摘要:

A triblock copolymer of styrene-butadiene-styrene (SBS) was blended with a high and a low molecular weight polybutadiene [designated as PB(H) and PB(L), respectively]. Electron micrographs of these blends show that PB(L) was solubilized into the butadiene domains of the SBS, while PB(H) was present in a separate phase. Dynamic mechanical data of the SBS&PB(L) blends indicate the presence of an intermediate loss peak between those of the glass transitions of the styrene and butadiene blocks in SBS, which can be attributed to the slippage of untrapped entanglements of PB(L) chains. Similar data for blends containing PB(H) also show an intermediate loss peak, which is, however, due to crystallization and melting of the polycisbutadiene chains. The peak due to the primary glass transition of the butadiene phase was shifted to lower temperatures upon incorporation of PB(L) as a result of plasticization effect of PB(L). The same transition for PB(H) blends is split into a doublet because of the presence of the homopolymer in a separate phase. Dynamic mechanical data for cross-linked blends were also taken for comparison.

ISSN:0022-2348    

DOI:10.1080/00222347508018912

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Melt crystallized polyethylenes with different crystallization histories were irradiated with γ-rays and examined for various properties. These include solubility (gel content), melting and recrystallization behavior, load extension behavior, and creep properties. Even for the same dose, very significant differences were observed for the different sample types. Although such differences have been reported previously, the present work reveals that these differences can be unusually large and that they are displayed by a range of different tests with a consistent correlation between them. The underlying trend is that in poorly crystallized samples the radiation is much more effective in forming networks than in samples of highly developed crystallinity. This finding may merely indicate that cross-linking is more abundant in the amorphous region than in the crystallites; nevertheless, analogy with single crystals suggests that in addition details of the fold surface morphology and the nature of the lamellar contact may also have a part to play. Among other properties, the elasticity of cross-linked melt was analyzed and found to be consistent with simple rubber elasticity theory, leading to an estimate of both the number of effective cross-links and of intrinsic entanglements acting as cross-links. The most conspicuous effects were observed in the creep behavior where different sample types irradiated to the same dose could behave as viscous liquids and true rubbers according to crystallization history. The relevance of such findings for the technological irradiation of polyethylene should be self-evident, particularly as the doses involved were those commonly employed in industrial applications.

ISSN:0022-2348    

DOI:10.1080/00222347508018913

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The specific heat of a resole-type phenolic polymer has been determined. A secondary transition is noted at 125° C. The thermodynamic Gruneisen parameter is 1.3 and the lattice Gruneisen parameter is 6.3. Interchain specific heat is about 21% of the total.

ISSN:0022-2348    

DOI:10.1080/00222347508018914

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

An electron microscopy and electron diffraction study of branched polyethylene crystallization from various solvents and solvent-nonsolvent mixtures proved that two extreme morphological structures could be observed: planar single crystals and crystalline globules. Depending on the solvent power and molecular weight, a large variety of morphologies may be prepared. Lower solvent power and higher molecular weight favors the formation of globular structures.

ISSN:0022-2348    

DOI:10.1080/00222347508018915

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

In this study, pulsed NMR techniques were used to probe the molecular motions occurring in poly(hexamethylenesebacate) (HMS), and its amorphous isomer poly(2-methyl-2-ethyl-1,3-propylenesebacate (MEPS), and in particular, to examine the perturbations in the molecular motions of HMS and MEPS that arise as a result of block copolymerization. The results show a low-temperature β-relaxation due to local motion of the methylenes of the chain backbone, an α-relaxation associated with the glass transition, and an αc-relaxation due to the melting of the crystalline phase. Both α-and β-relaxations in the block copolymer are only slightly perturbed, and this suggests that the blocks are incompatible. The β-relaxation of HMS is confined to the amorphous regions of the polymer. Although sample preparation had little effect on the degree of crystallinity, large differences in the relaxation behavior were observed when the sample preparation was varied.

ISSN:0022-2348    

DOI:10.1080/00222347508018916

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Observations by transmission electron microscopy and electron diffraction suggesting that thin molten polyethylene films have a smectic liquid crystal structure consisting of layers of folded molecules are reported. The thickness of each layer is observed to be about 400 to 500 Å.

ISSN:0022-2348    

DOI:10.1080/00222347508018917

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Under tensile strain the inhomogeneous surface microstructure of thin polystyrene films gave rise to the formation of ∼300 Å nuclei in which large strains were localized even at the glass transition. At lower temperatures these nuclei coalesced into disk-shaped microneck zones. Fibril formation within these zones and a stable craze structure was possible only with molecular weights higher than 10,000 to 37,500.

ISSN:0022-2348    

DOI:10.1080/00222347508018918

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The effect of pressure on the radiation-induced cross-linking of synthetic rubbers, cis-l,4-polybutadiene, cis-l,4-polyisoprene, poly(TFE-propylene), poly(styrene-butadiene), poly(ethylene-propylene), and trans-l,4-polybutadiene were studied. A remarkable acceleration of cross-linking by compression for unsaturated polymers is attributed to an acceleration of the propagation reaction of cross-linking, which does not require long-range migration of radicals, by reduction of the distance between polymer chains at high pressure while the termination reaction, which requires long-range migration of radicals to recombine with each other, is reduced by the decrease in mole-cular mobility at high pressure. The presence of an optimum pressure was observed for radiation-induced cross-linking of cis-l,4-polyisoprene and TFE-propylene copolymer. This is explained by a significant change in molecular motion occurring due to the glass transition or crystallization at high pressure.

ISSN:0022-2348    

DOI:10.1080/00222347508018919

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The impact strength of polycarbonate, exhibited over a wide temperature range, is due to the existence of overlapping dynamic mechanical loss peaks in this same temperature range. A dielectric analysis of the motions causing these peaks indicates they impart impact strength by providing a large number of degrees of motional freedom over which the energy of an impact may be dissipated. The magnitude of the impact strength is directly related to the magnitude of the dynamic mechanical dissipation factor measured under the same conditions.

ISSN:0022-2348    

DOI:10.1080/00222347508018920

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Most of the procedures employed so far in the literature for obtaining the amorphous volume of a polymer below its melting point have been based upon some kind of ad hoc assumptions. In this paper the principle of corresponding states, whose validity has been established for a number of polymers, is applied for obtaining the amorphous volume of polyethylene in the experimentally inaccessible region. The degree of crystallinity as a function of temperature is then calculated in a typical case using the actual sample volume data of Quinn and Mandelkern and the ideal crystal volume values obtained from X-ray measurements. Our results indicate the onset of a prominent relaxational transition at T1= 152°K. A careful analysis of the volume-temperature relationship indicates a much weaker transition at T2= 233°K. By making use of the isoprene volume concept, it is shown that the Simha-Boyer relation is valid in a more general form.

ISSN:0022-2348    

DOI:10.1080/00222347508018921

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor