摘要:

AbstractA theoretical treatment of the nonexponential relaxation behavior of the different proton nuclear magnetic resonance (NMR) relaxation processes in polymer melts is presented. Formulas are derived for a three‐component model given by two versions and a homogeneous distribution of correlation times. The theoretical results were tested with measurements ofT1,T2e, andT2as functions of frequency and molecular mass in linear fractionated polyethylene samples. While theT1relaxation always yields exponential magnetization decays, theT2eandT2measurements show biexponential relaxation behavior. From the calculations it was found that the correlation time of the local motion is independent of the molecular mass, whereas the correlation time of the slowest motional process increases withM2.8wfor the three‐component model and withM2.2wfor the distribution of correlation times, respectively. © 1992 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300901

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractWe report measurements of the nonlinear relaxation moduli after a step‐shear strain of polystyrene solutions with nearly monodisperse and with bidisperse distributions of molecular weight. We find, as have others, that for monodisperse solutions with M/Me>60, there are anomalies, such as an unusually low nonlinear modulus and a kink in a plot of shear stress versus time after the step strain. Here M is the polymer molecular weight andMeis the entanglement molecular weight. We find that in the bidisperse solutions the anomalies persist as long as Mw/Me>60, whereMwis the weight‐averaged molecular weight of the bidisperse solution. The persistence of the anomalies in bidisperse solutions disagrees with a theory of Marrucci and Grizzuti that attributes the anomalies to strain inhomogeneities similar to shear banding. The Marrucci‐Grizzuti theory predicts that as little as 10% short chains in the bidisperse mix should eliminate the anomalies, whereas in the experiments reported here at least 30% is required. Nevertheless the way in which the anomalies disappear at high strains when one increases the fraction of low‐molecular‐weight component is qualitatively similar to the theoretical predictions and supports the notion that strain inhomogeneities occur in these systems. © 1992 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300902

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractDecay kinetics of phenanthrene phosphorescence in atactic poly(methyl methacrylate) have been studied at 130–170 K in the presence of dissolved oxygen. The kinetics show anomalous behavior and cannot be described in terms of homogeneous diffusion of oxygen. Analysis of the dependence of the kinetics on oxygen concentration shows that such behavior is well accounted for by a polychromatic model assuming a dispersion of diffusion coefficients due to the inhomogeneity of the polymer structure. Possible errors in determining the diffusion coefficient from the phosphorescence quantum yield on the assumption of homogeneous diffusion are discussed. © 1992 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300903

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractIn elastomers the crosslink density, the presence of filler particles, and the volumetric confinement toward sorptive dilation can influence the extent of gas mass uptake. In this study the effects of filler particles on the high‐pressure gas mass sorption and the volumetric dilation of a silicone elastomer matrix has been investigated. Glass beads, ca. 30 μm radii, with different surface treatments were incorporated as inclusions in various specimens at relatively low concentrations of ca. 10% by volume. The high‐pressure gases used were N2and CO2up to a maximum ambient pressure of ca. 25 MPa at ca. 20°C and 42°C, respectively. The gas mass sorption was determined by a vibrating reed technique. The sorptive dilation was measured by an ultrasonic transducer operating as a displacement probe. In certain systems the absorbed CO2gas was able to disrupt the internal interfaces. This led to an increased gas mass uptake in the corrupted specimen. The N2gas did not affect the interfacial bonds. The amount of penetrant uptake was found generally to be reduced when the internal interfaces were not disrupted. The presence of various internal interfaces restrained the sorptive dilation of the elastomeric matrix. These hindrances to the natural sorptive dilation of the elastomer network suppressed the extent of the gas sorption process. This effect has also been investigated separately in detail using model ‘poker chip’ type of specimens of various aspect ratios. The sorptive dilational characteristics have been correlated with the mechanical properties of similar specimens. The influence of an almost complete volumetric confinement on the gas sorption capacity of the silicone elastomer specimen has also been studied. © 1992 John Wile

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300904

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe longitudinal penetration of micromolecular liquid solvents (acetone, dioxane) or swelling agents (methylene chloride, methanol) into unoriented (unstretched) cellulose acetate film has been studied in detail by a variety of techniques, including observation of visible penetrant fronts, birefringence profiles, colored tracer microdensitometry, and microinterferometry. The results, in conjunction with those of Part II, provide a fuller picture of the relevant phenomenology than was previously available, leading to further insight into the mechanism of micromolecular transport in stiff‐chain polymers and its dependence on the nature of the penetrant and the structural changes of the swelling polymer. © 1992 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300905

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe study of micromolecular transport in cellulose acetate film reported previously is here extended by investigation of the effect of different degrees of semipermanent uniaxial macromolecular orientation, produced by prestretching the film under suitable conditions. The changes noted in penetration rate and kinetics and in birefringence, tracer microdensitometry, and microinterferometry profiles for penetration along and across the axis of preferred orientation, are reported in detail and their implications in terms of the transport mechanism are discussed. © 1992 John Wiley&Sons, Inc

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300906

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe molecular weight distribution (MWD) of high‐molecular‐weight isotactic polypropylene is measured by a new method developed for polyethylene (PE) using the turbidity at the lower critical solution temperature (LCST). The attenuation of transmitted lighthiis measured atTias each fractioniis separated from the solution during a temperature increase ΔTi. From the thermogram, the set ofhi(Ti), the MWD can be calculated through a relationMi= f(Ti). The solvent chosen, a mixture of butane and 2‐methylbutane, optimizes resolution and relatively rapid dissolution. Homogenization and absence of degradation are verified by different methods including calorimetry in solution. © 1992 John Wiley&So

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300907

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA free‐volume theory is developed for the analysis of Fickian diffusion processes in glassy polymers. Equations are presented for the prediction of mutual diffusion coefficients in concentrated glassy polymer‐penetrant systems. The concentration dependence of the mutual diffusion coefficient is dependent on how much free volume the solvent contributes to the system and on how the addition of solvent affects the densification of the polymer matrix. © 1992 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300908

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe microphase separation transition (MST) has been studied for short chain diblock copolymers poly(styrene‐b‐isoprene) and poly(styrene‐b‐mma). A detailed analysis of small‐angle x‐ray scattering (SAXS) profiles in the homogeneous phase allows determination of the interaction parameter and the spinodal temperatureTsof the MST.Tsfor the PS/PI diblocks is found to be lower than the glass transition temperature of their hard blocks. This results in a coupling of the MST and the glass transition. Using both structural (SAXS) and thermal differential scanning calorimetry (DSC) methods it is shown that an endothermal peak found in the DSC diagrams is related to the combined effect of the MST and the glass transition. © 1992 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300909

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractNylon‐6/polystyrene (PS) blends were reactively compatibilized by addition of various anhydride functionalized polystyrenes. The morphology of the blends was examined using a scanning electron microscopy (SEM) technique. The particle size of the dispersed styrenic phase was about 3.2 μm for the uncompatibilized 8/2 Nylon‐6/PS blend while those of the compatibilized blends were decreased by as much as two orders of magnitude depending on the amount and type of the functionalized polystyrene (FPS) added. Several low‐molecular weight polystyrenes with terminal anhydride groups, prepared by two different functionalization methods, were examined. The effect of molecular weight on particle size reduction depended on the basis of comparison, mass of additive, or moles of anhydride units. A high‐molecular weight random copolymer of styrene and maleic anhydride was most effective when compared on a mass basis. The increase in adhesion between the Nylon‐6 and the styrenic phases caused by the in situ reaction was evaluated by a lap shear technique. The free polystyrene, Nylon‐6, and Nylon‐FPS copolymer formed were separated by solvent extraction technique using formic acid and toluene. The extent of coupling reaction between the functionalized polystyrenes and Nylon‐6 ranged from 25 to 43%. © 1992 Joh

ISSN:0887-6266    

DOI:10.1002/polb.1992.090300910

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY