摘要:

AbstractAn experimental study has been made to specify how the time‐temperature superposition and the linear viscoelastic characteristics vary with the degree of crosslinking for a broad class of noncrystalline peroxide‐cured EPDM networks. A new, very sensitive method is applied to determine the horizontal and vertical shift functions in an independent way. All uncrosslinked samples are thermoelasticoviscously simple with horizontal shift functionsaTof the WLF type and vertical shift functions almost independent of temperature, in agreement with recent theoretical understanding. Upon crosslinking, these materials become thermoviscoelastically complex networks, but superposition can still be accomplished by assuming different temperature dependences for the relaxational strength and the equilibrium modulus. TheaTfunctions can be taken independent of the degree of crosslinking. The vertical shift functionsbTfor the relaxational strength vary with the degree of crosslinking between theoretical predictions for uncrosslinked and perfectly crosslinked EPDM networks. The equilibrium moduli of the lightly cured networks decreases with increasing temperature, which is ascribed to the presence of interchain associations between ethylene sequences in thetransstate. Upon further crosslinking, these effects gradually vanish and eventually the networks can be described as viscoelastically simple with an energy elastic contribution due to the ethylenetrans‐gauchetransitions. The linear viscoelastic characteristics, namely the storage and loss moduli and compliances and phase‐angle master curves and the relaxation and retardation spectra are discussed as a function of the degree of crosslinking. A sol/gel analysis and equilibrium swelling measurements complete the experimental characterization of three familes of five EPDM networ

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220301

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractFar‐infrared (FIR) Fourier‐transform transmission spectra and x‐ray diagrams of poly(vinylidene fluoride) films are examined in terms of poling‐field action on the crystalline phase (α and β forms) and on the amorphous phase. We show that the poling field induces an increase of crystallinity in the α phase as well as in the β phase, and for the latter an orientation of dipoles in the field direction. For samples containing a mixture of phases α and β we note an α to β phase transition, a rotation of the dipoles in the β phase, and an increase of the crystallinity of the sample. Part of the β phase is generated from th

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220302

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractCopolymers of 1,1‐difluoroethene with tetrafluoroethene, chlorotrifluoroethene, and bromotrifluoroethene have been prepared by emulsion polymerization, and their crystallinity has been investigated by means of x‐ray diffraction. The results are discussed in relation to copolymer composition and struct

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220303

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractExperiments at the Cornell high energy synchrotron source (CHESS) have shown that it is possible to obtain 2‐D small‐angle x‐ray scattering patterns from single crystal mats of high density polyethylene with a time resolution of 0.3 s. However, it took up to 5 s to heat the 0.1‐mm‐thick specimen to the annealing temperature. A logarithmic increase of long spacing was quickly established, after an induction time of<2 s at the higher annealing temperatures. At lower temperatures the original reflection remains, weakening, while a continuous scatter to smaller angles builds up. At 10–20 s annealing time a new maximum becomes clear, and then the logarithmic increase of long spacing begins. The intensity of this reflection is intially low and increases with annealing time. On cooling it decreases again. It seems that here we can directly observe two mechanisms of lamellar thickening, melting then recrystallization at short times and diffusional thickening at

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220304

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractPolytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0–700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ3of 54 K, and θ1of 250 K, and a full set of group vibrations.CvtoCpconversion was possible with a Nernst–Lindemann constant ofA= 1.6 × 10−3mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔCpof 9.4 J/K mol. The room‐temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high‐temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinit

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220305

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe α and β relaxations of a variety of polyethylenes have been extensively studied using lowfrequency dynamic mechanical methods. The main focus of this work has been both the control and the quantitative measurement of the key structural factors that describe semicrystalline polymer systems. The structural factors that have been examined in detail include the level of crystallinity, the crystallite thickness, the interfacial content, and the supermolecular structure. Consequently a variety of other types of supplementary measurements were made to accomplish the necessary characterization. The location of the α transition is found to depend primarily on the crystallite thickness. There also is the distinct possibility that the interfacial structure exerts an important influence. The level of crystallinity and the supermolecular structure do not play a significant role in the location ofTα. A strong correlation is found with the carbon‐13 NMR crystallineT1, which is reported in a separate paper. From analysis of the influence of the different structural factors on the β transition, it is concluded that this transition results from the relaxation of chain units which are located in the interfacial region. The elusiveness of this transition and the contradictory reports that have existed in the literature are given a ready explanation. The enhancement of this transition by branching and copolymerization follows naturally as does its invariance with counit c

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220306

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA novel approach for the determination of the viscosity‐average molecular weight of polymers for which Mark–Houwink constants are not known is presented. This method can be applied to narrow as well as broad‐molecular‐weight‐distribution polymer samples and requires only the GPC chromatogram and viscosity data. The proposed method was tested using polystyrene and poly(methyl methacrylate) in toluene and THF. Molecular weights computed by the proposed approach are in good agreement with those obtained using conventional t

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220307

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe ternary self‐diffusion data of Ferguson and von Meerwall are analyzed using a generalized form of the free‐volume theory of diffusion proposed by Vrentas and Duda. It is shown that the predicative capabilities of this form of the theory are satisfactory and comparable to those of the Fujita version. The lack of significant differences in the predictive capabilities of the two theories for the two ternary systems studied is explained in terms of the properties of the materials utilized. The data of Ferguson and von Meerwall are consistent with the hypothesis that the size of a polymer jumping unit is a fixed property of the polymer and that the jumping units for sufficiently largen‐paraffins are smaller than the entire solvent mol

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220308

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA newly constructed far‐infrared laser interferometer was used to measure the birefringence of 1‐mm‐thick injection‐molded high‐density polyethylene test bars, manufactured at unusually high molding pressures. The long wavelength used, 70.5 μm, allowed nondestructive tests to be made, demonstrating the usefulness of far‐infrared techniques for probing crystalline polymers. The birefringence was shown to increase with increasing molding pressure, supporting the belief that molecular orientation increases with increasing molding pressure. The tensile modulus was also measured and was found to increase linearly with mold

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220309

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe tensile drawing behavior of a range of selected polyethylene copolymers has been studied. Sheets were prepared by quenching molten polymer into cold water. Two‐centimeter‐gauge‐length samples were then drawn in air at 75 or 115°C in an Instron tensile testing machine at a crosshead speed of 10 cm/min. It was found that even at the very low concentration of one side branch per 1000 carbon atoms there was a very marked effect on the strain hardening behavior and the maximum draw ratio that could be achieved. The reduction in draw ratio increased with increasing branch concentration, and long branches were more effective than short branches in limiting the draw ratios achieved. The similarity between these effects and the effects of increasing M̄wor radiation crosslinking is noteworthy. This suggests that even a very small concentration of branches can significantly reduces the moleculer motions required for the process of plastic deformation. The Young's modulus/draw ratio relationship follows a pattern virtually identical to that observed in the case of homop

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220310

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY