bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cationic polymerization of α,β‐disubstituted olefins. Part 12. Theoretical consideration of the reactivities of vinyl ethers and β‐substituted vinyl ethers
Authors: Higashimura T. , Masuda T. , Okamura S. , Yonezawa T. 
Published: April 2003

AbstractTo elucidate the propagation mechanism in the cationic polymerization of vinyl ethers and β‐substituted vinyl ethers, the electron distribution in these monomers was computed by the extended Hückel method. Propylene and styrene derivatives were also studied in comparison with the vinyl ether derivatives. Attempts were made to explain the experimental results by various calculated reactivity indices. With the unsaturated hydrocarbons, the reactivity indices on the β‐carbon parallel with the relative reactivity in the cationic polymerization or oligomerization. This agreement suggests that the transition state for the rate‐determining step of the propagation reaction is represented by a model in which the carbonium ion interacts with the β‐carbon of a monomer. On the other hand, the effect of β‐alkyl or alkoxyl groups on the reactivity of vinyl ethers could not be explained by the model in which the carbonium ion interacts with an olefinic carbon or an ether oxygen, or both with two atoms. The following model was proposed on the basis of the electronic stabilization energy due to the de‐
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localization from the occupied orbital of a monomer to the vacant orbital of a carbonium ion. This model can explain reasonably the relative reactivity of vinyl ethers and β‐substituted vinyl ethers observed in the cationic copolymerization catalyzed by BF3·O(C2H5)2.
Polymers derived from 2,5‐diamino‐p‐benzoquinone‐diimide and related compounds
Authors: Szita J. , Marvel C. S. 
Published: April 2003

AbstractA number of new polymeric materials have been prepared by the self‐condensation of 2,5‐diamino‐p‐benzoquinonediimide and by its condensation with 2,5‐diamino‐p‐benzoquinone, 2,5‐dihydroxy‐p‐benzoquinone, and 2,5‐dichloro‐p‐benzoquinone. Ladder polymers were expected, but in every case polymers with some open rings were obtained. 2,5‐Diaminohydroquinone was condensed with 2,5‐diamino‐p‐benzoquinonediimide and with 2,5‐diamino‐p‐benzoquinone to produce heat stable polymers but the expected ladder structures were not obtained. Thermogravimetric analyses of the polymers in nitrogen all showed a weight loss at 100–150°C of 3–14% which was presumably due to loss of either chemically combined or absorbed water on the polymer and then only a 5% weight loss up to about 600°C with a final weight loss of 19% at 900°C.
Structure and reactivity of α,β‐unsaturated ethers. VII. Electronic effects of the β‐methyl substitution on the cationic polymerizabilities of alkyl vinyl ethers
Authors: Fueno T. , Okuyama T. , Furukawa J. 
Published: April 2003

AbstractReactivities of propenyl alkyl ethers toward various cationic agents are summarized, and the effects of a β‐methyl group and geometrical isomerism are discussed on the basis of the extended Hückel molecular orbital theory. The reactions considered include cationic polymerization, acid‐catalyzed hydrolysis, and silver‐ion complexation. The effects of a β‐methyl substitution on the reactivity of vinyl ether are different depending on the type of the reactions. The substitution enhances the reactivity of vinyl ether in homogeneous polymerization, whereas it reduces the reactivity in hydrolysis. This contrasting effect of a β‐methyl group was found to be compatible with the results of the theoretical calculations of the electronic energy changes accompanying the formation of the relevant transition states. A π‐complex‐type transition state was concluded for the cationic polymerization. Several lines of experimental evidence in support of the conclusion are presented.
Primary radical termination rate constant at high conversion in radical polymerization
Authors: Ito Katsukiyo 
Published: April 2003

AbstractA primary radical termination rate constant given by: kti = A1iDi, where A1i is a constant and Di is the diffusion constant of the primary radical, was examined on the basis of the variation of conversion. It was proved that this rate constant is correct at high conversion. A relationship between primary radical termination rate constant and conversion was derived. The effect of variation of conversion on the gel effect is discussed.
Influence of defects on the infrared spectra of polymers
Authors: Opaskar C. G. , Krimm S. 
Published: April 2003

AbstractFor an infinitely repeated regular polymer chain structure the only vibrations which are optically active are those in which the phase of the motion is the same in each unit (the factor‐group modes). Frequencies for which the phase difference is nonzero are optically inactive but can become activated by the presence of defects in the chain. Such defects would normally be chemical impurities or conformational irregularities in the chain. A simple theory is developed which shows that for a dilute system of defects the major characteristics determining possible activation of the nonfactor‐group modes are: (1) the strength of the coupling between the defect vibration and the vibrations of the neighboring chain, and (2) whether or not the natural frequency of the defect vibration lies inside a lattice band of the regular chain. An analysis of the low‐ and high‐frequency regions of the spectrum of low‐density polyethylene, based on the above considerations, indicates that several features of the spectrum can be associated with defect‐induced absorption. A similar explanation can account for certain intensity changes in the CCl stretching region of syndiotactic poly(vinyl chloroide) when this polymer is submitted to mechanical treatment.
Effect of polymer surface morphology on adhesion and adhesive joint strength. II. FEP Teflon and nylon 6
Authors: Schonhorn Harold , Ryan Frank W. 
Published: April 2003

AbstractHeterogeneous nucleation and crystallization of FEP Teflon and nylon 6 melts against high energy surfaces (i.e., gold) produce an interfacial region, in these polymers, of high mechanical strength. Dissolution of the metal substrate rather than removal by mechanical means results in a polymer surface which is amenable to conventional structural adhesive bonding. Nucleation and crystallization of the polymer melts in contact with phases of low surface energy (e.g., vapor) result in the generation of weak boundary layers.
Energy dissipation by pulsating air bubbles in a viscoelastic medium
Authors: Stewart C. W. 
Published: April 2003

AbstractA theoretical discussion is presented on the mechanisms by which an isolated pulsating air bubble in a viscoelastic solid dissipates its energy. The analysis is limited to the situation where the amplitude of motion is assumed to be sufficiently small that the stress strain relations may be described by linear equations with convected differentiation replaced by ∂/∂t. The theoretical thermal, radiation, and viscous damping constants are calculated for resonant air bubbles in unvulcanized natural rubber; however, the results are typical of elastomers in general.
Derivation of distributions of the degree of polymerization by probability theory
Authors: Ito Katsukiyo 
Published: April 2003

AbstractA method of determining distributions of the degree of polymerization by means of probability theory is derived. This method, based on Kolmogorov's forward differential equation, is illustrated by application to two familiar kinetic schemes and is used to derive the distribution of degree of polymerization for free‐radical polymerization with diffusion‐controlled termination.
Mechanical anisotropy of regenerated cellulose films in relation to orientations of crystalline and noncrystalline phases
Authors: Nomura Shunji , Kawabata Sueo , Kawai Hiromichi , Yamaguchi Yutaka , Fukushima Akio , Takahara Hirokazu 
Published: April 2003

AbstractThe mechanical anisotropy of regenerated cellulose films is investigated, first, on the basis of the theory of infinitesimal elasticity. Fairly good agreement of calculated with observed results is obtained on the basis of orthogonal anisotropy with respect to the machine direction and the transverse and thickness directions of the films. The shear modulus G23 along the film plane and the Poisson ratio v32 are 1.5 times; 102 kg/mm2 and about 0.4, respectively, in the standard dry state. Second, the mechanical anisotropy in three different dry states is analyzed in terms of the degree of biaxial orientation of two kinds of structural units, cellulose II crystallites and noncrystalline chain segments, and their mechanical anisotropy. The calculation for averaging the mechanical anisotropies of these structural units on the basis of the homogeneous strain hypothesis gives results much higher than the experimental data, whereas the calculation on the basis on the homogeneous stress hypothesis gives results rather lower than experiment. As a modification of the two extreme calculations, a different averaging gives considerably better agreement between the calculated and observed results. The mechanical anisotropy in the wet state is further analyzed primarily in terms of the degree of biaxial orientation of noncrystalline chains by a modification of Krigbaum treatment, based on application of the kinetic theory of entropy elasticity for semicrystalline polymers, to anisotropic systems. The calculation gives results, however, much lower than those obtained experimentally, unless the ratio of the end‐to‐end distance of the noncrystalline chain to its fully stretched length is taken as unusually large. This may be due to underestimation of the contribution of the crystalline phase to terms of the same type as appear in the Krigbaum treatment.
Polyamides in solution. III. Viscometry of linear polycaprolactam
Authors: Mattiussi A. , Gechele G. B. , Francesconi R. 
Published: April 2003

AbstractThe viscometric behavior of linear polycaprolactam has been studied in the absence of the electroviscous effect in aqueous solvents containing 85% and 64.5% formic acid and in trifluoroethanol, as a function of temperature and also under unperturbed conditions. Results are discussed in terms of the existing theories; in particular, the negative temperature coefficient of the intrinsic viscosity arises only from the variation of the expansion coefficient, the molecule in the unperturbed state being a normal random coil. The absence of aggregation and draining effects in the above solvents has been varified.
Tensile yield‐stress behavior of glassy polymers
Authors: Bauwens‐Crowet C. , Bauwens J. C. , Homès G. 
Published: April 2003

AbstractIt is shown that, at the yield stress, glassy polymers exhibit viscous flow which is in agreement with the generalized theory of Eyring. The study of the yield stress over a wide range of temperatures and strain rates provides evidence on the secondary transitions found by other methods. From our measurements we conclude that every secondary transition corresponds to the liberation of one of the degrees of freedom of a segment of the main chain.
Statistical model of stereospecific polymerization of vinyl monomers
Authors: Luisi Pier Luigi , Mazo Robert M. 
Published: April 2003

AbstractA statistical model for the stereospecific polymerization of vinly monomers on Ziegler‐Natta catalytic systems is presented. The basic assumptions of the model are: (a) the catalytic centers are asymmetric, so that at a given catalytic center the monomer CH2CHR is inserted into the chain with two different rates according to the two different configurations of the opening carbon atom having the R group; (b) the insertion of a monomeric unit in the growing chain is affected also by interactions with the previous monomeric unit. Isotactic, syndiotactic, atatic, or stereoblock polymers are obtained according to the relative values of the two energy parameters expressing these two effects.
Effect of hydrogen bonds on the axial stiffnes of crystalline native cellulose
Authors: Gillis Peter P. 
Published: April 2003

AbstractPrevious theoretical calculations of elastic constants for cellulose based on force constants for bond stretching and bending of valence angles have yielded axial stiffness values admittedly too low. The present analysis accounts for a hitherto unexamined geometrical effect associated with deformation of interchain hydrogen bonds. To do this, most primary bond deformations are neglected so the resulting calculation gives an upper bound for the axial stiffness. By using two different sets of hydrogen bond force constants, values of 24.6 and 31.9 × 1011 dyne/cm2 were obtained for Young's modulus in the chain direction. These values are very much larger than earlier calculations and experimental determinations from cellulosic fibers, indicating both the importance of the effect considered here and the likelihood of an exact analysis yielding an acceptable result.
Transient effects in the crystallization of polyethylene
Authors: Schultz J. M. 
Published: April 2003

AbstractA specimen of linear polyethylene was subjected to isothermal secondary crystallization at a series of temperatures below the primary isothermal crystallization temperature, the melting and primary crystallization stages being held constant throughout the investigation. Dilatometric measurements exhibit an S‐character at low values of undercooling Tp – Ts, where Tp and Ts are, respectively, the primary and secondary crystallization temperatures, whereas at larger undercooling, an initial very rapid crystallization is followed by a very slow stage. When corrected for thermal contraction of the polymer, the net degree of secondary transformation is seen to peak at a temperature about 5°C below Tp. The S‐character of the isotherms and the peaked temperature variation of degree of transformation lead to the conclusion that a large portion of the secondary crystallization consists of the nucleation and growth of the new crystallites. Johnson‐Mehl‐Avrami analysis leads to a model of heterogeneous nucleation within the remaining amorphous zones, followed by one‐dimensional, diffusion‐controlled growth.
Effect of induced thermal stresses on the coefficients of thermal expansion and densities of filled polymers
Authors: Wang T. T. , Kwei T. K. 
Published: April 2003

AbstractIt is demonstrated that in a filled polymer the thermal stresses resulting from the difference in the thermal expansion coefficients of the filler and the polymer have significant effect on the apparent coefficient of thermal expansion of the composite. A model is constructed to aid the thermal stress analysis, and the results are found to agree well with the experimental data obtained from other sources. An expression for the apparent densities of filled polymers is also obtained but the agreement between the present prediction with an existing test result is found to be only qualitative.
Effects of ultraviolet radiation on aqueous polyelectrolyte solutions
Authors: Ishikawa Mitsuo 
Published: April 2003

AbstractThe effects of ultraviolet radiation on dilute aqueous solutions of poly(acrylic acid) and of other polyelectrolytes were studied by viscosity measurements in connection with the effects of ionizing radiation. It was found that ultraviolet light of wavelength below about 2300 Å brought about degradation of polymer chains mainly by indirect action via water, while light of wavelength above 2300 Å caused degradation by direct action in some polymers. It was deduced from the experiments that the protective effect of NaCl could be largely attributed to a decrease in the indirect action. It was also found that a low concentration of methanol was effective in preventing degradation by direct action, although methanol promoted degradation when present in high concentration. Since the promotive effect was not observed when light of wavelength below 3700 Å was eliminated by a filter, this effect was attributed to active products of the irradiation of methanol.
Raman spectra of extended‐chain syndiotactic poly(vinyl chloride)
Authors: Koenig J. L. , Druesedow D. 
Published: April 2003

AbstractRaman spectra have been obtained for a typical poly(vinyl chloride) (PVC) of low crystallinity and for a highly crystalline sample of syndiotactic PVC obtained by irradiation of a urea‐canal complex. Raman measurements have been made on the three different ordered chain structures possible for ordinary PVC. Extended and folded conformations for the syndiotactic structure and a helical structure for the isotactic molecule obey different selection rules and have different dichroic properties in the infrared and Raman spectra. The observed Raman spectrum is consistent with the model of the extended syndiotactic conformation for crystalline PVC. With the new Raman data some additional assignments can be made in the vibrational spectra of PVC.
Solid‐state characterization of the structure and deformation behavior of water‐soluble hydroxypropylcellulose
Authors: Samuels Robert J. 
Published: April 2003

AbstractA modus operandi is developed for determining the molecular structure of hydroxypropylcellulose (HPC), and characterizing, in quantitative terms, the morphological changes occurring when a water‐cast film of the polymer is deformed. This involves the application of the following eleven different physical measurements: wide‐angle x‐ray diffraction, differential scanning calorimetry, density, melt rheometry, infrared spectroscopy, refractive index, birefringence, sonic modulus, small‐angle light scattering, optical and electron microscopy. In addition, a computer was utilized as a mathematical diffractometer. Morphologically, water‐cast HPC was observed to have structure at all levels, from the molecular to the supermolecular. The HPC molecule has a backbone of anhydroglucose units twisted into an irregular 31 helix. Intramolecular hydrogen bonding of the poly(propylene oxide) side chains leads to a stiff, rodlike molecule. The molecules are packed into microfibrillar crystallites 470 Å long and 34 Å in diameter. The microfibrils in turn, associate into supermolecular rodlike structures. The structural rearrangements that occur at each morphological level during deformation of HPC film are quantitatively examined and described.
Electron microscopic study of deformation in polyethylene
Authors: Vadimsky R. G. , Keith H. D. , Padden F. J. 
Published: April 2003

AbstractThin films of polyethylene prepared from blends of fractionated polymer and a linear hydrocarbon (n‐C32H66) have been used to study the role of intercrystalline links in the deformation of semicrystalline polymer under uniaxial stress. These links have been found to be strong and virtually inextensible elements of the structure. It is shown that they are firmly attached to the chain‐folded lamellar crystals they bridge (both within the same spherulite and across boundaries between adjacent spherulites) and that, by concentrating applied stress, they commonly induce these lamellae to begin yielding in regions close to their points of attachment. Where there are many closely spaced links the stress is distributed fairly evenly, and drawing is relatively smooth and uniform. With more sparsely distributed links, however, stresses tend to be concentrated at widely separated points; deformation then tends to be severe and highly localized, often resulting in failure of the material upon drawing. There are indications that stress is also transmitted between chain‐folded lamellae in ways other than by intercrystalline links. One such way is by means of chain ends and molecular loops that emerge from the surfaces of these crystals and are embedded in interlamellar material. Experiments in which the deformed films were subsequently heated confirm earlier conclusions that extended chains in drawn polymer may undergo refolding during annealing.
Adiabatic compressibility of polyelectrolytes in aqueous solutions. II. Poly(4‐vinyl‐N‐n‐butylpyridinium bromide)
Authors: Roy‐Chowdhury Phanibhusan 
Published: April 2003

AbstractThe adiabatic compressibility for two samples (F‐1 with DP‐3748 and F‐2 with DP‐2114) of poly(4‐vinyl‐N‐n‐butylpyridinium bromide) in aqueous solution has been determined from ultrasonic velocity and density data. The sample (F‐1) with the higher degree of polymerization shows comparatively higher velocity and density in solution. However, the evidence for the difference in compressibility is not very decisive. The apparent molal volume ΦV2 and apparent molal compressibility ΦK2 for F‐1 are found to be slightly higher than for F‐2. In aqueous solution, the decrement of adiabatic compressibility per unit concentration, (β1 − β)/c, is found to be almost constant throughout the entire concentration range, whereas in the presence of excess added electrolyte (1.0M KBr solution), the compressibility decrement shows a decrease with dilution. The latter values are lower than those found in water, since the molecules, in the presence of excess electrolyte, are coiled up more and are less compressible. The ΦV2 and ΦK2 values in water are constant throughout the entire concentration range, as the free counterions formed on dissociation in the dilute region are not solvated and hence contribute little to the compressibility. On the other hand, in the presence of excess KBr (1.0M), the ΦV2 and ΦK2 values show a sharp decrease with increase of polyelectrolyte concentration and finally attain a constant value. This is explained by the fact that because of the formation of a charge‐transfer complex between the bromide ion and the polycation, more than the equivalent number of bromide ions is bound, leaving free an equal amount of K+ ions which are solvated and cause the lowering of apparent volumes and compressibilities. Condensation of charges begins at a certain polyelectrolyte concentration, and no further increase of K+ ions is observed. A special situation arises in 0.1M KBr solution. The ΦV2 and ΦK2 values at first increase sharply with increase of polyelectrolyte concentration, but then level off to attain a constant value, at comparatively high concentration. In 2.0% poly(4‐vinyl‐N‐n‐butylpyridinium bromide) solution, the concentration of polymer repeat unit (0.08M) is almost equal to the concentration of the added electrolyte (0.1M KBr) used to suppress dissociation. As the polyelectrolyte concentration in 0.1M KBr solution is progressively decreased, more bromide ions are made available for forming the charge‐transfer complex with the polycation, leaving the K+ ions free to contribute to the compressibility.
Raman scattering in nonplanar poly(vinylidene fluoride)
Authors: Boerio F. J. , Koenig J. L. 
Published: April 2003

AbstractThe Raman scattering of nonplanar (form 2) poly(vinylidene fluoride) (PVF2) is described. Unique Raman bands not observed in the infrared spectra are found at 2973, 1437, 1327, 1198, and 1059 cm−1. Band assignments are discussed by comparing infrared and Raman spectra of form 2 PVF2.
Effect of morphology on the mechanical and rheo‐optical properties of a styrene–butadiene–styrene block copolymer
Authors: Wilkes Garth L. , Stein Richard S. 
Published: April 2003

AbstractThe mechanical and rheo‐optical properties of a styrene–butadiene–styrene block copolymer of a given chemical composition are dependent upon the morphology of the polymer as affected by the solvent system from which a polymer film is cast. Films cast from methyl ethyl ketone and from toluene are compared. Properties found to differ are the stress–strain curve, the birefringence–strain curve, stress relaxation birefringence relaxation, and the dynamic mechanical spectra.