摘要:

AbstractThe relationships among glass transition, crystallization, melting, and crystal morphology of poly(aryl ether ketone) (PAEK)/poly(other imide) (PEI) blends was studied by thermal, optical and small‐angle x‐ray scattering (SAXS) methods. Two types of PAEK were chosen for this work: poly(aryl ether ether ketone), PEEK, and poly(aryl ether ketone ketone), PEKK, which have distinctly different crystallization rates. Both PAEKs show complete miscibility with PEI in the amorphous phase. As PAEK crystallizes, the noncrystallizable PEI component is rejected from the crystalline region, resulting in a broad amorphous population, which was indicated by the broadening and the increase ofTgover that of the purely amorphous mixture. The presence of the PEI component significantly decreases the bulk crystallization and crystal growth rate of PAEK, but the equilibrium melting temperature and crystal surface free energies are not affected. The morphology of the PEI segregation was investigated by SAXS measurements. The results indicated that the inter(lamellar‐bundle) PEI trapping morphology was dominant in the PEEK/PEI blends under rapid crystallization conditions, whereas the interspherulitic morphology was dominant in the slow crystallizing PEKK/PEI blends. These morphologies were qualitatively explained by the expression δ=D/G, whereGwas the crystal growth rate andDwas the mutual diffusion coefficient. © 1993 John Wiley&So

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310801

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractBlends of poly(aryl ether ketones) (PAEKs) and an amorphous poly(ether imide) (PEI) were used as model systems to study the broadening of the glass transition due to crystallization and the resulting depletion of PAEK from the amorphous phase. Two different PAEKs were studied, which are completely miscible with PEI in the amorphous state; poly(aryl ether ether ketone) (PEEK) and a slower crystallizing poly(aryl ether ketone ketone)(PEKK). Relatively rapid crystallization conditions were chosen in order to trap a significant fraction of PEI between the PAEK crystal lamellae or between bundles of lamellae. The broad glass transitions are apparently a result of the nonuniform nature of this process. The breadth of the glass transition was quantified by thermally stimulated currents (TSC) applied in the thermal sampling (TS) mode. The results compared favorably with DSC data. The magnitude of the apparent activation energy obtained by the TS method allows one to assign the relaxations as cooperative (glass transition‐like) or non‐cooperative and to define the limits of the glass transition with a higher degree of precision than other techniques. Cooperative relaxations can be resolved with this technique, even if they are only a small fraction of the overall relaxing species at a given temperature. In some cases the glass transition region was found to broaden to ca. 60°C after crystallization. © 1993 John Wiley&Sons

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310802

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractMelt‐spinning and mechanical properties of fibers of a new class of semirigid thermotropic liquid‐crystal polymers are presented. These copolyesters are synthesized from 4‐4′‐dihydroxybiphenyl (B), 4‐hydroxybenzoic acid (H), and flexible units provided by aliphatic diacids. The flexible units depress the melting temperature without strongly depressing the mechanical properties. These liquid‐crystal polymers can be easily spun at high draw ratios. Indeed, unlike rigid liquid‐crystal polymers, relatively high draw ratios are needed to attain high mechanical strength. Tensile moduli of about 28 GPa and tensile strengths of about 350 MPa are obtained. © 1993 John

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310803

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractMean permeability coefficients for CO2, O2, N2, and CH4in seven types of 6FDA polyimides with branched or extended diamine moieties were determined at 35.0°C (95.0°F) and at pressures up to 10.5 atm (155 psia). In addition, solubility coefficients for CO2, O2, N2, and CH4in six of these polyimides were determined at 35.0°C and at 6.8 atm (100 psia). Mean diffusion coefficients for the six gas/polyimide systems were calculated from the permeability and solubility data. The relationships between the chemical structure of the polyimides, some of their physical properties (glass transition temperature, mean interchain spacing, specific free volume), and their gas permeability, diffusivity, and solubility behavior are discussed. The 6FDA polyimides studied here exhibit a considerably lower selectivity for the CO2/CH4and O2/N2gas pairs than 6FDA polyimides with short and stiff aromatic diamines with comparable CO2and O2permeabilities. © 1993 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310804

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractWe report a strong dependence of the thermal stability of Nafion® perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation‐exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i.e., Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate‐coun‐terion interaction. © 1993 John Wiley&So

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310805

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe elimination reaction of polyelectrolyte films of poly(phenylene vinylene) precursor polymers into the fully conjugated chain was induced by irradiation with an Ar+laser emitting at 514.5 nm. The experiments were conducted using as cast precursor polyelec‐trolyte films of both the unsubstituted poly(phenylene vinylene), H‐PPV, and its 2,5‐dimethoxyphenylene derivative, DMEO‐PPV. Precursor polymer films impregnated with an azosulfonic dye, which had a strong absorption at the laser emission wavelength, were also irradiated. The elimination reaction was followed by comparing the elemental analysis and the infrared and visibleultraviolet spectra of the irradiated and nonirradiated areas. With the unsubstituted PPV film no elimination was detected even at power fluence levels up to approximately 350 W/cm‐2, but elimination and conversion to the conjugated polymer could be observed at 10 W/cm‐2when the dye was present. For DMEO‐PPV the elimination reaction occurred with or without dye impregnation, and similar marking threshold values were measured in both cases. The molecular mechanism used to explain such observations and the possible application in the area of microelectronics are also discussed. © 1993 John W

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310806

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractPosition annihilation spectroscopy (PAS) was used to measure the relative free‐volume fraction of protective epoxy coatings before and after exposure to liquid water at room temperature. The relative free volume fraction determined before water exposure was compared to the equilibrium water uptake of each coating and a correlation was found. The relative free‐volume fraction of the epoxy coatings decreased slightly after water exposure. This decrease is contrary to the free volume theory of plasticization, but is consistent with the antiplasticization process. Larger decreases in the relative free volume fraction were sought by repeating the water uptake experiments with nitrobenzene which in the bulk, liquid form quenchesortho‐positronium (o‐Ps). Since the o‐Ps lifetime remained approximately constant and the o‐Ps intensity decreased after nitrobenzene absorption, nitrcbenzene is believed to be inhibiting the formation of o‐Ps in the epoxy free volume cavities. Larger decreases in the relative free volume fractions were found after nitrobenzene exposure than after water exposure. These larger decreases are due to the fact that nitrobenzene is a better inhibitor of o‐Ps formation than water in the epoxy free volume cavities. Larger volume fractions of nitrobenzene were absorbed by the coatings than water and were interpreted to be due to interactions between nitrobenzene and the epoxies. © 1993 John

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310807

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe transport properties of the poly(arylether bissulfone) based on bisphenol A (PBSF) and the poly(arylether bisketone) s based on bisphenol A (PBK) and bisphenol S (PBK‐S) are reported at 35°C. Comparisons are made with the polysulfone and the polycarbonate also based on bisphenol A to determine the effect of the long, rigid bisketone and bissulfone groups on polymer properties. A direct comparison also is made between PBK and PBSF, which differ only by their ketone and sulfone groups. The bulkier sulfone group increases free volume andTgmore than the ketone group. This results in higher solubility and diffusivity coefficients for the bissulfone versus the bisketone polymer, both of which contribute to higher permeability coefficients. © 1993 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310808

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractGas transport properties of semicrystalline films of poly(2,2,4,4‐tetramethyl cyclobutane carbonate) (TMCBPC) were studied. Permeability coefficients for He, O2, N2, CH4, and CO2at 35°C for pressures between 1 and 20 atm are reported as well as sorption isotherms for N2, CH4, and CO2at the same conditions. The permeability coefficients for TMCBPC are larger than corresponding values for the aromatic bisphenol‐A polycarbonate (PC) and tetramethyl bisphenol‐A polycarbonate (TMPC), even though the TMCBPC films are semicrystalline. These results are explained on the basis of the larger free volume available for permeation in this polymer. Significant TMCBPC plasticization by CO2was also observed and this causes typical time‐dependent behavior. The plasticization process starts at very low pressures compared with the behavior of aromatic polycarbonates PC and TMPC. This early onset of plasticization seems to be related also to the larger free volume in the amorphous phase of TMCBPC which favors high gas sorption. The diffusion coefficients for TMCBPC are also larger than those reported for the aromatic polycarbonates PC and TMPC. Ideal gas separation factors were found to follow the usual trend; that is, as permeability increases, the ideal separation factor decreases. © 1993 John Wiley&

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310809

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe orientational order of three morphological components, identified previously as two crystalline components, C1and C2, and an amorphous component, A of four polyethylene fibers, including two gelspun ultrahigh molecular weight (PE‐I and PE‐II) and two meltspun moderate molecular weight (PE‐D and PE) polyethylene fibers are further analyzed by rotor‐synchronized two‐dimensional13C CP/MAS (ROSMAS) nuclear magnetic resonance (NMR) techniques. Our results indicate that the orientational order of these components differ substantially among themselves in a given fiber and among different fibers of the same component. Values of β1/2, the polar angle at which the orientational distribution function (ODF) P 〈β〉 decays to half its maximum, are determined to be: 18° (C2 of PE‐II), 21° (C2 of PE‐I), 29° (C2 of PE‐D), 31° (C1 of PE‐I) and 50° (C2 of PE). No orientational sideband can be detected for component A, suggesting that the A component is due to the amorphous domain. The implication of this results and the technical limit of this technique are analyzed.

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310810

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY