摘要:

Thin epitaxial layers of polyethylene, formed on the surface of alkali halide crystals by isothermal solution crystallization, were studied via electron microscopy and electron diffraction as a function of molecular weight, solution concentration, and degree of supercooling. Growth of the monoclinic form of polyethylene was found to increasingly predominate over the usual orthorhombic form as the thickness of the deposit decreased in the case of epitaxy on NaCl. This phenomenon was postulated to have occurred because of a favorable packing scheme for interfacial monoclinic layers and interactions between the polymer and the specific Van der Waals forces of the surface. Although this pseudomorphic growth pattern was relatively independent of molecular weight, initial growth rate perpendicular to the surface had a large molecular weight dependence. Concentration and degree of supercooling also were observed to have significant effects on growth rate. Lattice match between polymer crystallite and alkali halide was found to be an important consideration in the determination of growth rate, initial polyethylene crystal structure, and the supercooling required for nucleation. A model for the long-range electrostatic forces emanating from the alkali halide surface was presented and used to explain the “limiting crystal height” phenomenon at low supercoolings.

ISSN:0022-2348    

DOI:10.1080/00222347408219394

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The fine structure of polyethylene prepared by radiation-induced polymerization of ethylene at room temperature is investigated by differential thermal analysis (DTA). This polyethylene is difficult to affect by annealing, but does show a tendency to reorganize during heating. A double endotherm on the DTA heating curve is observed in samples annealed at temperatures between 121 and 125°C. The structure represented by the endotherm at the lower temperature shows a strong tendency to reorganize, but that represented by the endotherm at the higher temperature does not. These double endotherms do not disappear from the heating curve of a sample oxidized by fuming nitric acid. It is proposed that polyethylene prepared by radiation-induced polymerization has a large crystalline fraction but small crystallite size and a small amorphous part; the polymer molecules, in both parts, may be strained with some hindrance to thermal movement, for example, by the existence of long-chain branches.

ISSN:0022-2348    

DOI:10.1080/00222347408219395

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Stirring-induced solution grown fibrillar crystals of polyethylene have been obtained from solution in Decalin. The crystals were examined by electron microscopy, and their melting and annealing behavior as well as their response to attack by fuming nitric acid were investigated. Crystals formed at lower temperatures exhibit the morphology and properties of conventional shish kebabs. Crystals formed at higher temperatures have a ribbonlike morphology and exhibit different properties from those of conventional shish kebabs.

ISSN:0022-2348    

DOI:10.1080/00222347408219396

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A method is presented for determining complex shear moduli, C*44, C*55, and C*66, of an oriented polymer sheet having the orthorhombic symmetry. The method consists of measuring the frequency and the logarithmic decrement of free torsional oscillation for four specimens cut out from the sheet, each two of them having the torsional axes at 0 and 90° against the orientation axis and each of the two having a different aspect ratio. The method is applied to oriented high-density polyethylenes with various treatments. The results indicate that, while there exists a strong anisotropy in the real part of the elastic modulus, no anisotropy is observed in loss tangent. It is concluded from this result, along with a general consideration of the composite presented in the Appendix, that the amorphous phase, which contributes to a dominant part of the γ-relaxation of bulk polyethylene, is isotropic in oriented samples and the observed loss tangent is equal to the intrinsic loss tangent of the amorphous phase. The loss tangent is compared among samples with various treatments and the local mode mechanism is concluded to be most probable as the origin of γ-relaxation.

ISSN:0022-2348    

DOI:10.1080/00222347408219397

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

It is shown that unique information of the paracrystalline superstructure can only be obtained from high oriented polymers by applying a two-dimensional analysis of small-angle scattering with a high resolution pinhole camera.

ISSN:0022-2348    

DOI:10.1080/00222347408219398

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Viscoelastic measurements and X-ray analyses were made of linear and branched polyethylene (PE) single crystals prepared from dilute solution under isothermal crystallization conditions and on annealed crystals of the same samples. As the long period of the annealed samples increases, the absorption temperature of the crystalline absorption increases, but its intensity decreases. The primary absorption (αa) appears in branched PE single crystal mats following annealing, and its intensity is correlated with the αaabsorption. Defect regions are introduced into the crystalline phase of PE single crystals by annealing. These defect regions are interpreted in terms of a mosaic block structure from paracrystalline theory. In the case of annealing at temperatures below 100°C, where thickening of single crystals does not occur, the volume of a mosaic block within single crystals is invariable, while the defect regions surrounding the mosaic block increase with an increase in the annealing temperature. On the other hand, if the annealing is at temperatures above 100°C, where thickening of the single crystals occurs, the volume of a mosaic block increases and merging of the blocks results. Crystalline perfection of a mosaic block is discussed from the relationship between generating a mosaic block structure by annealing and its Viscoelastic behavior.

ISSN:0022-2348    

DOI:10.1080/00222347408219399

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The deformation mechanism of bulk-crystallized high-density polyethylene, upon stretching at various temperatures from 15 to 100°C in uniaxial and biaxial directions, has been extensively studied using detachment replicas of free surfaces onto which a thin metal film of Pt-Pd was vapor-deposited perpendicularly prior to stretching. The morphological changes related to the β-, the α1-, and the α2-relaxations have been observed for samples drawn in the corresponding temperature ranges. That is, various irreversible deformation behaviors, such as interlamellar slip, decomposition into small crystalline blocks with lateral sizes of 150 to 300 Å, and disruption into large crystalline blocks with lateral sizes of 1500 to 3000 Å, have been observed upon drawing in the temperature ranges of the β-, the α1-, and the α2-relaxation mechanisms. These deformations are mainly associated with micro-Brownian motion of loosely folded chains on the lamellar surface, with the deformation of the intermosaic block region within the limits of linear response, and with the translational or twisting molecular chain motion in the crystalline region, respectively. It has been confirmed, from external-internal strain relationships obtained from the magnitudes of the deformed and undeformed regions on the electron micrographs, that upon drawing in the temperature range of the α1-process, microcrazes or microcracks may be preferentially initiated from the mosaic block boundary without any deformation in the mosaic block core. Upon drawing in the temperature range of the α2-mechanism, shear deformation of the crystalline lamellae may occur in addition to their decomposition into large crystalline blocks with lateral sizes of 1500 to 3000 Å.

ISSN:0022-2348    

DOI:10.1080/00222347408219400

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A free-oscillating torsional pendulum was used to investigate the effect of the concentration of the HO—CH2—CH2—COO— and NH2CO— side chains and α-methyl groups of the main chains on the mechanical relaxation behavior of polymethacrylate and polyacrylate polymers and copolymers in the glassy state. The intensity of the low-temperature (γ) dispersion is linearly proportional to the volume fraction of 2-hydroxyethyl methacrylate (HEMA) in both series of copolymers and is independent of the content of the α-methyl groups. The temperature of the γ-dispersion, which for PHEMA is about —133°C (1 Hz), is lowered by the incorporation both of methacrylamide (MAAm) and—although to a lesser extent—of acrylamide (AAm) units. The secondary (β1) process of PHEMA (28°C; 1 Hz) is shifted toward higher temperature with increasing amount of MAAm, so that for the dry PMAAm it cannot be observed at temperatures up to 120°C. On the other hand, PAAm is characterized by the secondary relaxation at —25°C (1 Hz); however, the corresponding relaxation of the HEMA-AAm copolymers is somewhat indistinct. The effect of water leads to a decrease in temperature and an increase in the intensity by the β1-relaxation of PAAm, while in the case of PMAAm a new dispersion appears around —120°C. The dependence of molecular mobility on the copolymer composition and water content is qualitatively interpreted in terms of steric hindrances and intermolecular interactions.

ISSN:0022-2348    

DOI:10.1080/00222347408219401

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The morphology of single crystals of copolymers based on polyoxymethylene varies with type and amount of comer units. Changes in thickness, regular hexagonal shape, and number of overgrowths is attributed to exclusion and/or incorporation of comer units in the lattice.

ISSN:0022-2348    

DOI:10.1080/00222347408219402

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

In thermoplastic urethane elastomers, phase separation between hard and soft segments resulting in a domain structure is an essential condition for a sufficiently high heat distortion temperature. The state of segregation, i.e., the domain structure, is characterized by the following aspects: 1) the size distribution, i.e., the dispersion level of the domains; 2) the sharpness of diffuseness of the domain boundaries, and 3) hard segments dissolved in the soft segment matrix or soft segments included in the domains.

ISSN:0022-2348    

DOI:10.1080/00222347408219403

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor