bluuebunny/crossref_metadata_2025_split huggingface dataset:
A free volume study of miscible polyester blends
Authors: Zipper Marcus D. , Simon George P. , Tant Martin R. , Small J. Douglas , Stack Gary M. , Hill Anita J. 
Published: April 2003

AbstractFour blend systems (miscible binary polyester blends) have been examined by positron annihilation lifetime spectroscopy (PALS). The ortho‐Positronium pick off lifetime, τ3, is related to the mean free volume cavity size in these miscible blends. The measured free volume cavity size for the blends is compared to the size predicted from linear additivity of the homopolymers. A negative deviation from linear additivity is observed for τ3 in each of the blend systems, and this behaviour is interpreted as a contraction of the mean free volume cavity size due to the changes in molecular packing that occur on blending. The consequence of these free volume results for the mechanical properties of miscible polyester blends is discussed and tested for the polycarbonate/Kodar system. The glass transition data suggest weak specific interactions in the blends; however, the mechanical properties are significantly affected by blending.
Intramolecular energy transfer in polyesters and model compounds containing anthracene and naphthalene groups separated by methylene and oxyethylene spacers
Authors: Mendicuti F. , Saiz E. , Bravo J. , Mattice Wayne L. 
Published: April 2003

AbstractSteady state fluorescence has been used to study the efficiency of nonradiative single energy transfer for naphthalene → naphthalene and naphthalene → anthracene for polyesters and their bichromophoric model compounds. Polyesters containing only naphthalene groups were derived from 2,6‐naphthalene dicarboxylic acid as the rigid unit, and two series of glycols, HO(CH2)mOH and HO(CH2CH2O)n;OH, where m=2–6 and n=1–4, as flexible spacers. Bichromophoric model compounds were derived from 2‐naphthoic acid and the same glycols. In order to study the transfer for naphthalene → anthracene, a first attempt was made by studying bichromophoric model compounds D(CH2)mA, where D and A denote 2‐naphthoate (donor) and 9‐anthranoate (acceptor) groups, respectively. The fluorescence anisotropy measurements in a solid matrix of glassy poly(methyl methacrylate), for the compounds containing only naphthalene groups, and the simple excitation and emission spectra, for the compounds containing naphthalene and antharacene groups, clearly demonstrate the presence of non‐radiative singlet–singlet energy transfer, the efficiency of which depends mainly on n (or n). A theoretical treatment using the rotational isomeric state model of the conformatin of these molecules has also been performed. The combination of the experiments and the theoretical analysis establishes that the Förster radii are 1.2 and 1.4 nm for the naphthalene → naphthalene transfer in the bichromophoric model compounds and polyesters, respectively, and 1.6 ± 0.2 nm for the naphthalene → anthracene transfer in the model compounds studied.
Interface formation of Ca with poly(p‐phenylene α,α′‐diphenyl vinylene) and poly(p‐phenylene α‐phenyl vinylene)
Authors: Razafitrimo H. , Park K. T. , Ettedgui E. , Gao Y. , Hsieh B. R. 
Published: April 2003

AbstractWe have investigated the interface formation of Ca with poly(p‐phenylene α,α′‐diphenyl vinylene) (PPV‐DP) and poly(p‐phenylene α‐phenyl vinylene) (PPV‐P) using X‐ray photoemission spectroscopy (XPS). Similarly to our earlier findings in metal/PPV interface formation, the O 1s peak shifted toward a lower binding energy as soon as Ca was deposited on to the polymers. This was accompanied by the formation of CaO, suggesting a chemical origin for the O 1s shift. By contrast, the C 1s peak shift toward a lower binding energy was observed relatively later, after about 4 Å of Ca deposition. At the same time, a new C 1s component became noticable at about −1.5 eV relative to the initial C 1s peak. This component signifies the possibility of polymer disruption by the Ca atoms to form CaC species. The C 1s peak shift is attributed to Ca induced surface band bending and barrier formation as in the case of metal/PPV interface formation. The disruption of the polymer may also induce changes in the interface electronic states and contribute to the C 1s peak shift. From the intensity attenuation analysis, we conclude that the initial 15 Å of Ca overlayer is contaminated by the CaO and CaC species and the overlayer is pure beyond 15 Å of Ca coverage.
Reactive blending via coordination chemistry—extraordinary mechanical response for atactic 1,2‐polybutadiene complexed with palladium chloride
Authors: Belfiore Laurence A. , Bossé Francis , Das Pronab 
Published: April 2003

AbstractExperimental evidence in solution and in the solid state suggests that atactic 1,2‐polybutadiene and palladium chloride form coordination complexes with unusual mechanical properties. Ternary phase diagrams with tetrahydrofuran as the solvent highlight regions where gelation is favored relative to precipitation. The strongest evidence for a network structure is based on the facts that (i) solid films swell in heptane, and (ii) infrared spectroscopy identifies a new absorption characteristics of three‐membered rings and dihapto coordination of the olefinic sidegroup in 1,2‐polybutadiene to the metal center in palladium chloride‐bis(acetonitrile). Carbon‐13 solid state NMR spectroscopy suggests that the polymeric palladium complex is a glass when the salt concentration is 4 mol%. NMR linewidth data together with the pulse sequence parameters suggest that the chain backbone of the polymeric palladium complex experiences a significant reduction in molecular mobility which is consistent with diamagnetic glassy materials. Most importantly, the elastic modulus of polybutadiene increases by three orders of magnitude during the transition from rubbery to glassy behavior. This type of mechanical response cannot be explained by a filler effect, crystallite reinforcement, or antiplasticization. Transition‐metal coordination concepts applied to polymeric materials suggest that the enhancement in mechanical properties is a direct consequence of ‘coordination crosslinks’ where the palladium salt bridges different polymer chains. However, palladium‐catalyzed rections of the olefinic sidegroup, generating a chemically crosslinked network, represent a second explanation of the significantly enhanced macroscopic physical properties of 1,2‐polybutadiene in the presence of the transition‐metal salt. Reactive blending via metal‐ligand coordination represents a new mechanism to compatibilize polymeric mixtures that would otherwise exhibit phase separation.
Utility of pulsed‐field gradient—HMBC indirect detection NMR experiments for polymer structure determination
Authors: Rinaldi Peter L. , Ray Dale G. , Litman Vincent E. , Keifer Paul A. 
Published: April 2003

AbstractThe utility of pulsed‐field gradient (PFG)–heteronuclear multiple bond correlation (HMBC) 2D NMR experiments for characterizing polymer structure is demonstrated. Heteronuclear multiple quantum coherence (HMQC) and HMBC indirect detection experiments provide correlations indicating the presence of one‐bond and two‐or three‐bond connectivities, respectively; this information is vital for polymer structure determination. When HMBC methods are combined with PFG techniques artifacts are eliminated which normally limit the utility of HMBC. The elimination of these artifacts lowers the detection limit by almost two orders of magnitude, making it feasible to detect signals from the small number of repeat units bonded to defect structures, chain ends, branch points and block junctions, despite the presence of much larger resonances from the main‐chain repeat units. Spectra of poly(isobutylene‐b‐butadiene) diblocks and poly(isoprene‐b‐styrene) diblocks are used to illustrate these advantages.
Viscoelastic constitutive equations and rheology for high speed polymer processing
Authors: Leonov Arkady I. 
Published: April 2003

AbstractMany attempts to formulate viscoelastic constitutive equations (CEs) for polymeric liquids have resulted in a situation where as many as several tens of popular CEs are in competition nowadays. None of these can describe the available data for simple flows, consistently, and almost all of them display nonphysical instabilities in high Deborah number flows. This paper discusses the most important classes of viscoelastic CEs, present recent results on their stability, recommends some principles of choice of CEs for practical use, and highlights a certain class of CEs for the description of the available set of rheological data for the most well characterized polymers, while satisfying all the stability constraints.
13C CP–MAS NMR spectra of tropical hardwoods
Authors: Sosanwo Olumide A. , Fawcett Allan H. , Apperley David 
Published: April 2003

AbstractThe carbon‐13 cross‐polarisation and magic angle spinning nuclear magnetic resonance spectroscopy studies of more than 20 tropical hardwoods are presented. Because of their productivity and area, the tropical evergreen forests are the location of more than one‐third of the net primary production of the terrestrial biosphere, a product which is currently of the order of 5.1 × 1016 g of carbon per year. Samples are mainly from Nigeria, predominantly timberwoods such as Diospyros mespiliformis (ebony), Tectona grandis (teak), Nauclea diderichii (opepe), Chlorophora excelsa (iroko), Khaya ivorensis (lagos mahogany), Khaya senegalensis (sapele mahogany), Daniellia oliveri (ojia), Sterculia oblonga (aye), Brachystegia kennedyi (okwen), and Mitragyna cilliata (abura); also included are Hevea braziliensis (rubber tree) and Gmelina arborea, a source of paper pulp.Assignments of the various peaks of the spectra are given to the main components, lignin and holocellulose, and to other minor structures. The holocellulose features are those of cellulose, hemicellulose being masked, at least in woods in which it is known to be present. The signals from the holocellulose component indicate that about 35% of the material is cellulose in a recognisable crystalline form, presumably located at the centre of fiberes, but the type of crystal structure could not be identified because of interference from the rest of the holocellulose signals. The aromatic lignin signals were distinct, and were perceived to fall within a pattern of a smooth transition from the wood of aye, based upon a syringyl type of residue, to the woods of omo and mpingo, based on guaiacyl residues, the exceptions being the Khayas, ebony, teak and opepe, which contained a third structure. The proportion of lignin, according to the area of the aromatic region and the O—Me signals, was highest in mpingo (50%), a savanna wood; within the woods from the Nigerian rain forest, the population ranged from 22% for iroko to 44% for teak, a reasonable allowance being made for the extra lignin in the aliphatic network.
Structure and properties of polyolefin blends
Authors: Ślusarski Ludomir , Bieliński Dariusz , Włochowicz Andrzej , Ślusarczyk Czesław 
Published: April 2003

AbstractBlends of ethylene–propylene–diene rubber (EPDM) and low density polyethylene (PEid) or isotactic polypropylene (iPP) crosslinked by dicumyl peroxide (DCP) have been prepared. Their morphology, reactivity of the components and crystallinity have been studied. The blends are microheterogeneous. Both plastomers, but particularly iPP, decrease the crosslinking efficiency of EPDM by DCP. It was found that they also influence the mechanical properties of the blends. The effect of iPP is far more pronounced than that of PEId, because of an increase in crystalline phase content. iPP particles play a role as nuclei for propylene monomer units in EPDM, whereas PEId particles are solvated by the elastomer matrix.
Thermally modified acrylic polymers as sorbents
Authors: Simitzis Johannis 
Published: April 2003

AbstractAcrylic fibres were modified with ethylene diamine and pyrolysed at temperatures up to 600°C. According to IR spectroscopy, polymers pyrolysed at 300°C contain nitrile and other groups which are present in the initial polymer. The specific surface area is decreased by increasing the pyrolysis temperature. The pore size distribution reveals mainly the presence of macropores. Acrylic polymers and those pyrolysed at 300°C sorb more methylene blue and alizarin yellow from aqueous solution than a non‐polar commercial sorbent of high specific surface area. The experimental results for dye sorption were treated theoretically using a diffusion‐limited sorption method. The polymers can be ranked by the parameters of this method or their sorption ability. The dye sorption is little affected by the pores of the polymers and is mainly affected by the interactions between the functional groups of the polymers and those of the dyes.
Dielectric investigation on poly(methylmethacrylate) films doped with p‐nitroaniline
Authors: Shafee E. El. 
Published: April 2003

AbstractThe dielectric behaviour of solution‐grown thin films of poly(methylmethacrylate) containing p‐nitroaniline (p‐NA) as a dopant was investigated within the temperature range 60–90°C and a 20–105 Hz frequency band. It is shown that these mixtures exhibit only one relaxation process similar to that of pure PMMA. However, the addition of p‐NA increases both the height and the relaxation strength of the peaks and also shifts log fm to higher frequencies. The additive causes narrowing of the loss curves and increases the activation energy for relaxation. These results are interpreted in terms of the hydrogen bonding effects of p‐NA on localized motions of carboxymethyl dipoles in PMMA. An insight into the possible origins of the β‐ and α‐relaxations in PMMA is also presented.
Synthesis and rheological properties of soluble poly(hydroxyethyl methacrylate) and some copolymers
Authors: Perera Don I. , Shanks Robert A. 
Published: April 2003

AbstractMethods to synthesise soluble poly(2‐hydroxyethyl methacrylate) (PHEMA) with varying molar mass were developed. Conversions over 90% were achieved without losing solubility. Steady state tests (range 0.01–590 Pa) and oscillatory tests (range 0.001–40 Hz) were carried out on 40% solutions in dimethyl formamide using a Carri‐Med rheometer. Only PHEMA having molar mass over 500000 showed significant shear thinning and viscoelastic properties. The copolymers of 2‐hydroxyethyl methacrylate (HEMA) with n‐butyl acrylate (BA) and 2‐hydroxypropyl acrylate (HPA) showed higher viscosities and viscoelastic properties compared with PHEMA homopolymer prepared under identical conditions. Also, viscosity and viscoelasticity increased with increase in acrylate content in the initial mixture. This was attributed to the higher molar mass of copolymers, which resulted from faster polymerisation rates owing to the inclusion of relatively highly reactive acrylates. However, in the case of HEMA : BA copolymers, first, the viscosity and viscoelasticity increased with increasing BA content and then dropped again, giving a maximum around HEMA : BA 75 : 25. This anomaly was explained by taking the effects of changes in inter‐and intra‐molecular hydrogen bonding as well as conformational differences caused by inclusion of BA in the PHEMA chain into account.
Chain‐scission and yellowing in high impact polystyrene
Authors: Singh R. P. , Raj R. A. , Prasad A. Vishwa , Sivaram S. , Lacoste J. , Lemaire J. 
Published: April 2003

AbstractDifferent grades of impact‐modified polystyrene were studied by viscometry, tensile impact test and colour change upon exposure to polychromatic irradiation at 55°C in air. The samples underwent extensive reduction in intrinsic viscosity [η] and tensile impact strength, and yellowed upon polychromatic irradiation (λ ≥ 290 nm). Chain‐scission during photo‐oxidative degradation was also studied under conditions where evolution of volatiles was negligible. Tristimulus values were calculated for unirradiated and irradiated samples. The rate of oxidative degradation was maximum in the sample possessing higher unsaturation content.
Electrical properties of an insulating varnish
Authors: Bishai Augenie M. , Hakim Itedal K. 
Published: April 2003

AbstractA systematic dielectric study was carried out over a frequency range 60 Hz–300 kHz and at temperatures between 5 and 90°C on dehydrated castor oil mixed with different concentrations of styrene monomer to produce an insulating varnish. The volume resistivity was also studied. The results show that, when dehydrated castor oil is mixed with 10% styrene content by weight of the oil, epoxidised and then chemically treated with melamine resin and other additives, a varnish is produced with favourable electrical insulation properties.
Size‐exclusion chromatography of solutions of block copolymers in selective solvents
Authors: Quintana José R. , Villacampa Manuel , Katime Issa 
Published: April 2003

AbstractSolutions of polystyrene‐block‐poly(ethylene/propylene) and polystyrene‐block‐poly(ethylene/butylene)‐block‐polystyrene copolymers in 5‐methyl‐2‐hexanone and 4‐methyl‐2‐pentanone were studied by size exclusion chromatography. The association equilibrium was studied shifting from micelles to free copolymer chains by increasing the temperature. A remarkable tailing was observed in diblock copolymer micelle peaks that may be explained by the disturbance and restablishment of the association equilibrium during separation in the chromatographic column. This phenomenon was very small for triblock copolymers. In this case, micelle hydrodynamic volumes obtained from SEC curves were compared to those calculated from light scattering and viscosity measurements. The data agreement was very good. Comicellization was analysed by mixing two different micelle solutions and injecting the solution mixture at different elapsed times. The SEC curves showed an intermediate peak corresponding to mixed micelles. The results show that three micelle species coexist in solution during the first period after mixing, which suggests that comicellization proceeds via dissociation of pure micelles and association of both copolymer free chains to form uniform mixed micelles.
Sorption and diffusion of n‐alkanes into bromobutyl rubber membranes
Authors: Aminabhavi Tejraj M. , Munnolli Ravindra S. , Ortego J. Dale 
Published: April 2003

AbstractSorption and diffusion of n‐alkanes into bromobutyl rubber membranes were investigated in the temperature interval 25–60°C by a sorption gravimetric method. The Fickian diffusion equation was used to calculate the diffusion coefficients, which were dependent on the size of the alkanes, their interactions with the chain segments of the polymer and temperature. The diffusion coefficients varied from 0.34×10−7 cm2/s (n‐hexadecane) to 9.94×10−7 cm2/s (n‐hexane). The activation energy for diffusion varied from 14kJ/mol (n‐hexane) heptane to 2.0kJ/mol for n‐hexadecane. The sorption/swelling results are discussed in terms of first and second order kinetic equations. The molar mass between chain‐entanglement‐crosslinks was estimated from swelling data. The experimental and calculated results showed a systematic dependence on the increasing size of the alkanes. None of the solvents showed any degradative effects on the polymer.
Synthesis and characterization of epoxidized phenolic novolacs modified by furfuryl alcohol
Authors: Salabarría Inraini Ramos , Oyanguren Patricia A. , Fasce Diana P. , Williams Roberto J. J. 
Published: April 2003

AbstractThe possibility of reacting furfuryl alcohol with the p‐position of phenolic rings, under acid conditions, was proved using different experimental techniques: size exclusion chromatography, Fourier transform infrared spectroscopy and 13C NMR. This reaction was then used in the modification of phenolic novolacs with furfuryl alcohol. After reaction with epichlorohydrin, epoxidized phenolic novolacs (EPN) modified with furan rings were obtained. They could be cured with aromatic diamines in a similar way to conventional EPNs. The presence of furan rings should improve burning resistance and smoke emission characteristics of the resulting networks.
Transient currents in charging and discharging modes in ethyl cellulose
Authors: Gaur M. S. , Singh Reeta , Khare P. K. , Singh Ranjit 
Published: April 2003

AbstractTransient current in vacuum aluminized ethyl cellulose foil samples of thickness 75 μm were investigated in charging and discharging modes at different temperatures and fields. The occurrence of a peak in the current–time characteristics of charging current (Ic), and the dependence of such currents on field, characterized by a negative resistance region and followed by a superlinear region, are considered to indicate injection controlled transient currents modified by space‐charge arising from the localization of carriers in various traps. Carrier mobility values calculated from a knowledge of the peak in the charging current versus time characteristics were found to range from 10−11 to 10−9 cm2/V s.As times larger than the peak time, the charging current follows the relation I ∝ t−n at low temperatures with different poling fields (Vp). However, the current increases with time and finally tends to saturate for samples poled at higher temperatures with higher values of field.The isochronal characteristics (i.e. current–temperature plots at fixed times) constructed from discharge current versus time plots are characterized by a peak at 70°C or 100°C, depending upon the poling field values.
Morphology and melting behaviour of poly(butylene terephthalate)
Authors: Al‐Raheil Ismail A. , Qudah Ali M. A. 
Published: April 2003

AbstractA detailed description of the morphology and the complex melting behaviour of poly(butylene terephthalate) crystallized isothermally from the melt is presented. Triple, double, or single melting endotherms can deliberately be obtained by varying the heating rate in the differential scanning calorimeter (DSC). At low crystallization temperatures, Tc, triple melting endotherms were seen when the specimen was scanned at 10°C/min, while at high Tc a single endotherm was seen. In the case of the triple melting peaks, the first endotherm corresponds to melting of the imperfect crystals formed at the crystallization temperature. The second endotherm originates from melting of the perfect crystals in the initial distribution, and to some recrystallized meterial. The third endotherm is due to melting of the original crystalline material reorganized during the DSC scan. A detailed morphological study of the isothermally crystallized samples by electron microscopy showed that dominant and subsidiary lamellae in the spherulitic structure are related to perfect and imperfect crystals, respectively.
Metal chelates with some cellulose derivatives. Part III. Synthesis and structural chemistry of nickel (II) and copper (II) complexes with carboxymethyl cellulose
Authors: Hosny Wafaa M. , Hadi Afkar K. Abdel , El‐Saied Houssni , Basta Altaf H. 
Published: April 2003

AbstractCu(II) and Ni(II) complexes with three grades of carboxymethyl cellulose (CMC) with different degrees of substitution have been synthesized and characterized. Probable structures of the metal complexes are inferred from the electronic and IR spectra, elemental analysis data and magnetic moment measurements. CMC coordinates with cu(II) and Ni(II) via the carboxymethyl and hydroxyl groups. The effect of the degree of substition of the CMC on the mode of chelation is discussed. Ni(II) complexes show an octahedral geometry around the metal ion and exhibit the formula [NiL · 4H2O]Cl. Cu(II) complexes exist in the square planar form and have the formula Cu(L)2, where L is uninegatively charged bidentate CMC ligand. The ligand field parameters of Ni(II) complexes are also evaluated.