摘要:

AbstractThe relation between molecular weight, chain rigidity and the length of the high‐elasticity plateau is determined from frequency and temperature dependences of the storage modulus for polybutadienes and polystyrenes withMw/Mn⩽ 1.1. Use is made of the concept of equivalence of high‐elastic states characterized by equal lengths of high‐elastic plateaus for linear polymers. The high‐elastic states of the linear polymers studied are equivalent if the polymer chains have equal numbers of dynamic segments and if the reference temperature isT0= 1.22Tg, whereTgis the glass transition temperature. The viscoelastic properties of the polymers in the high‐elastic state are determined unambiguously byTgand the molecular weight of the dynamic segment. The quantitative relation between thermomechanical characteristics obtained by measuring deformation versus temperature under a constant time regime and dependence of storage modulus versus frequency under isothermal conditions i

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090701

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractPolyethylene single crystals differing in lamellar thickness, both as‐grown and annealed with different lamellar thickness, were irradiated by γ‐rays to a dose of about 107rad at liquid nitrogen temperaturein vacuo, and then ESR measurements were made. It was found for the as‐grown crystals that alkyl radicals were concentrated at the crystal surface. For the annealed crystals it was found that the radical concentration was greater than in the original crystals because of an increase in disorder with annealing. By assuming that the crystals form blocks upon annealing and that the surface and the interior of the blocks have the same trapping capacities for radicals as in the original crystals, the dependence of the size of the blocks upon variation in annealing temperature and the original lamellar thickness was estimated. This estimate is supported by the theory of the thickening process of single crystals. Two types of radical reactions with different reaction rates were found to occur simultaneously at room temperature. The rapid process was independent of lamellar thickness and was related to the reaction of radicals mainly in the surface region and the defects within the crystals. The slow process was strongly dependent on the lamellar thickness (i.e., the reaction rate was much depressed as the lamellar thickness was increased) and was inferred to be closely related to molecular motions manifested in viscoelastic measurements by the crystalline dispers

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090702

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractInfrared dichroism is employed to study the orientation of chain molecules in linear and ethyl‐branched polyethylene in the crystalline and noncrystalline regions during drawing and subsequent annealing. A crystalline (1894 cm−1) and a noncrystalline (1368 cm−1) band, as well as the bands at 909 cm−1and 1375 cm−1resulting from vinyl endgroups and methyl endgroups and sidegroups, are studied. For these bands relative orientation functions are derived and compared as a function of draw ratio and annealing temperature. It is shown that the relative orientation functions as derived from the dichroism of the noncrystalline, vinyl and methyl bands follow the same curve while the orientation function for the crystalline bands does not. These results support a two‐phase model for partially crystalline polyethylene and additionally favor segregation of the endgroups and sidegroups in the noncrystalline component during crystallization. It is further shown that shrinkage occurs at the temperature at which the noncrystalline chain molecules start to disorient. From the dichroism of the methyl groups in ethyl‐branched polyethylene, a value for the mean orientation of the noncrystalline chain molecules is calculated. We obtain for the orientation function of the noncrystalline regions at highest draw ratios (λ = 15–20),f= 0.35–0.57, while the chain molecules in the crystallites are nearly perfectly oriented (f≈ 1.0). On the assumption that the noncrystalline component consists of folds, tie molecules, and chain ends, the different contributions of these components to the overall orientation are estimated. From these the relative number of CH2groups incorporated into folds, tie molecules, and cilia can be derived. Further, on the basis of a simple structural model, the relative number of chains on the crystal surface contributing to the different noncrystalline components and their average

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090703

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractThe low‐frequency skeletal and intermolecular modes (below 900 cm−1) have been studied for a sample of “as‐polymerized” Ziegler‐Natta polyethylene for which extended‐chain conformations have been proposed. These results have been compared with data from a sample of stirred‐solution‐crystallized polyethylene and with previous measurements for highly crystalline samples of folded‐chain polyethylene. Measurements were also made of the temperature dependence of these modes for the as‐polymerized material and of the polarization dependence of these modes for an oriented sample of solution‐stirred polyethylene. In the neutron spectra and the corresponding derived frequency distributions, the observed major “singular” frequencies for both the skeletal and intermolecular modes are in reasonable accord with those previously observed for folded‐chain samples of high crystallinity and in Raman measurements. In addition, these frequencies agree with those predicted by theory for the singular frequencies corresponding to the phase‐frequency relationships for the skeletal and intermolecular modes of an infinitely extended chain in a crystal. However, in the spectra of the extended‐chain materials, these singular frequencies, in general, appear sharpened and enhanced in intensity relative to those for previously reported results on folded‐chain polyethylenes; consequently, assignment of their characteristic frequencies is easier. In addition, evidence is presented to show that, for the extended‐chain materials, these frequencies broaden less rapidly with increasing temperature, and the corresponding average vibrational amplitudes are smaller than those observed for highly crystalline samples of folded‐chain material. It is suggested that in these materials the reduction of the number of chain folds and the increased intramolecular ordering give rise to increased thermal stability of the configurations with regard to segmental rotation and to decreased vibrational amplitudes relative to folded‐chain materials. When the aspolymerized materials is preheated above the normal melting point for polyethylene, the neutron spectra revert to those more characteristic of the folded‐chain materials, indicating that a relaxation of chain extensions has occurred. However, on the basis of these results, on quantitative estimates of the characteristic relaxation time can be presented. Additional frequencies, besides those predicted by theory for the skeletal and intermolecular modes and those associated with either multiphonon contributions or the presence of chain folds, are observed. The origin of these frequencies remains unclear but ma

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090704

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractThe literature on polymer morphology contains many studies of structural and orientation changes occurring upon uniaxial stretching of films and fibers, but it has only an occasional reference to such studies on biaxially stretched film. This paper presents data on a structural change due to simultaneous biaxial stretching up to 6 × 6 stretch ratio of quenched linear polyethylene slightly below the melting temperature. At low stretch ratios thebaxis of the orthorhombic unit cell orients predominantly in the biaxial plane of stretching or film plane. At higher than 4 × 4 stretch ratio, a second crystal orientation appears which is a (110) orientation in the film plane. Differential scanning calorimetry scans show two melting peaks occurring concurrently with diffraction effects of two crystal orientations. The evidence for two populations of crystals differing in orientation are discussed in the light of current concepts of folded‐chain lamellae and their fragmentation with elongat

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090705

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractThe size and distortion of crystallites in samples of linear polyethylene were determined before and after plastic deformation. A slowly cooled sample, a quenched sample, and highly drawn films (draw ratio 16) were investigated by different methods. Wide‐angle x‐ray patterns were analyzed to study the average size of the crystalline mosaic blocks and their distortion. In addition, the longitudinal crystal thickness (in the chain direction) was evaluated by two other approaches, determination of the long period, and the melting temperature of irradiated samples. The results show clearly that the size of the crystalline mosaic blocks changes substantially with drawing of polyethylene. Not only is the lateral crystal thickness affected, but the longitudinal crystal dimensions also change during the drawing process. By the three independent methods we find that the longitudinal crystal thickness after drawing is independent of the value for the undrawn samples, as was reported earlier by Peterlin. The change in crystallite size after drawing is accompanied by a large decrease in crystal volume to about 10% of the value for the undrawn sample. The degree of distortion in the crystals seems not to be affected by the deformation process. These experimental data can be considered evidence for high chain mobility and for the possibility of rearrangement of chain molecules during the process of plastic deformat

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090706

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractWhen oriented polyethylene is sheared at an angle to the orientation axis, kink bands often develop and grow, with a resulting change of the crystalline orientation. Beside the crystalline reorientation, the following changes within the kink bands have been observed with wide‐angle x‐rays: (a) partial transformation to a monoclinic from the normal orthorhombic unit cell; (b) partial alignment of the orthorhombicbaxes; (c) rotation of the orthorhombiccaxes of a fraction of the crystals around the kinks by an extra 40 to 60° beyond that of the fibrils; and (d) misalignment of the orthorhombic (hk0) planes by a few degrees. These results are suggested to arise, at least in part, from crystal flattening and from crystal twinning or pseudotwinning on planes intersecting the molecular

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090707

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractThe viscoelastic behavior of two different ethylene–propylene copolymers was studied as a function of the molar ratios of the components and the distribution of the lengths of the ethylene and propylene sequences. The glass transition temperaturesTgagree with the values calculated from relations betweenTgand component ratio established by other authors. The copolymer with longer ethylene and propylene sequences was found to exhibit a relaxation spectrum with a slope less steep than −0.5. This broadening is explained by the broader distribution of friction factors of the statistical segments in this copolymer and by differences in crystallike nearest‐neighbor pa

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090708

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractThe viscoelasticity and volume expansion of the raw polymerizate of ethylene–propylene copolymer with vinyl chloride grafts, and of the individual components has been studied. The raw polymerizate (composite) and the pure ethylene–propylene–vinyl chloride graft copolymer were found to consist of two phases. The pure graft copolymer has an ethylene–propylene matrix containing some fraction of poly(vinyl chloride) (PVC) grafts and a microphase with the remainder of the PVC grafts. The raw polymerizate consists of a PVC matrix plasticized with ethylene–propylene chains and a microphase of the ethylene–propylene copolymer. An attempt has been made to calculate the participation of components in microphases and the minimum dimension of the PVC microphase

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090709

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractIt has been demonstrated that the fold surfaces of polymers can be specific towards chemical attack, if the reaction is mild and nondestructive of the fold. Bromination of suspensions of single crystals of polyethylene in carbon tetrachloride has been shown to be such a system. This chemical modification of a fold surface is a powerful means of extending the applications of the physical methods available. Several methods were used, among them DTA, DSC, infrared spectroscopy and small‐angle x‐ray diffraction. Experimental results from these methods lead to the following conclusions. (a) Bromination takes place preferentially at the folds and is consistent with a regular adjacent reentry fold model. (b) Annealing of these brominated crystals demonstrates the major role played by the crystal surface in this process. (c) The preparation and properties of a novel copolymer system has been demonstrated. It is felt that this copolymer system may prove a useful addition to those systems presently availa

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090710

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY