bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solid‐state polymerization of oxetanes. II. Investigation of the growth of the polymer phase as related to the mechanism of polymerization
Authors: Keggenhoff B. , Wegner G. 
Published: April 2003

AbstractThe radiation‐induced solid‐state polymerization of 3,3‐bischloromethyloxetane (BCMO) was investigated by direct observation of the development of the morphology of the growing polymer phase in single crystals of the monomer. Electron microscopy shows that the polymerization gives rise to amorphous polymer in the first step. The polymer forms irregular platelets which aggregate into larger units without reflecting the crystalline order of the monomer. Subsequent to polymerization, the amorphous polymer crystallizes to the β‐modification of poly‐BCMO. If the partially polymerized crystals are extracted by solvents of the monomer, crystallization of the polymer is enhanced, and morphological artifacts arise which were previously mistaken for the true morphology of the “as polymerized” polymer. The copolymerization behavior of solid solutions of 3‐ethyl‐3‐chloromethyloxetane (ECMO) and BCMO does not differ from the liquid bulk copolymerization with respect to copolymer composition, which is different from the composition of the monomer mixture. It is concluded that the polymer chains grow in noncrystalline zones as in a polymerization in the liquid state by which amorphous polymer is formed. No lattice control was observable in this solid‐state polymerization.
Generation and decay of peroxy radicals in deformed polyethylene
Authors: Davis L. A. , Pampillo C. A. , Chiang T. C. 
Published: April 2003

AbstractThe rate of peroxy radical accumulation as a function of strain at various temperatures in AC1220 high molecular weight polyethylene has been determined by EPR spectroscopy. The results of isothermal radical decay experiments are used, where appropriate, to correct the apparent accumulation rate to the actual rate. An exponential dependence of radical concentration [R], on true strain is observed at all temperatures investigated in the range from 160 to 294°K. For constant effective strain, measured from the approximate strain at which radical accumulation initiates, it is found that d[R]/de exhibits two sharp transitions as a function of temperature. One of these, at low temperature, is believed to be associated with the glass transition of the amorphous phase of the material; the other, at higher temperature, is believed to occur as a result of a change in the rate‐controlling mechanism of deformation.
Macrolattice based on a lamellar morphology in an SBS copolymer
Authors: Dlugosz J. , Folkes M. J. , Keller A. 
Published: April 2003

AbstractBy means of an extrusion technique, a uniformly oriented macrolattice based on an alternating sequence of polystyrene and polybutadiene lamellae has been obtained. This is confirmed by the techniques of low‐angle x‐ray diffraction, electron microscopy, and electron diffraction. Layer thicknesses and spacings have been derived, and good quantitative agreement exists between the values obtained by the different methods. In addition, the electron micrographs exhibit many singular features which are of potential importance both in their own right and for the macroscopic properties.
Polyethylene single crystals: Melting and morphology
Authors: Harrison Ian R. 
Published: April 2003

AbstractDetermination of important thermodynamic and physical properties of polymers has often been frustrated by the tendency of these materials to reorganize when heated. A novel technique has been developed which permits a more careful examination of the relationships existing between melting and morphology of single crystals. This has lead to the observation that high molecular weight polymers possess much narrower melting ranges than had been previously reported. By using this technique it has been possible to identify distinct transition temperatures for {100} and {110} fold sectors. DTA and DSC data have been previously reported for dried down single crystals. The applicability of this data to single crystals as they exist in suspension is questioned.
Environmental aspects of adhesion and adhesive joint strength
Authors: Schonhorn Harold , Frisch H. L. 
Published: April 2003

AbstractWe have outlined a theory which considers the durability of adhesive joints in the presence of a hostile environment. The approach is basically the Griffith theory modified for the presence of liquids. Two main conditions for spontaneous delamination of a composite appear to be immiscibility of the liquid in the environment with the members of the composite and complete interaction of the liquid (in a surface‐chemical sense) with one or more members of the composite. In the absence of chemisorption and interdiffusion in an A‐B composite, we find that (σfL/σf)2 = WABL/WAB, where σf is the critical stress to failure, WAB is the work of adhesion, and the superscript L refers to the presence of a liquid phase. When the liquid (L) interacts, in a surface‐chemical sense, with the composite, we have WAB > WABL, and σfL < σf. To illustrate the main features of the theory, composites are prepared whose interfacial tensions have been modified by the presence of an adsorbed monolayer of a fatty acid. In this instance, the interfacial tensions are changed so that WAB ≈ WABL and σfL ≈ σf. The composite then becomes more stable under an applied stress in the presence of an environment of high relative humidity.
Scattering of light from spherulitic polymers: Effect of internal structure
Authors: Prud'homme R. E. , Yoon D. , Stein R. S. 
Published: April 2003

AbstractThe scattering from a two‐dimensional spherulite is calculated on the basis of an assembly of anisotropic rods imbedded in an isotropic matrix and arranged in a spherulitic distribution. Provided the dimensions of the rods are small compared with the wavelength of the light, the scattering from such an assembly is shown to be identical with that from an internally uniform spherulite. The effective polarizabilities of this uniform spherulite in the radial and tangential directions are equal to the average polarizabilities in these directions of the constituent rods together with their surroundings.
Orientation of polymer molecules during melt spinning. II. Orientation of crystals in as‐spun polyolefin fibers
Authors: Kitao Toshio , Ohya Seigo , Furukawa Junji , Yamashita Shinzo 
Published: April 2003

AbstractThree different polyolefins, a linear polyethylene, an isotactic polypropylene, and an isotactic polybutene‐1, were melt‐spun into filaments. The degree of orientation of the filaments was measured by polarized‐light microscopy, x‐ray diffraction, and a retraction technique, and the results were then related to the melt‐draw ratio. The increase in the elastic deformation ratio of polymer chains by spin‐stretching, estimated by thermal retraction at a temperature above Tm, was monotonic with respect to the melt‐draw ratio. On the other hand, as‐spun filaments of polyethylene and polypropylene were characterized by a plateau in birefringence over the range of melt‐draw ratios from 8 to 80. The change in orientation functions for crystals in these filaments was similar to the change of birefringence. On the other hand, the birefringence and the crystalline orientation functions for polybutene‐1 increased smoothly with increasing melt‐draw ratio. The most highly melt‐drawn filaments of these polymers had a strongly oriented structure, corresponding to that in highly cold‐drawn specimens.
Elastic interaction between linear polymeric chains and periodic potentials
Authors: Kausch H. H. , Langbein D. 
Published: April 2003

AbstractThe elastic displacement of an axially stressed chain within crystalline surroundings, which was first treated by Chevychelov, is reexamined. We compare the results obtained for homogeneously distributed masses with that for discrete atoms, considering the nonuniformity of the potential of a crystal containing hydrogen bonds. In polyethylene and polyamide the maximum mechanical excitation of a chain penetrates into the crystal a distance of 15 to 20 chain atoms. The effect of the relative position of the crystal boundary on the stress‐strain field was studied and the energy of defects calculated.
Calculation of composition heterogeneity of block and graft copolymers
Authors: Vorlíček Jiří , Kratochvíl Pavel 
Published: April 2003

AbstractThe composition heterogeneity has been calculated for some block and graft copolymers. General relationships have been derived for a model of the poly(A‐g‐B) or poly‐(A‐b‐B) type fulfilling the assumption of random grafting. Numerical results have been calculated for special cases of particular interest. These include a copolymer having independent molecular weight contributions from units of species A and B (a special case of which is a block copolymer) and a graft copolymer where the grafting is not accompanied by crosslinking or degradation side reactions and no homopolymer B is formed. Two other model systems represent the effects of the presence or absence of both homopolymers. For the above models, the dependence of the composition heterogeneity on the structure‐determining parameters (average number of grafts in the molecule, polydispersity index of the molecular weight of the backbone and graft) is discussed. The heterogenities thus calculated are in many cases comparatively low. The composition heterogeneity of the system is in most cases increased by the presence of homopolymers.
Cryogenic tensile stress–strain properties of cis‐ and trans‐polybutadienes, polyisoprenes, and related copolymers
Authors: Morgan Roger J. 
Published: April 2003

AbstractThe low‐strain‐rate tensile stress–strain properties of cis‐ and trans‐polybutadienes and ‐polyisoprenes, polybutadiene (cis/trans/vinyl), butyl rubber, and two SBR copolymers have been investigated from 77°K to up to 25°K below the glass transition temperature Tg. The energy Ep dissipated in a stress–strain test in the region of previously reported secondary glass transitions is found to be a function of both the free volume f̄ at the Tg and the damping A from 4°K to Tg −25°K. The complex relationship between the impact strength, the free volume and the damping is briefly discussed. The effect of quenching through the Tg with liquid nitrogen was found to increase the value of Ep for all materials. In a number of cases this increase was associated with the presence of internal crazes. The surface‐craze initiation stress is increased by the presence of surface residual compressive stresses caused by quenching. The internal tensile stresses balancing the surface compressive stresses together with the applied tensile stress cause internal dilatation and hence preferential initiation of internal crazing.
Influence of molecular motions on radiation‐induced reactions in polymers
Authors: Wündrich Konrad 
Published: April 2003

AbstractThere have been several investigations dealing with the influence of the glass transition on the rate of radiation‐induced reactions, especially the crosslinking reaction. On the other hand, no correlation has been reported between secondary transitions and the variation of a reaction rate. In the present work, the degradation of poly(methyl methacrylate) in the temperature range of −196 to 160°C has been studied. Two breaks in the Arrhenius plot were found. The first one is located at −5°C and can be correlated with the γ transition, which has been assigned to the hindered rotation of the ester group whose scission initiates the degradation. It is concluded that the thermal excitation of the bond rotation can either increase the scission rate or decrease the recombination rate of reactive intermediates by expanding the cage of the surrounding molecules. If the second mechanism occurs, the rotation of the α‐methyl group should also be expected to favor the degradation. However, a second break in the Arrhenius plot was found at −130°C, and therefore significantly above the δ transition. The influence of this motion is therefore not clear. Certain radiation‐induced reactions of poly(vinyl chloride), known from literature, seem to be influenced by a secondary transition. It is concluded that secondary transitions may be significant for scission reactions. This suggests, with respect to the known significance of the glass transition, that the various types of molecular motions in polymers may influence radiation‐induced reactions.
Dynamic light‐scattering study of an ethylene–methacrylic acid copolymer and its salt
Authors: Prud'homme Robert E. , Stein Richard S. 
Published: April 2003

AbstractDynamic light‐scattering experiments were performed on an ethylene–methacrylic acid copolymer and its sodium salt. The in‐phase ΔI′ and out‐of‐phase ΔI″ components of the light scattering were measured in a temperature range between 25 and 65°C for both samples. No transition is seen in this temperature interval for the acid, but a clear transition occurs around 40°C for the salt. This transition is associated with the softening point of the ionic domains present in the sample.
Light scattering from assemblies of spherulites
Authors: Prud'homme Robert E. , Stein Richard S. 
Published: April 2003

AbstractA general equation describing the small‐angle Hv light‐scattering intensity for a system of N undeformed spherulites located at random within the sample and taking into account the truncation and interference effects is given. Scattering contour plots or radial scans are reported for various arrangements of the N spherulites. The results show that the interference effect may explain the speckled appearance of the experimental patterns. Moreover, the interference and truncation effects (for the special cases where truncation is considered here) do not seem to shift the position of the maximum scattering angle of the cloverleaf pattern as calculated from the single spherulite theory. Finally, the calculations show that the truncation effect increases the relative intensity of the pattern at large and low scattering angles and at azimuthal angles 0 and 90°C, as compared with the intensity at the position of maximum scattering angle.
Random grafting statistics in graft distribution analysis
Authors: Tung L. H. , Wiley R. M. 
Published: April 2003

AbstractGraft distribution functions have been derived from random grafting statistics. Among the functions, the weight fraction of ungrafted backbone chains, the molecular weight distribution of the ungrafted backbone chains and the GPC apparent molecular weight distribution of the graft copolymer have been found to agree with experimental values determined for a graft copolymer system in which grafting was expected to be random. The other functions, which are not directly measurable, are therefore probably also correct. In analytical work the entire set of graft distribution functions may be computed for a graft copolymer system from the following experimental data: (1) molecular weight distribution of the starting backbone chains; (2) the chemical composition of the mixture of the graft copolymer and ungrafted backbone; (3) the graft side‐chain molecular weight distribution, which may be assumed to be identical to that of the ungrafted homopolymer separable from the reaction mixture.
Experimental evidence for a low‐lying torsional mode in polymers
Authors: Madding R. P. , Fehl D. L. , Dillinger J. R. 
Published: April 2003

AbstractLongitudinal and transverse sound velocities have been measured in several samples of polystyrene crosslinked with various weight percentages of divinylbenzene. Specific heats of these same samples have been measured previously. These data obtained calorimetrically, together with similar data obtained by others for some other polymers, can be accounted for by postulating the existence of a fourth mode of vibration with a velocity close to that measured for the two transverse modes. It is suggested that this fourth mode is one arising from the torsional coupling of the side groups along the backbone chain of the polymer molecule.
Dielectric relaxations and molecular motions in poly(vinylidene fluoride) with crystal form II
Authors: Nakagawa Koichi , Ishida Yoichi 
Published: April 2003

AbstractMolecular motions in poly(vinylidene fluoride) were studied by dielectric measurements. Of the three relaxation processes, the αa and the αc were studied. The αa relaxation was attributed to the molecular motions in the amorphous regions and the αc relaxation to molecular motions in the crystalline regions and their surfaces. The relaxation time and the magnitude of the αa absorption were analyzed on the basis of the Adam‐Gibbs theory of the temperature dependence of the size of the cooperatively rearranging region. As a result it was concluded that the molecular structure of crystal form II holds locally, even in the amorphous regions. The relaxation time and the magnitude for the αc absorption were analysed on the basis of the two‐site model. It was concluded that the αc relaxation is attributable not only to molecular motions in the folds of the lamellar crystals, but also to those in the interior of the crystal; the folded chain is relatively mobile, while the molecular chain in the interior of the crystal executes restricted rotation around the chain axis.
Mass and momentum transfer in polymers. II. Effects of concurrent sorption or desorption of penetrant on tensile creep of an amorphous polymer
Authors: Machin D. , Rogers C. E. 
Published: April 2003

AbstractTechniques have been developed for the prediction of tensile creep behavior of rubbery amorphous polymers with concurrent sorption or desorption of penetrant. The procedures require knowledge of polymer–penetrant interdiffusion behavior and the creep behavior of dry polymer and of polymer swollen to equilibrium. The techniques are based upon a moving boundary treatment, proposed by Kishimoto and Fujita, which has been modified and extended to consider two types of boundary definition, desorption in addition to sorption, and extension of the analysis to longer times. Calculated curves for the concurrent processes of diffusion and creep in the systems poly(n‐butyl methacrylate) with ethanol, methyl ethyl ketone, or benzene vapors at 23°C agree to a good approximation with those measured directly. Diffusion coefficients calculated from the measured concurrent curves also are comparable with those measured directly in previous studies. The techniques are useful initial procedures which, with some further modification or extension, should lead to a more general description of concurrent mass and momentum transfer in polymer–penetrant systems.
Mass and momentum transfer in polymers. III. Effects of liquid penetrants on tensile stress relaxation of amorphous polymers
Authors: Machin D. , Rogers C. E. 
Published: April 2003

AbstractSorption, diffusion, swelling, and tensile stress relaxation measurements were made at room temperature (23°C) for the systems poly(n‐butyl methacrylate) (PBMA) with liquid methanol and ethanol, and poly(methyl acrylate) (PMA) with liquid water. Stress relaxation curves for the fully swollen polymers could be superimposed approximately with those for the dry polymers by appropriate shifting along the long axes. For PMA–water the measured curve for stress relaxation with concurrent sorption could be predicted accurately by using a moving boundary theory with data measurements of stress relaxation of the unswollen and swollen polymer combined with sorption data. The modified moving boundary theory is generalized to include the effects of dimension changes through swelling and the larger effects of plasticization associated with sorption of liquids. This improved theory accurately predicts measured curves of stress relaxation with concurrent sorption for the PBMA–alcohol systems from individual stress relaxation, sorption, diffusion and swelling data. The general approach should be applicable to other amorphous polymer–liquid swelling agent systems. The anisotropic nature of swelling of polymer films and its effect on calculated diffusion coefficients are discussed briefly.
Molecular weight distribution and molecular structure of polyethylene produced by radiation‐induced polymerization
Authors: Yamaguchi Kouichi , Wada Takeshi , Maruyama Shinsaku , Takehisa Masaaki 
Published: April 2003

AbstractThe molecular weight distribution of polyethylene produced by radiation was calculated according to a kinetic scheme. The calculated molecular weight distribution was compared with the results deduced from gel‐permeation chromatography. The observed distribution curve from GPC was broader and showed a lower degree of polymerization than the calculated one. Discrepancies between observed and calculated curves can be explained if the polymer contains nonsteady‐state products and if the reaction mechanism includes chain transfer to dead polymer. By this reaction long‐chain branching would occur. Several long‐chain branches per polymer molecule were indeed found, as inferred from solution properties.
Crystal structure of polychlorotrifluoroethylene
Authors: Mencik Zdenek 
Published: April 2003

AbstractThe crystal structure of polychlorotrifluoroethylene has been studied. The pseudohexagonal lattice parameters are a = 6.438, c = 41.5 Å. The polymer chain is found to be helical with on the average 16.8 monomer units in one turn of the helix (equal to c). The skeletal angles on the CF2 and CFCI atoms are found to differ by 5 to 7 degrees. The polymer chain is found to accommodate these alternating angles by twisting around the axis of the helix. The result of the x‐ray diffraction study agrees best with the assumption that the polymer is atactic with random position of the chlorine substituent. This randomness affects the microstructure of the polymer chain to such an extent that the diffraction effects are those of a system of continuous helices.
Scattering from truncated spherulites
Authors: Prud'Homme Robert E. , Stein Richard S. 
Published: April 2003

AbstractA general two‐dimensional theory is derived to explain the light scattering from truncated spherulites. The severity of the truncation is expressed by a statistical parameter σ2/ā2 which is the ratio of the variance σ2 of the size of the spherulite to the square of its average size ā. The Hv light‐scattering patterns are calculated for different values of the truncation parameter. It is observed that the truncation decreases the position of maximum scattering intensity of the pattern. It also increases the scattering intensity at small and large angles, but reduces it at intermediate angles. For a spherulitic polyethylene sample, the truncation parameter is found to equal 0.100 ± 0.030 as measured microscopically. The theory can also be used to calculate light‐scattering patterns from row‐nucleated spherulites. If it is assumed that the interference effect averages out to zero when a large number of spherulites is involved, a single “sliced” spherulite model can be used. Then, the scattering intensity per unit area decreases as the “slice” becomes very thin.
Thermoelasticity of stretched elastomers under small torsions: Effects of crosslinking, extension, and swelling
Authors: Gent A. N. , Kuan T. H. 
Published: April 2003

AbstractBy using a simple version of Treloar's torsion method the internal energy contribution Me to the restoring couple M has been determined for stretched testpieces subjected to small torsions. Values obtained for Me/M decreased significantly with increasing extension. Corresponding decreases were observed on swelling, but no specific effect of swelling liquids could be detected. The degree of crosslinking had no effect on Me/M. Thus, Me/M at small strains appears to reflect a characteristic molecular property, largely independent of local environment, network density, or type of deformation, as Flory has maintained. The present values are generally consistent with previously published data, except in the case of polyethylene, for which a much larger negative value is obtained, i.e., −1.6 compared to −0.5. The reason for this discrepancy is not known.