bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure‐property relationships in a reactively coupled ductile matrix/brittle dispersed phase blend
Authors: Liu T. M. , Xie H. Q. , O'callaghan K. J. , Rudin A. , Baker W. E.
Published: April 2003

Blends of t‐butylaminoethyl methacrylate grafted polyethylene (PE‐g‐tBAEMA) with methyl methacrylate‐methacrylic acid copolymer (PMMA‐MAA) and polymethyl methacrylate (PMMA) were prepared in a Banbury type batch mixer. The effects of component proportions and processing conditions on the melt flow index, morphology, impact, and tensile properties of the resulting polymer blends were investigated. The interfacial chemical reaction was studied using Fourier transform infrared (FTIR) technique. It was observed that the melt index of the blends was reduced with increasing melt processing temperature and mixing time, indicating the formation of PE‐g‐PMMA block copolymer. New IR bands at 1554, 1628, 1800, and 1019 cm−1 were observed only for PE‐g‐tBAEMA/PMMA‐MAA, the reactive blends, but not for PE‐g‐tBAEMA/PMMA, the nonreactive blend. These IR bands were attributed to the amide, carboxylate anion and methacrylimide formation resulting from the chemical reaction between the secondary amine on the PE‐g‐tBAEMA/PMMA moiety and the carboxylic acid on PMMA‐MAA segment. The morphology of the blends in various compositions was examined using scanning electron microscopy (SEM) and related to their mechanical properties. All of the blends have a domain structure whose morphology is strongly dependent on the concentration of the dispersed phase. Furthermore, the PE‐g‐tBAEMA/PMMA‐MAA reactive blends were shown to have much finer morphology than the corresponding nonreactive blends. For the reactive polymer blends consisting of brittle particles dispersed in the ductile matrices, the PE‐g‐tBAEMA/PMMA‐MAA, impact and tensile result higher than predicted by the additivity rule were observed. The toughening of polyethylene by PMMA was explained by a “cold‐drawing” mechanism. The Young's modulus of the blends and the extent of interfacial adhesion were analyzed with Takayanagi and Sato‐Furukawa's theories. © 1993 John Wiley & Sons, Inc.
Modeling of penetrant diffusion in glassy polymers with an integral sorption deborah number
Authors: Wu J. C. , Peppas Nikolaos A.
Published: April 2003

A mathematical model was developed to explain the anomalous penetrant diffusion behavior in glassy polymers. The model equations were derived by using the linear irreversible thermodynamics theory and the kinematic relations in continuum mechanics, showing the coupling between the polymer mechanical behavior and penetrant transport. The Maxwell model was used as the stress–strain constitutive equation, from which the polymer relaxation time was defined. An integral sorption Deborah number was proposed as the ratio of the characteristic relaxation time in the glassy region to the characteristic diffusion time in the swollen region. With this definition, an integral sorption process was characterized by a single Deborah number and the controlling mechanism was identified in terms of the value of the Deborah number. The model equations were two coupled nonlinear differential equations. A finite difference method was developed for solving the model equations. Numerical simulation of integral sorption of penetrants in glassy polymers was performed. The simulation results show that (1) the present model can predict Case II transport behavior as well as the transition from Case II to Fickian diffusion and (2) the integral sorption Deborah number is a major parameter affecting the transition. © 1993 John Wiley & Sons, Inc.
Dilation of poly[1‐(trimethylsilyl)‐1‐propyne] during sorption of n‐nonane
Authors: Witchey‐Lakshmanan L. C. , Hopfenberg H. B. , Chern R. T.
Published: April 2003

The linear expansion and contraction in the principal planar directions of poly[1‐(trimethylsilyl)‐1‐propyne] film were measured concurrently with the sorption of n‐nonane at 35°C. After the first sorption cycle, in which the polymer exhibited markedly nonisotropic volumetric dilation, the polymer expanded and contracted reproducibly during subsequent multiple sorption and desorption cycles. These reversible dilation isotherms were reproducible from sample to sample. The fractional change in length was identical in arbitrarily selected, orthogonal directions in the plane of the film, suggesting that the expansion and dilation of the sample are isotropic. When plotted versus the activity of n‐nonane, the linear expansions in the plane of the film are slightly concave to the activity axis, reaching levels over 10% at the highest activities. The experimental partial specific volume of the polymer is near its pure component value but that of the penetrant is much less than its pure component value. Moreover, the magnitude of dilation observed is described rather closely by the dilation which would result solely from the Henry's law portion of sorption, assuming zero volume‐change of mixing. These results are consistent with the explicit notions of “hole‐filling” associated with the Langmuir mode in the dual‐mode model. © 1993 John Wiley & Sons, Inc.
Spectroscopic studies on the effect of field strength upon the curie transition of a VDF/TrFE copolymer
Authors: Jin Kim Kap , Reynolds Nicholas M. , Ling Hsu Shaw
Published: April 2003

Infrared spectroscopic studies of the effects of field strength upon the ferroelectric phase transition behavior of a VDF/TrFE (75/25) copolymer upon heating and cooling in an electric field have revealed new findings. The paraelectric phase in the absence of an electric field resembles the α phase of PVDF with a trace of short trans sequences distributed randomly along the chain axis. The paraelectric phase in a high electric field is very different from that in the absence of an electric field. The paraelectric phase under an electric field has much longer trans sequences. The Curie transition temperature upon heating is a first‐order transition temperature (T↑c) and is dramatically elevated from 120 to 135°C under the field of more than 0.4 MV/cm. Upon cooling, the paraelectric phase in an electric field does not show a clear transition. The field‐induced phase transition and the loss of dipole switchability observed below a cooling temperature of 120°C, and their dependence on time and filed strength when exposed to a cyclic bipolar electric field are discussed. © 1993 John Wiley & Sons, Inc.
Study of terbium(III)–dextran and terbium(III)–α‐methyl glucoside interactions
Authors: De A. Soares Sandra , Rodrigues Judith F. , Alario Adelaide F.
Published: April 2003

The interaction of dextran with terbium(III) was studied in aqueous solution, pH 3.0–6.6, by fluorescence and optical rotatory dispersion. The polysaccharide enhances Tb(III) fluorescence intensity when the system is excited at the 290‐nm hypersensitive transition (7F6 → 5H4). The dextran rotatory power is decreased in the presence of the metal ion. The results indicate that a 38% maximum of the polymer repeat units are coordinated. Complex formation occurs with displacement of water from the cation coordination sphere by hydroxyl groups at the second and third carbon atoms of the pyranoside ring. As the pH increases, a more asymmetric complex is formed. The α‐methyl glucoside, low molecular weight dextran analogue, interacts with Tb(III) less strongly than dextran. Fluorimetric titrations indicated that the order of binding ability to polysaccharide is Tb(III) > Al(III) > Ca (II). © 1993 John Wiley & Sons, Inc.
Miscibility studies on blends of polycarbonate with syndiotactic polymethyl methacrylate
Authors: Kyu Thein , Ko Che‐Chian , Lim Dong‐Soo , Smith Steven D. , Noda Isao
Published: April 2003

Miscibility of bisphenol‐A polycarbonate (PC) and syndiotactic polymethyle methacrylate (sPMMA) blends was investigated by differential scanning calorimetry (DSC) and small‐angle light scattering. Cloud‐point measurements indicated the existence of both a lower critical solution temperature and an upper critical solution temperature, forming an immiscibility loop. This immiscibility gap was observed for PC blends with sPMMA of various molecular weights ranging from 8,300 to 55,000. The DSC study on solvent‐cast and coprecipitated PC/sPMMA blends from tetrahydrofuran solutions showed a single glass transition, shifting regularly with composition. The annealing of the 50/50 composition within the immiscibility loop exhibited dual glass transitions, but the system reverted to a single phase upon annealing above the loop. Phase dissolution took place during annealing above the loop, followed by thermoxidative branching (cross‐linking) reaction. Dry pellets of PC and sPMMA were melt mixed above the loop in a Mini‐Max mixer/molder; these molded blends exhibited a single phase. © 1993 John Wiley & Sons, Inc.
Computer simulation of crystallization kinetics and morphology in fiber‐reinforced thermoplastic composites. II. Three‐dimensional case
Authors: Mehl Nathan A. , Rebenfeld Ludwig
Published: April 2003

A three‐dimensional computer simulation has been used to predict crystallization kinetics and crystalline morphology in composite materials that are based on crystallizable thermoplastics. Reinforcing fibers in three‐dimensional simulations show similar behavior to those in two‐dimensional simulations; fibers suppress crystallization relative to an unreinforced polymer since they constrain spherulitic growth by an impingement mechanism, and also enhance crystallization by providing added surface nucleation sites. The effects of varying controlling parameters on crystallization kinetics and morphology are qualitatively the same as those observed in the two‐dimensional case. The relative bulk and fiber nucleation denisities, in addition to the fiber volume fraction, fiber diameter, and spherulitic growth rate control the crystallization kinetics and crystalline morphology that develop in reinforced thermoplastic composites. It is more difficult to achieve the transcrystalline morphology in slices of three‐dimensional composites than it is in two‐dimensional composites because nuclei in 3‐D systems are not constrained to positions in or near a 2‐D plane. © 1993 John Wiley & Sons, Inc.
Radiation degradation of poly(methyl methacrylate) in the soft x‐ray region
Authors: Yates Brian W. , Shinozaki Douglas M.
Published: April 2003

The molecular weight distribution change has been measured for the photoresist poly(methyl methacrylate) [PMMA] after in‐vacuo exposure to monochromatic soft x‐rays from the Canadian Synchrotron Radiation Facility [CSRF]. The experimental changes in the mo‐lecular weight distribations derived from gel permeation chromatography [GPC], were compared to a simple Monte Carlo simulation model that assumes random main chain scission. Using this model a scission radiation chemical yield of G(S) = 1.28± 0.10 at room temperature was found to give the best fit at a photon energy of 621 eV. This value is similar to values reported previously in the literature using electron beam and γ‐ray sources, but significantly larger than those reported for fast neutrons, α‐particles, or energetically charged particles. It was found that in this soft x‐ray energy regime, that degradation of PMMA involves primarily a random scission process of the main chain. The results of a least‐squares fit of this soft x‐ray G(S) data and all available literature values from other radiation sources, to the linear energy transfer [LET] dE/dx are discussed. © 1993 John Wiley & Sons, Inc.
Supermolecular morphology of thermoreversible gels formed from homogeneous and heterogeneous solutions
Authors: Prasad A. , Marand H. , Mandelkern L.
Published: April 2003

The supermolecular structures of thermoreversible gels formed from either homogeneous or heterogeneous solutions were examined by scanning electron microscopy. The morphologies of gels of polyethylene and polystyrene of various tacticities were then related to the phase diagram of the polymer–solvent system. We confirmed the morphological findings of Aubert on isotactic polystyrene gels formed either above the binodal or inside the spinodal and extended his study to gels prepared within the metastable region of the phase diagram. For polystyrenes and polyethylene, the morphology of the gels formed inside the coexistence curve differs markedly from that of gels formed outside. Inside the binodal, gels of polyethylene and polystyrenes exhibit remarkable morphological similarities, indicating a common gelation mechanism, namely, liquid‐liquid phase separation. Depending on the concentration, these gels exhibit either an open strut‐like network structure or smooth spherical globules. The former is attributed to gelation inside the spinodal whereas the latter is believed to result from gelation in the metastable region. For crystalline polymers, gels formed inside the coexistence curve subsequently undergo crystallization within their polymer‐rich phase. The morphology of isotactic polystyrene and polyethylene gels formed outside the binodal consists of overlapping lamellar structures, whereas that of atactic and epimerized polystyrene gels is characterized by a sheet‐like structure, differentiating the crystallization‐based mechanism from others. © 1993 John Wiley & Sons, Inc.
The absorption coefficient spectrum and radiation degradation of poly(butene‐1 sulfone) in the soft x‐ray region
Authors: Yates Brian W. , Shinozaki Douglas M. , Kumar Ashok , Meath William J.
Published: April 2003

The interaction of soft x‐rays with poly(butene‐1 sulfone) (PBS) has been examined in detail, using monochromatized synchrotron radiation from the Canadian Synchrotron Radiation Facility (CSRF). The total photoabsorption cross section and neutral fragment yields of poly(butene‐1 sulfone) (PBS) were measured over the photon energy range 20 ≤ hv ≤ 1000 eV. Energy deposition in this energy region results primarily in mass loss due to depolymerization. The chemical byproducts were detected using an in situ mass spectrometer. The experimental absorption data was corrected for spectral contamination of the incident monochromator radiation through the use of calculated photoabsorption cross sections. The calculations incorporated reliable dipole oscillator strength distributions of smaller molecules chemically related to PBS as input, and the results are reliable over the absorption regions away from the edges. The corrections thus applied to the initial experimental data have produced the most reliable spectrum available presently for PBS. The near‐edge extended x‐ray absorption fine structures (NEXAFS) were measured and assigned for the sulfur 2p (L2,3), carbon 1s (K) and oxygen 1s (K) edges. The sulfur 2p edge of PBS was found to be very similar to that found in the photoabsorption spectrum of gaseous SO2, particularly in the continuum region. The two broad peaks in the continuum have been assigned as σ*‐shape resonances caused by a centrifugal potential barrier. Ionization of the valence orbitals of PBS produced a significant increase in the depolymerization reaction, and subsequent neutral yields of sulfur dioxide (SO2) and 1‐butene. © 1993 John Wiley & Sons, Inc.
Melting behavior of poly(ether ether ketone) in its blends with poly(ether imide)
Authors: Chen Hsin‐Lung , Porter Roger S.
Published: April 2003

We detail the melting behavior of poly(ether ether ketone) (PEEK) and investigate its melting behavior in miscible blends with poly(ether imide) (PEI). The determination of the equilibrium melting point (Tm0) of PEEK is discussed by considering its inhomogeneous morphology. Tm0 is obtained by a long extrapolation of a Hoffman–Weeks plot to 384°C. Hindrance of PEEK crystal reorganization induced by PEI during heating is observed over the blend composition investigated (20–75 wt % PEEK). This behavior is correlated with the incorporation of PEI in the interlamellar zones of PEEK crystals. The interaction parameter χ of PEEK/PEI blends is estimated by the equilibrium melting point depression. This gives the interaction density B = −1.2 cal/cm3, and x = −0.40 at 400°C. © 1993 John Wiley & Sons, Inc.
Broadened glass transition in a liquid‐crystalline polymer studied by thermally stimulated currents, AC dielectric, dynamic mechanical, and DSC methods
Authors: Sauer Bryan B. , Dipaolo Nicholas V. , Avakian Peter , Kampert William G. , Starkweather Howard W.
Published: April 2003

Thermally stimulated currents (TSC), a. c. dielectric, dynamic mechanical (DMTA), and differential scanning calorimetry (DSC) methods were used to study the glass transition in a thermotropic liquid‐crystalline copolyester. All the techniques were consistent in the determination of the main glass transition temperature. Using the high sensitivity of the TSC thermal sampling method, it was shown that cooperative glass transition‐like relax‐ations occur down to 100°C below the main glass transition. DSC was sensitive only to a broadening of the glass transition to about ca. 30°C, so it was concluded that the thermal sampling method is sensing a very small fraction of cooperatively relaxing species which cannot be detected by DSC. Ac dielectric measurements and DMTA also indicated that the glass transition was broad, but difficulties with overlapping transitions prevented quantitative determination of the breadth of the glass transition. The results suggest that the broad glass transition, in this mostly amorphous LCP, is due to chemical heterogeneity of the copolyester chain. Other evidence indicates that the broadening is not due to the oriented nature of the glassy state. Some discussion is presented concerning how the heterogeneous nature of the LCP glass leads to compensation of the Arrhenius curves obtained by the thermal sampling method. © 1993 John Wiley & Sons, Inc.
Further EPR studies of molecular motions in polymer/plasticizer mixtures
Authors: Krishnan P. , Le H. , Lee S. H. , Gelerinter E.
Published: April 2003

Molecular motions in mixtures of the side chain polymer—poly(vinyl acetate) and dibuthyl phthalate were studied as a functionof polymer concentration and temperature using the technique of paramagnetic resonance (EPR). When the small spherical probe tempol (TPL) was used, we were able to approximate the observed EPR spectrum with a simulation using a single rotational correlation time τ. The peviously developed Grest–Cohen all‐temperature model matched the Arrhenius polts. The EPR spectra from a cigar‐shaped cholestane (COL) probe could not be adequately matched by single τ simulation when the polymer was at temperatures somewhat above the glass to rubber transition temperature (Tg). Points corresponding to these temperatures were left of the Arrhenius plot and a discontinuity was observed where the gap in the data occurred. As the concentration of plasticizer was increased, we found that the discontinuity became less steep, but the τ at which the gap occurs was always ≈ 10−8. The spectra observed at the temperature region of the gap were approximately 50–50 composites of experimental spectra observed at ± K. In both the TPL and COL cases, there was evidence of the existence of multiple correlation times. Preliminary studies of other polymers, both with and without side chains, also indicated the existence of the gap when COL is used as the probe. © 1993 John Wiley & Sons, Inc.
Short‐range order in noncrystalline polymers examined with spin‐polarized neutrons
Authors: Gabryś Barbara , Schärpf Otto , Peiffer Dennis G.
Published: April 2003

The application of spin‐polarized neutrons with spin polarization analysis to study diffraction patterns from polymers is discussed. The experimental separation of the coherent and incoherent parts of the scattering coupled with the use of the internal standard resulted in the quantitative analysis of the purely coherent scattering from unfunctionalized and functionalized polystyrene in terms of absolute units. This allowed us to model the scattering curves in terms of paracrystallinity. © 1993 John Wiley & Sons, Inc.
Molecular dynamics simulations of the hexagonal structure of crystals with long methylene sequences
Authors: Liang G. L. , Noid D. W. , Sumpter B. G. , Wunderlich B.
Published: April 2003

An unconstrained polymethylene crystal, consisting of 9600 CH2 groups, in which each CH2 is permitted to carry out stretching, bending, and torsional motion, has been studied at various temperatures using molecular dynamics simulations. Information about the atomistic details of the dynamics and structure of these crystals is presented. A significant disorder exists at tempratures well below the melting point. Close to melting, the disordered crystals have about 2% of gauche bonds that are distributed mainly at positions close to the surface of the crystal. The major disorder consists, however, of a collective twisting of the chains leading to a hexagonal crystal structure. The hexagonal structure of the symmetric motifs is caused by a dynamic multidomain arrangement of the chains. © 1993 John Wiley & Sons, Inc.
poly(4,4′‐oxybibenzoate): Polymerization, morphology, transitions, and crystal structures
Authors: Liu J. , Rybnikar F. , East A. J. , Geil P. H.
Published: April 2003

4‐Acetoxy 4′‐carboxy biphenyl has been polymerized from solution, the bulk melt, and in constrained thin films, all below the melting point of the monomer as measured by differential scanning calorimetry (DSC). An isothermal sublimation–recrystallization–melting (and chemical change)–polymerization–crystallization process is proposed. From solution and in the thin films, single crystals consisting of ca. 100 Å thick lamellae are observed, with evidence for monomer addition–reaction on the end (top and bottom) surfaces. The bulk samples are fibrous, the “fibers” consisting of whisker‐like single crystals. The polymer is highly heat and radiation (electron beam) resistant, with numerous successive electron diffraction (ED) patterns from the same crystal or sheared sample permitting comparison of the changes in ED patterns with transitions seen by DSC at ca. 350, 530, and 590°C. Phase I (a = 7.8, b = 5.5, c = 10.8 Å), a possible phase II (a = 15.6, b = 3.6 Å c = unknown), and a phase III (a = 9.0, b = 5.2 = √3a, c = 10.8 Å). Phases I and II are seen in samples polymerized at temperatures at and below 310°C; phase III is observed in samples polymerized at and above 350°C and in sheared samples. © 1993 John Wiley & Sons, Inc.
Structural investigations on lewis acid mediated solubilization of poly(p‐phenylenebenzobisthiazole) in an aprotic solvent
Authors: Venkatasubramanian N. , Polk Malcolm B. , Kumar Satish , Gelbaum Leslie T.
Published: April 2003

Investigations on aluminum chloride‐mediated solubilization of poly(p‐phenylenebenzo‐bisthiazole), PBZT, in nitromethane revealed that, in general, dilute solutions of the polymer prepared in nitromethane with a large molar excess of the Lewis acid with respect to PBZT were relatively stable and thus suitable for processing into films and coatings via regeneration with hydroxylic nosolvents while polymer solutions with minimum stoichiometrically required (PBZT:AlCl3 molar ratio 1:4) or marginal molar excess of AlCl3 relative to PBZT tended to gel during handling. Structural studies on polymer–Lewis acid complex solutions were performed using 1H and 27Al NMR. 1H NMR of the protonated structure of the model compound 2,6‐diphenylbenzo [1,2‐d:4,5‐d′] bisthiazole was useful for confirming the 1H NMR assignments of PBZT‐AlCl3 complex solution in CD3NO2. 27Al NMR was particularly useful in probing the different tetrahedrally coordinated environments of the Al nucleus in the polymer solution, pointing to a complexation interaction between the polymer molecule and the Lewis acid and also between the solvent and the Lewis acid. Direct evidence in the solid state for the presence of a reversible electron donor–acceptor complex (EDA complex) was obtained from FTIR spectra of complexed films, isolated and handled in an inert atmosphere. The structural changes upon PBZT complexation caused significant frequencly shifts in both aromatic as well as heteroring stretching modes relative to PBZT itself, and intensity variations indicative of changes in the resonance configuration between the 1,4‐phenylene moiety and the aromatic heterocyclic ring were also observed upon complexation. A preliminary comparison between the pristine PBZT fibers and regenerated PBZT by dilute solution viscometry indicates that the process results, to some extent, in polymer degradation leading to a decrease in the molecular weight of the polymer © 1993 John Wiley & Sons, Inc.
Molecular dynamics simulations of a poly(p‐phenylene) oligomer
Authors: Socci E. P. , Farmer B. L. , Adams W. W.
Published: April 2003

We have studied the conformation and coefficient of thermal expansion in the poly(p‐phenylene) oligomer p‐sexiphenyl (C36H26) by molecular dynamics simulations. Studies of the backbone phenyl–phenyl torsion angle in a simulated p‐sexiphenyl crystal at room temperature indicate the presence of torsional librations of approximately ±20°. Further analysis of the phenyl–phenyl backbone torsion angle in less closely packed regions of the simulated crystal (crystal ends) indicate the presence of 180° phenyl ring flips, in agreement with solid‐state deuterium NMR data on poly(p‐phenylene oligomers). The linear coefficient of thermal expansion was also calculated and found to be negative, in qualitative agreement with experimental data on rigid‐rod compounds. © 1993 John Wiley & Sons, Inc.
Second harmonic generation and optical anisotropy of a spin‐cast polymer film
Authors: Wang C. H. , Guan H. W.
Published: April 2003

The nonlinear susceptibilities (χ(2)33, χ(2)31), and the refractive index anisotropy, of a main chain accordion polymer, BCSC (see the text for the complete chemical formula), have been measured by the techniques of second harmonic generation (SHG) and waveguiding. A large birefringence, which is induced in the BCSC film by the spin‐coating process, is almost removed by electric field poling. Our results demonstrate the fundamental difference between the birefringence associated with quadrupolar orientational order and the dipolar order associated with SHG. © 1993 John Wiley & Sons, Inc.
Radiation‐induced dielectric loss in hydrocarbon polymers
Authors: Mopsik Frederick I.
Published: April 2003

The dielectric loss of several cables insulated with hydrocarbon polymers has been measured over the frequency range of 10−3–104 Hz at 50° after being subjected to neutron doeses of up to 65 Mrad. The loss data show that a new loss process appears upon irradiation and that the frequencies associated with this loss are not those that are characteristic of those found for the unirradiated polymaric relaxations, ruling out main‐chain motions. This loss seems to be related to dose and is probably due to local dipoles that are formed by the irradiation. It is also shown that the dominant behavior is not due to simple ionic conductivity. © 1993 John Wiley & Sons, Inc.
Effect of oligomers and acrylonitrile content on the interfacial adhesion between PC and SAN
Authors: Janarthanan V. , Stein Richard S. , Garrett Paul D.
Published: April 2003

The interfacial fracture toughness between polycarbonate (PC) and poly(styrene‐co‐acrylonitrile) (SAN) bilayers was measured using an asymmetric double cantilever beam geometry. The effects on fracture toughness of oligomer content and copolymer composition were investigated. Results showed that by removing residual oligomers from SAN, the fracture toughness of the PC/SAN interface was increased significantly. To study this effect in more detail, benzonitrile was used as a model oligomer and added in controlled amounts to pure SAN before attaching to PC and annealing. The PC/SAN interfacial fracture toughness in this case decreased monotonically with increasing benzonitrile content presumably due to migration of the small molecule to the interface. Interfacial toughness was also measured for five purified SAN materials with a range of 17–31 wt % acrylonitrile. A maximum in PC/SAN toughness was seen for a 24 % AN material. Evidence of possible chain scission during fracture in purified SAN and PC was observed from x‐ray photoelectron spectroscopy measurements. Optical microscopy showed that a single craze ahead of the crack is a possible failure mode during fracture of the SAN/PC interface. © 1993 John Wiley & Sons, Inc.
Influence of the crystalline phase on the molecular mobility of PVDF
Authors: Teyssedre G. , Bernes A. , Lacabanne C.
Published: April 2003

Dielectric relaxation and pyrocurrent of PVDF were studied by thermostimulated current spectroscopy. The transition spectrum of the material was investigated by differential scanning calorimetry. Two well‐resolved relaxation peaks have been observed in the temperature range [−100–100°C]. The molecular mechanisms of these phenomena have been discussed, based on a comparative study of α‐PVDF. and β‐PVDF. The β relaxation mode is located at −41°C in α‐PVDF and is slightly shifted toward higher temperatures in the stretched material. This mode has been ascribed to the dielectric manifestation of the glass transition (Tg) of PVDF. It is comprised of two components corresponding to the free and constrained amorphous phases, respectively, in the order of increasing temperatures. The αc transition/relaxation has been associated with molecular motions in the crystalline/amorphous interphase. At higher temperatures, a compensation phenomenon corresponding to cooperative movements liberated at the Curie transition has been observed in β‐PVDF. © 1993 John Wiley & Sons, Inc.
Water‐induced micellar structures of block copoly(oxyethylene‐oxypropylene‐oxyethylene) in o‐xylene
Authors: Wu Guangwei , Zhou Zukang , Chu Benjamin
Published: April 2003

We previously reported the water‐induced micelle formation of copoly(oxyethylene‐oxy‐propylene‐oxyethylene), Pluronic L64, in o‐xylene. The micellar properties could be controlled by varying the water to EO ratio (Z) in micelles. in micelles. In this paper, laser light scattering, transient electric birefringence (TEB), and synchrotron small‐angle x‐ray scattering (SAXS) were used to study the micellar structure at different Z values. Both TEB and SAXS results further confirmed the micellar shape transition from that of a sphere to a nonspherical shape. A comparison between TEB and dynamic light‐scattering results as well as the SAXS experiments showed an ellipsoidal shape for micelles when Z > 1.3 with the oblate being the more reasonable form for fitting all the experimental parameters. The degree of asymmetry appeared to be not high. © 1993 John Wiley & Sons, Inc.
Model experiments for the interfacial reaction between polymers during reactive polymer blending
Authors: Scott Chris , Macosko Chris
Published: April 2003

Bilayer film Fourier transform infrared (FTIR) model experiments are designed to provide a well‐defined interface for study which can be probed by infrared spectroscopy during the interdiffusion and reaction of two reactive polymers. This provides a model experiment to determine the kinetics and extent of reaction between functionalized polymers during reactive polymer blending. This type of experiment provides data on the reaction at a stagnant interface which is necessary for the analysis of the interface while it is simultaneously undergoing deformation. It is also useful as a screening or preliminary experiment on reactive blending systems in that the extent of reaction may be followed for different systems at different temperatures. Experiments reported here trace the reaction of a styrene–maleic anhydride copolymer with two different amine terminated polymers. Results are obtained for the interdiffusion and reaction of a styrene‐maleic anhydride copolymer with two amine terminated polymers: a butadiene‐acrylonitrile copolymer and Nylon 11. The kinetics from these experiments include contributions due to both interdiffusion and chemical reaction. The chemical reaction kinetics may be isolated from the diffusion kinetics by performing experiments on well‐mixed systems which are prepared by casting films of the polymer mixtures from a mutual solvent. © 1994 John Wiley & Sons, Inc.
Effects of solvent and electrolyte on the electrochromic behavior and degradation of chemically prepared polyaniline‐poly(vinyl alcohol) composite films
Authors: Morita Mitsuyuki
Published: April 2003

Effects of solvent and electrolyte on the electrochromic behavior and degradation of polyaniline in nonaqueous aprotic media, as well as its electrochemical redox and degradation mechanisms, were investigated with chemically prepared polyaniline‐poly (vinyl alcohol) composite films and polyaniline homogeneous films. Visible and FT‐IR absorption spectra of the polyaniline films, oxidized electrochemically at various polarization potentials, showed that the mechanisms in aprotic media involved two successive oxidation processes. In contrast to aqueous systems, the higher oxidation process involved further anion insertion without deprotonation, and the degradation was due to partial formation of the electrochemically inactive quinonediimine structure at excessive polarization potentials. From investigations of solvent and electrolyte effects, it is suggested that the electrochromic behavior and degradation of polyaniline are influenced by the electron‐donating and accepting ability of solvents, acceptor strength of electrolyte cations, and the nucleophilic character of electrolyte anions. It was also suggested that some anions like $\[ PF_6^ - , BF_4^ - , \] and $
$\[ CIO_4^ - , \] $
as well as protons, are constrained in the PVA matrix by specific electrostatic interactions and steric effects to improve the stability of polyaniline in the highly oxidized state. © 1994 John Wiley & Sons, Inc.
Mechanical properties of unsaturated polyester resins in relation to their chemical structure. I. Secondary relaxations and local motions
Authors: Melot D. , Escaig B. , Lefebvre J. M. , Eustache R. P. , Lauprêtre F.
Published: April 2003

Dynamic mechanical spectroscopy has been combined with high‐resolution solid‐state 13C NMR to characterize the molecular motions responsible for the γ and β secondary relaxations in unsaturated polyester networks. In DEG networks the 7γ transition is assigned to restricted phenyl group rotation in the styrene cross‐links whereas the motion of molecular groups in the vicinity of the residual maleic double bonds account for the β transition. © 1994 John Wiley & Sons, Inc.
Short branch effects on the creep properties of the ultra‐high strength polyethylene fibers
Authors: Ohta Yasuo , Sugiyama Hiroshige , Yasuda Hiroshi
Published: April 2003

Short branch (methyl branch) effects on the creep properties of the ultra‐high strength polyethylene fibers were investigated. The temperature and the stress dependence of creep rates of several high‐strength polyethylene fibers having different branch contents, which were prepared by blending of two polymers of highly and less branching, was evaluated according to a model described by Ward and Wilding, and the activation energies and the activation volumes were calculated in terms of their methyl branch contents and tensile moduli. The creep rates of ultra high strength fibers are strongly influenced by their methyl branch contents. The typical branching sample with ca.6 CH3 units per 1000 CH2 units shows ca. 1/20 lower creep rate than that of the less branching (1.0 CH3 per 1000 CH2) fiber sample at the room temperature. The activation energies of creep rate obtained by those highly branching samples are higher than those of lesser branching samples; the difference is nearly proportioal to their branch contents. Wide‐angle x‐ray diffraction results showed that the dimension of a‐axis of unit cell increases in proportion to their branch contents. These results imply that the creep mechanism of ultra‐high strength polyethylene fibers is dominated by chain slippage in the crystalline part, and also imply that some amount of methyl branch sites can be incorporated in the crystalline part in proportion to the branch content and those incorporated branch sites hinder the slippage motion of molecular chains in crystalline part, which results in the extreme lower creep rate. © 1994 John Wiley & Sons, Inc.
Experimental study of molecular entanglement in polymer networks
Authors: Gent A. N. , Liu G. L. , Mazurek M.
Published: April 2003

Elastomeric molecular networks have been prepared by endlinking polydimethyl siloxane molecules having functional chain ends, both in the presence of an unreactive polymeric diluent and in the undiluted state. Values of tensile (Young) modulus were found to be in good agreement with the simple molecular theory of rubberlike elasticity for networks prepared in a highly diluted state. For concentrated systems the modulus was anomalously high, however. The discrepancy can be attributed to chain entanglements. A second interpenetrating network was introduced into networks formed in the diluted state by replacing the diluent polymer by reactive polymer, which was then gelled in situ. The modulus of these combined networks was much higher than the sum of the moduli of the constituent networks, implying a large contribution from molecular entanglements. © 1994 John Wiley & Sons, Inc.
Effects of an electrostatic field on crystallization of poly(vinylidene fluoride)
Authors: Sajkiewicz Pawel
Published: April 2003

Melt crystallization of poly(vinylidene fluoride) (PVF2) under a static electric field was studied by optical microscopy. For most crystallization temperatures a mixture of α and γ spherulites was obtained. The growth rate of the spherulites was measured in the plane perpendicular to the direction of the field. The effect of an electric field on the growth rate of the γ spherulites corresponds in a qualitative way with the dependence predicted theoretically for the primary nucleation of the nonpolar form. It is shown, that the growth rate of γ spherulites is always reduced by the electric field. This reduction was larger the lower the undercooling. In the case of γ spherulites the interpretation of the results is more complicated. Both the morphology and the growth rate of γ spherulites under an electric field depend on electrode configuration. An increase of the growth rate of γ spherulites in an electric field was detected only when the sample was in direct contact with both electrodes. Under these circumstances, γ spherulites nucleate and grow at the PVF2‐positive electrode interface; and the increase of the growth rate is higher the lower the undercooling, and is greater in comparison with the decrease found for the nonpolar α phase. The reason for the sensitivity of the morphology of the γ form to the electrode configuration is not completely clear. © 1994 John Wiley & Sons, Inc.
Roll‐Casting of block copolymers and of block copolymer‐homopolymer blends
Authors: Albalak Ramon J. , Thomas Edwin L.
Published: April 2003

An improved technique for casting highly oriented films of block copolymers from solutions subjected to flow is presented. Polymer solutions were rolled between two counter‐rotating adjacent cylinders while at the same time the solvent was allowed to evaporate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. Using this method known as ‘roll‐casting’ we present in this paper a study of the morphology of polystyrene‐polybutadiene‐polystyrene (PS/PB/PS) triblock copolymer cast with and without additional high molecular weight homopolymers. The pure copolymer films consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix in a near single‐crystal structure. Blends of copolymer with high molecular weight polystyrene and/or polybutadiene, phase separated into ellipsoidal regions of homopolymer embedded in an oriented block copolymer matrix. Annealing the films resulted in conversion of the homopolymer regions to spheres accompanied by some misalignment of the copolymer microdomains. The morphology of these films as revealed by TEM is discussed. A brief discussion of the flow field that develops in the experimental system is also presented and its similarity to the flow field of our previous work is shown. © 1994 John Wiley & Sons, Inc.
FTIR and X‐ray study of polymorphs of nylon 11 and relation to ferroelectricity
Authors: Balizer E. , Fedderly J. , Haught D. , Dickens B. , Dereggi A. S.
Published: April 2003

Nylon‐11 polymorphs have been studied by x‐ray diffraction and by infrared spectroscopy. A γ or γ‐like phase of Nylon‐11 was produced by treating the metastable δ' phase with gaseous HCl or DCl and then exposing the resulting complex (amidonium salt) to 100% RH H2O or D2O vapor. An oriented form of the γ or γ‐like phase results from treatment of the oriented δ' phase, but stretching of the unoriented γ or γ‐like phase, obtained by treatment of the unoriented δ' phase, induces a transformation to the α phase stable at room temperature. The use of DCl and D2O produced highly deuterated samples with Fermi resonances indicating the relative strengths of the hydrogen bonds are weakest in the α phase, intermediate in the δ' phase and strongest in the γ or γ‐like phase. © 1994 John Wiley & Sons, Inc.
Toughening of a highly cross‐linked epoxy resin by reactive blending with bisphenol A polycarbonate. I. FTIR spectroscopy
Authors: Abbate M. , Martuscelli E. , Musto P. , Ragosta G. , Scarinzi G.
Published: April 2003

A highly cross‐linked thermosetting epoxy resin was modified by a reactive blending process carried out in the presence of bisphenol A polycarbonate (PC). Prior to the curing process the PC component was dissolved at high temperature in the uncured epoxy matrix. FTIR investigation of this reactive mixture demonstrated the occurrence of physical and chemical interactions among the blend components. Isothermal kinetic measurements performed by FTIR spectroscopy showed that the presence of PC does not affect the overall curing mechanism but decreases both the initial reaction rate and the final conversion of reactants. © 1994 John Wiley & Sons, Inc.
The effect of thermal annealing on the thermal properties and molecular weight of a segmented polyurethane copolymer
Authors: Hu Wenchun , Koberstein J. T.
Published: April 2003

The influence of thermal annealing on molecular weight, microphase mixing, and multiple melting behavior of a segmented block copolyurethane is reported. The material studied contained 55% of hard segment consisting of 4,4'‐diphenylmethane diisocyanate and butanediol, and a poly (propylene oxide) diol of molecular weight 2000 as the soft segment. The thermal stability of the materials was influenced greatly by the order‐disorder transition, estimated to occur at ca. 191°C. Upon annealing above this temperature, molecular weight increased rapidly as a result of chain branching reactions. Microphase separation increased under these conditions, while the degree of hard segment crystallinity decreased. Annealing below the order‐disorder transition temperature resulted in relatively small molecular weight increases for short annealing times, but large increases for annealing times greater than one hour. Glass transition temperature data for these thermal treatments was consistent with upper critical solution temperature behavior and selective solubility by hard segment sequence length according to the Koberstein‐Stein hard microdomain model. The critical hard segment sequence for segregation was estimated (for 30 min annealing) to contain ca. 5 diisocyanate residues at 80°C, ca. 8 residues at 185°C, and increased slowly with annealing time. © 1994 John Wiley & Sons, Inc.
Electrical relaxation in in situ dried acid‐form nafion
Authors: Fontanella J. J. , Mclin M. G. , Wintersgill M. C.
Published: April 2003

Electrical relaxation studies have been carried out on dried, acid‐form Nafion 117 (copolymer of tetrafluoroethylene and perfluoro 3,6‐dioxa‐4‐methyl‐7‐octenesulfonic acid and which has an equivalent weight of 1100). Significant electrical conductivity is found and the data are found to be non‐Arrhenius. The results are converted to the electrical modulus representation and a conductivity relaxation is observed. A stretched exponential is best‐fit to the conductivity relaxation and again, non‐Arrhenius behavior is observed for the peak position. Finally, at low temperatures, a new dielectric relaxation peak is found which has an activation enthalpy of about 0.57 eV (13 kcal/mol). This relaxation is analogous to the γ‐relaxation observed in mechanical relaxation studies. © 1994 John Wiley & Sons, Inc.
Physical aging studies in epoxy resins. I. Kinetics of the enthalpy relaxation process in a fully cured epoxy resin
Authors: Montserrat S.
Published: April 2003

The physical aging of an epoxy resin based on diglycidyl ether of bisphenol‐A cured by a hardener derived from phthalic anhydride has been studied by differential scanning calorimetry. The isothermal curing of the epoxy resin was carried out in one step at 130°C for 8 h, obtaining a fully cured resin whose glass transition was at 98.9°C. Samples were aged at temperatures between 50 and 100°C for periods of time from 15 min to a maximum of 1680 h. The extent of physical aging has been measured by the area of the endothermic peak which appears below and within the glass transition region. The enthalpy relaxation was found to increase gradually with aging time to a limiting value where structural equilibrium is reached. However, this structural equilibrium was reached experimentally only at an aging temperature of Tg‐10°C. The kinetics of enthalpy relaxation was analysed in terms of the effective relaxation time τeff. The rate of relaxation of the system given by 1/τeff decreases as the system approaches equilibrium, as the enthalpy relaxation tends to its limiting value. Single phenomenological approaches were applied to enthalpy relaxation data. Assuming a separate dependence of temperature and structure on τ, three characteristic parameters of the enthalpic relaxation process were obtained (In A = −333, EH = 1020 kJ/mol, C = 2.1 g/J). Comparisons with experimental data show some discrepancies at aging temperatures of 50 and 60°C, where sub‐Tg peaks appears. These discrepancies probably arise from the fact that the model assumes a single relaxation time. A better fit to aging data was obtained when a Williams‐Watts function was applied. The values of the nonexponential parameter β were slightly dependent on temperature, and the characteristic time was found to decrease with temperature. © 1994 John Wiley & Sons, Inc.
Physical aging and dye diffusion in polysulfone below the glass transition temperature
Authors: Zhang X. Q. , Wang C. H.
Published: April 2003

The effect of physical aging on the tracer diffusion coefficient D of camphorquinone in polysulfone is investigated. It is shown that if the sample is sufficiently annealed and physical aging is nearly complete, the temperature dependence of D will reflect the primary α‐relaxation process of the host polymer. In the temperature range between Tg (=185°C) and 165°C, D is found to be a function of time, and the time dependence of D is given by D = At−μ, with μ approximately equal to unity. © 1994 John Wiley & Sons, Inc.
Preparation of small poly(butylene terephthalate) spheres by crystallization from solution
Authors: Nichols Mark E. , Robertson Richard E.
Published: April 2003

The crystallization of poly(butylene terephthalate) (PBT) from moderately dilute solutions of PBT in a diglycidyl ether of bisphenol‐A epoxy has been investigated. PBT dissolves in this epoxy approximately 35°C below its usual melting temperature of 227°C to form a one‐phase solution. Cooling this solution below 165°C leads to rapid crystallization of the PBT. The resulting mixture of liquid epoxy and crystalline PBT has a low viscosity and contains highly birefringent, individual PBT spherulites. The PBT spherulites have a narrow size distribution and a high surface‐to‐volume ratio. These particles are suggested to arise from a rapid crystallization that follows liquid–liquid phase separation. © 1994 John Wiley & Sons, Inc.