摘要:

AbstractHigh‐density polyethylene and randomly branched linear low‐density polyethylene of varying branch length and content were used to produce oriented thin films. Sample morphology was investigated using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMA). Gelation studies suggested that the film preparation technique may have involved gel‐drawing. DSC characterization of samples with approximately equal average branch content revealed very different melting behavior, suggesting differences in crystal size distributions. This was attributed to variations in the distribution of branches within samples. For similar branching distributions, the average melting temperature (and, similarly, crystal size) generally decreased as branch content increased. This was corroborated by TEM, with which crystal thickness was found to decrease as branch content increased. TEM further revealed that the lateral alignment of mosaic blocks and the resultant lamellar character of the thin films was obscured as branch content increased, a result of reduced crystal size, crystallinity, and possibly increased interphase content. DMA of compression‐molded material revealed the presence of a beta peak in branched samples only. Moreover, the alpha transition temperature shifted to lower temperatures as branch content in

ISSN:0887-6266    

DOI:10.1002/polb.1988.090261201

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractSome layered inorganic compounds of interest in old and new polymerization processes by Ziegler‐Natta stereospecific catalysis have been studied. The results are reported of an investigation concerning the crystallographic disorder phenomena in α‐TiCl3, VCl3, FeCl3, ball‐milled α‐MgCl2, β‐MgCl2, and in a new catalytic system produced according to some recent trends in the field. Best fits are reported of the experimental x‐ray diffraction patterns with patterns calculated for a theoretical model that accounts for structural disorder; the different fits indicate that disorder phenomena due to stacking faults are rather frequent in the examined compounds. The catalytic systems are more and more dispersed, and the maximum of dispersion in heterogeneous systems is reached for the recently propose

ISSN:0887-6266    

DOI:10.1002/polb.1988.090261202

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractIt is shown that, on cooling, solvent present at the surface of swollen vulcanizates freezes before the onset of freezing in the gel solvent, causing gel solvent to diffuse to the sample surface where it adds to existing crystalline areas. At the freezing point of the gel solvent a liquid‐solid equilibrium does not exist, and a theory is postulated to account for the freezing point depression observed in swollen gels in terms of the conditions required for the formation of crystalline nuclei within the gel solvent. The theory is shown to apply to the freezing of cyclohexane and benzene in vulcanized and unvulcanized natural rubber. In line with the theory the presence of carbon black does not alter the solvent freezing point, but vacuole formation around nonreinforcing fillers leads to lower freezing point depression

ISSN:0887-6266    

DOI:10.1002/polb.1988.090261203

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractSolid‐state extruded polyethylene fibers have been prepared, with a wide range of draw ratios and constant processing temperature. The draw ratios vary from 4 up to 30, and the processing temperature was always 398 K. The extruded material behaves anisotropically, owing to the high degree of chain orientation in the drawing direction. The modulus and linear expansion coefficients in the fiber axis direction have been measured, over a wide temperature range, from 140 K up to 320 K. These two properties are closely related to the degree of structural continuity of the fibers. A fibrous structure model is proposed to explain the temperature effects and the values obtained for the modulus and expansion coefficients, in terms of crystallinity and volumetric fraction of extended‐chains structure. At least three relaxation processes can be identified which cause the structural continuity of the fibers to change with temperat

ISSN:0887-6266    

DOI:10.1002/polb.1988.090261204

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractSurface‐enhanced Raman scattering (SERS) has been observed from thin films of polystyrene (PS), diglycidyl ether of bisphenol‐A (DGEBA), and poly(4‐vinyl pyridine) (PVP) deposited on silver island films Degradation of the polymers occurred rapidly during laser irradiation and was accompanied by the appearance of strong bands near 1375 and 1575 cm‐1. These bands were attributed to the formation of graphite‐like species by the silver‐catalyzed thermal oxidation of the polymers induced by localized laser heating of the substrate. When the thin films of PS, DGEBA, or PVP were overcoated with much thicker films of a second polymer such as polystyrene sulfonate (PSS), the degradation was greatly reduced, and excellent SERS spectra of the PS, DGEBA, and PVP films were obtained. Overlayers reduced degradation within the first films deposited on silver island films by restricting the availability of oxygen at the interface to its solubility in the overlayer polymer or by altering the adsorption of oxygen onto the substrate. SERS was observed for the PS, DGEBA, and PVP films and the PSS overlayers when the films were deposited from relatively dilute solutions. When the PS, DGEBA, and PVP films were deposited from more concentrated solutions, SERS was not observed from the PSS overlayers. It was suggested that most of the SERS was due to a short‐range, charge‐transfer mechanism associated with sites of atomic scale roughness and that SERS was observed from the overlayer when the first film failed to occupy a

ISSN:0887-6266    

DOI:10.1002/polb.1988.090261205

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe nonlinear viscoelastic behavior of glassy polymers and its relationship to ductile yielding is studied by single‐ and double‐step stress relaxation experiments. In the latter case a small stress relaxation step is superimposed on a specimen at an elevated state of temperature or strain. The results show that the changes in the relaxation behaviors in the two cases closely parallel each other. The relaxation behavior at strains near yield closely approximates that at low strain but near Tg. The small strain relaxation response can be described well by a Kohlrausch‐Williams‐Watts (KWW) type function. The interpretation of these data in terms of a coupling model which includes the KWW form is di

ISSN:0887-6266    

DOI:10.1002/polb.1988.090261206

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractElectroinitiated polymerizations can be carried out by direct electron transfer via constant potential electrolysis.1–3In doing so, the anodic (Ep, a) and the cathodic (Ep, c) potentials of the monomers must be measured by cyclic voltammetry. The cathodic peak potentials of halophenols were measured on Pt0electrode versus Ag0/Ag+in acetonitrile.Electroinitiated polymerization of bis(pyridine), bis(4‐chloro‐2,6‐dibromophenoxide) copper (II) complex was studied in dimethylformamide‐tetrabutylammonium fluoroborate by direct electron transfer from the cathode. Poly(phenylene oxides) obtained from the anolyte revealed that the monomer undergoes 1,2 as well as 1,4 addition reactions.Lowest unoccupied molecular orbital energies of the monomers were calculated by Hückel molecular orbital theory. The experimental Ep, cvalues were correlated to theoretical LUMO energies and electron densities using a multivariable linear regres

ISSN:0887-6266    

DOI:10.1002/polb.1988.090261207

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractUltradrawn ribbons of solution‐cast blends of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) have been prepared by a solid‐state coextrusion in a capillary rheometer. An increase of noncrystallizable PMMA in the blends drastically decreased the drawability from a draw ratio of 36 for pure PEO to 5 for a mixture of PEO/PMMA 40/60% by weight. A low crystallinity and depression of melting temperature for PEO were observed with increasing draw. The Flory‐Huggins theory for melting temperature depression has been used to derive the binary interaction parameter for these b

ISSN:0887-6266    

DOI:10.1002/polb.1988.090261208

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe α relaxation of isotropic and drawn poly(vinyl alcohol) dried gel films was studied using dynamic mechanical analysis. The temperature of the relaxation Tαincreased from 160°C in the isotropic gel to 220°C in a fiber drawn 19 ×. The relaxation, which is associated with the crystalline regions of the material, also decreased continuously in magnitude as drawing proceeded, although crystallinity increased. At draw ratios over 12 ×, the relaxation became difficult to resolve, and no relaxation was observed in fibers drawn over 19 ×. The melting points of the fibers increased with draw ratio, but not enough to account for the large change in Tα. Crystal thickness in the fiber direction also increased with draw ratio. An analogy is drawn to the case of polyethylene where crystal thickness has been found to control Tα. The absence of a resolvable α relaxation is one reason why it is difficult to draw poly(vinyl alcohol) gels to extremely hi

ISSN:0887-6266    

DOI:10.1002/polb.1988.090261209

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractTwo cosolvent systems are studied by light scattering and viscosity measurements. The cosolvency mechanism is discussed in relation to the preferential adsorption, solubility parameter, and excess free energy of mixing of the two liquid components. The cosolvency effects are attributed to a “true” and an “apparent” cos

ISSN:0887-6266    

DOI:10.1002/polb.1988.090261210

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY