bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solid state 13C NMR study of hexa(methoxy methyl)melamine and melamine‐formaldehyde selfcondensates
Authors: Andreis M. , Koenig J. L. , Gupta M. , Ramesh S. 
Published: April 2003

AbstractThe structure and molecular dynamics of self‐condensation products of three different melamine resins based on hexa(methoxy methyl)melamine are studied by 13C NMR in the solid state. The application of direct (DP) and cross‐polarization (CP) pulse sequences shows that uncured and cured melamine resins are motionally heterogeneous systems, with the mobile and rigid parts consisting of the same basic structural units. Viscous lightly cured samples based on commercial melamine‐formaldehyde resins contain low‐molecular weight species which act as plasticizers. In these resins, three motionally different methyl groups are observed. Their existence is confirmed either by spectral deconvolution or by fitting the experimental signal intensities to the cross‐polarization dynamics with the assumption of two cross‐polarization‐transfer rates. Fast cross‐polarizing rigid methyl groups are accompanied with the spinning sidebands. On the basis of DP and CP relaxation measurements, quantitative results for three major structural units are calculated. Problems concerning the 14N‐13C quadrupolar interactions and quantitative analysis are discussed. ©1995 John Wiley & Sons, Inc.
A nuclear magnetic resonance study of toluene‐polyisobutylene solutions. 2. Vrentas‐Duda theory
Authors: Bandis Athinodoros , Inglefield Paul T. , Jones Alan A. , Wen Wen‐Yang 
Published: April 2003

AbstractThe self‐diffusion coefficients of toluene in polyisobutylene have been analyzed using the Vrentas‐Duda free volume diffusion model. The diffusion coefficients were determined at different temperatures and concentrations, using the pulsed field gradient nuclear magnetic resonance technique. The data were satisfactorily described by the model and the size of the polymer jumping unit was extracted. Comparisons were made with the Fujita free volume theory and the Fujita free volume parameters were extracted from the Vrentas‐Duda free volume parameters. From the diffusion data that now available, it can be concluded that for most polymers the jumping unit is about 1.5 times the polymer monomer molecular weight. The activation energy of the toluene diffusion in polyisobutylene is compared with the activation energies of other penetrants in the same polymer. The diffusion data presented in this work show that the energy per mole required to overcome the attractive forces which constrain a diffusing species to its neighbors should be considered to be zero, in order to be able to extract the free volume parameters (from viscosity and diffusion data) with an acceptable uncertainty. ©1995 John Wiley & Sons, Inc.
Synthesis and characterization of poly(vinylcyclohexane) derivatives
Authors: Gehlsen Mark D. , Weimann Peter A. , Bates Frank S. , Harville Steven , Mays Jimmy W. , Wignall George D. 
Published: April 2003

AbstractSix nearly monodisperse substituted poly(styrene) homopolymers, poly(styrene) (PS), poly(2‐methylstyrene) (P2MS), poly(3‐methylstyrene) (P3MS), poly(4‐methylstyrene) (P4MS), poly(tertiary‐butylstyrene) (PtBS), and poly(α‐methylstyrene) (FαMS) were anionically polymerized and subsequently saturated using heterogeneous hydrogenation techniques to poly(vinylcyclohexane) (PVCH), poly(2‐methylvinylcyclohexane) (P2MVCH), poly(3‐methylvinylcyclohexane) (P3MVCH), poly(4‐methylvinylcyclohexane) (P4MVCH), and poly(tertiary‐butylvinylcyclohexane) (PtBVCH), respectively. In each case, except PαMS, the materials were saturated to > 99% conversion with no chain degradation. PS hydrogenations required the addition of small amounts of tetrahydrofuran to the reaction solvent cyclohexane to enhance miscibility and eliminate large‐scale chain degradation. Density gradient and differential scanning calorimetry (DSC) measurements were used to characterize the density and glass transition temperature, Tg, of the unsaturated and saturated polymers. Saturation reduces the density by 3% to 11% and changes Tg substantially. The greatest variation in Tg is obtained with the 3‐methyl substituted species where a 63°C increase is observed, while the highest measured Tg is 186°C for P2MVCH. Small‐angle neutron scattering (SANS) experiments on binary mixtures of hydrogenous and deuterium labeled PVCH derivatives provided a determination of bulk chain statistics. The statistical segment length is relatively insensitive to vinylcyclohexane ring substitution, except with P3MVCH where a 20% greater value is obtained. ©1995 John Wiley & Sons, Inc.
Polystyrene (1)/poly(butyl acrylate/amide type functional monomer) (2) two‐stage emulsion polymers. Synthesis and thermomechanical properties of latex films
Authors: Hidalgo M. , Cavaillé J. Y. , Guillot J. , Guyot A. , Perez J. , Vassoille R. 
Published: April 2003

AbstractPolystyrene (PS) (1)/Poly (n‐butyl acrylate (BA)/amide type functional monomer) (2) structured latex particles were prepared through emulsion polymerization varying the hydrophilicity of the functional monomer employed. The second‐stage polymerization kinetics, the size and morphology of latex particles, and the location of the functional groups in the final latexes were studied, in order to relate them to the thermomechanical properties of films cast from these latexes. It has been shown that, as expected, increasing the hydrophobicity leads to a better homogeneity in the copolymer formed during the second‐stage polymerization, while the more hydrophilic functional monomer partly homopolymerizes in a separate phase. However, the functionalization by all the monomers used in this work, prevents the PS seed particles to form a continuous skeleton (percolated network). Further heat treatments at 140°C do not lead to the formation of a continuous PS phase as for pure BA/pure PS two‐stage particles. In addition, some thermally induced crosslinking effects are discussed in relation with the functional monomer location within the particles. © 1995 John Wiley & Sons, Inc.
Analysis of polyurethanes using core excitation spectroscopy. Part I: Model polyurethane foam polymers
Authors: Urquhart S. G. , Hitchcock A. P. , Leapman R. D. , Priester R. D. , Rightor E. G. 
Published: April 2003

AbstractThe C 1s, N 1s, and O 1s excitation spectra of model methylenediphenyldiisocyanate (MDI) polyurethanes with well known structures have been recorded using electron energy loss spectroscopy (EELS) in an electron microscope. These spectra are compared to the core excitation spectra of selected small molecule analogue species (recorded by gas phase EELS) in order to identify transitions characteristic of various structural components found in polyurethanes. A more detailed report on the small molecule analogue spectra is presented in the following article. Spectral features characteristic of the different structural components in polyurethanes are identified in the spectra of the model polymers. These can be used as the basis for chemical studies of micron or submicron sized segregated phases in flexible polyurethane polymers. © 1995 John Wiley & Sons, Inc.
Modelling the fractionation process in TREF systems: Thermodynamic simple approach
Authors: Borrajo Julio , Cordon Cristina , Carella José M. , Toso Susana , Goizueta Graciela 
Published: April 2003

AbstractA simple thermodynamic model, based on an extension of Flory‐Huggins theory, is applied to temperature rising elution fractionation (TREF). Dependence of the fractionation process on melting temperature, melting enthalpy, average crystallinity, average crystallizable sequence length, and polymer‐solvent interaction parameter is predicted. Results from the model fit experimental TREF data, and correctly predict number‐average branch points for TREF fractions. © 1995 John Wiley & Sons, Inc.
Elastic modulus of the crystalline regions of cellulose polymorphs
Authors: Nishino Takashi , Takano Kiyofumi , Nakamae Katsuhiko 
Published: April 2003

AbstractThe elastic modulus El of the crystalline regions of cellulose polymorphs in the direction parallel to the chain axis was measured by x‐ray diffraction. The El values of cellulose I, II, IIII, IIIII, and IVI were 138, 88, 87, 58, 75 GPa, respectively. This indicates that the skeletons of these polymorphs are completely different from each other in the mechanical point of view. The crystal transition induces a skeletal contraction accompanied by a change in intramolecular hydrogen bonds, which is considered to result in a drastic change in the El value of the cellulose polymorphs. © 1995 John Wiley & Sons, Inc.
Physical aging in poly(ethylene naphthalene‐2,6‐dicarboxylate) in relation to sorbed water, enthalpic relaxation, and mechanical properties
Authors: Rueda D. R. , Varkalis A. , Viksne A. , Baltá Calleja F. J. , Zachmann H. G. 
Published: April 2003

AbstractAmorphous poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN) films (∼ 220 μm thick), stored in ambient atmosphere for different periods of time and after annealing at different temperatures below Tg = 123°C, for different times, have been investigated by infrared spectroscopy (FTIR), microhardness, and differential scanning calorimetry (DSC). FTIR spectroscopy and weight measurements reveal the presence of water which is easily removed by annealing of the films. Films again recover their initial weight and absorption bands after 1‐2 days storage in ambient atmosphere. Samples annealed at different temperatures Ta for different times ta show an increasing microhardness for relatively short times of ta. The microhardness passes through a maximum at an annealing time depending on Ta, and it decreases toward values somewhat larger than the initial ones. The changes observed in the microhardness and in the values of the excess enthalpy with storage time of the samples at room temperature depend on the physical aging as well as on the content of water of PEN films. © 1995 John Wiley & Sons, Inc.
Blends of glycidyl methacrylate/methyl methacrylate copolymers with poly(vinylidene fluoride)
Authors: Gan P. P. , Paul D. R. 
Published: April 2003

AbstractBlends of glycidyl methacrylate (GMA)/methyl methacrylate (MMA) copolymers with poly (vinylidene fluoride) (PVDF) were found to be miscible when the GMA content of the copolymer is 35.7 wt % or less. The miscible blends did not phase separate upon heating prior to thermal decomposition. The melting point depression method, based on both the Flory‐Huggins theory and the equation of state theory of Sanchez‐Lacombe, was used to evaluate interaction parameters for each pair. The magnitude of these parameters appears to be much larger than interaction energies evaluated by other methods. Possible reasons for this are discussed. © 1995 John Wiley & Sons, Inc.
An XRD characterization of the thermal degradation of polyacrylonitrile
Authors: Chatterjee Nandini , Basu Sudhapada , Palit S. K. , Maiti Mrinal M. 
Published: April 2003

AbstractThermal degradation of polyacrylonitrile (PAN) has been studied by combined differential thermal analysis, thermogravimetry, and XRD analysis. On the basis of the experimental observations, it has been suggested that the intramolecular polymerization of nitrile groups to a conjugated polyimine structure is initially limited to only the amorphous zone of PAN, which involves little evolution of off‐gases. Polymerization of nitrile group in the crystalline zone starts with the melting of crystallites with the evolution of off‐gases from the amorphous‐crystalline zone interface. ©1995 John Wiley & Sons, Inc.
Microdeformation in thin films of 3FDA/PMDA polyimide and polyimide nanofoams
Authors: Plummer C. J. G. , Hedrick J. L. , Kausch H.‐H. , Hilborn J. G. 
Published: April 2003

AbstractTransmission electron microscopy has been used to investigate the microdeformation behavior of thermally imidized thermoplastic pyromellitic dianhydride/1,1‐bis(4‐amino‐phenyl)‐1‐phenyl‐2,2,2 trifluoroethylene (3FDA/PMDA) polyimide films with a Tg of ∼ 440°C, prepared by solution casting of a polyamic ester precursor. Failure of the films at room temperature was by unstable cracking at about 5% strain, accompanied by homogeneous shear deformation at the crack tips. As the temperature was raised to above 100°C, zones of mixed shear and crazing were observed, and a stick‐slip mode of cracking. Above about 300°C shear was once again the dominant deformation mechanism and the films became fully ductile. In films containing porosity on a scale of a few nanometers, prepared by thermal degradation/imidization of a 3FDA/PMDA/poly α‐methyl styrene graft copolymer, film failure at room temperature was also by unstable cracking, but a zone of multiple craze‐like features was observed at crack tips, rather than a single shear deformation zone. The increase in extent of this zone of craze‐like features as the temperature was raised was again associated with an increase in crack stability. ©1995 John Wiley & Sons, Inc.
Solution properties of exocellular polysaccharides of rhizobium leguminosarum. Static and dynamic light‐scattering: Characterization in dilute solution
Authors: Coviello T. , Burchard W. , Dentini M. , Crescenzi V. , Morris V. J. 
Published: April 2003

AbstractThree polysaccharides, Rhizobium leguminosarum 8002 EPS(I), Rhizobium trifolii TA1‐EPS (II), Rhizobium leguminosarum 127K87 EPS (III), produced by bacteria of Rhizobium genus have been investigated by static and dynamic light scattering combined with chirooptical measurements. All three polymers have the same backbone but differ in the length of the side chains and in the content of minor substituents. An isothermal conformational transition coil → helix was observed with I and II by adding salt (NaCl). The molecular parameters of the polysaccharides in the ordered state were determined by light‐scattering data. Increasing the ionic strength a shrinking of the helix was observed accompanied by a corresponding decrease in the radius of gyration. An extraordinary chain stiffness in terms of Kuhn segment lengths was found in both cases, similar to that already observed for other microbial polysaccharides. In the case of III no disorder → order transition was induced by the salt, and the scattering behavior corresponds to that of a rather flexible polymer with a characteristic ratio C∞ = 24. The incapability of III to form a helical structure is attributed to the effect of the very long side chain. The analysis of the time correlation functions revealed typical flexible chain behavior for all three polysaccharides. This behavior for the two ordered polymers is in agreement with a recent theory by Maggs and is due to bending modes of the rods. ©1995 John Wiley & Sons, Inc.
Polymer decoration study in chain folding behavior of solution‐grown poly(ethylene oxide) crystals
Authors: Chen Jianhua , Cheng Stephen Z. D. , Wu Scott S. , Lotz Bernard , Wittmann Jean‐Claude 
Published: April 2003

AbstractThe polymer decoration method based on the vaporization and condensation‐crystallization of polyethylene (PE) upon the fold surface of polymer crystals has been widely used to study the chain folding behavior of the crystals. When this method was utilized to study solution‐grown high molecular weight poly (ethylene oxide) (PEO) lamellar crystals, the highly anisotropic, low molecular weight fragment PE decorated become oriented parallel to the fold direction and form rods, which can be observed by transmission electron microscopy (TEM) and electron diffraction (ED). The growth sectors were clearly observed. From the ED patterns the {200} planes of the orthorhombic low molecular weight PE rod crystals can be observed, and the c‐axis of these crystals is aligned parallel to the {120} growth planes of the PEO crystals. The decoration results indicate that the major fold orientation of high molecular weight PEO single crystals grown from dilute solution is along the {120} planes. © 1995 John Wiley & Sons, Inc.
Interrelation between crystallization and liquid crystal formation: A calorimetric and polarizing microscopical study on a monotropic polymer system
Authors: Heberer D. , Keller A. , Percec V. 
Published: April 2003

AbstractThe crystallization of the monotropic liquid crystal forming polyether, poly‐n‐nonyl‐4 4′‐biphenyl‐2‐chloroethane, was investigated using DSC calorimetry and polarizing optical microscopy. The principal theme was the nature of crystallization from the nematic liquid crystalline state, which in the monotropic system could be directly compared with the more familiar crystallization from the isotropic melt using one and the same compound. Novel, polarizing optical structures were observed that combine features of both the usual LCPs (fine “grains”) and those of the conventional crystallizeable polymers (spherulites) with differing degrees of prominence of each according to crystallization conditions. The considerations of such structural observations, combined with the calorimetric results and the newly gained information on the kinetics of the crystallization process, reveal an acceleration of the overall crystallization rate at the stage where liquid crystal formation sets in as assessed by calorimetry but not as registered with the polarizing microscope, leading to wider issues regarding the conception of “amorphous crystalline ratio” and its extension to the liquid crystal state. Beyond polymers, the new findings lead to the more general considerations on metastable phases, specifically to their emergence and competition with the phases of ultimate stability. In this respect the present study on a monotropic LCP provides an illustrative example of a more general treatment presented previously. © 1995 John Wiley & Sons, Inc.
Molecular weight segregation induced by interfacial melt reactivity in polyamide 6/reactive rubber blends
Authors: Maréchal Philippe , Legras Roger , Dekoninck Jean‐Marc 
Published: April 2003

AbstractPolyamide 6 (PA) and ethylene‐propylene rubber with maleic functionality (EPMA) were blended in a batch mixer. EPMA anhydride groups react with amine chain ends of polyamide and form a grafted copolymer at the interface. The molecular weights of the grafted PA and of the free PA were measured. The molecular weight of the free PA decreases during the processing. This effect is due to the hydrolysis of the PA consecutively to its reaction with anhydride groups. The molecular weight of both grafted and free polyamide decreases during the processing. Moreover, the molecular weight of the grafted PA is lower than that of the free PA. At constant mixing time, a high conversion level produces grafted PA with a higher molecular weight. This is the result of molecular weight segregation for interfacial reaction. Small molecules react faster at the interface than larger ones. If we compare experimental results with model predictions, two segregation regimes are observed. For high shear and low EPMA concentrations, dispersion is very fast; the segregation only depends on molecular elasticity. In this case, the best correlation between model and experiment is obtained for low interfacial thicknesses. For low shear, or for EPMA concentrations close to the phase inversion composition, the segregation is more noticeable, which is mainly due to the diffusion of macromolecules through the brush of already grafted molecules. In this case, there is a clear competition between the compatibilization and the grafting reaction. Molecular weight segregation gives low ratio of the grafted PA molecular weight to the free PA molecular weight. This is detrimental to interfacial properties of the grafted copolymer formed by melt reactivity. Strategies are developed to improve this ratio in order to investigate its influence on the mechanical properties. © 1995 John Wiley & Sons, Inc.
Gas permeability and permselectivity of polyimides with large aromatic rings
Authors: Tanaka Kazuhiro , Osada Yasuharu , Kita Hidetoshi , Okamoto Ken‐ichi 
Published: April 2003

AbstractPolyimides with large aromatic rings were prepared from 3,6‐diaminocarbazole (CDA), N‐ethyl‐3,6‐diaminocarbazole (ECDA), 2,7‐diaminofluorene (DAF), 2,7‐diaminofluorenon (DAFO), and dimethyl‐3,7‐diaminodibenzothiophene‐5,5‐dioxide (DDBT) with 2‐bis(2,4‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA). Their physical properties, including gas permeability and permselectivity, were investigated in comparison with those of the related polyimides from 1,3‐phenylenediamine (mPD). Glass transition temperatures of the polyimides with large aromatic rings were much higher than those of the mPD‐based polyimides as a result of increased rigidity of the former polymer chains. With changing diamine from mPD to the large aromatic diamines, charge transfer (CT) interaction between the moieties of acid anhydride and diamine seems to be enhanced, judging from the red shift of absorption edge of the polyimide films and the red shift of CT excitation band of the 6FDA‐based polyimides in solution. Fraction of free space (VF) was a little smaller for the polyimides with large aromatic rings except DDBT than for the mPD‐based polyimides, probably because of enhancement in polymer chain‐chain interactions as a result of the increased CT interaction. The DDBT‐based polyimides had large VF than the mPD‐based polyimides because of the nonplanar structure of neighboring dibenzothiophene‐5,5‐dioxide and imide rings. For the 6FDA‐based polyimides, permeability coefficients to H2, O2, N2, CO2, and CH4 were in the order, DAFO < mPD ∼ DAF < CDA < ECDA < DDBT. As for the membrane performance for H2/CH4, CO2/CH4, and O2/N2 systems, it is significant to change diamine from mPD to DDBT or CDA, but not to DAF or DAFO. The DDBT‐based polyimides were excellent for H2/CH4 and CO2/CH4 separations. © 1995 John Wiley & Sons, Inc.
Changes in the properties of HDPE fibers upon radiation grafting with acrylic acid
Authors: Lindsjö Marie Christine , Ekman Kenneth B. , Näsman Jan H. 
Published: April 2003

AbstractThe morphology and the physical and mechanical properties of graft‐modified polyethylene fibers have been studied. Two types of fibers, with the diameters of 10 μm (1.1 dtex) and 40 μm (7.5 dtex), were modified by radiation‐induced grafting with acrylic acid. The extent of grafting was determined gravimetrically. Confirmation of gravimetrically obtained values was achieved using conductometric titration. The fibers were hydrated at pH 2 and pH 7. The degree of swelling was 120% at pH 2 and 200% at pH 7. The transversal distribution of polyacrylic acid in the fibers was determined. Fibers were stained and observed with an optical microscope. The diffusion of the monomer into the bulk was found to be rather fast. The changes in the total crystalline content and the lamellar thickness distributions in consequence of irradiation and grafting were determined by differential scanning calorimetry analysis. The measurements showed no effects of irradiation on the crystallinity in either type of fiber, whereas a decreasing crystallinity caused by grafting was noticed in the 40 μm fibers. The lamellar thickness distributions narrowed upon irradiation, indicating recrystallization as a result of chain scission. Wide angle x‐ray scattering and Raman analysis of dry and hydrated fibers were conducted to study the behavior of the fibers in an aqueous environment. These results both showed a decreasing crystalline content caused by fiber hydration. Tensile tests were carried out to evaluate how grafting, hydration and Ca2+‐crosslinking of grafts affected the fiber strength. Grafting and Ca2+‐crosslinking, as well as hydration, resulted in a decreasing E‐modulus for the 40 μm fibers, whereas no significant change could be noticed in the 10 μm fibers. © 1995 John Wiley & Sons, Inc.