摘要:

AbstractA reactive rubber obtained by isocyanation of hydroxyl‐terminated polybutadiene was used as toughening agent for an unsaturated polyester resin. Both the isocyanation and the successive reaction between the modified rubber and the polyester were investigated by Fourier‐transform infrared spectroscopy (FTIR). Fracture measurements at high and low strain rate were carried out on the cured materials to test their toughness. The failure mechanisms were established by morphological analysis of fractured surfaces, performed by scanning electron microscopy. © 1993 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310601

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractIntrinsic viscosities of poly(p‐phenylene terephthalamide) (PPTA) and poly(m‐phenylene isophthalamide) (PMIA) samples of the same molecular weight are determined in 90%, 96% and 100% sulfuric acid at temperatures from 0 to 130°C. Conditions are established under which the degree of coiling of PPTA molecule is close to that for PMIA. Experimental data are compared with the results of theoretical calculations of the Kuhn segment length. In the light of this comparison, some quantitative characteristics of the deformational flexibility mechanism for aromatic polyamide chains and the hindrance to intramolecular rotation are discussed. © 1993 John Wiley&Sons

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310602

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractOxygen permeability measurements have been made on uniaxially and biaxially oriented polypropylene samples. X‐ray diffraction pole‐figure measurements provided the crystalline orientation functions. These results combined with density and refractive index measurements provided the amorphous orientation functions based on the two‐phase model. A good correlation has been found between the amorphous orientation and the oxygen permeability of the samples. © 1993 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310603

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractSamples of poly(ethylene oxide), PEO, doped with neodymium acetate, Nd (Act)3, were prepared and found to be microphase separated. At an EO/Nd (Act)3molar ratio no less than 4, wide‐angle x‐ray diffraction (WAXD) patterns and small‐angle x‐ray scattering (SAXS) data suggest that bulk Nd (Act)3and ionic clusters are both absent. It is inferred from differential scanning calorimetry (DSC) thermograms that in the presence of PEO, Nd (Act)3forms an amorphous phase which is different from the amorphous phase formed by Nd (Act)3alone. The tighter binding of CH3COO‐to Nd3+, in comparison to Cl‐, appears to be responsible for the lack of true dissolution of Nd (Act)3in PEO, a behavior clearly distinct from a number of polymer‐metal salt complexes reported in the literature. © 1993 John W

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310604

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractIt has been demonstrated that use of polymeric emulsifiers under usual processing conditions in the melt state is a powerful technique for preparing polymer alloys. Digitized representation of optical micrographs of thin sections of blends of a low‐density polyethylene and polystyrene (20 wt % PE‐80 wt % PS) containing 2 and 5 wt % of two hydrogenated polybutadiene‐polystyrene block copolymers exhibit different degrees of homogeneity as well as different morphological structures which can be studied by a multifractal analysis. We show how these differences are reflected in thef(α)spectrum of singularities which can be obtained by a box counting method in the canonical approximation. We have found a correlation between thef(α)curves and the mechanical properties of the corresponding samples: the samples which area the less multifractals have the best mechanical properties. © 1993 John Wiley&S

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310605

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractHaze and extinction are studied for coreshell particles in a matrix near transparency. It is shown that, close to transparency, a core‐shell particle behaves optically differently from a nonstructured particle due to the presence of a minimum in the scattering pattern forany particle size. For small particles or domains (<λ/2), this difference is more pronounced. In particular, compositional effects on haze and extinction are studied. It is found that under certain conditions, for the same global composition, strongly optically stratified par‐ticles give lower haze than the homogeneously distributed one by one to two orders of magnitude. The same occurs with the extinction coefficient, however the global composition at which this becomes important differs from that corresponding to a minimum haze. The origin of this difference is discussed in the light of the structure of the scattering pattern in each case. This implies that, for a transparent polymer blend with stratified domains, the minimum haze, maximum transmission and the theoretically perfect matching com‐positions, are all different. Finally, it is shown that, for small highly optically inhomogeneous core‐shell particles, haze goes through an inflection point with increasing particle size, in contrast with the usual monotonically increasing, singly concave, behavior. © 1993 John Wiley&

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310606

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractEthylcellulose films cast from concentrated solutions of chloroform, benzene, and carbon tetrachloride were subjected to the NMR relaxation measurements including1H spin‐lattice relaxation time (T1H), rotating‐frame1H spin‐lattice relaxation time (T1ρH), and13C spin‐lattice relaxation time (T1C). The values ofT1ρHfor carbons in the glucose units of ethyl‐cellulose were of the same order of magnitude as those reported for the crystalline and noncrystalline regions of ramie cellulose. The values ofT1Cfor unsubstituted C2, C3 carbons were smaller than those for the corresponding carbons in the noncrystalline region of native celluloses. TheT1Cvalues for unsubstituted C2, C3, and substituted C6 carbons showed a small but definite dependence on the solvent from which the films were cast. © 1993 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310607

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of solvent on the curing reactions of PMDA/ODA polyamic acids has been investigated using Fourier transform (FT)‐Raman spectroscopy. Films of different thicknesses were cured by: (1) doctor blading 15% solids solutions onto glass slides, (2) removing all but the bound NMP, and (3) removing all theN‐methypyrrolidinone (NMP). The rate of cure and final degree of conversion of the PMDA/ODA polyamic acid to polyimide increased substantially in the presence of NMP, and this effect was attributed to the plasticizing effect of the solvent. Below a critical solvent concentration, which was estimated to be approximately 40% of the NMP concentration in the bound‐solvent limit, the rate of imidization slowed down considerably. Comparison of FT‐Raman data for PMDA/ODA polyamic acid: (1) in solution in NMP, (2) complexed with NMP in the solid state, and (3) in the solid state after all the NMP had been removed with water, indicated that intermolecular interactions were greatest in the latter case and weakest in solution. Spectra of PMDA/ODA in NMP solution provide strong evidence for binding of NMP to the amide carbonyl in solution. © 1993 John Wiley&S

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310608

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA previously proposed theoretical treatment to elucidate the pressure dependence of gas permeability is improved in order to apply it to polymer‐gas systems in which gas dissolution follows the Flory‐Huggins equation. Permeation rates of N2, CH4, and CO2in poly(ethylene‐co‐vinyl acetate) are measured in the pressure range below 90 atm at 10–40°C, and the effect of pressure on permeability is found for each gas. The data are analyzed using the improved method to estimate the contributions of concentration and hydrostatic pressure to the pressure dependence of permeability. The concentration effect decreases with increasing temperature, whereas the hydrostatic‐pressure effect is almost independent of temperature. Crystallinity dependence of the concentration effect is discussed in connection with high‐pressure permeation data of other semicrystalline polymers reported elsewhere. © 1993 John

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310609

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractNon‐Fickian diffusion is often observed at low concentrations and without any obvious irreversible changes. This contradicts some of the predictions of the existing theories, which in general work quite well. For these cases, it is suggested that the filling of microvoids give rise to such effects. The effective diffusivity and a memory‐dependent source/sink term are obtained for describing the overall transport in heterogeneous media under local volume averaging. Some comparisons with experiments are shown. This mechanism is confined to low concentrations and supplements the existing theories which are effective at higher concentrations. © John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310610

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY