摘要:

AbstractAn extension of Bunn's nomenclature of polymer conformation is given with several examples. The structures of polyethers expressed by a general formula [(CH2)mO]nwithm= 1–4 are described and discussed with respect to the properties. Poly‐oxymethylene molecule has a helical structure which contains nine chemical units and five turns in the fiber identity period, and is the sequence of the internal rotation angle 78°13′. Detailed structure analysis of this polymer was made by the method of three‐dimensional Fourier synthesis. The diffraction data were measured on a highly ordered sample prepared from a single crystal of tetraoxymethylene by solid‐state radiation polymerization. It was deduced from the experimental results that the polyoxymethylene crystallite is composed of only one type of helix, either right‐handed or left‐handed. The poly(ethylene oxide) molecule is a loosely turned helix, and is a succession of nearlytrans, trans, andgaucheconformations. The structure of polytetrahydrofuran is essentially a planar zigzag. It has been also found quite recently that the third member, polyoxacyclobutane, has three types of crytalline modifications. One is planar zigzag, and the other two have longer fiber periods;T3GT3Ǧ and (T2G2)2types. The structure of polyallene [CH2C(CH2)]nis also discussed; this polymer is a succession of nearlygaucheconformations, the internal ro

ISSN:0449-2994    

DOI:10.1002/polc.5070150103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

ISSN:0449-2994    

DOI:10.1002/polc.5070150104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractNuclear magnetic resonance linewidth studies are made concerning the molecular motions in crystalline polymers moh as polyethylene, polytetrafluoroethylene, andtrans‐1,4‐polybutadiene. (1) The γ (local mode) relaxation of polyethylene is studied based on the temperature variation of mobile fraction. The range of the β (primary) dispersion of linear polyethylene is shown to spread far wider than that of branched polyethylene, whereas its lower limit (Tg−) is the same for the two. (2) Concerning polytetrafluoroethylene, a third NMR component is found in addition to narrow and broad‐line components, and the third phase of molecular aggregation is assumed to be intermediate between the amorphous and crystalline phases. The notion of the intermediate phase (an array of rodlike molecules) is instrumental in clarifying the complicated viscoelastie behavior by admitting two glass transitions in the polymer. (3) At the solid‐phase transition oftrans‐1,4‐polybutadiene, a huge‐scale motional narrowing of the NMR absorption line takes place, indicating the onset of rodlike rotation of the molecules belonging to the crystalline phase. Above the phase transition temperature, the polymer cry

ISSN:0449-2994    

DOI:10.1002/polc.5070150105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractTo calculate the elastic constants, (Cij), of the polyethylene (PE), Born's dynamical theory of long wave method has been used for a model of interatomic interactions representing inter‐ and intramolecular force fields. Among various types of interaction potentials between nonbonded atoms, two sets of H‐H, C‐H, and C‐C interaction potentials have been adopted which give the best results in reasonable agreement with the data of the lattice parameters and the angle between plane of the zigzag chain and crystallographic axis in the PE lattice. It has been also verified that the lattice energy of PE can be calculated successfully by using the present, potentials. In order to calculate the elastic constant, H‐H and C‐H interactions with close distances have been taken into account for the intermolocular force fields. On the other hand the Urey‐Bradley force field has been used for intramolecular interactions. An expression is obtained which relates Horn's force constants to the macroscopic elastic constants in the orthorhombic system. The calculation has been also made on Cijin a rigid model of molecular chain, but it is found that the increments of elastic constants due to the rigid model are at most a few per cent. The elastic moduli along the a, b, and r, axes and also the normal of the (110) plane have been derived from Cijand compared with values experimentally determined by x‐ray diffractometry. Furthermore, the space averages for compressional, shear, and Young's moduli of PE polycrystals oriented in all directions, and the T3low‐temperature dependence of heat capac

ISSN:0449-2994    

DOI:10.1002/polc.5070150106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractElastic moduli of the crystalline regions in high polymers have been studied. Oriented specimens were used throughout. Lattice strains were measured by an x‐ray technique in the direction of the fiber axis as well as in that perpendicular to the fiber axis. The moduli for both directions were calculated on the basis of the assumption that the stress is homogeneous within a specimen held under a load. Remits obtained for various kinds of polymers were discussed in terms of the crystal structures of the polymers, pan icularly the skeleton conformation and the cross‐sectional bulkiness of the chain molecule in the crystal. It was shown that the moduli in the direction of the fiber axis are widely different depending upon the polymer. They vary from 240 × 104kg./cm.2for polyethylene to 4.1 × 104kg./cm.2for isotactic poly (vinyltert‐butyl ether). In the direction perpendicular to the fiber axis, the moduli were shown to take values within a narrow range of magnitude, 3–9 × 104kg./cm.2. Some of these moduli were compared with the calculated values reported by several authors. To find experimental support for the assumption of the homogeneous stress, measurements were made by using several oriented specimens of different fine textural structures. Inherent values of the lattice moduli were obtained, regardless of the specimens used, which gives a strong support for the

ISSN:0449-2994    

DOI:10.1002/polc.5070150107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

ISSN:0449-2994    

DOI:10.1002/polc.5070150108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractA theory of the relaxation phenomena associated with the molecular motion in polymer crystals (the so‐called crystalline relaxation) developed by the author is outlined. These relaxation phenomena are considered to arise from the viscous interaction between polymer chains in crystals due to the incoherent lattice vibrations. Based upon the equilibrium theory of the stability of polymer crystals developed by Peterlin et al., a semi‐quantitative theory of crystalline relaxation is given. The main conclusion reached is that the relaxation strength and the relaxation times depend strongly upon the thickness of platelike single crystals or lamellae. The experimental facts known so far agree, al least qualitatively, with the the

ISSN:0449-2994    

DOI:10.1002/polc.5070150109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractMechanical and dielectric relaxations in crystalline phase (crystalline relaxation), glassy phase (local mode relaxation), and paracrystalline phase (paracrystalline relaxation) are interpreted in terms of torsional motion of chains in respective phases. A theory is developed on the relaxation strength, and a satisfactory agreement is found between theory and experiment for mechanical crystalline relaxations in normal paraffins. Dielectric crystalline relaxations in oxidized paraffins, poly(vinyl alcohol), and polyoxymethylene, dielectric paracrystalline relaxation in polyacrylonitrile, and local mode relaxations in several polymers are studied both experimentally and theoretically.

ISSN:0449-2994    

DOI:10.1002/polc.5070150110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractA summary is given of recent work on the observation of dislocations in polyethylene crystals and the results are discussed in terms of the crystal‐defect model of polymer structure. Both inter‐ and intralamellar dislocations have been observed and their Burger's vectors determined. Most dislocations were observed to be imperfect or partials, indicating that there exist low energy stacking faults. Annealing single crystal brought about approximately a thousandfold increase in the dislocation density which indicates that dislocations are involved in the process of thickening. The observation of dislocation networks in the folds between lamella prove that these folds are sufficiently regular to pack crystallographically. Observed interactions between inter‐ and intra‐lamellar dislocations show that the interlamellar dislocations are glissile and therefore interlamellar slip can occur by a dislocation motion. These observations lend considerable support to the crystal‐defect model of polymer structure. However, it is pointed out that this model does not conflict seriously with tlie statistical equilibrium theory of polymer crystallization. Dislocations are non‐equilibrium defects and hence would not exist under true equilibrium

ISSN:0449-2994    

DOI:10.1002/polc.5070150111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY

摘要:

AbstractThe properties of molecular weight fractions of linear polyethylene, encompassing the range 3 × 103to 1.5 × 106, which were isothermally crystallised at low undercooling at. atmospheric pressure, were studied. Marked changes in various thermodynamic and mechanical properties are observed with molecular weight, which can be attributed to the finite sine of the crystallites in the chain direction and to the ratio of the crystallite size to the extended‐chain length. Electron microscopic examination of fracture surfaces indicates the formation of striated, lamella crystallites over the complete molecular weight range although the ratio of crystallite size to extended‐chain length varies from approximately unity at the lower molecular weights to extremely small values for the higher molecular weights. Concomitant with the changes in properties and sizes, the interfacial free energy of a mature crystallite increases significantly with molecular weight. Based upon these experimental results, a crystallization mechanism is developed which has as its basic tenents the relation between the critical size initiating nucleus and the extended‐chain length and the spatial requirements of chain units in random conformation in the interzonal regions. For molecular weights above which extended‐chain crystals are formed, the analysis and experiment indicate that the interfarnal region associated with the basal plane is of a nonregular structure, and that a significant number of chain units, which connect different crystallites, must exist, in a non‐ordered conformation. It is concluded that lamella‐type crystallites in bulk‐crystallized polymers are not to be associated with an interface comprised of regularly folded chains. The assumptions that either an initiating or growth nucleus is comprised of regularly folded chains or that such a structure is an equilibrium requirement, are not substantiate

ISSN:0449-2994    

DOI:10.1002/polc.5070150112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1967

数据来源: WILEY