摘要:

AbstractThe UV‐stabilizing ability and thermal loss from the polystyrene film of novel UV absorbers, 2‐[(3‐hydroxy‐4‐benzoyl) phenoxy] pentachlorocyclotriphosphazene (HBPC) and hexakis[ (2‐hydroxy‐4‐benzoyl) phenoxy]cyclotriphosphazene (HBPP), were investigated. The UV‐stabilizing ability of HBPC estimated by the formation of carbonyl groups in polystyrene was comparable to that of 2,4‐dihydroxybenzophenone (DHB), suggesting that the phosphazene moiety does not affect the efficiency of the stabilizing ability of DHB units. No significant difference of efficiency per stabilizing units between HBPC and HBPP was observed. HBPC and HBPP are noteworthy for their low thermal losses from the polystyrene film, i.e., the thermal loss of HBPP was completely suppressed and the diffusion coefficient of HBPC at 160°C was two orders of magnitude smaller than that of DHB. The thermogravimetric analysis and differential scanning calorimetry measurement showed that HBPC and HBPP are nonvolatile and stable up to 230 and 300°C, respectively. © 199

ISSN:0021-8995    

DOI:10.1002/app.1993.070501101

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

年代:1993

数据来源: WILEY

摘要:

AbstractPolyurethane (PU) microspheres were prepared by a novel and simple method using the condensation polymerization technique. Microspheres of different morphological characteristics were prepared using tolylene 2,4‐diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI). These microspheres were fully characterized by thermal analysis, scanning electron microscopy, and spectral techniques. MDI‐containing microspheres were found to be more porous as compared to TDI‐containing microspheres. The infrared spectra indicated the complete utilization of the isocyanate groups in the synthesis of microspheres. Bromothymol Blue (BTB) was used as a model drug for thein vitrorelease studies from the spheres. The results indicated that BTB released much faster using the MDI spheres as compared to the TDI spheres. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070501102

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

年代:1993

数据来源: WILEY

摘要:

AbstractDetailed photoproducts from photoirradiation of heterophasic ethylene‐propylene copolymers and their fractions have been compared by infrared spectroscopy combined with chemical derivatization. The oxidized films were treated with gaseous NH3, SF4, and NO for the rapid identification and resolution of the various carbonyl species, alcohols, and hydroperoxides. The photoproduct formation depends upon the composition of the sample. The heterogeneities in thin films were also determined by micro FTIR spectroscopy. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070501103

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn this article, two kinds of poly(phenylene sulfide) (PPS) with terminal groups predominated by chloro and thiohydroxy groups have been synthesized using endcapping by adding monomer. Compared with PPS with terminal thiohydroxy groups, PPS with terminal chloro groups possesses a greater crystallinity, larger crystallite dimensions, a larger particle size, higher thermal stability, and a longer gelation time. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070501104

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

年代:1993

数据来源: WILEY

摘要:

AbstractElectrical and magnetic properties of composite materials prepared by incorporating various nickel‐based fillers of different shapes into polyethylene were investigated. The fillers used were nickel powders, nickel filamentary powders, nickel flakes, and nickel‐coated graphite fibers. The particle‐size distributions of the fillers were determined both before and after the processing of the composite samples. A wide range of filler volume fractions were used. In some cases, the volume fraction approached the maximum packing fraction of the solid phase to significantly exceed the percolation threshold. The composite samples were characterized in terms of their volume resistivity, dielectric constant, and magnetic permeability values. Filler particles of asymmetric shapes were very effective in terms of altering the electrical properties of the composite samples. At the highest loading levels of the nickel fillers, the volume resistivity values of the composites decreased by more than 17 orders of magnitude. At such high filler concentrations, the dielectric constant values of the composite samples increased considerably, to values that were greater than 1000. The permeability values of the samples increased linearly with the volume fraction of the nickel filler and were insensitive to the shape of the fillers. The highest relative permeability value measured was 5.8 for composites with 67% by volume of nickel powder. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070501105

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

年代:1993

数据来源: WILEY

摘要:

AbstractPoly(phenylene sulfide) (PPS) made via the melt polymerization ofp‐diiodobenzene and sulfur has previously been reported to increase in melt viscosity with time during rheological testing. Analysis of the oligomer from cleavage of PPS chains at the disulfide bonds via solution in 1‐chloronaphthalene demonstrated that the disulfide content of the polymer decreased with rheological testing time. DSC of the polymer before and after rheological testing in combination with theTccandTmof the chain fragments after the dissolution/cleavage in 1‐chloronaphthalene showed that many samples exhibited primarily chain extension rather than chain branching, whereas for many others, some degree of chain branching occurred. This is currently only qualitatively understood. Chain branching as the exclusive mechanism of melt viscosity increase during rheological testing appears untenable in light of theTm, in particular, of the chain fragments and also the polymer prior to chain cleavage. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070501106

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe grafting of acrylic acid onto poly(ethylene terephthalate) fibers subjected to a noswelling treatment using benzoyl peroxide was investigated. The temperature was found to increase the graft yield. The grafting yield increased up to a benzoyl peroxide concentration of 4.0 × 10−3Mand slightly decreased at higher initiator concentrations. The effects of solvents such as dimethylformamide, dimethylsulfoxide, pyridine, and some alcohols upon the grafting were examined by carrying out the graft copolymerization at various water/solvent ratios. Pyridine was found to inhibit the grafting totally. The properties of the grafted fibers such as density, diameter, dyeability, and moisture regain were also investigated. It was concluded due to the observations made in these properties that the grafting took place mainly in the subsurface regions of the fibers and there occurred a diffusion barrier after the grafting value of 8–9%. The overall activation energy for grafting was calculated to be 9.9 kcal/mol. © 1993 John Wiley&Sons

ISSN:0021-8995    

DOI:10.1002/app.1993.070501107

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

年代:1993

数据来源: WILEY

摘要:

AbstractRheological experiments were performed on a series of thermotropic liquid crystalline aromatic copolyesters based on terephthalic acid (TPA), isophthalic acid (IPA),p‐hydroxybenzoic acid (HBA), and a family of bisphenols. The anisotropic melts behaved as non‐Newtonian fluids in a shear elongation flow. The non‐Newtonian exponents of the melts decreased with increasing the linearity of the bisphenol bridge group, and decreased with increasing the optical anisotropy in the liquid crystalline phase. The cross‐section morphologies along the longitudinal direction of the extrudates were surveyed by scanning electronic microscopy (SEM) and discussed with melt‐flow rate distributions. The extrudates exhibited skin–core microstructures and oriented fibril structures. The die swells of the extrudates decreased sharply to negligible levels when shear stress was above 1000 Pa. © 1993 John Wil

ISSN:0021-8995    

DOI:10.1002/app.1993.070501108

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe polymerization of propylene oxide by the benzoate anion was aided through the use of the tetrabutylammonium counterion. The effect of the tetrabutylammonium ion was to increase the solubility of the salt and to increase the ion separation. The polymerization was carried out in a pressure reactor at temperatures from 40 to 108°C, producing polymer yields of 2–78%. The study addressed the general effects of solvent, temperature, and ratio of initiator to monomer. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070501109

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

年代:1993

数据来源: WILEY

摘要:

AbstractPolymer morphology is controlled over a continuum from microspheres to interconnected bicontinuous networks to fibers with a versatile new process: precipitation with a compressed fluid antisolvent. The results are explained qualitatively as a function of phase behavior, mass‐transfer pathways, and the formation rates of skin on the flowing jet. By spraying dilute polystyrene in toluene solutions into liquid carbon dioxide, extremely small 100 nm microspheres are formed. For concentrations above the critical composition, fibers are produced that are not only microcellular, but, in some instances, even hollow. Mass‐transfer pathways that cross the binodal near the critical composition produce interconnected networks, likely due to spinodal decomposition. In this region, fibers composed of highly oriented microfibrils are produced at high shear rates. Preaddition of CO2influences the morphology because of dilution, in a similar manner as a liquid antisolvent, except that the viscosity reduction is larger due to added free volume. Because CO2diffuses through the glassy polystyrene skin faster than does a conventional liquid antisolvent such as methanol, it produces more porous fibers, which are also more cylindrical. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070501110

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

年代:1993

数据来源: WILEY