摘要:

AbstractA study of the thermal and mechanical characteristics of polyethylene oxide‐Fe(SCN)3complexes shows the existence of structures which can be described by considering a crystalline phase of pure polyethelene oxide (PEO) and an amorphous phase of PEO with dissolved salt. Increasing salt contents decrease the content of crystals, favoring the formation of complexes with a high degree of noncrystallinity as a result of strong polymersalt interactions which tend to enhance the distortion degree of the polymeric skeleton. The microscopic homogeneity of the complexes is also confirmed by the presence in the thermal and mechanical spectra of single glass transitions, which shift to higher temperatures with increasing salt content. Two molecular relaxations are present in the mechanical behavior of these systems, the γ‐and the αa‐processes at low and high temperatures, respectively, and show a relaxation strength which increases with decreasing degree of crystallinity of the polymer up to aX∼ 0.10 molar fraction. Both relaxations exhibit a marked nonexponentiality which has been well accounted for in terms of a gaussian distribution of relaxation times for the γ‐process and of the Kolrausch‐Williams‐Watt exponential function for the αa‐process. In the glassy region, the elastic modulusE' reveals a linear temperature dependence which has been interpreted as arising from the anharmonicity of vibrational modes. Increasing noncrystallinity of the system gives rise to an increase of the anharmonicity parameter, which has been ascribed to the influence of the “free volume” in determining the thermal expansivity. ©1

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330111

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

Abstractd‐Block transition‐metal‐containing polymer blends which form coordination complexes are described in this treatise. The model compounds are zinc acetate dihydrate, copper acetate dihydrate, nickel acetate tetrahydrate, cobalt chloride hexahydrate, palladium chloride bis (acetonitrile), and the dimer of dichlorotricarbonylruthenium (II). Two classes of ligands are of interest. Poly (4‐vinylpyridine), P4VP, and copolymers that contain 4‐vinylpyridine repeat units form complexes with zinc, copper, nickel, cobalt, and ruthenium salts. Atactic 1,2‐polybutadiene contains olefinic sidegroups that displace weakly bound acetonitrile ligands and coordinate to palladium chloride. Thermal analysis via differential scanning calorimetry suggests that the glass transition temperature of the polymeric ligand is enhanced by these low‐molecular‐weight transition‐metal salts in binary and ternary blends. In some cases,d‐block salts function as transition‐metal compatibilizers for copolymers that would otherwise be immiscible. The isothermal ternary phase diagram for polybutadiene with palladium chloride highlights regions of gelation, precipitation, and transparent solutions during blend preparation in tetrahydrofuran. Fourier transform infrared spectroscopy provides molecular‐level data that support the concept of polymeric coordination complexes. High‐resolution carbon‐13 solid‐state NMR spectroscopy identifies (1) near‐neighbor interactions between polymeric pyridine ligands and the ruthenium salt, and (2) a considerable reduction in the molecular mobility of the polybutadiene chain backbone when it forms a coordination complex with palladium chloride. The elastic modulus of polybutadiene increases by three orders of magnitude when the palladium salt concentration is 4 mol % in a solid‐state glassy film. A thermodynamic interpretation of ligand field stabilization energies appropriate to tetrahedral cobalt and octahedral nickel complexes is employed to estimate the synergistic enhancement of the glass transition temperature, particularly when coordination crosslinks are pr

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330112

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe mechanical properties of poly(ethylene terephthalate) (PET) fibers at temperatures above the glass transition are investigated by means of a specially constructed device. Measurements of the deformation rate and of the “dynamic” stress‐strain curves of the fibers are performed in nearly isothermal regime (after initial rapid heating) in a temperature interval 100–200°C. The results reported in the present work demonstrate that the high‐temperature mechanical characteristics of rapidly crystallizing polymers can be deduced to a satisfactory precision, while keeping the crystallinity development at low level. Our investigations indicate that if the high‐temperature deformation is sufficiently fast, the polymer behavior is similar to the deformation at sub‐Tgtemperatures. Based on this similarity, a qualitative model of the deformation in the high‐temperature region is proposed. The proposed model is fundamentally equivalent to the models describing mechanical deformation of glassy polymers at temperatures below the glass transition. ©1995 Joh

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330113

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe temperature dependence of gas sorption and transport properties is examined for two polyimide isomers. The permeabilities and solubilities of five gases in these materials are reported over an extensive temperature range from 35 to 325°C. Also, the activation energies for permeation, the heats of sorption, and the activation energies for diffusion obtained for both polyimides are compared and correlated with physical properties of the polymers and penetrants. The influence of temperature on the selective properties of these membrane materials is discussed for three gas separations; He/N2, CO2/CH4,and O2/N2.Thorough analysis of these data provides insight into the influence of the subtle difference in chain structure of the two isomers. The performance of the 6FDA‐6FpDA as a separation membrane at high temperatures suggests that it is an outstanding candidate for use in novel elevated temperature applications. ©1995 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330114

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractUsing a molecular model introduced previously, we study the effects of chain‐end segregation on the relationship between strength (σ) and diameter(d)in polymeric fibers. For segregated structures with a monodisperse molecular weight distribution, our results show a scaling law σ ∼d−α, with α in the range [0.4–0.5], in agreement with experimental observation. A weaker dependence is found for polydisperse systems. Further investigation also reveals that macroscopic cracks have little influence on the fiber strength/diameter relationship, unless the crack width shows a faster than linear increase with fiber diameter. Finally, our model results also indicate a very weak dependence of fiber strength on its length, in good agreement with experimental observation. ©1995 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330115

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractHDPE was γ‐irradiated at room temperature. The resistance to slow crack growth (SCG) was measured in single edge notched tensile specimens under constant load as a function of the dose. The resistance to SCG initially decreased to a minimum value at a dose between 0.05 and 0.10 Mrd. The minimum value was 45% less than for the undosed state. For doses greater than 0.10 Mrd, the resistance to SCG increased up to a dose of 50 Mrd, where its value had increased by a factor of 102. The gel point occurred at 1–3 Mrd. MI and the crack opening displacement exhibited maximum values at a dose of 0.1 Mrd. The behaviors of SCG, MI and crack opening displacement were consistent with the explanation that chain scission dominated for doses less than 0.1 Mrd, and cross‐linking dominated at the higher doses. For doses beyond 50 Mrd, the resin became so brittle that it cracked during the loading of the specimen. Beyond the gel point the density increased from 0.9694 to 0.9716 g/cm3at a dose of 160 Mrd. ©1995 John Wiley&So

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330116

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY