bluuebunny/crossref_metadata_2025 huggingface dataset:
The dielectric properties of liquid‐crystal random copolyesters of 4‐hydroxybenzoic acid and 2‐hydroxy 6‐naphthoic acid
Authors: Alhaj‐Mohammed M. H. , Davies G. R. , Jawad S. Abdul , Ward I. M.
Published: April 2003

Dielectric measurments made from 1 Hz to 10 kHz and from ‐80 to 150°C on random copolyesters of 4‐hydroxybenzoic acid (HBA) and 2‐hydroxy 6‐naphthoic acid (HNA) reveal three relaxation processes at low frequencies rather than the two seen at audio frequencies. The higher temperature α process is similar to a glass transition, with a high activation energy ∼ 170 kcal/mol, but the two lower temperature processes are identified as local mode processes associated with the HNA and HBA moieties, respectively. It is shown that the observed value of the permittivity above the glass transition is lower than that which would be expected for ester groups rotating freely about the local chain axis, and it is suggested that this may be due to several factors including immobilization of dipoles in the crystalline regions, correlated motion of dipoles, and librational rather than rotational motion.
Cooperative chain relaxation in miscible polymer blends
Authors: Saito Hiromu , Takahashi Mamoru , Inoue Takashi
Published: April 2003

Orientation relaxation of dissimilar chains in the molten miscible blends, poly(methyl methacrylate)/poly(vinylidene fluoride) and poly(methyl methacrylate)/poly(vinylidene fluoride‐co‐trifluoroethylene), were investigated by measuring (1) the change of infrared dichroic ratio with time after the uniaxial stretching of film specimens, (2) the shear stress relaxation spectrum, and (3) birefringence relaxation in shear. The dissimilar polymers showed an identical time variation of the normalized Hermans orientation function. The blend showed a relaxation spectrum with a single characteristic relaxation time τc, depending on the blend composition. The birefringence relaxed monotonically, remaining positive. These results suggest that the dissimilar polymers do not relax independently but cooperatively. This behavior may be induced by a constraint due to the specific interactions between the dissimilar polymers, e.g., weak hydrogen bonding. For the cooperative chain relaxation, a third power relationship was found; τc/τe vprop; (M/Me),3 where τe and Me are the relaxation time and molecular weight of entanglement strand, respectively, and M is the number average molecular weight in the blend.
On the rheology of cold drawing. I. Elastic materials
Authors: Coleman Bernard D. , Newman Daniel C.
Published: April 2003

In this, the first paper in a series on neck formation and steady‐state drawing of polymeric fibers and films under uniaxial tension, the emphasis is laid on those aspects of the mechanics of cold drawing that are not sensitive to viscoelastic effects and, therefore, can be treated by use of constitutive assumptions appropriate to elastic materials. It is here shown that a unidimensional theory which has been employed to model the mechanics of slender bars in tension6 can be derived as an approximation for three‐dimensional bars and, in a sense which can be made precise, is valid to within an error of the order of the fourth power of the thickness. A particular constitutive equation for incompressible, three‐dimensional, elastic materials is explored in detail and is found to yield, for such slender bars as thin fibers and wide (but thin) strips of film, equations of equilibrium whose solutions are in good qualitative accordance with the necks and drawing configurations observed in practice.
Aging phenomena in isotactic polypropylene drawn at different temperatures
Authors: de Candia F. , Russo R. , Tidjani A. , Vittoria V. , Peterlin A.
Published: April 2003

Fibers of isotactic polypropylene drawn at different temperatures show aging phenomena after drawing. In particular a modulus stiffening is observed at room temperature where the modulus increases with the aging time. In the same time scale the birefringence is constant, while drastic effects on the transport properties are observed. The aging phenomenon can be explained in terms of two mechanisms: a secondary crystallization and/or a densification of the amorphous component.
Molecular modeling of polymers. IV. Estimation of glass transition temperatures
Authors: Hopfinger A. J. , Koehler M. G. , Pearlstein R. A. , Tripathy S. K.
Published: April 2003

A method is described which allows molecular modeling to be combined with a group additive property model to estimate glass transition temperatures of linear polymers. Tg is assumed to be a function of conformational entropy and mass moments of the polymer. These two molecular properties are estimated in terms of the torsion angle units composing the polymer using conformational energy calculations. A “universal” Tg equation is derived using 30 structurally diverse polymers and multidimensional linear regression analysis. “Designer” Tg equations are also derived specifically for acrylate and methacrylate polymers. The work described here demonstrates how molecular modeling can be combined with group additivity theory to yield open‐ended models that are not restricted by lack of requisite group additive parameters and take advantage of three‐dimensional molecular information.
Cation binding properties of photodimerizable polymers bearing benzodiglyme units
Authors: Shirai Masamitsu , Ishida Haruyuki , Tanaka Makoto
Published: April 2003

The polymers which have glyme units as alkali cation binding sites and photodimerizable cinnamoyl units were prepared by the radical polymerization of corresponding monomers. The alkali cation binding ability and selectivity of the polymers, which were studied by a method of picrate salts extraction, were strongly dependent on the length of glyme chains. When irradiated with ultraviolet light, the cinnamoyl groups caused dimerization in dilute solutions. Although the photodimerization of the polymers with relatively short glyme chains enhanced their cation binding ability, the photodimerization of the polymers bearing long glyme chains reduced their cation binding ability. The use of alkali metal cations as templates emphasized the effect of photodimerization on the cation binding properties. The effect of alkali metal cations on the quantum yields of the photodimerization of the polymers showed that two or more benzodiglyme units took part in the binding of one cation. The polymers bearing benzodiglymes, crown ethers, and cinnamoyl moieties were also prepared by the radical copolymerization of the corresponding monomers. It was found that the crown ether units of the copolymers predominantly participated in the cation binding. The photodimerization of the copolymers with suitable alkali metal cations as templates strongly enhanced their cation binding ability.
FT‐IR studies of solvent and temperature effects on poly(diglycidal ether of bisphenol A) (epoxy)
Authors: Janarthanan V. , Thyagarajan G.
Published: April 2003

The infrared spectra of poly(diglycidal ether of bisphenol A) (epoxy) were studied in solutions of chloroform, benzene, and carbon tetrachloride separately to investigate the solvent effect through the behavior of the hydroxyl stretching band. The effect of temperature on the epoxy resin was also studied in this region. The results indicate that there is a varying degree of the weakening of the hydrogen bonding of the hydroxyl group in the epoxy, depending on the solvent. There is evidence also for the formation of hydrogen bonding between chloroform and the hydroxyl group of the epoxy and to a lesser extent between epoxy and benzene.
Angular dependence of 1H‐ and 2H‐NMR spectra of water and methanol absorbed in cellulose triacetate film
Authors: Matsumura Kazunori , Hayamizu Kikuko , Nakane Takashi , Yanagishita Hiroshi , Yamamoto Osamu
Published: April 2003

1H‐ and 2H‐NMR spectra of water (H2O and D2O) and methanol (CH3OD and CD3OH) absorbed in cellulose triacetate films have been observed as a function of the angle θ between the film surface and the magnetic field. 1H‐NMR signals of H2O and CH3OD are doublets and triplets due to dipole interactions, respectively. 2H‐NMR signals of D2O, CD3OH, and CH3OD are doublets due to quadrupole splittings. The magnitudes of these splittings change depending on θ. The analysis of the angle‐dependent patterns indicates that the motionally averaged axes of the dipole and the quadrupole moments orient in the direction perpendicular to the film surface. The alignment of water and/or methanol molecules originates from the film morphology, which is anisotropic in the perpendicular direction. From the angle dependence of the chemical shift, the volume diamagnetic susceptibility of the film is estimated to be 0.44 ppm.
Brownian motion of chains and crosslinks in a permanently linked network: The dynamic form factor
Authors: Vilgis T. A. , Boué F.
Published: April 2003

We consider the Brownian motion of crosslinks and chains in a well‐linked network far above the gel point. In a simple mean field approach we model the effect of permanent crosslink constraints by a harmonic potential. The two parameters in this model, the radius of gyration of the mesh and the monomeric friction coefficient, can be determined for most systems. Neglecting entanglements it turns out that the crosslinks and chains are localized within the range of the radius of gyration of a rubber strand between two crosslinks. This is in agreement with the classical phantom model of James and Guth. A crude extension to entanglements shows the restriction of the localization range of the crosslinks. The calculated incoherent scattering can be discussed in the context of experiments recently carried out by Oeser, Ewen, et al., and the coherent scattering is to be compared with current measurements by Oeser, Farago, et al.
Parallel superposition of small‐ and large‐amplitude oscillations upon steady shear flow of polymer fluids
Authors: Isayev A. I. , Wong C. M.
Published: April 2003

The parallel superposition of small‐ and large‐amplitude oscillations upon steady shear flow of elastic fluids has been considered. Theoretical results, obtained by numerical methods, are based upon the Leonov viscoelastic constitutive equation. Steady‐state components, amplitude, and phase angle of oscillatory components of the shear stress, the first and second normal‐stress differences as a function of shear rate, deformation amplitude, and frequency have been calculated. These oscillatory components include the first harmonic of the shear stresses and the first and second harmonic of the normal stresses. In the case of small‐amplitude superposition, the effect of the steady shear flow upon frequency‐dependent storage and loss moduli has been determined and compared with experimental data available in the literature for polymeric solutions and melts. In the case of large‐amplitude superposition, the effect of oscillations upon the steady shear flow characteristics has been determined and compared with our experimental data for a polymeric melt. The experimental results for shear stress components have been found to be in good agreement with theoretical predictions, although there are some deviations for storage modulus at high shear rates. The deviations seem to be dependent on material. Moreover, the theory is unable to describe experimental data available for the first harmonic of normal stresses.
Effect of short‐chain branching on the morphology of LLDPE‐oriented thin films
Authors: Brady Jean M. , Thomas Edwin L.
Published: April 2003

High‐density polyethylene and randomly branched linear low‐density polyethylene of varying branch length and content were used to produce oriented thin films. Sample morphology was investigated using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMA). Gelation studies suggested that the film preparation technique may have involved gel‐drawing. DSC characterization of samples with approximately equal average branch content revealed very different melting behavior, suggesting differences in crystal size distributions. This was attributed to variations in the distribution of branches within samples. For similar branching distributions, the average melting temperature (and, similarly, crystal size) generally decreased as branch content increased. This was corroborated by TEM, with which crystal thickness was found to decrease as branch content increased. TEM further revealed that the lateral alignment of mosaic blocks and the resultant lamellar character of the thin films was obscured as branch content increased, a result of reduced crystal size, crystallinity, and possibly increased interphase content. DMA of compression‐molded material revealed the presence of a beta peak in branched samples only. Moreover, the alpha transition temperature shifted to lower temperatures as branch content increased.
Surface‐enhanced Raman scattering from bilayers of polystyrene, diglycidyl ether of bisphenol‐A, poly(4‐vinyl pyridine), and poly(4‐styrene sulfonate)
Authors: Venkatachalam R. S. , Boerio F. J. , Roth P. G. , Tsai W. H.
Published: April 2003

Surface‐enhanced Raman scattering (SERS) has been observed from thin films of polystyrene (PS), diglycidyl ether of bisphenol‐A (DGEBA), and poly(4‐vinyl pyridine) (PVP) deposited on silver island films Degradation of the polymers occurred rapidly during laser irradiation and was accompanied by the appearance of strong bands near 1375 and 1575 cm‐1. These bands were attributed to the formation of graphite‐like species by the silver‐catalyzed thermal oxidation of the polymers induced by localized laser heating of the substrate. When the thin films of PS, DGEBA, or PVP were overcoated with much thicker films of a second polymer such as polystyrene sulfonate (PSS), the degradation was greatly reduced, and excellent SERS spectra of the PS, DGEBA, and PVP films were obtained. Overlayers reduced degradation within the first films deposited on silver island films by restricting the availability of oxygen at the interface to its solubility in the overlayer polymer or by altering the adsorption of oxygen onto the substrate. SERS was observed for the PS, DGEBA, and PVP films and the PSS overlayers when the films were deposited from relatively dilute solutions. When the PS, DGEBA, and PVP films were deposited from more concentrated solutions, SERS was not observed from the PSS overlayers. It was suggested that most of the SERS was due to a short‐range, charge‐transfer mechanism associated with sites of atomic scale roughness and that SERS was observed from the overlayer when the first film failed to occupy all of the sites.
Crystal growth of polyethylene from dilute solution: Growth kinetics of {110} twins and diffusion‐limited growth of single crystals
Authors: Toda Akihiko , Kiho Hiroshi
Published: April 2003

We have studied the growth kinetics of {110} twins and single crystals of polyethylene in dilute solution of tetrachlorethylene. In terms of {110} twins, we succeeded in obtaining twins without {100} sectors, using a relatively high molecular weight fraction Mw > 104. It is confirmed that the growth is enhanced at the reentrant corner of the twins, and the enhanced growth face inclines to the {110} face because of consecutive generation of steps at the corner. These facts are strong evidence for nucleation‐controlled growth of single crystals. The growth rates and obliquity are measured at various supercoolings and concentrations. From consideration of kinetics of steps on the growth face, the following rates and velocity are independently determined from the experimental data: nucleation rate on a flat face, velocity of step propagation, and generation rate of steps at the reentrant corner. The supercooling dependence strongly supports regime II growth. The results on concentration dependence show that the velocity of steps is proportional to concentration over the whole range examined, and the nucleation rate is independent of it in the usual range and becomes proportional to it in the lower range. This concentration dependence of nucleation rate is attributed to the density of adsorbed polymer on the growth face. From this evidence, it is suggested that the rate of travel of steps is limited by volume diffusion of solute polymer, whereas the growth face is saturated with adsorbed polymer at ordinary concentrations. This contradictory situation could be explained by the hypotheses that the saturation density is rather low and that surface diffusion of adsorbed polymer is much slower than volume diffusion of solute polymer. The lower limit of the rate of folding is also determined for the first time from the velocity of step propagation. As regards the single crystals, it is found that the habit maintains a lozenge shape with sharpened points, even at very high supercooling (δT < 50°C) if the concentration is very dilute. Diffusion‐limited growth is verified for the first time at the higher supercoolings, where the growth rate is almost independent of supercooling. The growth rate becomes almost equivalent to the velocity of steps determined in the experiments with twins, and this fact will support the accuracy of the evaluation of the step velocity. The order of magnitude of the growth rate obtained agrees with the value which is calculated from the balance between the flux of solute polymer to the growth face and the rate of growth of single crystals.
Crystallization studies of poly(ε‐caprolactone). II. Lamellar thickening and melting
Authors: Phillips P. J. , Rensch G. J.
Published: April 2003

Crystals of poly(ε‐caprolactone) thicken at a measurable rate at the crystallization temperature. Melting points have been converted into lamellar thicknesses for three molecular weights and the lamellar thickening behavior analyzed using the Sanchez‐Eby approach of a relaxation time for thickening. Isothermal thickening curves are S shaped and can be superposed through horizontal shifts for a given molecular weight. Data for different molecular weights can be superposed using a horizontal shift combined with a small vertical shift. Shift factors have been treated using an Arrhenius approach to give an activation energy for thickening of 100 kcal/mol. Analysis using the Sanchez‐Eby approach leads to the conclusion that the active unit in thickening is approximately one stem length.
Interactions in SMA‐SAN blends
Authors: Kim J. H. , Barlow J. W. , Paul D. R.
Published: April 2003

Styrene/maleic anhydride (SMA) and styrene/acrylonitrile (SAN) copolymers have previously been shown to form miscible blends when the MA and AN contents do not differ too greatly. It is shown here that this is the result of a weak exothermic interaction between the MA and AN units by measuring the heats of mixing for appropriate liquid analogs of the various monomer units. The region of copolymer compositions for miscibility of SMA‐SAN blends is predicted from the Sanchez‐Lacombe mixture theory using net interaction parameters calculated from the analog calorimetry results via a simple binary interaction model for copolymers. Lower critical solution temperature behavior was observed for blends of copolymers having compositions near the edge of the miscibility region. Various glass transition, volumetric, and FTIR results are discussed in terms of the interactions observed.
A rotational rheometer for rheological studies with prescribed strain or stress history
Authors: Berry G. C. , Park J. O. , Meitz D. W. , Birnboim M. H. , Plazek D. J.
Published: April 2003

A rheometer utilizing an eddy‐current torque transducer and an air‐bearing suspension is described. The rheometer is coupled with a computer‐based data acquisition system and permits studies of shear deformation for several strain or stress histories. A sinusoidal stress history is used to determine the shear storage and loss compliances J′(ω) and J″(ω), respectively. Step stress histories are used to determine the shear creep compliance J(t) and the recoverable complaince R(t) or more complicated linear and nonlinear rheological responses related to these. Deformation at constant strain rate is used to determine the stress growth function or the steady‐state viscosity. The rheometer may be used over the temperature range – 10–180°C, with torque from 1 to 106 dyn cm, and is adaptabel to use with a variety of sample geometrical shapes (e.g., cone and plate, parallel plate, etc.). Examples of measurements on on viscoelastic fluids and on gels below their yield strain are given.
Measurements of dynamic interactions in thin films of polymer melts: The transition from simple to complex behavior
Authors: Israelachvili Jacob N. , Kott Stephen J. , Fetters Lewis J.
Published: April 2003

Two techniques are described for measuring the shear viscosities of thin liquid films confined between two surfaces. Both techniques employ the surface forces apparatus, which has already been used extensively to measure the static interactions between surfaces in liquids. With either of the new dynamic techniques, shear viscosities of the confined liquids can be measured as a function of film thickness with a precision of about 0.1 nm (1 Å). The techniques complement each other: one is used to best advantage at high shear rates, the other at low shear rates. Results are presented for measurements made on low‐molecular‐weight polymer melts of polybutadienes. At low shear rates, these results provide detailed information on the relation between polymer molecular weight, the conformation of polymer molecules at the surfaces, the intermolecular forces between the surfaces, and the location of the shear plane (plane of no‐slip). At high shear rates, the results suggest the gradual evolution of non‐Newtonian behavior in submicron liquid films.
Structural studies of radiation‐crosslinked poly(ethylene oxide)
Authors: Minkova L. , Stamenova R. , Tsvetanov C. , Nedkov E.
Published: April 2003

The structure and thermal behavior of freeze‐dried gels of radiation‐crosslinked high molecular weight poly(ethylene oxide) (PEO) were investigated by optical and electron microscopy, wide‐angle x‐ray scattering (WAXS), DTA, TGA, and thermomechanical analysis. The gels are highly porous with thin crystalline walls. Small spherulite and hedrite structures are observed on the walls. A model for gel formation in solution is suggested. A statistically homogenous chemical network is formed as a result of intrachain and interchain crosslinking. Simultaneous grafting of macromolecular fragments formed by chain scission also occurs.

On increasing the irradiation dose from 1 to 15 Mrad, the degree of crystallinity determined by x‐ray diffraction and the total intensity of diffraction gradually decrease. The temperature and enthalpy of melting diminish steeply up to 5 Mrad, fall only slightly from 5 to 8 Mrad, and do not change from 8 to 15 Mrad. By comparing the x‐ray and DTA crystallinity values, this is shown to be due not only to reduced crystallinity at higher network density but also to Tree energy changes of entropic origin in crystalline and amorphous regions. Radiation chemical yields, G(‐units), for these dose ranges are 100, 38, and 0, respectively.

Thermomechanical analysis was used to determine the elastic modulus of compression as a function of the dose absorbed, and the average molecular weight $ \bar M_{\rm c} $
of network chains was estimated. $ \bar M_{\rm c} $
decreases with doses up to 10 Mrad and does not change with further irradiation.
Thermal and dielectric behaviors of poly(vinylidene fluoride‐trifluoroethylene) copolymers at the curie transition
Authors: Moreira R. L. , Saint‐Grégoire P. , Lopez M. , Latour M.
Published: April 2003

The thermal and dielectric behaviors of poly(vinylidene fluoride‐trifluoroethylene) copolymers near the ferroelectric‐to‐paraelectric phase transition are investigated for samples with 20, 25, 30, and 40 mol% trifluoroethylene (TrFE). The data suggest that the transition becomes continuous for a particular composition near 50 mol% TrFE. Experimental data are sensitive to thermal history (kinetics of crystallization, and kinetics and cycling over the structural transition). It is found that several anomalies are present at the structural change, and in particular the 30 mol% TrFE sample shows the most marked anomalies. These phenomena can be attributed to defects, but another possibility would be the existence of an intemediate supplementary phase. Both hypotheses are discussed.
Chain dimensions in plastically deformed semicrystalline polymers
Authors: Tanzer Joseph D. , Crist Buckley , Graessley William W.
Published: April 2003

The effect of plastic deformation on the chain dimensions of polymers in the semicrystalline state was investigated using linear hydrogenated polybutadiene (HPB), a model ethylene/butene‐1 copolymer having about 40% crystallinity at room temperature. Dilute blends of deuterium‐labeled chains with various molecular weights (20,000 ≤ M ≤ 214,000) in the same unlabeled matrix (M = 95,000) were uniaxially stretched at 25°C to extension ratios of α = 2.4 and 4.4. Radius of gyration normal to the stretch direction R⊥ was measured for the labeled chains by small‐angle neutron scattering. The molecular extension ratio inferred from these data αm = R/R was significantly smaller than α for short chains (M < 50,000) but increased to the affine range αm = α for M > 100,000. This variation in αm/α closely parallels the molecular weight dependence of mechanical strength and ductility in HPB over the same range.
A comparison of the Raman LAM and electron microscopy in determining crystallite thickness distributions: Polyethylenes with narrow size distributions
Authors: Voigt‐Martin I. G. , Stack G. M. , Peacock A. J. , Mandelkern L.
Published: April 2003

A detailed quantitative comparison between thin section electron microscopy, utilizing the chlorosulfonation technique, and the Raman low‐frequency acoustical mode (LAM) in determining the crystallite size distribution in polyethylenes having narrow distributions is made. Three different polyethylene systems have been analyzed, one of which was specifically prepared for this work. Very good quantitative agreement is obtained between these two analytical methods when account is taken of the chain tilt and the distribution is restrained to be narrow. Systems having broad crystallite size distributions introduce complexities into this comparison.
Effects of packing density on the gas‐transport properties of poly(phenolphthalein phthalate)s
Authors: Sheu F. R. , Chern R. T.
Published: April 2003

The gas transport and other pertinent properties of three aromatic polyesters, made by reacting phenolphthalein with terephthaloyl chloride (PPha‐tere), 50:50 terephthaloyl and isophthaloyl chlorides (PPha‐50:50), and isophthaloyl chloride (PPha‐iso), are reported. The glass transition temperatures of PPha‐tere, PPha‐50:50, and PPha‐iso are 299, 279, and 249°C, respectively. Unexpectedly, the densities are 1.297, 1.298, and 1.304 g/cm3 in the same order; PPha‐iso, therefore, has a higher packing density than PPha‐tere. The permeability of PPha‐tere to CO2, CH4, N2, and O2 is roughly 25% higher than that of PPha‐50:50, and roughly 100% higher than that of PPha‐iso. PPha‐tere is roughly five times as permeable as polysulfone but has slightly higher permselectivities for the above gases. On the other hand, the solubilities of each gas in these three aromatic polyesters are roughly the same, suggesting that the higher permeability of PPha‐tere is the result of a much larger gas diffusivity in the polymer. It is shown here that the significant difference in gas‐diffusivity is a manifestation of the effects of packing density on the transport properties of glassy polymers.
Effect of temperature and molecular weight on enthalpy relaxation in polystyrene
Authors: Agrawal A.
Published: April 2003

Isothermal enthalpy relaxation in polystyrene was measured as a function of temperature and molecular weight on a differential scanning calorimeter. Relaxation spectra were derived from the data and expressed as a distribution of relaxation times. For a given molecular weight the relaxation spectra at different temperatures could not be superimposed by a shift in time. The relaxation curves of samples of different molecular weights could be superimposed only when the difference between the temperature at which the relaxation was monitored (Ta) and their respective Tg was the same. The relaxation spectrum at any temperature for a given molecular weight was also expressed as a distribution of energies. The average energy represented by this distribution was associated with an activation energy required for the motion of a chemical repeat unit. The activation energy extracted from the temperature shift in the relaxation spectra corresponded to the motion of a statistical unit (Kuhn's segment) in polystyrene.
Cation interactions with polyamic acids
Authors: Linde H. G. , Gleason R. T.
Published: April 2003

Polyamic acid films interact as ion‐exchange substrates for dilute aqueous cation solutions. Three conditions were evaluated: basic solutions which form soluble amic acid salts and dissolve the film, weakly acidic solutions which encourage classical weak acid cation exchange, and strongly acidic solutions which discourage exchange. Thermal treatment of the generated cationamate salts generally causes degradation of the polymer backbone. Furthermore, lead and copper react directly with the polyamic acid to yield surface‐bound salts, but tin and aluminum seem unreactive.
Dielectric studies of the effects of thermal history on secondary relaxation in bisphenol‐a‐polycarbonate
Authors: Pathmanathan K. , Cavaillé Jean‐yves , Johari G. P.
Published: April 2003

The dielectric permittivity and loss of Bisphenol‐A‐polycarbonate (PC) was measured over the frequency range 100 Hz to 200 kHz and temperature range 77–383 K. One sub‐Tg relaxation peak is observed which rapidly broadens with a decrease in temperature. This is attributed to a progressive separation of the γ and β peaks, which at high temperatures are merged to form one peak of high strength. The strength of the sub‐Tg relaxations decreases on physical aging of PC but is increased if the sample is quenched from a temperature above its Tg. Slowly cooled PC has a lower strength of its sub‐Tg relaxation than a quenched specimen. The thermal history of PC affects the magnitude of its sub‐Tg relaxation.
The coagulation of cellulose from anisotropic solutions in the NH3/NH4SCN solvent system
Authors: Cho Jae Jeong , Hudson Samuel H. , Cuculo John A.
Published: April 2003

Coagulation of cellulose has been studied in cellulose/ammonia/ammonium thiocyanate anisotropic solutions. The effect of coagulation variables such as coagulant, bath temperature, and cellulose concentration on the coagulation process is reported. The coagulation rate was measured by microscopic observation of the moving boundary associated with coagulation. Results indicate that the coagulation rate increases with increasing cellulose concentration and bath temperature. Methanol has the highest coagulation power among the coagulants employed. Mass transfer rate difference and equilibrium swelling were also measured. The results on the mass transfer rate differences show that the mass transfer rate of NH3/NH4SCN is greater than those of the respective coagulants under all coagulation conditions. The equilibrium swelling decreases with increasing bath temperature and cellulose concentration.
Structure/permeability relationships of polyimide membranes. Applications to the separation of gas mixtures
Authors: Stern S. A. , Mi Y. , Yamamoto H. , Clair Anne K. St.
Published: April 2003

The permeability of nine different polyimide membranes to H2, N2, O2, CH4, and CO2 has been determined at 35°C and at applied pressures of up to 9 atm. The dianhydride monomers used for the synthesis of the polymides were PMDA and 6FDA, whereas the diamine monomers were ODA, BDAF, and p‐PDA. The selectivities of the 6FDA polymides toward CO2 relative to CH4 are higher than those of the PMDA polyimides at comparable CO2 permeabilities. Both types of polyimides exhibit significantly higher CO2/CH4 selectivities than more common glassy polymers, such as cellulose acetate, polysulfone, and polycarbonate. The selectivities of the PMDA and 6FDA polyimides to O2 relative to N2 are of the same magnitude and generally higher than those of common glassy polymers with similar O2 permeabilities. The polymides are more permeable to N2 than to CH4, whereas the opposite is true for many other glassy polymers. Possible factors responsible for the above behavior, such as segmental mobility, mean interchain distance, and formation of charge transfer complexes, are examined. The relevance of the study to the development of more highly gas‐selective and permeable membranes for the separation of gas mixtures is also discussed.
Modulus and yield resistance of glassy blends containing diluents manifesting varying degrees of mobility: Polyphenylene ether/polystyrene/diluent mixtures
Authors: Kambour R. P. , Kelly J. M. , McKinley B. J.
Published: April 2003

The glass temperatures, moduli, and yield stresses for shear failure have been characterized for homogeneous blends of poly(2,6‐dimethyl‐1,4‐phenylene ether), homopolystyrene (1/1), and a number of diluents of Tgs from −134 to +32°C. In a blend series based of a given diluent, the mechanical properties vary with blend Tg at rates that are characteristics of the particular diluent. These characteristic rates are found to depend strongly on the Tg of the neat diluent. Thus, for blends all with Tg = 90°C, for example, modulus and yield stress differ by as much as 50% over the range of diluents. Low‐temperature relaxation measurements together with a number of previous dynamic spectroscopy studies of polymer/diluent systems at low temperatures suggest that many single‐phase polymer/diluent blends may exhibit two primary relaxations—the depressed alpha relaxation of the resin and a somewhat elevated alpha relaxation of the diluent—at quite different temperatures. Both of these relaxations influence stiffness and strength properties at intermediate temperatures. The often‐studied antiplasticization phenomena are viewed as a aberrations from a much more general influence of plasticizers on properties at temperatures below the alpha relaxation of the resin.
Small‐angle scattering of polarized light. I. comparison of theoretical predictions for isotropic and anisotropic spheres
Authors: Meeten G. H. , Navard P.
Published: April 2003

This paper describes small angle light scattering (SALS) calculations and compares the results for isotropic and anisotropic spheres. For isotropic spheres the exact Mie theory is compared with the Rayleigh‐Gans‐Debye (RGD) and the anomalous diffraction (AD) approximations in order to study the validity of the approximations. For anisotropic spheres the RGD is compared with the AD approximation. A study of SALS in the RGD approximation shows that the first‐order intensity maximum corresponding to a lobe of the four‐leaf clover pattern is not only a function of the sphere diameter but also depends on the isotropic and the anisotropic refractive index of the sphere. The practical implications of this are discussed.
Determination of transition temperatures and crystalline content of linear, high‐molecular‐weight polyethylene by proton NMR spectroscopy
Authors: Kauffman Jon S. , Dybowski Cecil
Published: April 2003

Decomposition of the proton NMR spectra of linear, high‐molecular‐weight polyethylene into a Gaussian function and a Lorentzian function is discussed in terms of the Wilson‐Pake two‐component method for an inhomogeneous system. The results of a Goldman‐Shen experiment indicate that spin diffusion does not strongly couple the two regions. The temperature dependence of the Lorentzian (mobile) fraction is fitted to a function derived from the relation of English and Zoller. The critical temperatures give estimates of thermal transitions: Tα = 328 (± 5) K and Tγ = 163 (± 4) K. The fraction of Lorentzian spins excited by the γ relaxation correlates with the amorphous content of the sample as determined by differential scanning calorimetry and x‐ray diffraction.
Unit cell dimensions in model ethylene‐butene‐1 copolymers
Authors: Howard P. R. , Crist B.
Published: April 2003

The lattice parameters of a series of hydrogenated polybutadiene (HPB) model copolymers is measured as a function of branch content between 0 and 73 ethyl branches per 1000 C atoms. Expansion of the a and b axes nearly ceases for branch contents greater than 20 per 1000 C atoms. The c axis is seen to contract by a small amount with increased branching. The major cause of lattice expansion is limitation of crystal thickness by exclusion of branch points from the lamellar crystals coupled with surface stress on thin lamellae. A small fraction of ethyl branches are incorporated in the crystal; these expand the lattice by an additional amount.
Measurement of rotational diffusivity of rodlike molecules in amorphous polymer matrices by the dynamic kerr effect
Authors: Hill Davide A. , Soane David S.
Published: April 2003

Electrooptic (Kerr effect) relaxation experiments, designed to measure the rotational diffusivity of collagen (rodlike) molecules in aqueous poly(ethyleneoxide) (amorphous) semidilute solutions under various conditions have been performed. The experimental results have been compared with the predictions of a previously derived model giving the rotational diffusivity of dilute rods in semidilute amorphous polymer solutions as a function of rod length and amorphous polymer concentration. Excellent agreement is found between the predicted scaling Dr ∼ ϕL−7 (Dr = rod rotational diffusivity, pip = polymer weight fraction, and L = rod length) and the experiments.
Gas sorption and transport in substituted polystyrenes
Authors: Puleo A. C. , Muruganandam N. , Paul D. R.
Published: April 2003

The effects of pendant groups on gas transport were investigated using a series of substituted polystyrenes. Permeability coefficients were measured at 35°C and 1 atm for He, N2, O2, CH4, and CO2, and diffusion coefficients were calculated from time lag data. The absolute permeabilities for the polystyrenes are correlated reasonably well using a free volume model. All pendant group substitutions resulted in a reduction of the mobility selectivity for CO2/CH4 separation relative to polystyrene, although there was very little effect on the O2/N2 selectivity. The effects of the various substituents were individually analyzed in terms of their size, rigidity, and polarity. The addition of a methyl group to the backbone significantly decreases transport, while attachment to the para ring position increases permeation. Bulky rigid groups, such as t‐butyl, enhance permeation even more. Methoxy and acetoxy substitutions provided an excellent means of examining plasticization of polymers by CO2, such as cellulose acetate, which contain these same moieties. The response of these polymers indicates that the degree of plasticization is related to the polarity and flexibility of the pendant group.
Studies of ESR Nitroxide probe mobility in polymer blends
Authors: Jamil T. , Jamieson A. M.
Published: April 2003

We report studies of the temperature‐dependence of the ESR spectrum of the nitroxide spin radical 4‐(2‐bromoacetamide)‐2,2,6,6 tetramethyl‐1‐oxyl piperidine (BRAMO) dispersed in poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA), poly(vinyl acetate) (PVAc), and PVDF/PMMA and PVAC/PMMA blends of varying composition. In PVDF/PMMA blends which show a single composition‐dependent Tg, the mobility of BRAMO is identical to that in pure PMMA. On the other hand, in PVAC/PMMA blends, the mobility of BRAMO corresponds to that in pure PVAC. The results suggest that (1) BRAMO selectively binds to polymers based on hydrogen bonding affinity, (2) the spin probe is sensitive to segmental motions on a length scale shorter than those which give rise to the glass transition, and (3) compatible polymer blends are heterogeneous on the length scale of the BRAMO probe (ca. 8.3 Å).
On the possibility of using organic phosphors in thermoluminescence dosimetry
Authors: Moharil S. V. , Deshmukh B. T. , Muthal P. L.
Published: April 2003

Organic materials in general and polymers in particular have traditionally been considered as to be phosphors and have been ruled out as materials which could be useful in dosimetry of ionizing radiations by thermoluminescence. Some results reported during the past decade suggested possibilities of organic phosphors with good thermoluminescence characteristics. Experiments were undertaken to exploit the various possibilities. The results show that “crystalline polymers” can have adequate thermoluminescence properties to be useful in dosimetry. It is suggested that further studies on thermoluminesence in crystalline polymers and highly drawn fibers of high polymers will prove fruitful.
Free energy of an inhomogeneous polymer‐polymer‐solvent system
Authors: Ariyapadi M. V. , Nauman E. B.
Published: April 2003

The free energy of an inhomogeneous polymer‐polymer‐solvent system has been obtained by extending Debye's approach for a polymer‐solvent system. Our ternary result reduces to Debye's result for a binary polymer‐solvent system and to McMaster's result for a binary polymer‐polymer system at the appropriate limits. Like Debye's work, we neglect the entropic gradient contribution to free energy. Based on the ternary result we suggest a generalized expression for the free energy of multiple polymers dissolved in a common solvent. This expression is used to find the free energy of an inhomogeneous polydispersed polymer‐solvent system.
Effect of a block copolymer on the adhesion between incompatible polymers. I. Symmetric tests
Authors: Cho K. , Brown H. R. , Miller D. C.
Published: April 2003

We have studied the adhesion (welding) of polystyrene (PS) and poly (methyl methacrylate) (PMMA) and the effect of incorporating a thin layer of PS/PMMA block copolymer in the joint. The minimum thickness of copolymer layer necessary to increase the joint failure energy G to that of the bulk was about half the interlamellar spacing (long period) of the block copolymer. This tends to suggest a simple model of the block copolymer organizing on the interface with the two halves of the copolymer dissolved in the relevant homopolymers, however, we have no direct evidence for this. X‐ray photoelectron spectroscopy and optical microscopy were used to study the failure path. Without copolymer the crack propagated partly in the polystyrene and partly on the interface. Crazes grew from the interface into the polystyrene and the crack tended to follow such a craze for a short distance then jump back to the interface. With the copolymer, the failure mode was very similar, but there was evidence now of crazing on the interface. In no case was there evidence of a significant amount of PMMA on the PS side of the failure.
The effects of low molar mass diluents on the microstructure of ionomers
Authors: Fitzgerald J. J. , Weiss R. A.
Published: April 2003

The effect of polar and nonpolar low molar mass diluents on the microstructure of lightly sulfonated polystyrene (SPS) ionomers was studied using electron spin resonance spectroscopy, small‐angle x‐ray scattering, and dynamic mechanical analysis. Nonpolar diluents primarily affected the hydrocarbon ‐ rich phase, while polar diluents partitioned into the ion‐rich regions and disrupted the supramolecular structure. The ionic clusters remained intact, even at elevated temperatures, upon the addition of nonpolar solvents such as dodecane and dioctylphthalate. More polar solvents such as methanol and glycerol swelled the ionic domains and promoted increased mixing of the two phases.
A dielectric relaxation study of plasticization of poly(ethyl methacrylate) by carbon dioxide
Authors: Kamiya Yoshinori , Mizoguchi Keishin , Naito Yasutoshi
Published: April 2003

Plasticization of poly(ethyl methacrylate) (PEMA) by CO2 is investigated by dielectric relaxation spectroscopy. The dissipation factor of a dielectric cell containing the film and air gaps is measured as a function of frequency (1–10,000 kHz) and CO2 pressure (0–60 atm) over the temperature range 35–115°C. A maximum in the frequency dependence of the dissipation factor, which is attributed to the α relaxation of PEMA, shifts to higher frequency with increasing temperature, pressure, or concentration. The apparent activation energy of the isosteric relaxation decreases from 28 to 23 kcal/mol as the concentration is increased from 0 to 90 cm3 (STP)/cm3 (polym). The relaxation peak temperature at fixed frequency decreases with increasing concentration. The effect of hydrostatic pressure on the dielectric relaxation is estimated and compared with values for the PEMA‐He and PEMA‐Ar systems. The plasticizing effect of sorbed CO2 is discussed on the basis of the relaxation data.
Static and dynamic light scattering of poly‐(α‐methyl styrene) in toluene in the dilute region
Authors: Kim S. H. , Ramsay D. J. , Patterson G. D. , Selser J. C.
Published: April 2003

The scattered intensity function S(q, c) and the intermediate scattering function S(q, c, τ) of poly‐(α‐methyl styrene) (Mω = 5.71 × 105, 1.17 × 106, and 2.96 × 106) in toluene in the dilute concentration region were measured as functions of concentration and scattering vector q. In infinitely dilute solution, the intensity function S(q, 0) agrees well with the Debye function for u < 7, where u is (qRg)2. At finite concentration S(q, c) varies from its thermodynamic value at low u to the single chain value at high u. Theoretical calculations of S(q, c) are in quantitative agreement with the observed scattering function in very dilute solutions. The intermediate scattering function S(q, c, τ) is a single exponential decay with decay rate Dmq2 for u ≪ 1. For u > 1, S(q, c, τ) is nonexponential, and when analyzed with a discrete inversion method, yields a bimodal distribution of decay rates. Both components are well represented as single exponential decays. D0 can be obtained from the slower component. The decay rate of the faster component is a continuous function of u and approaches q2 dependence at high u.
Sorption and dilation properties of poly(p‐phenylene sulfide) under high‐pressure carbon dioxide
Authors: Bourbon Dominique , Kamiya Yoshinori , Mizoguchi Keishin
Published: April 2003

Sorption and dilation properties of the system poly(p‐phenylene sulfide) (PPS) and carbon dioxide have been investigated at pressures up to 50 atm over the temperature range 25–85°C. The shapes of the sorption isotherms are in agreement with those predicted by the dual‐mode theory. Analysis of the sorption and dilation isotherms confirms the occurrence of an isothermal glass transition. This occurrence and its corresponding disappearance in the range investigated is discussed. Values of the partial molar volume of CO2 sorbed in PPS are calculated below and above the isothermal transition. Compared with sorption by other polymers, these values were about the same in the glassy state, but were smaller in the rubbery state. Under 50 atm CO2 at 85°C crystallization of amorphous PPS was observed. The crystallinity estimated from the solubility before and after crystallization is about 20%.
Thermal cycling of glasses. III. Upper peaks
Authors: Hutchinson J. M. , Ruddy M.
Published: April 2003

The response of glasses to three‐step thermal cycles in which the glass is poorly stabilized prior to reheating has been examined both theoretically and experimentally. Theory predicts that, during the heating stage of these cycles, a type of peak (called an upper peak) occurs which is quite different from the type of peak (called a main peak) observed for well‐stabilized glasses. The dependence of the upper peak temperature and height on the experimental variables defining the thermal cycles have been derived theoretically, and have been compared with experimental data for polystyrene. All of the features predicted theoretically have been verified experimentally. In particular, the variation of the upper peak temperature is insensitive to the structure (or nonlinearity) parameter x, and cannot therefore lead to its evaluation. On the other hand, it is shown that, given the value of x obtained, for example, by the peak‐shift method, then an analysis of the upper peak height can yield information about the width of the distribution of retardation times.