bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methacrylate‐based block ionomers I: Synthesis of block ionomers derived from t‐butyl methacrylate and alkyl methacrylates
Authors: Deporter Craig D. , Long Timothy E. , McGrath James E. 
Published: April 2003

AbstractDiblock and triblock copolymers of t‐butyl methacrylate (tBMA) with 2‐ethylhexyl methacrylate (EHMA) and n‐hexyl methacrylate were prepared via alkyl lithium initiation and sequential addition techniques in THF at −78°C. The tBMA blocks were quantiatively and selectively hydrolyzed to afford poly(methacrylic acid) (PMAA) blocks which were then neutralized with alkali metal bases to form block ionomers. The unhydrolyzed copolymers had a phase mixed morphology as evidenced by thermal analysis while the hydrolyzed and neutralized polymers were multiphase materials. The carboxylic acid and ioncontaning triblock copolymers formed gels in nonpolar solvents which could be disrupted by the addition of polar additives. Certain carboxylic acid and ioncontaining EHMA/tBMA diblock copolymers also showed this behavior. The triblock ionomers did not show thermoplastic flow prior to degradation, except at the lowest ionic content studied (2%).
Fibre reinforced composites of multifunctional epoxy resins
Authors: Jagadeesh K. S. , Siddaramaiah  
Published: April 2003

AbstractGlass and carbon fibre reinforced epoxy composites were fabricated for N,N,N′,N′‐tetraglycidyl‐4,4′‐diaminodiphenyl methane (TGDDM) and its formulated systems with tri‐ and di‐functional reactive epoxy diluents using 30% diaminodiphenyl sulphone (DDS) as a curing agent. The epoxy laminates were evaluated for their physical, chemical and mechanical properties [at room (26°C) and high (100°C) temperatures]. A marginal increase (<20%) in the mechanical properties of CFRP was found compared with GFRP laminates. Incorporation of epoxy diluents altered the mechanical properties of the composites significantly. The incorporation of triglycidyl‐4‐aminophenol diluent to TGDDM systems resulted in an improvement in mechanical properties of about 2–6%.
Influence of the chemical modification of phenoxy resin on its miscibility with poly(2‐vinyl pyridine)
Authors: Eguiburu J. L. , de Ilarduya A. Martinez , Iruin J. J. , Fernández‐Berridi María J. 
Published: April 2003

AbstractThe influence of the chemical modification of the hydroxyl groups of phenoxy resin (PH) by benzoate, acetate and methoxy groups on its miscibility with poly(2‐vinyl pyridine) (P2VPy) is investigated. Both DSC and FTIR results permit the definition of three distinctive regions: up to 40% modification all 50/50 blends are miscible; between 40 and 55% modification all blends present partial miscibility and at higher than 55% modification the blends are totally immiscible. Specific interactions between the hydroxyl groups of PH and the amine groups of P2VPy are put forward as an explanation for these observations.
Influence of γ‐irradiation on proton spin–lattice relaxation of SBR used as antirads and its ESR investigation
Authors: El‐Sayed Adly H. , El‐Aziz Y. Abd , Rammadan T. , Badran B. M. , Medycki W. , Pislewski N. 
Published: April 2003

AbstractProton spin–lattice relaxation time t1 was measured on SBR samples with carbon black or kaolin filler using modified linseed oil. The NMR pulse technique at 90MHz was used in the temperature range from 180 to 400 K. The temperature dependence of t1 indicates that samples filled with carbon black have similar molecular dynamics to the standard unfilled SBR samples. The activation energy for the motion of the main chain for these samples amounts to 16.4kJ/mol. Samples containing linseed oil modified with para‐toluidine showed an activation energy of about 14.6kJ/mol and were not affected by γ‐irradiation. Values of the minimum relaxation time tmin1 were increased by γ‐irradiation in comparison with a standard SBR sample. ESR measurements carried out at room temperature by means of an X‐band spectrometer indicated that unidentified radicals within the rubber were formed during its mastication with vulcanizing additives. The ESR spectra did not change during the vulcanization process. Samples filled with carbon black showed a broadening of the ESR line; this is consistent with the increase in the electrical conductivity.
Electrical and electromagnetic shielding behavior of laminated epoxy–carbon fiber composite
Authors: Ramadin Y. , Jawad S. A. , Musameh S. M. , Ahmad M. , Zihlif A. M. , Paesano A. , Martuscelli E. , Ragosta G. 
Published: April 2003

AbstractThis paper reports results on the electrical properties of laminated epoxy composite containing 25 layers of carbon fibers in the form of mats. The dependence of the activation energy (calculated from DC resistivity measurements) on temperature reveals two independent conduction processes. The AC impedance is independent of the applied frequency below 75°C, and the real componet of the dielectric constant is also independent of temperature at high frequencies. The determined shielding effectiveness is dominated by the insertion loss. The observed optimum shielding effectiveness occurs at 30 mm spacing and applied frequency 9 GHz.
Dielectric investigation of isotropic and anisotropic solutions of hydroxypropyl cellulose in dioxan
Authors: Moteleb M. M. Abdel , Naoum M. M. , Shalaby M. M. , Saad G. R. 
Published: April 2003

AbstractThe dielectric behaviour of hydroxypropyl cellulose in dioxan has been studied at 10–50°C over a range of concentration of 10–55 wt% to include the isotropic and anisotropic phases. The study showed that the loss maximum ε″max magnitude of polarization ε0 − ε∞ relaxation time 1/2πfm degree of broadening of the absorption curves 1–h or α, and the mean‐square dipole moment 〈gμ2〉, steadily increase with concentration up to 42 wt%, above which a rapid decrease takes place. This indicates that the isotropic solution transforms to an anisotropic solution with a smaller mean dipole moment. The critical concentration is realized to be temperature invariant. This was evidenced by measuring the refractive index of solutions covering the same concentration and temperature ranges.
Copolymerization of styrene on to cellulose activated by corona
Authors: Bataille P. , Dufourd M. , Sapieha S. 
Published: April 2003

AbstractThe corona discharge technique was explored as a means of forming chemically active sites on cellulose surfaces. Paper thus treated was brought into contact with the reaction medium, a styrene–methanol mixture.The corona discharge was generated between two flat circular electrodes separated by a quartz disk. Scanning electron microscope analysis and wettability studies indicated that a hydrophobic film coated the cellulosic fibers.The molecular weights of both the homopolymer and the copolymer were characterized by GPC. Two peaks for grafted copolymer were observed, the first having about the same average molecular weight as the homopolymer, and the second having a molecular weight of about ten times the first fraction.A polymerization mechanism is proposed.
Transient currents in the discharge mode in pure and malachite green doped polymethylmethacrylate films
Authors: Khare P. K. , Singh Ranjeet 
Published: April 2003

AbstractThe transient currents in the discharge mode in polymethylmethacrylate (PMMA) and malachite green doped PMMA films measured as a function of temperature (363–383 K) and field strength (2.0 ×103‐2.0 × 104 V/cm) have been found to follow the Curie–von Schweidler law, characterized by different slopes in the short and long time regions. Various mechanisms which may be responsible for the time‐dependent transient currents of pure and malachite green doped PMMA films are discussed. The effect of doping with malachite green on the discharge current indicates the formation of molecular aggregates.
Microstructure and compatibility of PVDF/PS blends in the presence of PVA
Authors: del Rio C. , Acosta J. L. 
Published: April 2003

AbstractThis research refers to a compatibility study of binary and ternary PVDF blends with PS and PVA by means of the determination of the polymer polymer interaction parameter χ12 calculated from melting point depression analysis of the blends. In addition, a PVDF spherulite growth rate study was conducted in the binary and ternary blends with PS and/or PVA. The nucleation factor is determined by applying the Lauritzen–Hoffman theory.The results obtained show PVA to be capable of compatibilizing PVDF/PS systems when present in concentrations of 30 vol%.
The effect of polymers on the crystallisation of n‐alkanes from solution, part 2. Mode of action of fumarate–vinyl acetate copolymers
Authors: Davidson Iain G. , Cameron G. Gordon 
Published: April 2003

AbstractThe amount of octadecyl fumarate‐vinyl acetate (C18FVA) copolymer which co‐crystallised with dotriacontane from dodecane solution was measured by infrared and electron spin resonance (ESR) spectroscopy. It was found that the magnitude of the slow‐motion component in the composite ESR spectra of the system below its cloud point did not accurately reflect the amount of polymer which had co‐crystallised with the dotriacontane. ESR studies of isolated samples of the co‐crystallate showed the C18FVA to be less tightly bound than in the bulk polymer, suggesting that the polymer molecules are adsorbed on to the surface of the dotriacontane crystals.
Interaction of collagen with polypyrrole in the production of hybrid materials
Authors: Li Hwee Chze , Khor Eugene 
Published: April 2003

AbstractA series of collagen–polypyrrole hybrid materials have been synthesized by the chemical polymerization of pyrrole using FeCl3 as initiator in the presence of soluble collagen. The black color of the resulting materials indicates the presence of polypyrrole while collagen was verified by amino acid analysis of the hybrids. Collagen incorporation into the hybrid was found to be a function of pyrrole concentration used in the polymerization. When the concentrationof pyrrole was high, the collagen loading was low and vice versa. This inverse relationship was also found in the hybrids' electrical conductivity. A 26% collagen content in the hybrid gave a conductivity of 1.4 S cm−1 while a 4% collagen gave a higher value of 62.4 S cm−1. Thermogravimetric data suggest that the two polymers exist in the hybrid as a blend. The nature of the interaction of the components in the hybrid is believed to be strong since collagen could not be extracted despite denaturation with sodium dodecylsulfate.
Hardness of weakly and ‘late’ cross‐linked polymethylmethacrylate and its relationship to chain statistics
Authors: Gündüz Güngör , Kirkin Metin 
Published: April 2003

AbstractThe hardness of ‘late’ and weakly crosslinked polymethylmethacrylate was determined experimentally. As the time of the addition of the cross linker to the polymerizing polymer increases, the hardness first increases, passes through a maximum and then decreases. This change can be expressed by an asymmetric curve. The change of hardness is expressed in terms of a theoretical equation based on the distribution of chains. Some scaling relationships were obtained.
Dilute solution properties of poly(2‐methoxycyanurate) of bisphenol F and bisphenol A
Authors: Patel G. M. , Patel N. K. , Kansara Sujata 
Published: April 2003

AbstractPoly(2‐methoxycyanurate) of bisphenol F and bisphenol A (PMCBFA) was synthesized and fractionated by a fractional precipitation method. The fractions were characterized by viscometry, osmometry and gel permeation chromatography. The Mark–Houwink–Kuhn–Sakurada (MHKS) parameters were established in four solvents and at four different temperatures. The unperturbed dimensions and their coefficients in different solvents were computed using the Stockmayer–Fixman excluded volume theory. From the solution study it was found that PMCBFA is highly flexible. This may be due to the ether linkage present in the main chain.
A rheological model for polymer blends based on the concentric multilayer approach. I. Homogeneous polymer blends
Authors: Chu Line‐Hwa , Chiu Wen‐Yen , Tseng Hsieng‐Cheng 
Published: April 2003

AbstractThe melt rheological behavior of polymer blends was investigated by means of a capillary rheometer. The systems chosen for study were blends of polystyrene (PS) with different molecular weights and blends of polymethylmethacrylate (PMMA) with different molecular weights. A modified concentric multilayer model was proposed to correlate the rheological properties of the polymer blends with the composition and shear rate. The agreement between the calculated values and the measured ones is satisfactory.
Thermodynamics of random copolymers of N‐vinylcarbazole and 4‐alkylstyrenes
Authors: Privalko V. P. , Arbuzova A. P. , Korskanov V. V. , Zagdanskaya N. E. 
Published: April 2003

AbstractRandom copolymers of N‐vinylcarbazole (VC) and alkylstyrenes with variable molar content of VC (first series) or variable size of alkyl substituent (second series) were characterized by the heat capacity measured at normal pressure in the temperature interval 203–523 K, as well as by measurements of specific volume and thermal diffusivity in the temperature interval 303–523 K and in the pressure range 30–100 MPa. It was established that the increase of thermal mobility of chain repeating units with the molar ratio of hexylstyrene (in the first series) or with the alkyl chain length (in the second series) manifests itself as a shift to lower temperatures of the glass transition temperature, as well as an increase of heat capacity, thermal diffusivity and effective number of external degrees of freedom per chain repeating unit from the Simha–Somcynsky reduced equation of state. The inadequacy of the simple diad additivity scheme for a quantitative description of structure–property relationships for the copolymers studied is emphasized.
Relaxation in PMMA films doped with aniline derivatives for nonlinear optics
Authors: Zheng Guo‐qi , Xu Yue‐lian , Wang Wei‐li , Feng Zhun‐jie , Wang Xian‐shan , Wen Jian‐xun 
Published: April 2003

AbstractDynamic viscoelastic spectra, thermally stimulated current, optical absorption spectra and second harmonic generation (SHG) intensity have been measured in poled films of PMMA doped with aniline derivatives. These experiments have indicated that the volume, axial ratio and dipole moment of the dopant molecules, and doping level have significant influences on the stability of SHG of the poled polymers. A mechanism based on free volume theory is proposed which interprets the experimental observations satisfactorily.
Photoinitiation of polymerization of styrene by oxotris(dimethyl dithiocarbamato) vanadium(V)
Authors: Aliwi Salah M. , Abdullah Salah M. 
Published: April 2003

AbstractOxotris(dimethyl dithiocarbamato) vanadium(V) [VO(S2CN(CH3)2)3] sensitizes the polymerization of styrene when irradiated by light of λ = 365 nm at 25°C. Under the experimental conditions employed, no retardation occurs, and the rate of initiation is independent of monomer concentration. The mean values of the quantum yield of iniiation (ϕi) and polymerization (ϕo) are 2.85 × 10−3 and 6.72 respectively. Spectroscopic analysis shows that initiation occurs predominatly through scission of the N,N‐dimethyl dithiocarbamate ligand (—SC(S)N(CH3)2) with reduction of vanadium(V) to (IV), and VO (S2CN(CH3)2)2 is the final photolytic product.A reaction mechanism is proposed based on an intramolecular photoredox reaction which leads to the primary formation of SC(S)N(CH3)2 radicals and a vanadium(IV) chelate complex. The rellevant kinetic parameters are evaluated. The polystyrene produced shows a photoactivity when irradiated with UV‐light.
Influence of oxidation treatment of carbon powders on the cure kinetics of amine cured tetrafunctional epoxy resins
Authors: Andres M. A. , Miguez R. , Corcuera M. A. , Mondragon I. 
Published: April 2003

AbstractA tetraglycidyl 4,4′‐diaminodiphenylmethane (TGDDM) type tetrafunctional epoxy resin containing carbon powders was cured with the stoichiometric amount of a tetrafunctional curing agent, namely m‐phenylenediamine (mPDA). Carbon powders were oxidised with air or nitric acid. The influence of carbon powders on curing of the resin was followed by dynamic mechanical analysis, Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Gelation and vitrification times were determined as a function of the variations of dynamic properties. The evolution of viscoelastic modulus during curing of the different mixtures showed that untreated carbon powder clearly accelerated the kinetics of curing whilst oxidation of carbon powders could remove their catalysing effect. These results were confirmed by monitoring the changes in conversion of epoxy and amine groups during cure using the FTIR technique. DSC experiments also showed the influence of carbon powder as a catalyst and the loss of the catalysing effect as a consequence of chemical treatment.
A reinvestigation of electrolyte effects in the emulsion polymerisation of styrene
Authors: Said Ziad F. M. 
Published: April 2003

AbstractThe effects of adding potassium chloride in concentrations below that required to coagulate the latex to recips of emulsion polymerisation of styrene have been investigated using different concentrations of potassium octadecanoate, which has a low critical micelle concentration (CMC), and potassium dodecanoate, which has a moderately high CMC. At relatively high concentration of octadecanoate the final particle size is significantly increased; the rate of polymerisation is initially increased but later retarded. The effects of increasing micelle size and increased rate of coalescence are dominant. At lower concentration of this emulsifier, the rate is reduced from the onset of interval II.With dodecanoate, concentrations of electrolyte up to 0.3 M accelerate the rate. No significant change in the particle size was observed up to 0.2M electrolyte, thereafter it slightly increased. The increase in micellar concentration can only partially account for these effects. It is believed that the increase in the amount of solubilised monomer inside the micelles, and later inside the latex particles, and the resistance to coalescence (because of the favourable adsorption mechanism of this emulsifier) may account for these observations.With both emulsifiers, electrolyte reduces the induction period and latices with narrow particle size distributions are produced.
Polycondensation of tetramethyldisiloxane 1,3‐diol catalyzed by trifluoromethanesulfonic acid
Authors: Bischoff R. , Sigwalt P. 
Published: April 2003

AbstractThe kinetics of polycondensation of tetramethyldisiloxane 1,3‐diol (HD2OH) have been followed by stopping the reaction at increasing times (by neutralization of the acid and trimethylsilylation of the silanol end‐groups). Analyses of the linear and cyclic oligomers and of the higher polymer have been made by gas–liquid chromatography and by steric exclusion chromatography. At the beginning of the reaction (e. g. between 1 min and 1 h) the main products are linear oligomer H(D)2nOH and D4 (formed by cyclization of HD4OH). There are only very small amounts of large cycles. Linear high polymer is then formed slowly together with increasing amounts of cycles D5, D6, D7, …, formed by backbiting reactions. After 24h, the yield of D4 is 40–50% and that of linear polymer 40–30% (Mpeak × 104–105). With disilanol concentration 0.45–0.9 mol liter−1 and CF3SO3H concentration about 10−3 mol liter−1, the reaction is very rapid during 1–2 min and the medium becomes heterogenous with the formation of an inverse water emulsion. The reaction then slows down considerably, most of the hydrated acid being trapped in the water droplets. Silanol consumption is second order in [SiOH] and first order [TfOH]o. Polymerizations made in polar and non‐polar solvents have similar rates, which however increase moderately in the order toluene<1,2‐dichloro‐ethane<dichloromethane, this corresponding to an increasing solubility of the hydrated acid in these solvents. Polycondensation occurs in the organic phase near the interface, either by esterification of silanol followed by heterccondensation or by homocondensation catalyzed by the hydrated acid (or both).
Structure and morphology of small diameter electrospun aramid fibers
Authors: Srinivasan Gokul , Reneker Darrell H. 
Published: April 2003

AbstractVery small diameter fibers of poly(p‐phenylene terephthalamide) (PPTA) ranging in diameter from 40nm to a few hundreds of nanometers were made by the electrospinning process. The fibers have a circular cross‐section, are birefringent and stable at temperatures greater than 400°C. Electron diffraction patterns obtained from both as‐spun and annealed fibers show meridional and equatorial reflections demonstrating order in the material. The crystal structure and morphology of the fibers were characterized using bright and dark field electron microscopy, electron diffraction and atomic force microscopy.
Synthesis of porous hydrogel structures by polymerizing the continuous phase of a microemulsion
Authors: Bennett Darrell J. , Burford Robert P. , Davis Thomas P. , Tilley Heath J. 
Published: April 2003

AbstractA series of microemulsions have been formulated, with 2‐hydroxyethyl methacrylate (HEMA) or HEMA/water/propanol mixtures as the continuous phase and methylcyclohexane as the discontinuous phase. The effect of surfactant type was investigated with the utilization of both anionic and nonionic surfactants. The microemulsion continuous phase was polymerized by UV radiation and a thermal post‐cure. The resultant polymers were extracted to remove the discontinuous phase and the surfactant. On swelling, the majority of the polymers became opaque, although transparent PHEMA hydrogels were synthesized with an improved equilibrium water content (EWC). The cause of opacity was shown by field emission scanning electron microscopy (FESEM). The breakdown in the microemulsion on polymerization is caused by unfavourable interactions between the PHEMA and the stabilizing surfactants causing agglomerization of the discontinuous phase. All the hydrogels were found to have higher water retention than PHEMA, with EWCs of up to 70%. The modified polymers also demonstrated an increased rate of water diffusion into the matrix. A preliminary study of oxygen permability revealed that a significant improvement had been made over standard PHEMA membranes. The porous structure of the PHEMA gels has been shown to be dependent on the type of surfactant used during synthesis.
Dielectric investigation of the molecular dynamics in blends: polymers with similar molecular architecture (TMPC/PC blend)
Authors: Mansour Ashraf A. , Madbouly Samy A. 
Published: April 2003

AbstractBroad band dielectric spectroscopy was used in the investigation of the molecular dynamics and compatibility of tetramethyl polycarbonate/polycarbonate (TMPC/PC) blends. Frequency scan measurements in the range 10−2−10−5 Hz were carried out in the temperature range 50–220°C for several blends with different compositions, namely, 0, 12.5, 25, 50, 75, 87.5 and 100 wt% of TMPC. The results obtained show that these two polymers are ideally compatible over the entire composition range. The blends reveal only one common glass process. The dielectric relaxation strength and the common glass transition temperature, Tg, were found to vary linearly with composition. Moreover, it was found, surprisingly, that blending has no effect on the distribution of relaxation times of the common glass process of the blends. Furthermore, neither the kinetics (relaxation frequency at a certain temperature) nor the distribution of relaxation times of the local process were influenced by blending. It is concluded that the polymeric chains of the different components are not miscible on a segmental level although the blend exhibits only one glass transition temperature.