摘要:

AbstractThe effects of molecular weight, molecular weight distribution, crystallization temperature, quenching medium, and sample preparation on the formation of ringed spherulites in linear polyethylenes were studied by polarized light microscopy and small‐angle light scattering. When the samples were crystallized at a predetermined temperature, ringed spherulites were formed over a narrow range of temperature and molecular weight with both fractionated and unfractionated polymer samples. Quenching the samples in air at room temperature considerably extended the range of molecular weights for the formation of ringed spherulites. Minor modification of an airquench method further extended the range and yielded better‐defined structures. The results are interpreted in terms of the anisotropy of the melt, the thermal conductivity of the quenching medium, and the shear stress applied during the crystallization process. That highly specific conditions are necessary for spherulite formation, of both the conventional and ringed type, is a major conclusion of this st

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280801

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractBinary solid solutions ofn‐paraffins (n‐C50H102/n‐C60H122) epitaxially prepared on potassium hydrogen phthalate substrate from the vapor phase have been studied by electron diffraction to characterize their phase transitions and structure. The continuity of solid solution in then‐C50H102/n‐C60H122system is demonstrated once lamellar ordering of the crystal packing is achieved. However, such ordering is achieved only by annealing and proceeds through a series of intermediate chain packings. At first, the electron diffraction patterns from all samples prepared at room temperature resemble those from polyethylene, in which no spots corresponding to the interlayer spacings appear. Longitudinal chain translations are induced by annealing to cause the lamellar reflections to appear, while the “polyethylene” subcell reflections remain unsplit until the crystal structure with well‐defined methyl end pl

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280802

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractA high‐temperature, high‐resolution13C nuclear magnetic resonance spectroscopy technique was developed for the analysis of poly (p‐phenylene sulfide) (HT/HR NMR of PPS). This technique can be applied to the identification and quantitative analysis of end groups and polymer structure in high‐temperature polymers where solution temperatures above 200°C are required for analysis. Verification of calculated13C NMR shift values of chloro‐terminated and hydrogen‐terminated end groups was made by HT/HR NMR of two oligo (p‐phenylene sulfide) model compounds. Identification of the chlorine end group was made in high‐molecular weight PPS. On the high‐molecular weight PPS, identification and quantitative analysis of amino andN‐alkylamino end groups were possible only after derivatization of the polymer with13C‐enr

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280803

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe dielectric relaxation data of poly (n‐hexyl methacrylate) and poly (n‐octyl methacrylate) by Strella and Chinai are represented in terms of the relaxation function proposed by Havriliak and Negami using the multiresponse techniques developed by Havriliak and Watts to evaluate the parameters and their dependence on temperature. The parameter α which represents the width of the distribution of relaxation times was found to be dependent on temperature whereas the parameter β representing the skewness of the distribution function was found to be independent of temperature. The relaxation process parameters are discussed in terms of Mansfield's jump

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280804

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThis research contribution addresses mixing phenomena in a polymer blend that exhibits strong intermolecular association and bieutectic phase behavior. Molecular‐level observations of specific interactions between dissimilar blend components have been obtained from high‐resolution solid‐state proton and carbon‐13 nuclear magnetic resonance (NMR) experiments at ambient temperature. Results illustrate mixing effects on the isotropic chemical shifts of the critical component in a completely or partially phase‐mixed blend. Perturbations in the NMR spectra result from conformational changes, hydrogen bonding, molecular complexation, or altered packing geometries that occur concomitantly with the mixing process. More convincing evidence that two components of a strongly interacting blend reside in a near‐neighbor environment is obtained from the measurement of proton spin diffusion between dissimilar species. Proton spin diffusion is measured directly via the high‐resolution CRAMPS experiment (Combined Rotation and Multiple Pulse Spectroscopy) in a molecular complex of poly (ethylene oxide) and resorcinol. A primary objective of this research endeavor is to bridge the gap between macroscopic and molecular‐level probes of phase behavior and intermolecular association in mixtures that form molecular complexes. In this respect, the temperature ‐composition projection of the thermodynamic phase diagram is generated for binary mixtures of poly (ethylene oxide) and resorcinol, whose interaction sites are characterized via solid‐state NMR. Under fortuitous conditions that are related to the overall mixture composition, two morphologically and crystallographically inequivalent phenolic13C NMR signals are identified for resorcinol when the blends exist in a two‐phase region below the eutectic solidification temperature. The success of this proposed structure–property relationship scheme, which bridges molecular‐level mixing phenomena (via NMR) with solid‐state phase behavior (via differential scanning calorimetry) depends on our ability to understand material properties at a level where continuum hyp

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280805

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractUse of the accepted theories of polymer crystallization to interpret crystal growth rate data for a polyethylene fraction from dilute xylene solution leads to the conclusion that crystallization cannot proceed in either in regime I or regime II, nor in an intermediate regime. This apparent paradox means that the classical theory of polymer crystallization does not give the right order of magnitude of the rate of initiation and of the rate of spreading of a secondary nucleus.

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280806

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractFourier‐transform infrared (FTIR) spectroscopy has been used to investigate the segmental orientation of poly(vinyl chloride) (PVC)/poly (α‐methyl‐α‐n‐propyl‐β‐propiolactone) (PMPPL) blends in uniaxially stretched samples over a wide range of compositions and draw ratios. The results indicate that for pure PVC, syndiotactic segments reach a higher degree of orientation than isotactic segments andgaucheconformations. Similarly, for pure PMPPL, crystalline segments orient more than amorphous segments at any given elongation. Thus, for both polymers, the higher orientation is obtained for the more rigid segments or those located in a more rigid (crystalline) phase. The addition of the macromolecular plasticizer PMPPL has no effect on the orientation of PVC syndiotactic segments, but it lowers the orientation of PVCgaucheconformations, suggesting that the polyester is located in the amorphous regions of PVC. Finally, the PMPPL orientation function initially decreases with the addition of PVC and thereafter remains constant. The results are discussed in terms of interpenetrating networks and rela

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280807

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractSorption of N2, O2, Ar, CH4, CO2, C2H4, and C2H6in poly (dimethyl siloxane) liquid and rubber and the dilation of the polymers due to sorption of the gases are studied at 25°C under pressures up to 50 atm. In the liquid, the sorption isotherms for low‐solubility and high‐solubility gases are described by Henry's law and the Flory–Huggins equation, respectively. Gas sorption in the rubber, which contains a 29 wt % silica filler, follows the dual‐mode sorption model, though marked hysteresis is observed in the sorption of O2and CH4. The dilation isotherms increase linearly or exponentially in both polymers with increasing pressure. Considering that gas molecules adsorbed into micropores of the filler particles do not participate in the dilation, partial molar volumes of the dissolved gases in the rubber are determined from data of sorption and dilation. The values are nearly equal to the partial molar volumes in the liquid (48–6

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280808

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe mutual miscibility of random poly (styrene‐co‐methylmethacrylate)s with different compositions but a constant molecular weight ofMw≅ 150,000 was studied at room temperature and at 180°C. Compatibility was analyzed with films cast from solutions with different solvents. The reliability of the analytical technique is discussed. The miscibility windows {x,yx}, which define the limits of miscibility of the blends of a given copolymer P (SxMMA1−x) with other copolymers P (SyMMA1−y), were determined for allx. The widths |x−yx| of these windows are, contrary to the predictions of the Flory–Huggins model, different foryx>xandyx>x, and depend strongly onx. Miscibility is better for blends with a high MMA content. The windows are markedly wider at room temperature. Many blends are, therefore, “semicompatible,” i.e., have a critical point of the LCST type between room tem

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280809

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractA derivation is presented of a ternary diffusion model to describe the mass transfer processes associated with the quench bath period of the phase inversion process for membrane formation. The complete governing equations, initial conditions, and boundary conditions in the casting film and coagulation bath are presented. Equations for ternary chemical potentials and diffusion coefficients are consistently based on constant specific volume formulations. The model is applied to the analysis of mass transfer paths and their effects on membrane structure formation. Precipitation times are determined for given sets of conditions by superposing calculated mass transfer paths on the ternary phase diagram and observing when the miscibility gap is crossed. Comparisons are made with an earlier reported study on the membrane‐forming system: water‐acetone‐cellulose acetate (CA). Agreement between predicted and measured precipitation times is found to be excellent. The polymer film composition profile at the moment of precipitation is shown to be a useful indicator of both skin and sublayer structures, allowing distinctions to be made between conditions leading to spongelike and fingerlike morphologies. The influence of model parameters on the mass transfer paths and associated polymer profiles is also disc

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280810

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY