bluuebunny/crossref_metadata_2025_split huggingface dataset:
Block copolymers of poly(ethylene terephthalate)‐poly(butylene terephthalate). II. Small‐angle light‐scattering studies
Authors: Misra A. , Garg S. N. 
Published: April 2003

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

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

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

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

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

AbstractThe morphological features of poly(p‐benzamide) films cast in a magnetic field from solutions in N,N‐dimethylacetamide containing LiCl are reported. Three crystal modifications are found, one solvated and the other two containing no solvent. The solvated crystal grown in a magnetic field is oriented with the molecules parallel to the field. It transforms to an oriented amorphous phase by loss of solvent, and this conversion is accelerated by the presence of moisture. Upon annealing at an elevated temperature, the crystalline solvate transforms to a second crystal form, while the amorphous sample is converted to a third crystalline modification. All three crystalline forms have almost the same fiber identity period, which corresponds to a nearly fully extended chain conformation.
Dynamic melt rheology of poly(styrene‐co‐vinylpyridine) and their methyl iodide salts
Authors: Bazuin C. G. , Eisenberg A. 
Published: April 2003

AbstractThe dynamic melt rheology of random copolymers of polystyrene with 2–9 mol% 4‐vinylpyridine was examined in their quaternized and nonquaternized forms. Time–temperature reducibility applies in all cases. Relative to the glass transition, the master curves of the nonquaternized materials are identical. Melt flow in the quaternized materials is mildly retarded, the extent increasing with ion content. At the highest ion contents, the relaxation processes appear to be of Arrhenius type. As in the glass transition region, the ionic interactions in the plateau and terminal zones are thermally labile.
Dynamic mechanical properties of plasticized polystyrene‐based ionomers. I. Glassy to rubbery zones
Authors: Bazuin C. G. , Eisenberg A. 
Published: April 2003

AbstractThe plasticizing effect of a nonpolar and a polar diluent in ionomers was studied by dynamic mechanical methods in the glassy to rubbery regions. Specifically, a carboxylate and a sulfonate polystyrene‐based ionomer were investigated with variation of diethylbenzene content and of glycerol content. It was found that the nonpolar diluent plasticizes the transition by formation of ionic aggregates as well as lowering the glass transition temperature. However, the ionic regions of the carboxylate ionomer are plasticized more than those of the sulfonate ionomer. This corroborates the results of other studies which had found that the sulfonate groups in ionomers interact more strongly than the carboxylate groups. The polar diluent causes the ionic transition to disappear; this is probably due to solvation of the ions by the diluent.
Nucleation‐controlled growth. Observations on (110) twinned polyethylene crystals
Authors: Colet M.‐Ch. , Point J. J. , Dosiere M. 
Published: April 2003

AbstractThe growth of (110) twinned crystals of a sharp fraction of linear polyethylene (Mw/Mn = 1.10) of moderate molecular weight (Mw = 17,000) is followed during crystallization by the isochronous decoration method. New morphological features are observed. The fast‐growing tip of our laths presents, in addition to the two (100) facets usually observed, a possibly stable small reentrant (110) corner. This is a situation intermediate between the facies described by Dawson and Keller. Moreover, the slow tip of our laths presents various degrees of asymmetry with respect to the junction plane. A new characteristic length Ln = j/i is introduced to explain our morphological observations on (110) twinned crystals: j is the nucleation rate at a reentrant corner and i the nucleation rate on a smooth facet. Three linear growth rates Ghkl are calculated as a function of the length L of the face (hkl): Ghkl and Gĥkl or G′hkl are respectively the growth rates of a face bordered by two salient corners and by a reentrant corner. A distinction between Gĥkl and G′hkl is introduced to take into account the relative sizes of the two faces of the reentrant dihedral angle. The major points of the discussion concern (i) the stability of the (110) reentrant corner of the fast tip of the lath, (ii) the nearly constant shape of the twinned crystals, (iii) the effects of dislocations incorporated in the fast edge of the laths, and (iv) the various asymmetries observed in the slow tip of our laths. Theories of surface nucleation‐controlled growth explain our various morphological observations on (110) twinned PE crystals, and growth usually proceeds in regime II.
Characterization of PDMS model junctions and networks by solution and solid‐state silicon‐29 NMR spectroscopy
Authors: Beshah Kebede , Mark James E. , Ackerman Jerome L. , Himstedt Alan 
Published: April 2003

AbstractThe application of 29Si solution and solid‐state cross‐polarization/magic‐angle spinning (CP/MAS) nuclear magnetic resonance (NMR) techniques to the study of structural features in polydimethylsiloxane (PDMS) model endlinked elastomeric networks is explored. The relationship between the topological (network) functionality of a structural moiety, which determines network mechanical properties, and its chemical (spectral) functionality, which is reported by the NMR, is discussed. The second‐order spectral shifts corresponding to topographical functionality variation within a chemical functionality class are usually sufficiently well resolved in these networks to allow positive identification of a variety of structural features. The basic PDMS repeat unit, OSi(CH3)2, is found to possess an axially symmetric chemical shift tensor with σ∥ = −56.8 ppm downfield from TMS, and σ⊥ = −4.4 ppm. This axial symmetry does not result from rapid reorientation about the chain axis. The NMR spectrum reveals defects in model endlinked networks. In the case of vinyl‐endlinked systems, the defects are ascribed to the formation of elastically ineffective loops. Hydroxyl‐endlinked systems contain either loops or else trifunctional junctions (hydrolyzed before chain coupling could take place) and dangling chain ends. The CP/MAS technique provides an order‐of‐magnitude reduction over standard solution techniques in the time to acquire a spectrum from a network not containing paramagnetic doping. 13C spectra of PDMS systems are not as informative as 29Si spectra.
Structural changes induced in tussah silk (Antheraea pernyi) fibroin films by immersion in methanol
Authors: Tsukada Masuhiro 
Published: April 2003

AbstractThe crystalline transition induced by immersion in a methanol/water mixture of tussah silk fibroin (from Antheraea pernyi) film obtained by casting from a 1% solution was studied by x‐ray diffraction, differential scanning calorimetry, and infrared spectroscopy. The molecular conformation of the fibroin, consisting mostly of the α‐helix and random‐coil forms, was transformed into a random‐coil and β‐rich conformation containing only a small amount of α‐helix after immersion for no more than 5 min. The intersheet packing of the β‐crystal of the original tussah silk fibroin film was imperfect in the early stage of immersion. However, crystallization proceeded further when the immersion time exceeded 10 min. As a result the sheets in the β‐form crystal became closely packed because of the decrease in the content of the random‐coil form. The exothermic peak, which appeared at 226°C in the original fibroin and was attributed to the random‐coil → β‐structure transition, disappeared completely after immersion for 5 min.
Positronium annihilation in amine‐cured epoxy polymers
Authors: Jean Y. C. , Sandreczki T. C. , Ames D. P. 
Published: April 2003

AbstractPositronium annihilation spectroscopy (PAS) has been used to study the microstructural properties of amine‐cured epoxy polymers. We have determined the free‐volume “hole” sizes in these polymers by comparing the observed ortho‐positronium lifetimes with the known lifetime–free volume correlation for low‐molecular‐weight systems. The free volumes for four epoxies with different crosslink densities are found to vary significantly over the temperature range between −78° and 250°C. The free‐volume holes for these polymers are found to range from 0.025 to 0.220 nm3. Two important transition temperatures were found: one corresponds to the glass transition temperature Tg determined by differential scanning calorimetry (DSC), and the other occurs about 80–130°C below Tg. The sub‐Tg transition temperature is interpreted tentatively as being where hole size reaches dimensions adequate for positronium trapping or else the onset temperature for local mode or side‐chain motions. These two transition temperatures plus two additional onset temperatures are found to be correlated with crosslink densities calculated from stoichiometry.
Dielectric relaxation studies of dipolar aromatics in polyethylene I. Spherulitic low‐density polyethylene
Authors: Jang Y. T. , Phillips P. J. 
Published: April 2003

AbstractDielectric relaxation studies have been used as a means of investigating the behavior of aromatic molecules dissolved in a semicrystalline polymer. All molecules show a relaxation in the vicinity of the γ loss peak of polyethylene, while several show an additional peak at lower temperatures. The latter is interpreted as an indicator of molecular motions below the glass transition and the former is to be associated with the onset of molecular motions on a local scale as the glass transition is approached. The α loss process of polyethylene is seemingly unaffected by the presence of the molecules. Integration of loss curves shows that, at most, 50% of the molecules are able to relax but that the fraction relaxing increases with increasing temperature, suggesting the presence of a wide distribution of sites within the polymer.
Relaxation mechanism of epoxide resin cured with acid anhydrides. III. Effect of alkyl side chains on mechanical and dielectric β relaxations
Authors: Ochi Mitsukazu , Iesako Hiroshi , Shimbo Masaki 
Published: April 2003

AbstractMechanical and dielectric β relaxations were investigated for bisphenol‐A‐type epoxide resin cured with succinic anhydrides with and without substituent linear or branched alkyl side chains. The dielectric β relaxation is due solely to the motion of the diester segment which is formed in the network from the reaction with the acid anhydride. The mechanical β relaxation is attributed to the motion of both the diester segment and another nonpolar segment, i.e., the linear alkyl side chain. Thus it is concluded that the long alkyl side chain in the diester segment not only restricts the motion of that segment, but also introduces additional motion of the side chain itself.
A quantitative electron microscopic study of the crystalline structure of ethylene copolymers
Authors: Voigt‐Martin I. G. , Alamo R. , Mandelkern L. 
Published: April 2003

AbstractQuantitative thin‐section electron microscope studies were made on compositional fractions of ethylene copolymers crystallized under several extreme conditions. The co‐units chosen were such that the chains contained either ethyl, hexyl, or acetate side groups. Certain general features are independent of the chemical nature of the co‐unit. It was found that up to about 2 mol % co‐unit content lamellae are observed in all copolymers which were slowly cooled from the melt. The lateral dimensions of lamellae are not as large as in corresponding homopolymers and the lamellae are segmented. As the branch content increases the lamellae become shorter and eventually degrade into small crystallites. Within this broad outline of behavior, differences between the copolymer types are discerned and discussed. By comparison with the Raman LAM it is shown that quantitative values for the crystallite size distribution are obtained by the electron microscopy method used. Furthermore, when the specimen consisted of well‐ordered lamellar stacks the degree of crystallinity obtained from the electron micrographs was in quantitative agreement with the enthalpy of fusion.
Solvent‐induced crystallization. I. Crystallization kinetics
Authors: Durning C. J. , Rebenfeld L. , Russel W. B. , Weigmann H. D. 
Published: April 2003

AbstractThe kinetics of crystallization of quenched poly(ethylene terephthalate) (PET) films during the imbibition of methylene chloride (MeCl2) vapor is studied by density measurements. The effects of film thickness (0.0025–0.086 cm) and temperature (0–38°C) were examined. The data suggest that MeCl2 transport controls the crystallization in thick films and at elevated temperatures, but that spherulite growth controls in thin films and at reduced temperatures. The application of a mathematical model developed previously supports this mechanistic interpretation of the data.
Effect of flow on solutions of rodlike molecules
Authors: Bahar Ivet , Erman Burak 
Published: April 2003

AbstractA flow field imposed on a solution of rodlike particles tends to align the rods owing to friction between the fluid and the rods. The potential energy of rods in a steady‐state, homogeneous, and irrotational flow is superposed on the equilibrium Gibbs free energy of the quiescent solution to obtain the total free energy. The exact lattice treatment of Flory and Ronca is used in formulating the problem. Effects of flow on the orientational distribution function of rods and phase separation are analyzed with particular reference to elongational and pure shear flows. Calculations carried out for various compositions and flow characteristics reveal the presence of a region where the order parameter is sensitive to changes in prevailing flow conditions. Experimental determination of orientation by measuring flow birefringence is discussed.
Longitudinal acoustic mode in polymers. VIII. Nature of mass perturbations in terminally brominated paraffins
Authors: Chang Chih , Krimm S. 
Published: April 2003

AbstractRaman spectra have been obtained of the longitudinal acoustic mode (LAM) in α‐BrC20H41 and α, ω‐BrC20H40Br, and compared with such spectra for n‐C20H42. Normal coordinate analyses of these three molecules clearly account for (i) the frequency decreases on Br substitution; (ii) the presence of doublet LAM modes in both brominated molecules; and (iii) the decrease in the total intensity of the LAM mode resulting from the added masses, as distinct from the increase predicted by the elastic rod model. These results thus provide experimental support for predictions made from normal coordinate and intensity analyses regarding the influence on LAM bands of mass perturbations at the ends of paraffinic chains.
Vibrational spectroscopic studies of conformation of poly(oxyethylene). II. Conformation–spectrum correlations
Authors: Matsuura Hiroatsu , Fukuhara Koichi 
Published: April 2003

AbstractDetailed normal‐coordinate analysis has been carried out on a large number of conformers of model molecules of poly(oxyethylene); the model molecules treated are CH3(OCH2CH2)nOCH3 with n = 2,3, and 6. The systematic treatment provides well‐defined correlations between conformation and vibrational spectra of poly(oxyethylene). The vibrations in the region 1050–800 cm−1, which are associated with the CO and CC stretching and CH2 rocking modes, are highly dependent on the conformation of the polymer chain. On the basis of these correlations, the infrared and Raman spectra of the molten state and of the aqueous solution are interpreted in terms of the conformational states. The analysis indicates that the following conformational fragments are present in these phases: GT‐TG (T: trans; G: gauche), TT‐TG, GT‐GG, TT‐TT, and TT‐GG for the CH2CH2OCH2CH2 group, and TGT and TGG for the OCH2CH2O group. Conformational fragments GT‐TG′ and GT‐G′G′ are also possible in the analogy to GT‐TG and GT‐GG.
Molecular aggregation of solid aromatic polymers. III. Small‐angle X‐ray scattering from aromatic polyamideimide film
Authors: Kochi Masakatsu , Isoda Satoru , Yokota Rikio , Kambe Hirotaro 
Published: April 2003

AbstractMolecular aggregation in polytrimellitamideimide (PAI) was investigated by small‐angle x‐ray scattering (SAXS). PAI films annealed above the glass transition temperature show a scattering peak characteristic of two‐phase structure. A one‐dimensional model was used to analyze these SAXS curves. The more ordered phases are produced at higher annealing temperature. The average thickness of the ordered lamellae is comparable with the repeating length of the main chain. The relative difference of electron density between two phases is only a few percent, which shows that the two‐phase structure of PAI, like that of aromatic polyimide, differs essentially from that of ordinary crystalline polymers.
Solution properties of semirigid polyquinolines. I. Size‐exclusion chromatography with light‐scattering detection of poly[2,2′‐(P,P′‐oxydi‐P‐phenylene) 6,6′‐oxybis(4‐phenylquinoline)]
Authors: Cotts P. Metzger 
Published: April 2003

AbstractAn aromatic semirigid polyquinoline, poly[2,2′‐(p,p′‐oxydi‐p‐phenylene) 6,6′‐oxybis(4‐phenylquinoline)], has been studied in dilute solution using viscometry, light scattering, and size‐exclusion chromatography coupled with low‐angle light‐scattering detection (SEC/LALS). The SEC/LALS technique permits determination of the intrinsic viscosity and absolute molecular weight for a series of narrow fractions without preparative fractionation. Aggregation that was observed in dilute chloroform solutions was found to be related to protonation of the polyquinoline by HCI present in chloroform. Unperturbed dimensions calculated from the SEC/LALS results show the chain to have nearly freely rotating dimensions, as expected for a chain composed of long (12‐Å) rigid segments connected by ether linkages.