ray studies.
Spectrum of light scattered from polydisperse polymer solutions
Authors: Benbasat Julyet Aksiyote , Bloomfield Victor A. 
Published: April 2003

AbstractWe examine several methods for analyzing the spectrum of light scattered from polydisperse polymer solutions. General expressions are reviewed for the inelastic scattering spectra and integrated intensities due to the pure translational normal mode of motion, using both heterodyne and homodyne detection, in terms of the molecular weights, concentrations, scattering form factors, and diffusion coefficients of the individual polymeric species, These results are used to obtain general expressions for the limiting slopes and intercepts of various rearranged versions of the equation I(v) = (A/π)2/(v2 + γ2) that permit linear plotting: I(v) is the intensity of light scattered at frequency v, A is the integrated intensity, and γ is the spectral halfwidth, K2D/2π, where K is the scattering vector and D the diffusion coefficient. These results are applied to the special case of a Schulz‐Zimm distribution, neglecting form factors, to obtain explicit expressions relating the average diffusion coefficients determined by these procedures to other measurable quantities: the mean polymer radius; the diffusion coefficient of the weight‐average species; and, together with the weight‐average sedimentation coefficient, the weight‐average molecular weight. Numerical calculations for two particular cases indicate the relative merits of the various data analysis procedures. Homodyne detection gives average values that are closer to weight averages than does heterodyne detection.
Crystal orientation in a semicrystalline polymer in relation to deformation of polymer spherulites. II. Orientation distribution function of crystallites within crystal lamella as a function of lamellar orientation
Authors: Nomura Shunji , Matsuo Masaru , Kawai Hiromichi 
Published: April 2003

AbstractA model relating crystal orientation in a semicrystalline polymer to the deformation of polymer spherulites is proposed. The distribution function for orientation of crystallites within crystal lamellae is assumed to be a function of lamellar orientation. In addition to the orientation of crystal lamellae in affine fashion, several parameters are introduced to characterize the untwisting of the crystal lamellae and the four different types of orientations of the crystallites within the crystal lamellae in the undeformed and deformed states of the spherulite. The model was tested by experiments in uniaxial stretching of a low‐density polyethylene. The theoretical distributions of orientation of given reciprocal lattice vectors of the crystallites, such as the reciprocal lattice vectors of the (110) and (200) crystal planes, are compared with the results of x‐ray diffraction experiments. It was found that the most important factors in fitting the model to experimental results are: (a) the fraction of crystallites having random orientation within lamella and, in turn, representing the degree of imperfection of the lamella in the undeformed state; (b) the ease of transition of crystal orientation within lamella from b‐axis orientation parallel to the lamellar axis to two types of c‐axis orientations (type Ca and type Cr) parallel to the stretching direction; and (c) the fraction of crystallites having orientation in type Cr (unfolding mechanism) rather than type Ca (rotation mechanism).
Polarographic study of the effect of solvents on the reaction of Na amalgam with some vinyl monomers
Authors: Margel Sh. , Levy M. 
Published: April 2003

AbstractAcrylonitrile, methacrylonitrile, ethyl acrylate, anthracene, and Na+ were studied polarographically in four solvent media: diglyme, DMSO, 25% H2O in diglyme, and liquid NH3. Cathodic shifts were observed for Na+ and anodic shifts for the vinyl monomers in DMSO, H2O and NH3. The values of ΔE = (E1/2, monomer — E1/2, Na+) were used in interpretation of the solvent effects observed previously for the reaction of these monomers with Na amalgam. In diglyme ΔE is very large (0.49 V for MeAN and 0.37 V) for AN, and therefore very slow reaction takes place. In DMSO, MeAN still reacts very slowly (ΔE = 0.23 V), while AN (ΔE = 0.09 V) reacts considerably faster than in diglyme and 100 times faster than MeAN in DMSO. Liquid ammonia brings both MeAN and AN to very low ΔE (0.08 V and −0.05 V, respectively), and both reactions are very fast and yield only the hydrodimers. Water, on the other hand, has a large accelerating effect on the rate, but as it is a proton donor it yields only the reduced products.
Chlorinated polyethylene. II. Chlorine distribution on the polymer chains
Authors: Abu‐Isa Ismat A. , Myers Mark E. 
Published: April 2003

AbstractThe nature of substitution in a slurry‐phase chlorination of high‐density polyethylene was studied using NMR and IR spectroscopy. The ratios of γ (or greater) methylenes were obtained from the NMR at different chlorine levels and compared with the theoretically predicted values based on a statistical treatment for substitution polymers. The results indicted that, unlike chlorosulfonated polyethylene, chlorinated polyethylene shows a hindered‐type substitution. Molecular weight of the parent polyethylene, the degree of chlorination and the degree of residual crystallinity of the samples have no bearing on the type of substitution.