摘要:

AbstractThe dependence of physical properties on temperature and thermal history of glassy polycarbonate is examined. The average stress relaxation time increases during isothermal aging and with decreasing cooling rate. The temperature dependence of the stress relaxation time was compared with a free volume function calculated from specific volume data reported by Zoller by means of the Simha‐Somcynsky theory and with a fractional free volume measured byortho‐positronium annihilation. We report in addition comparisons between free volume fractions extracted from volume data, and creep measurements for polystyrene, and stress relaxation data for poly(vinyl acetate) given by Kovacs et al., Schwarzl and Zahradnik, and Meyer et al. These investigations suggest that in the glassy state the Doolittle equation is valid only in isothermal aging experiments. It follows that in expressing the polymer mobility not only a temperature‐dependent free volume but additional temperature‐dependent processes need to be considered. © 1995 John Wiley&S

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331701

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractPolyatomic density functional theory is applied to a binary polymer blend. The polymer reference interaction site model (PRISM) liquid state theory provides the homogeneous state correlation functions necessary for the application of density functional theory. An effective chi parameter can be recognized from the density functional expression; however, the phase separation criteria does not depend solely upon the chi parameter, rather it depends upon various combinations of the species‐dependent direct correlation functions of the blend. The Flory‐Huggins chi parameter along with the associated phase diagram is obtained when the monomer volumes of the blend species are equal and for a range of monomer‐monomer attractive interactions. Calculations are performed both with and without the assumption of incompressibility. The density functional theory along with the PRISM determined “input” predict that an isotopic polymer blend shows an upper critical solution temperature (UCST) phenomena. © 1995 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331702

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractIn the distribution function approach to the conformational and thermodynamic properties of polymeric liquids site‐site (pair) distribution functions are essential components of the theory. These site‐site pair distribution functions are basically mean fields obeying integral equations. In our recent works, a set of self‐consistent field equations has been proposed for site‐site pair correlation functions which allow us to study conformational and thermodynamic properties of polymeric liquids. In this article, we present a short review of the theory and its applications to a number of aspects of polymeric liquids we have made until now. We also present a self‐consistent version of the polymer reference interaction site model where the integral equations for the intramolecular site‐site correlation functions are obtained from the Kirkwood hierarchy on the basis of the present theory. The present theory is shown to predict correctly the scaling properties associated with swollen and collapsed polymers in good and poor solvents, respectively. At finite densities, self‐consistent solutions of the intra‐ and intermolecular equations yield the structures and thermodynamics of polymer melts which are favorably compared with Monte Carlo simulation results. Self‐consistent theory results are found to be more accurate than the non‐self‐consistent approaches that use an ideal Gaussian chain conformation distribution function. © 199

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331703

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractCrystallization and melting behavior are studied by small‐angle X‐ray scattering (SAXS) for a series of recently synthesized monotropic liquid crystalline polycarbonates based on α‐methyl stilbene mesogen and methylene flexible spacer. The one‐dimensional electron density correlation function is used to obtain long period, crystal thickness, and linear crystallinity from the Lorentz‐corrected SAXS intensity. Changes in these parameters during nonisothermal crystallization and melting are explained by a model of dual crystal populations. The primary crystals form first using the liquid crystalline phase as crystal nuclei, while smaller and less perfect crystals form later from the isotropic phase at low temperature. The results of the real‐time SAXS study of isothermal crystallization also support the view that the nematic phase serves as crystal nuclei for fast crystallization. An odd‐even effect in crystal thickness and linear crystallinity is observed in all the SAXS experiments mentioned above. The results of this study and our complementary wide‐angle X‐ray scattering (WAXS) investigation show clearly that the difference in the position of the neighboring carbonate dipoles on a chain affects structural organization both at the unit cell level and at the level of the crystal in these monotropic LCPs. © 1995 J

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331704

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe fluorescent molecular rotor probes 4‐tricyanovinyl‐[N‐(2‐hydroxyethyl)‐N‐ethyl]‐aniline, tricyano‐4‐(dimethylamino) benzylidene, and tricyanovinyljulolidene have been used as extrinsic fluorescence probes for quantitative monitoring of water uptake in polymeric coatings. The presence of water causes plasticization of the polymer, which results in increased local mobility within the film. The nonradiative decay pathways of the rotor probes are increased as local mobility increases, and the resulting decrease in fluorescence intensity of the probes is directly proportional to the amount of water sorbed. Beyond allowing for the characterization of sorbent content, this fluorescence technique can be used to determine the diffusion coefficient of water in a polymer film. The relative change in fluorescence fits well to a Fickian diffusion model, yielding a diffusion coefficient for water of 3 × 10‐8cm2/s in poly(vinyl acetate), and a value of 6 × 10‐9cm2/s in a room‐temperature cured epoxypolyamide, in excellent agreement with diffusion coefficient values determined from gravimetric analysis. Preliminary studies also demonstrate the utility of molecular rotor probes to monitor water uptake in individual layers of multilayered polymer systems. ©

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331705

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractWe have studied the segregation of a block copolymer of poly(d8‐styrene‐b‐2‐vinylpyridine) (dPS‐PVP) at the interface between polystyrene and a random copolymer of poly(styreneran‐4‐hydroxystyrene) (PS‐r‐PPHS). Forward recoil spectrometry (FRES) was used to measure the equilibrium excess (z*) of the dPS‐PVP chains at the interface as a function of its volume fraction in the bulk PS phase (ϕ∞). It was found that there is a sharp increase inz*at a critical value of ϕ∞. This upturn indicates the formation of a microemulsion of PS and the random copolymer PS‐r‐PPHS due to a vanishing of the interfacial tension caused by the strong adsorption of the block copolymer. Cross‐sectional transmission electron microscopy (TEM) of the interface shows that this microemulsion starts to form at the interface by forming a deeply corrugated structure where the “wavelength” of the corrugations is of the order of

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331706

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA procedure is used to analyze small‐angle neutron‐scattering (SANS) data from a pressurized polymer blend mixture (deuterated polystyrene/polyvinylmethylether). The Lattice‐Fluid (LF) equation‐of‐state model is used along with a compressible random phase approximation (RPA) in order to obtain free volume fractions and intermonomer interaction potentials. Solving the two sets of equations (LF and RPA) self‐consistently within the fitting procedure to the SANS data provides an improvement over the familiar incompressible RPA model. In this approach, the free volume fraction is the main varying parameter. Intermonomer interaction potentials were found to depend on pressure (weakly) and temperature (linearly). © 1995 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331707

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractFree‐volume hole sizes, fractions, and distributions in a series of polycarbonate‐based polymers are measured by using positron annihilation lifetime (PAL) spectroscopy. Correlations between the obtained free‐volume hole properties and gas diffusion coefficients are observed. © 1995 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331708

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractWe consider the surface of a nearly incompressible polymer melt, extending the usual ground‐state analysis of self‐consistent field theory to describe finite length polymers in the ground‐state potential. To maintain self‐consistency, further corrections to the potential are calculated within linear response theory. From this, we find an excess of ends near the surface, followed by a compensating depletion on theRglength scale, which relies crucially on the finite compressibility of the melt. The attraction of ends to the surface can be described as resulting from a surface potential for ends with a strength on the order ofkBT. Our results address the long‐standing controversies of the distribution of chain ends, the chain‐length dependence of the surface tension, and the interaction between objects immersed in a melt. © 1995 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331709

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe decay of the second‐order optical susceptibility χ(2)as a function of temperature and pressure has been studied in a variety of corona poled guest–host and side‐chain polymeric materials using second harmonic generation (SHG). The specific systems studied include the side‐chain copolymer poly(disperse red 1 methacrylate‐co‐methyl methacrylate) (DR1‐MMA) as well as the series of guest–host materials formed by individually dissolving the dyes Disperse Red 1 (DR1), Disperse Orange 3 (DO3), andN,Ndimethyl‐p‐nitroaniline (DpNA) in poly(methyl methacrylate) (PMMA), polycarbonate (PC), and polystyrene (PS). In each of these systems, the observed relaxation of χ(2)can be represented by a Kohlrausch‐Williams‐Watts stretched exponential, from which the decay time τ and decay distribution width β are determined. For pressures up to approximately 1000 atm, the natural log of the pressure shift factor is seen to vary linearly with applied pressure, yielding the activation volume for rotational reorientation of the chromophores in each system. The activation volumes are loosely correlated with dopant size in a given polymer host, but are not the same for a given dopant in different hosts. Modeling the chromophores as rotating cylinders, we show that the measured activation volumes do not correspond to the average volume swept out by the dye molecules as they reorient. On the other hand, the activation volumes for each of the three dyes dissolved in PS are seen to be in agreement with the measured activation volumes for the molecular motions associated with volume recovery in neat PS. Moreover, the activation volumes for DR1 and DpNA dissolved in PS are seen to correlate with the proposed couplings between the rotational reorientation of DR1 and the α‐relaxation dynamics of PS and the slight decoupling of DpNA from the α‐transition motion of PS. This correlation suggests a possible relationship between the activation volumes for chromophore reorientation and the size of the components of the host polymer or the volume swept through by the polymer components during structural reconfiguration. We demonstrate that assuming activation volumes for chromophore reorientation to be related to the size or motion of the polymer host constituents yields a consistent interpretation of the observed trends in the measured activation vol

ISSN:0887-6266    

DOI:10.1002/polb.1995.090331710

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY