摘要:

AbstractMeasurements are reported of the solubility and concentration of propane and propylene in polyethylene, at temperatures from −30°C to +30°C and pressures from 1.68 to 3.52 atm. Solubility of both gases in polymer depends on penetrant activity. Henry's law is not obeyed at high values of the penetrant activity, i.e., in the vicinity of the condensation point of the gas. The interaction between the solvent and the polymer is independent of pressure and a function of temperature. The propylene‐polyethylene interaction seems to reach a maximum at 10°C within the range investigated. A physical mechanism, based on opposite effects of temperature upon polymer and penetrant, is suggested to explain the r

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100501

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe mechanical properties of poly(ethylene terephthalate) are examined to see if the quantitative morphological criteria previously used to define the structural state of isotactic polypropylene will lead to similar quantitative structure‐property correlations when applied to PET. Tenacity, thermal shrinkage in oil and air, tensile modulus, dynamic loss modulus, long spacings, and small‐angle x‐ray intensities are included in the study. All of the data were obtained from the open literature. In all cases the physical properties correlate simply and quantitatively with the internal structure of the PET, and the character of the correlations leads to new insights into the nature of the internal mechanisms controlling the observed properties. The study shows that only by considering the structural state of a polymer, and not its fabrication parameters, can general, simplifying, quantitative, structure‐property correlations be a

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100502

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe rate equations for the thermal decomposition of a polymer by a random scission reaction followed by rapid depolymerization of a constant number of monomer units from both fragments together with rapid evaporation of low molecular weight species are solved by using a different approach from that used by previous workers. The results obtained are more specific and differ slightly from previous treatments.

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100503

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe melting behavior of isotactic polystyrene, crystallized from the melt and from dilute solutions intrans‐decalin, has been studied by differential scanning calorimetry and solubility measurements. The melting curves show 1, 2, or 3 melting endotherms. At large supercooling, crystallization from the melt produces a small melting endotherm just above the crystallization temperatureTc. This peak originates from secondary crystallization of melt trapped within the spherulites. The next melting endotherm is related to the normal primary crystallization process. Its peak temperature increases linearly withTc, yielding an extrapolated value for the equilibrium melting temperatureTc° of 242 ± 1°C as found before. By self‐seeding, crystallization from the melt could be performed at much higher temperature to obtain melting temperatures as high as 243°C, giving rise to doubt about the value ofTc° found by extrapolation. For normal values ofTcand heating rate, an extra endotherm appears on the melting curve. Its peak temperature is the same for both melt‐crystallized and solution‐crystallized samples, and independent ofTc, but rises with decreasing heating rate. From the effects of heating rate and partial scanning on the ratio of peak areas and of previous heat treatment on dissolution temperature, it is concluded that this peak arises from the second one by continuous melting and recrystallization dur

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100504

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractFrom thin films produced by vacuum evaporation and condensation of polyethylene, single crystals were grown by subsequent heat treatment of the films in xylene. Extended molecular chains composing the crystals are approximately 150 Å in length, i.e., about 1.5 times the thickness of the crystal layers. Electron microscopic examination of the crystals revealed that they were morphologically similar to ordinary polyethylene and paraffin single‐crystals, e.g., they sometimes exhibited a hollow pyramidal shape or typical spiral grow

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100505

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe interdependence of the enthalpic contributionA2,Hand the entropic contributionA2,sto the second osmotic virial coefficient for a given polymer‐solvent system has been investigated from the experimental and the theoretical point of view. Experimentally, the following common facts were observed for various systems at temperatures and pressures below the critical values for the solvent. Both the isobaric and isothermal dependences can be approximated over relatively wide ranges ofA2,Hby linear relations with a slope deviating only slightly, but in a characteristic manner from a value of −1. When the temperature is increased at constant pressure one moves along an isobar towards higherA2,H; when the pressure is increased at constant temperature, one moves along an isotherm in the opposite direction, i.e., towards lowerA2,H. Theoretically this behavior can be described in a qualitative manner, starting from a relation derived by Patterson and Delmas on the basis of the Prigogine corresponding‐states theory. The reasons for the lack of quantitative agreement are disc

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100506

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractIt was shown previously that in sedimented mats of solution‐grown nylon crystals the 001 wide‐angle reflection due to the unit‐cell period along the chain and the low‐angle reflection due to the lamellar periodicity are both along the same azimuth (meridian) in the x‐ray diffraction pattern.1Presently in photographs which contain both the wide‐angle and low‐angle regions a series of new meridional reflections have been observed between the low‐angle and 001 reflections and between 001 and 002 reflections. This finding implies that, with the large chemical repeat distances in question, diffraction effects at low and wide angles cannot be considered in isolation as is usual in most polymer crystal studies. In particular, the new reflections promise to provide a direct diffraction approach to the structure of the chain

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100507

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractFolded‐chain crystals of certain polyamides present some novel diffraction effects due to the small number of repeat units within the lamellar thickness. X‐ray diffraction evidence is available in the complete range from low to wide angles. This information is interpreted in terms of the structure factor of an individual lamella together with the lattice factor appropriate for the stacking of lamellae. When due account is taken of the lattice factor, whose effect can be detected even at large angles, three features of the lamellar structure can be deduced. First, the evidence is in favor of the straight‐chain stems traversing almost the total thickness of each lamella, implying sharp folds at the lamellar surfaces. Some consequences of this result on the interpretation of data obtained from annealed mats are mentioned. Second, the detailed determination of the stem structure demands that the majority of the folds in nylon 66 lie in the acid group. Third, there are regions of depleted electron density at the lamellar surfaces, though features of the crystal structure are still retained. This indicates the presence of some folds deeper in the crystal than the maj

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100508

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractSeveral important aspects of the flow in polymer melts through capillaries remain unexplored. This paper examines experimentally one such effect associated with the radial shear‐stress gradient in capillaries. During capillary melt flow of a polymer with a wide molecular weight distribution, migration of the large molecules away from the region of highest shear stress, i.e., at the capillary wall, has been predicted but only modestly investigated. This effect has the potential to produce a molecular weight spectrum over the cross section of extruded polymer. Studies of distribution in shear were conducted on a well‐characterized wide‐distribution polystyrene (M̄w= 234,000). An Instron Rheometer equipped with a long capillary (length/diameter ratio of 66.7) was used to perform the extrusion at temperatures of 160–250°C. A solvent coring procedure was used to dissolve away concentric layers of polymer from the extrudate for molecular weight analyses. The method has been shown to cut clean sections without selective extraction. Values ofM̄w,M̄nandM̄w/M̄nwere calculated from complete molecular weight distribution data obtained by calibrated gel permeation chromatography. For a wide range of shear rates and temperatures, no evidence for molecular fractionation was observed. Shear degradation of this polymer was found to be small. However, at high shear rates at 250°C, evidence indicating extensive shear‐induced thermal degradation was found. No evidence for oxidative degradation at the extrudate surface was found at either low or high shear rates at

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100509

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractDiffusion and tensile creep measurements were made for systems of poly(‐n‐butyl methacrylate) (PBMA) and sorbed ethanol, MEK, or benzene at 23°C. Rates of penetration of an inert spherical indenter into PBMA also were investigated and compared with the tensile creep behavior of the polymer. Creep measurements for various volume fractions of penetrant sorbed at equilibrium revealed that master curves, resulting from a time‐concentration superposition procedure, could be constructed for each penetrant. At long times, these master curves, particularly that for ethanol, show deviations from the corresponding time‐temperature superposition master curve. These deviations are interpreted in terms of probable long‐range entanglement coupling governed in part by the partially specific nature of polymer‐penetrant interactions. Parameters calculated by a free‐volume theory, describing both diffusion and tensile‐creep data, indicate that MEK is a more efficient plasticizing agent than the other penetrants and requires less local free volume for diffusion. Analysis in terms of the free volume concept was not attempted for the case of ethanol, where specific polymer‐penetrant interactions

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100510

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY