摘要:

AbstractForward recoil spectrometry is shown to be a useful technique for measuring diffusion of d‐polymer chains in h‐polymer melts. Concentration profiles of a deuterated diffusing species may be determined with a depth resolution of 80 nm and a sensitivity of 0.1 vol % d‐polymer in h‐polymer. Consequently diffusion coefficients as small as 10−16cm2/s can be readily measured. If polymer chains diffuse by a reptation mechanism, the concentration profile ø(x) of diffusing polydisperse polymer should be quite different from øm(x), the Fickian solution, which one obtains for monodisperse polymer. This idea was tested by measuring ø(x) of polydisperse d‐polystyrene (d‐PS) diffusing into h‐PS. The results are in excellent agreement with the ø(x) predicted from the reptation model and the experimentally determined molecular

ISSN:0887-6266    

DOI:10.1002/polb.1986.180240101

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe structure of crazes in plasticized polystyrene has been studied by means of small‐angle x‐ray scattering and optical interference microscopy. Addition of plasticizer causes a rapid increase in the mean fibril diameterDand a slow decrease in the craze fibril volume fractionvf. The crazing stress σcwas also measured and it was found that the productDσcis independent of plasticizer concentration. These results are shown to be consistent with the entanglement model for controllingvfand the meniscus instability model of craze thickness g

ISSN:0887-6266    

DOI:10.1002/polb.1986.180240102

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractTranslational diffusion and internal motion have been observed by dynamic light scattering of optically labeled single chains of polystyrene (PS) in a semidilute solution of poly(methyl methacrylate) and benzene for the case in which the dimensionRgof the PS chain is comparable to the correlation length of the matrix solution. The molecular weightMwdependence of the hydrodynamic radiusRhis expressed asRh∼M w0.91, whileRh∼M w0.54in pure benzene. The average linewidthΓfor internal motions (KRg>1) appears to depend on the magnitudeKof the scattering vector approximately asΓ∝ K4at higherKRg(>1), in contrast with the fact thatΓ∝K3approximately forKRg>1 in pure benzene. The scaling law for theKdependence ofΓdoes not hold in low‐molecular‐weight PS owing to theKdepend

ISSN:0887-6266    

DOI:10.1002/polb.1986.180240103

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe rheological properties of fractionated thermotropic nematic polyesters 4,4′‐dioxy‐2,2′‐dimethyl azoxybenzenenonanediyl (n= 7) (AZA‐9) and dodecanediyl (n= 10) (DDA‐9)have been determined under oscillatory shear in the nematic and isotropic phase. A markedly more pronounced shear thinning characterizes the polydisperse DDA‐9 polymer as compared to the fractionated polymer in the nematic state. This difference becomes less pronounced in the isotropic phase. In all cases, the elastic complianceJ′ in the isotropic state is much lower than in the nematic state. The values of relaxation time λ, although lower in the isotropic state, are not very different in the nematic state. The loss tangent tan δ is significantly higher in the isotropic phase for lower molecular weights. For molecular weights of 13,000 and above, this difference becomes smaller and shifts to lower angular frequencies. For AZA‐9 and DDA‐9, η ω*→0the limit of the dynamic viscosity can be represented by η*=M nawith a value of α similar for both ph

ISSN:0887-6266    

DOI:10.1002/polb.1986.180240104

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe degree of ionic dissociation of aliphatic ionene polymers, 3,3‐, 4,4‐, 6,6‐, and 8,8‐ionene bromide in salt‐free aqueous solutions at infinite dilution was obtained by emf measurements with a bromide ion electrode. The results show that the longer the methylene chain between neighboring charges on the polymer backbone, the greater is the degree of dissociation, as Manning's theory predicts. The distance between the neighboring charges on the polymer backbone was calculated by using Manning's equation. The distance was compared with that calculated geometrically on the basis of the contour length of the molecule according to Manning's definition. The former distance was much smaller than the latter. The former distance was then compared with the length calculated from Eyring's equation for the end‐to‐end distance of a freely rotating methylene chain. In this case, good agreement

ISSN:0887-6266    

DOI:10.1002/polb.1986.180240105

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe constant‐pressure heat capacityCpof poly(p‐xylylene) (PPX) has been measured from 220 to 625 K by differential scanning calorimetry. The constant‐volume heat capacitiesCvof both, PPX and its isomer polystyrene (PS) have been interpreted in the light of literature data on full normal‐mode calculations for PS and estimates from low‐molecular‐weight analogs for PPX for the 39 group vibrations. Nine skeletal vibrations were used in this discussion with characteristic temperatures θ1and θ3of 534.5 and 43.1 K for PS. It was also possible to calculate a heat capacity contribution of a phenylene group within a polymer chain. Single 48‐vibration θ1temperatures of 3230 K for PS and 2960 K for PPX are sufficient to describeCvabove 220 K. Below 140 K, PS heat capacity shows deviations from the T

ISSN:0887-6266    

DOI:10.1002/polb.1986.180240106

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractSingle‐crystal mats of ultrahigh‐molecular‐weight polyethylene can be drawn uniformly to high draw ratios, more than 20χ at the highest, after the necking process is completed. The dynamic mechanical modulus of the drawn mats increases markedly during the uniform drawing stage. The structural changes induced by the uniform drawing at 100°C have been followed by wide‐angle and small‐angle x‐ray scattering, infrared absorption, differential scanning calorimetry, and birefringence. The crystallinity is estimated from the x‐ray amorphous scattering intensity, the IR absorbance ofgauchebands, the heat of fusion from DSC, and the density. The estimated crystallinities of the drawn mats are all very high and increase slightly and monotonically with increased drawing after necking, though the values of the crystallinity depend on the method of estimation. IRgauchebands and the SAXS peak due to the long period disappear at a draw ratio of about 80χ. All the results suggest that the uniform drawing after necking destroys the two‐phase structure made up of alternately stacked crystalline and amorphous regions and then reorganizes it into a single‐phase c

ISSN:0887-6266    

DOI:10.1002/polb.1986.180240107

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractPolyhydroxybutyrate (PHB) is a bacterially produced thermoplastic. Melt‐cast PHB sheets are usually quite brittle. We show that this brittleness is due to cracks within the spherulites. These cracks, which may be either radial or circumferential within the spherulites, depending on the crystallization temperature, form under conditions of no externally applied stress. When the material is strained the cracks grow and join together, leading to brittle failure. It is possible to produce ductile PHB sheets in two ways: first, the cracks may be “healed” by a cold rolling process; second, special crystallization conditions can be used to produce ductile sheets consisting entirely of crack‐free spherulites. The relevance of this work to the ductility of crystalline thermoplastic in general is di

ISSN:0887-6266    

DOI:10.1002/polb.1986.180240108

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractElectron diffraction data from a series of paraffins epitaxially crystallized on benzoic acid are used to determine their crystal structures. Even‐chain paraffins fromn‐C32H66ton‐C60H122are shown to crystallize isostructurally as the orthorhombic polymorph described forn‐C36H74. Like the even‐chain compounds, odd‐chain paraffins do not crystallize in their lowest‐energy form. A quantitative zonal crystal structure analysis forn‐C33H74suggests that the molecular packing is in the B‐polymorphic form proposed earlier

ISSN:0887-6266    

DOI:10.1002/polb.1986.180240109

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractFracture mechanics was used to investigate the environmental stress cracking of low‐density polyethylene with 4.0 melt flow index. Annealed samples were prepared; a single edge notch was made and then the samples were fractured under constant load in four different liquid alcohols. The relation between the stress intensity factorKand the crack speeda˙has been investigated. The loga˙vs. logKcurves are influenced not only by temperature but also by the alcohol used as the environment. This influence has been studied in detail. The conclusions are as follows: the crack speed at highKis determined by the diffusion mechanism, and this mechanism cannot be explained in terms of hydrodynamics but can be explained in terms of thermally activated molecular motion. On the other hand, the crack speed at lowKis strongly related to the plasticization and the stress relaxation of the crack tip mater

ISSN:0887-6266    

DOI:10.1002/polb.1986.180240110

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY