摘要:

AbstractThe nonradiative energy transfer (NRET) method has been used to study the miscibility of polymer blends in the solid state. This can be done by labeling the polymers with fluorescence donor and acceptor chromophores. The efficiency of energy transfer, which reveals the interpenetration of the chains, is measured by following changes in the fluorescence intensity ratio of the donor and acceptor as a function of the concentration of the polymer mixture and by comparison with reference values corresponding to totally miscible and totally immiscible systems. It is shown that the reference ratio corresponding to the absence of energy transfer must be determined by using donor‐labeled and acceptor‐labeled polymer films, instead of making measurements in chromophore solutions in organic solvents, as has usually been done. It is also shown that fluorescence quenching is important in such studies, since it can lead to variations of the fluorescence intensity ratio by more than an order of magnitude; this factor varies with blend concentration and is particularly sensitive to the presence of halogen atoms. The NRET technique has been applied to several PVC/CPVC binary blends and to PCL/PVC/CPVC ternary blends in which PVC and CPVC were labeled by naphthalene and anthracene, respectively [PCL is poly(ε‐caprolactone), PVC is poly(vinyl chloride), and CPVC is chlorinated PVC]. For binary blends, the measured intensity ratios indicate the immiscibility of PVC with CPVC, although there is nonnegligible energy transfer between the two phases. For ternary blends, the intensity ratios indicate that the addition of up to 40 wt % of PCL to the immiscible PVC/CPVC binary system leads to the formation of two coexisting PCL/PVC and PCL/CPVC

ISSN:0887-6266    

DOI:10.1002/polb.1989.090271001

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractSmall‐angle neutron scattering (SANS) is a useful technique for investigating the anisotropy of density fluctuations when these have single orientation direction. The commonly used method for treating asymmetric SANS data is to analyze sectors of data parallel and perpendicular to the orientation axis. Other methods based on the use of all the available two‐dimensional (2D) data are discussed. These consist in least‐squares fitting of the 2D data to models that include nonuniform deformations of the sample. An inverse 2D Fourier transform of the raw data has also been used to obtain an asymmetric pair correlation function. A hot stretched partially deuterated homopolymer and a stretched microphase segregated rubbery random copolymer system are used as examples of anisotropic scatt

ISSN:0887-6266    

DOI:10.1002/polb.1989.090271002

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe glass temperatures, moduli, and yield stresses for shear failure have been characterized for homogeneous blends of poly(2,6‐dimethyl‐1,4‐phenylene ether), homopolystyrene (1/1), and a number of diluents ofTgs from −134 to +32°C. In a blend series based of a given diluent, the mechanical properties vary with blendTgat rates that are characteristics of the particular diluent. These characteristic rates are found to depend strongly on theTgof the neat diluent. Thus, for blends all withTg= 90°C, for example, modulus and yield stress differ by as much as 50% over the range of diluents. Low‐temperature relaxation measurements together with a number of previous dynamic spectroscopy studies of polymer/diluent systems at low temperatures suggest that many single‐phase polymer/diluent blends may exhibit two primary relaxations—the depressed alpha relaxation of the resin and a somewhat elevated alpha relaxation of the diluent—at quite different temperatures. Both of these relaxations influence stiffness and strength properties at intermediate temperatures. The often‐studied antiplasticization phenomena are viewed as a aberrations from a much more general influence of plasticizers on properties at temperatures below the alpha rela

ISSN:0887-6266    

DOI:10.1002/polb.1989.090271003

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThermotropic poly(sulfonyl hydroquinone terephthalate) with either H or CH3in the lateral substituent was aligned by drawing from nematic melts. Virtually identical x‐ray intensity distributions were recorded consisting of “disks” of intensity periodically spaced along the meridian and concentric rings of intensity lying in the equatorial plane of reciprocal space. They correspond to what is expected for the hexagonal packing of parallel periodic chains that are randomly displaced along the chain axes. Using interactive graphics, appropriate molecular models were deduced in conformity with the observed diffraction intens

ISSN:0887-6266    

DOI:10.1002/polb.1989.090271004

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractSemiflexible thermotropic aromatic polyesters with lateral groups were aligned magnetically and mechanically in monodomains after separation into high‐molecular‐weight (polymer) and low‐molecular‐weight (oligomer) fractions. Based on the x‐ray intensity distributions recorded for a series of seven different substituents in the arylsulfonyl substituted group, a novel smectic structure was determined for H, F, Cl, OCH3, and CH3in theparaposition while a normal nematic alignment prevailed when it contained

ISSN:0887-6266    

DOI:10.1002/polb.1989.090271005

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractHigh frequency dielectric measurements in the range 10 MHz to 10 GHz have been performed on poly(ethylene oxide) (PEO) and its complexes with lithium perchlorate using time domain spectroscopy. Measurements were made over a wide polymer‐to‐salt composition range and in the temperature range 50–75°C. All samples were amorphous. A relaxation was observed for PEO and its complexes with LiClO4in the GHz region and is attributed to the β (αa) relaxation arising from long‐range segmental motion of the polymer or the ion‐polymer complex. Good agreement was found between conductivity values determined by TDS and those quoted in the literature An increase in salt concentration in the polymer increases the distribution of relaxation times which may be explained in terms of increased intermolecular and intramolecular transient crosslinks. The dispersion amplitude (ε ′0−ε ′∫) has a maximum value between an O/Li ratio of 20:1 and 12:1 and shows a similar dependence on salt concent

ISSN:0887-6266    

DOI:10.1002/polb.1989.090271006

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper describes small angle light scattering (SALS) calculations and compares the results for isotropic and anisotropic spheres. For isotropic spheres the exact Mie theory is compared with the Rayleigh‐Gans‐Debye (RGD) and the anomalous diffraction (AD) approximations in order to study the validity of the approximations. For anisotropic spheres the RGD is compared with the AD approximation. A study of SALS in the RGD approximation shows that the first‐order intensity maximum corresponding to a lobe of the four‐leaf clover pattern is not only a function of the sphere diameter but also depends on the isotropic and the anisotropic refractive index of the sphere. The practical implications of this are di

ISSN:0887-6266    

DOI:10.1002/polb.1989.090271007

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractNew experimental measurements are reported of small‐angle polarized and depolarized light scattering from almost monodisperse isotropic, spherical particle, polystyrene latexes. The shape and intensity distribution of the scattering patterns is shown to compare closely with the calculated patterns based on the exact Mie scattering theory from a single spher

ISSN:0887-6266    

DOI:10.1002/polb.1989.090271008

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractPoly(p‐phenylene vinylene) (PPV) undergoes a first‐order crystal‐crystal phase transition when chemically doped with AsF5, SbF5, or H2SO4or electrochemically oxidized with ClO‐4as the counterion. These structures have been observed using wide‐angle x‐ray diffraction. Doping with these agents does not disrupt the original orientation of the PPV crystallites. The crystalline phases obtained with all dopants employed here are similar in character, indicating a closely related family of electrically conductive structures having orthorhombic symmetry. An electrically conductive phase consisting of layers of polymer chains separated by a layer of the chemical dopant

ISSN:0887-6266    

DOI:10.1002/polb.1989.090271009

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractX‐ray photoelectron spectroscopy (XPS) studies have been performed on charge transfer complexes oftrans‐polyphenylacetylene (PPA). The acceptors used included halogens, such as I2and Br2, and organic electron acceptors, such as 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ), chloranil, fluoranil, and 7,7,8,8‐tetracyano‐p‐quinodimethane (TCNQ). Incomplete and relatively weak charge transfer interactions were observed in most of the complexes. These help to account for the relatively low conductivity levels observed in most of the PPA complexes when compared with the corresponding complexes of other conjugated polymers. PPA has also been found to interact with molecular oxygen to some extent in solution. In complexes involving O2, Br2, and fluoranil, XPS data suggest that the charge transfer interaction may have proceeded further than the pure formation of molecular charge

ISSN:0887-6266    

DOI:10.1002/polb.1989.090271010

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY