bluuebunny/crossref_metadata_2025 huggingface dataset:
Accumulation of monomolecular polystyrene particles from a water surface onto a substrate
Authors: Kumaki Jiro
Published: April 2003

Monomolecular particles of polystyrene (Mw/Mn = 1.04, Mw = 3.84 ? 106) formed by spreading of a dilute solution in benzene over a water surface were successfully accumulated onto a hydrophobic substrate by the horizontal lifting method. The accumulation was quantitative (up to 66 layers) to give a multilayer film. The substrates used were silicon single crystals, quartz coated with an iron(III) stearate monolayer, and poly(methylmethacrylate) plates. The film contained voids amounting to 20‐30 vol%. The surface structure observed by transmission electron microscopy clearly showed a multilayer, particle structure. These facts indicate that the molecules exist as monomolecular particles in the film. The film should be a suitable material to study properties of polymeric monomolecules in a very unusual state as compared with the ordinary solid.
Chemical modification of poly(substituted‐acetylene): II. Pervaporation of ethanol / water mixture through poly(1‐trimethylsilyl‐1‐propyne) / poly(dimethylsiloxane) graft copolymer membrane
Authors: Nagase Yu , Ishihara Kazuhiko , Matsui Kiyohide
Published: April 2003

Poly(1‐trimethylsilyl‐1‐propyne)/poly(dimethylsiloxane) (PTMSP/PDMS) graft copolymer was prepared to evaluate the permeation characteristic at pervaporation of aqueous ethanol solution through the graft copolymer membrane. For the preparation of PTMSP/PDMS graft copolymer, an improved synthetic procedure was released in this paper, which comprised a one‐pot reaction of PTMSP in lithium bis(trimethylsilyl)amide followed by treatment with hexamethylcyclotrisiloxane and trimethylchlorosilane. PDMS content of the graft copolymer was controlled in the range 5–74 mol%. Very tough and thin membranes could be prepared from these copolymers having various PDMS content by the solvent casting method. The permselectivity of the membranes was investigated by pervaporation of ethanol/water mixture at 30°C. Preferential permeation of ethanol was observed for the membranes. It was also found that the selectivity of every copolymer membrane was higher than that of the PTMSP membrane. Moreover, the selectivity depended on the PDMS content of the graft copolymer. The separation factor and permeation rate assumed the maximum values at 12 mol% PDMS content. At the maximum point, 7 wt% aqueous ethanol solution was concentrated to about 70 wt% ethanol solution, and the separation factor and permeation rate were 28.3 and 2.45 × 10−3g · m/m2 · h, respectively. Such a high permselectivity for ethanol might be due to a delicate alteration of membrane structure, which was induced by the introduction of a short PDMS side chain into a PTMSP backbone.
Rate of physical aging of polycarbonate at a constant tensile strain
Authors: Ricco T. , Smith Thor L.
Published: April 2003

A study was made of the physical aging of an annealed polycarbonate film at a constant extension of 2.6% at 5 temperatures from 30 to 110°C. During stress relaxation at the constant extension, the storage modulus in tension, E′, was determined by imposing a sinusoidal strain of small amplitude at frequencies up to 25 Hz during an aging period, commonly of 5 h. Plots of log E′ against log f, where f is the frequency, gave parallel straight lines, each at a different aging (elapsed) time te. These lines were superposed by shifts along the abscissa. The obtained shift factors log a varied linearly with log te, the slope being the aging rate μ, a quantity introduced by Struik. The results show that μ is about 1.37 at 30°C and that it increases progressively with the temperature and becomes approximately 2.13 at 110°C. Another measure of the aging rate is the rate of increase of E′ with te, expressed as the percent increase per decade of the aging time. This quantity also increases progressively with the temperature from about 2.6% at 30°C to nearly 3.5% per decade of time at 110°C.
Structure‐property relationships of copolyamides. II. crystal structure of drawn copolyamide films
Authors: Baik Doo Hyun , Jo Won Ho
Published: April 2003

The crystal structures of drawn copolyamides 6/6.6, 6/6.T, 6/6.1, 6/PXD.6, 6/MXD.6, and 6/MXD.I were examined by wide‐angle x‐ray diffraction. Copolyamide 6/6.6, which follows the inclusion model, shows only α‐characteristics at all the comonomer compositions examined (0–33.3 mol%). However, the other copolyamides, which follow either the partial‐inclusion or complete‐exclusion model, show γ‐characteristics more predominantly as the comonomer content increases. The interplanar spacing of the (200) planes, which corresponds to the hydrogen bond distance between antiparallel chains, remain constant, whereas the spacing of the (020) planes corresponding to the distance between hydrogen bonded sheets increases monotonically with increasing the comonomer content. It is also observed that both the crystal perfection index and the crystal thickness decrease as the comonomer content increases.
Ethylene‐propylene copolymerization initiated with solubilized ziegler‐natta macromolecular complexes. II. Characterization of [styrene]‐b‐[ethylene‐co‐propylene] copolymers
Authors: Cansell François , Siove Alain , Belorgey Georges
Published: April 2003

Copolymerization of ethylene (E) with propylene (P) initiated with soluble (polystyrene)100‐butadiene3‐Li/TiCl4 complexes leads to [St]‐b‐[E‐co‐P] diblock copolymers with a random [E‐P] block. GPC and 13C‐NMR analyses of copolymers with various compositions and block lengths disclose well‐defined linear structures. From DSC measurements of such materials, three different endothermal transition regions are observed: two glass transition regions corresponding, respectively, to the Tg of styrenic and olefinic blocks, and one [E‐P] block melting region in which propylene units play a primary role. Furthermore, an additional endotherm is observed, depending on the thermal history of the sample.
Permeability of pure and mixed gases in silicone rubber at elevated pressures
Authors: Jordan S. M. , Koros W. J.
Published: April 2003

The transport properties of silicone rubber are reported at 35°C for a series of pure gases (He, N2, CH4, CO2, and C2H4) and gas mixtures (CO2/CH4 and N2/CO2) for pressures up to 60 atm. The effects of pressure and concentration on the permeability of various gases have been analyzed to consider plasticization and hydrostatic compression effects. Over an extended pressure and concentration range, both compression of free volume and eventual plasticization phenomena were observed for the various penetrants. In pure component studies, plasticization effects tended to dominate hydrostatic compression effects for the more condensible penetrants (C2H4 and CO2) while the reverse was true for the low sorbing N2 and He. These issues are discussed in terms of penetrant diffusion coefficients versus pressure to clarify the interplay between the opposing effects for the penetrants of markedly different solubilities. Additional insight into the somewhat complex interplay of the plasticization and hydrostatic compression effects are given by mixed gas permeation results. It was found that the permeability of nitrogen in a 10/90 CO2/N2 and a 50/50 CO2/N2 mixture was increased by the presence of CO2 because the plasticizing nature of CO2 is able to overcome nitrogen's compression effect.
A study of wet PVC gels by raman spectroscopy
Authors: Jackson R. S. , Bower D. I. , Maddams W. F.
Published: April 2003

Raman spectroscopy has been used to study PVC gels made in cyclohexanone in the wet state at concentrations from 21 to 93% by weight of PVC. Parallel and perpendicular spectra were obtained in the C‐Cl stretching region, and after subtraction of the solvent spectrum they were analyzed into a set of overlapping peaks due to various structural components. The positions of the peaks found were in good agreement with those found earlier for PVC samples in the solid state. The fractional contribution of the areas of peaks assigned to crystalline material to the total area under the C‐Cl stretching region was used to estimate the crystallinity of the gels, and changes in their depolarization ratios and relative intensities were interpretated as providing further evidence for the presence of two types of crystallites in PVC gels. From a determination of the crystallinity at the gel transition point and reasonable assumptions, the contributions of the two types of crystallites to the total crystallinity were estimated.
Temperature dependence of swelling of crosslinked poly(N,N′‐alkyl substituted acrylamides) in water
Authors: Bae You Han , Okano Teruo , Kim Sung Wan
Published: April 2003

The swelling of crosslinked poiy(N,N′‐alkyl substituted acrylamides) in water was studied in relation to temperature changes. Conventional swelling theory and separation of the polymer solvent interaction parameter into enthalpic and entropic contributions were used to characterize the temperature dependence of swelling in water. The thermosensitivity of swelling can be attributed to the delicate hydrophilic/hydrophobic balance of polymer chains and is affected by the size, configuration, and mobility of alkyl side groups. A sharp swelling transition may occur at an optimum hydrophilic/hydrophobic balance but was found only in the N‐isopropylacrylamide network among the networks tested. This swelling transition pattern was also reflected by the endothermic peak of the DSC thermogram of the swollen sample.
Structure and properties of propylene‐ethylene block copolymers and the corresponding blends
Authors: Wang Lixiao , Huang Baotong
Published: April 2003

Structure and properties of presumed polypropylene(PP)‐b‐polyethylene(PE) block copolymers (PPPE) and the corresponding blends (PP/PE) have been investigated by wide‐angle x‐ray scattering (WAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), torsional pendulum apparatus, and other techniques measuring mechanical properties. Crystallinity, morphological structure, and mechanical properties of the block copolymers and blends vary with the PP and PE compositions. Compared with PP homopolymers and PP/PE blends, PP and PE segments in PP‐PE block copolymers have a reduced crystallinity, especially PE segments. An additional peak at about −40°C is observed in dynamic relaxation spectra; substantially different morphology is revealed; and mechanical properties are greatly improved for the sequentially copolymerized PP‐PE block copolymers, indicating the existence of PP‐PE block structure.
Transport of hexane vapor in polystyrene at 25°C I. Analysis of integral sorption data
Authors: Kang Yong Soo , Meldon Jerry H. , Sung Nakho
Published: April 2003

A series of measurements of integral n‐hexane vapor sorption at 25°C and moderate activity, in polystyrene microspheres of varying radii, exhibits typical non‐Fickian behavior: nonoverlap of curves of fractional uptake versus (square root of time)/radius. The data are examined in light of a sorption isotherm indicating hexane solubility in excess of that predicted by the Flory–Huggins equation, up to the hexane activity at which the glass transition apparently occurs. A transport analysis is developed based on the assumption that below the transition temperature Tg the rate of sorption is limited by the rate of polymer chain relaxations induced by the penetrant, which facilitate hexane entry into, and immobilization in, glassy microvoids.
Epitaxial crystallization of polyoxymethylene on NaCl single crystal in dilute solution
Authors: Sato Yukihiko
Published: April 2003

The epitaxial crystallization of polyoxymethylene (POM) is observed from 0.01% cyclohexanol solution on the (001) cleavage face of NaCl. High‐resolution electron microscopy reveals that the crystals are definitely triangular, rather than rectangular prisms, although the crystals have previously been interpreted as “edge‐on” arrangements of lamellar crystals. An electron diffraction pattern obtained from films, which were piled up with a maximum of nine sheets per grid, shows that plane spacing of the epitaxial crystals is 3.87 Å and almost the same as the
\[
\left\{ {10\bar 10} \right\}
\] spacing (3.86 Å) of hexagonal single crystal of POM: the axes of POM fold chains in the crystals are parallel to the (001) plane. A possible mechanism for the epitaxial crystallization of POM is proposed.
Sorption and partial molar volume of gases in poly (dimethyl siloxane)
Authors: Kamiya Yoshinori , Naito Yasutoshi , Hirose Takuji , Mizoguchi Keishin
Published: April 2003

Sorption of N2, O2, Ar, CH4, CO2, C2H4, and C2H6 in poly (dimethyl siloxane) liquid and rubber and the dilation of the polymers due to sorption of the gases are studied at 25°C under pressures up to 50 atm. In the liquid, the sorption isotherms for low‐solubility and high‐solubility gases are described by Henry's law and the Flory–Huggins equation, respectively. Gas sorption in the rubber, which contains a 29 wt % silica filler, follows the dual‐mode sorption model, though marked hysteresis is observed in the sorption of O2 and CH4. The dilation isotherms increase linearly or exponentially in both polymers with increasing pressure. Considering that gas molecules adsorbed into micropores of the filler particles do not participate in the dilation, partial molar volumes of the dissolved gases in the rubber are determined from data of sorption and dilation. The values are nearly equal to the partial molar volumes in the liquid (48–60 cm3/mol).
Polyurethane cationomers. II. Phase inversion and its effect on physical properties
Authors: Chen Show‐An , Chan Wu‐Chung
Published: April 2003

The three series of polyether polyurethane cationomers based on MDI, HDI, and TDI that are the subject of Part I, undergo emulsification (or phase inversion) on addition of water to solutions in MEK. The phase inversion mechanism depends on the structure of hard segment, ionic content, and dispersion temperature. The dispersion process can be divided into three stages involving a separation of hard segment aggregates due to adsorption of water on their surface, water entering into disordered and then ordered hard domains, and finally a rearrangement of agglomerates to form microspheres. The extent of penetration of water into the disordered hard domains decreases with increasing glass transition temperature; while in ordered hard domains, penetration depends on the dissociation temperature of urethane–urethane hydrogen bonds. Thus the penetration of water into the hard domains is strongly dependent on the dispersion temperature. Films cast from the emulsions have both ordered and disordered hard segment regions, this is also true of films cast directly from solution. The dispersion can disrupt the order in hard domains, leading to an increased phase separation for the MDI system and to a slightly increased phase mixing for the HDI and TDI systems. Films cast from solutions have a morphology with soft domains as a continuous phase and hard domains as a fibrillar network dispersed in the continuous phase. After dispersion, the hard segments originally distributed in the dispersed phase can be inverted to become a hard domain network or a continuous phase.
Relaxation dynamics of carbon dioxide sorbed in poly (dimethyl siloxane) rubber
Authors: Cain Edward J. , Jones Alan A. , Inglefield Paul T. , Jost Robert D. , Liu Xiangzhe , Wen Wen‐yang
Published: April 2003

We have probed the dynamics of 13CO2 molecules sorbed in poly (dimethyl siloxane) rubber by nuclear magnetic resonance (NMR) relaxation. The spin‐lattice and spin‐spin relaxation times as well as nuclear Overhauser enhancements were determined as functions of temperature at three magnetic field strengths. The relaxation mechanisms found to be important are intermolecular dipole‐dipole relaxation and spin rotation relaxation with a minor contribution from chemical shift anisotropy relaxation. Our analysis shows that the assumption of a single correlation time for each motional mechanism is inconsistent with the NOE data and spin‐spin relaxation times. However, if a distribution of correlation times is assumed, one can interpret all of the experimental data in a reasonable manner. We have quantitatively elucidated the spin relaxation mechanisms and determined the parameters which characterize the distribution times for 13CO2 Collisional motions, rotational motions, and translational motions in the silicone rubber. A fractional exponential correlation function of the Williams‐Watts type with a fractional exponent of 0.58 is used in our description of the 13CO2 dynamics. This exponent is typical of the distribution of time scales associated with segmental motion in polymeric rubbers. The broad distribution needed to describe the data has implications for the coupling of diffusion to segmental motion and for the relationship between macroscopic permeability and the molecular level character of diffusion.
NMR and dynamic mechanical studies of miscibility enhancement via ionic interactions in polystyrene/poly (ethyl acrylate) blends
Authors: Zhang Xinsheng , Eisenberg Adi
Published: April 2003

Direct ion‐ion interactions in ionomer blends are achieved through microion elimination by mixing the two ionomers, poly (styrene ‐co‐tetraalkylammonium methacrylate) and poly (ethyl acrylate‐co‐Nmethyl‐4‐vinyl pyridinium. iodide), in a benzene/ methanol mixture. The pyridiniumcarboxylate ionion interactions are compared with pyridinium‐sulfonate interactions which were described before. It is shown that carboxylate ions are much less effective than sulfonate ions in enhancing miscibility in the polystyrene/ poly (ethyl acrylate) system. Complete miscibility is not attained for this polymer pair even with up to 10 mol % ions. In another system, ion pair‐ion pair blends were prepared by mixing poly (styrene‐co‐sodium styrenesulfonate) with poly (ethyl acrylateco‐N‐methyl‐4‐vinyl pyridinium iodide), also in a benzene/ methanol mixture. The results show that ion pair‐ion pair associations are also a much weaker driving force for miscibility enhancement in this polymer pair than the corresponding direct pyridinium‐sulfonate ion‐ion interactions. A ranking is presented of the relative strengths of the various ionic interactions in their effect on miscibility enhancement, which also includes ion‐dipole interactions (sodium sulfonate‐pyridine).
Solid‐state 13C NMR characterization of annealed poly (p‐phenylene vinylene) PPV Films
Authors: Simpson Jeffrey H. , Egger Norbert , Masse Michael A. , Rice David M. , Karasz Frank E.
Published: April 2003

Solid‐state 13C cross‐polarization magic‐angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectra have been obtained for annealed films of poly (p‐phenylene vinylene) (PPV), prepared through the precursor route and for a deuterated PPV‐d4, poly (p‐2,3,5,6 tetradeuterophenylene vinylene). 13C CPMAS spectra of PPV are of high resolution, typically characteristic of a nearly fully crystalline structure. All four phenylene and vinylene resonances have been assigned, and for stretched films the 13C CPMAS linewidth and the quality of crystallinity are independent of the draw ratio. 13C CPMAS resolution and crystallite size (as determined by transmission electron microscopy, TEM) depend upon final annealing temperature. The greatest NMR resolution and largest crystallite size are obtained for films annealed at 300°C. The 13C CPMAS NMR spectra show the presence of phenylene ring 180° rotational jumps, and 13C CPMAS resolution is affected by rotational disorder about phenylene‐vinylene bonds. NMR data show that PPV films possess molecular motion at elevated temperatures. Enhancement of this motion during annealing may provide a means for improving the quality of PPV crystallinity.
Synthesis and unperturbed dimensions of poly(diphenylmethyl methacrylate)
Authors: Mays Jimmy W. , Hadjichristidis Nikos , Lindner J. S.
Published: April 2003

The synthesis, fractionation, and characterization of poly(diphenylmethyl methacrylate) (PDPMM) are described. Analysis of tacticity by 13C nuclear magnetic resonance (NMR) revealed a high (25%) isotactic content. Results of low‐angle light scattering and intrinsic viscosity measurements in toluene indicate that PDPMM chains behave as random coils and that toluene is a thermodynamically good solvent. The characteristic ratio C∞ of the chains was determined from viscosity measurements in a near‐theta solvent, 3‐heptanone at 45°C. The corresponding value of C∞ = 14.0 is consistent with previous work on poly(triphenylmethyl methacrylate), C∞ = 20.3, and poly(benzyl methacrylate), C∞ = 10.0, and reflects the bulkiness of the side group and the increase in isotactic content of the chains with increasing substitution.
On the melting behavior of a thermotropic rigid random copolyester based on terephthalic acid and substituted hydroquinones
Authors: Ghanem Antoine M. , Dickinson L. C. , Porter Roger S. , Zachariades Anagnostis E.
Published: April 2003

Thermotropic liquid crystalline random copolyesters, based on terephthalic acid and substituted hydroquinones, display an unusually large heat for the crystal‐nematic transition; this phenomenon is related to their highly ordered structures. To modify the structures, annealing was carried out in the solid state at different temperatures over different times. As the annealing time or temperature is increased, the melting peaks shift to higher temperatures, whereas the heat of fusion shows no significant change or is lowered, respectively. An explanation is offered in terms of crystal perfection and a molecular weight increase. No evidence for a random‐to‐block conversion on annealing is found.
Thermal expansion of poly(ether‐ether‐ketone) (PEEK)
Authors: Choy C. L. , Leung W. P. , Nakafuku C.
Published: April 2003

Thermal expansivities along the a, b, and c axes of the orthorhombic unit cell of poly (ether‐ether‐ketone (PEEK) crystals have been determined from 160 to 470 K by wide‐angle x‐ray diffraction. The expansivities along the a and b axes are positive while the expansivity along the c (chain) direction is negative, with values of
\[
\alpha _a^c = 11.3 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}} ,{\rm }\alpha _b^c = 4.6 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}} ,
\] and
\[
\alpha _\parallel ^c = ‐ 1.4 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}}
\] at 300 K. The negative α arises from the effective shortening along the chain axis caused by the torsional and bending motions of the chain, whereas the large and positive α and α reflect the weak interactions across the chains. Using a dilatometric technique we have also studied the expansion behavior of isotropic PEEK as a function of crystallinity (X = 0−0.34) and have measured thermal expansivities of oriented PEEK (draw ratio 1–4) parallel and perpendicular to the draw direction. The effects of crystallinity and orientation can be understood by treating semicrystalline PEEK as a composite consisting of crystallites embedded in an amorphous matrix.
Effect of a methylmethacrylate–butadiene–styrene modifier on the dynamics of the viscoelastic beta process in poly(vinyl chloride)
Authors: Havriliak S. , Shortridge T. J.
Published: April 2003

The viscoelastic properties of a methylmethacrylate–butadiene–styrene (MBS) modifier over the temperature range −140 to 20°C and frequency range 0.01592 (0.1 Rad/s) to 79.62 Hz (500 Rad/s) is represented in terms of a relaxation function proposed by Havriliak and Shortridge to represent the viscoelastic beta process of MBS‐modified and unmodified poly(vinyl chloride) (PVC). The parameters of the expression as well as their temperature dependence were determined from the multiresponse methods developed by Havriliak and Watts. The complex modulus of PVC/MBS modifier blends at 8.26, 10.71, and 13.04 wt % modifier, over a temperature range −140–20°C, and at a frequency of 1 Hz can be represented, nearly within experimental error, in terms of the complex modulus of the neat components, the volume fraction of the modifier, and the blend equations of Uemura and Takayanagi. The small but persistent deviations that are observed are discussed in terms of hydrostatic stresses due to differential coefficients of expansion.
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

A 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

Long‐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

Heat 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

The 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

A 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

Poly(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

The 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

Polyurethanes 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

The 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

Depolarized 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

Small‐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

Positron 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

The 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

The 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

The 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

The 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

The 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.
Study of the dielectric β‐relaxation in poly(ethylene terephthalate) and ethylene isophthalate terephthalate copolyesters
Authors: Tatsumi Tomiwo , Ito Eiko , Hayakawa Reinosuke
Published: April 2003

The dielectric β‐relaxation in poly(ethylene terephthalate) and ethylene isophthalate terephthalate copolyesters with various ethylene isophthalate contents was investigated over a wide range of frequencies. Isothermal spectra and normalized plots show that the dielectric β‐relaxation is characterized by the molecular structure between the aromatic rings. The equilibrium polarizability of the motional segment, which was estimated from the dielectric increment obtained by the best fit of the Havriliak‐Negami equation to the Cole‐Cole plot, indicates that torsional vibrations of the main chain are correlated over a length corresponding to one monomer.