bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and properties of aromatic polyimides from 2,2′‐bis(p‐aminophenoxy)biphenyl or 2,2′‐bis)p‐aminophenoxy)‐1,1′‐binaphthyl and aromatic tetracarboxylic dianhydrides
Authors: Liou Guey‐Sheng , Maruyama Masaki , Kakimoto Masa‐Aki , Imai Yoshio
Published: April 2003

New aromatic polyimides containing a biphenyl‐2,2′‐diyl or 1,1′‐binaphthyl‐2,2′‐diyl unit were prepared by a conventional two‐step method starting from 2,2′‐bis(p‐aminophenoxy) biphenyl or 2,2′‐bis(p‐aminophenoxy)‐1,1′‐binaphthyl and aromatic tetracarboxylic dianhydrides. The polyimides having inherent viscosities of 0.69–0.99 and 0.51–0.59 dL/g, respectively, were obtained. Some of these polymers were readily soluble in a variety of organic solvents including N,N‐dimethylacetamide (DMAc), N‐methyl‐2‐pyrrolidone (NMP), dimethyl sulfoxide, and pyridine. Transparent, flexible, and pale yellow to brown films of these polymers could be cast from the DMAc or NMP polyamic acid solutions. These aromatic polyimides containing biphenyl and binaphthyl units had glass transition temperatures in the range of 200–235 and 286–358°C, respectively. They began to lose weight around 380°C, with 10% weight loss being recorded at about 470°C in air. © 1993 John Wiley & Sons, Inc.
Polymeric organosilicon systems. XVII. Synthesis and photochemical and conducting properties of poly[o‐and m‐(disilanylene)phenylene]s
Authors: Ishikawa Mitsuo , Sakamoto Hiromu , Ishii Michie , Ohshita Joji
Published: April 2003

Poly[o‐(tetramethyldisilanylene)phenylene] (2a), poly[o‐(1,2‐dimethyldiphenyldisilanylene)‐phenylene] (2b), poly[m‐(tetramethyldisilanylene)phenylene] (2c), and poly[m‐(1,2‐dimethyldiphenyldisilanylene)phenylene] (2d) were prepared by the sodium condensation reaction of the corresponding 1,2‐and 1,3‐bis (chlorosilyl)benzenes in toluene. Irradiation of thin films of 2a‐2d in air resulted in a rapid decrease of absorption maxima in the ultraviolet region. The photolysis of 2b and 2d in benzene afforded photodegradation products with low molecular weights. When thin films of 2b and 2d were doped with antimony pentafluoride vapor, films which have conductivities of semi‐conductor level were obtained. © 1993 John Wiley & Sons, Inc.
Surface fixation of poly(ethylene glycol)via photodimerization of cinnamate group
Authors: Nakayama Yasuhide , Matsuda Takehisa
Published: April 2003

This article reports a new fixation method for hydrophilic layers on substrates. The method is based on the photochemistry of the cinnamate group, which is capable of intermolecular dimerization upon ultraviolet (UV) light irradiation. The method used was as follows. First, two photoreactive polymers were sequentially coated on a polymeric surface: a polycinnamate as an adhesive layer and a cinnamated poly(ethylene glycol) (PEG) as a hydrophilic layer. Subsequently the surface was exposed to UV light. No delamination occurred upon washing with water and methanol; the photoreactive PEG was chemically bonded onto the surface via the polycinnamate. The higher the molecular weight of PEG, the higher the wettability of the surface was formed. Minimal cell adhesion was observed on such a surface. The biomedical applications of the method are discussed. © 1993 John Wiley & Sons, Inc.
Electrical dc conductivity in iodine‐doped pseudo‐IPNs of conjugated polymer network (C‐PDMS/L‐P4BCMU)
Authors: Frisch Harry L. , Chen Xiaomeng
Published: April 2003

We have prepared pseudo‐IPNs (PIPN) of crosslinked PDMS and linear P4BCMU and characterized them by DSC and SEM. The proposed theory about electrical hopping conduction along the linear chain is supported by the observed electrical conductivity properties of these IPNs of conjugated linear polymers. We also studied the low‐temperature (T) DC conductivity of the single‐phase PIPN and these showed a change from minus to plus in dσ/dt below 120 K. At 4 K, σ was about seven times larger than at 120 K. This reversal is not shown by the bulk polymers composing these PIPNs and polymer blends of linear conjugated polymer in linear insulating host polymer. We speculate that this may indicate some degree of quantum coherence in σ of the one‐dimensional pseudo‐ PIPNs. © 1993 John Wiley & Sons, Inc.
Model studies on the structure of poly(amide oxime)s and their cyclodehydration reactions leading to poly(1,2,4‐oxadiazole)s
Authors: Jung Jin Chul , Park Sang‐Bong
Published: April 2003

To obtain an understanding of the low molecular weight character of wholly aromatic poly(1,4‐arylene acyldiamide oxime)s (PAAs) having n‐alkyloxymethyl side braches and the additional decrease in molecular weight during their cyclodehydration reaction leading to the corresponding poly(1,4‐arylene‐1,2,4‐oxadiazole)s (PAOs), tautomeric structures of poly[1,4‐phenylene‐2,5‐bis(n‐octyloxymethyl)terephthaldiamide oxime] (C8‐PAA) were 1H‐NMR‐spectroscopically investigated by using two model compounds: O,O'‐dibenzoyl terephthaldiamide oxime (H‐PAA‐M, 4) and O,O'‐dibenzoyl‐2,5‐bis(n‐octyloxymethyl) terephthaldiamide oxime (C8‐PAA‐M, 5). In solution H‐PAA‐M existed exclusively as oximino isomer, while C8‐PAA‐M consisted only of imino tautomer and C8‐PAA contained both the oximino and imino form, the former being dominant in composition. It was found that the presence of imino tautomer caused serious effects both on the low molecular weight character of C8‐PAA and on the additional decrease in molecular weight during thermal cyclodehydration to C8‐PAO, whereas the presence of oximino tautomer showed practically little effect. A discussion on the results is provided from mechanistic viewpoint. © 1993 John Wiley & Sons, Inc.
The conformational effect of form I helical poly(L‐proline) and form II helical poly(L‐proline) to the complex formation with helical poly(L‐glutamic acid) through hydrogen bonding
Authors: Jung Jaechang , Kim Hyun Don , Ree Taikyue , Jhon Mu Shik
Published: April 2003

The complex formation between helical poly‐L‐glutamic acid (PLGA) and helical poly‐L‐proline (PLP) was studied in a methanol‐water (2 : 1) cosolvent and a propanol‐water cosolvent (9 : 1). Reduced viscosity, circular dichroism, pH, and molar absorptivity were measured. The experimental results exhibit that the interpolymer complex was formed between helical PLGA and helical PLP through hydrogen bonding. When the complex was formed the unit mole ratio of PLGA : PLP(II) is 2 : 1 and PLGA : PLP(I) is 1.5 : 1, the ability of complex formation of PLP (II) with PLGA is better than that of PLP(I). On complexation the conformations of PLGA and PLP change and this change is more enhanced in the PLGA‐PLP(II) than the PLGA‐PLP(I) complex; its cause is studied. © 1993 John Wiley & Sons, Inc.
Polymerization of 2‐(substituted methyl)acrylate bearing ω‐methoxyoligoethyleneoxy groups as side chains to new low Tg polymer
Authors: Yamada Bunichiro , Kobatake Seiya , Aoki Shuzo
Published: April 2003

The polymerization of methyl 2‐(ω‐methoxyoligoethleneoxymethyl)acrylates, which were synthesized from reactions of methyl 2‐bromomethylacrylate with ω‐methoxyoligoethylene glycol, was investigated. All these monomers polymerized readily to high molecular weight despite expectation of the considerable steric hindrance against propagation. No influence of ceiling temperature was observed. The 2‐(2‐methoxyethyleneoxymethyl)acrylate exhibited similar reactivities to methyl 2‐alkoxymethylacrylate reported previously in copolymerization with styrene and methyl methacrylate. The homopolymers synthesized, except for those from methyl 2‐methoxymethyl‐ and 2‐(2‐methoxyethyleneoxymethyl)acrylates, were soluble in water, and all were soluble in benzene. These polymers were thermally less stable than poly(methyl methacrylate) as confirmed by thermogravimetric analysis, and all showed glass transition temperatures below 0°C. © 1993 John Wiley & Sons, Inc.
Synthesis and properties of new crystalline poly(arylene ether nitriles)
Authors: Matsuo Shigeru , Murakami Tomoyoshi , Takasawa Ryuichi
Published: April 2003

Crystalline poly(arylene ether nitrile) could be prepared by the polycondensation of 2,6‐dihalobenzonitrile with resorcinol at 200°C in N‐methylpyrrolidone in the presence of sodium carbonate. A reaction temperature of at least 200°C was necessary to attain high molecular weight polymer. Spectral data indicated that the polymer had the structure of a poly(meta‐phenylene ether) with pendent nitrile groups on every other phenylene unit. Despite this structure, the crystallinity and the crystallization rate of the polymer were greater than those of the corresponding polymer with a para‐linked structure. The glass transition temperature and the melting temperature of the polymer were almost the same as those of poly(etheretherketone) (PEEKTM). A series of other new poly(arylene ether nitriles) were also examined. The polymers derived from 4,4′‐biphenol, dihydroxytetra‐phenylmethane, dihydroxydiphenylsulfone, and 1,5‐isoquinolinediol had high glass transition temperatures. The poly(arylene ether nitriles) exhibited excellent tensile strength compared with the corresponding ketone‐ or sulfone‐containing polymers. Comparing the three different kinds of polymers containing the same bisphenol units, the order of glass transition temperature was found to be sulfone‐ > nitrile‐ > ketone‐containing polymers, while the order of tensile strength was nitrile‐ > ketone‐ > sulfone‐containing polymers. The excellent mechanical properties are attributable to dipole‐dipole interactions of nitrile groups. © 1993 John Wiley & Sons, Inc.
Co‐ and terpolymerization of ethylene with 1‐butene and 1‐decene by using Cp2ZrCl2‐methylaluminoxane catalyst
Authors: Seppälä J. V. , Koivumäki J. , Liu X.
Published: April 2003

Copolymerizations of ethylene/1‐butene, and ethylene/1‐decene and terpolymerization of ethylene/1‐butene/1‐decene were carried out in n‐heptane with various concentrations of comonomer in the feed. Cp2ZrCl2‐methylaluminoxane (MAO) was used as catalyst. When comonomers were added into the ethylene polymerization, the activity of the catalyst increased significantly and continued to do so as the concentration of the comonomer was increased. At the same time as the comonomer concentration and catalyst activity increased, the molecular weight and crystallinity of the polymers decreased. An important reason for the activity enhancement may, therefore, be that the comonomer takes part in the activation of catalytic centers, decreasing the activation energy required for monomer to insert into the active centers. Use of Cp2ZrCl2‐MAO catalyst allowed the preparation of ethylene/1‐decene copolymers containing 20 wt % of 1‐decene. © 1993 John Wiley & Sons, Inc.
A kinetic model for steric hindrance effects on quaternization of poly(vinylpyridines)
Authors: Hu Guo‐Hua , Wang Wei
Published: April 2003

Quaternization reactions of poly(vinylpyridines) with alkyl halides show retardation in excess of that predicted by the classical second‐order kinetics. Based on the classical collision and transition state theories, a kinetic model has been developed to quantify such retardation, in which the overall reaction rate is characterized by a rate constant k0 of the intrinsic reactivity between a pyridyl group and an alkyl halide group, and by a steric hindrance effect parameter α. The latter accounts for the degree to which the rate of collisions of reactants is reduced, or to which the freedom of movement of the reactants in the transition state is restricted as the reaction proceeds. The resulting kinetic expression has been validated using experimental results reported in the literature and those of our own. The functional dependence of k0 and α values on the nature of poly(vinylpyridines) and that of alkyl halides is explained. Other factors affecting k0 and α, including changes in macromolecular dimensions and/or in the distribution of residue environment, quality of solvent, and reaction temperature, are discussed. © 1993 John Wiley & Sons, Inc.
The effect of adsorbed water on the dielectric properties of CaCO3 filled polyethylene composites
Authors: Banhegyi G. , Karasz F. E.
Published: April 2003

The dielectric dispersion and loss of a polyethylene–CaCO3 composite have been investigated in the 50 Hz–100 kHz frequency and 20–140°C temperature ranges, and compared with those for a normal mechanical mixture. The different theoretical interpretations are reviewed and compared with the data. The observed dispersion and loss are probably due to adsorbed water at the PE‐CaCO3 interface; both disappear on heating. The high‐frequency permitivities can be well approximated by theoretical models, but the frequency‐dependent phenomena cannot be interpreted in terms of a simple interfacial polarization mechanism. The universal response theory provides a useful tool for interpreting the measurements.
Mechanical relaxation mechanism of epoxide resins cured with acid anhydrides. II. Effect of the chemical structure of the anhydrides on the β relaxation mechanism
Authors: Ochi Mitsukazu , Iesako Hiroshi , Nakajima Shin , Shimbo Masaki
Published: April 2003

The mechanism of low‐temperature mechanical relaxation of acid‐anhydride‐cured epoxide resins has been investigated in detail. One mechanical relaxation, denoted as the β relaxation, is observed from −80 to −50°C for all epoxide resin systems cured with aromatic, alicyclic, and aliphatic anhydrides. The β relaxation increases in peak height and shifts to higher temperature with increasing molecular volume of the diester segments formed by the reaction of acid anhydrides. From these results, it is concluded that the β relaxation for anhydridecured systems is due to the motion of the diester segment, and that the intensity and peak position of the β relaxation depend on the molecular volume of this segment. Moreover, it was shown that the tensile impact strength of the anhydride‐cured systems is governed by the intensity of the β relaxation of these systems when the parameters Tg and v of these systems are nearly constant.
Phase separation temperatures in the ternary system polystyrene/poly(α‐methyl styrene)/cyclopentane
Authors: Saeki S. , Tsubotani S. , Kominami H. , Tsubokawa M. , Yamaguchi T.
Published: April 2003

Phase separation temperatures of the ternary system polystyrene (PS) (Mw = 1.67 × 104)/poly(α‐methyl styrene) (PαMS) (Mw = 9.0 × 104)/cyclopentane with a blend ratio PS/PαMS = 55/45 have been determined over the polymer concentration range 0.02 ≤ ψPS + PαMS ≤ 0.52, where ψ PS + PαMS is the segment fraction of polymer in ternary system. Phase separation temperatures for the upper critical separation in the ternary system decrease with increasing ψ PS + PαMS over the range 0.1 ≤ ψ PS + PαMS ≤ 0.52. The vapor—liquid equilibrium in this system with a blend ratio PS/PαMS=50/50 has been determined over the concentration range 0.925 ≤ ψPS + PαMS < 0.995 and the temperature range 60–100°C by the piezoelectric vapor sorption method. The polymer—polymer interaction parameters χ′12 determined are positive except at 100°C and increase with increasing ψ PS + PαMS. Values of χ′12 extrapolated to zero solvent concentration are positive (0.0–1.3) over the temperature range measured. Phase separation behavior is discussed in terms of phase separation temperature in a ternary system and the polymer–polymer interaction parameter.
Experimental criterion for the crystallization regime in polymer crystals grown from dilute solution: Possible limitation due to fractionation
Authors: Point J. J. , Colet M. Ch. , Dosiere M.
Published: April 2003

By integration of equations previously derived by Frank, the growth rate of polymer crystals is shown to be dependent on their size, provided that the persistence length Lp or the kinetic length Lk = (2g/i)1/2 are significantly larger than the primary nucleus. A new method of decorating the fold surface (isochronous decoration) allows the measurement of the quasi‐instantaneous growth rate of very small crystals obtained from dilute xylene solution of a sharp polyethylene fraction of moderate molecular weight (Mw = 17,000, Mw/Mn = 1.11). Although the theory predicts that the growth rate increases with the size of the crystals as long as its dimension is smaller than the persistence length and/or the kinetic length, such an increase is not observed experimentally with the sharp PE fraction presently used. Therefore it appears that both the kinetic length and the (hypothetical) persistence length are beyond the resolution limit of electron microscopy and that crystallization occurs in the polynucleation regime. An upper bound is obtained for the rate g at which a locally new layer spreads in two directions on the substrate. The rate is lower than is estimated by the commonly Accepted theories. These theories lead also to an abnormally high value for the lateral surface free energy. The possibility that the observed initial linearity of the growth‐rate curve may results from a balance of opposite effects (an increase with the size of the crystals on the one hand, a decrease with decreasing concentration and possible fractionation on the other) is thoroughly examined and ruled out. In fact, it must be stressed that at the early beginning of crystallization, negligible parts of the sample are crystallized and it is only at the end of crystallization that these effects appear. The fall in the growth rate as crystallization ends is due neither to progressive exhaustion of the solution alone nor to a depletion of the concentration by diffusion for this sharp fraction of low‐molecular‐weight PE. The major effect comes from fractionation. This segregation of the various molecular weights is predicted on the basis of a simple model and is verified by gel permeation chromatography (GPC). The fact that in such a sharp fraction significant fractionation occurs precludes any accurate determination of the supercooling and of the concentration of the polymer actually crystallizing. Subtle differences in the molecular weight distributions may result in significant variation of the growth rate. In conclusion, as the data used in the first part of this work were obtained with only a small percentage of the dissolved polymer sample crystallized, the observed constancy of the growth rate does not result from mutual compensation of opposite effects, and our conclusions about crystallization regime, order of magnitude of the kinetic and persistence lengths, and value of the rate of lateral spreading of a secondary nucleus are well founded.
Solute and penetrant diffusion in swellable polymers. II. Verification of theoretical models
Authors: Korsmeyer Richard W. , Von Meerwall Ernst , Peppas Nikolaos A.
Published: April 2003

A mathematical model developed to describe diffusion of a penetrant and a solute in a swellable polymer slab was applied to the case of a hydrophilic polymer loaded with a soluble drug in which the penetrant (water) is sorbed and solute (drug) is desorbed. An exponential dependence of the penetrant and solute diffusion coefficients on penetrant concentration was chosen and shown to be adequate for description of the systems studied. Experimental verification of the model was conducted by using copolymers of 2‐hydroxyethyl methacrylate (HEMA) and N‐vinyl‐2‐pyrrolidone (NVP). The monomers were bulk polymerized with benzoyl peroxide initiator and cut into thin disks. Monomer mole fractions of HEMA in the copolymers were 0.707, 0.446, and 0.211. Swelling behavior of the samples was observed in water at 37 and 0°C. Solute‐containing samples were prepared and solute release from these samples into water was followed by monitoring the UV absorption of the release medium. The concentration dependence of the diffusivity of water and two model solutes, sodium trifluoroacetate and sodium heptafluorobutyrate, in the gels was studied by using the pulsed‐gradient spin‐echo NMR technique. The diffusivities measured by this technique followed the concentration dependence predicted by the free‐volume theory. The simple exponential dependence used in the model was an adequate approximation of this behavior in the case of a transient diffusion experiment.
Formation of band textures in hydroxypropylcellulose liquid crystals
Authors: Navard P.
Published: April 2003

Upon shearing, some polymeric liquid crystals develop a particular texture, called “band texture,” consisting of fine equidistant black lines as viewed between crossed polarizers. In mesomorphic hydroxypropylcellulose–water solutions, these bands are due to relaxation of the shear. The band texture appears after shearing at low shear rates and seems to exist during shearing at high shear rates (> 200 S−1). In the latter case, the steady‐state first normal‐stress difference is negative. The bands relax in a few minutes and parts of the bands form elongated domains. This texture gives a Hv light‐scattering pattern which can be interpreted by the theory of scattering by anisotropic rods. These domains lose their elongated shape with time.
Solvent self‐diffusion, polymer NMR relaxation, and free volume in polymer solutions
Authors: Blum Frank D. , Durairaj Bojayan , Padmanabhan Alapat S.
Published: April 2003

The self‐diffusion coefficient of chloroform in poly(isopropyl acrylate)—chloroform solutions has been studied as a function of concentration and temperature by using the pulsed‐field‐gradient spin‐echo NMR method. It is found that the self‐diffusion coefficient of the solvent can be adequately fitted by using a simple free‐volume approach with either a concentration or temperature superposition. It was noted that the free‐volume parameters derived from the self‐diffusion data are the same as those derived from deuterium NMR transverse relaxation‐time measurements of the polymer in the same system. The equality of these two sets of experiments suggests a fundamental relationship between the two different processes. The simplest explanation is that the free volume necessary for the local segmental motion of the polymer and the translation of the solvent are similar.
Diffusion of Cu2+ catalysts from Cu‐metal polymer or Cu‐oxide/polymer interfaces into isotactic polypropylene
Authors: Jellinek H. H. G. , Wei You Ching
Published: April 2003

Diffusion coefficients of Cu2+ in the form of its carboxylate have been measured in isotactic polypropylene as a function of temperature (90–128°C) and extent of preoxidation. Diffusion take place from the metal catalyst/polymer interface into the bulk polymer. The diffusion is dependent on the extent of preoxidation and temperature but not on the type of catalyst (Cu, CuO, CuO0.67). Analysis of polymer sections for Cu2+ ions was carried out with a selective Cu2+ electrode. Diffusion in isotactic polypropylene is about 1000 times faster than in lowdensity polyethylene. The carboxylate anion appears to have about 7 C‐atoms for diffusion in isotactic polypropylene compared with 29 C‐atoms for low‐density polyethylene.
Analysis of meridional x‐ray diffraction pattern of the γ form of nylon 6 and comparison of paracrystalline and microstrain models of lattice disorder
Authors: Murthy N. S.
Published: April 2003

Analysis of the increase in the width of the seven meridional (OkO) reflections of the γ form of nylon 6 suggests microstrain rather than paracrystallinity as the source of lattice disorder along the chain axis. It is shown that the intensity of the (020) reflection depends not only on the amount of γ phase present in the fiber, but is also influenced by orientation, Lorentz factor, and crystallite size. Calculations confirm the presence of a weak, diffuse meridional band at 2θ=6° (Cu Kα) when the coherence length along the chain axis corresponds to less than two unit cells.
An application of an homogenization method to a model of diffusion in glassy polymers
Authors: Sangani Ashok S.
Published: April 2003

The sorption of gases in polymers below their glass‐transition temperature Tg is known in many cases to be described by the “dual sorption” theory, according to which the gas is held in accordance with both the Langmuir and Henry's laws. Based on this theory, expressions for the “effective diffusion coefficient” in the glassy polymers have been obtained by investigators in the past, notably by Paul and Koros.2 The present analysis regards the glassy polymers as inhomogeneous with regions on which the gas sorption follows the Langmuir law. Assuming that the linear dimensions of these regions, which are often referred to as “microvoids” (although they are not space filled by vacuum), are small compared to the macroscopic length of interest but large compared to the mean free path of the penetrant gas molecules, we derive a rigorous relation between the average flux and the concentration gradient in the polymer and show that this relation can be expressed in terms of an “effective diffusion coefficient” Deff which depends on the details of the microstructure, i.e., the size, shape and spatial distribution of the “microvoids.” This expression for Deff is shown to reduce to that of Paul and Koros2 in two situations: (1) when the “voids” consist of slabs running parallel to the concentration gradient, and (2) when the “voids” are spherical and the temperature of the polymer is not too different from Tg. The results of the present study lead to an alternative procedure for interpreting the experimental data on sorption and permeation which may have some advantages over the procedure currently employed. Finally, the analysis presented here is also applicable to polymers containing adsorptive fillers.
Small‐angle x‐ray scattering from polyethylene
Authors: Kifle Z. , Harrison I. R. , Herman R. M.
Published: April 2003

A new theoretical model for the description of small‐angle x‐ray scattering from oriented polymer systems is developed and intensity functions are derived. The scattering system considered can be represented by a set of stacks of approximately parallel lamellae where the stack dimensions are assumed large in comparison with correlation distances within the stacks. Each point within the sample is envisioned as being surrounded by such a domain, so the theory is based on a concept of continuously varying local conditions. Fluctuations in the local lamellar distribution parameters are taken into account through a gross disorder parameter which specifies a spread in the local mean long periods. In addition, a long‐range disorder parameter has been included as a measure of the randomness of the actual amorphous layer spacings about the local mean lamellar spacing within each lamellar stack. Important characteristics of the diffraction curves such as the peak positions, heights, and widths; the number of observable orders; and the higher‐angle behavior allow one to obtain the mean lamellar spacing, the fluctuation parameters, and the effective widths of the refractive index perturbations associated with the amorphous regions. The number of lamellae that scatter x‐rays coherently can be predicted with ease. We show that geometric corrections are negligible for oriented samples. In addition, the Lorentz correction is shown to be unnecessary in all cases. We have measured diffraction patterns for polyethylene (PE) precipitated from solution using a Kratky system. Good agreement between theoretical and experimental results on PE 87 and PE 91 is achieved for three‐parameter fits. Finally, we have considered non‐Gaussian distributions of the local mean long periods, with excellent results being generated for a slightly positively skewed three‐Gaussian distribution.
Ordered structures of syndiotactic poly(methyl methacrylates) studied by a combination of infrared, Raman, and NMR spectroscopy.
Authors: Dybal Jiří , Spěváček Jiří , Schneider Bohdan
Published: April 2003

The C  O stretching vibrations in Raman and infrared spectra of poly(methyl methacrylate) (PMMA) samples of various stereoregularity in solutions and in the solid state were measured. It was found that for ordered structures of syndiotactic (s) PMMA, transition dipole coupling of ester groups in ordered s‐PMMA sequences leads to a splitting of the C  O stretching vibration into three components with wavenumbers equal in the solid state and in solution, and of different activity in Raman and infrared spectra. A comparison of the time dependences of self‐aggregation of s‐PMMA as measured by NMR and infrared spectroscopy indicates that the first phase of the aggregation process is detected by both methods. NMR analysis of the effect of the degree of stereoregularity on the self‐aggregation of s‐PMMA shows that the prerequisite for the generation of a stable ordered structure is the mutual interaction of two s‐sequences of a minimum length of 9 monomer units. The experimental data obtained lead to the conclusion that, in self‐aggregated s‐PMMA, some of the ester groups are in close contact, with the interacting s‐sequences probably forming a double helix.
Kinetics of transitions involving condis crystals
Authors: Grebowicz Janusz , Cheng Stephen Z. D. , Wunderlich Bernhard
Published: April 2003

The kinetics of condis (conformationally disordered) crystal formation from the melt and of rigid crystals from condis crystals has been studied by differential scanning calorimetry for trans‐1,4‐polybutadiene and polytetrafluoroethylene. Generally very low two‐stage Avrami exponents between 0.02 and 1.74 were needed to describe the fast and often incomplete crystallizations. None of the commonly accepted crystal nucleation and growth models seems to fit the data.
Kinetics of phase separation in polymer blends for deep quenches
Authors: Voigt‐Martin I. G. , Leister K.‐H. , Rosenau R. , Koningsveld R.
Published: April 2003

Electro microscopy was used to study the phase separation kinetics of a polystyrene/polyvinylmethylether system subjected to a critical deep quench. The size of the phase‐separated domains was found to increase linearly with time, implying that hydrodynamic effects control the rate of growth of the domains in the time scale and temperature range under consideration. From these measurements the growth velocity and approximate diffusion constants can be determined for three different temperatures. Comparison of these results with those obtained by light scattering on other systems and with theoretical predictions is possible by replotting in dimensionless units.
Cumulative erasing effect in the melt memory of nylon 6
Authors: Avramova N. , Fakirov S.
Published: April 2003

The effect of melt annealing over a wide range of temperatures (240–300°C) and durations (0.5–120 min) on the induction period and the heat of crystallization of nylon 6 was studied by means of differential scanning calorimetry. It was found that the crystallization characteristics are determined by the total annealing time experienced by the melt at a given temperature; i.e., a cumulative effect on the erasure of the melt memory is observed. Complete destruction of the crystalline nuclei is achieved after annealing for 90 min at 280°C, the equilibrium melting point of nylon 6; the nuclei cannot be regenerated by nonisothermal crystallization. All the effects observed are explained by the existence of a wide distribution of size and perfection of nuclei.
Volumetric properties of water–poly(acrylic acid) salt systems from the pure solid to highly concentrated solutions
Authors: Hiraoka Kyoko , Yokoyama Tetsuo
Published: April 2003

Volumetric properties of poly(acrylic acid) alkali‐metal salts (Li, Na, K, Rb, and Cs) with different degrees of neutralization and water contents were studied in the range from pure solid to highly concentrated solutions. The apparent partial molar volume ϕ2 of the polymer and the partial molar volume V1 of water were calculated from density data. The value of ϕ2 decreased with decreasing polymer concentration and eventually leveled off. Values of V1, which at low water contents were much smaller than that of free water, increased with increasing water content and eventually reached a constant value equivalent to that of free water, thus indicating the appearance of free water. Water contents corresponding to the appearance of free water increased in the order of Li < Na < K < Rb < Cs, differing from the usual trend of hydration numbers observed in dilute solutions. The change of the slope of the plots of V1 versus composition suggested a change in the hydration mechanism. For Li, Na, and K salts, the limiting values of V1 at very low water content is considerably smaller than the 18 cm3/mol of free water. In contrast, for Rb and Cs salts, these values were relatively large, indicating the relatively weak electrostriction effects of these ions.
Solution and solid‐state NMR characterization of poly(p‐phenylene terephthalamide)
Authors: English A. D.
Published: April 2003

NMR spectroscopy has been used to characterize poly(p‐phenylene terephthalamide) in the solid state and in solution in sulfuric acid. Solid‐state13C NMR spectra illustrate that the chain structure is highly ordered in the solid state and is of lower symmetry than in solution. Solid‐state13C and1H NMR results show that only very limited motion takes place over the temperature range of −170 to +200°C. High‐resolution NMR spectra can be observed only in very dilute isotropic solutions because it is the overall rotational motion of the polymer, not segmental motion, that averages the nuclear spin interactions to their isotropic values. These results demonstrate that previous solution NMR studies that were interpreted as reflecting the presence of isotropic and anisotropic high‐molecular‐weight polymer phases over a wide range of concentrations actually are representative of polymer degradation.
Translational diffusion of polystyrene in 1,4‐dioxane at infinite dilution determined with the extended Taylor dispersion method
Authors: Barooah A. , Sun C. K. J. , Chen S. H.
Published: April 2003

The extended Taylor dispersion method was used to determine the translational diffusion coefficients of a series of polystyrene standards in 1,4‐dioxane at infinite dilution at temperatures from 323.2 to 378.2 K. The experimental data suggest that in the context of Kirkwood's theory the Monte Carlo chain represents real polystyrene molecules better than does the Guassian chain with physically reasonable values for the hydrodynamic interaction parameter h*. The feasibility and accuracy of the simultaneous determination of the diffusivities of several polystyrene standards from a single dispersion measurement were also analyzed using a binary mixture of polystyrenes with molecular weights of 2000 and 100,000 as an example.
Fourier‐transform infrared study of the nematic order in thermotropic main‐chain polyesters
Authors: Wu P. P. , Hsu S. L. , Thomas O. , Blumstein A.
Published: April 2003

Infrared spectroscopy has been used to analyze the microstructures of liquid‐crystalline polymers in various mesophases. It was quite evident that there is little indication of conformational order associated with the flexible polymethylene sequences in the nematic or isotropic phases. However, additional spectroscopic evidence does suggest that polyesters with an even number of methylene units have a higher degree of lateral order when compared to those with an odd number in the liquid‐crystalline state.
Electric relaxation currents in a cured polyester resin with nitroaniline additives
Authors: Sodolski H. , Słupkowski T.
Published: April 2003

The influence of a small amount of nitroaniline additive on the thermally stimulated discharge current in a cured polyester resin was investigated. The height of dipole relaxation and space charge relaxation peaks increased and the maxima of the dipole peaks shifted to lower temperatures. The observed effects are explained by the nitroaniline—polyester resin interaction, which causes a structural plasticization of the polymer.
Effect of introducing acrylic and methacrylic acid groups on molecular relaxation of poly(ethyl methacrylate)
Authors: Kihira Yasuhasru , Yamamura Hitoshi , Murakami Ichiro
Published: April 2003

Dielectric and infrared data have been obtained over a wide temperature range on copolymers of ethyl methacrylate with methacrylic and acrylic acid synthesized by radical copolymerization. The dissociation energy ΔH0 for the acid dimer in the copolymer is estimated from the temperature dependence of the relaxation strength Δεα of the α relaxation, which is associated with the glass transition. The value of δH0 obtained by this method is in fair agreement with that determined by infrared (IR) spectroscopy. The strength of the α relaxation and its activation energy are both increased by the incorporation of methacrylic acid units but are decreased by acrylic acid units. This behavior is attributed to the restriction of main‐chain motions by hydrogen‐bonded acid dimers in the copolymers with methacrylic acid and to the incorporation of more flexible links in the copolymers with acrylic acid. The β relaxation observed below the glass transition temperatures is almost unaffected by the incorporation of methacrylic acid.
Electrical resistivity correlations in rigid and plasticized polymers
Authors: Hartmann Bruce , Warfield R. W.
Published: April 2003

Empirical correlations in the literature between room‐temperature electrical resistivity and activation energy in various polymers are shown to be equivalent to the compensation law. Assuming that electrical conduction is an ionic process, following the Eyring theory, the compensation law can be expressed as a direct proportionality between activation energy and activation entropy. It is found that plasticizers do not change the ion number density or the ionic jump distance but only the temperature at which energy and entropy effects balance. An approximation of the ion number density is consistent with the idea that the mobile ions result from the dissociation of absorbed water.
Dilation of polycarbonate by carbon dioxide
Authors: Sefcik Michael D.
Published: April 2003

A new technique is described for dilatometry under high pressure. The technique is based on optical interferometry and is analogous to measuring the thickness of thin, nonabsorbing films and coatings. The procedure is demonstrated for the well‐characterized system of n‐pentane sorption by polyisobutylene, and then results for the dilation of polycarbonate by the sorption of carbon dioxide are presented. The dilation of polycarbonate by CO2 is nearly linear with concentration; the partial molar volume of CO2 decreases slightly with increasing pressure. This result indicates that all sorbed CO2 molecules contribute equally to the dilation of the polymer matrix and that none reside in microvoids or in preexisting free‐volume elements which do not contribute to volume expansion of the polymer.
Dilation and plasticization of polystyrene by carbon dioxide
Authors: Sefcik Michael D.
Published: April 2003

We have used an optical interference technique to measure the dilation of polystyrene films in the presence of carbon dioxide or helium at pressures up to 20 atm. Dilation isotherms (plots of dilation versus gas pressure at constant temperature) were obtained for three samples of polystyrene which had widely differing molecular weights. The dilation isotherms have the same general shape as sorption isotherms, which means that all of the sorbed gas molecules contribute to volume dilation and non can be thought of as occupying molecular‐sized voids in the polymer. Using sorption results from the literature we show that the partial molar volume of CO2 at 35°C is about 39 cm3 mol−1 and appears to be independent of polystyrene molecular weight. For a polystyrene sample with Mn = 3600, the partial molar volume of sorbed CO2 increases to 44 and 50 cm3 mol−1 at 45 and 55°C, respectively. The sorption of CO2 in polystyrene is shown to depress the glass transition temperature of the mixture, consistent with theoretical predictions. The shape of the dilation and sorption isotherms are consistent with the depression of the glass transition temperature.
Molecular design of multicomponent polymer systems. X. Emulsifying effect of poly(styrene‐b‐methyl methacrylate) in poly(vinylidene fluoride)/noryl blends
Authors: Ouhadi T. , Fayt R. , Jérôcme R. , Teyssié Ph.
Published: April 2003

The emulsifying activity of block copolymers is investigated in blends of incompatible engineering polymers such as polyvinyldene fluoride (PVF2) and Noryl (high impact polystyrene‐poly‐2,6‐dimethyl‐1,4‐phenylene oxide mixture). When the blends are modified by a poly(styrene‐b‐methyl methacrylate) copolymer, (PS‐PMMA) each block of which being selectively miscible with Noryl and PVF2 respectively, Phase dispersion, interfacial adhesion and ultimate mechanical properties are significantly improved; major effect is observed upon addition of 12 percent copolymer, resulting in intermingled and firmly adherent phases and a rough additivity of both tensile strength and elongation at break. All these features clearly demonstrate the important emulsifying effect of PS‐PMMA in these very attractive PVF2/Noryl blends.
Block copolymers of poly(ethylene terephthalate)‐poly(butylene terephthalate). II. Small‐angle light‐scattering studies
Authors: Misra A. , Garg S. N.
Published: April 2003

Small‐angle light‐scattering (SALS) studies were carried out on block copolymers of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), the synthesis and characterization of which have been reported in an earlier paper. Samples were crystallized isothermally from the melt at 95°C for predetermined crystallization times in order to follow the formation and growth of crystalline superstructure. During the early stages of crystallization, the block copolymers showed unusual Hv patterns with the four lobes along the polarizer directions, while at later stages they showed the usual Hv patterns with the four lobes at 45° to the polarizer directions. The unusual patterns are characteristic of PBT superstructure, while the usual patterns are characteristic of PET superstructure. These results show that PBT, which is the faster‐crystallizing component, crystallizes first and provides nucleation sites for the crystallization of PET, which crystallizes later. Similar behavior was not observed in PET homopolymer and random copolymers of equivalent compositions. In each case the spherulite size increased with the time of crystallization. The ultimate spherulite size decreased with increasing PBT content in the block copolymer, thus showing an increase in nucleation density. It was demonstrated that light scattering is a useful tool to characterize block copolymers of two crystalline components which have different types of superstructure.
Mechanical and transport properties of highly drawn isotactic polypropylene
Authors: Vittoria V. , De Candia F. , Capodanno V. , Peterlin A.
Published: April 2003

Quenched films of isotactic polypropylene were drawn at 110°C up to draw ratio λ = 18. The axial elastic modulus was measured as function of λ up to the highest achieved λ. The sorption and diffusion of CH2Cl2 at 25°C in the undrawn and drawn samples were studied. Exclusively transparent samples were used for the measurement of the density and transport properties. This reduces the maximum usable draw ratio to 15. The drawing process is inhomogeneous with neck propagation. In the neck the draw ratio increases by about 6. As a consequence of the increasing fraction of taut tie molecules the axial elastic modulus increases faster than the draw ratio. The transport parameters D, S, and λ indicate that the original lamellar morphology is completely transformed into the microfibrillar structure.
Dynamic melt properties of ionic blends of polystyrene and poly(ethyl acrylate)
Authors: Bazuin C. G. , Eisenberg A.
Published: April 2003

Ionic interactions in blends of poly(styrene‐co‐styrene–sulfonic acid) and poly(ethyl acrylate‐co‐4‐vinylpyridine) result in greatly extended rubbery regions. Measurements of dynamic shear moduli as a function of frequency at various temperatures above the glass transition indicate that time–temperature superposition is applicable in almost all cases. Relative to a blend of pure polystyrene with pure poly(ethyl acrylate), the copolymeric blends strongly resemble one another regardless of either compatibility or ion content. Higher ion content appears to enhance the extension of the rubbery plateau. True flow is not achieved even at temperatures as high as 220°C (0.1 rad/s). Flow is clearly evident in the nonionic blend at 170°C (0.1–1.0 rad/s). It is postulated that the ionic interactions are such that bond breaking and reforming are more rapid than the rate of chain slippage.
Radical and void formation in ultradrawn polyoxymethylene
Authors: Takeuchi Y. , Yamamoto F. , Konaka T. , Nakagawa K.
Published: April 2003

In the production of ultrahigh‐modulus (45–60 GPa) polyoxymethylene (POM) by microwave heating drawing, ultradrawing to draw ratios over 20 causes formation of numerous voids and radicals. The volume fraction of the internal voids is proportional to the drawing‐induced radical concentration. On the basis of the idea that the rupture of taut tie‐molecules (TTM) is responsible for void and radical formation, the relationship between the fraction of tiemolecules that are taut and the fraction that are ruptured is discussed by assuming both a Takayanagi structure model and the normal distribution of the tie‐molecule lengths. The results indicate that longer tie‐molecules are successively converted to TTM's followed by ruptures of shorter TTM's in the ultradrawing process; a small variance in the tie‐molecule length distribution is effective for increasing TTM's without void formation. The maximum value of the volume fraction of taut tie‐molecules for highly oriented POM tubes is estimated to be about 0.5.
Electron‐irradiated isotropic polyethylene: Structure and mechanical properties of oriented monofilaments produced by drawing
Authors: Klein P. G. , Ladizesky N. H. , Ward I. M.
Published: April 2003

The structure and properties of oriented (draw ratio 12:1) polyethylene filaments, produced by drawing electron‐irradiated isotropic monofilament, have been studied by rubber elasticity measurements, x‐ray diffraction, differential scanning calorimetry, and tensile creep behavior. The apparent molecular weight M̄c between network junctions, has been calculated from the Flory and Mooney–Rivlin theories, as a function of dose, and extrapolation back to zero dose gives a value of about 16,000 g mol−1, which is related to the molecular weight between entanglements in the linear polymer (M̄n 28,000). The WAXS and SAXS patterns of the unirradiated and 6.0 Mrad samples were identical, indicating an equivalent extent of crystallite orientation and a constant long period of about 170Å. Up to a gel dose of 2.4 Mrad, the degree of crystallinity (DC) of the drawn filaments remains constant, but the melting temperature Tm decreases slightly owing to network junctions at the fold surfaces. Above the gel dose, DC drops significantly and Tm falls more sharply, as a result of crystallite distortion. Irradiation dramatically affects the creep behavior, decreasing the equilibrium creep rate by up to four orders of magnitude. For all samples, the constant‐flow behavior can be described by a combination of two activated processes in parallel: one associated with the amorphous network and the other with the crystalline regions. Irradiation increases the activation volume of the process occurring in the crystal and is ascribed to an increase in crystallite imperfections.
Poly(p‐benzamide): Magnetic field orientation, solvation, and crystal–crystal transformations
Authors: Takase M. , Krigbaum W. R. , Hacker H.
Published: April 2003

The morphological features of poly(p‐benzamide) films cast in a magnetic field from solutions in N,N‐dimethylacetamide containing LiCl are reported. Three crystal modifications are found, one solvated and the other two containing no solvent. The solvated crystal grown in a magnetic field is oriented with the molecules parallel to the field. It transforms to an oriented amorphous phase by loss of solvent, and this conversion is accelerated by the presence of moisture. Upon annealing at an elevated temperature, the crystalline solvate transforms to a second crystal form, while the amorphous sample is converted to a third crystalline modification. All three crystalline forms have almost the same fiber identity period, which corresponds to a nearly fully extended chain conformation.