摘要:

AbstractNylon‐11 is prepared by casting from the solvents trifluoroacetic acid andm‐cresol and by melt‐crystallization. Room‐temperature infrared spectra are compared in terms of possible crystal structures. The spectra are examined for the presence of Fermi resonance which occurs between the N‐H stretching fundamental mode and the overtone and combination modes of the amide I and II vibrations. An analysis of peak frequencies and intensities is used to provide support for the assignment of the amide II overtone and the amide I + II combination modes. A newly observed peak in the spectra is assigned to the amide I overtone. Symmetry considerations are discussed which predict the resonance of the overtone and combination modes with the N‐H stretching fundamental. © 1992 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1992.090301001

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe self‐diffusion of benzene, toluene, and ethylbenzene in polystyrene have been analyzed using the Vrentas/Duda free‐volume diffusion model. Diffusion coefficient predictions suggest an exponential concentration dependence of the activation energy required to overcome attractive forces,E. Without the use of any diffusion data approximatingEas zero over the entire concentration range yields self‐diffusion coefficient predictions which are in good agreement with experimental data. © 1992 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1992.090301002

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractBrillouin light‐scattering measurements of H2O imbibed in hydrogels of poly(2‐hydroxyethyl methacrylate) of two cross‐linking densities have been made at 294 K. Increase in the amount of water imbibed in 19‐30 Å size pores of the cross‐linked network causes the velocity of sound to decrease monotonically from a value, which differs for the two pure polymers, to a limiting value for pure water. The absorption coefficient reaches a maximum at about 30% water content and then decreases toward that for pure water. The velocity and absorption coefficient of both pure polymer and hydrogel containing 32% water were measured from 110 to 300 K. The former decreases and the latter increases with increasing temperature, and both show a change in the slope at about 160 K for the hydrogel, which agrees with the calorimetric glass transition temperature of the hydrogel. The effect of the water on the velocity and absorption coefficient of the polymer increases with temperature. © 1992 John Wile

ISSN:0887-6266    

DOI:10.1002/polb.1992.090301003

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractChemisorption of polybenzimidazole on silver and copper etched with nitric acid has been observed by surface‐enhanced Raman scattering (SERS). The polymer is found to react chemically with silver, forming a complexed film on the surface. The SERS spectra show that polybenzimidazole film inhibits oxidation of the metal at high temperature, unlike chemisorbed benzimidazole, benzotriazole, and poly(4‐vinyl pyridine). © 1992 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1992.090301004

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe hydration of four amorphous acrylic and methacrylic poly(zwitterions) bearing the ammonium sulfopropylbetaine function as a side‐groups () was studied by differential scanning calorimetry over broad ranges of temperature (150‐400 K) and water content (weight fraction W1250 K, decreases with temperature in the glassy systems, but never disappears, even at 185 K. The depression of the glass transition temperature of the hydrated polymers obeys Couchman's equation:Tg= ΣiWiΔCpiTgi/ ΣgiWiΔCpi. Freezable bound water, about 6.7 ± 0.9 mole/monomeric unit, shows multipeak melting endotherms in the range 242–272 K. Because of their charged sites, the hydration process of the poly(zwitterions) appears more similar to that of poly(electrolytes) than to that of uncharged hydrophilic polymers. © 1992 John W

ISSN:0887-6266    

DOI:10.1002/polb.1992.090301005

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractWater sorption by four amorphous acrylic and methacrylic poly(zwitterions) bearing ammonium sulfopropylbetaine side groups () was studied at a constant temperature of 23°C and over a broad range of water activity (0.14‐0.90). Whatever the physical state of the hydrated polymer, glassy or viscoelastic, water diffusion is Fickian (average diffusion coefficientD̄sin the range 2‐16 × 10−8cm2s−1), and the sorption isotherms may be quantitatively analyzed according to the Guggenheim‐Anderson‐De Boer amended BET equation for multilayer sorption processes. The number of sitebound water molecules per monomeric unit is in the range 1.5–2.0, and apparently there is no great energy difference between direct site binding and indirect binding in the successive solvation layers. The polymer‐water interaction parameter (−0.6<χ Flory<0.6) is an increasing function of the water content of the hydrated poly(zwitterions) over the whole composition range (water volume fraction<0.5), without any clear transition from the glassy to the viscoelastic state. Clustering of water molecules (Zimm‐Lundberg theory) is never observed, even at high water content. Because of the charged structure of their dipolar units, the poly(zwitterions) show a water sorption process similar to that of the corresponding poly(electrolytes) of the tetra‐alkylammonium sulfonate type. ©

ISSN:0887-6266    

DOI:10.1002/polb.1992.090301006

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe number of chain scissionsnsper unit fracture area by impact in high‐molecular weight polystyrene is determined to be approximately 3.3 × 1014/cm2at room temperature. This is almost 20 times larger than would be expected if chain scissions took place only at, or very close to, fracture surfaces. This result was obtained by measuring the molecular weight decrease and the total fracture area of the impact fragments by using size exclusion chromatography and statistical particle size measurements, respectively. The largensstrongly indicates that significant chain breakage occurs during crazing before the propagation of cracks. An average craze thickness before breakdown under impact is estimated fromnsto be around 2 μm. In a diluted polymer,nsis found to be significantly lower than the extrapolated value, assuming a linear dilution of entangled chain crossings at the fracture surface. This low chain scission density, however, can be explained by taking into account the reduction of craze breakdown strain in the diluted polymers. Finally, the broken chain ends of polystyrene appear to be stable under ambient conditions. © 1992 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1992.090301007

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractDynamic mechanical and gas transport properties for homogeneous homopolymer blends and random copolymers of bisphenol‐A and tetramethyl bisphenol‐A polycarbonates (PC‐TMPC) were determined. The gas transport measurements were performed at 35°C for the gases He, H2, O2, Ar, N2, CH4, and CO2. The results show that the copolymers have lower permeability, apparent diffusion, and solubility coefficients than the blends. Permeability coefficients for blends follow a semilogarithmic ideal mixing rule while copolymers exhibit negative deviations from this. Specific volume measurements show that the free volume available for gas transport is slightly larger in copolymers than in blends of the same composition. These apparently contradictory results may relate to the differences in local mode chain motions observed for the copolymer and blend series. The γ relaxation processes in PC and TMPC seem to operate independently in the blends (no intermolecular coupling) while there is clear evidence for intramolecular coupling in the copolymers. © 1992 John Wiley&S

ISSN:0887-6266    

DOI:10.1002/polb.1992.090301008

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractQuasiharmonic equations are derived for stress‐induced vibrational frequency shifts in the infrared and Raman spectra of polymer chains subjected to a tensile stress. The expressions are applied to the helical chains of polyoxymethylene and isotactic polypropylene. Observed frequency shifts can be reproduced well by using reasonable anharmonic force constants. A semiquantitative interpretation is given for the close relationship between stress‐induced vibrational frequency shifts and the deformation mechanism of the polymer chains. Stress‐induced frequency shifts are also calculated for an orthorhombic polyethylene crystal subjected to uniaxial tension along the chain axis or to hydrostatic pressure. The results consistently and reasonably reproduce observed data, not only for the intramolecular vibrational modes but also for the external lattice modes. © 1992 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1992.090301009

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractSeveral methods for measuring directly the interaction parameterXas a function of polymer concentration are presented. These methods are applied to symmetric ternary mixtures of homopolymers and copolymers in solution under the zero average contrast condition. They can be used for an arbitrary concentration from dilute solution to the bulk and at any value of the scattering wavenumberq. Possible combinations of static and dynamic measurements are presented. © 1992 John Wiley&Sons, Inc

ISSN:0887-6266    

DOI:10.1002/polb.1992.090301010

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY