摘要:

AbstractApproximations in the Avrami treatment of impingement which arise when the growing crystalline bodies are rods or disks are discussed, with particular reference to the single‐crystal model. This model, previously fitted to the isolated primary crystallization of polymethylene, is extended to discuss the growth of the composite lamellar structures, axialites, and spherulites, and is here fitted to the crystallization of poly(ethylene oxide) and polystyrene. Both polymers are found to yield anomalous values of the Avrami exponent when analyzed in terms of the conventional Avrami equation. The new analysis reveals similarities in the behavior of all three polymers. The residual deviations remaining after the fit of the model to polymethylene and poly(ethylene oxide) follow the same pattern, and the temperature dependence of the rate constants associated with the model is similar for all three polymer

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040101

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractOf nine glassy polymers so far investigated, eight yield evidence that fracture propagation involves the formation and breaking of craze material. All eight produce fracture surfaces exhibiting interference colors to one extent or another and even the colorless areas cause low angle x‐ray scattering. Ranked in terms of decreasing ease of colored surface formation, these polymers are poly(methyl methacrylate), poly(ethyl methacrylate), polystyrene, acrylonitrile—styrene copolymer, poly‐α‐methylstyrene, poly(vinyl acetate), a polyhydroxy ether, and polycarbonate. Only rigid poly(vinyl chloride) has failed to show evidence of precrack craze f

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040102

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractCopolymers of ethylene with vinyl acetate, vinyl alcohol, and butene‐1 have been investigated by differential thermal analysis. The method of fast heating is used to approximate a zero entropy production heating path. The activity of crystallizable units in the melt, the crystallinity, and the a‐axis spacings are determined and compared with previous results for copolymers of ethylene and propylene and carbon monoxide. Carbonyl and hydroxyl groups form point defects, forming solutions in both the crystalline and amorphous regions. Methyl, ethyl, and acetate groups form large amorphous defects. The maximum melting point of polyethylene is calculated to be 142.

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040103

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractThe dynamic moduli,E′ dyn, and loss tangents, tan δ, of polydimethylsiloxane and polydimethyldiphenylsiloxane polymers have been investigated by anin situtechnique during γ‐irradiation. These viscoelastic properties were calculated and plotted as a function of irradiation exposure time by measuring the free end displacements and resonance frequencies of polymeric cantilever reeds. The reeds were swept through a small frequency range from about 20 to 100 cycles/sec. The moles of effectively elastic chains per unit volume (v) of the two unfilled polysiloxahes were calculated fromin situmodulus data and compared to values obtained utilizing the swelling technique. The approximate molecular weights between entanglements,Me, of these unfilled polymers were determined by extrapolation of moduli data to zero radiation exposure. The addition of a large silica filler, SiO2, into the polymers did not alter the crosslinking rates, and the filler did not enter into polymer—filler

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040104

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractEthylene—propylene and ethylene—butene‐1 copolymers with up to 1.7 side groups per 100 carbons have been crystallized at 227°C. and under 4100–4900 atm. pressure. The resulting crystalline polymers are at least partially of extended‐chain crystal morphology. Comparison with the same polymers crystallized at atmospheric pressure, which gives folded‐chain crystal morphology, revealed: (1) a density higher by 0.008–0.019 g./cm.3depending on copolymer content; (2) a similar decrease of crystallinity with side group concentration; (3) a similar decrease of the beginning of melting from 125°C. for homopolymer to 65°C. for 1.7 side groups per 100 carbons; (4) a higher (138 ± 0.8°C.) experimental maximum melting point which, in contrast, is independent of copolymer content and seems to vary only with the fraction of low molecular weight material; (5) a decreasing amount of high‐melting crystals with increasing copolymer content (72–8%) and an increasing amount of low‐melting crystals (27–53%) with increasing copolymer content. In addition, superheating, which reached 5.5°C. for 50°C./min. heating rates, was detected. It was concluded that high‐pressure crystallization leads, at least for part of the crystals, to solid solution formation, while atmospheric pressure crystallization does not. Which mode of crystallization is achieved seems kinetically determined. Experimental techniques were dil

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040105

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractA theory of tensile strength, based on the observation of cracks in specimens strained to breaking, is formulated. The treatment involves the assumption that a crack grows to a critical size by a nucleation process. When this critical size is exceeded the crack becomes unstable and propagates spontaneously to produce rupture. By comparing the predicted and measured strength, one can estimate the magnitude of the stress concentration factor in fibers. An interpretative analysis of experimental data obtained at various strain rates indicates that the resulting changes in tensile strength are due primarily to the changes in modulus.

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040106

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractThe effect of birefringence on the intensity of polarized scattered light from an oriented polymer film is analyzed on the basis of a model in which the scattering element is imbedded in a homogeneous birefringent matrix. The scattering intensity is shown to depend upon the polarizer and analyzer angles, the scattering angles, the sample birefringence and thickness, and the scattering coefficients for the four polarization combinations. Computer calculations for reasonable values of these parameters indicate that these corrections can be quite appreciable.

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040107

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractThe performance of the gel permeation chromatography (GPC) technique was studied with several commercial samples of linear high density polyethylene. A comparison of these data was made with those obtained from the elution column technique based on fractional dissolution. GPC gave reproducible fractionation data in the molecular weight range of 103–106. These data were obtained from two columns in series with nominal capacity of 1–104and 1–106A. Polyethylene fractions of known molecular weights are required as calibration standards and for many commercial polyethylenes it is necessary to increase sensitivity at molecular weight higher tha

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040108

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractA device for measuring the elasticity of polymer melts has been designed by one of us (B. Maxwell). The device was used to obtain the relaxation modulus in shear of a linear polyethylene melt. From these data a discrete relaxation spectrum was derived. The range of the obtained spectrum was confirmed to correspond to the terminal zone of the “entanglement plateau” of the spectrum. The limiting dynamic viscosity (as frequency approaches zero) was obtained by integrating the relaxation modulus with respect to time. The viscosity and its activation energy were found to agree closely with the flow viscosity and the flow activation energy, respectively, involved in capillary f

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040109

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY

摘要:

AbstractCrystalline polymers derived fromcis‐ andtrans‐2‐butene oxides were studied by x‐ray diffraction methods. X‐ray fiber and powder photographs of poly(trans‐2‐butene oxide) were indexed by an orthorhombic unit cell with the dimensionsa= 13.72 A.,b= 4.60 A., andc(chain axis) = 6.90 A.; the space group isP212121. The crystal structure of this polymer has been determined in projection. The chain has anerythro‐diisotactic structure with ‐dl,dl‐ carbon sequences. The polymer has a nonplanar zigzag backbone with carbon and oxygen atoms of alternate monomer units lying nearly in a plane. Two chain molecules pass through the unit cell. The unit cell of poly(cis‐2‐butene oxide) is orthorhombic with lattice constantsa= 11.20 A.,b= 10.44 A.,c(chain axis) = 7.01 A. The polymer has athreo‐diisotactic structure with ‐dd,dd‐ or ‐ll,ll‐ carbon sequences. Four chain molecules pass through the unit cell. The crystal lattice is body‐centered but the space group has not yet been established. The polymer has an almost fully extended zigzag chain configuration. Polymers prepared by either metal halide catalysts (FeCl3, SnCl4) or organometallic catalysts were essentially identical; the latter catalysts did, however, yie

ISSN:0449-2978    

DOI:10.1002/pol.1966.160040110

出版商:John Wiley&Sons, Inc.    

年代:1966

数据来源: WILEY