bluuebunny/crossref_metadata_2025_split huggingface dataset:
An improved method for measuring the thermal coefficient of linear expansion of flexible polymer films
Authors: Kim Churl S. , Smith Thor L. 
Published: April 2003

AbstractA novel method has been developed and tested to determine accurately the linear coefficient of thermal expansion α of flexible films without subjecting a specimen to a tensile load continuously during the measurement of expansion data. Other methods have invariably required the application of a tensile load which commonly leads to creep during the experimental time. The new method involves mounting an Invar jig in the lower grip in a Dynastat. The closed‐loop servo control in the Dynastat enables the length of a specimen to be determined at a series of decreasing or increasing temperatures without subjecting the specimen to a tensile load, except momentarily on occasion while length data are being determined. Otherwise, a specimen is subjected to a small bending force. To demonstrate that the method gives valid results, α for an aluminum foil was determined and found to agree exactly with literature data. Expansion coefficients and values of the glass transition temperature (Tg) were determined on FEP and PFA Teflon films and also on a commercially available polyimide film, Upilex‐SGA.
Kinetics of CO2 conditioning of copolymers and blends containing MMA units
Authors: Raymond P. C. , Paul D. R. 
Published: April 2003

AbstractLong‐term, high‐pressure CO2 permeation 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 CO2 permeability changes with time increased dramatically with content of MMA units in both series when compared at a constant upstream CO2 pressure of 20 atm. The higher solubility of CO2 in 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 systems.
Thermodynamic properties of liquid and semicrystalline linear aliphatic polyamides
Authors: Xenopoulos Alexander , Wunderlich Bernhard 
Published: April 2003

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:

where NC and NN are 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 mobility.
Structure/permeability relationships of polyimide membranes. II
Authors: Yamamoto H. , Mi Y. , Stern S. A. , St. Clair A. K. 
Published: April 2003

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 CH4 was 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 separation processes is discussed.
Chain structure of homogeneous ethylene‐propylene copolymers showing inversion, described on the basis of 13C‐NMR data. I. Theory
Authors: Mathot V. B. F. , Fabrie Ch. C. M. 
Published: April 2003

AbstractA first‐order Markovian terpolymer model is used to describe the arrangement of ethylene (1), inverted propylene (2), and normal propylene (3) units in an ethylene‐propylene chain by means of chain propagation probabilities (P set) and corresponding reactivity ratios (r set). From nuclear magnetic resonance data on the weight fractions of methylene sequences, w1:m up to and including w5:m, P11 and the methylene, ethylene, and propylene sequence length distributions can be calculated, as well as the mole fraction of ethylene (x1) and the average sequence lengths sn, sw, sz. With the usual fitting procedures, these results can be obtained for quite different P sets and r sets. This unsatisfactory situation is characterized by the assignment of different values to the degree of inversion I = x2/(x2 + x3). Insight into this indeterminacy was obtained by distinguishing the methylene sequences (s : m) ending with 2 and sequences ending with 3 (s : m, 2 and s : m, 3, respectively), the weight fractions of which appear to be independent of I except for w1:m,2, and w1:m,3. In the constant sum w1:m, the ratio of the two is determined by I. The limit values of I (Imin and Imax) are fixed within the model used and are reached for w1:m,2 = 0 and w1:m,3 = 0, respectively. The values of P12 and P13 are I‐independent; by any particular choice of I, the other Pij's and hence a P set is fixed. For every P set there is a P″ set symmetrical with it, with I′ = 1 − I, which describes an identical chain formed in the opposite direction.
Characterization, processing, and properties of an aromatic poly (ether ketone)
Authors: Bai S. J. , Dotrong M. , Soloski E. J. , Evers R. C. 
Published: April 2003

AbstractPoly(oxy‐1,3‐phenylenecarbonyl‐1,4‐phenylene), mPEK, was synthesized in a methane sulfonic acid/phosphorus pentoxide medium through the polycondensation of 3‐phenoxybenzoic acid. The polymer was soluble at room temperature in strong acids and common organic solvents. Differential scanning calorimetry on mPEK indicated a glass transition temperature of 132°C and no detectable crystal melting behavior. The polymer was thermo‐oxidatively stable up to 420°C in air as determined by thermogravimetric analysis. Thermal degradation resulted in a crosslinked polymer. Compression molding was successfully applied to consolidate mPEK powder into bulk specimens without causing degradation. Tensilefractured surfaces of the consolidated specimens were examined by scanning electron microscopy which strongly indicated adequate fusion of mPEK powder but also disclosed microvoids of uniform size, shape, and distribution. X‐ray scattering revealed that mPEK powder was amorphous and that the consolidated mPEK specimens were structurally isotropic as well as amorphous. The bulk specimen density was determined to be 1.29 ± 0.01 g/cm3 and the three‐dimensionally isotropic bulk tensile properties were shown to be 4.10 ± 0.10 GPa (modulus), 0.07 ± 0.01 GPa (strength), and 0.021 ± 0.006 (elongation at break). Tensile properties of the amorphous mPEK specimens compared favourably with literature values of state‐of‐the‐art semicrystalline thermoplastics. Crystaline phases could be realized for mPEK by melt‐processing, or precipitating from a solvent.
Blends of styrene/maleic anhydride copolymers with polymethacrylates
Authors: Brannock G. R. , Barlow J. W. , Paul D. R. 
Published: April 2003

AbstractThe phase behavior of a series of styrene/maleic anhydride (SMA) copolymers with various polyacrylate and polymethacrylate homopolymers has been investigated using various techniques. None of the polyacrylates are miscible with SMA copolymers. Poly (methyl methacrylate) (PMMA) poly(ethyl methacrylate) (PEMA) and poly(n‐propyl methacrylate) (PnPMA), are miscible with these copolymers over a certain range of maleic anhydride contents; whereas, the higher methacrylates apparently have no region of miscibility. For PEMA and PnPMA, the miscibility windows extend through 0% MA; hence, polystyrene is miscible with these polymethacrylates although the lower critical solution temperature is quite low. The exothermic heat of mixing styrene and ester analogs found here supports the observed miscibility of polystyrene with ethyl, n‐propyl, and cyclohexyl (reported elsewhere) methacrylates. Lattice fluid interaction parameters for styrene‐methacrylate obtained from the cloud points of these blends agree quite well with the Flory—Huggins parameters obtained from copolymer miscibility windows.
Carboxylate‐containing chain‐extended polyurethanes
Authors: Yang Chang‐Zheng , Grasel Timothy G. , Bell Jennifer L. , Register Richard A. , Cooper Stuart L. 
Published: April 2003

AbstractPolyurethanes based on methylene bis(p‐phenyl isocyanate), bis(hydroxymethyl) propanoic acid, and poly (tetramethylene oxide) were synthesized, and their morphology and physical properties investigated. The acid polyurethanes exhibited very poor phase separation and mechanical properties, but upon neutralization with alkali metals phase separation improved dramatically and the materials resembled tough elastomers. The choice of cation played a much less important role than hard segment content in determining morphology and properties. Small‐angle x‐ray scattering patterns of these ionic polyrethanes exhibit two peaks, one characteristic of scattering between the hard and soft domains and the other reflecting scattering from aggregates of ionic groups residing within the hard domains. While ionic aggregation is the primary driving force for phase separation in these materials, their morphology more closely resembles that for nonionic polyurethanes than that for conventional ionomers, because the ionic groups exist in blocks composed primarily of rigid diisocyanate residues.
Small‐angle light scattering from an anisotropic sphere: The mueller matrix approach
Authors: Holoubek Jaroslav 
Published: April 2003

AbstractThe explicit form of the Mueller scattering matrix, which characterizes the small‐angle light scattering from an anisotropic sphere when the requirements of the Rayleigh‐Gans‐Debye (RGD) approximation are fulfilled, contains all information obtainable about the RGD scattering from an anisotropic sphere taken as a model for a spherulite. A comparison of angular dependences of single matrix elements for the Lorenz‐Mie sphere, the Rayleigh particle, and the simplified form of the presented matrix (taking a sphere without inherent anisotropy, i.e., Δn = 0) shows very good agreement within the limits of RGD approximations. The polarized small‐angle light scattering intensities Hυ and Vυ are combinations of the single matrix elements. Their explicit form is in accord with the expressions for Hυ and Vυ intensities recently rederived from a 2 × 2 amplitude scattering matrix. It has been shown that the angular dependence of matrix elements is determined by the (n̄ — 1)/Δn parameter, where n — is the mean refractive index andδ n is the anisotropy, both measured relative to the surrounding medium. The expressions for Hυ and Vυ intensities derived by Stein and Rhodes fail for a sphere without inherenet anisotropy ( δ n = 0); and the commonly used procedure of size determination from a maximum of Hυ intensity has limited validity (it holds only approximately under the condition of a small phase shift and small (n̄‐1)/ δ n). Further theoretical work must be done to understand and construct scattering models for situations where the RGD approximately is inappropriate.
Depolarized light scattering studies on single‐phase mixtures of dissimilar polymers: Evidence for local ordering
Authors: Saito Hiromu , Matsuura Motoshi , Inoue Takashi 
Published: April 2003

AbstractDepolarized light scattering measurements on single‐phase mixtures of dissimilar polymers, poly(methyl methacrylate) (PMMA)/poly (acrylonitrile‐co‐styrene) (SAN, AN content = 15 wt %) and PMMA/poly (vinylidene fluoride) (PVDF) were carried out. The effective mean‐square optical anisotropy γ2 of the mixtures was found to be much higher than that estimated by the simple additivity of γ2 of component polymers. From the deviation, the order parameter (1 + J12) was estimated to be in a range of 2–13, depending on the blend composition. This suggests local ordering in the single‐phase mixtures, i.e., nematic alignment of the locally stretched dissimilar chains. In contrast, the deviation was slight in the polymer/solvent systems, SAN/MMA (monomer) and PVDF/butanone. The degree of ordering decreased with increasing temperature. T. The Specific interaction evidenced by FTIR spectroscopy exhibited a similar temperature dependence. Thus, local ordering seems to be induced by specific interactions and chain connectivity. The temperature dependence of J12 was successfully described by the Landau‐de Gennes theory; J ∞ (T + T0)/ T, T0 being the isotropic‐nematic transition temperature, as in the case of liquid crystals.
SANS from hot‐stretched polystyrene revisited
Authors: Schroeder J. R. , Hammouda B. , Bubeck R. A. , Chang J. W. 
Published: April 2003

AbstractSmall‐angle neutron scattering (SANS) has been used to investigate macromolecular orientation of uniaxially hot‐stretched partially deuterated polystyrene. Principle radii of gyration and degree of eccentricity were measured over a range of hot‐stretch temperatures, strain rates, and external draw ratios (EDR). Results show affine deformation for EDR <4 and an increase in the degree of local molecular orientation with increasing rate of strain and decreasing stretching temperature. It also is found that although the macromolecules follow the external stretching affinely on average, they do not deform uniformly.
Effect of cyclic stress on structural changes in polycarbonate as probed by positron annihilation lifetime spectroscopy
Authors: Liu Liang B. , Gidley David , Yee Albert F. 
Published: April 2003

AbstractPositron annihilation lifetime spectroscopy (PALS) is used to probe structural changes in glassy polycarbonate in terms of changes in the hole volume and the number density of holes during fatigue (cyclic stress) aging. The ortho‐positronium (o‐Ps) pickoff annihilation lifetime τ3, as well as the intensity I3, were measured as a function of cyclic stresses and various previous thermophysical aging histories. It is found that τ3, the longest of the three lifetime components resolved in the PALS of glassy polycarbonate, increases when a cyclic stress is applied. These results indicate that there is a structural change during fatigue aging. The “holes” where o‐Ps can localize become larger upon fatigue aging. These results also suggest that a significant distinction exists between structural changes induced by thermophysical aging and fatigue aging. The o‐Ps annihilation intensity, which is a relative measure of the hole density in a material, showed a continuous decrease upon fatigue aging, indicating the possibility of hole coalescence, which could be a precursor of crazing. The interaction between thermophysical aging and fatigue aging corresponds very well with the enthalpy relaxation behavior as reported previously, viz., a well‐aged sample is much more sensitive to cyclic stress. More importantly, it is hypothesized that fatigue failure initiation is probably closely related to hole size and density fluctuation.
The dielectric properties of dry and water‐saturated nylon‐12
Authors: Pathmanathan K. , Cavaillé J.‐Y. , Johari G. P. 
Published: April 2003

AbstractThe dielectric relaxation of 30% crystalline Nylon‐12 of molecular weight 20,000 has been studied at frequencies from 12 Hz to 0.1 MHz and temperatures from 77 to 375 K, and the effect of water on the relaxation spectra has been investigated. Absorbed water increases both the rate and the intensity of both its α‐and β‐relaxation processes and increases the rate but decreases the intensity of its γ‐relaxation process. These results are interpreted in terms of the hydrogen bonding effects of water on localized motions of dipoles in Nylon‐12. The relatively large half‐width of the α‐relaxation, which becomes better resolved at high temperatures, is attributed mainly to the random distribution of crystalline regions in the polymer. It is suggested that water lowers the steric hindrance for the localized mode of dipolar reorientation and causes a redistribution of local sites such that the β‐relaxation process grows at the expense of the γ‐process.
Relaxations in thermosets. XII. Dielectric effects during curing of nonstoichiometric DGEBA‐based thermosets
Authors: Mangion M. B. M. , Wang M. , Johari G. P. 
Published: April 2003

AbstractThe dielectric permittivity ε′ and loss ε″ of diglycidyl ether of bisphenol‐A thermosets cured with nonstoichiometric amounts of diamino‐diphenyl methane have been measured during the course of their chemical reactions from the sol to gel to glass‐formation regions. ε′ monotonically decreases with time and ε″ initially decreases, increases to a peak value, and finally decreases to extremely low values characteristic of the glassy state. The initial decrease in ε″ is due to the decrease in the dc conductivity, and the peak is due to the dipolar reorientation. The appearance of these features shifts to longer time when the thermoset is stoichiometrically starved by decreasing the amount of the curing agent and, at a molar ratio of 4 : 1 of the epoxide to diamine, the ε″ peak does not appear during the curing process. Complex plane plots of ε′ and ε″ have the shape of an arc in all cases except when the molar ratio of the epoxide to diamine is 4 : 1. The dielectric consequences of the chemical changes with time during the crosslinking of a thermoset are analogous to the frequency dependence of ε″ of a condensed phase. The time dependence of ε″ follows a stretched exponential decay, ϕ(t = exp − [(t/τ)γ], where 0 < γ < 1. The parameter decreases with decreasing amine content. ε″ has been analyzed to obtain the increase in the relaxation time as curing progresses. A representation of ε* in terms of electrical modulus M* shows the occurrence of, first a Maxwell relaxation due to dc conductivity, and second a dipolar relaxation, during the period of a typical isothermal cure. Changes in the features of the isothermal cure that occur on changing the amount of the curing agent are discussed in terms of network formation in the thermoset, and the change in the electrical conductivity with curing time has been analyzed in terms of both a power law for gel formation and by a new equation that suggests an approach toward a singularity.
Miscibility diagrams of random copolymer blend systems
Authors: Braun D. , Yu D. , Kohl P. R. , Gao X. , Andradi L. N. , Manger E. , Hellmann G. P. 
Published: April 2003

AbstractThe miscibility of copolymers AxB1−x and AyB1−y, derived from the same monomer pair (A, B) but differing in composition, was studied. The systems (A, B) were (S, MMA), (BMA, MMA), (S, BMA), and (CIS, BMA) (S: styrene, CIS: p‐chlorostyrene, MMA: methylmethacrylate, BMA: n‐butylmethacrylate). Miscibility diagrams were recorded, at low and high temperatures, using cast films and dry films. All blend systems feature hightemperature miscibility gaps. Unusual effects of the compositions x and y on miscibility in blends AxB1−x/AyB1−y were observed. The classical prediction that miscibility should depend only on the composition difference |x – y| usually is too simple. It appears necessary to consider dyad interactions.
Dynamic study of the noncrystalline phase of 13C‐labeled polyethylene by variable‐temperature 13C CP/MAS NMR spectroscopy
Authors: Chen Qun , Yamada Takeyoshi , Kurosu Hiromichi , Ando Isao , Shiono Takeshi , Doi Yoshiharu 
Published: April 2003

AbstractThe 13C spin‐lattice relaxation times T1 of 13C‐labeled polyethylene crystallized under different conditions were measured at temperatures from −120 to 44°C by variable‐temperature solid‐state high‐resolution 13C nuclear magnetic resonance (NMR) spectroscopy, in order to determine accurately the dynamics of the noncrystalline region of the polymer. From these results, it was found that the T1 minimum for the CH2 carbons in the noncrystalline region of solution‐crystallized polyethylene with high crystallinity appears at higher temperature by about 20°C than that of melt‐quenched polyethylene with low crystallinity. This means that the molecular motion of the CH2 carbons in the noncrystalline regions is more constrained at a given temperature in the material of higher crystallinity. Furthermore, dynamics of the noncrystalline region is discussed in terms of the 13C dipolar dephasing times.
Relaxations in thermosets. XVI. Dielectric studies of negative feedback during curing of an epoxide‐ethylene‐diamine thermoset
Authors: Parthun M. G. , Johari G. P. 
Published: April 2003

AbstractThe complex dielectric permittivity of thermosets of diglycidly ether of bisphenol‐A cured with ethylene diamine has been studied during their isothermal curing at several temperatures. As cross‐linking progresses, the dc conductivity decreases. At the beginning of the cure the dc conductivity can be fitted to both the scaling laws with a critical exponent of about 4 and an equation indicating approach toward a singularity. In the later stage of the cure, the change in permittivity corresponds to dipolar relaxation of an infinitely connected network, and the Argand diagram for the complex permittivity measured at a fixed frequency obtained as the curing process proceeds at 305 K is similar to that for the complex permittivity as frequency is varied for a time‐invariant system which obeys a stretched exponential relaxation function with the curing parameter or exponent, γ = 0.29. Increase in the temperature of isothermal curing lowers both γ and the net decrease in the equilibrium permittivity on curing. A plot of the calculated relaxation time with curing time is sigmoidal and shifts to shorter times on increasing the curing temperature. Measurement of the dielectric properties during the cure but for different frequencies show that the various parameters for the curing kinetics are independent of the frequency of measurement. These observations confirm the development of our concepts of thermoset curing in terms of a phenomenon of negative feedback between molecular diffusion and chemical reactions.