bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface studies of tetraalkylammonium bromides and iodides using atomic force microscopy
Authors: Wang Qiguang , Annis Brian , Wunderlich Bernhard
Published: April 2003

The surface structures of two series of tetra‐n‐alkylammonium halides, N(CxH2×+1)4I and N(CxH2x+1)4 Br have been investigated with atomic force microscopy (AFM) and compared to hexatriacontane (C36H74). The surfaces could be imaged with atomic resolution. The observed primitive, square surface‐patterns of tetra‐n‐butyl chloride and bromide are in good accord with x‐ray single‐crystal structure. For n > 4, x‐ray powder diffraction showed that increasing the alkyl chain‐length leads mainly to an appropriate increase of the unit cell along the c‐axis, which suggests similar layer structures for all long‐chain salts beyond the butyl homologue. Within the centers of the molecular layers of these crystals reside the halide anions and the quaternary nitrogens. The surfaces accessible for AFM consist of methyl end‐groups. As the number of carbon atoms increases beyond four, the surface symmetry changes to the face‐centered square patterns characteristic of many paraffins. The chains of the tetraalkyl ammonium salts pack, however, less dense than paraffins. © 1994 John Wiley & Sons, Inc.
Hydration in semicrystalline polymers: Small‐angle neutron scattering studies of the effect of drawing in nylon‐6 fibers
Authors: Murthy N. S. , Orts W. J.
Published: April 2003

Water absorbed by nylons appears to be partitioned into interlamellar and interfibrillar spaces. The amount of water in the interfibrillar region remains essentially unchanged with increasing draw ratio, whereas that in the interlamellar regions decreases with draw ratio; the latter accounts for the decrease in the water uptake in the drawn fibers. These results suggest that the amount of the amorphous material in the interfibrillar regions remains unchanged during drawing, and the increase in the crystallinity during drawing results from the incorporation of the amorphous chain segments in the interlamellar regions into the crystalline lamellae. Further, the interfibrillar water is more tightly bound than the interlamellar water. The length of the longitudinal channels into which water diffuses is about the same as that of the fibrils, and increases from ca. 1500 to 2000 Å upon drawing. The longitudinal channels are highly oriented even in undrawn fibers, and their misorientation increases from 5° to 15° upon drawing. These channels can be described as surface fractals of dimension 3.4–3.6. © 1994 John Wiley & Sons, Inc.
Crystal structure, morphology, and phase transitions in aromatic polyimide oligomers. 3. Poly(1,4‐phenyleneoxy‐1,3‐phenylene pyromellitimide)
Authors: Liu Jiang , Kim Doyun , Harris Frank W. , Cheng Stephen Z. D.
Published: April 2003

An aromatic polyimide oligomer, poly(1,4‐phenyleneoxy‐1,3‐phenylene pyromellitimide) (PMDA‐3,4'‐ODA), was synthesized from pyromellitic dianhydride (PMDA) and 3,4'‐oxydianiline (3,4'‐ODA) via a melt‐polymerization method. This method permits growth of PMDA‐3,4'‐ODA lamellar crystals and the crystal structure can be studied via electron diffraction (ED) and wide‐angle x‐ray diffraction (WAXD) experiments. Our structure analysis indicates that this polyimide possesses a two‐chain orthorhombic crystal lattice with dimensions of a = 0.848, b = 0.562, and c = 3.365 nm. It has also been found that poly(amic acid) precursors with little imidization possess the same ab lateral lattice packing, but statistical departure from the ordered packing along the c‐direction. Upon increasing the degree of imidization through annealing at elevated temperatures, the order along the c‐axis was progressively enhanced. Increasing the annealing temperature caused the dimensions of the a‐ and the b‐axes to expand while the crystal correlation lengths decreased laterally. Simultaneously the dimension of the c‐axis shrinks with an increase of the crystal correlation length along the chain direction. Crystal morphological study via transmission electron microscopy (TEM) indicates a mainly lamellar crystal texture with different thicknesses depending upon the polymerization conditions. The end lamellar surface is usually smooth. After annealing at elevated temperatures, the lamellar end surfaces become rough, which may be due to chain motion along the c‐axis. The annealed PMDA‐3,4'‐ODA lamellar crystals still show a large amount of defects. © 1994 John Wiley & Sons, Inc.
An analysis of ionic conductivity in polymer electrolytes
Authors: Chung S. H. , Such K. , Wieczorek W. , Stevens J. R.
Published: April 2003

Conductivities for a wide variety of ionically conducting polymer electrolytes with a range of salt compositions have been investigated over the temperature region Tg to 370 K. When the conductivity data are analyzed as a function of temperature using the empirical Vogel‐Tammann‐Fulcher (VTF) equation a common trend is observed in that deviations in the fits to the data invariably occur in the temperature range 1.2 Tg to 1.4 Tg for all of the samples investigated. This deviation is interpreted as a decoupling of the ions from polymer segmental motion. Recent 23Na NMR and 22Na positron annihilation studies of sodium salt‐based polymer electrolytes support this interpretation with evidence of a change in dynamics at about 1.2Tg. © 1994 John Wiley & Sons, Inc.
Strongly stretched polymer brushes
Authors: Milner Scott T.
Published: April 2003

Polymer “brushes” are formed when long‐chain molecules are somehow attached by one end at an interface with a relatively small area per chain. Such adsorbed brushes in the presence of solvent may be used to modify surface properties, stabilize colloidal particles, etc. Strongly segregated block copolymer phases, or interfacial layers of such “polymeric surfactants” may also be modeled in terms of “melt brushes,” (i.e., brushes without solvent). In both cases, when chain attachments are crowded on the interface, the chains stretch out to avoid neighboring chains. The resulting physical state has properties markedly different from polymer solutions, gels, or weakly adsorbed polymer layers. When the chains are strongly stretched, their statistical mechanics become simpler, as fluctuations around the set of most probable conformations are suppressed. This makes possible many pencil‐and‐paper calculations of brush properties, including bending and compressional moduli, and detailed knowledge of the chain conformations. As a recent example, I will describe calculations of phase diagrams of strongly segregated block copolymers including bicontinuous double‐diamond phases. © 1994 John Wiley & Sons, Inc.
Experimental and theoretical analysis of the right angle extrusion of polyethylene at room temperature
Authors: Ashok Babel K. , Moosbrugger J. C. , Campbell G. A.
Published: April 2003

In order to obtain high‐performance polymer and products, processing of crystalline polymers below their softening temperature has been employed and studied in recent years. It has gathered attention, for example, in the area of producing high‐strength polymer rods and filaments of higher cross‐sectional area for special applications. Die drawing and extrusion techniques dominate the processes used to achieve these products. Extrusion is primarily achieved by forcing the polymer through converging dies of circular and other cross‐sections. The methods of solid‐state extrusion processing practiced are primarily ram extrusion and hydrostatic extrusion. In this study, we investigate the process of producing cylindrical rods by ram extrusion of plastics at room temperature. Instead of using a converging die, right angle dies of varying extrusion ratios are employed to extrude three commercial grades of polyethylene. A theoretical analysis is also performed to predict the forces required during extrusion. The theoretical analysis closely follows the methodology presented by Coates et al. for the circular extrusion of polymers below their softening temperatures. ©1995 John Wiley & Sons, Inc.
Rheological and dielectric changes during isothermal epoxy‐amine cure
Authors: Simpson Joycelyn O. , Bidstrup Sue Ann
Published: April 2003

Dynamic viscosity and ionic conductivity were measured simultaneously during the cure of a digylcidyl ether of bisphenol‐A (DGEBA) epoxy resin with diamino‐diphenyl sulfone (DDS) by mounting a microdielectric sensor into the plates of a rheometer. Two different cure temperatures were examined. Periodically, throughout the cure, samples were removed from the plates of the rheometer, quenched, and analyzed for the glass transition temperature and epoxide conversion. The relationship between conductivity and viscosity appeared to be independent of cure temperature. A linear relation with a slope of −1 was observed between the natural logarithms of conductivity and viscosity during the cure up to approximately 85% cure conversion. It was hypothesized that the reaction rate was hindered by diffusion at this stage in the polymerization. A free volume relationship was used to successfully correlate conductivity with viscosity up to the diffusion limited region. ©1995 John Wiley & Sons, Inc.
Rotor‐synchronized two‐dimensional 13C CP/MAS NMR studies of the orientational order of polymers 2. Melt‐extruded poly(ethylene terephthalate) fibers
Authors: Tzou D. L. , Desai P. , Abhiraman A. S. , Huang T.‐H.
Published: April 2003

Determination of the orientational order of morphological components in polyethylene terephthalate (PET) is sought through quantitative application of two‐dimensional rotor synchronized magic angle spinning (ROSMAS) 13C NMR technique. Previous study in our laboratories had established a procedure for resolution of the carbonyl carbon (CA) and glycol ethylene carbon (GE) resonances into those corresponding to four morphological components.1 Due to paucity of sidebands in the GE resonances, the focus has been on the CA resonances in this attempt to obtain orientation distributions. A set of PET fibers possessing a broad range of crystalline and orientational order has been used to infer the meaning of NMR‐based orientation measurements vis‐a‐vis other techniques. A surprising finding of this study is the observation that the orientational orders of the broad component in the 13C CP/MAS spectrum and the narrow component are very similar in these fibers. ©1995 John Wiley & Sons, Inc.
Ferroelectric and piezoelectric properties of nylon 11/poly(vinylidene fluoride) bilaminate films
Authors: Su J. , Ma Z. Y. , Scheinbeim J. I. , Newman B. A.
Published: April 2003

The ferroelectric and piezoelectric properties of a new class of polymer ferroelectric and piezoelectric materials, nylon 11/polyvinylidene fluoride (PVF2) bilaminate films, prepared by a co‐melt‐pressing method, is presented. The bilaminate films exhibit typical ferroelectric D‐E hysteresis behavior with a remanent polarization, Pr, of about 75 mC/m2, which is higher than the value of 52 mC/m2 observed for PVF2 or nylon 11 films measured under the same conditions. The coercive field, Ec, of the bilaminate films is ∼ 78 MV/m, which is higher than that of either PVF2 or nylon 11 films. Measurements of the temperature dependence of the piezoelectric strain coefficient, d31, and the piezoelectric stress coefficient, e31, were also carried out. The bilaminate films exhibit a piezoelectric strain coefficient, d31, of 41 pC/N at room temperature, which is significantly higher than the PVF2 films (25 pC/N) and the nylon 11 films (3.1 pC/N). When the temperature is increased to 110°C, d31 of the bilaminate films reaches a maximum value of 63 pC/N, more than five times that of PVF2 (11 pC/N) and more than four times that of nylon 11 (14 pC/N) at the same temperature. The piezoelectric stress coefficient, e31, of the bilaminate films shows a value of 109 mC/m2 at room temperature, almost twice that of the PVF2 films (59 mC/m2) and about 18 times that of the nylon 11 films (6.2 mC/m2). Measurement of the temperature dependence of the hydrostatic piezoelectric coefficient, dh, of the bilaminate films also shows an enhancement with respect to the individual components, PVF2 and nylon 11. ©1995 John Wiley & Sons, Inc.
The effect of γ‐irradiation on slow crack growth in polyethylene
Authors: Lu X. , Brown N. , Shaker Manal , Kamel I. L.
Published: April 2003

HDPE was γ‐irradiated at room temperature. The resistance to slow crack growth (SCG) was measured in single edge notched tensile specimens under constant load as a function of the dose. The resistance to SCG initially decreased to a minimum value at a dose between 0.05 and 0.10 Mrd. The minimum value was 45% less than for the undosed state. For doses greater than 0.10 Mrd, the resistance to SCG increased up to a dose of 50 Mrd, where its value had increased by a factor of 102. The gel point occurred at 1–3 Mrd. MI and the crack opening displacement exhibited maximum values at a dose of 0.1 Mrd. The behaviors of SCG, MI and crack opening displacement were consistent with the explanation that chain scission dominated for doses less than 0.1 Mrd, and cross‐linking dominated at the higher doses. For doses beyond 50 Mrd, the resin became so brittle that it cracked during the loading of the specimen. Beyond the gel point the density increased from 0.9694 to 0.9716 g/cm3 at a dose of 160 Mrd. ©1995 John Wiley & Sons, Inc.
Effect of sample preparation conditions and degree of neutralization on the dynamic mechanical properties of poly(styrene‐co‐sodium methacrylate) ionomers
Authors: Kim Joon‐Seop , Eisenberg Adi
Published: April 2003

A study was undertaken of the effect of sample preparation conditions, especially moisture content, annealing conditions, and degree of neutralization, on the dynamic mechanical properties of poly(styrene‐co‐sodium methacrylate) ionomers. Water plasticizes the ionic cores; however, very small amounts of water do not affect the cluster glass transition mechanism. The study of the annealing effect showed that the morphology of ionomers is fixed during sample molding. No clustering was observed in samples below a degree of neutralization of 50%, possibly due to a decrease in the lifetime of the multiplets. The 50 and 75% neutralized samples showed weak clustering, with the cluster tan δ peaks shifting to higher temperatures with increasing degree of neutralization. The addition of neutralizing agents causes an increase in the size of multiplets; as a result, the strength of the electrostatic interaction between ion pairs increases. The 100–150% neutralized samples showed identical tan δ peaks and also very similar SAXS peaks. Therefore, it is speculated that excess NaOH resides in or near the multiplets and does not affect the electrostatic interaction between ion pairs. The 200–300% neutralized samples showed increased flow above the cluster Tg, as well as a strong small‐angle upturn in the SAXS profile. In agreement with previous results, it appears that in these materials, the excess NaOH resides in the hydrocarbon phase in the form of NaOH crystals, which can act as sites on which the carboxylate ion pairs can reside temporarily; the binding, however, is believed to weaken at high temperatures, which allows flow to occur. The 200% overneutralized Ba2+ sample showed the cluster Tg at much higher temperatures than the 100% neutralized sample, which implies that, for this sample, the stability of the multiplets is higher. © 1995 John Wiley & Sons, Inc.
Transmission electron microscopy of saturated hydrocarbon block copolymers
Authors: Khandpur Ashish K. , Macosko Christopher W. , Bates Frank S.
Published: April 2003

Contrast for transmission electron microscopy (TEM) of microphase‐separated saturated hydrocarbon diblock copolymers has been obtained using ruthenium tetroxide (RuO4). This technique exploits differences in the rate of transport of the oxidizing stain in rubbery amorphous versus semicrystalline, or glassy, microdomains. Rapid quenching from above the melting (Tm), or glass transition (Tg) temperature is shown to preserve the equilibrium melt morphology in poly(ethylene)‐poly(ethyl‐ethylene) (PE‐PEE), poly(ethylene)‐poly(ethylene‐propylene) (PE‐PEP), and poly(vinylcyclohexane)‐poly(ethyl‐ethylene) (PVCH‐PEE) diblock copolymers; PE melts at 108°C, PVCH is glassy up to about 140°C, while PEE and PEP remain rubbery down to approximately‐20°C and −56°C, respectively. Treatment of ultrathin sections of the quenched specimens with RuO4 vapor led to welldefined TEM images, that revealed microdomain type and order. These results are consistent with SANS data taken under equilibrium conditions. © 1995 John Wiley & Sons, Inc.
Fundamentals of polymer coagulation
Authors: Termonia Yves
Published: April 2003

Polymer coagulation is studied by a Monte Carlo diffusion model in which coagulant, solvent, and polymer particles move on nearest neighbor lattice sites according to the change in local interaction energy. Our approach has allowed, for the first time, to describe the coagulation process beyond the initial quench state and to reproduce the wide variety of different polymer structures that can be obtained, ranging from dust‐ to finger‐ to spongelike morphologies. We show that these morphologies are fully controlled by the coagulation rate which is itself strongly dependent on the degree of miscibility between solvent and coagulant. © 1995 John Wiley & Sons, Inc.
Preferential sorption and permeation of binary liquid mixtures in poly (vinyl chloride) membrane by pervaporation
Authors: Okuno H. , Nishida T. , Uragami T.
Published: April 2003

Preferential sorptions and pervaporation selectivities in poly (vinyl chloride) (PVC) membrane for various binary liquid mixtures were investigated. Methanol/n‐propanol, benzene/n‐hexane, and ethanol/water mixtures were selected as the binary liquid mixture. In the methanol/n‐propanol mixture, methanol was preferentially sorbed in the PVC membrane and predominantly permeated. In the benzene/n‐hexane mixture, benzene was incorporated and permeated preferentially. In the ethanol/water mixture, ethanol was preferentially sorbed in the PVC membrane and water was preferentially permeated. The preferential sorptions were analyzed according to Mulder's model derived from Flory‐Huggins thermodynamics. The pervaporation selectivity in these systems were discussed using a sorption selectivity and diffusion selectivity. © 1995 John Wiley & Sons, Inc.
Polymorphism in alternating polyketones studied by x‐ray diffraction and calorimetry
Authors: Klop E. A. , Lommerts B. J. , Veurink J. , Aerts J. , Van Puijenbroek R. R.
Published: April 2003

Differential scanning calorimetry and high temperature x‐ray diffraction were used to study the perfectly alternating copolymer of ethene and carbon monoxide (polyketone; POKC2). It was found that oriented POK‐C2 fibers show a crystalline phase transition at a temperature between 110–125°C with a 10% change in crystalline density. At this temperature, the crystal structure reported recently (POK‐α) is transformed to a crystal structure that was reported in the past for room temperature imperfectly alternating polyketone. The latter structure will be designated as POK‐β. The influence of chain defects on the crystal structure was studied by synthesizing terpolymers (POK‐C2/C3), in which small amounts of propylene‐CO units are incorporated into the polymer backbone. The resulting terpolymers differ from the copolymer by the presence of methyl groups randomly distributed along the polyketone backbone chain. Evidence is presented that indicates that the methyl groups are built into the crystal lattice as defects. With more than 5 mole‐% propene the terpolymer fibers crystallize exclusively in the β‐modification. Below this level the α/β ratio (at room temperature) increases with decreasing amounts of propene. Both as‐synthesized and as‐spun POK‐C2 were found to consist of both POK‐α and POK‐β; the α/β ratio depends on the method of preparation. Because the drawn POK‐C2 fibers studied here consist exclusively of POK‐α, the process of spinning and drawing leads to the transformation of unoriented β‐rich material into oriented POK‐α. © 1995 John Wiley & Sons, Inc.
Local chain motions of poly(β‐hydroxyoctanoate) in the bulk. 13C NMR relaxation study
Authors: Spyros A. , Dais Photis , Marchessault R. H.
Published: April 2003

Variable‐temperature 13C NMR spin‐lattice relaxation times (T1) and Nuclear Overhauser Enhancements (NOE) at two magnetic fields have been used to study the dynamics of the amorphous part of a semicrystalline sample (33% of crystallinity) of poly(β‐hydroxyoctanoate) (PHO). The interpretation of the relaxation data of the backbone carbons was made by employing a number of motional models. Among these, the DLM model offered the best interpretation of the relaxation data in terms of conformational transitions and librational motions of the backbone CH vectors, and proved to be superior to unimodal distribution functions. The interpretation of temperature‐ and frequency‐dependent T1 and NOE data of the carbon nuclei in the n‐pentyl side chain was made by employing a newly developed composite spectral density function for multiple internal CC bond rotations of restricted amplitude and chain segmental motion. The temperature dependence of the linewidths of the various protonated carbon resonances of PHO has been discussed in terms of the semicrystalline character of this polymer. © 1995 John Wiley & Sons, Inc.
NMR studies of water in polyimide films
Authors: Li S. Z. , Chen R. S. , Greenbaum S. G.
Published: April 2003

Commercial polyimide films containing up to ∼ 3 wt % water have been studied by proton, deuteron, and oxygen‐17 nuclear magnetic resonance (NMR). Comparisons between NMR results and previous dielectric relaxation (DR) results for a variety of Kapton films show that there is a one‐to‐one correspondence between specific dielectric loss peaks and features of the 2H or 17O NMR spectra. It is concluded that water molecules, which interact only weakly with the polymer, reside in the polyimide matrix in two configurations, randomly oriented single molecules and chains of water molecules oriented perpendicular to the plane of the film. The correspondence between NMR and DR observed in water in Kapton extends to water in Upilex and to methanol and acetic acid in Kapton. © 1995 John Wiley & Sons, Inc.
NMR characterization of styrene‐divinylbenzene gel beads using freezing point depression of benzene
Authors: Ogino Kenji , Sato Hisaya
Published: April 2003

Freezing processes of benzene in the presence of styrene‐divinylbenzene gel beads were investigated by proton nuclear magnetic resonance spectroscopy. Some portion of benzene in the pore did not freeze below its freezing point, which was detected until −80°C. Temperature dependence of the amount of unfrozen benzene was discussed in relation to the pore size and the cross‐linking density of gel beads. The small pore size and high crosslinking density increased the amount of unfrozen benzene, whereas the polymer matrix concentration showed little effect on the freezing processes. © 1995 John Wiley & Sons, Inc.
Structure and properties of a photosensitive polyimide: Effect of photosensitive group
Authors: Ree Moonhor , Nunes Thomas L. , Chen K.‐J. Rex
Published: April 2003

The photosensitive poly(p‐phenylene biphenylteracarboximide) (BPDA‐PDA) precursor was synthesized by attaching photocross‐linkable 2‐(dimethylamino)ethyl methacrylate (DMAEM) monomer to its poly(amic acid) through acid/base complexation. The polyimide thin films were prepared by a conventional cast/softbake/thermal imidization process from the photosensitive precursors with various concentrations of DMAEM. The structure and properties of the polyimide films were investigated by small‐angle and wide‐angle x‐ray scattering, refractive indices and birefringence analysis, residual stress and relaxation analysis, stress‐strain analysis, and dynamic mechanical thermal analysis. In comparison with the polyimide film from the poly(amic acid), the films, which were imidized from the photosensitive precursors, exhibited a better molecular order and microstructure; however, they exhibited less molecular orientation in the film plane. Despite the enhancement in both the molecular order and microstructure, the film properties (i.e., mechanical properties, thermal expansion, residual stress, optical properties, dielectric constant, and water sorption) degraded overall due to both the decrease in molecular in‐plane orientation and the formation of microvoids caused by the bulky photosensitive group during thermal imidization. That is, on one hand, the PSPI precursor formation provides an advantageous, direct patternability to the BPDA‐PDA precursor, and on the other hand, it results in degraded properties to the resulting polyimide film. © 1995 John Wiley & Sons, Inc.
Gas transport properties of polymers based on spirobiindane bisphenol
Authors: Pessan L. A. , Koros W. J. , Schmidhauser J. C. , Richards W. D.
Published: April 2003

Transport properties of pure gases in polycarbonates, polyesters, and polyetherimides based on 6,6′‐dihydroxy‐3,3,3′,3′‐tetramethyl‐1,1′‐spiro biindane (SBI) and bisphenol‐A (BPA) are compared at 35°C. The SBI monomer contains two spiro‐linked five‐membered rings which are fused to the phenyl rings at the meta and para positions to the hydroxyl groups. This molecular structure gives SBI‐based polymers with higher fractional free volume (FFV) and lower intramolecular motions as compared to the BPA‐based analogs. The inhibition of chain packing due to the SBI moiety yields polymers with much higher permeabilities for all the gases studied, despite the hinderance of mobility associated with the SBI structure. Simultaneous increase in selectivity was also observed for some gas pairs. Oxygen permeabilities up to 5.9‐fold higher with increases of up to 13% in O2/N2 selectivities were observed for a polyester based on SBI as compared to its analog based on BPA. Higher permeabilities of up to 4.3‐fold for He and up to 4.8‐fold for CO2 were observed due to the substitution of SBI for BPA. Not surprisingly, lower values of He/CH4 and CO2/CH4 selectivities were obtained for the more open SBI‐containing polymers. The changes in fractional free volume and inhibition of small‐scale mobility for some materials caused by the SBI moiety were measured and used in the interpretation of the gas transport properties. The individual contributions of diffusivity and solubility to the overall transport behavior of the polymers are discussed and correlated to the structural alterations caused by the SBI substitution for BPA monomer. © 1995 John Wiley & Sons, Inc.
Star‐shaped polymers by living cationic polymerization. VIII. Size and shape of star poly(vinyl ether)s determined by dynamic light scattering and computer simulation
Authors: Kanaoka Shokyoku , Sawamoto Mitsuo , Higashimura Toshinobu , Won Jongok , Pan Chuanbin , Lodge Timothy P. , Fujiwara Masaaki , Hedstrand David M. , Tomalia Donald A.
Published: April 2003

The sizes and shapes of star‐shaped poly(vinyl ether)s, prepared by living cationic polymerization, were studied by dynamic light scattering and molecular mechanics‐based computer simulation. The hydrodynamic radii (Rh) of star poly(isobutyl vinyl ether)s (4a; M̄w = 2.2 × 104 − 1.7 × 105) determined by dynamic light scattering were in the range from 30 to 90 Å in tetrahydrofuran or ethyl acetate. Consistent with the expected multiarmed architecture of 4a, the radius for a given number (f) of arms per molecule increased with the degree of polymerization [DP(arm)] of the arms, and for a fixed DP(arm), the radius increased with f. The relationship between arm number f and the “shrinking” factor h [Rh(star)/Rh(linear)] was consistent with multibranched structures for the star polymers. These results are supported by those for the molecular weight itself; the apparent weight‐average molecular weights by size‐exclusion chromatography are less than the corresponding absolute values by static light scattering. The dependence of h on f suggests some degree of asymmetry in the star shape. Similar results were also obtained by the computer simulation of potential energy‐minimized conformations of the arms, which implied almost spherical but slightly asymmetric shapes. The computer simulation also demonstrated that the star polymer (4b) with pendant hydroxyl groups in the arms is smaller in size than the corresponding alkyl (isobutyl) (4a) with the identical arm number and arm degree of polymerization. © 1995 John Wiley & Sons, Inc.
Isotope and pressure effects in polymer solutions. Demixing of polystyrene(h/d) poly‐2‐chlorostyrene blends
Authors: Zywocinski Andrzej , Wieczorek Stefan A. , Van Hook W. Alexander
Published: April 2003

Liquid‐liquid demixing, following spinodal quenches of poly‐2‐chlorostyrene/polystyrene blends, was followed by light scattering at 632.8 nm. The dependences of demixing on H/D substitution and molecular weight of the polystyrene, and on pressure, are reported. In the region of interest, the phase diagram is of the lower critical solution (LCS) type, and demixing is induced by raising the temperature. The transition temperature is lowered by deuterium substitution. At constant quench depth the transition proceeds more rapidly at elevated pressure. © 1995 John Wiley & Sons, Inc.
The effect of aryl nitration on gas sorption and permeation in polysulfone
Authors: Ghosal Kanchan , Chern Rey T. , Freeman Benny D. , Savariar Raj
Published: April 2003

CO2, CH4, O2, and N2 permeability and solubility of unmodified and aryl‐nitrated polysulfone were determined at 35°C and pressures up to 20 atm. The degree of nitration was varied from 0 to 2 nitro groups per repeat unit. The permeability and diffusion coefficients for all gases decreased with increasing degree of nitro substitution. The decrease in gas diffusivity is attributed to a combination of decreased fractional free volume and decreased torsional mobility with increasing degree of substitution. The solubilities of N2, O2, and CH4 do not show a systematic dependence on degree of substitution. However, CO2 solubility apparently goes through a minimum as the degree of substitution is increased. CO2 solubility may be influenced by a competition between increases in polymer polarity (favoring higher solubility) and lower free volume (favoring lower solubility) that accompanies increases in the polar nitro substituent concentration. CO2/CH4 solubility selectivity increases monotonically as the degree of substitution increases. CO2/CH4 permselectivity and diffusivity selectivity increased with increasing degree of substitution. © 1995 John Wiley & Sons, Inc.
Block copolymers as compatibilizers for blends of linear low density polyethylene and polystyrene
Authors: Li T. , Topolkaraev V. A. , Hiltner A. , Baer E. , Ji X. Z. , Quirk R. P.
Published: April 2003

Compatibilization of blends of linear low‐density polyethylene (LLDPE) and polystyrene (PS) with block copolymers of styrene (S) and butadiene (B) or hydrogenated butadiene (EB) has been studied. The morphology of the LLDPE/PS (50/50) composition typically with 5% copolymer was characterized primarily by scanning electron microscopy (SEM). The SEB and SEBS copolymers were effective in reducing the PS domain size, while the SB and SBS copolymers were less effective. The noncrystalline copolymers lowered the tensile modulus of the blend by as much as 50%. Modulus calculations based on a coreshell model, with the rubbery copolymer coating the PS particle, predicted that 50% of the rubbery SEBS copolymer was located at the interface compared to only 5–15% of the SB and SBS copolymers. The modulus of blends compatibilized with crystalline, nonrubbery SEB and SEBS copolymers approached Hashin's upper modulus bound. An interconnected interface model was proposed in which the blocks selectively penetrated the LLDPE and PS phases to provide good adhesion and improved stress and strain transfer between the phases. © 1995 John Wiley & Sons, Inc.
Microwave frequency dielectric properties of poly(vinylidene fluoride) films
Authors: Osaki Shigeyoshi
Published: April 2003

The frequency dependence of dielectric constant ϵ′, dielectric loss ϵ″, and dielectric anisotropy were determined for poly(vinylidene fluoride) (PVDF) in microwave frequencies from 4 to 13 GHz. The ϵ′ and ϵ″ for PVDF films decreased with increasing frequency. Both ϵ′ and ϵ″ were larger in the transverse direction than in the machine direction or draw direction, but the values at 12 GHz were smaller than those observed at 4.0 GHz. The angular dependence of ϵ″ at microwave frequency reflects the orientational distribution of molecules in the amorphous region. The orientation function was determined to be about 0.04 and 0.01 for uniaxially and biaxially stretched PVDF, respectively. © 1995 John Wiley & Sons, Inc.
Structural characterization of polypyrrole in the solid state by high resolution 15N NMR spectroscopy [II]
Authors: Kurosu Hiromichi , Kikuchi Mizuyo , Ando Isao
Published: April 2003

The solid‐state 15N CP/MAS NMR spectra and 15N spin‐lattice relaxation times (T1) of doped and dedoped 15N‐labeled polypyrroles prepared by electrochemical polymerization, have been measured by means of high‐resolution solid‐state 15N NMR. The 15N signal of polypyrrole consists of four peaks decomposed by line shape analysis. The four peaks obtained have been assigned to the various structures of polypyrrole. Further, the half‐width of the 15N NMR spectra of polypyrroles is discussed as related to the electrical conductivity. © 1995 John Wiley & Sons, Inc.
Heat capacity of water in poly(methyl methacrylate) hydrogel membrane for an artificial kidney
Authors: Ishikiriyama Kazuhiko , Todoki Minoru
Published: April 2003

The heat capacities of a poly(methyl methacrylate) hydrogel membrane for an artificial kidney have been determined over the range of temperatures from 228 to 298 K as a function of water content. At least two kinds of water were found: freezable water and nonfreezable water. The partial specific heat capacities of both waters were calculated from the dependence of heat capacity of the hydrogel on the water content. The heat capacities of freezable water were estimated to be 1.04 cal g−1 K−1 at 298 K and 0.47 cal g−1 K−1 at 228 K. The mobility must therefore be similar to that of bulk water at 298 K, though the melting temperature was lower than that of bulk water. Consequently, the freezable water was not assigned to bound water but to pore water for which the melting temperature was depressed due to interfacial tension. On the other hand, the heat capacities of nonfreezable water were estimated to be 1.02 cal g−1 K−1 at 298 K and 1.06 cal g−1 K−1 at 228 K. The mobility of the water would be similar to that of free water at both 298 and 228 K. © 1995 John Wiley & Sons, Inc.
Elastic and quasielastic light scattering from mixtures of three polymers and a solvent: The effects of polymethylmethacrylate concentration and molecular weight on the properties of polystyrene/polydimethylsiloxane/toluene solutions
Authors: Strazielle Claude , Duval Michel , Benmouna Mustapha
Published: April 2003

Elastic and quasi‐elastic light scattering data obtained from PS/PDMS/PMMA/toluene mixtures are reported. Several systems characterized by different concentrations and different molecular weights of PMMA are considered. For each of these systems, a systematic investigation is performed as a function of the scattering angle and the concentration of the PS/PDMS mixture using both techniques. The PMMA does not contribute directly to the scattered light since its increment of refractive index is zero. However the data show that its presence modifies substantially the apparent interaction parameter of PS and PDMS and the single diffusion coefficient of these polymers in the solution. The variations of these quantities with the concentration and molecular weight of PMMA are obtained. The data are analyzed within a simplified model combining based on the random phase approximation and the Rouse dynamics for ternary polymer mixtures. © 1995 John Wiley & Sons, Inc.
Long‐chain branching in free‐radical polymerization due to chain transfer to polymer
Authors: Tobita Hidetaka , Hatanaka Koji
Published: April 2003

The Monte Carlo sampling technique is used to investigate the branched structure formation during free‐radical polymerization that involves chain transfer to polymer. This method accounts for the history of the generated branched structure and can provide virtually any structural information, because one can observe each polymer molecule directly. In this paper, we investigate the whole molecular weight distribution (MWD) for both pre‐ and postgelation periods, the MWDs for polymer molecules containing 0, 1, 2, 3, … branch points, the branching density of polymer molecules as functions of both size and the number of branch points, the spatial distribution of the branched chains at the theta state, etc. Contrary to the term ‘long‐chain’ branching, many branch chains are relatively small, and the branched structures formed are significantly different from those usually depicted to introduce ‘branched polymers’ in many introductory textbooks. The radii of gyration at the theta state can be approximated by the Zimm‐Stockmayer equation for random branching, in spite of various violations against the assumptions used in deriving the equation © 1995 John Wiley & Sons, Inc.
Role of polyester resin on the epoxy matrix system
Authors: Mukherjee G. S. , Saraf M. N.
Published: April 2003

Interpenetrating polymer network (IPN) as a polymer blend matrix was prepared using different ratios of polyester (PE) to epoxy (E) resins. It was observed that 11.33 wt % PE in the blend provides maximum mechanical properties, particularly the modulus for the casting, and such a blend is referred to as “optimum casting” (OC). The density of the blends containing up to 11.33% PE, especially of OC, was found to have increased by the presence of PE in the E network significantly more than would have been estimated from the calculation based on the rule of additivity. The thermal expansion coefficient parameter (Δαi) of the OC was found to be 2.68 × 10−4K−1. The scanning electron micrograph (SEM) of the fracture surface of OC only showed a glass‐like smooth surface. The change in the mechanical properties due to the varying proportions of PE in the blend was studied critically on the basis of failure mechanisms and morphological features. The differential thermogravimetric analysis (DTGA) of OC indicated only one peak in spite of the presence of two resin constituents, whereas castings with an excess of PE in the blend showed multiple peaks. Interestingly, as far as the DTGA is concerned, a domain of seemingly OC origin was found to remain, even in the blends containing PE resin above its optimum level (> 11.33 wt %). ©1995 John Wiley & Sons, Inc.
Properties of an amphoteric cellulose derivative containing anionic carboxymethyl and cationic 2‐hydroxy‐3‐(trimethylammonio) propyl substituents
Authors: Zheng Guo‐Zhen , Meshitsuka Gyosuke , Ishizu Atsushi
Published: April 2003

An amphoteric cellulose derivative, O‐carboxymethyl‐O‐2‐hydroxy‐3‐(trimethylammonio) propylcellulose (CM‐HTMAPC), was prepared by the etherification of O‐carboxymethylcellulose (CMC) with (3‐chloro‐2‐hydroxy‐n‐propyl)‐trimethylammonium chloride in a NaOH solution. Apparent molecular sizes of the amphoteric cellulose derivative in aqueous solutions of different NaCl concentrations under various pH conditions were investigated by gel permeation chromatography (GPC), and results were evaluated in terms of inter‐ and intramolecular ionic interactions. Relation between GPC and viscosity results was also discussed. A titration method to determine the apparent acidic dissociation constants of carboxymethyl substituents was developed and the effect of cationic substituents on apparent acidic dissociation constants was examined. ©1995 John Wiley & Sons, Inc.
Holographic grating relaxation studies of probe diffusion in amorphous polymers
Authors: Xia Jiulin , Wang C. H.
Published: April 2003

Probe diffusion of camphorquinone, thymoquinone, and diacetyl in polymers was studied by the laser‐induced holographic grating relaxation (HGR) technique in polymers. The effects of changing the probe size and various parameters of the polymer, such as the molecular weight, chain conformation, and the glass transition temperature, on the probe diffusion coefficient have been investigated. Furthermore, effects of cross‐linking and plasticizing the chains of the polymer host on the probe diffusion coefficient were also studied. Temperature‐dependent studies show that except for the very low molecular weight poly(methyl methacrylate), all probe diffusion coefficient data above the glass transition temperature fit well to the WLF equation. ©1995 John Wiley & Sons, Inc.
Unique crystalline structure and performance of poly(ethylene terephthalate) melt spun fibers
Authors: Zhou Qiang , Wu Gang , Tucker Paul A. , Cuculo John A.
Published: April 2003

Modification of the threadline dynamics has effected significant alternations in the structure and improvements in the properties of high‐speed melt spun poly(ethylene terephthalate) (PET) fibers. Key process parameters extant in the threadline dynamics, such as temperature, tensile stress, and deformation time, were independently controlled through proper implementation of on‐line perturbations. The placement of a liquid isothermal bath in close proximity to the spinneret in the melt spinning threadline provided tremendous increase in the spinning stress while at the same time controlled the filament temperature corresponding to development of the desired fiber structure. Characterization of the fiber structure and physical properties has been carried out using birefringence measurements, density, shrinkage, x‐ray diffraction, DSC, FTIR spectroscopy, and tensile tests. The results provided sufficient evidence to support the existence of a unique crystalline morphology that led to the significantly improved tensile properties and excellent dimensional stability of the resulting fibers. This unique crystalline morphology was typically characterized by the presence of a larger amount of extended chain segments and an enhanced molecular connectivity. ©1995 John Wiley & Sons, Inc.
Thermal expansion of the crystal lattice of novel thermoplastic polyimides
Authors: Brillhart Mark V. , Cebe Peggy
Published: April 2003

Measurements of the coefficient of thermal expansion (CTE) of the crystalline lattice of two semicrystalline thermoplastic polyimides are reported. NEW‐TPI and LARC‐CPI polyimides were studied using elevated temperature wide‐angle x‐ray scattering (WAXS) from 25°C. To 325°C. To examine possible shifts in the c‐axis, a novel approach developed in our lab was used to create highly oriented samples. Films were treated in 1‐methyl‐2‐pyrrolidinone (NMP) at the reflux temperature, washed and then dried under constraint. The films treated in this manner were highly oriented, with c‐axes preferentially aligned along the film normal. The advantage of this orientation is that it allows numerous reflections of type (00l) to be examined for temperature shifts of the c‐axis using reflection mode WAXS. No systematic shift of the c‐axis lattice parameter as a function of temperature was observed in either NEW‐TPI or LARC‐CPI. The c‐axis thermal expansion is concluded to be smaller than 8 x 10−6/°C for LARC‐CPI, and for NEW‐TPI may be weakly negative. From WAXS of unoriented films, systematic shifts in the a and b lattice parameters were deduced as a function of temperature. The linear CTEs relating these unit cell parameters at temperature T to their values at 0°C are:

©1995 John Wiley & Sons, Inc.
Structures of poly(p‐hydroxybenzoic acid) (PHBA) at ambient temperature
Authors: Iannelli Pio , Yoon Do Y.
Published: April 2003

The molecular structure of poly (p‐hydroxybenzoic acid) (C6H4COO)x at ambient temperature was determined by x‐ray powder diffraction analysis. The diffraction pattern is explained as a mixture of two orthorhombic phases having the same space group Pbc21 with four C6H4COO chemical repeats in the unit cell and the following cell parameters: a = 7.42 Å, b = 5.70 Å, and c = 12.45 Å for phase I (ρcalc = 1.51 g cm−3); and a = 3.83 Å, b = 11.16 Å, and c = 12.56 Å for phase II (ρcalc = 1.48 g cm−3). The chain conformation is the same in both phases, involving two benzoyl rings staggered by ca. 120° along the chain. Disorder has been considered in the packing of phase I by giving equal occupancy to the two molecules oriented up or down along the c chain axis. ©1995 John Wiley & Sons, Inc.
Memory effects in polymers. V. Processing history versus thermally induced self‐orientation of unoriented poly(chlorotrifluoroethylene) films
Authors: Khanna Y. P. , Kuhn W. P. , Macur J. E. , Messa A. F. , Murthy N. S. , Reimschuessel A. C. , Schneider R. L. , Sibilia J. P. , Signorelli A. J. , Taylor T. J.
Published: April 2003

A peculiar phenomenon is reported whereby a melt‐extruded, low‐crystallinity, unoriented film of poly(chlorotrifluoroethylene) upon unconstrained thermal treatment, self‐extends in the machine direction (MD) while shrinking along the transverse (TD) and normal/thickness (ND) directions. In addition to the expected increase in crystallinity, the annealing process leads to an unexpected development of crystalline orientation along the MD. This phenomenon is an example of “processing‐induced memory effects” since it depends on the processing history of the starting film, e.g., melt‐extrusion leads to the subject behavior whereas compression molding does not. We must mention that the melt‐extruded films of poly(chlorotrifluoroethylene) are isotropic to start with, that is, MD and TD are indistinguishable prior to the annealing process. Furthermore, this phenomenon has not been observed for any other semicrystalline polymer and is believed to be the first citation for poly(chlorotrifluoroethylene) since its commercialization in 1957. Thermomechanical analysis (TMA) is the analytical technique that led to this novel phenomenon which was later substantiated by x‐ray diffraction (XRD). ©1995 John Wiley & Sons, Inc.
Slow crack growth in blends of HDPE and model copolymers
Authors: Zhou Z. , Brown N. , Crist B.
Published: April 2003

The resistance to slow crack growth (SCG) was measured in binary blends of high density polyethylene (HDPE) and 5–10% concentrations of model ethylene‐butene random copolymers by measuring the time to failure (tf) under a constant stress intensity. An increase of tf with the addition of the copolymer if the copolymer could crystallize and the increase was greater the higher branch density. The copolymer with 117 branches/1000C could not crystallize and therefore its blend had a tf that was less than that of the HDPE. The fracture energies of the blends as determined by their resistance to SCG were compared with the energy by rapid fracture, Jc, as previously measured by Rhee and Crist. It is concluded that SCG is more sensitive to variations in the microstructure than is rapid fracture and that the differences in SCG behavior can be qualitatively explained in terms of the differences in microstructure of the blends. ©1995 John Wiley & Sons, Inc.
Morphologies of microporous polyethylene and polypropylene crystallized from solution in supercritical propane
Authors: Pradhan Debjeet , Ehrlich Paul
Published: April 2003

The morphologies of solvent‐free, microporous, mechanically self‐supporting cylinders of linear polyethylene and isotactic polypropylene, crystallized from solution in supercritical propane, were examined by an SEM technique. The morphology of gels (or foams), obtained with little or no shrinkage from 2% to 35% solutions by weight of polyethylene (99% to 85% porosities), is shown in some detail. Lamellae with very little or considerable mutual organization occur, often in the form of stacks with straight or coiled axes (axialites). Further growth of these can lead to particles with a roughly spherical overall shape and a predominantly radial orientation of the lamellae at the particle surface. Subcooled isotactic polypropylene, on the other hand, crystallizes in the form of perfectly shaped birefringent microspheres of very uniform size. ©1995 John Wiley & Sons, Inc.