bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic parameters for some poly (n‐alkyl methacrylates)
Authors: Havriliak S.
Published: April 2003

The dielectric relaxation data of poly (n‐hexyl methacrylate) and poly (n‐octyl methacrylate) by Strella and Chinai are represented in terms of the relaxation function proposed by Havriliak and Negami using the multiresponse techniques developed by Havriliak and Watts to evaluate the parameters and their dependence on temperature. The parameter α which represents the width of the distribution of relaxation times was found to be dependent on temperature whereas the parameter β representing the skewness of the distribution function was found to be independent of temperature. The relaxation process parameters are discussed in terms of Mansfield's jump model.
Prediction of microstructures for polydisperse block copolymers, using continuous thermodynamics
Authors: Spontak Richard J. , Williams Michael C.
Published: April 2003

A generalization of an earlier theory (Leary–Henderson–Williams) developed for microphase separation in monodisperse block copolymers is made for copolymers having moderate degrees of polydispersity and illustrated for the Schultz molecular weight distribution (MWD). First, an explicit study is made of molecular weight (M) effects for monodisperse poly (styrene–butadiene) diblock (SB) and triblock (SBS) copolymers. For a fixed temperature, it is shown how the critical molecular weight (Mc)—above which the copolymer is phase‐separated at equilibrium —varies with molecular composition (ϕS, volume fraction of S component) for both molecular architectures. Also predicted are the microstructural parameters ΔT(M) andf(M)—interphase thickness and volume fraction, respectively—and the high‐Mlimiting functions ΔT∝︁Mα2,f∝︁Mα3,D∝︁Mα4(Dis domain repeat distance) andTs∝︁Mα5(Tsis separation temperature). Then, for polydisperse systems in the range 1 ≲p≲ 3 ( where\[ P = \bar M_w /\bar M_n \]) corresponding predictions at constant\[ \bar M_n \]are made after identifying the mixture free‐energy‐minimum state with a weight average of the free energy minima of each fraction of the MWD. Calculations are made specifically for ϕS= 0.50 andTs= 298 K. It is shown that, even when\[ \bar M_n < M_c \], polydispersity can induce microphase separation ifpis sufficiently large. Good success is obtained in comparisons ofDpredictions with data on blends of two polydisperse diblock samples.
Physical and chemical aging in PMMA and their effects on creep and creep rupture behavior
Authors: Crissman John M. , McKenna Gregory B.
Published: April 2003

Samples of PMMA were aged at 80°C for between 1 h and 254 days and tested in creep in uniaxial extension at large stresses and at room temperature. Both chemical and physical aging effects were found to be important in determining the failure behavior of the samples. This behavior was found to be describable within the context of a commonly used failure criterion that the time to failure multiplied by the strain rate at failure is constant. The creep behavior was found to follow classical time–aging time and time–stress correspondence principles.
Polyurethane cationomers. I. Structure‐property relationships
Authors: Chen Show‐An , Chan Wu‐Chung
Published: April 2003

Polyether polyurethane cationomers are prepared using poly (tetramethylene oxide) of molecular weight 2000 as soft segments, N‐methyl‐diethanolamine as chain extender, glycolic acid as quaternization agent, methyl ethyl ketone as solvent, and three different diisocyanates. The three diisocyanates are 4,4′‐diphenylenemethylene diisocyanate (MDI), hexamethylene diisocyanate (HDI), and toluene diisocyanate (TDI). Properties of the films cast from solutions of the three series of ionomers are studied by infrared spectroscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, wide angle x‐ray diffraction, and tensile elongation testing. In the un‐ionized and ionized systems, the hard segments exhibit disordered and ordered arrangements, respectively. Ionization disrupts the order and produces increased cohesion in the hard domains, which have opposing effects on the tensile elongation properties. In the MDI and TDI systems, cohesion is predominant, leading to an increased tensile strength and modulus and decreased elongation at break. But in the HDI system, the disruption of the order is predominant, leading to decreased tensile strength and only insignificant reduction in the elongation at break. In the TDI system, the tensile strength is rather low, which is attributed to the poor order in the hard domains resulting from the high content of the asymmetric 2,4‐isomer of the urethane.
PMMA stereocomplex: Study of the aggregation process by electron microscopy
Authors: Quintana J. R. , Stubersfield R. , Price C. , Katime Issa
Published: April 2003

The structure of stereocomplex aggregates formed from isotactic and syndiotactic poly (methyl methacrylate)s was studied in tetrahydrofuran (THF) by transmission electron microscopy (TEM). We have found that the primary stereocomplex particles are nearly spherical and, as the complexation advances, the particles lengthen. Eventually aggregates branch to form a three‐dimensional network.
Improving tensile mechanical properties of aromatic polyimides by thermal imidization after cold drawing of poly (amic acids)
Authors: Kochi Masakatsu , Yokota Rikio , Iizuka Taka Yuki , Mita Itaru
Published: April 2003

A new technique of thermal imidization after cold drawing of poly (amic acid) films is used to improve the tensile mechanical properties of various aromatic polyimide films. By this method PI (BDA/PPD) with linear, rigid main chains can be obtained as a high‐modulus and high‐strength material with Young's modulus of ca. 60 GPa and tensile strength of ca. 1.2 GPa. The enhancement of mechanical properties is favored by the rapid development of molecular order during imidization. The tensile properties of flexible polyimides such as PI (BDA/DDE) and PI (PMDA /DDE) are not significantly improved, because the orientation of cold‐drawn poly (amic acid) chains is easily relaxed at the temperature of imidization.
Local order and elasticity of polymer networks with nematiclike interactions
Authors: Walasek Janusz
Published: April 2003

The influence of nematiclike interactions on local order and elasticity of crosslinked polymer systems is considered. A molecular mean‐field approach is used to describe interactions between system segments. The orientation‐dependent potential is assumed to be proportional to the square of the cosine of the angle between the direction of the orienting field and the chain segment vector. The orientation factor is calculated from a self‐consistent equation, with no restrictions on the strength of intersegmental interactions. Isotropic (slightly oriented) and nematic (highly oriented) phases are observed. The influence of local order on the stress‐strain relation is derived for various values of network structural parameters (contraction coefficient, length of network chains) and the strength of segment‐segment interaction. For some values of these parameters, local order can modify considerably the elastic properties of the network system.
Chain structure of homogeneous ethylene‐propylene copolymers showing inversion, described on the basis of 13C‐NMR data. II. Application
Authors: Mathot V. B. F. , Fabrie Ch. C. M. , Tiemersma‐Thoone G. P. J. M. , Van Der Velden G. P. M.
Published: April 2003

For a series of homogeneous ethylene‐propylene copolymers with mole fraction ethylene (x1) ranging between 0.40 and 0.85, the inversion (I) independent propagation probabilities (Pijs) and reactivity ratios ( rijs) and the methylene, ethylene, and propylene sequence length distributions have been determined from 13C nuclear magnetic resonance (NMR) data, using a first‐order Markovian terpolymer [ethylene (1), inverted propylene (2), and normal propylene (3)] model. For each sample, the limiting values of I (Imin, Imax) are given. Calculations of the common parameters for 19 samples show that the polymerization direction characterized by the r set and I is statistically more probable than the opposite direction, which is characterized by the r′ set and I′. Further, I = Imin appears to be close to the most probable value of I. The resulting r set is r12 = 119, r13 = 19.7 and, for I = Imin, r21 = 0, r31 = 0.034, r32 = 2.98. In the limited range 0.60 < x1 < 0.85, there appears to be no preference for either polymerization direction, so that the solutions characterized by the r set and I = Imin and by the r′‐set and I = I′max, respectively, are about equally probable. If the copolymer reactivity ratios re and rp are defined in the usual manner, it follows that for the limited range re = 17. In the model used here, rp is found to be dependent on the ethylene‐propylene ratio in the reactor. Nevertheless, it can be stated that rp ≅ 0.029 and re rp ≅ 0.50.
Quasiharmonic treatment of infrared and raman vibrational frequency shifts induced by tensile deformation of polymer chains
Authors: Tashiro Kohji , Wu Gang , Kobayashi Masamichi
Published: April 2003

Stress‐induced vibrational frequency shifts in the infrared and Raman spectra of polymer chains are interpreted theoretically on the basis of the quasiharmonic lattice dynamical treatment. The calculated frequency shifts are in good agreement with experiment for planar‐zigzag polyethylene and helical polyoxymethylene. The anharmonic terms of the force constants are estimated numerically in order to obtain the parameters of anharmonic potential functions such as the Morse potential. The close relationship between stress‐induced frequency shifts and molecular deformation mechanisms is discussed in terms of the force field and the geometry of the polymer chain.
Characterization of orientation clustering in short‐fiber composites
Authors: Ranganathan Sridhar , Advani Suresh G.
Published: April 2003

During flow of concentrated fiber suspensions, the proximity of the fibers induces interactions in their orientation space. These fiber‐fiber interactions may lead to clustering in orientation of fibers and a nonhomogeneous fiber orientation field. An orientation cluster is a group of fibers in a specific neighborhood sharing the same orientation state. It is important to characterize clustering to understand and quantify fiber‐fiber interactions. Such characterization will also be useful in the prediction of the mechanical and physical properties of the resulting composite material. An image of the fiber distribution at a location in a composite is divided into a number of partitions, and the variance of the fiber orientation states within the partitions, between the partitions and of the entire sample are compared to establish the existence and the extent of clustering in the orientation space. Statistical methods such as analysis of variances and techniques analogous to the scale of segregation used in mixing theory are modified and adopted to identify and quantify orientation clusters. Simulated examples that describe clustering quantitatively in magnitude and direction of planar orientations are presented. This method is then extended to identify clustering in model injection molding experiments performed in a center‐gated square mold with suspensions of 1% and 10% volume fractions.
An improvement in the flory corresponding‐states theory of polymer solutions
Authors: Li Pantong , Krause Sonja , Hollinger Henry B.
Published: April 2003

The original Flory corresponding‐states theory of polymer solutions requires an entropic correction parameter Q12, the sign and value of which seem to be arbitrary, and the physical meaning of which is obscure. Moreover, calculated excess volumes of mixing for many polymer solutions are often in significant disagreement with experimental data. In order to eliminate these problems, we have modified the kinetic part of the partition function, introduced an effective mass for the mixture segment, and adopted the nonlinearity of the number of degrees of freedom with respect to the composition for the mixture segment. In addition, the effect of nonrandom configurations of the segments in the mixture has been included. In the improved equations, derived in this work, the Flory interaction parameter χ can be considered to comprise three parts: (a) a kinetic part due to the contribution of the average number of degrees of freedom and the effective mass of the mixture; (b) a free volume part; and (c) an interaction part including the contributions due to the contact interaction and the nonrandom configuration of the segments in the mixture, caused by the interaction. The improved theory is in good agreement with literature data on polystyrene solutions and poly (dimethyl siloxane) solutions.
Gas transport properties of annealed polyimide films
Authors: Hachisuka H. , Tsujita Y. , Takizawa A. , Kinoshita T.
Published: April 2003

Sorption and permeation of CO2 in various annealed polyimide (PI) films were investigated. Dual‐mode sorption and partial immobilization models were used to analyze the data. Sorption of CO2 in PI film quenched from above the glass transition temperature (Tg) is greater than in film as received. In fact, sorption is decreased over the entire pressure range by cooling the film slowly. These changes in sorption of CO2 can be attributed to a change in the Langmuir sorption capacity C′H by annealing, since the other dual‐mode sorption parameters, kD and b, are almost independent of annealing. The value of C′H is increased by quenching, and decreased by slow cooling from above Tg. The two diffusion coefficients DD and DH according to the Henry and Langmuir modes, respectively, for CO2 also depend markedly on annealing. Diffusion coefficients of quenched PI films are increased and those of film cooled slowly are decreased compared with values for PI film as received. The change in DH is larger than that in DD. The permeability coefficient of quenched PI films at 100 cmHg is about 1.7 times that of PI film as received. The film structure formed by quenching can enhance permselectivity.
The evolution of the viscoelastic retardation spectrum during the development of an epoxy resin network
Authors: Plazek Donald J. , Chay In‐Chul
Published: April 2003

The evolution of the viscoelastic behavior of an epoxy resin at various stages of curing has been followed with the changes in the retardation spectrum. The creep J(t) and recoverable creep compliance Jr(t) curves of the neat epoxy resin Epon l00lF (Shell) were determined at temperatures between 30 and 77°C. The viscosity decreased over 8 orders of magnitude as the temperature was increased. Specimens with eight stages of network development were prepared by reacting all of the epoxy resin's oxirane rings with amine hydrogens from varying ratios of a monofunctional amine (methyl aniline) and a tetrafunctional amine 4,4′‐diamino diphenyl sulfone (DDS). Preparations in which 25, 35, and 40% DDS were used did not result in a molecular network, so they were viscoelastic liquids. With 45% DDS, the product had a nascent network and was judged to be just beyond the point of incipient gelation. The remaining preparations from 0.50, 0.60, 0.70, and 1.0 DDS yielded tighter less compliant molecular networks. The creep and recoverable compliance curves were measured over a range of temperatures above the glass transition temperature, Tg. They were reduced to Tg, and retardation spectra L(ln τ) were calculated.
Dependence of slow crack growth in polyethylene on butyl branch density: Morphology and theory
Authors: Huang Yan‐Ling , Brown Norman
Published: April 2003

A theoretical equation has been developed to described the rate of slow crack growth in an ethylene‐hexene copolymer in terms of the basic morphological parameters. These parameters are spacing of the butyl branches, number of tie molecules, and the thickness of the lamellar crystal. Experimentally, the thickness of the lamellae and the long period were determined as functions of the branch density. The calculation of the number of tie molecules is based on the values of the molecular weight and the long period. The model of slow crack growth is based on the rate of disentanglement of the tie molecules. The rate of disentanglement varies inversely with the number of tie molecules and directly with the number of tie molecules that are not pinned by the branches.
Single‐molecule single crystals
Authors: Bu Haishan , Pang Yanwan , Song Dandan , Yu Tongyin , Voll T. M. , Czornyj George , Wunderlich B.
Published: April 2003

Various approaches to the preparation and verification of single‐molecule single crystals are discussed for polyethylene and poly (oxyethylene). Analytic tools are electron microscopy, electron diffraction, and differential scanning calorimetry. The main difficulty in producing a single‐molecule single crystal is to keep crystals from joining during growth.
Third virial coefficient of polystyrene in benzene
Authors: Nakamura Yo , Norisuye Takashi , Teramoto Akio
Published: April 2003

Second virial coefficients A2 and third virial coefficients A3 for benzene solutions of ten polystyrene fractions ranging in weight‐average molecular weight Mw from 104 to 2 × 107 at 25°C were determined by light scattering. The third coefficient is represented approximately by A3 = 8.0 × 10−6 M mol g−3 cm6 for Mw above 105. In this molecular weight region, the factor g defined by A3/AMw/ This trend of g is consistent with predictions of early two‐parameter theories but not with those of renormalization group theories. In particular, quantitative agreement is observed between the present experiments (for Mw ≳ 2 × 105) and the mean‐field two‐parameter theory of Stockmayer and Casassa.
Interfacial effects on stress distribution in model composites
Authors: Fan Cun Feng , Waldman David A. , Hsu Shaw Ling
Published: April 2003

Raman mechanical spectroscopy was used to examine interfacial effects on the stress distribution in model polydiacetylene fiber/epoxy composites. Epoxy release agents were coated on fiber surfaces to modify the interfacial adhesion properties. The modified fiber surfaces were then characterized by scanning electron microscopy and x‐ray photoelectron spectroscopy as well as optical microscopy. No difference in the maximum stress value or stress distribution was observed for the two types of fibers, coated or uncoated, used in composites. This suggests that adhesion properties at the composite interface do not affect tensile stress transfer efficiency nor, therefore, the composite tensile modulus along the fiber axis direction in uniaxial composites. Experimental data were also compared with theoretical calculations assuming perfect bonding between fiber and matrix, and idealized frictional force transfer mechanism at the fiber–matrix interface.
Nonintegral and integral folding crystal growth in low‐molecular mass poly (ethylene oxide) fractions. II. End‐group effect: α,ω‐methoxy‐poly (ethylene oxide)
Authors: Cheng Stephen Z. D. , Chen Jianhua , Zhang Anqiu , Heberer Daniel P.
Published: April 2003

Differential scanning calorimetry (DSC) and in situ small‐angle x‐ray scattering (SAXS) indicate that in an α ω‐methoxy‐poly(ethylene oxide) (MPEO) fraction (MW 3000) a transient nonintegral folding (NIF) crystal initially forms during crystallization throughout a wide range of crystallization temperatures. Subsequent transformations of the NIF to IF (integral folding) crystals at low temperatures occur mainly through isothermal thickening or thinning via perfection processes or, at higher temperatures, through primary crystal formation. The NIF crystal is thermodynamically the least stable state among the crystal forms, but its growth is the most rapid. The overall crystallization and crystal melting of this MPEO fraction reveal that the NIF crystal and the NIF → IF crystal transformations are common to low‐molecular mass PEO fractions without regard to the end group. Nevertheless, diffusion coefficient and viscosity measurements provide clear evidence of an end‐group effect in PEO and MPEO fractions. The difference in the overall crystallization and isothermal thickening and thinning kinetics of low‐molecular mass PEO and MPEO fractions can lead to further understanding of end‐group effects.
Nonintegral and integral folding crystal growth in low‐molecular mass poly (ethylene oxide) fractions. III. Linear crystal growth rates and crystal morphology
Authors: Cheng Stephen Z. D. , Chen Jianhua
Published: April 2003

Correlations of the linear crystal growth rates with the change in crystal morphology for poly (ethylene oxide) (PEO) (MW 3000) and α,ω‐‐methoxy‐poly (ethylene oxide) (MPEO) (MW 3000) fractions have been established over a wide range of supercooling (ΔT= 25 K). Two linear crystal growth rates were measured, namely, the linear crystal growth rate of spherulites or hedrites and the lateral (linear) crystal growth rate of single lamellar crystals along different crystalline planes (below ΔT= 11–12 K). At a low supercooling of 5 K, the crystal growth rate of the MPEO fraction passes through a minimum. Subsequently, the rate increases abnormally and reaches a maximum at even lower supercooling. This crystal growth retardation has been attributed to the competition between differing chain conformations during crystal growth. In this case, particularly, these conformations are the extended chain and the once‐folded chain conformations. This retardation is not observed in the PEO fraction, since in this low supercooling region any once‐folded chain conformations formed during crystal growth are of the double‐layer lamella type. The change in morphology in this region supports this judgement. Above ΔT= 7.6 K, the crystal growth behavior in these two fractions can be described by the present nucleation theory on flat crystal growth faces. Below that ΔT, however, different crystal growth mechanisms can be clearly seen. This may be associated with the crystal growth on the highly serrated growth faces in these two fractions.
Fatigue crack propagation in high‐density polyethylene
Authors: Yeh J. T. , Runt J.
Published: April 2003

An investigation of the influence of crystalline microstructure on fatigue crack propagation (FCP) in high‐density polyethylene (HDPE) is reported. Various thermal histories were used to generate samples with the same crystallinity and supermolecular structure for three different molecular weight HDPEs. Estimation of tie chain densities were obtained from measurements of brittle fracture stress and predicted from the estimated chain dimensions of the polymers using the modified version of the approach originally taken by Huang and Brown. A significant decrease in FCP resistance and a clear transition to a more brittle fracture surface was observed with decreasing molecular weight. Detailed studies of damaged zones preceding the growing crack show a transition to a more highly branched crack structure for those samples associated with a higher FCP resistance. These results strongly suggest that the branched damaged zone structure improves the FCP resistance by enlarging and blunting the crack tip and, therefore, consuming more energy during the fatigue crack propagation. Additional efforts were made to prepare samples with the same crystallinity and tie chain density, but different supermolecular structure. However, in contrast to reports in the literature, no significant difference in FCP resistance was observed for specimens with different average spherulite sizes. This is probably because the propagating crack front is preceded by a significant zone of plastic deformation and is not expected to directly encounter the spherulites.
Nuclear magnetic relaxation of α‐13C nuclei of helical poly(γ‐hexyl‐L‐glutamate) and poly(γ‐benzyl‐L‐glutamate)
Authors: Raby Philip , Budd Peter M. , Heatley Frank , Price Colin
Published: April 2003

Spin‐lattice relaxation times (T1), spin‐spin relaxation times (T2), and nuclear Overhauser enhancements (NOE), at 75.5 MHz are reported for α‐13C nuclei of poly (γ‐benzyl‐L‐glutamate) in deuterated dimethylformamide at 60°C and of poly(γ‐hexyl‐L‐glutamate) in cyclohexanone at 48 and 79°C. It is shown that for molecular weights above 105, the polypeptides cannot be considered as essentially rigid helices with internal librational motions; additional backbone flexing motions contribute to the relaxation behavior.
Theories for network formation in multistage processes
Authors: Tiemersma‐Thoone G. P. J. M. , Scholtens B. J. R. , Dušek K. , Gordon M.
Published: April 2003

Two different theoretical approaches have been developed to describe network formation in a six‐component, three‐stage process with the stochastic theory of branching processes. Both approaches make use of probability‐generating functions and cascade substitutions. In the POLYM approach, the products of the previous stage, namely, complete (branched) molecules, are used as building units in the subsequent stage. The molar masses and unreacted functionalities are identified by means of dummy variables. In the resulting formulas the sequence of the three stages is clearly visible. In the MONOM approach, the system is treated as a quasi‐one‐stage process; the original monomers are the building units in all three stages, the sequence of which is only apparent from the input parameters. In the MONOM approach the original monomers are used as building units, irrespective of the stage in which they react. A separate dummy variable is chosen for each possible reaction in each stage in the MONOM approach, so that the two approaches give analytically identical results, but along completely different derivations. This avoids correlation errors in the MONOM approach. Both approaches have incorporated kinetic effects by way of substitution effects in two of the monomers. The two approaches are prefaced by the treatment of several paradigms of increasing complexity to show the unity and strength of the theory and to warn against typical pitfalls.
Crystal transition and structure of poly (γ‐n‐alkyl glutamate)s
Authors: Sasaki Shintaro
Published: April 2003

The nature of the crystal transition of the α‐helical forms of poly (γ‐n‐alkyl glutamate)s (alkyl = ethyl, propyl, and butyl) is described. The transition is thermally reversible, and its temperature T2 is much higher than the glasslike transition temperature T1 associated with the side‐chain motion. The main chains undergo large‐scale motion (librational about the chain axis and translational along the axis) above T3 ≈ 200°C. The structure observed below T2 is anomalously disordered compared with that observed between T2 and T3. The crystal structure emerging above T2 is analyzed for a typical sample of poly(γ‐n‐propyl L‐glutamate). The trigonal unit cell contains three α‐helices so that each helix is surrounded by other helices in the same fashion, but the helices are not interrelated by a crystallographic symmetry element. The side chains suffer no particular change at T2. The main‐chain motion gives rise to the T2 transition by inducing attractive forces between interpenetrating side chains.
Light‐scattering studies on solutions of cellulose in the ammonia/ammonium thiocyanate solvent system. I. Classical light‐scattering
Authors: De Groot A. W. , Guinnup D. E. , Theil M. H. , Cuculo J. A.
Published: April 2003

This article reports the use of classical light scattering to study cellulose in the NH3/NH4SCN solvent system. Three solvent compositions were used, 27.01 73.0,25.5/ 74.5, and 24.51 75.5 weight ammonia/weight ammonium thiocyanate. The coefficient, (dn/dc)υ, was determined by back calculating using the molecular weight determined by solution viscometry in the solvent system cupriethylenediamine and the classical light‐scattering results. Second virial coefficients were found to be similar to those values measured for cellulose in the FeTNa and LiCl/DMAC solvent systems. The characteristic ratios were found to vary with solvent composition with the highest values being at a composition of 25.5/74.5 weight ammonia/ weight ammonium thiocyanate. Persistence lengths were also found to vary with solvent composition with the highest value being 264 × 10−8 cm at solvent composition 25.5/74.5.
A composite methodology for multistage degradation of polymers
Authors: Nam Jae‐do , Seferis James C.
Published: April 2003

Five different analytical schemes for examining isothermal and nonisothermal degradation of polymers were reviewed and found inadequate for describing multistage decomposition. The different schemes were experimentally tested using thermogravimetric analysis data for an ethylene‐vinyl acetate (EVA) copolymer, which exhibited a well‐behaved two‐step decomposition process in a nitrogen environment. Based on these experimental and analytical findings, a generalized methodology was developed capable of describing the exhibited complex decomposition behavior of polymers by combining two or more kinetic mechanisms in a series or parallel arrangement. This composite of combinational methodology thus extends established analytical schemes for describing complex decomposition of polymers in a rational manner, incorporating both experimental and theoretical considerations.
Thermal, dielectric, and mechanical relaxation in poly(benzimidazole)/poly(etherimide) blends
Authors: Liang Kuiming , Bánhegyi György , Karasz Frank E. , MacKnight William J.
Published: April 2003

Thermal, dielectric, and mechanical relaxation measurements on miscible blends of polybenzimidazole (PBI) and a polyetherimide (PEI, Ultem 1000) prepared by solution casting from dimethylacetamide (DMAc) reveal a number of structurally related features. Annealing below the glass transition temperature induces an enthalpy relaxation process typical of single‐phase glasses of nonequilibrium structure. Dielectric relaxation experiments on samples annealed at ambient conditions reveal two relaxation processes below 400°C. At lower temperatures (50–200°C), the desorption of water is observed. Above 200°C in the first run, a composition‐dependent relaxation is seen at the highest frequencies (100 kHz) while a relaxation approximately independent of composition appears in the second run. The latter corresponds to the glass transition of the PEI phase. The glass transition of PBI at this frequency is above the degradation temperature. At lower frequencies a strongly dispersive electrode polarization process masks the high‐temperature relaxations. Dynamic mechanical results show similar features with respect to phase separation; the main difference is that the tan δ curves in the first run are complicated by the desorption of residual solvent.
Charge transfer interactions in some poly[[o‐(trimethylsilyl)phenyl] acetylene]‐acceptor complexes
Authors: Kang E. T. , Neoh K. G. , Tan K. L.
Published: April 2003

Charge transfer (CT) interactions between poly[[o‐(trimethylsilyl)phenyl]acetylene] or poly(o‐Me3SiPA) and some electron acceptors were studied by ultraviolet‐visible and infrared absorption spectroscopy and by x‐ray photoelectron spectroscopy, (XPS). The electron acceptors used included iodine, bromine, o‐chloranil, o‐bromanil, 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ), and tetracyanoethylene (TCNE). Varying degrees of CT interactions were observed in all of the polymer/acceptor complexes studied. The electrical conductivities σ of the organic acceptor complexes exhibited a strong acceptor concentration dependence at low acceptor levels, with the DDQ complex exhibiting the highest σ. The extent of CT and the redistribution of charges resulting from the CT in all the complexes were revealed by XPS. The poly (o‐Me3SiPA)/I2 complex film lost iodine spontaneously while more than half of the bromine in the poly (o‐Me3SiPA)/Br2 complex existed as covalently bonded bromine, even at low halogen loading.
Effect of annealing on structure and permeability of poly [(l‐trimethylsilyl)‐l‐propyne]
Authors: Tasaka Shigeru , Inagaki Norihiro , Igawa Masaaki
Published: April 2003

The permeability of annealed poly (l‐(trimethylsilyl)‐l‐propyne) was studied from the viewpoint of structural information obtained from x‐ray diffraction and density. The sample cast from benzene solution had low density (0.82 g/cm3) and high permeability, whereas the annealed sample had a higher density (0.88 g/cm3) and permeability lower by two orders of magnitude. The smaller‐angle x‐ray diffraction peak for each sample, which was likely to reflect the distance between intermolecular chains, increased in intensity and shifted toward higher angle, corresponding to the change of the density with annealing. The logarithmic oxygen permeability was proportional to the density, namely the free volume fraction correlated with the diffusion coefficient and controlled by annealing and swelling by alcohols.
Relaxations of thermosets. VIII. Brillouin light scattering during the curing of diglycidyl ether of bisphenol‐A thermosets
Authors: Mangion M. B. M. , Vanderwal J. J. , Walton D. , Johari G. P.
Published: April 2003

The kinetics of sol‐gel‐glass transformations have been studied in the thermosets of diglycidyl ether of bisphenol A cured with diamino diphenyl methane and diamino diphenyl sulfone, at different temperatures using Brillouin light scattering. The Shape of the Brillouin peak is generally broad. This is attributed to the damping of elastic waves in the mixture of unpolymerized low‐molecular weight fluid and the polymer chains forming the networks. The Brillouin peak becomes sharp and narrow at complete curing of the thermosets. The phonon velocity increases and the attenuation decreases with the curing time. These changes occur in two steps with the second step appearing near the gelling time of the thermosets. A semilogarithmic plot of the time for the velocity and attenuation to reach half of their total change against the reciprocal temperature yields a straight line with different slopes for the two thermosets. It is suggested that Brillouin light scattering is a useful non‐destructive, in‐line, method for control in the processing of epoxy thermosets.
Structure and properties of complex transition‐metal (II) salts of ethylene‐methacrylic acid copolymer with 1,3‐bis (aminomethyl) cyclohexane
Authors: Hirasawa Eisaku , Tadano Kenji , Yano Shinichi
Published: April 2003

Thermal properties by differential scanning calorimetry, stiffness, and melt flow rate (MFR) were measured for the complex transition‐metal (Zn(II), Cu(II), Mn(II), and Co(II)) salts of ethylene‐methacrylic acid copolymer (EMAA) with 1,3‐bis(aminomethyl)‐cyclohexane (BAC). It was found that the strength of both ionic interactions of metal cations with carboxyl groups and coordination bonds of amino groups to metals differ among metal species. In particular, the complex Mn salts are weaker than the complex salts of the other transition metals, which corresponds with Irving‐Williams series of stability constants of transition metal‐ion complexes. Stiffness depends predominantly on the degree of crystallinity of ionic crystallites in ionic clusters, which depends on the ionic species.
Mechanical anisotropy in biaxially oriented polyvinyl chloride
Authors: Guney H. Yuksel , Oskay Taner , Ozkan H. Sinan
Published: April 2003

The mechanical anisotropy of polyvinyl chloride oriented in two perpendicular directions with different draw ratios has been studied. The results are compared with the anisotropy of uniaxial samples oriented at a common draw ratio. The propagation velocities of ultrasonic pulses have been measured by an immersion technique. Longitudinal wave velocities have been measured in three principal planes over a wide range of propagation directions. The limitations of measuring velocities in the planes containing the draw axes were mitigated by use of a special slicing technique. Measurements were performed at 2 MHz and 25°C. Velocities of the transverse waves were measured for incident wave angles greater than the critical angle. From these measurements, five elastic moduli were calculated for the uniaxially oriented samples, and nine elastic moduli were obtained for the biaxially oriented samples. In biaxially oriented samples, the moduli along the draw axes are directly proportional to the draw ratio in the same direction.
Molecular motion and 1H NMR relaxation of aqueous poly(N‐isopropylacrylamide) solution under high pressure
Authors: Ohta Hideo , Ando Isao , Fujishige Shoei , Kubota Kenji
Published: April 2003

In order to obtain useful information about the molecular motion and structure of poly(N‐isopropylacrylamide) (PNiPAM) in aqueous solution, proton spin‐lattice relaxation times, proton spin‐spin relaxation times, and volume changes were measured at pressures from 1 to 400 kg/cm2 as a function of temperature. We found that the molecular motion and the structure of water and PNiPAM in PNiPAM/water solution transitionally change at gelation temperature (31°C). The effect of pressure on such transitional changes is studied. It is suggested that application of pressure to the system prevents the gelation.
Prediction of the glass transition temperature of cycloaliphatic amine–epoxy networks
Authors: Won Yong‐Gu , Galy Jocelyne , Pascault Jean‐Pierre , Verdu Jacques
Published: April 2003

Stoichiometric, completely cured binary or ternary mixtures of the diglycidylether of bisphenol A (DGEBA), isophorone diamine (IPD), and trimethylcyclohexylamine (TMCA) monomers were studied by differential scanning calorimetry. The relations between the glass transition temperature Tg and the structure of the copolymer networks were investigated. Good predictions of Tg can be obtained on the basis of the following hypothesis: (1) the molar contributions MiT−1gi to the “copolymer effect” of difunctional groups are additive, (2) the crosslinking effect can be expressed by the DiMarzio relation in which the molar contribution of crosslink mers is an increasing function of the stiffness of linear segments. For the seven systems under study, the deviation between calculated and experimental Tg values is within experimental scatter.
Separation of styrene‐methacrylate copolymers by composition using normal and reversed‐phase high‐performance liquid chromatography
Authors: Sato Hisaya , Ogino Kenji , Maruo Susumu , Sasaki Masato
Published: April 2003

The separation of styrene‐methacrylate copolymers by chemical composition was studied using high‐performance liquid chromatography (HPLC). With the combination of acrylonitrile (polar) gel and nonpolar eluent or of styrene (nonpolar) gel and polar eluent, poly(styrene‐co‐methylmethacrylate) was separated by the adsorption mechanism. The former is designated as normal and the latter as reversed phase. With other combinations, the copolymer was separated mainly by fractional dissolution mechanism. The sample eluted slightly earlier as molecular weight decreased. The molecular weight effect on the reversed‐phase HPLC was smaller than that on the normal phase. A gel with an exclusion limit of 3 × 103 exhibited greater molecular weight dependence and worse resolution than a gel with an exclusion limit of 50 × 104.

Poly(styrene‐co‐n‐butyl methacrylate) also was separated on the basis of chemical composition by normal and reverse‐phase HPLC. However, poly(styrene‐co‐t‐butyl methacrylate) was separated only by reverse‐phase HPLC. When octadecyl methacrylate gel was used instead of styrene gel in reverse‐phase HPLC, a good separation was not obtained. This indicates a specific interaction between the phenyl group of the styrene gel and the sample.
Heat capacities and entropies of linear, aliphatic polyesters
Authors: Varma‐Nair Manika , Pan Robert , Wunderlich Bernhard
Published: April 2003

New measurements of the heat capacity in the melt of poly(trimethylene succinate) (PTMS), poly(trimethylene adipate) (PTMA), and poly(hexamethylene sebacate) (PHMS) from 310 to 400 K are presented. Based on these data and literature data on eight other molten polylactones and poly(ethylene sebacate) (PES), an addition scheme is developed for linear, aliphatic polyesters that leads to the equation:

which represents the ATHAS‐recommended melt heat capacities for all linear polyesters. Combining previously discussed solid heat capacities, derived from an approximate frequency spectrum, with the new liquid heat capacities, the various thermodynamic functions (enthalpy, entropy, and Gibbs function) could be derived using the ATHAS computation scheme. The average value of residual entropy at zero kelvin of 5.3 ± 1.8 J/(K mol) per mobile bead for glassy linear polysters was found to be somewhat higher than for many other polymers in the data bank, but closer to that observed for linear, aliphatic polyamides. The phase transitions of PTMS, PTMA, and PHMS are also analyzed using the quantitative baselines available from the heat capacity study.
Relaxations in thermosets. IX. Ionic conductivity and gelation of DGEBA‐based thermosets cured with pure and mixed amines
Authors: Mangion Michel B. M. , Johari G. P.
Published: April 2003

The results obtained during the isothermal curing of diglycidyl ether of bisphenol‐A‐based thermosets cross‐linked with pure diaminodiphenyl methane and pure diaminodiphenyl sulfone and with their mixtures have been analyzed to determine how the dc conductivity changes with time during the conversion of its liquid to a gel. The complex permittivity data are first analyzed to show that ac measurements can be used to obtain the ionic conductivity over a considerable period of the curing process. The procedure allows one to obtain the dc conductivity without having data as a function of frequency. The shape of the complex plane plots of the electrical modulus are semicircles, but with small deviations that appear at long times during the curing process. The dielectric consequences of the chemical changes with time during the cross‐linking of the thermoset are analogous to the frequency dependence of the complex permittivity of a liquid. The analysis shows that the dc conductivity σo of a thermoset during its cure follows a power law, σo∝ (tg—t)x, where t is the curing time (t < tg). The results can also be described equally well by a new equation, σo ∝ exp[—B/(to—t)], where x, tg, B, and to are empirical constants all of which vary with the temperature of the cure. tg is close to the time for gelation known from independent studies and to is close to but longer than the time for vitrification. These conclusions are discussed in terms of scaling concepts for the gelation phenomenon.
Characterization of a single sample of an unknown polymer by size exclusion chromatography
Authors: Vilenchik Lev Z. , Rubinsztajn S. , Zeldin Martel , Fife Wilmer K.
Published: April 2003

The relationship between viscosity constants, k', a and Kη from the equations of Huggins and Mark‐Kuhn‐Houwink has been considered. It is shown, theoretically, that the sum of k' and a must be constant for all flexible‐chain macromolecules irrespective of the solvent used. On this basis, a combination of chromatography and viscometry measurements can be used to characterize a new species. The method has been applied to the new polymer, poly[methyl(pyridin‐3‐yl) siloxane] (1) where no suitable calibration standards are available. The value of a, k', and Kη for 1 has been calculated. The calculated constants enabled an estimation of different average molecular weights (MnMwMz) and polydispersity (Mw/Mn) from a minimum of experimental data. The new method is general and can be applied to any homogeneous linear flexible‐chain nondraining macromolecule.
A raman LAM study of lamellar thickness of virgin polyethylene powder
Authors: Wang Li Hui , Ottani Stefano , Porter Roger S.
Published: April 2003

The lamellar thickness of polyethylene virgin reactor powder has been successfully measured using the Raman longitudinal acoustic mode (LAM). Relatively high lamellar thicknesses have been found. These values change with polymerization temperature in an unusual way, with lamellar thickness being larger for lower polymerization temperature, i.e., at higher undercooling for crystallization. Agreement within an experimental error of 10% has been obtained between values from LAM and those calculated by the Thompson—Gibbs equation from the melting point measured by differential scanning calorimetry.
Structure and thermochromic solid‐state phase transition of poly (3‐alkylthiophene)
Authors: Tashiro Kohji , Ono Keiko , Minagawa Yasuhisa , Kobayashi Masamichi , Kawai Tsuyoshi , Yoshino Katsumi
Published: April 2003

In order to clarify the structural changes that occur in the thermochromic phase transition of poly (3‐dodecylthiophene) [P3DT] and poly (3‐hexylthiophene) [P3HT], the temperature dependence of x‐ray diffraction and Fourier transform infrared spectra was measured. (1) Orthogonal unit‐cell parameters were determined at room temperature: a=25.83 Å, b=7.75 Å, c (fiber axis)=7.77 Å for P3DT and a=16.63 Å, b=7.75 Å, and c=7.77 Å for P3HT. A large variation of the a‐axis length between P3DT and P3HT indicates the extended trans conformation for the alkyl side chains which are oriented along the lateral a‐axis direction. (2) The interplanar spacing, intensity, and integral width of the x‐ray (h00) and (00l) reflections were found to change drastically in the transition region. (3) Polarized infrared measurements at high temperature revealed a marked increase of the gauche band intensity for the alkyl side group modes followed by a decrease in the band intensity of the thiophene ring modes. (4) The layer reflections of the x‐ray fiber diagram become diffuse at high temperatures, indicating that the transition occurs in a liquidcrystalline manner with the orientation of the main chain axes preserved but with almost no axial correlation between the neighboring main chains. These results provide experimental support for the structural model proposed earlier: as the temperature increases, the trans‐type side chains begin to disorder by introduction of gauche bonds. This disordering disrupts the regularity of the main chain conformation and decreases the effective length of the polythiophene conjugated system.
The influence of crystallinity distribution on small‐angle x‐ray scattering from semicrystalline polymers
Authors: Lee Y. D. , Phillips P. J. , Lin J. S.
Published: April 2003

Theoretical x‐ray scattering curves have been developed for the lamellar structure in semicrystalline polymers in which there are present distributions of lamellar thickness and crystallinity. The models have been tested against samples of linear low‐density, low‐density and crosslinked polyethylenes. When variation in crystallinity is present in a material, a major effect is an increase in the magnitude of near‐zero angle scattering. The Bragg maximum can appear as an ill‐defined hump on an apparently high level of background scattering. The shape of the Bragg peak is influenced more by crystallinity distribution than by lamellar thickness distribution. Of the polymers we have studied so far only linear low density polyethylene shows significant crystallinity distribution effects. A “rule‐of‐thumb” method for rapid estimation of crystallinity distribution effects has been developed, obviating the need for lengthy simulation.