摘要:

AbstractBecause a study of the results reported for the chain dimensions of polydimethylsiloxane (PDMS), critical for the onset of this polymer's non‐Newtonian flow behavior, obtained from the viscosity‐molecular weight relationships available from the literature, clearly revealed that considerable differences exist between the reported data, a detailed analysis of these data was performed together with an additional examination of 10 new PDMS samples that were selected so as to have molecular weights that would fill the gaps observed in the polymer viscosity–chain length relationship constructed from the accepted literature data. The results obtained were analyzed by using several different procedures integrated into a recently described comparative method that could allow for determination of what is called the most realistic critical value,Zwc. The latter was determined as 930 PDMS main‐chain atoms, which corresponds to this polymer's degree of polymerization of 464.5 and the weight‐average molecular weight of 34,500. It is not only shown that after elimination of some clearly erroneous data points from the previously reported relationships the obtained critical chain‐length values could very well fit the earlier relationships, but also that appropriate “master” relationships were constructed including 48 pairs of the old and 10 pairs of the new data points. It is suggested that this relationship be accepted as the best‐fit viscosity–polymer chain‐length dependence for PDMS, and it is pointed out that the obtained PDMS critical chain‐length value ranks this polymer's macromolecules as the most flexible of the corresponding long‐chain molecules presently known. ©

ISSN:0021-8995    

DOI:10.1002/app.1993.070490901

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

年代:1993

数据来源: WILEY

摘要:

AbstractPhase‐separation behaviors of latex dispersions, using commercial latices of three different median sizes, and pigmented coatings are examined. Both the dispersions and pigmented coatings at a 0.32 volume fraction of total dispersed phase were thickened with water‐soluble polymers, with and without surfactant hydrophobes. Latex dispersions thickened with water‐soluble polymers without hydrophobe modification follow the phase‐separation behavior described by the volume restriction flocculation (VRF) concept (i.e., molecular weight of the thickener or particle size of the latex). This is surprising since commercial latices contain a variety of surface‐stabilizing moieties, in addition to surfactant. Latex dispersions thickened with commercial and model hydrophobically modified ethoxylated urethane (HEUR) polymers do not follow the phase‐separation behavior predicted by the VRF concept. The lack of correlation of phase behavior with latex median size in HEUR‐thickened formulations led to an examination of four secondary thickeners, noted for providing high viscosities at low shear rates. With an all‐acrylic, large median‐size latex, the combinations of commercial HEURs with secondary thickeners are effective in eliminating phase separation; only partial reduction in phase separation is observed with a vinyl acetateacrylic large‐particle latex. The influence of HEUR/secondary thickener blends on the film properties also is discussed. © 1993

ISSN:0021-8995    

DOI:10.1002/app.1993.070490902

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

年代:1993

数据来源: WILEY

摘要:

AbstractPreparation of sodium salt of di(2‐ethylhexyl)dithiophosphoric acid (DTPANa) by reaction of the corresponding DTPA with sodium hydride has been described. Nucleophilic substitution of chlorine on poly(vinylchloride) (PVC) by a di(2‐ethylhexyl)dithiophosphate group resulting in modified polymer (MP) was characterized by the second order rate constant equal to 6.6 × 10−5M−1s−1. Formation of homogeneous stable gelled phases composed of MP and DTPA, as well as MP, PVC, and DTPA, was demonstrated. The gelled material is capable of selective separation of metal ions under the conditions of extraction chromatography. © 1993 John Wile

ISSN:0021-8995    

DOI:10.1002/app.1993.070490903

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

年代:1993

数据来源: WILEY

摘要:

AbstractThermal expansion property at 288°C and methylene chloride resistance of poly(2,6‐dimethyl‐1,4‐phenylene ether (PPE)/epoxy laminate were found to be affected by the functionality on PPE resin. Nonlofting PPE/epoxy laminates were prepared with the PPE grafted with fumaric acid or the PPE having (di‐n‐butylamino) methyl substituent on the polymer backbone. Employing vacuum‐vented PPE extrudate or phenol‐redistributed PPE was also effective in improving the PPE/epoxy laminate properties. Attempts to preparing a real PPE/epoxy interpenetrating network as the matrix material for the laminate were also made by incorporating both PPE crosslinker and epoxy curing catalysts in the same formulation. © 1993 John

ISSN:0021-8995    

DOI:10.1002/app.1993.070490904

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

年代:1993

数据来源: WILEY

摘要:

AbstractWood plastic composites (WPC) of simul were prepared by gamma radiation using butylacrylate (BA) and methylmethacrylate (MMA) as the monomer and methanol as the swelling agent at 9:1 (v/v) ratio. IR spectra of simul, bulk polymer of BA (or MMA) film, and WPC of different polymer loadings ranging from 18 to 115% were studied. Increase of the characteristic peak intensity at 1735 cm−1(CO vibration for acetyl groups) over that of 1620 cm−1(conjugated aryl carbonyl groups) along with the increase of polymer loading of simul with the monomer indicates that the graft copolymerization took place between the monomer and the simul wood matrix. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070490905

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

年代:1993

数据来源: WILEY

摘要:

AbstractCrosslinked polymer networks ofN‐isopropylacrylamide (NiPAAm) containing small amounts of either anionic or cationic comonomers, or mixtures of both were fabricated and characterized in terms of their aqueous swelling and critical behavior. These gels demonstrate critical transition temperatures in aqueous media between a highly solvated, swollen gel state and a collapsed, dehydrated network over temperature ranges comparable to that of pure NiPAAm, with modifications of gel critical points and respective temperature ranges dependent upon comonomer type and content. Copolymer gel swelling ratios are significantly larger than those reported for pure homopolymer NiPAAm gels, even when only 0.5 mol % of comonomer is incorporated. At temperatures exceeding the collapse transition point, all copolymer gels collapse to a state of nearly complete dehydration, demonstrating short‐time collapsed‐state swelling ratios far lower than those of pure NiPAAm networks. Collapse kinetics for the ionomeric gels are much more rapid than those of pure NiPAAm, achieving collapse state equilibrium on time scales of seconds. Swelling behavior as a function of pH, buffer type, ionic strength, crosslinking, and temperature is detailed over a range of copolymer compositions. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070490906

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe mechanical and physical properties, as well as the crystalline structure of silk fibers grafted with a binary mixture of styrene (St) andn‐butyl methacrylate (BMA) were studied as a function of the weight gain. The size of the fibers increased linearly with the extent of grafting. The strength, the elongation at break, and the tensile modulus decreased with increasing weight gain, but the breaking load remained almost unchanged. The difference among the tensile properties measured in dry and wet states decreased beyond weight gain of 50% because of the hydrophobic properties of grafted silk fibers. The thermal behavior was determined by differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA) measurements. Silk fibers attained a higher thermal stability as the amount of loaded polymer increased. The thermally induced molecular movement of St/BMA‐grafted silk fibers was enhanced as judged by shifting the onset and the position of the dynamic loss modulus (E″) peak to lower temperature when the weight gain increased. X‐ray diffraction curves demonstrated that the crystalline structure of silk fibers remained unchanged regardless of the St/BMA grafting. © 1993 John Wiley&S

ISSN:0021-8995    

DOI:10.1002/app.1993.070490907

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

年代:1993

数据来源: WILEY

摘要:

AbstractA unique series of ethylene and propylene sequential polymerization experiments have been carried out in a stirred bed gas phase reactor using unsupported Stauffer AA catalyst (TiCl3·\documentclass{article}\pagestyle{empty}\begin{document}$\frac{1}{3}$\end{document}AlCl3). Several interesting kinetic results were observed. It was found that propylene causes rate enhancement for a subsequent ethylene polymerization but that ethylene causes a rate reduction for a subsequent propylene polymerization. Furthermore, the rate enhancement/reduction effect increases with the duration of the preceding polymerization. Chemical/kinetic effects were found to be the likely causes of both the rate enhancements and the rate reductions observed during sequential polymerization. It was also shown that enhanced monomer sorption caused by the presence of a more soluble component, such as a heavier comonomer, does contribute to rate enhancement duringsimultaneouscopolymerizations, but is not a factor forsequentialpolymerizations. © 1993 John Wiley&Sons, In

ISSN:0021-8995    

DOI:10.1002/app.1993.070490908

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn this article we propose a new equation that combines behaviors of Bingham and Williamson pseudoplastic materials. We compare this equation with other ones, and in the Appendix, we consider its theoretical foundation. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070490909

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis research reports on the effect of a diazide, i.e., 1.4‐carboxybenzenesulfonyl diazide, which had been incorporated onto fiber by a chemical reaction, on the formation of an interphase between the elastomeric SBR matrix and polyester fiber. The existence of the interphase becomes manifest not only in the variation of the mechanical properties, but especially through swelling measurements and dynamic properties. The effect of the new system based on diazide is similar to that obtained from a conventional adhesive system, but presents certain benefits, such as a shorter curing time due to absence of resin, enhanced tensile strength, and the formation of a more flexible interphase, which entails lesser heat generation due to mechanical energy loss. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070490910

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

年代:1993

数据来源: WILEY