摘要:

AbstractIn this paper we demonstrate that the polydispersity µ =M̄w/M̄Nof narrow polymer fractions can be readily obtained by measuring band broadening and its velocity dependence in a thermal field–flow fractionation (thermal FFF) system. The thermal FFF method is shown to be more accurate than size exclusion chromatography for the determination of polymer polydispersities due to the simpler band dispersion function and the higher selectivity inherent to the technique. The polydispersities of a series of four narrow polystyrene samples prepared by anionic polymerization were consequently determined by thermal FFF and found to be much smaller (1.003–1.006) than the ceiling values (1.06) suggested by the suppliers. As part of this investigation, an experimental study of band dispersion in thermal FFF is used to examine current theory. The data show nonequilibrium to be the dominant factor, whereas relaxation effects are insignificant at lower flow rates and can be subdued at higher flow rates. A high correlation between nonequilibrium theory and experiment allows for the estimation of diffusion coefficients from plate height–veloc

ISSN:0021-8995    

DOI:10.1002/app.1987.070330111

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe Abbé refractometer provides a convenient way to measure the refractive indices and birefringence of polymeric liquid crystalline solutions. The cholesteric mesophase formed by (acetoxypropyl) cellulose and its solutions in dibutyl phthalate were examined at 26°C and 50°C. The measured refractive indices were dependent on the direction of shear when the polymer was applied to the refractometer plates. The initial shear‐induced nematic‐like order relaxed slowly to the equilibrium planar cholesteric structure. The refractive index for the isotropic solutions and the two refractive indices for the anisotropic solutions all varied linearly with polymer concentration, and the width of the intermediate two‐phase region was readily determined. The changes in refractive index with polymer concentration and with orientation on the refractometer plate were rationalized with a simple model of the cellulosic mesophase, and an order parameter of 0.7 was estimated. The layer birefringence calculated from optical rotatory dispersion measurements of the cholesteric reflection band intensity was in good agreement with the birefringence meas

ISSN:0021-8995    

DOI:10.1002/app.1987.070330112

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

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper describes the improved processibility of 4,4'‐bis‐maleimidophenyl methane (BM) chain extended by 4,4'‐diaminodiphenyl methane (DADPM) by coreaction with triallyl cyanurate (TAC). Curing of BM, chain‐extended BM, and mixture of BM and DADPM (1 : 0.3 molar ratio) in the presence of 5, 10, 15, and 20% (w/w) of TAC was followed by differential scanning calorimetry (DSC) and thermal stability of cured resins was evaluated by thermogravimetric analysis. TAC had insignificant effect on char yield (at 800°C) of BM resin. Glass‐ and graphite fabric‐reinforced composites were fabricated using chain‐extended BM containing 10% TAC and methyl ethyl ketone (MEK) as solvent. Interlaminar shear strength was found to be 7620 psi for graphite fabric laminate containing 40% resin. Good retention of mechanical properties of laminates at 220°C up to 320

ISSN:0021-8995    

DOI:10.1002/app.1987.070330113

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

年代:1987

数据来源: WILEY

摘要:

AbstractA difference between surface and bulk morphologies of extruded low density polyethylene (LDPE) has been observed through measurement of the contact angle of glycerol on both exterior and interior surfaces of the extrudate. The sessile drop contact angle on the exterior surface of LDPE rods prepared in a Brabender plasticorder increasea with increasing screw speed (40–180 rpm) and correspondingly increased die pressure at each extrusion temperature (110–130°C). On the other hand, the sessile drop contact angle on the interior surface of LDPE rod, exposed by grinding, decreased with increased screw speed. Qualitative trends were identical with exterior contact angle measured by the Wilhelmy plate method or with the interior surface exposed by fracture. Contact angle variations were interpreted in term of density or crystallinity to suggest that the bulk or interior crystallinity increased with increasing die pressure (even at constant screw speed), while the crystallinity of the exterior decreased with increasing screw speed (even at nearly constant die pressure). The difference between surface and bulk morphologies was consistent with that deduced from DICUP absorption kinetics and optical microscopy [J. Appl. Polym. Sci.,29, 2383 (1984)], although differences were noted in the effect of screw speed on surface morpho

ISSN:0021-8995    

DOI:10.1002/app.1987.070330114

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

年代:1987

数据来源: WILEY

摘要:

AbstractA new type of microcrystalline polymer prepared by aggregation has been discussed. The effect of the parameters of the preparation process on the properties of microcrystalline chitosan in hydrogel and solid forms has been studied using also microscopy and spectroscopy. The product obtained according to the method discussed shows the average molecular weight within a range 2.2–5.0 X 105, WRVs≈ 260–520%, WRVg≈ 700–1000%, and CrI

ISSN:0021-8995    

DOI:10.1002/app.1987.070330115

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe chemical modification of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) by electrophilic sulfonylation and acylation of the aromatic structural units has been investigated. A maximum monosubstitution degree of 79.4 has been reached. Higher substitution levels were difficult to achieve because of both a decrease in the remaining position nucleophilicity and steric hindrances. Minor changes in thermal stability and a broadening of the solubility range of substituted PPO compared with the parent PPO have been recorded. Very good permeation properties to gases, better than for PPO, have been detected for the modified struc

ISSN:0021-8995    

DOI:10.1002/app.1987.070330116

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

年代:1987

数据来源: WILEY

摘要:

AbstractNylon–asbestos composites comprise a significant proportion of reinforced nylon thermoplastics. To improve the cooperation between matrix and fibers the coating of the asbestos by interfacialin situpolymerization is proposed. Previous work on the system chrysotile‐nylon 6,6 is extended so that the reactants application order is now inversed, in order to consider any differences in the extraction resistance and the polymerization yield, in conjunction with thermal analysis studies. Experimental results gathered provide severe, but indirect, indications for the development of a strong interface bond between polymer and asbestos fib

ISSN:0021-8995    

DOI:10.1002/app.1987.070330117

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

年代:1987

数据来源: WILEY

摘要:

AbstractTwo latex interpenetrating polymer networks, one from a supposedly compatible pair and the other from an incompatible pair of polymers, were prepared by two‐stage emulsion polymerization. The synthesis conditions in each case were varied by altering the ratio of the glassy polymer to the rubbery polymer and also by reversing the order of synthesis. Fabricated samples of these latex interpenetrating polymer networks were subjected to hardness, stress‐strain, and dynamic mechanical measurements. Hardness and stress‐strain measurements showed that, although the second formed polymer dominated the final mechanical properties, the compatibilities of the polymer pairs played an important role. Dynamic mechanical analysis for the inverse systems showed evidence of enhanced m

ISSN:0021-8995    

DOI:10.1002/app.1987.070330118

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe effect of steric hindrance on the attack of growing polymer radicals to the reaction sites on a trunk polymer was examined in the graft copolymerization of styrene onto a trunk polymer with pendant aromatic nitro groups by chain transfer reaction of growing polymer radicals to the pendant nitro groups. The nitro groups on ethylene‐vinylp‐nitro benzoate copolymer (EVNB) are more effectively utilized in the graft copolymerization than those on the vinylp‐nitro benzoate homopolymer (PVNB) previously used as a trunk polymer, because the nitro groups are distributed less frequently on the trunk polymer in the former than in the latter. This was also confirmed by the higher chain transfer constant of growing polystyrene radicals to EVNB compared to that of

ISSN:0021-8995    

DOI:10.1002/app.1987.070330119

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

年代:1987

数据来源: WILEY

ISSN:0021-8995    

DOI:10.1002/app.1987.070330120

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

年代:1987

数据来源: WILEY