摘要:

AbstractX‐ray diffraction of the UHMWPE gel‐films has shown that high heating rate annealing of the films causes deformation of the crystallites. The apparent crystal sizes change with the annealing temperature (Ta). WithTabelow 110°C, the dimensions of the crystallites in c‐axis (Lc) increase associated with the decreasing in a‐axis (La) and b‐axis (Lb), but the changes are small because of the higher energy barrier. WhenTais raised to 138°C,Lcis nearly doubled its value at 60°C whereasLbincreases andLaremains unchanged. IR spectral subtraction was applied to reveal the morphological changes of the gel‐films upon annealing. It has been found that bands of the same type of conformation have different sensitivities subject to the thermal treatment at different annealing temperatures. The results can be understood by assuming the changing process being completed through chain segments sliding along the (020) sectors. © 1995 John

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330501

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA series of lithium and sodium salts of sulfonated polyethylene oxide (PEO) polyurethane ionomers in different levels of ionization were prepared. It has been found that this material is a new type of ionic conductive polymer, characterized by a single‐ion transport mechanism and good mechanical properties. The ionization level significantly influences the ionic conductivity of the samples. When the mole ratio of the metal ion and ether oxygen atom is about 0.05, the ionomers exhibit maximum cationic conductivity. An optimal cationic conductivity of 1.0 × 10−5S/cm is obtained at about 70°C without any addition of organic plasticizer. The conductivity increases apparently when propylene carbonate and low MW PEO are added to the polyurethane ionomer. © 1995 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330502

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractCrystallization behavior of syntheticcis‐1,4 polyisoprene mixed with methyl linolate was investigated by differential scanning calorimetry and dilatometry. At isothermal crystallization temperature of −25°C, a rate of crystallization decreased with the addition of 1 wt % methyl linolate, whereas it increased with a large amount of methyl linolate, about 30% by weight. Although Avrami constant ofcis‐1,4 polyisoprene was 2.82, that of mixtures containing 1 and 30 wt % methyl linolate was found to be approximately 4. This implies the same crystallization mechanism was in operation in the mixtures. Since glass transition temperature,Tg, ofcis‐1,4 polyisoprene decreased as the methyl linolate content of mixture increased, methyl linolate was found to be plasticizer forcis‐1,4 polyisoprene. The increase in the rate of crystallization in the mixtures was corresponding to the decrease inTg. © 1995 John Wile

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330503

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractUltrahigh molecular weight polyethylenes GUR, UTEC 2540, and UTEC 3540 were fractionated by precipitation from cooling of solutions with stirring [stirring‐induced fractional precipitation (SIFP)]. The samples were dissolved in decalin and precipitated over the temperature range of 100‐78°C. Three types of procedures were investigated. From fractionation data, the integral and differential molecular weight distribution (MWD) of the polymer were calculated. The MWD and average molecular weights,$\bar M_w$and$\bar M_n$, by size exclusion chromatography (SEC) and the limiting viscosity number of the fractions and whole polymer were determined. From these data, the Mark‐Houwink constants were calculated. The ‘K’ and ‘aη’ values obtained were 6.70 × 10−4and 0.69, respectively. The MWD curves calculated from SIFP technique by using these constants are in accordance with the MWD by SEC. Fractionation depended on the chemical nature of the stirrer and the cooling rate of the solution during precipitation. The methodology is reproducible. Faster fractionation was observed compared with other methods. © 1995 J

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330504

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe solid‐state15N CP/MAS NMR spectra and15N spin‐lattice relaxation times (T1) of doped and dedoped15N‐labeled polypyrroles prepared by electrochemical polymerization, have been measured by means of high‐resolution solid‐state15N NMR. The15N signal of polypyrrole consists of four peaks decomposed by line shape analysis. The four peaks obtained have been assigned to the various structures of polypyrrole. Further, the half‐width of the15N NMR spectra of polypyrroles is discussed as related to the electrical conductivity. © 1995 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330505

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe permeation rate curves and sorption rate curves of oxygen and nitrogen below 1.3 atm were measured for seven polyimides of which chemical structures were systematically changed. These rate curves were applied Fickian model curves. The Fick's law was found to hold from the pressure independencies of diffusion coefficients for both the experiments. The solubility was better described according to dual‐mode sorption model rather than Henry‐s law from the sorption experiments. The diffusivities of both the gases were correlated with packing density (reciprocal of specific free volume) of the polymer, except two polyimides. The packing density of these two polymers could not be successfully calculated from Bondi's method. However, all the diffusion coefficients decreased linearly with an increase in the cohesive energy density (CED), which was calculated by the group contribution method of van Krevelen. These results suggest that the gas diffusions in polyimides better correlate with CED than with the packing density. Therefore, the cohesive energy density may be considered as a more reliable indication of the efficient gas separation. © 1995 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330506

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractSubstrate‐free thin film of Nylon 13,13 has been prepared continuously by casting the polymer on a water surface fromm‐cresol solution. The uniform thickness of film is ca. 500 A, as measured with a Profilometer. Film morphology and properties have been characterized by transmission electronic microscopy (TEM), x‐ray photoelectron spectroscopy, wide‐angle x‐ray scattering, differential scanning calorimetry and by contact angle measurements. Results show that there is no preferential accumulation of the amide group toward the water surface. A spherulite structure exists in this film with a crystallinity of 26% by DSC. Fibers were drawn from the films which had a tensile modulus of 5 GPa, stiffer than reported for this nylon as prepared by other means. Other members of the nylon series, such as Nylon 6, Nylon 12, have also been prepared in films by the same casting method under modified conditions. © 1995 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330507

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe heat capacities of a poly(methyl methacrylate) hydrogel membrane for an artificial kidney have been determined over the range of temperatures from 228 to 298 K as a function of water content. At least two kinds of water were found: freezable water and nonfreezable water. The partial specific heat capacities of both waters were calculated from the dependence of heat capacity of the hydrogel on the water content. The heat capacities of freezable water were estimated to be 1.04 cal g−1K−1at 298 K and 0.47 cal g−1K−1at 228 K. The mobility must therefore be similar to that of bulk water at 298 K, though the melting temperature was lower than that of bulk water. Consequently, the freezable water was not assigned to bound water but to pore water for which the melting temperature was depressed due to interfacial tension. On the other hand, the heat capacities of nonfreezable water were estimated to be 1.02 cal g−1K−1at 298 K and 1.06 cal g−1K−1at 228 K. The mobility of the water would be similar to that of free water at both 298 and 228 K. © 1995 John

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330508

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractPolyethylene–polystyrene blends containing small amounts of polyethylene (20 wt %) display a cocontinuous phase morphology that is very unstable in the absence of an emulsifier. The kinetics of coalescence at high temperature is therefore very sensitive to differences in the interfacial activity of added polymeric emulsifiers. The morphology of blends added with a pure or a tapered hydrogenated polybutadiene‐b‐polystyrene block copolymer is investigated as a function of annealing time at 180°C. Various image treatments (standard granulometry, opening size granulometry distribution, and multiscaling analysis) were used to quantify the morphological evolution of these blends. The results clearly demonstrate that the tapered block copolymer is definitely more efficient than the corresponding pure diblock for stabilizing the cocontinuous structure of these blends. The differential behavior is assumed to results from differences in the tendency of the two copolymers to segregate and form their own domains. © 1995 John Wiley&So

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330509

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThin sheets of isotactic polypropylene (iPP) and linear low‐density polyethylene (LLDPE) blends were studied by tensile testing, optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Eyring's two‐process yielding theory was used to analyze the data of yield stress as a function of strain rate and temperature, and satisfactory curve‐fitting results were obtained. Furthermore, stress whitening was found to have occurred in the necked regions of tensile specimens under a certain range of yielding conditions. These conditions corresponded to the activation of Process II yielding of Eyring's theory. The whitening was found to be a result of formation of microvoids that initiated at the interface between iPP and LLDPE. © 1995 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330510

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY