摘要:

AbstractA statistical theory of light scattering from deformed isotropic and textured heterogeneous polymer materials is formulated. Two types of textured structures are analyzed: assemblies of optically isotropic and anisotropic rods and a spatially anisotropic distribution of isotropic spherical inclusion centers. The small‐angleHvlight‐scattering patterns are calculated. The appearance of scattering from isotropic rods and spheres in deformed materials has been demonstrated. The changes of theHvscattering patterns as a function of elongation and strucuture parameters are discussed. © 1993 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311201

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractWhen stretched under uniaxial stress, ductile polymers usually exhibit unstable plastic deformation, which embodies two phases: (a) yielding with the formation of a neck and (b) cold‐drawing with the propagation of necking shoulders. The mechanical state associated with this deformation behavior is analyzed. The discussion is divided into three parts. The first part is a general treatment of the constitutive function of flow stress in the plastic state, in which a series of relations among various characterizing parameters are formulated. The second part provides three mechanical criteria for necking deformation and propagation of necking shoulders: the condition of unstable plastic deformation requiring\documentclass{article}\pagestyle{empty}\begin{document}$ D_P = - \left( {\partial {{\ln \dot \varepsilon } \mathord{\left/ {\vphantom {{\ln \dot \varepsilon } {\partial \varepsilon }}} \right. \kern-\nulldelimiterspace} {\partial \varepsilon }}} \right)_P0 $\end{document}and the obvious localization of unstable plastic deformation. The third part describes a mathematical model which can be used in calculations to fit the contour of the necking shoulder. This model is developed according to rational considerations for the relation of In\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}to ε. Experimental data on PE rod specimens are well fitted by this model. © 1993 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311202

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA body of experimental evidence suggests that reinforcing fibers influence both the crystallization kinetics and morphology of those composite materials that are based on crystallizable thermoplastics. The absence of an analytical model to predict the effect of fibers on crystallization has hindered data analysis. A new approach, using computer simulation of polymer crystallization, makes it possible to study the influence that reinforcing fibers have on the crystallization kinetics and morphology of semicrystalline polymers. Fibers depress the crystallization rate relative to an unreinforced polymer since they constrain spherulitic growth by an impingement mechanism. On the other hand, reinforcing fibers can also enhance crystallization rate by providing added surface nucleation sites. This work describes a two‐dimensional simplification of the crystallization process that occurs in bulk materials. It is demonstrated that the relative bulk and fiber nucleation densities, in addition to the fiber fraction, fiber diameter, and spherulitic growth rate control the crystallization kinetics and also the spherulitic and transcrystalline morphologies that develop in reinforced thermoplastic composites. © 1993 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311203

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA three‐dimensional computer simulation has been used to predict crystallization kinetics and crystalline morphology in composite materials that are based on crystallizable thermoplastics. Reinforcing fibers in three‐dimensional simulations show similar behavior to those in two‐dimensional simulations; fibers suppress crystallization relative to an unreinforced polymer since they constrain spherulitic growth by an impingement mechanism, and also enhance crystallization by providing added surface nucleation sites. The effects of varying controlling parameters on crystallization kinetics and morphology are qualitatively the same as those observed in the two‐dimensional case. The relative bulk and fiber nucleation denisities, in addition to the fiber volume fraction, fiber diameter, and spherulitic growth rate control the crystallization kinetics and crystalline morphology that develop in reinforced thermoplastic composites. It is more difficult to achieve the transcrystalline morphology in slices of three‐dimensional composites than it is in two‐dimensional composites because nuclei in 3‐D systems are not constrained to positions in or near a 2‐D plane. © 1993 John

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311204

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractLight scattering from a swollen textured heterogeneous polymer network is discussed using example of a network composite filled by spherical inclusions anisotropically distributed in the matrix. The dependence of the scattering intensity on the Fourier transform of the correlation function dry‐state shear moduli fluctuations has been established.Hvscattering patterns from uniaxial textures and their ratio with the composite anisotropy parameter are analyzed. The sensitivity of theHvscattering pattern on restrictions during the swelling is emphasized. © 1993 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311205

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractModel living oligomers ofN‐benzoyl‐8‐octanelactam initiated by the model octanoylium hexachloroantimonate, SbCl5, and by Ph3C+AsF6−, were studied by1H and13C one‐ and two‐dimensional nuclear magnetic resonance using the COSY, S‐INEPT, COLOC, and ROESY methods. If prepared in the more solvating mixture of 1,1,2,2‐tetrachloroethane (TCE) with 1,2‐dichlorobenzene, the oligomers were found to be linear with the acylium ion as a living group on one end; in TCE only, the oligomers are highly branched. In both cases, the propagation center appears to be strongly coordinated to the nearest benzoylamide chain group. © 1993 Jo

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311206

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThin films of SiPc(OH)2(Pc = phthalocyanine) were formed epitaxially on the (001) surface of mica by vacuum deposition and were then polymerized by heat treatment. The molecular packing of the SiPc(OH)2was determined by electron diffraction and high‐resolution electron microscopy as triclinic\documentclass{article}\pagestyle{empty}\begin{document}${\rm P\bar 1} $\end{document}having dimensionsa= 0.727,b= 1.307,c= 0.688 nm, α = 102.5, β = 104.2, and γ = 97.4°. This monomer crystal grows with itsc‐axis parallel to the a‐axis of the substrate mica and itsbc‐plane parallel to the (001) surface of mica. By heat treatment at 320°C, the SiPc(OH)2polymerized with thec‐axis of the polymer parallel to thec‐axis of the monomer. At 420°C, thec‐axis of the polymer became parallel to thea*‐axis of the monomer (i.e., perpendicular to the film surface). From high‐resolution electron microscopy of partially polymerized specimens, the polymerization was shown to start at the edges of small monomer crystals. This may be considered to be due to the volume expansion during the polymerization. © 1

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311207

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractConformational parameters for a wide variety of aromatic cyclochain polymers have been computed assuming free rotation about virtual bonds. The flexibility with free rotation is shown to be determined by the geometry of the repeat unit and can vary over a wide range (15–1500 Å). Experimental values of the Kuhn segment lengthAare calculated from literature data on the hydrodynamic behavior of polymeric macromolecules of this class in solution. For most polymersAfrfor free rotation is equal to the experimentalAexp, and hindered rotation is mainly due to bulky substituents. © 1993 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311208

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractFiber spinning and mechanical properties of four rigid polyesters with alkoxy substituents of different length and placement were evaluated. Properties of oriented fibers from the polymer with dodecyloxy substituents on the terephthalate moiety, PTA12HQ, were significantly affected by the crystal modification. At room temperature the following properties (tensile modulusE, tensile strength σb, and strain at break εb) could be obtained:E= 9.5 GPa, σb= 85 MPa and εb= 1.1% for phaseLf(the “frozen in layered mesophase”);E= 10.4 GPa, σb= 59 MPa and εb= 0.6% for modification A; E = 17.3 GPa, σb= 158 MPa and εb= 1.2% for modification B. Because of the higher amount of main chains per cross sectional area the polymer with hexyloxy side chains, PTA6HQ, showed better properties at a comparable degree of molecular orientation: E = 24 GPa, σb= 270 MPa, εb= 1.4%. Fibers obtained from the polyester with dodecyloxy substituents on the hydroquinone moiety, PTAHQ12, were too brittle to handle. The polyester with dodecyloxy substituents on both moieties, PTA12HQ12, was spun from the isotropic melt. Because of the obtained low degree of orientation, properties (E= 1 GPa, σb= 40 MPa, and εb= 6.3%) were governed by interactions between the chains (the main chains are not load‐bearing). © 1993 Jo

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311209

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractDynamic mechanical analysis coupled with polarized step‐scan FTIR transmission and two‐dimensional correlation analysis (2D FTIR) has been used to monitor the submolecular orientational responses of the components of a semicrystalline 50 : 50 blend of low‐density polyethylene (LDPE) and perdeuterated high‐density polyethylene (d*‐HDPE) to a small amplitude uniaxial 23.47 Hz sinusoidal mechanical strain. Perdeuteration of the HDPE component allowed the distinction of its response from that of the LDPE in the blend samples. The experiments were carried out at room temperature. Analysis of the data indicates that the crystalline parts of the two components reorient at different rates, with the functional groups of the high‐density portion reorienting faster, in general, than those of the LDPE in response to the mechanical strain. © 1993 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1993.090311210

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY