摘要:

AbstractThe free volume of poly(trimethylsilyl propyne) (PTMSP), a glassy polymer distinguished by extremely high gas permeability and diffusion coefficients, was determined by means of two probe techniques—the positron annihilation method and the electrochromism method. Lifetime analysis of positron annihilation spectra revealed an additional long‐lived component that is not typical for most of previously studied polymers. A model that has been developed earlier predicts that this lifetime corresponds to the larger size of free‐volume elements having an intrinsic radius of about 6 Å. Therefore, PTMSP should be similar to porous inorganic sorbents. A comparison with the literary data for zeolites and silica gel confirms this. According to the electrochromism method, the temperature dependence of the size of free‐volume elements for PTMSP is much weaker than that for regular glassy polymers like polystyrene. It was concluded that the great free volume in glassy PTMSP is associated with very loose packing of the chains. © 1993 John Wiley&

ISSN:0021-8995    

DOI:10.1002/app.1993.070470111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractElectrochemical copolymerization of styrene andN‐(3‐carboxyphenyl)maleimide was performed in an aqueous sulfuric acid solution using AS‐4 graphite fibers as the working electrode. Cyclic voltammetric analysis results suggest radical initiation of polymerization via the reduction of theN‐(3‐carboxyphenyl)maleimide and sulfuric acid. Radical chain electrocopolymerization was strongly suggested by the inhibition of chain growth in the presence of hydroquinone and 2,2‐diphenylpicrylhydrazyl (DPPH). Compositional analysis of copolymers and reactivity ratiosrs∼ 0.014 andrm∼ 0.041 for styrene andN‐(3‐carboxyphenyl)maleimide [N‐(3‐CMI)], respectively, confirmed a 1 : 1 alternating electrocopolymerization. Kinetic analysis shows a first‐ and 1/2‐order dependence of the rate of chain growth on initial monomer concentration and initiator concentration, respectively. A model incorporating these data is presented.

ISSN:0021-8995    

DOI:10.1002/app.1993.070470112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractTwo kinds of polymer blends, polyacetals (POMs) and ethylene–propylene–diene terpolymer (EPDM), have been prepared by mechanical blending. The rubbery EPDM was added to the rigid POM matrix to increase toughness. The mechanical, physical, thermal, dynamic mechanical, and morphological properties of these samples have been measured. The notched Izod impact strength and the elongation of the blends reaches a maximum at 7.5 wt % EPDM content. Scanning electron micrographs (SEM) showed that the domain sizes of EPDM vary from 0.25 to 1.0 μm and were independent of the composition. The POM/EPDM blends were determined to be immiscible by SEM, but showed singleTgbehavior as determined by differential scanning calorimetry (DSC) and dynamic mechanical analyses up to 7.5 wt % EPDM. Because of that, theTg's of POM and EPDM were very similar in value. © 1993 John Wiley&Sons

ISSN:0021-8995    

DOI:10.1002/app.1993.070470113

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractDeformation of poly(vinyl alcohol)–poly(sodium acrylate) composite hydrogel (PVA–PAA gel) under sinusoidally varying electric fields was studied in electrolyte solutions. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixed solution of PVA and polyacrylic acid. A cyclic bending–straightening motion of the PVA–PAA gel rods of about 1 mm in diameter have been observed in Na2CO3aqueous solutions under the fields. The PVA–PAA gel had a response time of less than several hundreds milliseconds. The bending has also been observed in organic solvents containing an electrolyte when the organic solvent is electrolyzed. It was found that the motion of the gel under electric fields of less than 1 Hz occurred mainly through swelling due to the change of the osmotic pressure based upon the difference of the ion concentration. However, it has not been determined whether the motion at higher frequencies is caused by the osmotic effect. © 1993 John Wil

ISSN:0021-8995    

DOI:10.1002/app.1993.070470114

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe polycondensation reaction between maleic anhydride and 1,6‐hexanediol, withp‐toluenesulfonic acid as catalyst has been carried out. The product has been analyzed spectroscopically and the molecular weight determined by endgroup analysis and gel permeation chromatography. The influence of spatial interactions between condensed groups on the isomerization of maleate into fumarate is discussed, as well as the effects of even‐ and odd‐ numbered carbon atom glycols. © 1993 John Wiley&S

ISSN:0021-8995    

DOI:10.1002/app.1993.070470115

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractDepending on the processing conditions, poly(arylene ether ketone) exhibits unique structural gradients as a result of its thermomechanical history when it is injection‐molded. Gapwise structure gradients change from a fully amorphous to multilayer amorphous–semicrystalline–amorphous and, finally, to a uniformly semicrystalline one when mold temperature is increased. When injection speed is decreased, the crystallized layers become thicker, and at very slow injection speeds, the crystalline layers developed near the two surfaces of the parts approach each other at the core. These structure variations were characterized by differential scanning calorimetry, optical microscopy, and a matrixing microbeam X‐ray diffraction (MMBX) technique developed in our laboratories. The relationship between the structure gradients developed and the processing variables and the cavity geometry are discussed. © 1993 John Wiley&S

ISSN:0021-8995    

DOI:10.1002/app.1993.070470116

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractHigh‐temperature thermoplastics such as poly(arylene ether ketone) form multilayer structures when they are molded at low mold temperatures. The cavity geometry, particularly the cavity thickness, plays an important role in forming these structural gradients. In this paper, we present our results on relatively thick large dumbbell specimens. Unlike the thin specimens (reported in Part I of this series of papers) that show structural gradients composed of amorphous skin‐crystalline intermediate zone and amorphous core, thicker dumbbell specimens exhibit structural gradients with increasing crystallinity from skin to core at low mold temperatures. Optical profiling on thin‐sliced specimens indicate the presence of six layers from skin to core at low mold temperatures, and the number of layers decrease with the increase of mold temperature. As the mold temperature increases, the regions near the surface increase in crystallinity while the core crystallinities remain high and unaffected by the changes in the process variables. At very high mold temperatures where thermally activated crystallization is dominant, the crystallinities become uniform throughout the thickness of the specimens. Wide‐angle X‐ray pole figure investigations indicate that the skin layers possess high preferential orientation with uniplanar axial (200) [001] texture and the core regions possessing lower orientation levels exhibit simple uniaxial texture with the chain axes oriented primarily along the flow direction. Elongation to break, tensile strength, and impact strength increase with the decrease of injection speed. The implications of these structural gradients on the mechanical properties are discussed. © 1993 John Wiley

ISSN:0021-8995    

DOI:10.1002/app.1993.070470117

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMelt rheological properties of the ternary blend of isotactic polypropylene (PP), styreneethylene–butylene–styrene terpolymer (SEBS), and polycarbonate (PC), PP/SEBS/PC, are studied in a wide range of composition, such that PP is the matrix and SEBS and PC are the minor components, with the proportion of one varying from 0 to 30% at various fixed compositions of the other. The respective binary blends, PP/SEBS and PP/PC, studied as the reference systems for interpretation of results on the ternary blends yielded interesting new information about the morphology development and its correlation with melt rheological properties of these binary blends. The studies include the measurement of melt rheological properties on a capillary rheometer in the shear rate range 101–104s−1at a fixed temperature of 240°C. The data presented as conventional flow curves are analyzed for the effect of blend composition and shear rate on pseudoplasticity, melt viscosity, and melt elasticity, and role of each individual component is identified. Morphology of dispersed phases of these blends is studied through scanning electron microscopy of the cryogenically fractured and suitably etched surfaces. Variations of morphology with blend composition and shear rate showed interesting correlation with melt rheological properties, which are discussed in detail. An important finding of the morphological studies is that in the PP/SEBS/PC ternary blend the SEBS phase forms two types of morphologies depending on the blend composition and shear rate: (i) simple droplets and (ii) boundary layer at the surface of the PC droplets. © 1993 John Wiley&

ISSN:0021-8995    

DOI:10.1002/app.1993.070470118

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0021-8995    

DOI:10.1002/app.1993.070470119

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY