摘要:

AbstractThe orientation of the crystalline and amorphous phases in uniaxially drawn samples of polytetramethylene oxide has been studied by x‐ray and NMR methods. Pole figure measurements give the orientation of the crystalline phase. Its dependence on the draw ratio does not obey the pseudoaffine model. The crystalline fraction is derived from NMR measurements at temperatures betweenTgandTm, where the free induction decay (FID) of the unoriented sample can be analyzed in terms of a rigid (crystalline), a constrained, and an amorphous phase. Low temperature (T

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260801

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe nine independent stiffness constantsCpqfor rolled nylon 66 at thickness reduction ratios λt= 2.4, 4.9, 7.6 have been measured from −40 to 50°C by an ultrasonic method at 10 MHz. Analysis of x‐ray pole figures indicates that at high λtthe material has a uniplanar‐axial texture, with hydrogen‐bonded (010) planes parallel to the roll plane and the molecular chains along the roll direction. The mechanical behavior is determined not only by the alignment of molecular chains and hydrogen bonds but also by the microfibrillar morphology. On the basis of this idea the magnitudes of the tensile moduli along the three principal axes can be understood in terms of the Takayanagi model. The effects of water absorption have also been in

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260802

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractA modified diffuse reflectance technique is used to characterize the surface hydrolysis of Kevlar‐49 fibers. Treatment with 10 wt% NaOH solution produces carboxylate groups on the surface which increase rapidly up to treatment times of about 20 min at room temperature or 50 min in boiling solution. After this maximum the carboxylate groups decrease and then level out. This behavior can be explained by considering the increase as due to hydrolysis of the surface amide groups, competing with the decrease due to removal of the extensively hydrolyzed, fragmented molecules into the treatment solution. Our results shows that mild conditions (10 wt% NaOH and room temperature) as well as relatively small treatment times (less than 20 min) can be used for modifying the surface of the Kevlar‐49 fiber without destroying the skin and thus deteriorating the mechanical properties of the fi

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260803

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe compatibility of poly(vinyl chloride) (PVC) with linear polyethers is examined over the entire composition range. This study examines blends with poly(methylene oxide) (PMO) and poly(ethylene oxide) (PEO) of medium (MMW) and high (HMW) molecular weight. The techniques used are dynamic mechanical analysis, DSC, and optical microscopy (phase contrast and polarizing). The results indicate that all polyethers show limited miscibility in the melt at high PVC contents. Proper analysis of theTmdata using the Kwei‐Frisch and Hoffman‐Weeks procedures allows the determination of the thermodynamic interaction parameter, which is found to be close to zero for all pairs of ble

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260804

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe symmetry of the orientational distribution function of dye molecules in stretched PVA films is studied using polarized fluorescence. The different symmetries are monitored by a simple experimental technique in which angle‐resolved fluorescence depolarization ratios are measured. A uniaxial distribution of rhodamine 6G molecules is obtained on stretching the film at temperatures above 60°C. In contrast a biaxial distribution of trypaflavine molecules is found for stretch temperatures in the 50–115°C range. It is suggested that the hydrogen bonding between the PVA chains, and between the dye molecules and the PVA chains, influences the symmetry of the distribution upon stret

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260805

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe integral of loss modulus versus temperature plots in the vicinity of the glass transition temperature (loss area, LA) was characterized for various homopolymers, statistical copolymers, and interpenetrating polymer networks (IPNs), based on acrylics, vinyls, and styrenic mers. The quantity LA was found to be a molecular characteristic, governed by the structure of the individual mers. The LA of both IPNs and statistical copolymers obeys an additive relation of the component polymers. A group contribution analysis for LA was developed in which each moiety contributes a specific value to LA. A table derived via this group‐contribution analysis permits the prediction of LA values. The results show that backbone motions and the moieties attached directly to the backbone contribute the most to the damping peak, and that long side chains act as diluent

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260806

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractHigh‐temperature polyimide films with metallic gold surfaces can be fabricated by the incorporation of a soluble metal salt into a solution of polyamic acid. Thermal treatment of these solutions produces the polyimide, decomposes the metal salt to metallic gold, and promotes the formation and growth of the metallized surface. What appeared to be a continuous metallic surface was actually composed of large gold aggregates. It is suspected that the formation of colloidal gold during the initial thermal treatment provides precursors to the large metal aggregates. Thermal treatment has been shown to influence the size and distribution of the aggregates. The shape of the aggregates suggests that diffusion‐limited aggregation may be responsible for the unique shape of some of the gold aggrega

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260807

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractInteractions between rheology and fluid→solid transformations through crystallization are demonstrated through an experimental study of crystallization of polyethylene terephthalate in uniaxial stress fields. Effect of the strength of the stress field on the kinetics of crystallization is shown to diminish greatly beyond the initiation of crystallization. Consequences of crystallization in anisotropic stress fields in the generation of mechanical properties are also described. This experimental study points clearly to the deficiencies in current theoretical formulations of kinetics of crystallizatio

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260808

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractEffect of extrusion conditions, particularly temperature, on the structure development of fibers from poly(ethylene terephthalate) modified with 60 mol%p‐hydroxybenzoic acid was investigated. Light microscopy revealed that the structure of the liquid‐crystalline fiber was highly dependent on the extrusion temperature: low‐temperature‐spun fibers exhibited a structure with domains or clusters of crystallites randomly oriented, whereas the fibers spun at high temperatures had a well‐developed fibrillar texture. Anisotropy of the fibers, as evidenced by dichroism and by the variation of brightness or darkness of the fibers between crossed polars, was significantly higher for those spun at relatively high temperatures. Scanning electron microscopy revealed that the fibers spun at relatively low temperatures had poorly oriented, nonuniform morphology. Those produced at relatively high temperatures, on the other hand, consisted of well‐developed fibrils. X‐ray diffraction patterns showed that the molecular orientation increased with increasing extrusion temperature. A model for the development of fiber structure from thermotropic liquid‐crystalline polym

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260809

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractOrganic semiconductor devices using electrochemically prepared poly(N‐methylpyrrole) (PNP) were characterized by capacitance‐voltage (C‐V) measurements. A device with aluminum evaporated on the PNP behaved as a MOS (metal‐oxide semiconductor) diode in vacuum. Assuming the oxide layer between the metal and the PNP to be pure Al2O3, the MOS parameters were calculated. The values obtained for depletion widthW= 166 Å and acceptor densityNA= 1018cm−3in the PNP were reasonable by comparison with the previously reported values obtained by Schottky analysis. An indium/poly(p‐phenylene)‐1,3,4‐oxadiazole (POD)/PNP diode was prepared, and C‐V measurements were carried out in air. The diode behaved like an MIS (metal‐insulator semiconductor) device, but the characteristics showed large variation with frequency. We have proposed a schematic model for this mechanism on the basis of the results obtained by dielectric measurements of POD and the temperature dependence of the

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260810

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY