bluuebunny/crossref_metadata_2025 huggingface dataset:
Local compositional fluctuations in PPO/HIPSand PPO/SBS blends
Authors: Li S. , Charles Dickinson L. , Chien James C. W.
Published: April 2003

Solid‐state NMR relaxation has been used to explore the distribution of components in poly(phenylene oxide) (PPO) high impact polystyrene (HIPS) and PPO/poly(styrene‐b‐butadiene‐b‐styrene) (SBS) blends. The nuclear relaxation of PPO in the former system is single exponential for all compositions, but the relaxation of PS in the blend is simple exponential only when the PPO content is low but is otherwise nonexponential. The nuclear magnetization decay curves were analyzed in terms of statistical compositional fluctuation at the scale of spin diffusion distances of several nm. Distribution functions for nuclear relaxation and for blend composition have been derived. Extraction of low molecular weight occluded PS from HIPS resulted in blends having reduced homogeneity. Addition of low molecular weight PS enhanced homogeneity in both the PPO/HIPS and PPO/SBS blends. © 1994 John Wiley & Sons, Inc.
Liquid–liquid phase separation in linear low‐density polyethylene
Authors: Nesarikar A. , Crist B. , Davidovich A.
Published: April 2003

The issue of multiple equilibrium phases in compositionally heterogeneous random copolymers is studied with an ethylene‐butene copolymer representative of many linear low‐density polyethylenes (LLDPE). This material has a dispersed minority phase (volume fraction ƒβ ≈ 0.02) of highly branched, amorphous chains. A thermodynamic calculation of the equilibrium liquid state is done using the distribution of chain branching from temperature rising elution fractionation and the Flory‐Huggins interaction parameter χAB for linear and ethyl branched C4H8 repeat units. The calculation indicates that this copolymer is metastable, between the binodal and spinodal at a melt temperature of 150°C. The predicted volume fraction of the second phase, ƒβ = 0.016, is in good agreement with experiment. This work is the first to compare directly the observed and calculated two‐phase behaviors in a random copolymer. © 1994 John Wiley & Sons, Inc.
A high‐speed, high‐precision data acquisition and processing system for experiments producing steady‐state periodic signals
Authors: Winther Grethe , Parsons Donald M. , Schrag John L.
Published: April 2003

A wide variety of experiments investigate the response of a sample to a steady‐state periodic excitation. We describe a computerized data acquisition and processing system for experiments of this type assembled from relatively inexpensive, commercially available components which has been optimized for highly precise determinations of the magnitude and relative phasing of drive and response signals having frequencies from 1 μHz to approximately 1 MHz. Through the use of timing control with a precision of 1 part in 109 and high speed on‐line signal processing, the system combines a very high rate of data acquisition with extended signal averaging times, enabling it to acquire an uninterrupted data stream consisting of at least 109 samples. Furthermore, the system acts as a digital filter which can be tuned to completely reject unwanted signals of any frequency other than the exact signal frequency. This allows accurate characterization of sample response even when obscured by other, extraneous signals of substantially larger magnitudes as long as they have at least somewhat different frequencies. Oscillatory experiments on very dilute polymer solutions, including oscillatory flow birefringence, dynamic viscoelasticity, oscillatory electric birefringence and dielectric measurements, are important examples of this type of measurement situation, in which the experiment depends critically on accurate determination of the magnitude and phasing of weak response signals, frequently under extremely poor signal‐to‐noise conditions. The system has an aggregate sampling rate of 1 MHz and up to four input channels. The potential for distortion of the results by aliasing frequencies may limit the input signal frequency to less than 500 kHz for one channel. © 1994 John Wiley & Sons, Inc.
Hydrodynamic fluctuations and spinodal decomposition in ternary systems
Authors: Bobba Ratnaleela , Cohen Claude
Published: April 2003

Time correlation functions of concentration fluctuations are obtained from hydrodynamic fluctuation theory extended to ternary systems. The coupling between the concentrations of the different species is accounted for and leads naturally to symmetric correlation functions unlike those previously reported. The time correlation functions of concentration fluctuations incorporating the effect of thermal noise are used to obtain the initial scattering intensity of ternary polymer‐polymer‐solvent systems undergoing spinodal decomposition. It is shown that the scattering function is represented by a sum of three exponentials. Single exponential growth is predicted under certain conditions which appear to have been met in the limited experimental data available. © 1994 John Wiley & Sons, Inc.
Thermal history and enthalpy relaxation of an interpenetrating network polymer with exceptionally broad relaxation time distribution
Authors: Sartor Günter , Mayer Erwin , Johari G. P.
Published: April 2003

Differential scanning calorimetry (DSC) of an interpenetrating network polymer of composition 25% polyurethane–75% poly(methyl methacrylate) shows a slowly increasing heat capacity, instead of the usual glass transition endotherm, whose onset temperature is not clearly discernible. On aging of the polymer at several temperatures between 193 and 333 K, an endothermic peak is observed whose onset is in the vicinity of the respective temperature of aging. The area under these peaks increases with increasing aging time at a fixed temperature. The effects are attributed to a very broad distribution of relaxation times, which may be represented by either a sum of discrete structural relaxation times of local network arrangement or by a nonexponential relaxation function which is equivalent to a distribution of relaxation times. In either view the vitrified state of the polymer can be envisaged as containing local structures whose own Tgs extend over a wide range of temperature. Aging decreases the enthalpy and produces an endothermic region which resembles an increase in Cp on heating because of relaxation of that local structure. The interpretation is supported by simulation of DSC scans in which the distribution of relaxation times is assumed to be exceptionally broad and in which aging introduced at several temperatures over a wide range produces endothermic effects (or regions of DSC scans) qualitatively similar to those observed for the interpenetrating network polymer. © 1994 John Wiley & Sons, Inc.
Effect of structure on the temperature dependence of gas transport and sorption in a series of polycarbonates
Authors: Costello Lora M. , Koros William J.
Published: April 2003

The permeabilities and solubilities of five gases are reported for bisphenol‐A polycarbonate (PC), tetramethyl polycarbonate (TMPC), and tetramethyl hexafluoro polycarbonate (TMHFPC) at temperatures up to 200°C. The temperature dependence of permselectivity is discussed in terms of solubility and diffusivity selectivity changes with temperature for CO2/CH4 and He/N2 gas separations. The activation energies for permeation and diffusion and the heats of sorption are also reported for each gas in the three polycarbonates. Analysis of these values provides a better fundamental understanding of the effect of polymer‐penetrant interactions and polymer backbone structure on the temperature dependence of the transport and sorption properties of gases in membrane separation processes. Important factors affecting the solubility and diffusivity selectivity losses or gains with increased temperature are also identified through correlation of these data with physical properties of the gases and polymers. These conclusions provide a framework for choosing the most promising membrane materials for particular gas separations at elevated temperatures. © 1994 John Wiley & Sons, Inc.
The chain conformations of a polyether based on bis(4‐hydroxyphenoxy)‐p‐xylylene and 1,11‐dibromoundecane (HPX‐c11) in its mesophase states, derived from 13C NMR
Authors: Cheng Jinlong , Jin Yimin , Chen Wei , Wunderlich Bernhard , Jonsson Håkan , Hult Anders , Gedde Ulf W.
Published: April 2003

A thermotropic main‐chain polyether based on bis(4‐hydroxyphenoxy)‐p‐xylylene and 1,11‐dibromoundecane has been studied by variable‐temperature solid‐state 13C NMR. Between isotropization and glass transition temperatures, the material can be identified to be semicrystalline, consisting of two conformationally and motionally distinguishable phases. The more mobile component is liquid‐like and thus, can be attributed to an amorphous phase. In the more rigid component, the molecules have a conformationally disordered methylene sequence. In the low‐temperature ordered phase approximately ⅔ of the carbon‐carbon bonds are trans (t). Starting from the bond between the oxygen and the first methylene carbon, the bond conformations are: dtdttttttdtd, where d stands for disordered (i.e., it represents the common dynamic interchange between gauche and trans with an overall gauche content of perhaps 40%). The motion of the αα′‐diphenoxy‐p‐xylylene unit consists mainly of 180° ring‐flips, which cause no entropy increase relative to ordered phenylene groups in a crystal, but significantly changes the 13C NMR spectra. The central p‐xylylene ring starts its flipping motion at a lower temperature than the two phenoxy rings. The high‐temperature mesophase contains a methylene sequence of the bond conformations: dtdddttdddtd. Thus, the difference between the low‐temperature and high‐temperature mesophases consists of different degrees of conformational disorder. Thermal analysis seems to indicate that additional mesophases may be possible. © 1994 John Wiley & Sons, Inc.
Crystallization study of a thermoplastic polyimide (new‐TPI)
Authors: Hsiao Benjamin S. , Sauer Bryan B. , Biswas Amit
Published: April 2003

Crystallization, melting, and morphology of a thermoplastic polyimide (New‐TPI) containing pyromellitic dianhydride (PMDA) and 3,3'‐bis(4‐aminophenoxy) biphenyl diamine (33BAPB) moieties have been studied. This material showed a glass transition temperature (Tg) of 250°C, an equilibrium melting temperature (T°m) of 406°C and a heat of fusion (ΔH) for 100% crystallinity of 6.38 kJ/mol. Measurements of the crystallization bulk rate (by DSC) and spherulite growth rate (by optical microscopy) indicated that the maximum crystallization temperature was about 320°C and the crystallization growth process was three‐dimensional under thermal nucleation (the Avrami exponent n ca. 4). The rate of nucleation density was estimated to decrease with increasing temperature, and the product of two crystal surface free energies σeσo was calculated to be 1176 erg2/cm4. The meltgrown spherulite consistently showed a Maltese cross pattern with negative birefringence under cross‐polars. The calculation of polarizability along the three unit cell axes suggested that the crystal b axis may be along the spherulite growth (radial) direction. Two scattering maxima were seen in small‐angle x‐ray scattering (SAXS) profiles. The dominant peak indicated a long period of ca. 20 nm which varied as a function of crystallization temperature. The weak peak at a d‐spacing of 2.5 nm was independent of temperature and has been attributed to the chemical repeat distance determined by Okuyama et al. (indexed as 001). The lamellar thickness lc, estimated by the correlation function analysis of the SAXS data, was found to be similar to that determined by the Scherrer analysis of the 001 reflection peak. © 1994 John Wiley & Sons, Inc.
Comparison of the molecular dimensions of di‐alkyl and aryl‐alkyl‐substituted polysilanes in solution using SEC/LS
Authors: Cotts Patricia M.
Published: April 2003

Polysilanes provide an opportunity for exceptional control of the chain hindrances to rotation through the choice of substituents on each backbone silicon. Two alkyl substituents on each silicon result in a large characteristic ratio of at least 19 for poly (di‐n‐hexylsilane), determined by extrapolation of intrinsic viscosities. Bulky aromatic substituents provide even more hindrance to backbone rotations, and can be expected to result in a more extended polymer chain. Direct measurement of the dimensions of these polymers by scattering techniques has been limited by the small quantities available, and by the polydispersity of samples. The recent introduction of light‐scattering detectors for size exclusion chromatography enables the simultaneous measurement of light scattered at as many as 15 scattering angles as the fractionated polymer elutes from the column. Determination of both M and the root‐mean‐square radius of gyration Rg of narrow fractions eluting from a column allows determination of the Rg M relation over as much as a decade in M with less than a milligram of sample. Values of Rg and M across the distribution have been determined for alkyl and aryl substituted polysilanes with this technique. Estimation of Rg,0/M unperturbed by long‐range interactions is made by an extrapolation procedure. The dependence of Rg,0 on M across the distribution is compared among the different substituents and with other measurements reported for these polymers. © 1994 John Wiley & Sons, Inc.
Interdiffusion of PMMA and PVF2, studied by solid‐state NMR
Authors: Maas W. E. J. R. , Papavoine C. H. M. , Veeman W. S. , Werumeus Buning G. H. , Vankan J. M. J.
Published: April 2003

A previously published new solid‐state nuclear magnetic resonance (NMR) method is applied to the interdiffusion of poly(methacrylate) (PMMA) and poly(vinylidene fluoride) (PVF2) above their Tg. Via a variation of the cross‐polarization technique magnetization is transferred from protons to fluorines. When this magnetization is made to disappear at the fluorine sites, only those protons that are distant from fluorines greater than the distance over which cross‐polarization functions will retain their magnetization. In this way we detect the fraction of PMMA near (ca. 20 Å) PVF2. Starting from sheets of PMMA and PVF2, which are then heated at 190°C for a variable time, and applying the above technique, we can determine the fractions of PMMA and PVF2 that have diffused within a distance of a few Å of each other. The intrinsic diffusion coefficients of PMMA and PVF2 determined from such experiments compare well with literature data. Initial attempts to fit the experimental data suggest that the concentration dependence of the diffusion coefficients cannot be neglected. © 1994 John Wiley & Sons, Inc.
Glass transition and melting behavior of poly(ether‐ester) multiblock copolymers with poly(tetramethylene isophthalate) hard segments
Authors: Phillips Roger A. , McKenna J. Michael , Cooper Stuart L.
Published: April 2003

The glass transition and melting behavior of poly(ether‐ester) multiblock copolymers with poly(tetramethylene isophthalate) (PTMI) hard segments and poly(tetramethylene oxide) (PTMO) soft segments are studied by differential scanning calorimetry (DSC) and small‐ and wide‐angle x‐ray scattering (SAXS and WAXS). Thermodynamic melting parameters for the PTMI homopolymer are estimated by WAXS and from the dependence of melting point on crystallization temperature. The melting behavior of PTMI is characterized by dual endotherms which are qualitatively representative of the original morphology, although reorganization effects are present. The composition dependence of the glass transition temperature parameters after rapid quenching from the melt are well described by mixed phase correlations for copolymers in the range 30‐100 wt% hard segment. Combined with SAXS characterization at melt temperatures, a single phase melt is suggested in these materials which extends to temperatures below the hard segment melting point. © 1994 John Wiley & Sons, Inc.
Mechanism of adhesion of polyurethane/polymethacrylate simultaneous interpenetrating networks adhesives to polymer substrates
Authors: Jia Demin , Pang Yongxin , Liang Xi
Published: April 2003

Polyether‐based polyurethane/poly (methyl methacrylate‐co‐ethyleneglycol dimethacrylate) interpenetrating polymer networks [PU/P (MMA–co–EGDMA)‐IPNs] were synthesized and used as adhesives to adhere vulcanized natural rubber (NR) and soft polyvinyl chloride (PVC). The structure and morphology of the IPN adhesives in bulk and near the adhesive/substrate interfaces were investigated. A new mechanism of adhesion called conjugate interpenetration of networks across interfaces, which is suitable for IPN adhesives and polymer substrates, was put forward. According to this mechanism, while forming simultaneous interpenetrating networks in the adhesive, the monomers in the IPN adhesive can permeate polymer substrates and polymerize in situ to form gradient IPNs, thereby producing conjugate three‐component IPNs near the adhesive/substrate interfaces. It is the conjugate interpenetration of the networks across the interfaces that strengthens interfacial combination remarkably and results in high bond strength of IPN adhesives. © 1994 John Wiley & Sons, Inc.
The effect of orientation on thermal expansion behavior in polyimide films
Authors: Pottiger Michael T. , Coburn John C. , Edman James R.
Published: April 2003

The anisotropy of the thermal expansion of polyimide films was investigated . Out‐of‐plane or thickness direction coefficients of linear thermal expansion (CTE) were calculated from the difference between the coefficient of volumetric expansion (CVE) and the sum of the in‐plane or film direction coefficients of linear thermal expansion for commercial and spin‐coated PMDA//ODA and BPDA//PPD films and spin coated BTDA//ODA/MPD films. The CVEs were obtained from a pressure‐volume‐temperature (PVT) technique based on Bridgeman bellows. The CVE was shown to be essentially constant, independent of molecular orientation and thickness. A decrease in the in‐plane CTEs therefore occurs at the expense of an increase in the out‐of‐plane CTE. In all cases the calculated out‐of‐plane CTE was higher than the measured in‐plane CTE. The ratio of the out‐of‐plane CTE to the in‐plane CTE was 1.2, 3.8, and 49.3 for the spin‐coated BTDA//ODA/MPD, PMDA//ODA, and BPDA//PPD films, respectively. © 1994 John Wiley & Sons, Inc.
Effect of crystallization temperature on the crystalline phase content and morphology of poly(vinylidene fluoride)
Authors: Gregorio, Jr. Rinaldo , Cestari Marcelo
Published: April 2003

The effect of temperature on the crystallization of α, β, and γ phases of PVDF from dimethylacetamide (DMA) solution was studied. Variation in the crystallinity content of these three phases was obtained as a function of temperature using infrared spectroscopy, differential scanning calorimetry (DSC) and x‐ray diffraction techniques. Such variation is related to the dependence of the crystallization rate of each phase with temperature, and allowed a better understanding of some results found in the literature about the crystallization and interconversion of these phases. Micrographs of samples present morphologies that corroborate with the proposed explanations. © 1994 John Wiley & Sons, Inc.
The annealing and thermal analysis of poly(butylene terephthalate)
Authors: Kim Junkyung , Nichols Mark E. , Robertson Richard E.
Published: April 2003

When poly(butylene terephthalate) (PBT) is annealed, a second endotherm is often displayed in a subsequent scanning thermal analysis at a temperature below that of the original endotherm, and this new endotherm appears to grow with annealing at the expense of the original. This growth is not due to chemical changes, because the thermogram obtained before annealing is recovered after complete melting. But a physical change would also seem unlikely because the transformation of higher‐melting into lower‐melting crystals is generally prohibited by thermodynamics. Two hypotheses to explain the result were tested. The first is that higher‐melting crystals are not transformed into lower‐melting crystals. Instead, because of recrystallization during thermal analysis, the single endotherm that results without annealing overestimates the population of high‐melting crystals present before the analysis. This hypothesis was tested by extending to annealing a mathematical analysis previously used to describe the thermal scanning behavior of specimens crystallized at different cooling rates. Though most features of the thermograms obtained after annealing were able to be described, the decrease in the higher‐temperature endotherm concomitant with growth of the lower endotherm was not. The second hypothesis is that the transformation of higher‐melting to lower‐melting crystals during annealing is allowed because it is coupled to the crystallization of formerly amorphous material. The amount of such crystallization observed for PBT was found to be sufficient to satisfy thermodynamic requirements, suggesting that this hypothesis is correct. © 1994 John Wiley & Sons, Inc.
A simulation model for long‐chain branching in vinyl acetate polymerization: 1. Batch polymerization
Authors: Tobita Hidetaka
Published: April 2003

A new simulation model for the kinetics of long‐chain branching formed via chain transfer to polymer and terminal double‐bond polymerization is proposed. This model is based on the branching density distribution of the primary polymer molecules. The theory of branching density distribution is that each primary polymer molecule experiences a different history of branching and provides information on how each primary polymer molecule is connected with other chains that are formed at different conversions, therefore making possible a detailed analysis on the kinetics of the branched structure formation. This model is solved by applying the Monte Carlo method and a computer‐generated simulated algorithm is proposed. The present model is applied to a batch polymerization of vinyl acetate, and various interesting structural changes occurring during polymerization (i.e., molecular weight distribution, distribution of branch points, and branching density of the largest polymer molecule) are calculated. The present method gives a direct solution for the Bethe lattice formed under nonequilibrium conditions; therefore, it can be used to examine earlier theories of the branched structure formation. It was found that the method of moments that has been applied successfully to predict various average properties would be considered a good approximation at least for the calculation of not greater than the second‐order moment in a batch polymerization. © 1994 John Wiley & Sons, Inc.
Gel formation in free radical polymerization via chain transfer and terminal branching
Authors: Zhu S. , Hamielec A. E.
Published: April 2003

Gel formation in free‐radical polymerization via chain transfer to polymer, recombination termination, and terminal branching due to either chain transfer to monomer or disproportionation termination is investigated using the method of moments. It is found that no gel can possibly form in the systems consisting of initiation, propagation, and one of the above reactions. However, systems with the following combination of reactions are found to be capable of gelling. They are: chain transfer to polymer + recombination termination; chain transfer to polymer + terminal branching due to disproportionation termination; and terminal branching due to transfer to monomer + recombination termination. Systems with the following combination of reactions are incapable of gelling; transfer to polymer + terminal branching due to transfer to monomer; and terminal branching due to disproportionation termination + recombination termination. An examination of the gelation mechanisms reveals that the formation of multivinyl macromonomers during the course of polymerization is the reason that systems involving terminal branching gel. Sol/gel diagrams are generated to give critical kinetic parameters required for gelation. It is found that terminal branching does not always promote gelation due to the adverse effect on chain length through chain transfer to monomer and termination by disproportionation, reactions which generate terminal double bonds. © 1994 John Wiley & Sons, Inc.
Sol‐gel transition of polyacrylonitrile/propylene carbonate solution
Authors: Ko Moon Bae , Kwon Ick Hwan , Jo Won Ho , Son Tae Won
Published: April 2003

The thermoreversible gelation of polyacrylonitrile (PAN)/propylene carbonate (PC) solution was investigated by calorimetric, thermomechanical, optical, and rheological measurements. Two endothermic signals are observed for PAN/PC gels in DSC thermograms, and the peak temperature of the higher melting endotherm coincides with the gel melting temperature determined from the TMA thermogram. SEM micrographs show that the overall structure is separated into two phases and is composed of sperical domains, which may be formed upon passing through the thermodynamically unstable or metastable state via the liquid‐liquid phase separation. The gelation rate increases with the aging temperature. This is also discussed on the basis of the elasticity theory of the fishnet gel. © 1994 John Wiley & Sons, Inc.
Crystallization of polypropylene, nylon‐66 and poly(ethylene terephthalate) at pressures to 200 MPa: Kinetics and characterization of products
Authors: He J. , Zoller P.
Published: April 2003

The crystallization kinetics of polypropylene (PP), polyamide (PA66), and poly(ethylene terephthalate) (PET) were studied, using a pressure dilatometer (to 200 MPa) to follow the volume changes associated with the crystallization process. The commonly used Avrami equation fitted the isothermal/isobaric crystallization data of PP and PA66 well. The Avrami exponent n was between 1.3 and 1.7, independent of crystallization pressure and temperature. Lines of constant Avrami rate parameter Z in the P‐T plane were essentially parallel to the pressure dependence of the melting points and crystallization temperatures. However, the Avrami equation was not suitable for PET. The Malkin, Dietz, and Kim equations provided better fits. The crystallization half‐time of PET increased with pressure at constant supercooling, in contrast to PP and PA66, for which it remained essentially unchanged. X‐ray diffraction, differential scanning calorimetry, and pressure dilatometry were used to study the effect of formation pressure on the crystal structure, the melting point, and the density of products which were crystallized for short times (minutes) at various temperatures and pressures. No new crystal structures were found for PA66 and PET, but a mixture of monoclinic and triclinic crystals existed in PP above a formation pressure of 50 MPa. The melting points increased with formation pressure for PET, but remained unchanged for PP and PA66. Density at ambient conditions decreased with formation pressure for PP, but increased for PET and PA66. © 1994 John Wiley & Sons, Inc.
Photon correlation spectroscopy of syndiotactic poly (n‐butyl methacrylate) near the glass transition
Authors: Patterson G. D. , Jue P. K. , Ramsay D. J. , Stevens J. R.
Published: April 2003

Slow relaxing longitudinal density fluctuations in bulk syndiotactic poly (n‐butyl methacrylate) [PBMA] were studied by photon correlation spectroscopy as a function of temperature from 70 to 90°C. The shape of the light‐scattering relaxation function broadened as the temperature approached the glass transition (Tg = 55°C). The average relaxation time shifted with temperature, consistent with previous studies of PBMA. The relaxation functions were analyzed in terms of a distribution of relaxation rates. The calculated distribution was clearly bimodal and the shape altered with temperature. The higher frequency peak in the distribution corresponds well with previous mechanical and dielectric relaxation studies of the intramolecular relaxation of the acrylate ester side chain. The resolution of the distribution into two modes is due to a well‐defined side‐chain motion with relaxation strength comparable to the primary glass‐rubber relaxation. © 1994 John Wiley & Sons, Inc.
Isothermal phase behavior of Nylon‐6, ‐66, and ‐610 polyamides in formic acid–water systems
Authors: Cheng Liao‐Ping , Dwan An‐Hwa , Gryte Carl C.
Published: April 2003

Concentration‐dependent ternary interaction parameters are experimentally determined for the polyamide homopolymers, Nylon‐6, ‐66, ‐610, and for the Nylon‐66/610/6 terpolymer in formic acid‐water systems. The binodal envelope, the tie lines, and the crystallization isotherms at 25°C are given for each of the ternary systems. © 1994 John Wiley & Sons, Inc.
Phase separation and the kinetics of phase coarsening in commercial impact polypropylene copolymers
Authors: Mirabella, Jr. Francis M.
Published: April 2003

The phase segregation and subsequent minor phase coarsening of a commercial impact polypropylene copolymer was studied. The major components of the impact polypropylene copolymer studied were 82.4 wt % polypropylene homopolymer and 17.6 wt % ethylene‐propylene rubber (EPR). The system was artificially manipulated to ensure homogeneity by precipitation from solution with a nonsolvent. This ensured that the initial system did not exhibit large‐scale phase segregation. The homogeneous initial system was subjected to storage in the melt at 193°C for a series of times. The two‐phase morphology of commercial impact polypropylenes was generated in the melt state by storage in the melt for various periods of time from 5 s to 1 h. Small nuclei of particles appeared at short time and increased in volume with increasing time in the melt state. The coarsening of the minor phase EPR component was shown to follow the theoretically predicted d ∼ t1/3 and N ∼ t−1 (where d = diameter, N = number of particles, and t = time in the melt) relationships to a close approximation in accord with Ostwald ripening theory. At short times these relationships were not obeyed. The indication was that the long‐time coarsening regime was not entered until several minutes elapsed in the melt state. The particle size distribution was initially quite narrow and exhibited a trend of broadening at longer times of coarsening. This may be due to a shift from the short‐time regime to the long‐time coarsening regime. The initial polymer, which was precipitated from solution, was shown not to have undergone large‐scale phase segregation in that it exhibited a one‐phase morphology (i.e., no particles with > 0.1 μm diameter) as determined by 129Xe NMR spectroscopy. The precipitated blend produced incipient particle nuclei (> 0.1 μm diameter) after a very short time (5 s) in the melt state. © 1994 John Wiley & Sons, Inc.
The effect of crystallinity on chain mobility and free volume in the amorphous regions of a miscible polycarbonate/polyester blend
Authors: Zipper M. D. , Simon G. P. , Cherry P. , Hill A. J.
Published: April 2003

Homopolymers and blends of polycarbonate/ThermX have been investigated by differential scanning calorimetry, dynamic mechanical analysis, density measurements, and positron annihilation lifetime spectroscopy. The study focuses on the chain mobility and free volume in the amorphous miscible regions of the blends and how this mobility and free volume are affected by increasing crystallinity. It is proposed that judicious annealing, which results in increasing crystallinity (while avoiding ageing or transesterification), induces a constraint on the amorphous region leading to an increase in Tg and coalescence of free volume sites. © 1994 John Wiley & Sons, Inc.
Degradation on freezing dilute polystyrene solutions in p‐xylene
Authors: Zysman Viviane , Nguyen Tuan Q. , Kausch Henning‐H.
Published: April 2003

Chain scission was observed during the crystallization of p‐xylene in dilute polystyrene solutions. Degradation yields were determined by gel permeation chromatography, as a function of the number of freeze‐and‐thaw cycles, polymer concentration, and initial polymer molecular weight (M). The rate constant for chain scission Kc increases with the polymer chain length, from 0.021%/cycle at M = 110·103 to 4.7%/cycle at M = 8.5·106. Over the two decades range of investigated molecular weights, Kc follows an empirical scaling law of the form Kc ∼ (M − Mlim)1.17578, where Mlim is a limiting molecular weight ≅ 29,000 g. mol−1 below which no degradation could be induced. Some propensity for midchain scission was detected, although this tendency was much weaker in comparison to flow‐induced degradation.

A chain scission model based on crack propagation failed to reproduce the experimental results. To explain the observed dependence of Kc with the square of the radius of gyration, an interfacial stress transmission mechanism between the crystallization fronts and the polymer coil has been proposed. © 1994 John Wiley & Sons, Inc.
Stress in polyimide coatings
Authors: Coburn John C. , Pottiger Michael T. , Noe Susan C. , Senturia Stephen D.
Published: April 2003

The effect of film thickness on in‐plane molecular orientation and stress in polyimide films prepared from pyromellitic dianhydride with 4,4′‐oxydianline was investigated using a prism coupling technique to measure the refractive index. Film thickness was controlled by varying both solution concentration and spinning conditions. Birefringence, the difference between the in‐plane and out‐of‐plane refractive indices, was used to characterize the in‐plane molecular orientation. The observed birefringence is a combination of the birefringence resulting from molecular orientation and the birefringence induced by the residual stress present in the films. The birefringence decreases with increasing film thickness over the range of thicknesses studied (3–20 μm) indicating that the molecular orientation decreases with increasing film thickness. The in‐plane coefficient of linear thermal expansion (CTE), controlled by the level of orientation in the film, increases from 18 to 32 × 10−6/°C over the same thickness range. The birefringence of free‐standing films was lower than that of adhered films due to the release of residual stress in the film once the film is removed from the substrate. The residual film stress arises primarily from the mismatch in CTEs between the polyimide film and the substrate to which the film is adhered. Thus, since the film anisotropy decreases with increasing thickness, the film stress increases with increasing thickness. Residual stress calculated by integrating the product of the film modulus and the CTE mismatch assuming temperature‐dependent properties is comparable to experimentally measured film stress. Ignoring the temperature dependence of the film properties leads to an overestimation of stress. Moisture uptake was used to study the stress dependence of the optical properties. Moisture uptake increases both the in‐plane and out‐of‐plane refractive indices by equal amounts in free‐standing films due to an isotropic increase in the polarizability. In adhered films, an increase in moisture uptake leads to a decrease in the birefringence due to a swelling‐induced decrease in the residual film stress. © 1994 John Wiley & Sons, Inc.
Miscibility predictions for poly(phenylene sulfide): Heats of mixing of model compounds
Authors: Landry Christine J. T. , Teegarden David M.
Published: April 2003

Calorimetry was used to gain insight into the thermodynamics of mixing of unlike species, designed to represent organic polymers. These results are to be useful in predicting miscibility between various polymers and poly(arylene sulfides). Phenyl sulfide (PS) and phenyl disulfide (PSS) were used as models for poly(phenylene sulfide) (PPS) and were mixed with model compounds that are representative of other polymer classes. The enthalpy of mixing was measured for a large number of combinations. The results are interpreted in terms of a summation of the effects of specific interactions and dispersive forces. It is seen from these data that the presence of aromatic side groups enhances the miscibility of the species with the poly(phenylene sulfide) model compound. Furthermore, exothermic heats of mixing were observed between the PPS model and compound. Furthermore, exothermic heats of mixing were observed between the PPS model and compounds that contain carbonyl, amide, or amine moieties. Finally, the sulfur atom in PPS seems to play only a minor role in determining its interactions with other species. Replacing sulfur with oxygen (or even an alkyl group) is seen to have very little effect on the heats of mixing results. © 1994 John Wiley & Sons, Inc.
Physical and chemical properties of tussah silk fibroin films
Authors: Tsukada Masuhiro , Freddi Giuliano , Gotoh Yoko , Kasai Nobutami
Published: April 2003

Physical and chemical structure, as well as thermal behavior of solution‐cast regenerated films, prepared from tussah (Antheraea pernyi) silk fibroin, were compared with those of solution‐cast native films, in order to ascertain whether treatment (degumming, dissolution) used for preparation affected their properties. Regenerated fibroin films exhibited a higher thermal stability than native ones, as shown by differential scanning calorimetry, thermomechanical analysis, and dynamic mechanical behavior. Glass transition temperature and other relevant thermal transitions of the regenerated silk specimen shifted to higher temperatures compared with those of native specimen. Molecular conformation and crystalline structure did not show significant differences between the two kinds of silk films. Amino acid composition and molecular weight, however, distribution changed markedly after dissolving tussah silk fibroin fiber in concentrated LiSCN in polypeptide size was the main features for the regenerated silk fibroin. © 1994 John Wiley & Sons, Inc.
Cellulose‐polyamide 66 blends. I. Processing and characterization
Authors: Garcia‐Ramirez M. , Cavaillé J. Y. , Dupeyre D. , Péguy A.
Published: April 2003

Each homopolymer, cellulose and polyamide 66 (PA66), was separately dissolved in a mixture of N‐methyl morpholine N‐oxide and phenol (80/20 w/w). Then, the two solutions were mixed together. This step leads to the crystallization of PA66 in small aggregates (about 1 μ) regularly dispersed in the cellulose solution. It appeared that this morphology remains independent of further processing such as spinning or casting. Finally, fibers or films were precipitated in methanol. The entire preparation technique used here results mainly in two‐phase systems in which PA66 domains are embedded in an amorphous cellulose matrix. The specimens obtained were at first characterized by differential scanning calorimetry, scanning electron microscopy, and wide angle x‐ray scattering. © 1994 John Wiley & Sons, Inc.
Relaxations in thermosets. XXVI. Ultrasonic studies of the temperature dependence of curing kinetics of diglycidyl ether of bisphenol‐A with catalyst
Authors: Alig I. , Nancke K. , Johari G. P.
Published: April 2003

Longitudinal velocity and attenuation of the unreacted diglycidyl ether of bisphenol‐A and dimethylbenzylamine mixture have been measured for 1 MHz ultrasonic frequency. These are combined with our earlier data [Alig et al., Acta Polymerica, Vol. 40, p. 590 (1989)], which were measured during the curing process of the thermoset, and then analyzed in terms of a process involving a negative feedback between molecular diffusion and chemical reaction. The complex plane plots of the real and imaginary components of the longitudinal modulus are fitted to a stretched exponential relation, and the structural relaxation time is calculated at different stages of curing at temperatures in the range 333‐403 K. The results are compared against the calorimetric, dielectric, and viscosity measurements and it is shown that, at least for two cases, gelation time can be observed from the longitudinal modulus data. © 1994 John Wiley & Sons, Inc.
An x‐ray pole figure analysis on biaxially deformed polyethylene film
Authors: Pazur Richard J. , Prud'homme Robert E.
Published: April 2003

The orientational states induced upon two‐step biaxially stretching low‐density polyethylene at 25°C have been investigated. A pole figure analysis of the (200), (020), and (002) crystalline planes has been employed to elucidate the evolution of the molecular crystalline orientation as a function of biaxial stretching. The initial uniaxial‐like orientation induced along the extrusion direction of the films was gradually lost upon transverse stretching and, consequently, replaced by a biaxial orientation as suggested by the orientation functions. In these cases, the a crystallographic axis was observed to be strongly oriented along the film normal, thus confining the c and b axes to the film plane. The pole figures clearly indicate that the c and b axes are preferentially aligned 45° with respect to the stretching directions. This unique orientational state of the orthorhombic unit cell of polyethylene has been termed a biaxial‐double orientation. Birefringence measurements on the biaxial samples indicated that the amorphous and crystalline regions are simultaneously biaxially oriented. The evolution of the crystalline orientation as a function of stretching was conveniently followed on a White/Spruiell orientation triangle. Quantification was hindered, however, by the presence of different crystal populations in the biaxially stretched samples. © 1994 John Wiley & Sons, Inc.
Structural stabilization of phase separating PC/polyester blends through interfacial modification by transesterification reaction
Authors: Yoon H. , Feng Y. , Qiu Y. , Han C. C.
Published: April 2003

Competition between phase separation and transesterification in immiscible polymer blends of polycarbonate (PC) and a copolyester (PET) is studied as a function of time and temperature by differential scanning calorimetry (DSC) and small‐angle neutron scattering (SANS). We found that (1) Global structure coarsens at T ≤ 200°C due to the dominance of phase separation over transesterification and melts at T ≤ 220°C due to the dominance of transesterification at the domain interface. However, transesterification is slow but still significant even at T ≤ 200°C. (2) An intricate balance of transesterification and phase separation rates controls global and interfacial structures. (3) Interfacial structures become measurable under certain conditions, and the interfacial thickness between PC or PET and the copolymers generated by transesterification increases with time. (4) DSC results are consistent with results obtained by SANS, but the latter is more sensitive than the former and differentiates the structural change at different length scales caused by phase separation and transesterification. © 1994 John Wiley & Sons, Inc.
Intramolecular formation of excimers in model compounds for polyesters obtained from 2,6‐naphthalene dicarboxylic acid and cyclohexanediols
Authors: Bravo Julio , Mendicuti Francisco , Mattice Wayne L.
Published: April 2003

The fluorescence in dilute solution has been measured as a function of solvent viscosity for four bichromophoric models for polyesters with naphthalene in the rigid aromatic unit and diols derived from cyclohexane as the flexible spacer. The spacers are 1,2‐cis‐cyclohexanediol, 1,2‐trans‐cyclohexanediol, a 1:2 mixture of 1,3‐cis‐ and 1,3‐trans‐cyclohexanediols, and a 1:2 mixture of 1,4‐cis‐ and 1,4‐trans‐cyclohexanediols. The shape of the emission spectra for the molecules in this series is less sensitive to the viscosity of the medium than was the case for an analogous series in which a methylene or oxyethylene spacer replaces the cyclohexanediol spacer. The dependence of the excimer emission on the type of spacer is different also in the series in which the rigid units contain naphthalene or benzene. When the rigid units contain naphthalene, excimer formation is maximal if the spacer contains 1,2‐trans‐cyclohexanediol, but this spacer produces a molecule with a very small tendency for excimer formation in its polymers with terephthalate. A conformational analysis correctly concludes that the spacer most conducive to excimer formation should be 1,2‐trans‐cyclohexanediol, but it does not identify the correct order of the remaining three bichromophoric model compounds. The problem may reside in the method for taking into account the finite width of the torsional well associated with each rotational isomer. © 1994 John Wiley & Sons, Inc.
Stoichiometry and morphology in terbium nitrate‐poly(ethylene oxide) macromolecular complex
Authors: Twomey Conor J. , Chen Shaw H. , Blanton Thomas N. , Schmid Ansgar , Marshall Kenneth L.
Published: April 2003

The Tb (NO3)3‐PEO system was characterized to have a solubility limit equivalent to n ≅ 6.5 and a coordination number of 12.4 ± 0.1, compared to 5.0 and 10.9 ± 0.1 for the Nd(NO3)3‐PEO system. The greater coordination involving Tb3+ appears to be responsible for the lower asymptotic glass transition temperature at high doping levels of the Tb(NO3)3‐PEO complex. In both systems, anhydrous amorphous complexes were obtained below the respective solubility limits, over which apparent solubilities were found to be enhanced by the presence of tightly bound moisture while retaining the amorphous character of the complexes. Whereas partial precipitation was observed in the Tb(NO3)3‐PEO system upon exposure to ambient moisture, both complexation and amorphous character were found to persist in the Nd(NO3)3‐PEO system in the presence of absorbed moisture. © 1994 John Wiley & Sons, Inc.
Crystallization and thermoreversible gelation of poly(butylene terephthalate)–epoxy mixtures
Authors: Nichols Mark E. , Robertson Richard E.
Published: April 2003

The thermoreversible gelation of solutions of poly(butylene terephthalate) (PBT) and a liquid diglycidyl ether of bisphenol‐A epoxy has been investigated. The morphology of the gels and the conditions under which they form have been characterized by optical microscopy, thermal analysis, and x‐ray scattering. Gels were found to form under two different conditions and with different morphologies. Gels formed after a considerable delay when homogenous PBT‐epoxy solutions were cooled to slightly below the dissolution temperature of crystalline PBT. These gels contained large, irregular PBT spherulites and smaller birefringent interspherulitic matter. The melting of these gels and the onset of macroscopic flow coincided with the melting of the interspherulitic matter, and occurred before the melting of the large spherulites. Thermoreversible gels formed very quickly when PBT‐epoxy solutions were self‐nucleated by heating a dispersion of crystalline PBT in epoxy slightly and briefly above the dissolution temperature and then cooling. These gels displayed only a weak background birefringence and were molten when the weak birefringence disappeared. In both cases, gelation occurred by the formation of a three‐dimensional PBT network in the epoxy liquid, and the nodes of the network were crystalline PBT particles. $ 1994 John Wiley & Sons, Inc.