摘要:

AbstractA nematogenic side‐chain polysiloxane is investigated by means of absorption and fluo‐rescence spectroscopy.4‐Dimethylamino‐4′‐nitrostilbene (DANS) is dissolved in the poly‐meric matrix as a guest probe. The orientational order and the molecular distribution function have been determined from measurements of polarized absorption and fluorescence spectra. It has been found that fluorescence spectroscopy affords a method for determination of the phase transition temperatures of liquid–crystalline polymers. © 1993 John

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310401

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA comparison of rigorous and approximate models for the build‐up of epoxy‐amine networks with simultaneous etherification is presented. Contrary to a recent publication, it is shown that naïve statistical models perform very well in predicting statistical parameters when the different directions of network growth are distinguished in the statement of the recursive procedure. Slightly lower values of gel conversions are predicted by the approximate model, a fact that is consistent with the wider distribution of chain lengths resulting from the random recombination procedure. © 1993 John Wiley&Sons

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310402

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe protonation of leucoemeraldine in power form and inN‐methylpyrrolidinone (NMP) solution by HCIO4and HBF4has been studied by x‐ray photoelectron spectroscopy (XPS), infrared (IR), and ultraviolet (UV)‐visible absorption spectroscopy. In powder form, less than 25% of the amine nitrogens can be protonated in the absence of oxygen. The effects of oxygen on the degree of protonation and the distribution of amine and imine units upon deprotonation of the salt are investigated. The degree of protonation in leuccemeraldine can be increased to about 50% with 3 M HCIO4, similar to that achievable with emeraldine base in powder form. In NMP solution, leucoemeraldine is easily oxidized by dissolved oxygen. Protonation of both leucoemeraldine and emeraldine base in NMP solutions results in metastable species which gradually undergo deprotonation. The resulting products are affected by the O2content of the solutions. © 1993 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310403

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractDiffusion, solubility, and permebility coefficients were measured for He, Co2, Ar, and CH4in polybutadiene (PB) and in polybutadiene reacted in the solid state to various extents with aqueous bromine. Analysis of the sorption curves and X‐ray emission spectra showed that the bromination created a heterogeneous membrane with an outer brominated skin and an unreacted core. At relatively low extent of bromination, the diffusion and permeability coefficients for CO2, Ar, and CH4decreased by two orders of magnitude, while the transport coefficients for He were virtually unchanged. The permeability coefficients for CO2, Ar, and CH4became immeasurably small after about 3% bromination. The ideal separation factor for gas pairs with different molecular size increased with bromination, suggesting applications in gas separation processes. © 1993 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310404

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe solid‐state NMR isotropic line shape of the carbonyl13C resonance is useful as a qualitative diagnostic probe of the polyester component′s morphology and molecular mobility in partially miscible blends with poly(vinylphenol), PVPh. The main‐chain polyesters chosen for investigation in this study are poly(ethylene succinate), poly(ethylene adipate), poly(butylene adipate), and poly(caprolactone). A crystalline phase exists for polyester‐rich mixtures in all cases. Verification of this claim is provided by DSC endothermic tran‐sitions that map out melting point depression in the temperature‐composition phase dia‐grams. The carbonyl13C‐NMR signal in the crystalline domains exhibits a full width at half height of 1–2 ppm when the glass transition temperature of the blends is below the temperature of the NMR experiment. In all cases, a single concentration‐dependent glass‐transition temperature is measured by DSC, which increases monotonically from below ambient for polyester‐rich blends to well above ambient for blends that are rich in poly(vinylphenol). When the concentration of the amorphous proton donor PVPh is suf‐ficient to thwart crystallization of the polyester and increase the glass transition temperature of the blends above the temperature of the NMR experiment, the line width of the carbonyl resonance increases three‐ to fourfold to ca. 5–6 ppm. When the blends are completely amorphous andTgis above ambient, the polyester carbonyl13C line shape reveals at least two morphologically inequivalent microenvironments. A partially resolved carbonyl signal in rigid amorphous blends is (a) identified at higher chemical shift relative to the crystalline component, and (b) attributed to hydrogen bonding in the amorphous phase. This inter‐action‐sensitive hydrogen‐bonded carbonyl signal accounts for an increasing fraction of the overall NMR absorption envelope of the carbonyl carbon site when the polyester is saturated with PVPh. The main‐chain polyesters were chosen to probe the effect of chemical structure of the proton acceptor on the potential for hydrogen‐bond formation. Aliphatic CH2spacers between the carbonyl groups dilute the concentration of interacting sites, and the dependence of the carbonyl13C‐NMR line shape on blend concentration reveals unique spectroscopic behavior in each of the four blend systems

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310405

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractOptimized membranes made by a dry/wet phase inversion process using forced‐convective evaporation consist of an ultrathinandpore‐free skin layer supported by a nodular transition layer underlying open‐cell, sponge‐like substructure. It is suggested that the out‐ermost region of such case membranes undergo phase separation by spinodal decomposition in the initial stages of the evaporation process. As a result of the small scale of phase separation present in polymer‒solvent systems, an appreciable capillary pressure occurs in the interstitial space filled with the polymer‐poor phase in contact with air. The resulting force acts normal to the membrane–air interface, which tends to consolidate the polymer‐rich phase to form a nonporous surface layer. © 1993 Jo

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310406

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractCloud‐point data to 180°C and 2800 bar are presented for polyethylene, poly(methyl acrylate), and two poly(ethylene‐co‐methyl acrylate) copolymers (10 and 31 mol % methyl acrylate) in propane and chlorodifluoromethane with two cosolvents, acetone and ethanol. The addition of small amounts of either cosolvent to the copolymer–solvent mixtures shifts the cloud‐point curve to lower pressures and temperatures, as both cosolvents provide favorable polar interactions with the acrylate group in the backbone of the copolymer. Ethanol has a larger effect than acetone since ethanol hydrogen bonds to the acrylate group. However, if the concentration of ethanol is increased above ca. 10 wt %, it self‐associates and reverts to antisolvent behavior, forcing the copolymer out of solution. For nonpolar polyethylene–propane mixtures, the polar cosolvents behave as traditional an‐tisolvents. In poly(methyl acrylate)–chlorodifluoromethane mixtures, both polar cosolvents enlarge the single‐phase region. The cloud‐point curves for the (co)polymer–propane–acetone mixtures are modeled reasonably well using the Sanchez–Lacombe equation of state with two adjustable mixture parameters. No attempt is made to model the mixtures that exhibit hydrogen bonding.

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310407

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractCatenate network formation by end‐linking reactions of linear chains with bifunctional regents is studied theoretically and by computer simulations. It is found that the reaction cannot reach its stationary limit, and catenate networks are never formed by this method. An alternative method that will lead to catenate networks nearly in the topological equilibrium state is proposed. It is pointed out that catenate networks are an ideal system for studying the role of entanglement in rubber elasticity. © 1993 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310408

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractRecently we presented a dual‐mode interpretation of the nuclear spin relaxation for13CO2sorbed in polycarbonate [E. J. Cain, W.‐Y. Wen, A. A. Jones, P. T. Inglefield, B. J. Cauley, and J. T. Bendler,Journal of Polymer Science, Part B, Polymer Physics, Vol. 29, p. 1009 (1991)]. We have made similar investigation on spin relaxation for13CO2sorbed in polystyrene and are presenting the results in this report.13C spin‐lattice relaxation, spin‐spin relaxation, and nuclear Overhauser enhancements (NOE) are reported for13CO2sorbed in glassy polystyrene. These spin relaxation parameters were determined as a function of temperature and Larmor frequency. A quantitative interpretation is based on a two‐site, rapid exchange model, which is consistent with the NMR result. Gas molecules in the dissolved site have rotational, collisional, and translational dynamics typical of low molecular weight liquids. Sorbed molecules in the Langmuir site have much slower rotational and translational motions. The activation energy for motions in the dissolved site is about 7.5 KJ/mol, while that for the Langmuir site is about 15.5 KJ/mol. The translational diffusion constants derived from the NMR data range from 10−7to 10−9cm2/s and are consistent with the apparent diffusion constant from the permeability measurements of 4.9 × 10−8cm2/s at 35°C. A relation between the permeability value and the NMR values is available from a theoretical description of the dual‐mode model in terms of a random walk on a lattice containing two sites. As a modification of our previous lattice model (E. J. Cain et al.,Journal of Polymer Science, Part B, Polymer Physics, Vol. 29, p. 1009 (1991)), the temperature dependence of the fraction of Langmuir sites in the lattice is taken into account. Parameter values characterizing the motion of CO2in polystyrene are found to be similar to the corresponding ones in polycarbonate. © 1993

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310409

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractOn the basis of rotational isomeric state theory, first‐order, second‐order, and third‐order conformation energies Eσ, Eωand Eφirespecively, are calculated for poly(dimethylsilmethylene) (CH2—Si(CH3)2)xusing the Lennard–Jones potential function. With the third‐order interaction included, the characteristic ratios and temperature coefficients 〈R2〉0and 〈μ2〉0are obtained:\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{c} {\langle R^2 \rangle _0 /nl^2 = 5.4,\,\, d\ln \langle R^2 \rangle _0 /dT = \left(0.11 \pm 0.01\right) \times 10^{ - 3} \deg ^{ - 1} } \\ {\langle \mu ^2 \rangle _0 /nm^2 = 0.34,\,\,d\ln \langle \mu ^2 \rangle _0 /dT = \left( - 0.09 \pm 0.01\right) \times 10^{ - 3} \deg ^{ - 1} } \\ {\left(n = 2x, n \ {\rm is a number of bonds} \right).} \\ \end{array}$$\end{document}These results are in satisfactory agreement with the experimental data previously reported. © 1

ISSN:0887-6266    

DOI:10.1002/polb.1993.090310410

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY