摘要:

AbstractThe diphenylethane initiator 3,4‐diethyl‐3,4‐(p‐methoxyphenyl)‐hexane (T–OCH3) was synthesized. By cocondensation of bisphenol A or C and the bisphenol derivative (“T”) of T–OCH3with phosgene, polycarbonate macroinitiators PC(TxA1‐x) and PC(TxC1‐x) with different compositionsxwere made. The thermal fragmentation of T–OCH3and the copolycarbonates was investigated with and without a radical scavenger both in solution and in the bulk state. The primary dissociation of T–OCH3is a monomolecular Arrhenius process with a characteristic temperature ofT*(τ = 1h) = 140°C (τ: average life time of the intact molecule). When the radicals are not intercepted, the dissociation is excessively reverted by radical recombination, which raises T*to T*= 163°C. The reaction ends then exclusively in radical disproportionation. The chain fragmentation of the copolycarbonates is of the type of a random decondensation. The counits CT dissociate in solution almost exactly like T–OCH3. In the highly viscous bulk state, the reaction proceeds in matrix cages, which have a stabilizing effect, so thatT*is increased toT*= 170°C. These copolycarbonates are model polymers for a novel method to study the hitherto unmeasurably slow chain diffusion processes in polymers near

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281201

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe miscibility in binary blends of ferroelectric copolymers of vinylidene fluoride (VF2) and trifluoroethylene ( F3E) has been investigated over the full range of blend compositions for three different random copolymers containing 52, 65, or 73 mol % VF2. We found these copolymers miscible in the melt with each other but not with the parent homopolymer, PVF2. In thin solid films we demonstrated, for all blend compositions, the very rare phenomenon of isomorphic cocrystallization in both the ferroelectric and paraelectric phases of the 52 + 65 and the 65 + 73 mol % VF2copolymers. However, the blend having the largest compositional difference (52 + 73 mol % VF2) was found to consist of two separate ferroelectric and paraelectric phases. These results demonstrate the very close chemical and structural similarities required for coexistence of two different macromolecules within a single crystalline lattice. Moreover, they allow us to probe the compositional limits for such similarity in both the ferroelectric and the paraelectric lattices. Phase diagrams of these blends have been constructed and are discussed. The Curie transition is shown to be an exceptionally sensitive probe of compatibility in the ferroelectric phase.

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281202

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractSynchrotron x‐ray radiation was used to study structural changes during deformation of asinglehigh‐modulus, high‐strength fiber of polyethylene (Spectra 1000, Allied Corp.) 20–40 μm in diameter. The high brightness of the synchrotron beam allowed x‐ray diffraction patterns to be obtained from 0.5 μg fiber samples in ca. 1 min. The (002) chain axis reflection shifted and broadened when the fiber was loaded in tension. When a model of crystals and disordered material in series was used for the fiber, the measured lattice strain at stresses up to 1 GPa gave a crystal modulus of 250 GPa. At stresses above 1 GPa the (002) reflection no longer shifted with increasing load. A noncrystalline part of the material deforms and takes up the load; this effect has been observed by Raman spectroscopy. The (002) peak also broadens under stress. When fiber bundles were used as samples, broadening could be due to uneven loading of fibers, but with a single fiber sample, one can be sure that the loading at the fiber level is uniform. Broadening of the (002) reflection then indicates inhomogeneities within the fiber. Deconvolution with the line profile of the fiber at zero stress should give the distribution of crystal strains. The strain distributions are symmetric and during loading the full width at half maximum (fwhm) is approximately equal to the mean strain. With an assumed constant crystal modulus this describes the stress distribution as extending from zero to twice the

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281203

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractLong‐term, high‐pressure CO2permeation experiments were conducted for styrene/methyl methacrylate (SMMA) random copolymers and bischloral polycarbonate/poly (methyl methacrylate) miscible blends to investigate the effects of gas conditioning. The extent and rate of CO2permeability changes with time increased dramatically with content of MMA units in both series when compared at a constant upstream CO2pressure of 20 atm. The higher solubility of CO2in PMMA than polystyrene or the polycarbonate was found to be responsible for a part but not all of this response as shown by isobaric versus isoconcentration experiments. The rate of conditioning cannot be described by a single relaxation time. The conditioning process discussed here seems to be intimately connected to the plasticization process reported earlier for these same syst

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281204

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe axial thermal expansion coefficients of a series of highly oriented thermotropic liquid crystal copolyesters with random phenylene‐naphthalene main‐chain sequences are reported. In common with many other highly oriented polymers the values are negative. Generally, there are two transitions in the slope of the expansion‐temperature curves. The positions of these transitions are correlated with high activation energy relaxations in the mechanical spectra. Comparison of the thermal expansion properties determined by x‐ray and macroscopic techniques on two of the samples reveals little difference between the bulk material and a unit with a segmental length of ten m

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281205

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractExpressions for the interdiffusion and the tracer‐diffusion coefficients in terms of the time‐integrals of force‐correlation functions are obtained using a microscopic description of the inter‐diffusion and tracer‐diffusion processes in a two‐component liquid. The present approach provides a systematic and direct derivation, as well as an extension, of the results of Bearman et al. in their pioneering work in the late 1950s which have been used recently by Cohen and Foley to discuss the two possible relationships between the interdiffusion and tracer diffusion coefficients, referred to as the “fast‐mode expression” of Hartley and Crank and the “slow‐mode expression” based on the random phase approximation. In our analysis we find an additional three‐particle friction term in the exact expression for the interdiffusion coefficient, which is not present in Bearman's work. It is concluded that not much can be said in favor of the fast‐mode or slow‐mode expressions, unless this additional three‐particle friction is neglected. We also show that the center‐of‐volume reference frame, in which the hydrodynamic fluxes are measured, naturally follows from the microscopic descripti

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281206

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractFick's first law is modified to be applicable for the transport of gases in inhomogeneous polymeric membranes having continuous, concentration‐dependent, gradients of solubility and diffusivity along the flux direction (xaxis). The membranes are considered to be in the rubbery state, and all gases in the membranes are assumed to be mobile. The modified Fick's law is derived from the consideration of standard chemical potential difference between the membrane and gas phases, and of fugacity coefficients in the membrane.\documentclass{article}\pagestyle{empty}\begin{document} $J=-D\left\{dC/dx - C(d\ln {S/dx})\right\}/L$\end{document}whereJis the flux,Dis the diffusion coefficient,Cis the concentration in the membrane;xis the dimensionless space coordinate (0 ≦x≦ 1);Sis the solubility; andLis the membrane thickness. The above equation is applicable for the cases whereDandSare dependent on concentration. It is also solved analytically or numerically by a simulation method for some model membranes. Flux difference due to the flow direction and concentration profiles in the model membranes are disc

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281207

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe influence of composition on phase size in immiscible polymer blends is examined both experimentally and theoretically. It was found for eight noncompatibilized blends, of widely varying particle size morphology, that a master curve of phase size versus log‐relative composition could be obtained by shifting the data along the volume fraction axis. The magnitude of the shift factors (aϕ) correlates with the interfacial tension and viscosity ratio of the systems. The theoretical dependence of the master curve is proportional to ϕ + ϕ2dependence as in Tokita's theory, but estimation of the coefficients to the ϕ and ϕ2terms indicates that the influence of power and shear stress on breakdown of the dispersed phase is significantly overestimated by the theory. A master curve is also generated for four compatibilized blends and the dispersed phase sizes are significantly less dependent on compo

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281208

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractHeat capacities have been measured for liquid and semicrystalline nylon 6, 11, 12, 6.6, 6.9, 6.10 and 6.12 from above their respective glass transition temperatures (ca. 320 K) to 600 K. Combining those data with all prior literature, a new set of ATHAS recommended values is derived, including a general equation of heat capacities as a function of amide content:\documentclass{article}\pagestyle{empty} \begin{document} $${\rm C}_{\rm p}^{\rm nylon} = {\rm N}_{\rm C} (7.4506 + 0.0745{\rm T}) + {\rm N}_{\rm N} (86.8483 - 0.0226{\rm T})$$ \end{document}where NCand NNare the numbers of methylene and amide groups, respectively, in the average repeating unit. A full set of thermodynamic functions (H, G and S) is available through the ATHAS data bank. Large amounts of reorganization during heating and the possible existence of a rigid amorphous fraction in semicrystalline nylons make the analysis of the detailed thermal behavior of semicrystalline nylons between the glass and melting transition uncertain. It seems, however, that the heat capacity of the crystalline portion above 330–410 K is higher than predicted from the heat capacity of vibration. A similar observation was also made for polyethylene and has recently been linked to conformational disorder and mobilit

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281209

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe permeability of 6FDA‐m‐PDA, 6FDA‐2,4‐DATr, 6FDA‐2,6‐DATr, and 6FDA‐3,5‐DBTF membranes to H2, O2, N2, CO2, and CH4was measured at 35°C in the pressure range from about 1.4 atm (20 psi) to 8.2 atm (120 psi). The permeability coefficients,\documentclass{article}\pagestyle{empty}\begin{document}${\bar P}$\end{document}, for the penetrant gases in any of the four polyimides studied decrease in the order:\documentclass{article}\pagestyle{empty}\begin{document}$\bar P({\rm H}_2 )>\bar P({\rm O}_2 )>\bar P({\rm N}_2 )>\bar P({\rm CH}_4 )$\end{document}. The values of\documentclass{article}\pagestyle{empty}\begin{document}${\bar P}$\end{document}are generally independent of Δp, the pressure difference across the membranes, or decrease slightly with increasing Δp. The gas permeability of three of the polyimides increases, and their selectivity to some gas pairs decreases, in the polymer order: 6FDA‐m‐PDA<6FDA‐2,4‐DATr<6FDA‐2,6‐DATr. This appears to be due to an increasing mean interchain distance in these polymers. The gas permeability of 6FDA‐3,5‐DBTF is higher, and its selectivity lower, than expected from its mean interchain distance, possibly because of a higher segmental mobility. The potential usefulness of the above polyimides as membrane materials for gas

ISSN:0887-6266    

DOI:10.1002/polb.1990.090281210

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY