bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology of CaCO3‐filled polyethylenes
Authors: Chacko V. P. , Karasz F. E. , Farris R. J. , Thomas E. L.
Published: April 2003

The morphology of one novel “homogeneous composite” and some conventional CaCO3‐particulate‐filled polyethylenes (PEs) has been investigated by transmission and scanning electron microscopy. It is found that for three different linear polyethylenes (Mw = 37,000, 200,000, and 1.5 × 106) studied, ordering on the scale of spherulites was absent in the CaCO3‐filled polymer. However, PE lamallae were observed growing normal to the filler interface. Changes in molecular weight of the polyethylene result in easily observed differences in morphology, while DSC studies indicate that crystallinity decreases in the presence of filler for the two lower‐molecular‐weight polyethylenes.
Molecular design of multicomponent polymer systems. III. Comparative behavior of pure and tapered block copolymers in emulsification of blends of low‐density polyethylene and polystyrene
Authors: Fayt R. , Jérôme R. , Teyssié Ph.
Published: April 2003

Poly(hydrogenated butadiene‐b‐styrene) copolymers are very effective emulsifiers for blends of polystyrene and low‐density or high‐density polyethylene. It is shown that the extent of improvement in mechanical properties is dependent not only on the molecular weight but also on the structure of the diblock copolymer. A comparative study of the morphology and the mechanical behavior of modified low‐density polyethylene/polystyrene blends demonstrates that a tapered diblock is more efficient than a pure diblock with the same composition and molecular weight. It is assumed that the unique behavior of the tapered sample results from its particular miscibility characteristics at the blend interface. The tapered copolymer could behave essentially as a solu‐bilizing agent for the homopolymers at the interface and provide a “graded” modulus responsible for the improved mechanical response of the material.
Tensile strength of highly oriented polyethylene. II. Effect of molecular weight distribution
Authors: Smith Paul , Lemstra Piet J. , Pijpers Jacques P. L.
Published: April 2003

The tensile strength of oriented polyethylene filaments is discussed in relation to molecular weight. Short‐term tensile properties at room temperature were obtained in our laboratory and from the literature for polymer samples covering the molecular weight (Mw) range from 54 × 103 to 4 × 106, and polydispersities ranging from 1.1 to 15.6, oriented by solid‐state extrusion, melt spinning/drawing, solution spinning/drawing, and “surface growth.” It was found that both the molecular weight and its distribution markedly affected tensile strength. The breaking stress σ of highly oriented fibers varied with molecular weight roughly as σ ∝, M0.4, at constant Mw/Mn over the entire range studied. Reduction of polydispersity from 8 to 1.1 by an increase of Mn with Mw approximately constant at 105 increased tensile strength of oriented polyethylene filaments by a factor of nearly 2.
On the use of Raman‐active longitudinal acoustic modes in the study of polyethylene lamellar structures
Authors: Glotin M. , Mandelkern L.
Published: April 2003

The first‐, third‐, and fifth‐order low‐frequency, Raman‐active, longitudinal acoustical modes of the n‐alkane C94H190 and different morphological forms of semicrystalline polyethylene have been obtained. An analysis of the results shows that the correction needed to obtain the extended planar‐zigzag ordered sequence length is maximum for the n‐alkane and very small for the polymer systems. These represent solution crystals as well as bulk‐crystallized material. For the latter, samples were prepared so that the crystallite thickness is either comparable to or very much smaller than the extended chain length. An approximate method is also developed which enables the natural linewidth to be determined.
Structure‐property relationships in polycaprolactone‐polyurethanes
Authors: Van Bogart John W. C. , Gibson Philip E. , Cooper Stuart L.
Published: April 2003

The structure‐property relationships of polycaprolactone‐based segmented polyurethanes were studied using differential scanning calorimetry (DSC), small‐angle x‐ray scattering (SAXS), wide‐angle x‐ray diffraction (WAXD), dynamic mechanical, and stress‐strain testing. The materials studied varied in hard‐segment type [4,4′‐diphenylmethane diisocyanate/butanediol (MDI/BD) or 4,4′‐dicyclohexyl methane diisocyanate/butanediol (H12MDI/BD)], soft‐segment molecular weight (830 or 2000 MW polycaprolactone), hard‐segment content (23–77% by weight), and thermal history. The materials with aromatic (MDI/BD) hard segments had semicrystalline hard‐segment domains, while the materials with aliphatic (H12MDI/BD) hard segment had mostly amorphous domains. Materials with the shorter polycaprolactone soft segment (830 MW) exhibited thermal and mechanical behavior which indicated a considerable degree of hard‐ and soft‐segment compatibility. The materials which contained a 2000‐MW polycaprolactone soft segment exhibited better‐defined microphase separation. SAXS was used to characterize the microphase structure of each system. The effects of hard‐segment content and soft‐segment molecular weight were similar for the aromatic (MDI) and aliphatic (H12MDI) hard‐segment‐based block copolymers. Changing the hard segment from aromatic to aliphatic gave materials with larger interfacial area and slightly higher tensile strength. A range of morphologies between isolated hard domains in a rubbery matrix and isolated rubbery domains in a hard matrix was observed.
A structural model for high‐modulus polyethylene derived from entanglement concepts
Authors: Grubb D. T.
Published: April 2003

Starting from the concept that the entanglement network is a controlling factor in polymer deformation, a molecularly based model has been constructed for polyethylene, drawn or extruded to high extension ratios λ. It predicts the experimentally observed form of the increase of Young's modulus E with λ: E−1 = B + Cλ−2. The model structure consists of imperfect crystalline microfibrils 10‐30 nm in diameter and length αλ2, about 1 μm at λ = 30. The microfibrils terminate at clusters of entanglements, and are embedded in a matrix of low modulus. This structure is very similar to that derived from solution‐grown shish‐kebab material. Available melting‐point data for highly extended material fit the structural model well.
Unsuccessful search for a liquid‐liquid transition in compression isotherms of polystyrene
Authors: Loomis L. D. , Zoller Paul
Published: April 2003

In a search for a liquid‐liquid transition in the melt of polystyrene, we have measured and analyzed a number of compression isotherms to 1800 kg/cm2 in a relevant temperature range (1.2Tg < T < 1.4Tg). Volume data were recorded at pressure intervals of 10 kg/cm2, i.e., at pressure intervals 5‐20 times smaller than used in previous work. For the analysis the data were fitted to the Tait equation. Deviations between fits and data are small, typically 0.0004 cm3/g, but nonrandom. From the absence of any systematic shifts of the nonrandom deviation patterns with temperature, we conclude that the deviations are not manifestations of a pressure‐dependent liquid‐liquid transition, and that there is, in fact, no evidence for the existence of such a transition in our data.
Polymorphic structure and physical properties of the polyester/ether poly(ethylene‐1,2‐diphenoxyethane‐p,p′ ‐dicarboxylate)
Authors: Shimizu Jiro , Okui Norimasa , Imai Yoshitaka , Nishide Shingo , Takaku Akira
Published: April 2003

X‐ray diffraction studies of fibers of the polyester/ether poly(ethylene‐1,2‐diphenoxyethane‐p,p′ ‐dicarboxylate) (PEET) produced by high‐speed melt spinning show the existence of two polymorphic forms, designated α and β, in the solid state. The α form is obtained by annealing filaments melt spun at takeup speeds below 3000 m/min and is also found in samples crystallized from the melt and from dilute solutions. The α form has a monoclinic unit cell with dimensions a = 7.83, b = 10.33, c = 18.68 Å, and β = 83.1°. The equilibrium melting temperature and heat of fusion of the α form are 288.3°C and 19.1 cal/g, respectively. The β form predominates in highly oriented filaments obtained at takeup velocities above 6000 m/min. The unit cell is orthorhombic with dimensions a = 7.28, b = 5.65, and c = 18.64 Å. The β form does not transform to the α form on annealing.
A Raman‐spectroscopic study of solution‐crystallized polyethylenes
Authors: Glotin M. , Domszy R. , Mandelkern L.
Published: April 2003

An analysis of the Raman internal modes of dilute‐solution‐crystallized homopolymers and co‐polymers of ethylene has been made, similar to the work previously reported for the bulk‐crystallized polymers. The crystallite structure can be described in terms of the relative amounts of the crystalline orthorhombic phase, the liquidlike amorphous phase, and the interfacial region. These quantities change with the molecular constitution of the chains and the crystallization conditions. The level of crystallinity decreases significantly with increasing counit content as would be expected. In addition, an appreciable interfacial structure develops in copolymers as compared with the homopolymers. A possible relationship between the interfacial content and the relaxation transitions in polyethylene is discussed.
The heat of fusion of poly(ethylene terephthalate)
Authors: Starkweather Howard W. , Zoller Paul , Jones Glover A.
Published: April 2003

By use of the Clapeyron equation for the dependence of the melting point on pressure, the heat of fusion was found to be 32.5 cal/g, in good agreement with values determined by other methods. An equation for the dependence of the melting point on the degree of polymerization gave a heat of fusion of 27.6 cal/g when applied to hydroxyl‐terminated oligomers. This simple relation applied all the way down to the smallest member of the series, di(hydroxy ethyl) terephthalate.
Further annealing studies of the calcium salt of an ethylene‐methacrylic acid copolymer
Authors: Brozoski B. A. , Coleman M. M. , Painter P. C.
Published: April 2003

Annealing studies of the calcium salt of an ethylene‐methacrylic acid copolymer are reported. Fourier‐transform infrared spectroscopy and differential scanning calorimetry were applied to the investigation of the effect of polyethylene crystallization on ionic structure as a function of annealing temperature and time. The spectroscopic changes observed in the spectra of the calcium salt annealed at 80°C differ from those seen in the spectra of the calcium salt annealed at room temperature. These changes are interpreted in terms of the multiplet‐cluster model and the effect of the polyethylene‐type crystallinity on the ionic microstructure.
Chain folding in single crystals of polytetrafluoroethylene
Authors: Giglio E. , Morosetti S. , Palleschi A. , Pavel N. V.
Published: April 2003

Potential‐energy calculations are performed in order to obtain satisfactory models for folding in single crystals of polytetrafluoroethylene crystallized in the phase stable below 19°C. The folds are assumed to be tight with adjacent reentry. Folds with a variable number of bonds are analyzed. Their conformation is deduced by a method which obtains closure between two semifolds into which each fold is decomposed. The allowed models are subsequently investigated by using an energy minimization program. Some possible models are proposed. The calculations show that the folds must be described by a number of rotational isomeric states higher than is usually assumed.
Dynamic x‐ray diffraction studies of high‐density polyethylene
Authors: Cembrola Robert J. , Kyu Thein , Stein Richard S. , Suehiro Shoji , Kawai Hiromichi
Published: April 2003

Dynamic x‐ray diffraction is conducted to explore the structural origin of the α and β mechanical dispersions of a melt‐crystallized high‐density polyethylene. It is shown that the real component of the strain orientation coefficient for the crystal c axis C decreases with increasing frequency at a rate which decreases with decreasing temperature. Values of C for the c axis are positive, C for the a axis negative, and C for the b axis close to zero, suggesting that the predominant relaxation process is crystal rotation about the b axis. The activation energy found from Arrhenius plots of C corresponds to that of the α1 mechanical dispersion. The dynamic birefringence in this region is dominated by the contribution from crystal orientation changes. At low temperatures, the imaginary component KC of the strain‐optical coefficient of the crystal phase approaches zero, while KC of the amorphous phase exhibits a somewhat broad dispersion peak corresponding to the β birefringence dispersion. This suggests that the principal contribution to the β birefringence dispersion arises from the amorphous phase, probably owing to the amorphous orientation process. Contrary to the case of low‐density polyethylene, the dynamic crystal lattice deformation and compliance functions reveal distinct frequency dispersions corresponding to the α1 and α2 mechanical processes. The α1 lattice dispersion is thought to be associated with the α1 crystal orientation dispersion, while the α2 lattice dispersion is believed to be the inherent one arising from the onset of intracrystalline chain motions.
The use of small‐angle electron scattering to compare the structure of craze found in thin films with that found in bulk materials
Authors: Brown H. R.
Published: April 2003

Small‐angle electron scattering (SAES) has been used to examine the structure of crazes in polystyrene. It has been shown theoretically that the analysis of SAES is similar to the equivalent x‐ray patterns (SAXS) except perhaps for the higher‐angle scattering. A direct comparison of the SAES patterns from crazes in films of ca. 400 nm thickness with SAXS patterns from crazes in films of ca. 1 mm thickness has shown that the craze structures are similar in form for the thin and thick films but the fibrils are about three times larger in the thin films.
Electrical properties of ion‐implanted poly(p‐phenylene sulfide)
Authors: Mazurek H. , Day D. R. , Maby E. W. , Abel J. S. , Senturia S. D. , Dresselhaus M. S. , Dresselhaus G.
Published: April 2003

Ion implantation of impurities into thin films of poly(p‐phenylene sulfide) (PPS) is found to increase the conductivity of the material by up to 12 orders of magnitude. The increase is stable under exposure to ambient conditions, in contrast to the instability of the conductivity increases in PPS produced by chemical doping with AsF5. PPS films 0.1–0.2 μm thick are spin cast from solution onto interdigitated electrodes patterned on an oxidized silicon substrate. The room‐temperature interelectrode resistance is measured as a function of implantation fluence. An estimate of film conductivity is obtained from this resistance with a simple model for the electrode and film geometry. A first experiment yielded similar conductivity increases for implantation of either arsenic or krypton. At a fluence of 1 × 1016cm−;2, which corresponds to an average impurity concentration of 2.5 × 1021cm−3, the conductivity reaches an apparently saturated value of 1.5 × 10−5 (Ω cm)−1. Infrared spectra of the films before and after implantation suggest that crosslinking may be present in the implanted films, and Auger studies show stoichiometric changes throughout the implanted layer. These results suggest that the observed conductivity changes are the result of molecular rearrangements produced by the implantation rather than the result of specific chemical doping. Specific chemical doping may, however, explain the results of a second experiment in which implantation of bromine resulted in substantially larger conductivities found to increase at an approximate linear rate from a value of 1.0 × 10−4 (Ω cm)−1 at a fluence of 1 × 1016 cm−2 to a value of 4.0 × 10−4 (Ω cm)−1 at a fluence of 3.16 × 1016 cm−2.
Photon correlation spectroscopy of polystyrene as a function of temperature and pressure
Authors: Patterson G. D. , Carroll P. J. , Stevens J. R.
Published: April 2003

Photon correlation spectroscopy is employed to study the slowly relaxing density and anisotropy fluctuations in bulk atactic polystyrene as a function of temperature from 100 to 160°C and pressure from 1 to 1330 bar. The light‐scattering relaxation function is well described by the empirical function ϕ(t) = exp[−(t/τ)β], where for polystyrene β = 0.34. The average relaxation time is determined at each temperature and pressure according to 〈τ〉 = (τ/β)Γ(1/β) where Γ(x) is the gamma function. The data can be described by the empirical relation 〈τ〉 = 〈τ〉0 exp[(A + BP)/R(T − T0)] where R is the gas constant and T0 is the ideal glass transition temperature. The empirical constant A/R is in good agreement with that determined from the viscosity or the dielectric relaxation data (1934 K). The empirical constant B can be interpreted as the activation volume for the fundamental unit involved in the relaxation and is found to be comparable to one styrene subunit (100 mL/mol). The quantity B appears to be a weak function of temperature. The use of pressure as a tool in the study of light scattering near the glass transition now has been established.
Photon correlation spectroscopy of poly(methyl methacrylate) near the glass transition
Authors: Patterson G. D. , Carroll P. J. , Stevens J. R.
Published: April 2003

Poly(methyl methacrylate) (PMMA) has been studied by photon correlation spectroscopy in the temperature range 120–150°C. The relaxation functions for longitudinal density fluctuations were determined and analyzed using the empirical function ϕ(t) = exp[−(t/τ)β]. The average relaxation times were calculated for each temperature and compared to mechanical and dielectric relaxation data. The agreement between the various techniques for the primary glass–rubber relaxation was good. The relaxation function observed by light scattering became increasingly broad as the temperature was lowered. This is similar to the results reported previously for poly(ethyl methacrylate) (PEMA). In fact, the light‐scattering relaxation function is dominated by the secondary relaxations in these two polymers. Nevertheless, the average relaxation time 〈τ〉 is dominated by the longest relaxation times associated with the primary glass–rubber relaxation.
Electron‐beam‐induced conduction in fluorinated ethylene propylene copolymer and its acrylonitrile graft copolymer
Authors: Joshi S. G. , Ghatge N. D. , Jog J. P. , Walzade S. J. , Bhoraskar S. V.
Published: April 2003

Electron‐beam‐induced conductivity (EBIC) studies were carried out on fluorinated ethylene propylene copolymer (FEP) and its acrylonitrile graft copolymer (FEP‐g‐AN). The current transport parallel to the surface under the influence of an electron beam of medium energy (6–30 keV) is reported. The gain in EBIC is calculated and its characteristic variation as a function of beam energy is studied. Minima in the gain versus energy curves have been obtained around 21 keV for FEP, 12 and 18 keV for FEP‐g‐AN, and 12 keV for polyacrylonitrile (PAN). This behavior is explained by assuming the existence of electron trapping bands close to the surface, at characteristic distances below the surface of the polymeric film corresponding to the range of incident electrons. Gains of the order of 5, 12, and 30 have been obtained respectively for FEP, FEP‐g‐AN, and PAN for the maximum energy of incident electrons used.
The elastic constants of ultradrawn polypropylene
Authors: Leung W. P. , Choy C. L.
Published: April 2003

The five independent elastic constants C11, C12, C13, C33, and C44 for uniaxially drawn polypropylene with draw ratios 1 < λ ≤ 20 have been measured from −40 to 130°C by an ultrasonic method (2.5 MHz). The crystalline and amorphous orientation functions fc and fa were also determined from wide‐angle x‐ray diffraction and birefringence; fc increases sharply at low λ and becomes saturated above λ = 8, but fa increases monotonically up to λ = 20. Below the glass transition temperature (ca. 60°C at 2.5 MHz) only the axial longitudinal and tensile moduli, C33 and E0, show large increase. At 110°C, however, all the moduli increase with λ; E0, E90 (tranverse tensile modulus), C44 (axial shear modulus), and C66 (tranverse shear modulus) increase 30, 3, 5, and 2.5 times, respectively, as λ increases from 1 to 20. The improvement in the mechanical properties can be attributed to the increase in the fraction of taut tie molecules which was monitored by fa. The results were analyzed in terms of the two‐phase models of Takayanagi and Seferis et al. The effects of annealing were also studied.
Longitudinal piezoelectric strain measurements of poly(vinylidene fluoride) films
Authors: Uchino K. , Cross L. E.
Published: April 2003

The longitudinal piezoelectric strain of poly(vinylidene fluoride) (PVF2) films has been measured at room temperature using a high‐sensitivity ac capacitance‐type dilatometer. The dc bias field dependence of the piezoelectric strain coefficient d33 has been determined. The polarization‐related electrostrictive coefficient Q33 obtained is several hundred times larger than the value in normal piezoelectric oxide crystals and is of opposite sign.
One‐dimensional models of polymer dynamics. I. Dashpot‐spring models applied to a single rotor
Authors: Mansfield Marc L.
Published: April 2003

The proposion of Clark and Zimm that a dashpot and a spring can be used in place of a set of rotational barriers in polymer dynamics is studied. The simplest possible case is examined here, that of a single rotor. Reasons for altering the Clark–Zimm diffusion equation are presented and an alternative diffusion equation is proposed. The results of both diffusion equations for the correlation function 〈exp[−iθ(0)] exp[iθ(t)]〉 (θ is the angular position of the rotor) are compared with the correlation function for a rotor in an n‐fold cosine potential. Although the two diffusion equations differ, both agree well with the n‐fold cosine model for barriers above a few kBT. This agreement is obtained in the absence of adjustable parameters, and motivates the application of these two diffusion equations to polymeric systems.
One‐dimensional models of polymer dynamics. II. A dashpot‐spring model
Authors: Mansfield Marc L.
Published: April 2003

The assumption of Clark and Zimm that coupled dashpots and springs can be used to model the dynamics of polymer molecules is here applied to a model different from that of Clark and Zimm. The precise differences are given in the preceding paper. The dielectric relaxation spectrum of the model is computed in time and frequency domains. The relaxation spectrum can be fitted reasonably well by the empirical Williams–Watts and Havriliak–Negami functions. The best‐fit Williams–Watts and Havriliak–Negami parameters are given as functions of the parameters of the model. The model is compared with several related models found in the literature and possible interpretations are given.
Photon correlation spectroscopy of polymer solutions
Authors: Cha C. Y. , Min K. W.
Published: April 2003

A polynomial subdistribution method for analyzing the correlation profile in photon correlation spectroscopy of polymer solutions is described. This method generates a continuous distribution function from the measured photoelectron time‐correlation function, which can be related to particle size or molecular weight distribution of solute. The method is tested using simulated data for unimodal and bimodal distributions and compared with cumulant and histogram methods, respectively. The polynomial subdistribution method has an advantage in that it not only generates a continuous distribution curve but also works well for bimodal distributions whose peaks are close together.
The melt anisotropy of ultrahigh‐molecular‐weight polyethylene
Authors: Zachariades Anagnostis E. , Logan J. A.
Published: April 2003

In the course of melt‐flow crystallization studies with ultrahigh‐molecular‐weight polyethylene (UHMWPE), we observed that the melt of UHMWPE is highly anisotropic above its equilibrium melting point and has a tendency to fibrillate. An examination of the melt anisotropy of UHMWPE by optical, Thermal, and x‐ray analysis indicates that the melt anisotropy persists at 345°C, i.e., the temperature at which the polymer degrades under nitrogen, and appears similar to a smectic liquid‐crystalline phase.
Dynamic small‐angle x‐ray scattering from crystalline polymers
Authors: Young Ping , Kyu Thein , Suehiro Shoji , Lin J. S. , Stein R. S.
Published: April 2003

The variation in small‐angle x‐ray scattering (SAXS) for samples of crystalline polymers subjected to oscillatory strains has been observed employing the 10‐m SAXS apparatus with a two‐dimensional position‐sensitive detector at the National Center for Small‐Angle Scattering Research at Oak Ridge National Laboratory. Signal averaging has been carried out in accordance with the π/2‐sector technique by gating the detection of scattered intensity in synchronism with the sample strain. In‐phase and out‐of‐phase intensity changes have been observed for a high‐density polyethylene at various frequencies (0.05–3.2 Hz) and temperatures (0–70°C). Changes are greatest at small scattering angles. Frequency dependence is greatest at lower temperatures, indicating a time‐dependent response of the structural changes leading to scattering at these temperatures. The behavior is not pronounced at elevated temperatures. The similarity of the scattering at both azimuthal angles of 0° and 90° suggests the existence of an additional mechanism, perhaps microvoid formation. To evaluate void contribution, the dynamic invariant function is determined as a function of frequency and temperature. It appears that the microvoid formation lags behind the applied strain. The static and swelling SAXS studies present further evidence of void generation during elongation.
Small‐angle x‐ray scattering studies of crazed glassy polymers
Authors: Westbrook Paul A. , Fellers John F. , Hendricks Robert W. , Lin J. S.
Published: April 2003

A small‐angle x‐ray scattering (SAXS) study of the relaxed craze structure in polystyrene was performed using the Oak Ridge National Laboratory 10‐m SAXS facility. Coupled with known results from transmission electron microscopy studies, the SAXS patterns can be interpreted as scattering from an open‐cell foam with void spaces interspersed among the fibrils. Results have shown the scattering centers in crazed polystyrene can be modeled as cylinders the axes of symmetry of which are parallel to the tensile axes. Scattering centers are bimodal in their size distribution, with aspect ratios of 1.0 and 2.6. Crazes in lower‐molecular‐weight polystyrene have more and larger scattering centers than crazes in higher‐molecular‐weight polystyrene, while variations in strain rate and test temperature during craze formation have no effect on the relaxed craze morphology. A comparison of SAXS patterns from polystyrene and polycarbonate indicates that the morphologies of their respective crazes are significantly different.
Friction coefficients in self‐diffusion, velocity sedimentation, and mutual diffusion for poly(ethylene oxide) in aqueous solution
Authors: Brown Wyn , Stilbs Peter , Johnsen Robert M.
Published: April 2003

The concentration dependences of the friction coefficient(s) for poly(ethylene oxide) have been determined on well‐defined fractions in dilute aqueous solution. Three independent techniques have been used: FT‐pulsed field gradient NMR (self‐diffusion), photon correlation spectrosccpy (mutual diffusion), and velocity sedimentation, in the concentration range 1‐25 kg m−3. The results establish that, at a given concentration, the friction coefficient in self‐diffusion is appreciably smaller than that operating in mutual diffusion and sedimentation; the friction coefficient in the latter processes are identical within experimental error.
Solid‐state 13C NMR evidence for gas–polymer interactions in the carbon dioxide–poly(vinyl chloride) system
Authors: Sefcik M. D. , Schaefer Jacob
Published: April 2003

The presence of small amounts of CO2 in poly(vinyl chloride) (PVC) results in increased main‐chain molecular motions of the polymer as measured by the carbon rotating‐frame relaxation rate. This effect increases with increasing gas concentration. Since molecular motions of the polymer and the diffusion coefficient of the gas are related, the latter must be concentration dependent. Main‐chain motions of PVC also increase upon exposure to CO2 followed by degassing. This result is interpreted in terms of the effect of the penetrant gas on the interchain packing in amorphous PVC. These results cannot be reconciled with the dual‐sorption‐mobility model, which claims that gas molecules preferentially occupy preexisting sorption sites in a conditioned polymer with no perturbation of the polymer matrix.
Relationship between piezoelectricity and superstructure in highly oriented poly(vinylidene fluoride) film prepared by zone drawing
Authors: Yamada K. , Oie M. , Takayanagi M.
Published: April 2003

The oriented superstructure of poly(vinylidene fluoride) is controlled by using a forced‐quenching type of zone drawing apparatus. Systematic variation of the weight fraction χ(I) of form‐I crystals and the orientation function fa of amorphous chains shows that the piezoelectricity increases with increasing χ(I) and fa. A change in the state of molecular aggregation during poling is also effective in increasing the piezoelectricity and the orientation of the crystal b axis along the poling direction. Equations relating piezoelectricity to the form‐I crystallinity, the orientation of amorphous chains, and the orientation of the crystal b axis along the poling direction are derived. These are based on a mechanical model having regions of taut tie molecules in parallel with composite regions consisting of crystalline and amorphous blocks in series.
Effects of pressure on the compressibility and crystallization of fiber‐forming polymers
Authors: Wei Kei‐Yi , Cuculo John A. , Ihm Dae Woo
Published: April 2003

The effects of pressure on the compressibility and crystallization of three fiber‐forming polymers, poly(tetramethylene terephthalate), nylon 66, and Qiana® nylon, have been studied. The Instron capillary rheometer was adapted as a high‐pressure dilatometer for all the high‐pressure experiments. The compressibility results reaffirmed that polymers are highly compressible, and their compressibilities are nonlinear at temperatures above the glass transition temperatures. Polymer melts show higher compressibility than do polymers in the solid state. The kinetics of crystallization of these polymer melts under high pressures were studied. Analysis of the data revealed low Avrami exponents at high pressures. It seems that the kinetics of crystallization of these polymers from the melt under high pressure are different from those at normal pressure. Crystallization temperatures of these polymers were also measured. The crystallization temperatures are considerably higher at higher pressures.
Thermotropic homopolyesters. I. The preparation and properties of polymers based on 4,4′‐dihydroxybiphenyl
Authors: Asrar J. , Toriumi H. , Watanabe J. , Krigbaum W. R. , Ciferri A. , Preston J.
Published: April 2003

A homologous series of polyesters was prepared from 4,4′‐dihydroxybiphenyl and dibasic acids having 5‐12 methylene units. The mesophases formed at elevated temperatures were studied by differential scanning calorimetry and polarized light microscopy. This family exhibits an unusual odd‐even effect when the transition temperatures are plotted as a function of the number of methylene units in the dibasic acid. Not only do the points for odd and even members fall on different curves, but the odd members exhibit a nematic phase over a very short temperature interval, while the even members form a highly ordered smectic phase. For both the odd and even series, the transition temperatures are significantly depressed when the inherent viscosity falls below 0.2 dL/g. The largest depression occurs for the crystal melting transition, so that polymers of low ηinh show anisotropic and biphasic regions over wider temperature ranges. A copolymer formed from an equimolar mixture of sebacic and chiral (+)‐3‐methyl adipic acid forms a cholesteric phase. Evidently copolymerization destabilizes the smectic phase which would have been expected. The results are discussed in terms of existing theory.
Stress‐optical behavior of polydimethylsilmethylene [Si(CH3)2CH2], a hydrocarbon analog of polydimethylsiloxane, and a silicon analog of polyisobutylene
Authors: Llorente M. A. , Mark J. E. , Saiz E.
Published: April 2003

Elastomeric networks were prepared from polydimethylsilmethylene (PDMSM) [Si(CH3)2CH2], a polymer closely related to polydimethylsiloxane (PDMSO) [Si(CH3)2O] and polyisobutylene (PIB) [C(CH3)2CH2]. The birefringence of PDMSM in elongation was found to be qualitatively similar to that of PDMSO, in that there was no evidence for strain‐induced crystallization. However, the values of the optical‐configuration parameter Δa were considerably larger, and both Δa and its temperature coefficient are essentially the same as those of PIB. Swelling the PDMSM networks generally decreased Δa; the largest decreases, obtained as expected with the most nearly symmetrical diluent, were also approximately the same as those observed for PIB. Use of cyclic PDMSO pentamer as diluent in a PDMSM network was found to increase the birefringence, presumably because of orientational effects. Various network‐diluent combinations involving the significantly anisotropic PDMSM and the more nearly isotropic PDMSO should be extremely useful for elucidating the nature of these intermolecular correlations. Results obtained from rotational isomeric state theory considerably underestimate both Δa and its temperature coefficient for PDMSM, as they do for PIB. Although the origin of the discrepancy is not necessarily the same for both polymers, the results on PDMSM suggest that the discrepancy for PIB is not due to the severe steric congestion known to be present in this polymer.
Tests of a free‐volume model for the permeation of gas mixtures through polymer membranes. CO2‐C2H4, CO2‐C3H8, and C2H4‐C3H8 mixtures in polyethylene
Authors: Stern S. A. , Mauze G. R. , Frisch H. L.
Published: April 2003

Steady‐state permeability coefficients have been measured for equimolar mixtures of CO2‐C2H4, CO2‐C3H8, and C2H4‐C3H8, as well as for a mixture of 74.9 mol % CO2 and 25.1 mol % C2H4 in polyethylene membranes. The measurements were made at 20, 35, and 50°C and at pressures of up to 28 atm. Each component of the permeating mixtures studied had the effect of increasing the permeability coefficient for the other component. Furthermore, at equal partial pressures and at the same temperature, the component exhibiting the highest solubility in the polymer had the largest effect in increasing the permeability coefficient of the other component. This behavior is in agreement with the predictions of a free‐volume model for the permeation of gas mixtures proposed by Fang, Stern, and Frisch. From a quantitative viewpoint, the permeability coefficients for the components of the mixtures agreed, on the average, to better than 25% with the predicted values. The theoretical permeability coefficients can be estimated from the model by using parameters determined with the pure components only.
Localized volume deficiencies as an effect of spherulite growth. I. The two‐dimensional case
Authors: Gałeski A. , Piórkowska E.
Published: April 2003

Two‐dimensional spherulite growth leads to the encirclement of regions of molten polymer in a polymer film. On further crystallization localized volume defects arise, resulting in thin spots in the film. Since this effect lowers the mechanical strength of films, we call these volume defects “weak spots.” A computer program is developed to evaluate the number, size, and shape of such volume defects for athermal, thermal, and mixed modes of primary nucleation of spherulites. It is shown that the total area of weak spots exceeds 10% of the sample area for all types of nucleation studied. The largest weak spots arise in samples crystallized via athermal and mixed nucleation; their size is of the same order as that of an average spherulite. Formation of weak spots is observed in thin films of poly(ethylene oxide) and poly(methylene oxide). The disadvantageous role of weak spots is confirmed by observation of electric breakdown occurring preferentially in weak spots in polypropylene films.
Formation, structure, and elasticity of loosely crosslinked epoxy‐amine networks. I. Statistics of formation
Authors: Dušek K. , Ilavský M.
Published: April 2003

Using the theory of branching processes based on cascade substitution, relations are derived for structural parameters characterizing network formation from diepoxide, monoepoxide, and diamine for various initial compositions. The different reactivities of the hydrogen atoms of the primary and secondary amino groups (the latter being formed in the reaction) and possibly different reactivities of epoxy groups in diepoxide and monoepoxide are taken into account. Relations are derived for the critical conversion at the gel point and for changes as a function of conversion in the average molecular weight in the pregel stage, changes in the sol and gel contents, effective functionality of the crosslinks, and concentration of elastically active network chains. The derivation includes the trapping factor that appears in the theory of permanent interchain interactions (trapped entanglements) of the Langley type. An analysis of the approximation usually employed in the statistical theory based on network formation from dyads of structural units shows that this approach is quite satisfactory for small differences in the reactivities of epoxy groups in diepoxide and monoepoxide.
Ab initio calculation of polyethylene deformation including electron correlation effects
Authors: Suhai S.
Published: April 2003

The longitudinal acoustic elastic modulus of polyethylene has been calculated with the aid of the ab initio crystal orbital method applying corrections also for electronic correlation effects. The basis set and correlation dependence of the elastic modulus have been investigated. The best theoretical value of 305 GPa of this modulus is in reasonable agreement with the published experimental values. At an elongation of ca. 0.1 the deviation from Hooke's law is found to be substantial.
EXAFS studies of nickel nafion ionomers
Authors: Pan H. K. , Yarusso D. J. , Knapp G. S. , Cooper S. L.
Published: April 2003

Nafion membranes neutralized with Ni2+have been examined by extended x‐ray absorption fine‐structure (EXAFS) and x‐ray absorption near‐edge‐structure (XANES) spectroscopy. The results indicate that in both the dry and water‐soaked membranes, the nickel is in an octahedral site with six oxygen atoms as nearest neighbors. The degree of disorder in the NiO distance is comparable to that in ionic crystals in both the dry and hydrated materials. A contribution from a second shell of neighbors is very weak in the dry samples but, surprisingly, this contribution is strongly accentuated in the hydrated membranes. The data indicate that this contribution is due to neighboring Ni2+cations. Thus the water absorption seems to enhance the local ordering of the cation environment. The local structure does not depend strongly on the concentration of ionic groups in the materials.
Thermal expansivity of oriented poly(ethylene terephthalate)
Authors: Choy C. L. , Ito Masayoshi , Porter Roger S.
Published: April 2003

The linear thermal expansivity of poly(ethylene terephthalate) extruded at 50 and 90°C to extrusion ratios λ of 1–4.8 has been measured between 120 and 300 K. With increasing λ, the expansivity along the extrusion direction (α∥) decreases sharply, while that in the transverse direction (α⊥) shows a slight increase. For λ < 3, the large drop in α∥ and the accompanying increase in the axial Young's modulus E∥ can be ascribed to chain alignment in the crystalline regions and to an increase in number and tautness of intercrystalline tie chains. At higher λ, however, the crystalline orientation apparently becomes saturated, so that taut tie molecules are solely responsible for further changes in both α∥ and E∥. On the other hand, α⊥ is mainly determined by crystalline orientation for all λ, thus showing very little increase at large λ. For the highly oriented samples (λ ≥ 3), the Takayanagi model provides a reasonable description of the behavior of α∥ and α⊥.
Small‐angle X‐ray scattering studies of microdomain structure in segmented polyurethane elastomers
Authors: Koberstein Jeffrey T. , Stein Richard S.
Published: April 2003

The small‐angle x‐ray scattering (SAXS) technique has been used to characterize the detailed microphase structure of two crosslinked segmented polyurethane elastomers. Both copolymers contain trifunctional polypropylene ether triols in the rubbery elastomeric block, but are synthesized with different hard segments: a symmetric 4,4′‐diphenylmethane diisocyanate (MDI) chain extended with butanediol (BD); and an 80/20 mixture of asymmetric 2,4‐toluene diisocyanate (TDI) and symmetric 2,6‐toluene diisocyanate (TDI) chain extended with ethylene glycol (EG). Calculations of SAXS invariants and determinations of deviations from Porod's law are used to examine the degree of phase segregation of the hard‐ and soft‐segment domains. Results show that the overall degree of phase separation is poorer in the asymmetric TDI/EG‐based copolymer than in the symmetric MDI/BD‐based copolymer. Determination of diffuse phase boundary thicknesses, however, reveals that the domain boundaries are sharper in the asymmetric TDI/EG system. The contrasting morphologies found in the two systems are interpreted in terms of differences in hard‐soft segment compatibility, diisocyanate symmetry, and diisocyanate length. Coupled with conformational considerations, this information is used to construct a new model for polyurethane hard‐segment microdomain structure. Important features of the model are that it takes into account the effects of hard‐segment sequence length distribution and allows for folding of the longer hard‐segment sequences back into the hard‐segment domain.
An analysis of local flow effects in flow‐induced orientation and crystallization
Authors: Dairanieh I. S. , McHugh A. J.
Published: April 2003

An analysis is presented of the effects of external flow kinematics on the so‐called local flow in seeded, flow‐induced crystallization and orientation. The flow field around a growing crystal or nucleation seed is modelled by the Stokes flow equations past a prolate ellipsoid of high aspect ratio. Exact solutions for various flow kinematics, worked out elsewhere by the singularity method, are applied here to the analysis of local gradients. The results show that along the symmetry axis of the spheroid, the extensional gradients which result for various free‐stream velocity fields are primarily the result of the constant‐velocity free‐stream component. However, free‐stream, extensional flow can significantly enhance the region of such high gradients. Along the symmetry plane of the spheroid, primarily shearing gradients result, with small extensional gradients occurring when the free‐stream flow has extensional components. Results of chain extension and birefringence calculations are also presented and discussed.
Influence of the chemical composition and comonomer distribution on the dipole moments of 3,3‐dimethyloxetane/tetrahydrofuran copolymers
Authors: Garrido L. , Riande E. , Guzmán J.
Published: April 2003

Experimental values of the dipole moment ratio 〈μ2〉/nm2 and its temperature coefficient d ln 〈μ2〉2/dT, where 〈μ2〉 is the mean‐square dipole moment of a chain with n skeletal bonds and m2 is the mean square of the skeletal bond dipole moments, are reported for well‐characterized random copolymers of 3,3‐dimethyloxetane and tetrahydrofuran. The results are interpreted in terms of the rotational isomeric state theory in a manner consistent with that developed for the parent homopolymers. The theory gives a good account of the experimental results corresponding to copolymers in which the mole fraction of tetrahydrofuran lies in the range 0.11–0.89. It is found that whenever the copolymerization obeys Bernouillan statistics, the dipole moments are quite insensitive to the comonomer distribution. The theoretical analysis suggests, however, that the value of the dipole moment ratio of alternating copolymers of 3,3‐dimethyloxetane and tetrehydrofuran should be near that of the parent homopolymer of lower polarity.
Low‐frequency raman scattering from methylene‐oxyethylene‐methylene triblock oligomers
Authors: Swales T. G. E. , Teo H. H. , Domszy R. C. , Viras K. , King T. A. , Booth C.
Published: April 2003

Low‐frequency Raman spectra are reported for monodisperse methylene‐oxyethylene‐methylene triblock oligomers. Assignments are made to the longitudinal acoustical modes (LAMs) of the oxyethylene block and the methylene block. The results for LAM‐1 can be modeled by the vibrations of rods with perturbing forces and masses. The results for LAM‐3 are not so readily modeled.
Flow‐induced crystallization by surface growth of polyethylene fibers
Authors: Rietveld J. , McHugh A. J.
Published: April 2003

A series of experiments has been carried out investigating several features of the surface growth method for observing longitudinal growth of polyethylene fibers in Couette geometry. Attempts to obtain limiting steady‐state takeup rates using a Teflon rotor were hampered by fiber breakage; however, maximum growth rates before breakage were found to be considerably higher than those observed in previous studies. Growth rates were also obtained using a static method, and for the Teflon rotor indicated above a critical concentration a linear growth rate equal to the stirrer velocity with rates essentially independent of temperature. With a silanized glass rotor, the same method gave much lower growth rates at comparable stirrer speeds and temperatures and showed a temperature dependence suggestive of a nucleation‐controlled mechanism. The implications of these results for other studies of the mechanisms of growth by the surface method are also discussed.
Dynamics and mechanism of iodine sorption by polyacetylene
Authors: Danno Tetsuya , Miyasaka Keizo , Ishikawa Kinzo
Published: April 2003

Sorption of iodine by bulk polyacetylene was studied under various I2 gas pressures at 25°C. The sorption dynamics show that the penetration of iodine into PA is not Fickian and the diffusion coefficient increases with time of sorption. A discontinuous increase in the sorption isotherm is observed at P/P0 = 0.25 (P is the pressure of the I2 gas and P0 is the saturation value at 25°C). It is due to iodine penetration into PA crystals, as evidenced by x‐ray analysis. The distribution of iodine within crystals is apparently inhomogeneous: some unit cells are changed into “iodine‐PA” cells, while others remain unchanged. The electrical conductivity depends not only on the amount of iodine but also on the I2 gas pressure under which sorption is carried out. At given iodine content, the conductivity of a sample doped under higher I2 pressure is greater than that of a sample doped under lower pressure.
Spectroscopic characterization of solvent‐induced crystallization of PET
Authors: Lin Shaow‐Burn , Koenig Jack L.
Published: April 2003

Using recently developed quantitative FTIR methods, the gauche and trans conformer compositions have been measured for polyethylene terephthalate (PET) samples exposed to benzene and acetone. The kinetics of the primary and secondary isomerization stages of the solvent‐induced crystallization process have been studied and compared with the thermally crystallized system. The Arrhenius activation energies of isomerization in the primary stage in which Fickian diffusion behavior is followed for the benzene‐ and acetone‐induced PET systems are 8.2 ± 0.4 and 7.7 ± 0.4 kcal/mol, respectively.