bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymerization of alkylene oxides by dialkylzinc–lewis base systems
Authors: Furukawa Junji , Kawabata Nariyoshi , Kato Akira 
Published: April 2003

AbstractDialkylzinc–Lewis base systems are found to be active catalysts for the polymerization of alkylene oxides. The diethylzinc–dimethyl sulfoxide system is especially effective in the preparation of high polymers of ethylene oxide and propylene oxide. Diethylzine does not react with dimethyl sulfoxide, but there is strong association between the compounds. The proton magnetic resonance spectrum of a poly(ethylene oxide) prepared by the catalyst system suggests that the n‐butoxyl group is attached to the end of the polymer chain. Polymerization of ethylene oxide seems to be initiated by the ethyl–zinc bond. The active species of the system seems to be diethylzinc coordinated with dimethyl sulfoxide. The efficiency of the catalyst system for the formation of high molecular weight polymer is 10−1−10−2. The other part of the catalyst is responsible for the formation of low polymers.
Persulfate‐initiated polymerization of acrylamide
Authors: Riggs J. P. , Rodriguez F. 
Published: April 2003

AbstractA dilatometric technique was used to obtain conversion–time data for the polymerization of acrylamide initiated by potassium persulfate in water. The results are summarized by the empirical rate expression, −d[M1]/dt = Rp = k1.25[K2S2O8]0.5[M1]1.25, and k1.25 = 1.70 × 1011 exp {−16,900/RT} 1.0.75/mole−0.75‐min. Persulfate was varied over the range 9.5 × 10−4 to 5.2 × 10×2 mole/l., and initial monomer concentration [M1] was varied from 0.05 to 0.4 mole/l. The temperature range was 30−50°C. Results of analysis of the kinetics and energetics of the polymerization favor a cage‐effect theory rather than a complex‐formation theory to explain the order with respect to monomer.
Studies of micro‐brownian motion of a polymer chain by the fluorescence polarization method. I. Fluorescent conjugates of polyacrylamide
Authors: Nishijima Yasunori , Teramoto Akio , Yamamoto Mashide , Hiratsuka Shozaburo 
Published: April 2003

AbstractPolyacrylamide having a fluorescent residue at the chain end was prepared by polymerization of acrylamide in the presence of a fluorescent dye. The segmental motion of the chain end in dilute solution was studied by the fluorescence polarization method on the fluorescent polyacrylamide conjugates thus obtained. The linear relation between 1/p and T/η0 held for every sample studied in aqueous media, where p is the degree of polarization of the fluorescence, T is the absolute temperature, and η0 is the viscosity of the medium. The mean relaxation time 〈ρ〉 of the conjugate was evaluated from these data as a function of the molecular weight of the conjugate. The value of 〈ρ〉 increased slightly with molecular weight, varying from 3.3 × 10−9 to 7 × 10−9 sec. The absolute values of 〈ρ〉 and its molecular weight dependence suggest that 〈ρ〉 represents the mean rotational relaxation time for the cooperative motion of about ten monomeric units at the chain end. The effect of the mean extension of polymer chain on the segmental motion was found to be negligible.
Studies of micro‐brownian motion of a polymer chain by the fluorescence polarization method. II. Segmental motions in concentrated polymer solutions
Authors: Teramoto Akio , Hiratsuka Shozaburo , Nishijima Yasunori 
Published: April 2003

AbstractThe fluorescence polarization method has been used to study the micro‐Brownian motion of a terminal segement of a polymer chain in concentrated solutions. A new apparatus for determining the fluorescence intensity and its polarization degree was designed. By using this apparatus, the rotational relaxation time 〈ρ〉 of the terminal segment of the fluorescent conjugates of polyacrylamide in aqueous polyacrylamide solutions was obtained as a function of polymer concentration from 0 to 65%, molecular weight of the conjugate from 3.5 × 104 to 3 × 105, and temperature from 10 to 30°C. The logarithm of 〈ρ〉 increased approximately linearly with increasing polymer concentration. This increase in 〈ρ〉, amounting to a factor of 20 times, was less marked than that in macroscopic viscosity. At concentrations less than 30%, 〈ρ〉 depended appreciably on the molecular weight of the conjugate.
Structural studies of polyethers. IV. Structure analysis of the polyoxymethylene molecule by three‐dimensional fourier syntheses
Authors: Uchida Toshio , Tadokoro Hiroyuki 
Published: April 2003

AbstractDetailed structure analysis of the polyoxymethylene molecule was carried out by the method of three‐dimensional Fourier synthesis. The diffraction data were measured on a highly ordered polyoxymethylene sample prepared from a single crystal of tetraoxane by solid‐state radiation polymerization. By assuming the anisotropic thermal factors for the oxygen and carbon atoms and taking into account the contribution of the hydrogen atoms, good agreement between the observed and calculated structure factors was obtained; the R factor is 8.8%. The distance between the oxygen atom and the helix axis r(O) = 0.671 A. is slightly shorter than r(C) = 0.691 A. The bond distance CO = 1.421 A., the angle ∠COC = 112°24′, and ∠OCO = 110°49′. All the internal rotation angles of the skeletal bonds are 78°13′. It is deduced from the experimental results that each crystallite of polyoxymethylene is composed of only one type of helix, right‐handed or left‐handed.
On the predictability of the high‐frequency elastic modulus of semicrystalline polymers as function of crystallinity
Authors: Bondi A. 
Published: April 2003

AbstractThe relation of the high‐frequency elastic moduli of semicrystalline polymers to volume fraction crystallinity is correctly described by the Hashin‐Shtrikman theory, without any disposable constants, as a function of the ratio of the modulus of the amorphous to that of the crystalline phase. Hence the (high‐frequency) reduced modulus of semicrystalline polymers is largely a function of the temperature T/Tg. The importance of T/Tm for the modulus of the crystalline phase precludes the existence of a single universal reduced modulus versus temperature curve.
Crystallization of poly(tetramethyl‐p‐silphenylene)‐siloxane (TMPS) polymers. Part II
Authors: Magill J. H. 
Published: April 2003

AbstractThe crystallization kinetics and morphology of poly(tetramethyl‐p‐silphenylene)siloxane spherulites have been investigated over a temperature range of 25–130°C. The effect of molecular weight on the spherulitic growth rates, ranging from the monomer to molecular weights about 106, is discussed in terms of conventional rate theory. Surface free energies of crystal growth are computed on the basis of a spherulitic model in which the polymer chains are presumed to be incorporated within the lamellar crystallites which are comprised in the spherulites. Mention is made of the change in mechanical properties with molecular weight.
Radiation‐induced catalytic polymerization. I. Theory
Authors: Temkin A. Ya. 
Published: April 2003

AbstractThe kinetics of radiation polymerization on a solid catalyst is discussed, under the condition that only linear termination of the chain takes place. All the kinetic equations are balance equations of particles of each type adsorbed by unit mass of the catalyst, and this makes it possible to account for the effect on the kinetics of the time dependence of the magnitude of the part of its surface on which the reactions we are considering may take place. Integro‐differential equations are used for calculating the molecular weight distribution of the resulting polymer; this ensures higher accuracy of the formulas obtained than when differential equations are used and makes it possible to eliminate a number of limitations generally involved in the transition to differential equations. An expression has been found for the molecular weight distribution of the polymer product which allows for the possibility of radiation‐induced catalytic polymerization on the resulting adsorbed polymer. Expressions have been derived for the average molecular weight and yield (weight and molecular) of the polymer formed. Asymptotic formulas have been obtained (for large irradiation times) for all the above values. The conclusions that can be drawn concerning the mechanism of the process based on a comparison of the formulas obtained with kinetic curves plotted from experimental data are given. It is shown how such a comparison can be utilized for calculating the rate constants for polymerization and chain termination reactions.
Wideline NMR studies of polyacrylonitrile
Authors: McMahon P. E. 
Published: April 2003

AbstractNMR linewidth studies of molecular motion in several polyacrylonitrile samples have been carried out. The motional transition temperature is found in the 105–124°C. range and depends upon polymerization conditions. In addition, the thermal activation energy for the motional process underlying this transition was evaluated at 16.4 kcal./mole. Finally, measurement of the transition temperature for one of the specimens in three different physical states (bulk, spun only, and spun and drawn with a ratio of 3:1), revealed that no change in the transition temperature was effected by either spinning or drawing.
Infrared technique for the measurement of structural changes during the orientation process in polymers
Authors: Koenig J. L. , Cornell S. W. , Witenhafer D. E. 
Published: April 2003

AbstractPolarized infrared measurements were made on polymer samples to obtain the structural changes occurring during the orientation process. The absorbances of the infrared bands were measured by determining the three components of the absorbance. Two components were obtained directly with plane‐polarized light while the third is obtained by tilting the sample and extrapolating. Corrections were made for machine optics polarization, sample birefringence, polarizer inefficiency, anisotropy of the index of refraction, and scattering from the film surface. Data are reported for polyethylene obtained from cold‐drawn specimens as a function of draw temperature. Polyethylene exhibits no strain‐induced crystallization as a result of the chain‐alignment process. Annealing of the drawn samples reperfects the distorted crystals.
Effect of polydispersity on liquid–liquid phase equilibrium
Authors: Baysal B. M. , Stockmayer W. H. 
Published: April 2003

AbstractThe effect of polydispersity on liquid–liquid phase equilibrium in systems containing polymer, solvent, and nonsolvent is investigated numerically in the Flory‐Huggins approximation for several special cases. The resulting phase diagrams indicate that, except in the immediate vicinity of the critical region, the degree of swelling of a polymer precipitate phase with a given number‐average molecular weight is essentially independent of polydispersity.
Gel permeation chromatography of branched polyethylene
Authors: Salovey R. , Hellman M. Y. 
Published: April 2003

AbstractThe effect of long‐chain branching must be considered in gel permeation chromatography to evaluate the molecular weight polydispersity of branched polyethylenes. Osmotic molecular weights of fractions of branched polyethylene were correlated with elution volumes; weight‐average and number‐average molecular weights of a branched polyethylene were determined. Molecular weight changes on crosslinking polyethylene by ionizing radiation are accompanied by branching and cannot be simply interpreted by gel permeation chromatography.
Intrinsic viscosity of polydisperse branched polymers
Authors: Graessley William W. , Mittelhauser Henry M. 
Published: April 2003

AbstractThe relationships between molecular weight distribution and structure in polymerizations with long‐chain branching were reviewed and extended. Results were applied to an experimental examination of intrinsic viscosity in polydisperse, trifunctionally branched systems. Several samples of poly(vinyl acetate) were prepared by bulk polymerization under conditions of very low radical concentration. The relative rate constants for monomer transfer, polymer transfer, and terminal double‐bond polymerization were established from the variation of Mn and Mw with the extent of conversion. Average branching densities were then calculated for each sample and ranged as high as 1.5 branch points/molecule. Intrinsic viscosities [η]B were measured in three systems: a theta‐solvent, a good solvent, and one that was intermediate in solvent interaction. These results were compared with calculated viscosities, [η]L, which would have been observed if all the molecules had been linear. The values of [η]B/[η]L were substantially the same in all three solvents. The variation of this ratio with branching density was compared with the theory of Zimm and Kilb as adapted to polydisperse systems. Discrepancies were noted, and the adequacy of present model distribution functions for branched polymers was questioned.
Experimental anomalies and the conformational theory of polymers
Authors: Majerus John N. 
Published: April 2003

AbstractThe influence of the size and shape of the torsional potential upon the theoretical temperature coefficient (T∂ ln 〈r02〉/∂T) of a polymeric chain was studied. The uncorrelated end‐to‐end distance equations for isotactic, syndiotactic, and completely atactic chains were differentiated with respect to temperature and the integrals in the resulting equations were evaluated by the method of Gaussian quadrature. The calculated coefficients were found to be nonlinear functions of the energy ratio Umax/KT, where Umax is the maximum potential barrier and possess real roots which critically depend upon the size and shape of the potential. Qualitative anomalies between experiment and theory disappeared when the entire torsional potential was used in the conformational theory. It appears that quantitative agreement between theory and experiment can be established for polymeric materials if the entire potential is used, rotations within bulky side groups are included, and the potential is determined by the method of minimum conformational energy.
Gel permeation chromatography: On the shape of the calibration plot and molecular size separability
Authors: Osterhoudt H. W. , Ray L. N. 
Published: April 2003

AbstractData obtained from the calibration of GPC columns of different permeabilities with standard polystyrenes are reported. For single columns the logarithm molecular weight–elution volume plot is linear for approximately one and one‐half decades in molecular weight. GPC separations are such that the separability of two samples of similar molecular weight improves as their mean molecular weight decreases. Because of this the analysis of high molecular weight polymers can best be accomplished on a series of columns in which each column has a high permeability limit. The elution volume for columns in series is shown to be the sum of the elution volumes of the individual columns. As higher molecular weights are eluted a pronounced tailing effect is observed.
Some optical and mechanical properties of poly(vinyl chloride)
Authors: Utsuo A. , Stein R. S. 
Published: April 2003

AbstractThe optical and mechanical properties of poly(vinyl chloride) film were examined by observing both the stress and birefringence during stretching at constant rate, during relaxation at constant length and during a dynamic birefringence experiment. Experiments were also done by varying the temperature at constant length. The changes in birefringence are interpreted in terms of changes in negative distortional birefringence, changes in positive orientation birefringence, and possible reversible changes in birefringence with temperature arising from conformational changes in the polymer chain and changes in the contribution of birefringent crystals.
Morphology of polypropylene crystals. II. Twinning of lamellar crystals
Authors: Kojima Morio 
Published: April 2003

AbstractTwinned crystals were obtained from fractionated isotactic polypropylene of M̄w = 600,000 by isothermal crystallization at 130°C. for 20 hr. from dilute α‐chloronaphthalene solution (0.005 wt.‐%). Electron microscopic observations confirm that the molecular chains of polypropylene lamellar crystals extend along the [100] direction while the folding itself occurs within the (010) planes in the monoclinic crystal form. On this basis it is shown that polypropylene forms twinned crystals in which the composition plane is the (1k0) planes. It can be deduced that the formation of twin nucleus occurs before twinning, and then growth occurs from the neighboring region of the crystal boundary by chain folding along the [100] direction.
Diffusion theory of the post‐irradiation oxidation of polyethylene
Authors: Böhm Georg G. A. 
Published: April 2003

AbstractThe primary reaction of oxygen with irradiated polyethylene has been followed by observing the rapid disappearance of the ultraviolet absorption bands at 258 and 285 mμ, bands attributed to the allyl and dienyl free radicals. A mathematical theory based on diffusion equations has been developed by means of which a quantitative estimate of the total initial free‐radical concentration can be made. From the shape of the free‐radical decay curve it can be concluded that the initial oxygen–free‐radical reactions occur about three times as frequently in the amorphous regions as in the crystalline.
Selective polymeric effects on solvent NMR relaxations
Authors: Liu Kang‐Jen 
Published: April 2003

AbstractMeasurements of the spin‐lattice relaxation times (T1) of solvent protons have been performed on systems containing mixed solvents with and without polymer. It has been found that the motion of solvent is selectively affected by polymers present in the system. Polyisobutylene (10%) in mixed solvents of carbon tetrachloride (or cyclohexane) and dichloromethane at various proportions produces little effect on T1 values of dichloromethane, but it affects significantly the T1 values of cyclohexane; whereas poly(methyl methacrylate) (10%) in carbon tetrachloride and dichloromethane (or acetone) selectively associates with dichloromethane (or acetone), resulting in an approximate 50% reduction of the T1 values for dichloromethane (or acetone). In systems of poly(methyl methacrylate) and three mixed solvents of carbon tetrachloride, dichloromethane, and cyclohexane, the polymer (10%) has a negligible effect on the T1 values of cyclohexane, but brings about a 50% reduction of the T1 values of dichloromethane. These phenomena are discussed in terms of local selective interactions between the solvent molecules and the polymeric chain segments.
Influence of stereoregularity on binding of counterions by poly(methacrylic acid)
Authors: Costantino L. , Crescenzi V. , Quadrifoglio F. , Vitagliano V. 
Published: April 2003

AbstractThe activity coefficient γ, of sodium ion, in aqueous solutions of both isotactic and conventional poly(methacrylic acid) (PMA) has been studies throughout the whole range of degree of neutralization α with a Beckman Na electrode and membrane electrodes. The results show that the fraction of sodium ions bound to isotactic PMA is higher than that bound to conventional (or syndiotactic) PMA over the entire range of α. The binding of divalent counterions (Mg+2, Cu+2, Co+2, and Ni+2) by the two forms of PMA (at α = 0.95) has been evaluated from the release of Na+ ions with the Beckman Na electrode. Turbidimetric determinations of the critical amount of various divalent cation chlorides necessary to bring about precipitation of both isotactic and conventional PMA (at α = 0.95) have also been carried out.
Measurement of concentration gradients in swelling crosslinked polymer beads
Authors: Gurnee Edward F. 
Published: April 2003

AbstractThe concentration of solvent in the gel phase of a swelling polystyrene–divinylbenzene copolymer bead has been measured as a function of the radius by optical interference techniques. It is found that an appreciable gradient exists even shortly after the core disappears. Results are presented for two cases: a very lightly crosslinked bead that exhibits negligible birefringence while swelling, and a more tightly crosslinked network in which the birefringence must be considered. It is also found that the refractive index of the unswollen bead is considerably less than that found by extrapolation from the swollen state; this effect is reasonable when the “free volume” in the bulk polymer is considered.
Network behavior of polyurethane elastomers
Authors: Puett D. 
Published: April 2003

AbstractThe present study is concerned with some network properties of polyurethane elastomers in which stability is acheived via physical crosslinkages such as microcrystallites or secondary bonding. The techniques of isothermal, thermo‐, and photoelasticity have been used to gain better insight into the mechanisms which occur during the deformation of these materials. It was found that stable networks are obtained only after mechanical and thermal conditioning. The well‐known stress lowering which is observed during the second deformation is manifested primarily in the entropy component of the retractive force. This implies that the stress lowering results from a reduction in the number of effective network chains and not from time‐dependent effects or crystallinity changes. Depending upon the chemical structure of the material, both positive and negative energy components of the force have been found.
Investigation of the viscosity of solutions of graft copolymers
Authors: Połowinski S. 
Published: April 2003

AbstractLiving polystyrene was grafted on fractions of poly(methyl methacrylate) by an anionic grafting reaction. Unreacted polystyrene was separated by fractional precipitation. The composition of copolymer, i.e., the molecular weight of main chains and side chains, was determined. The influence of molecular weight and structure of graft copolymers on the intrinsic viscosity of solutions was examined. This may be expressed in the form [η] = KMagn. The dependence between a and n in this equation was established.
Adhesion of high polymers. II. Wettability of elastomers
Authors: Lee Lieng‐Huang 
Published: April 2003

AbstractData on wettability of elastomers should be considered basic to the understanding of all phases of elastomer adhesion. However, no such data in the form of critical surface tensions were available for elastomers other than polydimethylsiloxane. For this study, 18 elastomers were selected to determine the effects of functional groups, of geometrical and structural isomerisms, of copolymerization, and of the induced orientation upon wettability. Most results support the constitutive law of wettability established by Shafrin and Zisman. The effect of structural isomerisms in the form of a vinyl side group and cyclization is discussed. An equation for the calculation of critical surface tension of a copolymer or of a mixture of isomers is proposed as follows:

where Ni is the mole‐fraction of the individual monomer in the copolymer and \documentclass{article}\pagestyle{empty}\begin{document}$ \gamma _{c_i } $\end{document} is the critical surface tension of each homopolymer. Most elastomer adhesion studies conducted in the past were concerned with the diffusion theory of adhesion. This study further supports the conclusion on the role of diffusion and adsorption in adhesion advanced in Part I, especially with respect to the physical state of polymer at the time of application. The wettability data in this study could shed some light upon major basic mechanisms involved in elastomer reinforcement.
Statistics of substitution polymers
Authors: Frensdorff H. K. , Ekiner O. 
Published: April 2003

AbstractEquations are developed for predicting the distributions of degree of substitution and block length in substitution copolymers which result when homopolymers are subjected to substitution reactions. Several different cases are treated differing in complexity from entirely random substitution to substitution affected by substituents already present on the same and on the neighboring repeat units. The equations are then applied to chlorinated polyethylene as an example of their use.