摘要:

AbstractDiffusion of small molecules in polymers is described quantitatively in terms of segmental mobility processes. The diffusion coefficient depends on a diffusive jump length, which is characteristic of the polymer, and a jump frequency, which is equated to the segmental mobility rate. The presence of a particular solute increases mobility of the surrounding polymer segments by a predictable amount, which is related to the partial molar volume of the solute. The theory is fit to experimental diffusion data, and partial molar volumes are calculated from the fitting parameters. Good agreement with experimental partial molar volumes is obtained.

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280201

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractInvestigations on the effects of γ irradiation on poly(methylene oxide) (POM) and poly(ethylene oxide) (PEO) have been made employing electron spin resonance (ESR) spectroscopy. The ESR sextet and doublet spectra, recorded for POM and PEO, respectively, on irradition in air at room temperature are broadened as the temperature is lowered and show a reversible change in line shape with temperature. The spectra are analyzed by computer simulation, employing Lorentzian line‐shape functions and the least‐squares method of total curve fitting. The component spectra are evaluated and are assigned. Superposition of the component quartet, triplet, and doublet spectra, corresponding to the radicals ĊH3, ĊH2O , and OĊHO , respectively, together with a singlet due to the radicals ȮCH2is considered to be the best fit to the observed spectrum for POM. The doublet spectrum recorded for PEO has been assigned to the radicals ĊHO . The reversible broadening of the spectra has been associated with the mechanism of molecular motions around the glass transition temperatures of these

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280202

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280203

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractAs we have reported recently, the application of association models has provided a theoretical basis for the calculation of the free energy changes and phase diagrams of binary polymer blends in which hydrogen bonding plays a significant role. Here we report theoretical calculations of spinodal phase diagrams of a series of polyisophthalamide‐polyether blends and compare the predictions with experimental observations of the miscibility of these polymer blend systems. The general agreement between theory and experiment is very encouraging and has important ramifications to discussions of polymer‐induced crystallnity, the minimum number of hydrogen bonding sites necessary to ensure significant molecular mixing, and the effect of hydrogen bonding on the breadth of “miscibility win

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280204

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractSolid state13C‐NMR was used to investigate the miscibility and subsequent separation of solution‐cast blends of poly(vinylidene fluoride) (PVF2) and poly(methyl methacrylate) (PMMA) with aging for a range of compositions. It was found that one amorphous phase and intimate mixing of the polymer chains in this phase existed for all compositions of the blends, even after 2 months of aging at room temperature as determined by the proton spin lattice relaxation timeT1ρHin the rotating frame, and the time constantTCHfor transfer of magnetization. TheT1ρHis sensitive to the spatial homogeneity of the blend via spin diffusion and would indicate the presence of phases or domains in the amorphous component of the blend larger than approximately 19 Å. TheTCHis proportional to the inverse sixth power of the interatomic distances needed for transfer of magnetization from proton to carbon and would be sensitive to a separation of polymer chains in the amorphous phase with aging on the order of 4–5 Å. There was an increase of theT1ρHandTCHvalues with aging, indicating that a subtle separation between unlike chains in the amorphous phase was occurring although a single amorphous phase w

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280205

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractA thermotropic liquid‐crystalline copolyester of 20% hydroxybenzoic acid, 40% isophthalic acid, and 40% hydroquinone polymer was studied at elevated pressures. The characterization techniques at elevated pressures (0–1000 bar) included high‐pressure differential thermal analysis and dilatometry; at atmospheric pressure, differential scanning calorimetry, thermal optical analysis, and x‐ray analysis were employed. The mechanical properties of the solid specimens prepared at different pressures were studied by compression and dynamic rotation mechanical testing techniques. High‐pressure induced a new crystal habit in the solid state and a new mesophase in the melt. These transitions are summarized in a proposed phase diagram. Mechanical tests on the material produced at elevated pressure indicate the possibility of improved properties, implying that the pressure‐dependent morphological changes in thermotropic copolyesters could be of practical significance. The finding of a pressure‐induced mesophase also confirmed the possibility of extending the range of polymers which might exhibit liquid crystallinity via the applicatio

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280206

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractTransport properties of a thermotropic liquid‐crystalline polymer with the mesogenic group in the main chain were analyzed. Different samples were examined as films obtained by pressure molding and rapid quenching to 0°C. Thermal and transport parameters of the quenched films were measured. The results show that the isotropization enthalpy and sorption coefficient are interdependent, while the diffusion coefficient is substantially constant in all the samples analyzed. These results suggest that the permeable component behaves in the same way in the different samples but is present in different amounts, the transport phenomena occurring in amorphous, or less ordered, interphase regions within impermeable mesomorphic and crystalline domai

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280207

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe adsorption, desorption, and orientation characteristics of two long‐chain chlorosilane compounds, octadecyltrichlorosilane and 1‐undecylene‐dimethylchlorosilane, onto poly(methyl methacrylate) (PMMA) and poly(2‐hydroxyl‐ethyl methacrylate) (PHEMA) are studied using Fourier‐transform infrared attenuated total reflection (FTIR‐ATR) spectroscopy. Quantitative monitoring of the amount of silane adsorbed is also attempted. It is believed that the surface modification reaction has been successfully confined to monolayer coverages and that sufficient detection sensitivity has been achieved to observe the reaction at these low levels on both PMMA and PHEMA. Also, ATR polarization studies indicate that on both substrates, a definite preference for orientation exists such that the long molecular axis is perpendicular to the substrate surface. The silanes are observed to be only physisorbed onto the PMMA surface under the anhydrous conditions applied during adsorption, whereas a chemical reaction is observed on the

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280208

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractPotentiometric titration in various 1‐1 salt solutions was carried out to study the dissociation behavior of the poly(allylammonium) cation (PAAH+). The titration curves show that proton release from cationic PAAH+is markedly suppressed by addition of simple salt and depends on the counterion species. From an analysis of the titration curves it is found that the electrostatic free energy change ΔGelupon the proton release is negative in all systems examined, and its absolute value decreases with increasing ionic strength of the medium. Also, at a constant added salt concentration (0.1 mol L−1) ΔGeldepends significantly on the counterion species added and increases in the order$\[ {\rm ClO}_{\rm 4}^ ->{\rm NO}_3^ ->{\rm Cl}^ ->{\rm Br}^ ->{\rm SCN}^ ->{\rm I}^ - . \]$The value of ΔGelcorrelates well with the electron donor constant En of the counterions. The dissociation behavior of PAAH+is discussed in terms of electrostatic interaction among the ionized groups on the chain, the charge shielding effect, and the ion‐solvent interaction of the added cou

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280209

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280210

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY