摘要:

AbstractThe elastic behaviors of simple networks consisting of but a few chains have been calculated on the basis of the James and Guth theory of elasticity. The calculations show that the number of elastically effective chains in a network is less than the actual number of network chains, and that the total number of chain backbone links distribute themselves equally (approximately) among the effective chains. It is also demonstrated that a chain molecular weight distribution could be of consequence in non‐Gaussian elasticity. Extrapolation of the findings to a macroscopic network suggests that the number of effective chains is one half the number of network chains, and that each effective chain behaves as if it contained twice as many of backbone links as a network chai

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131101

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractDielectric experiments were performed in the β temperature region on poly(ethylene terephthalate) films of different draw ratios. The proportion of various conformations, crystallinity, and orientation were estimated from infrared, density, and birefringence measurements. The dielectric relaxation strength was determined from the Cole–Cole plot of the dielectric constants over a wide frequency range. An attempt was made to modify the Fröhlich equation, originally for isotropic systems, for application to systems of oriented dipoles. When the experimental data are analyzed through this modified equation, it is evident that the changes in the dielectric constants of PET with stretching could not be accounted for by improvement in the alignment of chain molecules alone. The relative abundance of thetransconformation, both crystalline and amorphous, andgaucheconformation appears to be a factor which cannot be ignored. The calculation indicates that the dipole moment seems to be greater in thetransconformation than in thegaucheconformat

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131102

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractNovel ionic polymers of the typex,y‐oxyethylene ionenes (x,y‐OEI), have been synthesized, forxandyvarying from 2 to 5. The 2,2‐, 2,3‐, 2,4‐, and 3,3‐OEI are crystalline; the 3,4‐, 4,4‐, 4,5‐, and 5,5‐OEI are amorphous. The temperature dependence of the dynamic mechanical properties of these polymers, studied by torsional braid analysis over a temperature range from −170° to +150°C, shows two types of dispersion in each polymer. The dispersions lying between −6° and +90°C appear to be primary dispersions due to the amorphous phase. The dispersions between −110° and 0°C, on the other hand, are attributed to local modes. The temperature of the primary dispersion depends linearly on the charge density along the main chains of the polymer. However, the dependence of the local mode dispersion temperature on the charge density shows no regular pattern. Both dispersions are greatly influenced by the presence of absorbed water. Measurements ofTgat various water contents reveal the existence of abnorma

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131103

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractA theory pertinent to the nucleation of polymer‐diluent systems for molecules of finite molecular weight has been developed. These results have been applied to the crystallization from polyethylene‐α‐chloronaphthalene mixtures using molecular weight fractions of polyethylene ranging from 4,000 to 250,000. This analysis is carried out over the composition range extending from pure polymer to a polymer fraction of 0.30. According to this theory, the interfacial basal free energy decreases as either the molecular weight or diluent concentration dec

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131104

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe morphological details of the nucleation and growth of spherulites incis‐polyisoprene at elevated pressures are discussed on the basis of transmission electron microscopy of films stainedin situby osmium tetroxide and cold‐stage electron diffraction of unstained films. The crystalline structure is unchanged but growth habits are modified. Spherulites begin, as in crystallization at atmospheric pressure, with a single lamella. The formation of a spherulite proceeds primarily through “spawning” and is unaffected by the imposition of pressure. Lamellae tend to propagate as plates or hedrites at supercoolings in excess of 50–60°C (e.g., 1 kbar at 0°C) unlike at atmospheric pressure where only ribbonlike lamellae are observed. Propagation is invariably as sheafs since nucleation of lamellae which grow perpendicular to the primary lamella is suppressed. The nucleation density varies considerably with pressure, a maximum being observed in the pressure plane at constant temperature (e.g., 0.70 kbar at 0°C). It is difficult to resolve clearly the morphological details in the diffusion controlled region because of fine texture. Although much more difficult to achieve experimentally, the effects of pre‐orienting the melt are similar to those occurring at atmosp

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131105

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe peel strength found in the trousers‐type peeling process is treated for the case in which the adherends, assumed to be flexible but inextensible are bonded by rubbery viscoelastic adhesives.Taking into consideration energy dissipation during deformation of the adhesive, Griffith's criterion is extended to the peeling of viscoelastic materials. For the peeling force per unit widthfit is deduced that 2f= Γ +u′h, where T is twice the surface energy,u'is the energy dissipation per unit volume of adhesive, andhis the thickness of the adhesive layer. Values ofu'obtained from peeling tests for various thicknesses are compared with those from the tensile tests and found to agree with the above relation. The deduction that the peel strength is independent of the thickness for adhesives with no energy dissipation is also verified experiment

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131106

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractA Langevin equation of motion for a charged bead‐spring statistical chain is written in difference form and the relaxation and equilibrium behavior of the chain is studied by computer simulation. Results are presented for the behavior of end‐to‐end lengthh, principal axes of the polymer ellipsoidL1,L2,L3, and chain contour lengthcin terms of their averages, root mean square values, root mean square fluctuations, orientations, and relaxation strengths and times. The simulation was made with various sets of parameters, bead numberN, charge on the beadq, and radius of ion atmosphere around the beadk−1. It is found that 〈h2〉1/2and 〈L12〉1/2increase more strongly with increasingqand decreasing κ than 〈L22〉1/2, 〈L32〉1/2, and 〈c12〉1/2, indicating that the chain is expanded in three dimensions and at the same time is extended along the end‐to‐end direction. The relaxation time τrotof rotation of the end‐to‐end vector, which is proportional toN2atq= 0, increases with increasingqand tends to be proportional toN3for an extended chain, while the relaxation time τconfof the magnitude ofhis almost independent ofqand is always proportional toN2. It is concluded that the extended chain possesses a well‐defined end‐to‐end axis and the chain rotates as a whole with a relaxation time τrotwhich is much longer than τconf. The complex viscosity of the chain is calculated from the Fourier transform of the time–correlation function of momentum flux and is found to have a frequency spectrum similar to that observed for aqueous solutions of poly(acrylic acid). The dominant mode appearing in the low‐frequency range is evidence

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131107

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe effects of diluent on molecular motions and glass transition in the polystyrene–toluene system was studied by means of dielectric, thermal, and NMR measurements. Three dielectric relaxations were observed between 80 and 400°K. On the basis of NMR measurements on solutions in toluene and in deuterated toluene, relaxation processes were assigned to segmental motions of polystyrene, rotations of toluene, and the local motions of polystyrene and toluene in order of appearance from the high‐temperature side. The concentration dependence of the relaxation strength and of the activation energy for the primary relaxation (that at the highest temperature) show a step increment at about 50% by weight. The activation plots for the primary process were expressed by the Vogel–Tamman equation. With this equation, the temperatures at which the mean dielectric relaxation time becomes 100 sec is determined. This agrees well with the glass‐transition temperatureTgand henceTgin concentrated solution is expressed by\documentclass{article}\pagestyle{empty}\begin{document}$$ T_g \approx \frac{{ {B} }} {{ {A + 3} }} + T_0 $$\end{document}in terms of the parametersA, B, andT0of the Vogel–Tamman equation. The values ofAandBare, respectively, about 12 and 0.65 and independent of the concentration. The physical meaning of these parameters is

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131108

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe unit cell of poly(tetramethylene terephthalate) is triclinic with parametersa= 5.96 Å,b= 4.83 Å,c(fiber axis) = 11.62 Å, α = 115.2. β = 99.9, and γ = 111.3°; space groupP1, calculated crystalline density 1.41 g/cc. The plane of the benzene ring is found to be inclined by about 15° from the fiber axis, contributing to a shortening of the fiber period as compared to the period expected on the basis of analogy with other members of the terephthalate ester series. The remaining shortening of the fiber period occurs in the O°CH2°CH2segment of the chain. No abnormally short distances among neighboring chain atoms were observed. A typical texture pattern was found in specimens of this polymer that were cold rolled and subsequently annealed. In this texture thecaxis of the unit cell is highly oriented in the rolling direction; theaandbaxes of the unit cell are oriented preferentially so that the terephthalate residue lies as close as possible to the

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131109

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractMelting and crystallization behavior of polytetrafluoroethylene as polymerized in emulsion and suspension is shown to depend on molecular weight. DSC heating curves for virgin PTFE with low molecular weight below 3 × 105have a single peak, whereas curves for higher molecular weight samples have double peaks. With increasing heating rate the areas of higher melting peaks become larger than the lower melting peaks. The morphology of polymer exhibiting double melting peaks is mainly folded ribbons or granular particles. The phenomenon of double melting is explained on the basis of two different crystalline states which correspond to the “fold regions” and the “linear segments” in a folded ribbon.The melting temperature of virgin PTFE is almost constant at ca. 330°C for molecular weights below 1 × 106, and rises as the molecular weight increases above 1 × 106. The heat of melting of virgin PTFE is nearly independent of molecular weight.On the basis of these results, we propose a model for melting and crystallization of low and high molecular weight PTFE and for the crysta

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131110

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY