bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of surface dynamics of polymers. III. Surface dynamic stabilization by plasma polymerization
Authors: Yasuda T. , Yoshida K. , Okuno T. , Yasuda H. 
Published: April 2003

AbstractAs demonstrated in Part II of this series of studies, the hydrophobic character of CF4 plasma‐treated Nylon 6 and poly(ethylene terephthalate) (PET) decay with time of water immersion, and the rate of decay can be used as a measure for the surface mobility of (substrate) polymers. The same method of using fluorine‐containing moieties introduced by CF4 plasma treatment as surface labeling is applied to investigate the influence of a thin layer of plasma polymer of methane applied onto the surface of those polymers. An ultrathin layer of plasma polymer provides a barrier to the rotational and diffusional migration of the introduced chemical moieties from the surface into the bulk of the film. The influence of operational parameters of plasma polymerization on the surface dynamic stability are examined by measuring the decay rate constants for (subsequently) CF4 plasma‐treated samples. The rate constant was found to decrease sharply with increasing value of plasma energy input manifested by J/kg monomer, and no decay was observed as the energy input reached a threshold value (about 6.5 GJ/kg for PET, about 7.0 GJ/kg for Nylon 6), indicating that unperturbable surfaces can be created by means of plasma polymerization.
Copolymerization of ethylene and butadiene with supported titanium catalyst
Authors: Sun Lixin , Lu Zejian , Lu Yun , Lin Shangan 
Published: April 2003

AbstractThe copolymerization of ethylene and butadiene with a supported titanium catalyst (TiCl4/MgCl2/EB/Φ2SiCl2/AlEt3) is described. The resulting products were characterized by IR, 13C‐NMR, x‐ray diffraction, differential thermal analysis, electron microscopy, and solvent extraction. It was found that the butadiene units are substantially in trans‐1,4 configuration and blocked sequences. Both ethylene and butadiene blocks form crystalline phases. The presence of unsaturated bonds made it possible to graft MMA and maleic anhydride. The influences of monomer composition, temperature, Al/Ti ratio, catalyst concentration, and solvents on the copolymerization were investigated.
Radiation hardening of polytetrafluoroethylene against chemical etching
Authors: Rye R. R. 
Published: April 2003

AbstractExposure of polytetrafluoroethylene (PTFE) to MgKα x‐rays (1253.6 eV) for times as short as 10 min is observed to lead to permanent radiation hardening toward chemical etching. X‐ray‐dosed surfaces are visibly less etched, and the loss of F is over a factor of 2 smaller. For PTFE itself, the x‐ray photoelectron spectrum shows only slight changes for x‐ray exposures up to several hours, but thermal desorption spectroscopy yields a direct correlation between the desorption of low‐molecular‐weight fluorocarbons and x‐ray exposures down to the order of minutes. Irradiation of PTFE is know to lead to molecular weight degradation and branching and/or crosslinking through free radical reactions. The degradation reactions are the source of the low‐molecular‐weight fluorocarbons which desorb at elevated temperatures. Branching and/or crosslinking, which produce a more rigid, thermally stable structure, are proposed as the mechanism for resistance to chemical etching. Similar resistance to chemical etching, in the absence of x‐rays, is observed for the fluorinated ethylene‐propylene copolymer which contains intrinsic fluorinated methyl group side chains.
The effect of morphology on the transport of dichloromethane in poly(aryl‐ether‐ether‐ketone)
Authors: Grayson Michael A. , Wolf Clarence J. 
Published: April 2003

AbstractA study of the transport of the dichloromethane in neat poly(aryl‐ether‐ether‐ketone) (PEEK) samples with thicknesses from 0.08 to 3.0 mm with different morphologies was conducted at 35°C. Both sorption and desorption of the solvent were studied. Thermal annealing was used to vary the sample morphology, and density measurements were used to determine the crystallinity of the samples. The equilibrium concentration of solvent and rate of solvent sorption were found to vary with sample morphology. The density of the dichloromethane when in the PEEK resin was found to be 1.65 g/cm3. Solvent desorption was independent of sample morphology or any previous sample treatment and depended only upon desorption temperature. Solvent sorption appears to alter the morphology of amorphous samples by increasing the crystallinity to about 20% after one sorption/desorption cycle. Small amounts of the solvent, less than 0.5 wt.%, remain trapped in fully desorbed samples. The micromorphology of solvent‐induced crystallization appears to be different from that induced by thermal treatment.
Elastomer reinforcement from a glassy polymer polymerized in situ
Authors: Fu F.‐S. , Mark J. E. 
Published: April 2003

AbstractCross‐linked networks of poly(dimethylsiloxane) were swelled with styrene containing benzoyl peroxide. Polymerization of the styrene in situ, by increasing the temperature, gave novel elastomeric composites. Scanning electron micrographs suggest that low concentrations of styrene (∼ 14 wt.%) gave primarily low‐molecular‐weight polystyrene (PS), which acted merely as a diluent in the networks. Larger amounts gave PS which phase separated into glassy particles having diameters in the approximate range 0.05–1.5 μm. In these cases, an increase in wt.% PS gave networks showing large increases in ultimate strength, which was to be expected. Surprisingly, there were also increases in maximum extensibility, which usually decreases in response to modifications which increase the ultimate strength.
Blends of poly(vinyl methyl ether) with styrenic copolymers
Authors: Min K. E. , Paul D. R. 
Published: April 2003

AbstractBlends of poly(vinyl methyl ether) (PVME) with styrene/acrylonitrile (SAN), with styrene/maleic anhydride (SMA), and with styrene/acrylic acid (SAA) copolymers were examined for glass transition and lower critical solution temperature behavior. These copolymers were found to be completely miscible with PVME at levels of 3% or less of AA; below 10–11% AN, and below 15% MA (w%). Small amounts of the comonomers raised the temperature at which blends with PVME undergo phase separation on heating. This effect was greatest in the order AA > AN > MA. An interpretation of these results is given in terms of recent theories for homopolymer‐copolymer blends, and the extent to which solubility parameter theory can be useful is considered.
Rheology and phase separation in polystyrene/poly(vinyl methyl ether) blends
Authors: Ajji A. , Choplin L. , Prud'homme R. E. 
Published: April 2003

AbstractBlends of monodisperse polystyrene and poly(vinyl‐methyl‐ether) of various compositions were prepared from solution in benzene. Dynamic rheological properties of these blends were studied at different temperatures below, near, and above Ts, the temperature of phase separation, and in a frequency range from 0.05 to 100 rad/s. A flattening in the storage modulus and an initial plateau for the complex viscosity were observed near and above Ts in the low‐frequency region; in contrast, below Ts the behavior of the blends was similar to that of the homopolymers. The WLF superposition principle applies only at temperatures below Ts, i.e., in the miscible and homogeneous region. G″ versus G′ representations for the blends were found to be independent of temperature and to vary with composition in the miscible region but are temperature and composition‐dependent in the immiscible region. It is also shown that the η″ versus η′ representation is a useful tool for characterizing phase separation of blends and is more sensitive than the classical frequency dependence of the material functions.
Network architecture and modulus of miscible heteropolymer blends
Authors: Tsenoglou Christos 
Published: April 2003

AbstractThe architecture and entanglement density of a multicomponent polymer network composed of miscible, flexible chains is related to the corresponding properties and concentrations of the pure components. It is assumed that the coupling frequency between different chain species is proportional to their fractional participation in the blend and that the entanglement ability of polymers can be affected by the presence of heteropolymer neighbors. The theory, equally applicable to temporary and permanent networks, estimates the molecular weight between entanglements and their total number along a chain in the blend. This information is used in establishing a mixing law for the rubbery plateau modulus of a fluid polymer blend and in deriving a relationship for the equilibrium modulus of an interpenetrating polymer network containing trapped entanglements and dangling segments. The theoretical predictions are compared with experimental results from the literature on several miscible polymer blends.
Thermal cycling of glasses. II. Experimental evaluation of the structure (or nonlinearity) parameter x
Authors: Hutchinson J. M. , Ruddy M. 
Published: April 2003

AbstractThe structure parameter x (also known as the nonlinearity parameter), which in the KAHR model determines the relative contributions of temperature and structure to the retardation times of polymers in the glass transition region, is evaluated experimentally for a narrow molecular weight fraction of atactic polystyrene by the peak‐shift method. This method is based on the dependence on heating rate and annealing time of the endothermal peak temperatures Tp, obtained by differential scanning calorimetry during the heating stage of well‐defined three‐step thermal cycles. The results obtained from the shifts of Tp, with both heating rate and the amount of isothermal recovery during the annealing stage before reheating, are consistent with the theoretical predictions of the KAHR model. The appropriate analysis of the data for a polystyrene fraction of molecular weight 30,100 leads to a value of x = 0.46 ± 0.02. Furthermore, this value of x is constant for a wide range of annealing times and heating rates and for two different annealing temperatures, in full agreement with the theoretical model. The advantages of the peak‐shift method over that used by most other workers, the curve‐fitting method, are critically discussed.
Computer simulation of a binary polymer mixture in three dimensions
Authors: Cifra P. , Karasz F. E. , MacKnight W. J. 
Published: April 2003

AbstractThe behavior of a binary polymer mixture was simulated on a cubic lattice over both the miscibility and immiscibility regions. The number and distribution of interactions in the mixture were found to be different from the mean‐field picture; however, the observed phase behavior agrees with that predicted by the mean‐field theory and is not affected by the observed concentration fluctuations. The relationship between the phenomenological χ parameter and the heterosegmental interaction energy was investigated. Polymer chains show nearly ideal behavior, even for strongly interacting mixtures; this simplifies the theoretical treatment of polymer mixtures analogous to homopolymer melts.
Relaxation processes and structure of ultradrawn polyethylene
Authors: Failla M. D. , Carella J. M. , De Micheli R. 
Published: April 2003

AbstractSolid‐state extruded polyethylene fibers have been prepared, with a wide range of draw ratios and constant processing temperature. The draw ratios vary from 4 up to 30, and the processing temperature was always 398 K. The extruded material behaves anisotropically, owing to the high degree of chain orientation in the drawing direction. The modulus and linear expansion coefficients in the fiber axis direction have been measured, over a wide temperature range, from 140 K up to 320 K. These two properties are closely related to the degree of structural continuity of the fibers. A fibrous structure model is proposed to explain the temperature effects and the values obtained for the modulus and expansion coefficients, in terms of crystallinity and volumetric fraction of extended‐chains structure. At least three relaxation processes can be identified which cause the structural continuity of the fibers to change with temperature.
Strain and temperature accelerated relaxation in polycarbonate
Authors: Yee A. F. , Bankert R. J. , Ngai K. L. , Rendell R. W. 
Published: April 2003

AbstractThe nonlinear viscoelastic behavior of glassy polymers and its relationship to ductile yielding is studied by single‐ and double‐step stress relaxation experiments. In the latter case a small stress relaxation step is superimposed on a specimen at an elevated state of temperature or strain. The results show that the changes in the relaxation behaviors in the two cases closely parallel each other. The relaxation behavior at strains near yield closely approximates that at low strain but near Tg. The small strain relaxation response can be described well by a Kohlrausch‐Williams‐Watts (KWW) type function. The interpretation of these data in terms of a coupling model which includes the KWW form is discussed.
NMR Approach to the kinetics of polymer crystallization. II. Polydimethylsiloxane solutions
Authors: Feio G. , Buntinx G. , Cohen‐Addad J. P. 
Published: April 2003

AbstractThe dilution effect on the crystallization kinetics of PDMS/toluene solutions, ranging from a polymer volume fraction of ϕ = 1.00 (pure PDMS) to ϕ = 0.32, was studied using 1H high‐power NMR. Spin‐spin magnetic response was analyzed into relaxation components, arising from the different phases of the semicrystalline sample, through a spin‐echo technique. The intensity and shape of the amorphous component provide relevant information concerning (1) the global crystallization process and (2) the state of hindrance of the amorphous chains induced by the growing crystalline domains. It was shown that, in solutions, the main effect on the crystallization kinetics of changing concentration is to depress the equilibrium melting temperature of the system. However, a radically distinct crystallization rate between the pure and the more concentrated system must be explained in terms of the activation energy for interphase chain transport. Thermodynamic parameters of PDMS crystallites were also deduced from a model. Comparison between the isothermal development of the overall crystallinity and the variation of a characteristic relaxation time of the amorphous PDMS proton response gives an insight into the relative predominance of nucleation or growth rates in the crystallization mechanisms.
Infrared study of phase transitions in thermotropic liquid crystal polyesters
Authors: Benedetti Enzo , Galleschi Franco , Chiellini Emo , Galli Giancarlo , Lenz Robert W. 
Published: April 2003

AbstractThree samples of semiflexible thermotropic liquid‐crystalline polyesters based on mesogenic aromatic triads and a decamethylene spacer have been investigated by IR spectroscopy at various temperatures between room temperature and 290°C. The crystal‐to‐liquid crystal (either nematic or smectic) phase transition was accompanied by fairly strong spectral variations, whereas slight, but significant, changes in the IR profiles were detected at the liquid crystal‐to‐isotropic transition. By comparing the results obtained with the spectral behavior recorded for corresponding structural analogs of low molar mass, it was possible to attribute the spectral variations observed in the polymer samples to a decrease in intermolecular interactions rather than to conformational changes. The thermal transitions indicated by IR spectra were in good agreement with the analogous data obtained by calorimetric or optical microscopy techniques.
The transport of oxygen through oriented poly(ethylene terephthalate)
Authors: Slee J. A. , Orchard G. A. J. , Bower D. I. , Ward I. M. 
Published: April 2003

AbstractThe transport of oxygen through oriented PET at 25 and 60°C has been studied using the dynamic diffusion method. It did not prove possible to determine the diffusion and solubility coefficients with reasonable accuracy, and only the permeability coefficients are discussed in terms of the structure of the samples. The results suggest that the lowering of the oxygen permeability on drawing is related to the production of additional material with the trans conformation of the glycol residue, either in crystallites or in amorphous regions, rather than solely to the overall development of orientation or crystallinity.
Stochastic concepts in the study of size effects in the mechanical strength of highly oriented polymeric materials
Authors: Wagner H. D. 
Published: April 2003

AbstractA study of size effects in the ultimate mechanical properties of crystalline and semicrystalline polymeric materials (fibers, single crystals) is conducted. The concept of size effect and its importance are discussed. A statistical/stochastic approach is adopted and is shown to yield analytical predictions which are at least as accurate as other modeling schemes (mainly based on fracture mechanics theory) previously proposed in the literature. Within this framework, we propose a possible scheme for simultaneous interpretation of both longitudinal (gauge length) and transversal (diameter) size effects, which provides some interesting information regarding the type of flaw population present in a given polymeric material. The statistical scheme used is based on the Poisson/Weibull model, and variants of it, since this model is relatively well established from both physical and experimental viewpoints. Some unsolved problems inherent to the Weibull/weakest link model for failure are discussed, and a new distribution function for the strength of solids is derived. This is illustrated through an analysis of available experimental data for ultrahigh‐molecular‐weight polyethylene, poly‐p‐phenylene terephthalamide (Kevlar), polydiacetylene, and polyoxymethylene. A maximum likelihood approach is used for the first time for interpreting the effect of diameter variability on the mechanical strength of polymeric fibers. We propose a procedure by which the Weibull shape parameter is maximized over a continuous range of values of the size exponent. Finally, we conjecture on the relative roles of defect populations distributed over the boundary and in the bulk.
On the diffusion of gases in partially crystalline polymers
Authors: Horas J. A. , Rizzotto M. G. 
Published: April 2003

AbstractThe diffusion of gases through partially crystalline polymers is studied. The effective diffusion coefficient Deff is obtained as the result of the averaged superposition of two fundamental mechanisms, namely, diffusion through the crystallites is considered to be zero, and diffusion through the rubbery fraction of the polymer obeys a Fujita‐like free‐volume theory. The predicted Deff is compared with experimental data of Kreituss and Frisch. The behavior of the diffusion coefficient in terms of concentration and crystalline fraction is satisfactorily explained through the model.
The effect of plasticization on the transport of gases in and through glassy polymers
Authors: Zhou S. , Stern S. A. 
Published: April 2003

AbstractThe effects of plasticization on the transport of gases and vapors in and through glassy polymers are examined from the viewpoint of the “dual‐mode” sorption model with partial immobilization. The analysis assumes the existence of two penetrant populations with different mobilities in the Henry's law and Langmuir domains of the glassy polymers. These mobilities are characterized by their mutual diffusion coefficients DD and DH. The plasticization of the polymer by penetrant gases is reflected in the concentration dependence of DD and DH. Expressions for the effective (apparent) diffusion and permeability coefficients are derived assuming that DD and DH are exponential functions of the penetrant concentration in the polymers. The results of this study are compared with a similar analysis which assumed the existence of a single mobile penetrant population. The present analysis provides information on the effects of plasticization on the penetrant transport in the Henry's law and Langmuir domains separately. The effects of antiplasticization or clustering of penetrant molecules on the effective diffusion and permeability coefficients are also examined.
Fourier transform infrared study of conformational changes occurring at the yield point in uniaxially drawn polymers
Authors: Xu Z. , Jasse B. , Monnerie L. 
Published: April 2003

AbstractFourier‐transform infrared measurements on atactic and amorphous isotactic polystyrenes have been made during application of strain. On passing through the yield point, spectra indicate an increase of the amount of higher‐energy conformation. In atactic polystyrene it corresponds to an increase of gauche conformations whatever the state may be: pure or plasticized samples, blend with another compatible polymer, or styrene‐acrylonitrile copolymer. In amorphous isotactic polystyrene an increase of higher‐energy trans conformation is observed. These results strongly support the theory developed by Robertson to explain plastic deformation of polymers.
The solution and transport of gases in poly(N‐butyl methacrylate) in the glass transition region. I. Absorption‐desorption measurements
Authors: Stern S. A. , Vakil U. M. , Mauze G. R. 
Published: April 2003

AbstractSolubility coefficients, S, and diffusion coefficients, D, have been determined for ethane and n‐butane in poly(n‐butyl methacrylate) (PnBMA) by the microbalance technique in the temperature range from −14 to 50°C, which encompasses the glass transition of the polymer (22–35°C). S and D for ethane were found to be independent of penetrant pressure and concentration at all temperatures studied No transition to “dual‐mode” sorption behavior, as reported for a number of penetrants in glassy polymers, was observed with ethane, even at the lowest experimental temperature. Plots of log S and log D versus 1‐T, the reciprocal absolute temperature, were linear for the ethane‐PnBMA system and did not exhibit discontinuities in the glass transition region. The above results suggest that the same mechanism of solution and transport of ethane in PnBMA is operative both above and below the glass transition of the polymer under the experimental conditions. This behavior is attributed to the low “excess” free volume of glassy PnBMA, as indicated by the small difference between the coefficients of thermal expansion of this polymer in its rubbery and glassy states. Possible conditions for the appearance of dual‐mode gas sorption are discussed. A similar study with the n‐butane‐PnBMA system showed that the polymer was plasticized by the penetrant below 20°C, due to the higher solubility of n‐butane compared with that of ethane in PnBMA.
The effect of soft‐segment length and concentration on phase separation in segmented polyurethanes
Authors: Petrović Zoran S. , Javni Ivan 
Published: April 2003

AbstractThree series of polyurethanes, based on three polyols, diphenylmethane diisocyanate (MDI), and three chain extenders were synthesized. Polypropylene glycol (PPG) soft‐segment length (MW 1000, 2000, and 3000), soft‐segment concentration (30%, 50%, and 70%), and the type of chain extender (ethylene glycol, butane diol, and hexane diol) were varied and their effect on the amount of phase separation studied. Methods for assessing phase separation quantitatively, based on shifts of the glass transition temperature Tg and the enthalpy jump at the glass transition were tested. It was shown that they give incorrect results, especially with PPG 1000 as the soft segment. Dependence of the soft segment Tg on the polyol length was explained by the “network effect.” True phase mixing was found only with PPG 1000 series at low soft‐segment concentration, whereas, no clear indication of the phase mixing with PPG 2000 and PPG 3000 based polyurethanes was observed.