bluuebunny/crossref_metadata_2025 huggingface dataset:
Shrinkage and retractive forces during the annealing of drawn low‐density polyethylene
Authors: Decandia F. , Russo R. , Vittoria V. , Peterlin A.
Published: April 2003

Shrinkage of unconstrained low‐density polyethylene samples and the retractive stress of samples with ends fixed have been investigated as a function of the annealing time tA and temperature TA on material drawn at room temperature to draw ratios λ between 4 and 6. The shrinkage increases with tA and TA. The retractive stress on a sample annealed with ends fixed goes through a maximum as the sample is annealed and then drops to a limiting value which increases with TA as long as TA is at or below 80°C and rapidly decreases with higher TA. The drop from the maximum to the limiting retractive stress, slow at lower TA and rapid at higher TA, seems to be a consequence of rapid pulling of chain segments out of crystal block in which interfibrillar tie molecules are anchored. This process is facilitated by the high TA, which softens the crystal matrix. At constant end‐to‐end distance, the contour length of the tie molecules is irreversibly increased, and this causes a reduction in the contribution of the affected tie molecules to the overall retraction stress. Hence one finds a substantially higher retraction stress during first heating than during subsequent cooling and heating of the drawn sample.
Etude cinétique des effets de fluence énergétique, de débit de fluence, et d'effacement induits par des ions lourds et des photons γ dans le triacétate de cellulose
Authors: Moliton J. P. , Boutinaud C. , Vareille J. C. , Decossas J. L. , Teyssier J. L. , Delaunay B.
Published: April 2003

The kinetic interpretation of the damage produced by heavy ions (Kr and Cl from 1 MeV/amu) and γ radiation in cellulose triacetate leads to an exponential dependence on the ion fluence. A comparison of the fading effect produced by heavy ions and γ rays shows that the heavy ions, unlike γ rays, cause irreversible damage. Finally, a nonlinear dependence on the flux of ions and γ rays is found in the kinetics of radiation damage. This result is contrary to the usual assumption that heavy‐ion flux, like γ‐ray flux, is additive, at least for the fluxes of 109−2 × 1010 ions/cm2s and dose rates of 103–104 Gy/h used in this work.
Liquid‐crystalline textures in binary and ternary block copolymer–solvent systems
Authors: Wittmann J. C. , Lotz B. , Candau F. , Kovacs A. J.
Published: April 2003

A number of characteristic liquid‐crystalline textures can be obtained in binary and ternary systems (i.e., including one or two solvents) based on polystyrene‐poly(ethylene oxide) (PS‐PEO) and polystyrene‐polyisoprene block copolymers. These textures include oily streaks, myelinic figures, and vesicles, all characteristic of a lamellar structure; fan‐shaped textures of cylindrical structure; and isotropic domains indicative of a cubic structure. Experimental conditions used to systematically produce the mesomorphic textures are described, and the rather critical solubility conditions which the solvents must meet are indicated. The rules and described procedures should be quite general and applicable to other copolymers as well. Finally, highly unusual examples of “pseudomorphosis” typical of liquid‐crystalline textures occurring in bulk upon melting and crystallization of the PEO sequences in PEO‐PS copolymers are also reported.
Infinite‐dilution oscillatory flow birefringence properties of polystyrene and poly(α‐methylstyrene) solutions
Authors: Lodge Timothy P. , Miller James W. , Schrag John L.
Published: April 2003

Oscillatory flow birefringence (OFB) measurements have been carried out for an extensive series of solutions containing narrow‐distribution, atactic, linear polystyrenes PS (10, 000 or 390, 000 Mw) or poly(α‐methylstyrene) PMS (400,000 Mw) in a high‐viscosity solvent, Aroclor 1248. The concentration ranges examined are such that the concentration dependence is obtained in both the “dilute” and “semidilute” regimes; the data are sufficiently precise to permit extrapolation to obtain for the first time the infinite‐dilution properties. Various plotting formats are explored to determine an appropriate extrapolation procedure. The infinite‐dilution OFB properties are compared with the bead‐spring model (Zimm) theory which predicts quantitatively the frequency dependence of the observed properties for the PS and PMS solutions studied except for the high‐frequency regime. The sensitivity and precision of the OFB experiment is such that the extrapolation curves–and the resulting infinite‐dilution properties–show substantially less scatter than comparable visco‐elasticity (VE) data. There is no evidence of a change in the character of the concentration dependence for the range of concentrations studied.
Effects of data analysis on accuracy and precision of GPC results
Authors: Tchir W. J. , Rudin A. , Fyfe C. A.
Published: April 2003

The effects of data imprecision and baseline uncertainties have been investigated by computer simulation of GPC data from a polymer sample with a truncated log‐normal molecular weight distribution. If the data are very accurate, as few as five data points can be sampled without serious error in computed molecular weight averages. The number of data points required is much larger, however, if these are taken at equal increments of molecular weight rather than elution volume. The effects of noise can be counteracted by increasing the sampling frequency. Baseline uncertainties present a more serious problem, especially for broad‐distribution samples. If the detected signal is too noisy to permit accurate location of the baseline, errors can be minimized by using a second, more sensitive detector to determine the peak start and end. It is very difficult to estimate M̄z and higher molecular weight averages accurately if the noise level is greater than 0.5%.
Light‐scattering studies on polystyrenes in isorefractive poly(methyl methacrylate)–toluene “solvents”
Authors: Lin C.‐Y. , Rosen S. L.
Published: April 2003

The rms radii of gyration 〈S2〉1/2 and second virial coefficients Γ2 of five monodisperse polystyrenes (M × 10−5 = 1.6, 2.8, 4.2, 6.6) were measured in isorefractive toluene–poly(methyl methacrylate) (M̄v = 4.0 × 104, 1.6 × 105, and 6.3 × 105) “solvents.” For a given PMMA, the concentration at which the θ condition (defined by Γ2 = 0) was reached was independent of PS molecular weight, but varied inversely with PMMA molecular weight (0.10, 0.056, and 0.023 g/mL, respectively). When this θ condition is reached by adding PMMA to toluene, the radii of gyration are decreased by only about 15%, much less than when it is reached by going to a poor, low‐molecular‐weight solvent. This reflects the exclusion of PMMA from the PS coils, the internal environment of which is essentially pure toluene.
Microphase separation in sulfonated polystyrene ionomers
Authors: Peiffer D. G. , Weiss R. A. , Lundberg R. D.
Published: April 2003

Small‐ and wide‐angle x‐ray scattering results for a series of un‐neutralized and neutralized sulfonated polystyrenes are presented for the range of sulfonation from 0 to 7.26 mol %. From the small‐angle scattering it is shown that above the 3 mol % level for both the zinc and sodium salts, a Bragg spacing (37 Å) and diameter (6.9–8.4 Å) of the scattering unit can be calculated. When the concentration of salt is increased, there is no appreciable change in the latter two measurements. The wide‐angle data indicate that the cations do not influence to any large extent the basic intramolecular and intermolecular structure of polystyrene. All the data are consistent with the onset of clustering above a critical ion concentration.
Properties of aqueous salt solutions of poly(ethylene oxide)
Authors: Ataman M. , Boucher E. A.
Published: April 2003

The determination of the properties of aqueous salt solutions of poly(ethylene oxide) has been extended to cloud‐point and θ‐temperature measurements in sodium acetate, potassium fluoride, sodium thiosulfate, and potassium phosphate. The Hofmeister series for the decreasing effect of anion species in salting out the polymer is accordingly extended. However, the order of the effect depends on whether it is made on the basis of molar anion concentration the molar concentration of unit anion charge, or the ionic strength. Viscosity measurements on θ and non‐θ solutions containing zinc sulfate, potassium fluoride, and potassium phosphate gave polymer dimensions (in addition to limiting viscosity numbers etc.), and characteristic ratios in good agreement with theoretical predictions (Abe and Mark), and enthalpy and entropy parameters χH and χs; the latter values, nominally −0.14 and 0.63, are identical at 298 K for the three salt species.
Polymerization and reptation, an analytical treatment
Authors: Boots H. M. J.
Published: April 2003

Free‐radical polymerization without crosslinking is considered. By taking the chain length as a continuous variable the reaction kinetics is treated in a simple way for the stationary state. Equations for instantaneous average degrees of polymerization and related quantities are generalized to allow for chain‐length dependence of the termination rate constant. For the Ito model, which treats reptation‐controlled termination, approximate versions of these equations are derived in the limits of low and high conversion. The observed structure in the peak of the gel permeation chromatograms is shown not to be related to the bimodality in the instantaneous molecular weight distribution. None of the results is very sensitive to the precise reptation behavior.
A new look at the crystallization of polyethylene. III. Crystallization from the melt at high supercoolings
Authors: Barham P. J. , Jarvis D. A. , Keller A.
Published: April 2003

Polyethylene melts normally cannot be crystallized in an isothermally controlled manner below ca. 110°C as crystallization is too fast owing to the presence of preexisting nuclei. We here present a new simple method for producing droplets enabling crystallization to be conducted isothermally down to 75°C and allowing measurements to be performed on them, together with the results of these measurements. We conclude that in contrast to the earlier claims the homogeneous nucleation regime has not been attained even at these low temperatures, the crystal nucleation being dominated by the polymer‐substrate interface. The droplets crystallized at these low temperatures have a lamellar morphology as revealed by electron microscopy and grow at rates exceeding 1 m s−1[i.e., six orders of magnitude faster than growth at more usual crystallization temperatures previously considered as “low” (110–120°C)]. We have measured the lamellar thicknesslas a function of growth temperature, thus extending the fundamentally importantlvs. ΔT(supercooling) relation beyond the previously realizable limits towards high ΔTvalues. The implications of all these results for the existing ideas of polymer crystallization are likely to be far reaching. Further, the new method for achieving high supercoolings opens up new possibilities for the study of annealing phenomena and the effect of nucleating agents.
Thermoelastic and dielectric studies of poly(3,3‐dimethyl oxetane) chains
Authors: Garrido L. , Riande E. , Guzmán J.
Published: April 2003

Poly(3,3‐dimethyl oxetane) was synthesized by ring opening polymerization of 3,3‐dimethyl oxetane. Elongation experiments were performed on unswollen elastomeric networks prepared from this polymer over the temperature range 30–90°C. The changes in the tensile stress while the networks crystallized were examined at various elongations. From thermoelastic data which were free from the effects of network crystallization, the temperature coefficient of the chain dimensions was found to be 1.1 × 10−3 K−1 in the vicinity of 60°C. The dipole moment ratio and its temperature coefficient were also measured; the average values of these parameters at 30°C were 0.206 and 2.5 × 10−3 K−1, respectively. All of these experimental‐configuration‐dependent properties were critically interpreted in terms of the rotational isomeric‐state model. In comparing theory and experiment, conclusions were obtained which confirm earlier results according to which gauche states about C—C skeletal bonds in poly(3,3‐dimethyl oxetane) are strongly favored over the alternative trans states.
Singlet energy migration and excimer formation in polymers of 2‐tert‐butyl‐6‐vinylnaphthalene
Authors: Nakahira Takayuki , Sakuma Takashi , Iwabuchi Susumu , Kojima Kuniharu
Published: April 2003

The homopolymer of 2‐tert‐butyl‐6‐vinylnaphthalene (BVN) and its copolymers with styrene were prepared to examine the effects of the bulky tert‐butyl groups on singlet energy migration and excimer formation among the naphthalene chromophores. The intensity of naphthalene excimer emission relative to that of monomer emission was found to depend linearly on the concentration of the potential excimer forming site, i.e., the BVN dyad fraction of the polymer. The rate of fluorescence quenching by biacetyl, on the other hand, increased only slightly with the increase in the BVN content. These results are consistent with the slow energy hopping model and suggest that the neighboring naphthalene chromophores are virtually isolated from one another owing to the unfavorable interactions of the tert‐butyl groups.
Bisphenol‐A polycarbonate–poly(butylene terephthalate) transesterification. II. Structure analysis of the reaction products by IR and 1H and 13C NMR
Authors: Devaux J. , Godard P. , Mercier J. P. , Touillaux R. , Dereppe J. M.
Published: April 2003

The structure of the four‐component copolyester resulting from the exchange reaction between molten bisphenol‐A polycarbonate and poly(butylene terephthalate) is analyzed as a function of the reaction time by infrared and nuclear magnetic resonance spectroscopy. By applying a statistical method developed earlier, the mean chain length of the various sequences as well as the degree of randomness is computed. The exchange reaction leads initially to the formation of a block copolyester with reduced solubility. As the reaction proceeds, a soluble random copolycondensate is progressively formed.
Epitaxial morphologies of polyoxymethylene. I. Electron microscopy
Authors: Balik C. M. , Tripathy S. K. , Hopfinger A. J.
Published: April 2003

Epitaxial crystallization of polyoxymethylene (POM) from 0.5% iodobenzene solution has been attempted between 150 and 165°C on 11 different substrates having surface energies ranging from 136 to 1240 ergs/cm2. Included in this series are several substrates such as CaF2, SrF2, BaF2, graphite, mica, and silicon which had not been previously tested as substrates for POM epitaxy. The fluorite series materials are not good substrates for the epitaxial crystallization of POM from solution. In contrast, both rodlike and fold‐plane epitaxial morphologies have been found on the (001) surfaces of NaCl, NaF, and mica. A possible mechanism for the formation of fold‐plane epitaxy is discussed which involves solution nucleation followed by adsorption and growth of the nuclei on the substrate. It is suggested that variations observed in nucleation density of rodlike epitaxial crystals from substrate to substrate are a result of differences in degree of preferential solvent adsorption. Substrates having higher surface energies should tend to adsorb solvent more strongly and thus inhibit profuse nucleation of polymer crystals on the surface.
A two‐dimensional position‐sensitive detector for small‐angle light scattering
Authors: Tabar R. J. , Stein R. S. , Long M. B.
Published: April 2003

A device has been developed for the rapid detection of intensity in two‐dimensional small‐angle light‐scattering patterns. The device utilizes a vidicon detector and a microprocessor. Examples of applications of the device for small‐angle light scattering from thin polymer films are presented.
Threshold tear strength of elastomers
Authors: Gent A. N. , Tobias R. H.
Published: April 2003

Tear strengths have been measured for a wide variety of molecular networks under threshold conditions; i.e., at high temperatures, low rates of tearing, and with swollen samples. For all of the polymers examined, the threshold tear strength was found to be proportional to the square root of the average molecular weight Mc of network strands, in agreement with theory. However, for the same Mc, and hence for similar values of elastic modulus, different polymers showed major differences in threshold tear strength. The tear strength of polydimethylsiloxane networks was only about one‐third that for networks of polybutadiene and cis‐polyisoprene, and the values obtained for polyphosphazene networks were only about one‐fifth as large, at the same Mc. These striking differences are attributed to differences in network strand length and extensibility for the same molecular weight. The threshold tear strengths are shown to be in satisfactory quantitative agreement with theoretically predicted values on this basis.
Chemically bound sensitizers: Dye sensitization of poly(N‐vinylcarbazole) via sulfonation and ion exchange
Authors: Pochan John M. , Gibson Harry W.
Published: April 2003

Photogeneration in a series of surface‐sulfonated and dye‐exchanged poly(N‐vinylcarbazole) films has been studied as a function of depth of the resultant sensitizing (photogeneration) layer. It has been shown that increasing the depth of this layer greatly affects the observed photogeneration rate, decreasing the efficiency with increasing sulfonation. Formed generator depths were from 50 to 250 Å. These results have been attributed to changes in the product μgτg, where τg is the carrier lifetime in the generation layer and μg the carrier mobility in the generation layer. Collection efficiency in the monomer dye absorption maximum and the “mer” absorption maxima are comparable.
Crack propagation in poly(2,6‐dimethyl‐1,4‐phenylene oxide), polystyrene, and their blends
Authors: Kambour R. P. , Smith S. A.
Published: April 2003

Cracks have been propagated in double‐cantilever beam specimens of poly(2,6‐dimethyl‐1,4‐phenylene oxide), polystyrene, and their blends. The plane‐strain crack propagation energy varies with crack speed, distance from crack arrest following an instability, molecular weight, and blend composition. Auxiliary measurements of moduli, yield properties, and craze initiation resistances at crack tips were carried out together with microscopic studies of the crack‐tip plastic zone. Fracture instabilities are rationalized in terms of the interplay of shear deformation with crazing in the crack‐tip plastic zone. Negative deviations from ideal behavior in the crack propagation resistance of the blends are rationalized in terms of the concurrent negative deviation in crazing resistance which in turn is thought to be related to positive deviations in shear resistance and thus to negative volumes and heats of mixing.
Low‐frequency and high‐frequency relaxations in dynamic electric birefringence of poly(γ‐benzyl‐L‐glutamate) in m‐cresol
Authors: Mori Yasushi , Ookubo Norio , Hayakawa Reinosuke , Wada Yasaku
Published: April 2003

The dc component Δn of the electric birefringence of poly(γ‐benzyl‐L‐glutamate) in m‐cresol is measured under an ac electric field at frequencies from 0.5 Hz to 200 kHz for solutions covering the dilute and semidilute regions. The dispersion curve indicates that at low frequencies Δn decreases with increasing frequency (low‐frequency relaxation). For high‐molecular‐weight polymers at high concentration, Δn becomes negative at high frequency and its absolute value decreases with further increase in frequency (high‐frequency relaxation). A unified theory for the two relaxations is developed on the basis of a model in which, in the semidilute regime, the rodlike polymer is confined in a cage formed by neighboring polymers and the lifetime of the cage lies between relaxation times of the two relaxations. The low‐frequency relaxation is ascribed to end‐over‐end rotation of the polymer and the high‐frequency relaxation to the rotation within a limited angle in the cage. The dependences of relaxation parameters on polymer concentration and molecular weight are reasonably explained by the theory.
Melting studies of poly(vinylidene fluoride) and its blends with poly(methyl methacrylate)
Authors: Morra Bruce S. , Stein Richard S.
Published: April 2003

Blends of poly(vinylidene fluoride) (PVF2) and poly(methyl methacrylate) exhibit complex melting behavior when crystallized at low undercoolings. Three crystals comprised of two different PVF2 forms grow. Hoffman‐Weeks plots of the observed melting points Tm of these crystals versus crystallization temperatures are constructed. The lowest‐melting‐point species, the α form, shows a change in slope which is attributed to fewer head‐to‐head PVF2 units trapped in the crystal at higher temperatures. Defect energies in the crystal due to these units are calculated to be from 6.3 to 10.3 kJ/mol. Estimating lamellar thicknesses from the slopes of the two regions gives much more reasonable values when the high‐temperature data are used. Removal of kinetic effects that lower the observed Tm by extrapolating the data to obtain T permits the thermodynamic interaction energy density B between the two polymers to be obtained. The low‐temperature α‐form data give B = −8.83 × 106 J/m3. The high‐temperature α‐form data and the T of the γ‐form crystals both show B to vary from −5.40 × 106 to −2.96 × 107 J/m3 as the blend composition goes from 40.1 vol % to pure PVF2.
Morphological studies of poly(vinylidene fluoride) and its blends with poly(methyl methacrylate)
Authors: Morra Bruce S. , Stein Richard S.
Published: April 2003

Both pure poly(vinylidene fluoride) (PVF2) and its blends with poly(methyl methacrylate) (PMMA) develop a variety of morphologies when they are crystallized above the 420–424 K range. Two populations of spherulites as well as axialitelike growths are observed. Addition of the PMMA lowers the temperature where these new morphologies develop, makes the spherulites more open, causes the banding periodicity to decrease, and increases the number of small, coarse spherulites. These structures melt in three regimes. The highest‐melting‐point crystals arise only from a solid‐solid transformation of the lowest‐melting‐point ones. This solid‐state transition sometimes causes mixed spherulites to be formed in the blends. Electron and wide‐angle x‐ray diffraction show the lowest‐melting‐point species to be α crystals, while the other two are γ crystals. The highest‐melting‐point species, labeled γ′, and the α crystals seem to be more ordered than the other γ crystals.
Comparative Raman studies of molecular interactions at a dye/polymer and a dye/glass interface
Authors: Rabolt J. F. , Schlotter N. E. , Swalen J. D. , Santo R.
Published: April 2003

Integrated optical techniques and resonance Raman spectroscopy have been combined to investigate the intermolecular interactions at dye/polymer and dye/glass interfaces. Frequency shifts and intensity changes of bands assigned to the stretching vibrations of the bridged quinoline rings of the cyanine dye chromophore have been utilized to gain insight into the relative strength of adhesive forces at the surface. Polarized Raman measurements were made to determine the orientation of the chromophores on a poly(vinyl alcohol) surface. This was done to assess the possibility of hydrogen bond formation between the ring nitrogen atoms and the polar hydroxyl groups at the surface.
Inclusion of mobile crosslinks and lateral crystallite growth in the theory of stress‐induced crystallization
Authors: Smith K. J.
Published: April 2003

The theory of stress‐induced crystallization is broadened to include a reshuffling of crosslink positions as a result of changing sizes of crystalline domains and multiple crystallites of varying lateral dimensions (i.e., lateral growth). A continuous state of equilibrium throughout the amorphous component of the stretched network is postulated and, consequently, effected by requiring crosslinks to anchor about their most probable locations, which vary continuously as crystallization changes. Such features incorporated into Flory's model of stress‐induced crystallization broaden its theoretical base, placing it on a stronger, more realistic foundation.
The numerical solution of fujita's integral equation to provide estimates of molecular weight distributions
Authors: Jeffcoate J. M. , Wragg A.
Published: April 2003

A standard model of the behavior of polymers under ultracentrifugation results in Fujita's equation for their molecular weight distribution. Fujita's and related equations are examples of Fredholm integral equations of the first kind and are thus ill posed. Two methods are described for solving the equations numerically and hence providing estimates of the molecular weight distribution. The first method involves expanding the distribution in terms of orthogonal polynomials whose coefficients are calculated from estimates of the moments of the distribution. In the second method the distribution is reconstructed by using matrix singular‐value decomposition techniques combined with an approximant expressed as a sum of B‐splines. The potential and practical limitations associated with the methods are illustrated by numerical results from a series of tests on four problems designed to represent distributions with different modal properties.
Phase transitions in mesophase macromolecules. VI. The transitions in poly(oxy‐2,2′‐dimethylazoxybenzene‐4,4′‐diyloxydodecanedioyl)
Authors: Grebowicz Janusz , Wunderlich Bernhard
Published: April 2003

The transitions of poly(oxy‐2,2′‐dimethylazoxybenzene‐4,4′‐diyloxydodecanedioyl) (PDAD) have been analyzed by differential scanning calorimetry, optical microscopy, and light scattering. The mesophase glass devitrifies at 288 K [ΔCp = 220 J/K mol]. Crystallization from the liquid mesophase can be described between 322 and 362 K by an Avrami expression with an exponent between 3 and 4. Results of light scattering and optical microscopy are in accord with a spherulitic morphology grown after athermal nucleation. Melting of the semicrystalline samples (crystallinity up to 58%) occurs at about 391 K. The heat of fusion of the completely crystalline sample is calculated to be only 13.55 kJ/mol. The mesophase to isotropic phase transition occurs at 418 K with a heat of transition of 4.1 kJ/mol. A general discussion of these transitions is given.
Concentrated solutions of polydisperse rodlike polymers in the isotropic and lyotropic liquid‐crystalline phases. II. Model simulation of the dielectric relaxation behavior of poly(n‐alkylisocyanates) in toluene and comparison with experimental results
Authors: Moscicki J. K. , Williams G.
Published: April 2003

A simulation has been made of the dielectric relaxation behavior of poly(n‐hexylisocyanate) in solution covering the isotropic, biphasic, and anisotropic ranges. The simulation incorporates the Flory‐Abe statistical mechanical theory for the phase behavior of rodlike macromolecules in solution and the Warchol, Vaughan, Wang, and Pecora theory for the dynamics of a rodlike molecule in a virtual cone prescribed by the neighboring molecules. It is shown that asymmetric Gaussian, Gaussian, or Poisson distributions of molecular weight do not lead to dielectric behavior of the type observed experimentally by Moscicki, Williams, and Aharoni but addition of a high‐molecular‐weight “tail” to such distributions and taking account of the dependence of relaxation time on molecular length gives a simulation of the dielectric increment Δε, the loss maximum ε, and frequency of maximum loss fm, which vary with polymer concentration in a manner entirely consistent with the experimental data.
Interdependence of motional processes in polymers: correlation functions for nmr relaxation
Authors: Henrichs P. M.
Published: April 2003

The roles of both anisotropic motion and the interdependence of multiple motions in leading to nonexponential correlation functions for NMR relaxation data are explored. A motional model is developed in which rotational motions of segments of various lengths are controlled by the formation and disappearance of a suitable conformation. Such a model gives correlation functions which can be made, through adjustment of parameters, to be almost identical to correlation functions from other, quite different, models. The ability of NMR relaxation data to identify unique motional models is thus questioned.
Thermodynamics of mixtures of poly(tetramethylene oxide)s and 1, 4‐dioxane
Authors: Sharma Subhash C. , Lakhanpal Madan L.
Published: April 2003

Vapor pressures and densities of solutions of poly(tetramethylene oxide) fractions (molecular weights 650, 1000, and 2000) in 1, 4‐dioxane have been determined at 30 and 40°C. The data have been utilized to determine the activities and thermodynamic functions of dilution. Excess volumes have been determined from the density data. Flory's equation of state theory quantitatively predicts the reduced residual functions X, Xh, and Xs. Predicted as well as experimental values of Xs are found to be negative. The theory predicts correctly the sign of the excess volume but quantitative agreement between theory and experiment is not obtained.
Blends of poly(butylene terephthalate) and a polyarylate before and after transesterification
Authors: Kimura Masao , Porter Roger S. , Salee Gideon
Published: April 2003

Blends of poly(butylene terephthalate) (PBT) and a copolyester of bisphenol‐A with 50% terephthalate‐50% isophthalate (PAr), before and after transesterification, have been studied by thermal and dynamic mechanical tests to determine crystallinity and phase behavior. Blends without transesterification, as prepared by solution precipitation, show a single Tg, indicating amorphous miscibility of PBT and PAr. A melting‐point depression for PBT crystals is not observed; this means that PBT crystallizes excluding PAr and the entropy of melting is small. The highest fractional crystallinity for PBT is obtained at 20‐35% of PAr. Transesterified blends were obtained by holding the physical blends at 250°C for up to 16 h. The transesterified systems show higher Tg's than the corresponding physical blends and also show a marked melting‐point depression and lesser PBT crystallinity at the corresponding increased PAr content.
Orientation studies on hot‐drawn tubular blown films of isotactic polypropene
Authors: Bottin Marie Francoise , Boudeulle Micheline , Guillet Jacques
Published: April 2003

Orientation studies of hot‐drawn polypropene films were performed using small‐angle light scattering and wide‐angle and small‐angle x‐ray scattering over a wide range of deformation. At low deformation, the classical scheme of affine deformation, as several authors have pointed out, seems to be quite realistic. However, for high deformations, i.e., up to 500%, a new conception of the microfibrillar state is proposed. The microfibrils are formed of fully extended crystals which have a high degree of parallel orientation, but deviations of the units from their ideal position occur. “Wrong” chains are embedded in the lattice, long‐range order is lost, and paracrystallinity appears. A nematic arrangement develops gradually, and we suppose that the “needlelike entities” have some cylindrical symmetry with a crystalline core. The true amorphous component acts as a connection between these zones.
The diffusion of CO2, CH4, C2H4, and C3H8 in polyethylene at elevated pressures
Authors: Kulkarni S. S. , Stern S. A.
Published: April 2003

Diffusion and solubility coefficients have been determined for the CO2−, CH4−, C2H4−, and C3H8‐polyethylene systems at temperatures of 5, 20, and 35°C and at gas pressures up to 40 atm. Diffusion coefficients were obtained from rates of gas absorption in polyethylene rods under isothermal‐isobaric conditions by means of a new diffusivity apparatus. The concentration dependence of the diffusion coefficients was represented satisfactorily by Fujita's free‐volume model, modified for semicrystalline polymers, while the solubility of all the penetrants in polyethylene was within the limit of Henry's law. Semiempirical correlations were found for the free‐volume parameters in terms of physicochemical properties of the penetrant gases and the penetrant‐polymer systems. These correlations, if confirmed, should permit the prediction of diffusion and permeability coefficients of other gases and of gas mixtures in polyethylene as functions of pressure and temperature.
Radiation‐induced crystallinity changes in linear polyethylene
Authors: Bhateja S. K. , Andrews E. H. , Young R. J.
Published: April 2003

Two kinds of ultrahigh‐molecular‐weight linear polyethylene (UHMW PE), together with conventional high‐density polyethylene (HDPE), were subjected to β irradiation, and changes in their properties were monitored. Elastic modulus increased steadily with dose for all materials, as did the yield stress. A dramatic rise of density with dose was observed in the UHMW PE specimens accompanied by a corresponding increase in heat of fusion, x‐ray crystallinity, and peak melting temperature. The magnitude of such changes in HDPE was much smaller. In UHMW PE specimens, the x‐ray long period simultaneously decreased but crystal thickness remained constant. No changes in long period occurred in HDPE. The effects are attributed to the scission of tie molecules in UHMW PE followed by a growth in the perfection of the crystal lamellae, and suggest a method for assessing the tie‐molecule content of such materials.
Crystallization in oriented polymers: A framework for analyzing orientation distributions
Authors: Abhiraman A. S.
Published: April 2003

A framework is presented for analyzing the changes that occur in the orientation distribution of polymer segments when crystallization occurs in an initially amorphous precursor. Existing theories which relate crystalline orientation distribution to that of the precursor can be incorporated in this framework in a straightforward manner. The orientation distribution of segments that remain uncrystallized is inferred from a kinetic analysis of the incorporation of precursor segments into growing crystals. The relevance of such a framework in understanding polymer fabrication processes is discussed briefly with examples in fiber formation from the melt.
Ionomeric blends. II. Compatibility and dynamic mechanical properties of sulfonated cis‐1,4‐polyisoprenes and styrene/4‐ vinylpyridine copolymer blends
Authors: Zhou Zheng‐Long , Eisenberg A.
Published: April 2003

Dynamic mechanical and optical transparency methods were used to investigate the compatibility of a series of blends of sulfonated cis‐1,4‐polyisoprene and styrene/4‐vinylpyridine copolymers. It was found that compatibilization occurs at a degree of substitution less than 5%. It is suggested that proton transfer from the sulfonic acid group to vinyl pyridine, which results in the generation of specific anion‐cation interactions, is responsible for the compatibilization, since the removal of ionic interactions through esterification destroys the compatibility.
Optical absorption spectrum of PMMA via laser calorimetry
Authors: Avakian P. , Hsu W. Y. , Meakin P. , Snyder H. L.
Published: April 2003

The optical absorption spectrum of poly(methyl methacrylate) (PMMA) has been obtained in the wavelength range 570–780 nm via laser calorimetry (employing a dye laser source). Because of the low thermal conductivity of PMMA, the complete solution to the heat conduction equation (carried out numerically) was required in the analysis of the data. At the wavelength of minimum absorption (near 647 nm), the absorption coefficient had the value 153 dB/km.
Preoriented poly(ethylene terephthalate) yarns: Influence of the gauche‐trans transformation on crystallization
Authors: Galli R. , Canetti M. , Sadocco P. , Seves A. , Vicini L.
Published: April 2003

Effects of macromolecular orientation on the crystallization of preoriented poly(ethylene terephthalate) filaments were studied. Infrared spectrophotometry and differential scanning calorimetry analyses showed that macromolecular segments in the trans conformation begin to crystallize below the glass transition temperature. Since filaments prepared by stretching at room temperature have different degrees of orientation, it is possible to evidence correlations between crystallization from an anisotropic matrix and the resulting morphology.
Local composition effect in poly(dimethyl siloxane) solutions: A comparison of two models
Authors: Cánovas A. , Rubio R. G. , Renuncio J. A. R.
Published: April 2003

Two polymer solution models have been used to analyze poly(dimethyl siloxane) (PDMS) + alkane and PDMS + ketone systems. The free‐volume and nonrandom interaction contributions are studied separately in order to compare the expressions for the local site fractions used in the two models. Predictions of the reduced residual chemical potential and excess volumes are discussed and compared with those found in the literature for these systems.
Densification effect on physical properties of atactic polystyrene
Authors: Destruel P. , Ai Bui , Hoang‐Thê‐Giam
Published: April 2003

Atactic polystyrene has been densified under hydrostatic pressure, up to 2 kbar, at about 180°C. Dielectric measurements were made on densified and nondensified polystyrene samples by using the thermally stimulated depolarization current (TSDC) and the absorption and resorption current methods. The dielectric loss is modified by the densification. This effect can be explained in terms of the free‐volume reduction and the internal stress induced in the material during densification.
Vapor‐pressure osmometry and inverse gas chromatography in the analysis of thermodynamic properties of polymer solutions
Authors: Fernández‐Berridi M. J. , Eguiazábal J. I. , Elorza J. M. , Iruin J. J.
Published: April 2003

The primary objective of this work is to check the utility of vapor‐pressure osmometry as an experimental technique in obtaining thermodynamic data on polymer/solvent systems. The second objective is to obtain experimental values for the exchange energy parameters ΔP, X, and ζ of the theory of Sanchez and Lacombe. With respect to the first objective, solvent activities of polyiso‐butylene/benzene mixtures have been measured at several concentrations up to 600 g/kg of the solvent and at two temperatures. From the activities, it is possible to determine free energies, entropies, and enthalpies and their concentration dependence. Satisfactory agreement has been found between the results obtained and data provided by other techniques such as membrane osmometry and the Cahn electrobalance. These and other data obtained by inverse gas chromatography for the same mixture in the range 35–200°C have been used in calculating the exchange energy parameter of the lattice fluid theory at different concentrations and temperatures.
Nonhomogeneous state of stress, strain, and swelling in amorphous polymer networks
Authors: Erman Burak
Published: April 2003

The total free energy of an amorphous, crosslinked polymer is given as ΔA = ΔAmix + ΔAel, where ΔAmix indicates the free energy of mixing of the crosslinked polymer and the solvent to which the network is exposed throughout the deformation process; ΔAel indicates the elastic free energy of the network as a function of strain, including the effect of dilation with the solvent. The explicit forms of the mixing and the elastic free energies are obtained from the molecular theory of rubber elasticity. Recent developments in this field allow accurate representation of the behavior of swollen networks under strain. Expressions for the stress in terms of strain and swelling ratio are obtained from the free energy. Formulation of boundary‐value problems are discussed. Bending of a cuboid subject to the action of a swelling agent is analyzed as an example. Material parameters are chosen for a crosslinked amorphous network. The distribution of stresses, strains, and solvent in the bent cuboid are calculated numerically. The magnitude of moments applied at the two ends are calculated for different degrees of flexure. Results are compared with those obtained for the same network in the dry state.
Drawing by solid‐state coextrusion of blends of atactic and isotactic polystyrene with poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: Wang Li‐Hui , Porter Roger S.
Published: April 2003

Atactic polystyrene (aPS)/poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) and isotactic polystyrene (iPS)/PPO compatible blends of varied composition were subjected to solid‐state coextrusion. The efficiency of drawing, orientation, and crystallinity development were studied as a function of composition and draw ratio. The efficiency of drawing, as measured by elastic recovery, is high for coextrusion at temperatures ≲40°C above the glass transition temperature of the particular blend. The maximum attainable draw ratio for the blends decreased with increasing PPO concentration; the highest blend draw ratio attained was 6.5 for 25 wt % PPO. The orientation on drawing, as measured by birefringence, increased with draw but decreased with increasing PPO component at the same draw ratio. When PPO was <50% in iPS/PPO blends, iPS crystallized on draw. The morphology of drawn blends was studied by electron microscopy and wide‐angle x‐ray scattering.
Some electrophysical properties of polyphthalocyanines under the action of high pressure and shear deformation
Authors: Zhorin V. A. , Beshenko S. I. , Makarova L. I. , Sherle A. I. , Berlin Yu. A. , Enikolopian N. S.
Published: April 2003

The effect of high pressure or the combined action of high pressure and shear deformation on the conductivity G and capacitance C of metal‐free polyphthalocyanines (PPhCs), differing in macromolecular size, order, and degree of crosslinking, has been studied. It has been found that both G and C increase with compression. A similar phenomenon is observed under the combined action of high pressure and shear deformation on PPhC, but in this case the critical pressure needed for change in G is lower than that observed in uniaxial compression experiments. Spectroscopic investigations show that the effects of pressure and deformation on the electrophysical properties of samples under load is not connected with changes in the chemical structure of PPhC, but appear to be due to the change in the average distance between the regions of continuous conjugation. The sizes of such regions may be increased by preliminary thermal treatment.
Ionic conductivity of hybrid films composed of polyacrylonitrile, ethylene carbonate, and LiClO4
Authors: Watanabe Masayoshi , Kanba Motoi , Nagaoka Katsuro , Shinohara Isao
Published: April 2003

The electrical conductivity of hybrid films consisting of polyacrylonitrile (PAN), ethylene carbonate (EC), and LiClO4 was investigated. In these films, EC and LiClO4 are found to be molecularly dispersed in PAN, forming solid solutions over a wide composition range. The ionic character of the electrical conductivity is demonstrated. The conductivity is not correlated with the content of LiClO4 or of PAN, but primarily with the mole ratio [EC]/[LiClO4] in the films. An increase in the [EC]/[LiClO4] ratio enhances the conductivity. When the ratio is about 2, the conductivity attains 10−4–10−5 S cm−1 at 25°C. This change in conductivity results from a change in carrier mobility. PAN makes the films solid without decreasing the carrier mobility. In the hybrid films, the carrier mobility and the macroscopic viscosity are not related by Walden's rule. The high conductivity is due to regions in the film characterized by a low microscopic viscosity. This is determined by the mole ratio [EC]/[LiClO4] and largely controls the carrier mobility.
Radiation chemistry of linear low‐density polyethylene. I. Gel formation and unsaturation effects
Authors: Basheer Rafil , Dole Malcolm
Published: April 2003

Quenched and annealed samples of linear low‐density polyethylene (LLDPE) were irradiated with 60Co γ rays in vacuo at room temperature. The data follow rather accurately Charlesby's equation s = k/r, where s is the soluble fraction, r the dose, and k a constant from which G(X), the G‐value for crosslinks, was calculated. Crosslinking in the LLDPE is about twice as extensive at equal doses as in LHDPE. Production of vinylene unsaturation was approximately the same in the two types of polyethylene.
Temperature effects in the environmental stress cracking of polyethylene
Authors: Shanahan M. E. R. , Debski M. , Bomo F. , Schultz J.
Published: April 2003

An already existing model describing three types of behavior in the environmental stress cracking (ESC) of polyethylene (PE) subjected to uniaxial tensile loading at 25°C has been extended to cover the temperature range 25‐50°C. Three effects have been observed and are found to be qualitatively consistent with the model. The transition between “pure” ESC (zone 1) and liquid‐flow‐controlled behavior (zone 2) occurs at shorter times for higher temperatures—an effect mainly due to reduced liquid viscosity. “Pure” ESC is less temperature dependent than failure occurring without the liquid playing a significant role (zone 3). This has been attributed to a compensation of reduced mechanical resistance of the polymer at higher temperatures, by reduced stress concentrations at the crack tip due to local absorption of the liquid. The transition time between zones 2 and 3 increases with temperature. Although it is surprising at first sight, this effect is shown to be compatible with the ESC model.
Solid‐state coextrusion of poly(ethylene terephthalate). I. Drawing of amorphous PET
Authors: Pereira Jose R. C. , Porter Roger S.
Published: April 2003

Films of uniaxially oriented poly(ethylene terephthalate) (PET), Mv = 81,000, have been drawn by solid‐state coextrusion in the range 40–100°C surrounded by polyethylene. This is well below the PET melting temperature and in some cases below its glass transition temperature. Properties of the extrudates, such as degree of crystallinity, mechanical and thermal properties, were investigated as a function of coextrusion temperature and draw ratio (EDR ≤ 4.4). The results show that the percent crystallinity depends strongly on draw ratio, whereas its sensitivity to extrusion temperature is limited only to the highest draw ratio (4.4). On the other hand, Young's modulus was sensitive to both extrusion temperature and draw ratio, exhibiting a maximum at EDR = 4.4 and Text = 65°C. Above this temperature, moduli decrease apparently because of increased chain mobility, resulting in dissipation of chain orientation. Furthermore, changes in yield and tensile strength followed the changes in mechanical properties, suggesting that they are dominated by the same factors. The cold‐crystallization temperature TCC also revealed information about the morphological changes occurring during the extrusion drawing. For samples of EDR = 4.4, TCC increased with extrusion temperature, suggesting again dissipation of orientation by thermal motions. On the other hand, TCC decreases with EDR, and a ΔTCC as high as 73°C was found. Conventional drawing of amorphous PET has been widely reported. To our knowledge this is the first time oriented PET has been prepared using the advantages of solid‐state coextrusion.