bluuebunny/crossref_metadata_2025_split huggingface dataset:
Grafting onto wool. IV. Interaction of polymer radicals in the viscous media of wool fibers
Authors: Arai Kozo , Shimizu Masamichi , Shimada Machiko 
Published: April 2003

AbstractIn order to study the termination reaction of polymer radicals in the viscous media of wool fibers, reduced, methylated, and S‐carboxymethylated wool fibers were used for graft copolymerization of methyl methacrylate and styrene. With termination of poly(methyl methacrylate) radicals, two different termination reactions, recombination and disproportionation, were together involved in the grafting systems studied. The occurrences of two termination reactions in the system could be correlated with the mobility of the wool chain controlling the radical end mobility. With decreasing disulfide content in the fibers, disproportionation predominantly takes place among the mobilized chains. At a constant disulfide, the thiol content or the concentration of thiol anions becomes the determining factor for the termination reaction. A possible explanation for these phenomena in terms of the thiol and disulfide interchange reaction is presented. On the grafting of styrene, additional evidence was obtained that prevention and retardation of the interchange reactions followed mechanochemical bond scission of the disulfide and other covalent bonds and produced new free radicals which could initiate chain reactions.
Unsaturated condensation polymers by the friedel–crafts reaction
Authors: Huck P. J. , Pritchard G. 
Published: April 2003

AbstractReaction between stilbene and a difunctional ether, in presence of Lewis acid catalyst, produces low molecular weight condensation polymers containing substantial olefinic unsaturation. These resins have been studied by various analytical techniques. Some evidence is presented concerning structure. The condensation polymers are soluble in organic solvents and may be cross linked by free‐radical methods to form thermosetting networks.
Initial steps of thermal degradation of PVC prepared at various temperatures
Authors: Millan J. , Madruga E. L. , Bert M. , Guyot A. 
Published: April 2003

AbstractPVC samples were obtained by bulk polymerization initiated with AIBN and ultraviolet irradiation at 40, 25, 0, −30, and −50°C. They were characterized by 13C NMR measurements, infrared spectroscopy, GPC in hexamethylphosphoramide and B.E.T. surface area measurements. Their thermal degradation was studied between 110 and 185°C by using continuous titration of HCl evolved through a conductimetric cell. The ultraviolet spectra were recorded at various steps of the degradation. At high degradation temperatures, the more syndiotactic the polymer, the longer the polyene average sequences are. The amount of HCl evolved is minimum for a polymerization temperature of 0 or 25°C, depending on the degradation temperature and on the morphology of the polymer. The results are discussed in terms of chemical factors (tacticity distribution, molecular weight) as well as of physical factors (morphology, interval viscosity).
Absorption currents and photocurrents in polyethylene
Authors: Wintle H. J. , Tibensky G. M. 
Published: April 2003

AbstractIt is shown that an optically excited current in polyethylene does not interact with the dark absorption current. This implies that the carriers are different for the two processes. We suggest that holes are photo‐injected and traverse the full thickness of the specimen, while the absorption currents are due to surface barrier processes, as proposed by other workers.
Drawing of nylon 6 fibers (bristles)
Authors: Sakaoku K. , Morosoff N. , Peterlin A. 
Published: April 2003

AbstractBy means of electron microscopy of surface replicas and both small‐angle and wide‐angle x‐ray scattering, nylon 6 fibers were investigated in the as‐spun state, after drawing at 180°C to a draw ratio up to 4.95, and after subsequent annealing. As spun, the fiber exhibits a small fraction of row‐nucleated cylindrites and a great many spherulites (with an average diameter of a few microns) side by side. Drawing deforms the spherulites into spindle‐shaped structures (λ = 2) and subsequently produces well‐aligned microfibrils. Small‐angle x‐ray scattering yields a two‐point diagram at small λ and a fourpoint diagram at high λ. The long period seems to decrease slightly with draw ratio. Annealing at temperatures above the temperature of drawing increases the long period to a greater extent with samples of lower λ. The crystal lattice orientation is nearly complete at λ = 4.95.
Tetrachlorobisphenol‐A adipate polymers. I. Crystallization of poly(tetrachlorobisphenol‐A adipate)
Authors: Lanza E. , Berghmans H. , Smets G. 
Published: April 2003

AbstractThe properties of melt‐crystallized poly(tetrachlorobisphenol‐A adipate) were studied by using a differential scanning calorimeter. The dependence of melting point and the degree of crystallinity are reported as a function of the crystallization conditions. The heat of fusion is equal to 8.1 kcal/mole, while the equilibrium melting point, as determined by extrapolation, is 283°C. The polymer crystallized from the melt has a maximum degree of crystallinity of 0.53.
Heterogeneous nucleation in the crystallization of polyolefins. III. Theory and mechansim
Authors: Binsbergen F. L. 
Published: April 2003

AbstractThe nucleating activity of a large number of nucleating agents for the crystallization of polyolefins is not based on a high surface free energy of the substrate or on epitaxy, or on a minimum particle size just compatible with the thickness of the crystallizing polymer lamellae, or on any persistance of crystalline material in holes of the nucleating particles. The relevant mechanism is thought to be nucleation at steps of limited length in the surface of the nucleating particles. The nucleation is enhanced by a high degree of accommodation of polymer molecules at the surface of the substrate through the presence of ditches in the latter which cause prealignment of polymer chains and thus facilitate crystallization.
Crystal structure of α‐gutta percha: Modification of the constrained least‐squares method
Authors: Takahashi Yasuhiro , Sato Takefumi , Tadokoro Hiroyuki , Tanaka Yasuyuki 
Published: April 2003

AbstractThe crystal structure of α‐gutta percha has been determined by x‐ray diffraction. The unit cell parameters are a = 7.98 Å, b = 6.29 Å, c (fiber period) = 8.77 Å, and β = 102.0° (monoclinic). The space group is P21/c–C2h5. Two molecular chains of nearly trans‐CTS‐trans‐CTS̄ conformation pass through a unit cell; C, T, S, and S̄ being the cis, trans, and two types of skew forms, respectively. The constrainedle astsquares method was modified so that the order of the least squares matrix could be reduced and was applied to the refinement of the crystal structure.
Melting behavior of ethylene oxide–propylene oxide (sym‐PEP) block copolymers
Authors: Booth C. , Pickles C. J. 
Published: April 2003

AbstractMelting points and lamellar thicknesses have been measured for ethylene oxide–propylene oxide block copolymers (sym‐PEP) with central poly(ethylene oxide) block lengths of 70–100 chain units and end poly(propylene oxide) block lengths of 0–30 chain units. Melting points of the block copolymers are lower than those of the corresponding poly(ethylene oxide) homopolymer by an amount (up to 15°C) which increases as the poly(propylene oxide) block length increases. Most samples have more than one melting transition, which can be assigned to variously folded chain crystals. End interfacial free energies σe for the various crystals have been estimated by use of Flory's theory of melting of block copolymers. For a given crystal type (e.g., once‐folded‐chain) σe is higher the longer the chain length of the end poly(propylene oxide) blocks. For a given copolymer σe is lower, the more highly folded the poly(ethylene oxide) chain.
Melting behavior of ethylene oxide–propylene oxide (sym‐EPE) block copolymers
Authors: Booth C. , Dodgson D. V. 
Published: April 2003

AbstractMelting points have been measured for several ethylene oxide–propylene oxide block copolymers (sym‐EPE) chosen from the Pluronic range. Melting points of the block copolymers are lower than those of the corresponding poly(ethylene oxide) homopolymer by up to 4°C. The melting point depressions are much smaller than those observed for comparable sym‐PEP block copolymers.
Elastomeric adhesives: Effect of cross link density on joint strength
Authors: Andrews E. H. , Kinloch A. J. 
Published: April 2003

AbstractThe dependence of joint strength upon the molecular weight between crosslinks Mc of an adhesive has been investigated for joints which consist of a crosslinked, amorphous rubber adhering to a rigid polymeric substrate. The joint strength was found to be independent of Mc if results were compared at the same effective rate of testing. If, however, values of joint strength were compared at a particular test temperature and rate, the joint strength generally increased as the value of Mc decreased. This result can be explained by the increase of the glass transition temperature of the adhesive with increasing crosslink density.
Microbial degradation of polymer solids. I. Cellophane
Authors: Engler P. , Carr S. H. 
Published: April 2003

AbstractSpecimens of regenerated cellulose films (cellophane) have been inoculated with cellulolytic fungi and the resulting degradation monitored through change in physical properties. Investigation of structure–property relationship in cellophane have revealed that surface microfibrils are highly oriented parallel to the manufacturing machine direction, while those in the film interior exist in a somewhat disordered array. Cellulase enzymes have been observed to diffuse appreciable distances from their point of application and to attack disordered regions more readily than the crystallites. Damage to surface microfibrils appears to involve their being cleaved into short segments. The fungus studied in this work forms a network of hyphae that covers much of the specimen surface soon after growth starts; hyphae penetrate into the film and proceed to remove its core more rapidly than surface layers. Tensile strength declines progressively as this degradation occurs, but vapor barrier properties remain essentially unchanged over the period of these studies. The suggests that intrusion of hyphae, in combination with enzymatic digestion of cellulose, rapidly lowers load‐bearing characteristics, but moisture permeation rates stay nearly constant owing to the presence of fungal material at sites where cellulose has been removed.
Dilute solution properties and molecular characterization of poly(butyl methacrylate‐co‐styrene)
Authors: Srinivasan K. S. V. , Santappa M. 
Published: April 2003

AbstractDilute solution properties of fractionated poly(butyl methacrylate‐co‐styrene) PBMAS prepared by bulk polymerization, have been investigated by means of light scattering, viscometry, and osmometry. As the composition heterogeneity was narrow, the characterization of the copolymer was effected in a single solvent by light scattering. Infrared and nuclear magnetic resonance spectra were used to determine the composition and sequence distribution of monomer units of the copolymer. The molecular weight dependence of the limiting viscosity number and of the root‐mean‐square end‐to‐end distance have been established. The Mark‐Houwink relation showed that methylethyl ketone is a good solvent compared with cyclohexane. The validity of various extrapolation procedures that have been proposed to calculate the unperturbed dimensions have been examined. Root‐mean‐square end‐to‐end distances have been calculated from the Debye‐Bueche and Kirkwood‐Riseman methods and compared with the experimental values. The molecular weight dependence of the second virial coefficient agreed well with that calculated from the Orofino‐Flory equation. The value of the steric hindrance parameter σ for the copolymer has been found to be 2.27 compared to 2.05 for poly(butyl methacrylate) and 2.22 for polystyrene, which indicates that PBMAS is a stiffer chain in solution than those of the constituent homopolymers.
NMR of dissolved water in ultrathin and thick membranes of cellulose acetate
Authors: Krishnamurthy S. , McIntyre D. , Santee E. R. , Wilson C. W. 
Published: April 2003

AbstractWide‐line proton magnetic resonance spectra of thick (100 μ) and ultrathin (0.25 μ) membranes of cellulose acetate have been obtained in the “bone‐dry” state and in the wet state up to 2.5% water by weight. The NMR spectra were recorded with the membrane face aligned parallel and perpendicular to the magnetic field direction. The first derivative spectra of wet thick membrane (above 0.4% water) show a sharp center peak and at least one broad outer peak, both in the parallel and perpendicular orientations. The spectra of wet ultrathin membrane, on the other hand, show a pseudodoublet in the perpendicular orientation and a broad singlet in the parallel orientation. The differences in the spectra of the thick and ultrathin membranes are discussed in terms of “free” and restricted water believed to arise from the differences in the structure of thick and ultrathin membranes.
Pulsed NMR study of molecular motion in the diglycidyl ether of bisphenol‐A cured with 4,4′‐methylenedianiline
Authors: Larsen David W. , Strange John H. 
Published: April 2003

AbstractThe monomeric diglycidyl ether of bisphenol‐A cured with methylenedianiline has been studied by pulsed NMR. Values of the proton relaxation times T1, T1p, and T2 have been measured over the temperature range −160 to 200°C. The system was studied after being fully postcured at 180°C and after being cured at 100°C and at 54°C. The relaxation times are interpreted in terms of molecular motion in the cured resins, i.e., methyl group reorientation, segmental motions, and general molecular motion. The results are compared with those obtained previously by us for the uncured resin. Correlation frequencies for the segmental motions are compared with those obtained from dielectric relaxation and mechanical loss studies. There are at least two principal segmental motions present in the cured system, and the nature of these motions is found to depend on the cure temperature. These effects are discussed in terms of crosslinking and annealing of the system.
Thermodynamics of n‐alkane systems and the solution theories of flory and prigogine
Authors: Hammers W. E. , De Ligny C. L. , Vaas L. H. 
Published: April 2003

AbstractThe partial molar excess free enthalpies and enthalpies as well as the molar excess enthalpies of a number of n‐alkane systems were reexamined within the scope of the polymer solution theory of Flory, Orwoll, and Vrij and that of Prigogine in the version after Delmas, Patterson, and Somcynsky. A semiempirical method was used to obtain characteristic n‐alkane data, which obey the principle of corresponding states. By using these data (instead of those from the partition function after Flory and collaborators), a physically realistic interpretation of the excess free enthalpies over the whole concentration range is possible if the combinatorial contribution is purely athermal in nature. Both theories give an enthalpy interaction parameter near zero as expected, whereas neither a significant end effect nor an entropic interaction contribution is apparent from the analyses of the excess free enthalpies. The poor results obtained for the partial excess enthalpies and the enthalpies of mixing reflect the inadequacy of the partition functions on which these modern solution theories are based.
Spectroscopic method for the analysis of polyalkenamers
Authors: Tosi Camillo , Ciampelli Federigo , Dall'Asta Gino 
Published: April 2003

AbstractA method based on use of NMR and infrared spectroscopy is described for the quantitative determination of the structural units generally occurring in polyalkenamers. The possibilities offered by both techniques are pointed out: in particular, the values found for the absorptivities of the infrared bands typical of unsaturated alkenamer units are extensively discussed.
Effect of the reference chain dimension on the viscoelastic and stress–strain behavior of poly(n‐butyl methacrylate) networks
Authors: Ilavský M. , Hasa J. 
Published: April 2003

AbstractThe linear viscoelastic and stress‐strain behavior of poly(n‐butyl methacrylate) networks at a content of crosslinking agent (ethyleneglycol dimethacrylate) of c0–1 × 10−4 mole/cm3 was investigated in the main transition and rubberlike region in the temperature interval from 20 to 150°C. The dependence of the unperturbed chain dimensions on temperature was determined from thermoelastic measurements in the rubberlike region; this dependence was unaffected by the content of crosslinking agent. Application of time–temperature superposition to the linear viscoelastic behavior did not give a continuous superimposed curve in the proximity of the rubberlike region; superposition within the whole time region required introducing the change of the unperturbed chain dimensions with temperature. This correction was sufficient for a sample with a higher content of the crosslinking agent. However, for loose networks (c< 0.1 × 10−4 mole/cm3) it was insufficient, because of another relaxation mechanism in the region of high temperatures. It was found that the intensity and temperature dependence of this relaxation mechanism, which is probably due to a change of the number of entanglements with temperature, are connected with the magnitude and the temperature dependence of the C2 constant of the Mooney‐Rivlin equation.
Numerical calculations of the viscoelastic properties of solutions of branched polymers based on the Zimm‐Kilb theory
Authors: Osaki Kunihiro , Schrag John L. 
Published: April 2003

AbstractNumerical calculations were performed for the viscoelastic properties of dilute solutions of branched star polymers with equal branch lengths as formulated in terms of a bead‐spring model by Zimm and Kilb without using the integrodifferential equation approximation method to calculate the eigenvalues. The complex modulus and complex viscosity were calculated as functions of frequency for various combinations of the number of branches f (4, 8, and 13), the number of beads in one branch Nb (= N/f; 20 to 100, where N + 1 is the total number of beads, N the number of springs in the molecule) and the reduced hydrodynamic interaction parameter h* (= h/N1/2 0.05 to 0.3, where h is the hydrodynamic interaction parameter of Zimm and Kilb). The frequency dependence of the complex modulus in the low‐frequency range depends mainly on h* and not on Nb if Nb is large enough, and it is very close to that calculated from the eigenvalues for h→∞ obtained by Zimm and Kilb, if h* is about 0.25. As h* decreases from 0.25, the frequency dependence gradually approaches that of the free‐draining cash (h→0). Calculations may be carried out for h* values somewhat larger than 0.25 and result in a frequency dependence that is not intermediate to the h → 0 and h → ∞ cases as evaluated by Zimm and Kilb. The physical meaning of such “super‐non‐free‐draining” values of h* is uncertain, however. The intrinsic viscosity ratio g′ = [η]f/[η]lin is an increasing function of h* and changes very slowly with N. For h* = 0.25, g′ is close to the non‐free‐draining limit for any value of N.
Raman spectral changes during the solid‐state polymerization of diacetylenes
Authors: Melveger A. J. , Baughman R. H. 
Published: April 2003

AbstractRaman spectral changes resulting from the solid‐state 1,4‐addition polymerization of conjugated diacetylenes are reported. The monomers show an intense CC stretching frequency near 2260 cm−1, where as the polymers showed two strong bands, a CC vibration near 2100 cm−1 and a CC vibration near 1500 cm−1. The presence of both double and triple bonds in the polymers suggests the backbone structure (CCCC)n. The alternate mesomeric structure (CCCC)n can be eliminated as a possibility by the presence of the strong CC vibration in the polymer. Sequential Raman spectra obtained during radiation‐induced polymerization revealed intermediate spectral states between the initial monomer and final polymer. Intermediate‐state vibrations first increase and then decrease in intensity as polymerization proceeds. However, the observed vibtrational frequencies of intermediate states were not dependent upon the extent of polymerization. Whether polymerization occurred thermally or as a result of radiation did not appear to influence the spectrum of the final polymer, but the observed number of intermediate states differed. Polymerization mechanisms, required molecular motions, and resulting structural changes are discussed.
Conformational energies, stereoregularity, and the role of nonstaggered conformations in polymer chains
Authors: Flory Paul J. 
Published: April 2003

AbstractThe role of nonstaggered conformations in polymethylenes and in vinyl polymers is discussed in some detail. In incorporating such conformations into rotational isomeric state treatments, it is essential to so choose rotational states as to assure equitable sampling of configuration space. Tacit identification of rotational states with minima in the conformation energy surface, a common practice at present, may lead to serious errors. The significance and limitations of conformational energy calculations are discussed. It is pointed out that the alleged discrepancy between theory and experiments on the spatial configurations of isotactic polymers of α‐olefins in general and of polypropylene in particular is unsupported by valid experiments on polymers of established stereochemical constitution.
Dielectric relaxation of collagen and gelatin
Authors: Chang E. P. , Chien James C. W. 
Published: April 2003

AbstractDielectric dispersions of reconstituted collagens and gelatin were measured from 0.1 to 10 kHz and −160 to +160°C. At 0.1 kHz there is a γ transition at −80°C which is attributed to the H2O‐coupled local modes. The process has an activation energy of 7.5 kcal. A devitrification process is observed at 10–20°C. Both of these processes have their counterparts in the dynamic mechanical measurements. The tan δ values are up to 3 times as great for the dynamic mechanical dispersions. There is an additional hightemperature dielectric loss transition which does not correspond to any seen with the mechanical experiments. A probable mechanism for this absorption is the Maxwell‐Wagner‐Sillars effect.
Roughness and anisotropy effects on wettability of polytetrafluoroethylene and sodium‐treated polytetrafluoroethylene
Authors: Cirlin Eun Hee , Kaelble David H. 
Published: April 2003

AbstractThe effect of roughness on wettability of skived polytetrafluoroethylene (PTFE or Teflon) and Na‐treated PTFE film were studied by advancing contact angle measurements. The effect of an anisotropic force field of elongated Na‐treated PTFE on the shear bond strength were also studied as a function of elongation. The results are analyzed in terms of London dispersion γsd and Keesom polar γsp contributions to surface energy γs.It was found that the roughness effect on wettability of PTFE is significant for untreated PTFE and negligible for Na‐treated PTFE. Our shear bond strength σb analysis of elongated Na‐treated PTFE showed that σb is influenced by an anisotropic force field and the σb increases with the fractional polarity p = γsp/γs but decreases with the dispersion fraction d = γsd/γs of solid‐vapor surface tension γs = γsd + γsp