bluuebunny/crossref_metadata_2025_split huggingface dataset:
In vitro degradation of polylactide and poly(lactide‐co‐glycolide) microspheres
Authors: Zhu Jia‐Huei , Shen Zheng‐Rong , Wu Lan‐Ting , Yang Shi‐Lin 
Published: April 2003

AbstractPolyactide (PLA) and poly(lactide‐co‐glycolide) (PLGA) were prepared by bulk ring‐opening polymerization of lactide or lactide/glycolide using stannous octoate as initiator. PLA and PLGA microspheres with an average diameter of 65–100 μm were prepared by a solvent evaporation process. An in vitro degradation test of different molecular weight PLA and of different composition PLGA were carried out in pH 7.4 buffer solution at 37°C in the form of microspheres. Quantitatively, the degree of degradation was monitored by gel permeation chromatography (GPC), by measurement of mass loss and determination of lactic/glycolic acid in degradation medium, and qualitatively, by observing the morphological changes of microspheres with a scanning electron microscope (SEM). The decrease in weight average molecular weight (Mw) for PLA with higher molecular weight is faster at the first degradation stage; afterward, the tendency of Mw to decrease for PLA with different molecular weight is almost the same. PLGA degrades much faster than does PLA, and the degradation rate is significantly enhanced with the increase of glycolic acid (GA) content in copolymers.
Synthesis and blend morphology of BA/BC‐type binary graft copolymers composed of polyelectrolyte trunks
Authors: Ishizu Koji , Minematsu Satoru , Fukutomi Takashi 
Published: April 2003

AbstractPoly(α‐methylstyrene) (PMS) macromonomer having one vinylbenzyl group per polymer chain was prepared by the couplings of living PMS with p‐chloromethylstyrene (CMS). Subsequently, well‐defined poly[acrylic acid (AA)‐g‐α‐methylstyrene (MS)] and poly[4‐vinylpyridine (4VP)‐g‐MS] graft copolymers composed of polyelectrolyte trunks were prepared by radical copolymerization of PMS macromonomer with AA and 4VP monomers, respectively. Binary poly(AA‐g‐MS)/poly(4VP‐g‐MS) or poly[AA · triethyl amine (Et3N) salt‐g‐MS)/poly(4VP‐g‐MS) graft copolymer blend films were cast from a benzene/methanol mixture. The morphological results of binary graft copolymer blends are discussed with respect to three‐phase separated structures.
A kinetic investigation of butyl acrylate polymerization
Authors: Dube M. A. , Rilling K. , Penlidis A. 
Published: April 2003

AbstractAn experimental investigation of the kinetics of the bulk free radical polymerization of butyl acrylate initiated with 2,2′‐azobisisobutyronitrile (AIBN) was conducted at 50° and 60°C using two initiator concentrations. Conversion levels were measured by gravimetry and were independently confirmed using replicate runs. The experiments, conducted in glass ampoules, were performed over the full conversion range. A mathematical model for process simulation purposes was developed. The model was able to predict conversion at the two temperatures and initiator concentrations, thus providing a better understanding of the butyl acrylate homopolymerization kinetics.
Hygroscopic‐aging behavior of pure and NaCl‐filled polyurethane rubber
Authors: Chiu Wen‐Yen , Ding Ding‐Kuo , Chen Chao‐Cheng 
Published: April 2003

AbstractThe aging phenomenon of highly filled rubber in humid environment was investigated. HTPBD was reacted with MDI and mixed with salt at the same time. The mixture was then hot‐pressed for 24 h at 90°C to prepare the sample. The changes in mechanical properties and glass transition temperature of the sample were followed when they were subjected to different humidity at 30°C for 7 days. Furthermore, the effects of humidity on chemical structures were studied with IR.The results showed that unfilled rubber suffered no changes in mechanical properties after 7 days in environment of high humidity (RH 97). However, for NaCl‐Filled rubber, its strength decreased because of a loss of stiffness of salt after salt deliquesced. The glass transition temperature of unfilled rubber seems not to be affected by various humid conditions, but the Tg of filled rubber decreased slightly. From SEM pictures, we observed that interior holes were left after salt deliquesced. This was the main cause for the reduction in mechanical properties of filled rubber.
Infrared spectra of jute stick bleached with sodium chlorite and hydrogen peroxide
Authors: Roy A. K. , Bag S. C. , Sardar D. , Sen S. K. 
Published: April 2003

AbstractJute stick was bleached with sodium chlorite and alkaline hydrogen peroxide solutions. The infrared (IR) spectra of bleached samples and jute stick were analyzed and compared. The bleached samples were characterized by higher absorbance intensity ratios (Av/A2900) of the bands attributed to hemicellulose. Among the bleached samples the chlorite‐bleached sample showed higher intensity for the bands mentioned. The bands attributed to lignin are either absent or very weak in the chlorite‐bleached jute stick as compared to that of peroxide‐bleached jute stick, although some residual lignin was present in the substrate. The 1635 cm−1 band attribute to the vibration of adsorbed water molecules in the noncrystalline regions in cellulose appears as a sharp peak in chlorite‐bleached jute stick and as a shoulder in peroxide‐bleached jute stick. This can be attributed to the difference in the nature of the two bleaching processes.
Modification of natural rubber latex. III. Natural rubber–polystyrene composite latexes synthesized using azobisisobutyronitrile as initiator
Authors: Hourston D. J. , Romaine J. 
Published: April 2003

AbstractMaterials which may be classified as interpenetrating polymer networks have been prepared by the in situ polymerization of styrene in natural rubber latex using azobisisobutyronitrile (AIBN) as the initiator. The resulting materials have been characterized by electron microscopy, Soxhlet extraction coupled with proton nuclear magnetic resonance spectroscopy, dynamic mechanical analysis, and stress‐strain analysis. The styrene polymerizes within the natural rubber latex particles to give a relatively fine phase‐separated morphology with some evidence for a limited degree of segmental mixing. Moreover, it is clear that AIBN, despite what is stated in the literature, does lead to some grafting of polystyrene, and, in addition, causes significant degradation of the natural rubber molecules when the styrene content is low.
Application of a macromolecular Sn (II) complex to the preparation of 99mTc radiopharmaceuticals
Authors: Nakayama Morio , Terahara Takaaki , Wada Masao , Harada Kumiko , Sugii Atsushi , Egawa Hiroaki 
Published: April 2003

AbstractTo develop insoluble Sn2+ complexes for the preparation of 99mTc radiopharmaceuticals, the adsorption of Sn2+ to macroreticular chelating ion exchange resins having various functional groups was investigated. Among them, a resin containing aminophosphonic acid groups showed a high adsorption capacity for Sn2+, which was bound strongly to the resin by chelation. This macromolecular Sn2+ complex was very stable against hydrolysis and oxidation, and could be applied satisfactorily for the reduction of 99mTc.
Competitive primary amine/epoxy and secondary amine/epoxy reactions: Effect on the isothermal time‐to‐vitrify
Authors: Wang Xiaorong , Gillham John K. 
Published: April 2003

AbstractThe effect of temperature on the ratio of the kinetic rate constants, k2/k1, has been investigated using FTIR spectroscopy for the competing reactions of epoxy with secondary amine (k2) and primary amine groups (k1) in a trimethylene glycol di‐p‐aminobenzoate/diglycidyl ether of the bisphenol A system. The ratio of the rate constants increases from 0.16 to 0.33 in the temperature range 100−160°C. The corresponding difference in the activation energies for the competing reactions is about 3.7 kcal/mol. The effect of the ratio on the time‐to‐vitrify contour of the isothermal time–temperature–transformation (TTT) cure diagram is discussed: The effect is more significant at higher curing temperatures.
The effect of sorbed penetrants on the aging of previously dilated glassy polymer powders. IV
Authors: Osborne J. L. , Hopfenberg H. B. , Koros W. J. 
Published: April 2003

AbstractUniform, submicron‐diameter polystyrene (PS) and poly(methylmethacrylate) (PMMA) microspheres were dilated by preswelling with pure organic vapors followed by rapid removal of the preswelling penetrant by protracted evacuation of the preswelling chamber to a pressure of 10−3 mm Hg. Aging of the preswollen polymers was carried out both in vacuum and in the presence of various penetrants at sorbed concentrations typically less than 2 wt%. Inferences about relaxations of the polymers were based upon changes in concentrations of the penetrants within the microspheres, at a given temperature and penetrant activity, which result from aging in vacuum or in the presence of penetrant. The kinetics of the relaxations were monitored by probing the expanded glasses with relatively low concentrations of penetrants. In general, the continuous presence of these low concentrations of probe molecules either arrested or retarded the ensuing relaxation as compared with the aging that occurred in vacuum. A series of lower monohydric alcohols, lower n‐alkanes, and some other similar penetrants were used as probes to test explicitly and systematically the effects of size and structure of the penetrant contacting the polymer during aging on the decay of excess sorption capacity of the preswollen glassy polymers. Decay of excess sorption in the presence of penetrant was evident only when molecularly small penetrants with interactive functional groups, alcohols for example, were sorbed into preswollen PMMA. This result suggested that the relaxation occurring in the presence of penetrant involved specific interactions between the penetrants and the carbonyl groups in the PMMA.
The electron beam‐induced cationic polymerization of epoxy resins
Authors: Crivello James V. , Fan Mingxin , Bi Daoshen 
Published: April 2003

AbstractThe rapid, efficient electron beam‐induced cationic polymerization of multifunctional epoxy monomers has been carried out in the presence of diaryliodonium and triarylsulfonium salts. These polymerizations take place at low doses (1–3 Mrad), which make them attractive for commercial applications. The factors that contribute to the high reactivity of these monomers are discussed.
Electrochemical polymerization of acrylonitrile with quaternary salts
Authors: Bhadani Suraj N. , Ansari Qayumuddin , Gupta Sumanta K. Sen 
Published: April 2003

AbstractThe electrochemical polymerization of acrylonitrile was carried out in the solutions of tetrabutylammonium bromide and tetrabutylphosphonium bromide in N,N‐dimethylformamide in a divided electrolytic cell. The formation of polyacrylonitrile of high molecular weight (7.6 × 104) took place in the cathode compartment. The kinetics of the polymerization was investigated for different initial monomer concentrations, current levels, and electrode materials. The polymerization mechanism is anionic.
Bending of poly(vinyl alcohol)–poly(sodium acrylate) composite hydrogel in electric fields
Authors: Shiga Tohru , Hirose Yoshiharu , Okada Akane , Kurauchi Toshio 
Published: April 2003

AbstractBending of poly(vinyl alcohol) hydrogel mixed with poly(sodium acrylate) chains, PVA–PAA gel, under the influence of dc electric fields was studied. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixture of PVA and polyacrylic acid aqueous solutions. The PVA–PAA gel was a hydrogel with the PAA chains, which were entangled with the PVA polymer network and were fixed in the gel. The PVA–PAA gel bent toward the negative electrode in electrolyte solutions under dc electric fields as did the polyelectrolyte gel with negatively charged polyions. The PVA gel, free of PAA, was insensitive to dc electric fields. The deflection of the bending and the bending speed were influenced by the filed intensity, the concentration of the polyion in the gel, and the thickness of the gel. The bending of the PVA–PAA gel was qualitatively explained by a bending theory of polyelectrolyte gel, based upon the change of the osmotic pressure due to the ion concentration difference between the inside and the outside of the gel.
Polyether–polyimide thermoplastic elastomers. I. Synthesis and properties
Authors: Yu Xuehai , Song Chunkang , Li Chi , Cooper Stuart L. 
Published: April 2003

AbstractA series of polyether–polyimides based on polycondensation of poly(tetramethylene oxide) glycol di‐p‐aminobenzoate with different molecular weights (650, 1000, 2000) and benzenetetracarboxylic acid dianhydride (BTDA) or 3,3′,4,4′‐benzenetetracarboxylic acid anhydride (BPTDA) was synthesized. Infrared spectroscopy (IR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and stress–strain tests were used to follow the imidization process and to study the structure–property relations of this family of polymers. FTIR data showed that the imidization was completed after 6 h at 140°C, which is a much lower temperature than that required for polyimides synthesized from low molecular weight diamines. DSC and DMA results indicated that the block copolymer exhibited a well‐phase‐separated structure and had a broad rubbery plateau from about −70°C to 260°C, which varied with dianhydride type and hard‐segment content. The BTDA series had enhanced mechanical properties compared to the BPTDA series. The excellent tensile properties of the polyether–polyimides suggest that they could be potentially used as heat‐resistant thermoplastic elastomers.
Simulation of microstructure development in injection molding of engineering plastics
Authors: Yu Jeong S. , Wagner Alan H. , Kalyon Dilhan M. 
Published: April 2003

AbstractMathematical models were developed to predict the various microstructural properties, including birefringece, residual stress, and density distributions, in the freely quenched compression molded samples as well as in the injection molded samples. To model the birefringence distribution in the injection molded samples, the BKZ type integral constitutive equation was employed to account for the nonisothermal stress relaxation, which takes place during the cooling stage of the molding cycle. The predicted birefringence agreed well with the experimental data near the mold walls. The residual stress distribution was modeled by the existing thermoelastic theory. The residual thermal stress distribution in the freely quenched samples was predicted very well by the model. However, the predicted residual thermal stresses in the injection molded samples were much larger than the measured ones. A phenomenological model to predict the density distribution in injection molded sample is proposed by including the effects of both cooling rate and the pressure on the density development. The predicted results agreed well with the experimental data.
An approach to yielding and toughness in rubber‐modified thermoplastics
Authors: Cigna Giuseppe , Maestrini Claudio , Castellani Leonardo , Lomellini Paolo 
Published: April 2003

AbstractAn interpretation of yielding and fracture of rubber‐toughened polymers is attempted, considering the fracture mechanics behavior of the matrices, with the rubber particles as stress‐intensification sites. The fit of effective tensile yield stresses of composites vs. particle radii defines a stress‐intensity factor KYc for craze yielding much smaller than the classical fracture factor Kc, values are found for polystyrene and poly(styrene‐co‐acrylonitrile)‐based polymers. These factors are considered characteristic for craze initiation and propagation in the matrices, while Kc, in turn, would include also the craze‐crack transformation contribution. KYc appears independent of the rubbery‐phase volume fraction and characteristics, but two different values are found and discussed for poly(styrene‐co‐acrylonitrile)‐based materials in two different particle‐size ranges. A similar treatment on notched specimens' yield stress indicates the presence of a maximum in different radius ranges for polystyrene and poly(styrene‐co‐acrylonitrile) matrices, with higher values than their breakdown stresses. This stress increment is in relation to the minimum particle size inducing and still stabilizing crazes and preventing crack formation. This maximum seems to control the reinforcing extent of the polymer matrix conditioning the Izod fracture initiation energy.
The chemical and physical properties of electrochemically prepared polyaniline hexafluorophosphate (PAPF6)
Authors: Choi Kyung Moon , Kim Keu Hong 
Published: April 2003

AbstractPolyaniline hexafluorophosphate (PAPF6) was synthesized by electrochemical oxidation from 0.2 M aniline in acetonitrile solution containing 0.1 M TEAPF6 as the supporting electrolyte. From polarographic and cyclic voltammetry results, the values of the half‐wave potential \documentclass{article}\pagestyle{empty}\begin{document}$\left( {{\rm E}{\textstyle{1 \over 2}}} \right)$\end{document} and αn were calculated to be 774 m V and 0.589, respectively. The morphology of the PAPF6 sample was determined from SEM. Thermal analyses for PAPF6 and other polyaniline‐based systems show distinguishable, thermal characteristics depending on the doping methods for the anions. Also, the maximum values (Rmax) of the reaction rates (R) for these polymers were obtained. The electrical conductivity of the PAPF6 pellet was measured at temperatures from −170 to 25°C. From a plot of conductivity vs. 1/T, an activation energy (Ea) of 0.057 eV was obtained. The conduction mechanism in the pressed pellet of PAPF6 is suggested to be hopping conduction. The various ESR‐parameters were obtained from the ESR curve at room temperature.
Column studies on metal ion removal by dyed cellulosic materials
Authors: Shukla S. R. , Skhardande V. D. 
Published: April 2003

AbstractCellulosic materials, namely bleached bamboo pulp, jute fibers, and sawdust dyed with a reactive dye of monochlorotriazine type were used in the column studies for removal of different metal ions. The use of an adsorption column makes the process continuous, so that it is economically viable on an industrial scale. After the adsorption of metal ions such as Cu2+, Pb2+, Hg2+, Fe2+, Fe3+, Zn2+ and Ni2+, the adsorbents were successfully regenerated by using dilute acids. These columns were then used repeatedly for adsorption either of the same salt for more than ten times or of different salts in succession. No loss in adsorption power was observed.
Some recent studies on metal/polyaniline schottky devices
Authors: Pandey S. S. , Misra S. C. K. , Malhotra B. D. , Chandra Subhas 
Published: April 2003

AbstractAn attempt has been made to estimate various electronic parameters such as work function, barrier height, and ideality factor through I‐V measurements carried out on metal/polyaniline Schottky junctions. The results of optical studies conducted on chemically synthesized polyaniline used in the fabrication of such Schottky devices have been presented.
Relaxational behavior of CR‐39 polycarbonate used as nuclear track detector
Authors: Vanderschueren J. , Yianakopoulos G. , Niezette J. , Chatry C. , Gasiot J. 
Published: April 2003

AbstractThe relaxational behavior of CR‐39 (poly allyl diglycol carbonate) nuclear track detectors was determined over a large temperature range (−100 to 125°C) including the glassy, glass transition, and ionic conduction regions by means of dynamic mechanical and dielectrical measurements, differential scanning colorimetry, linear coefficient of expansion, and especially thermally stimulated current methods owing to their high sensitivity and resolving power. This investigation was carried out as a first step aimed, on the one hand, at finding possible correlations between dosimetric performances, polymer morphology, and intrinsic or extrinsic relaxations and, on the other hand, at determining the origin of the inconsistent background and response properties, which are still a serious obstacle to the use of this material as a personnel dosimeter in spite of its high sensitivity and wide response range. Six distinct relaxation regions have been evidenced, most of which being to some extent dependent on the sample investigated and its thermal history. From higher to lower temperatures, these various relaxations have been ascribed to charge carrier migration over macroscopic distances (ρ), glass transition (α), nonequilibrium precursor motions of the glass transition (ά), and local mode motions of the diethylene‐glycol dicarbonate links (β), diethylene glycol segments (γ), and carbonate groups (δ). In addition to these intrinsic relaxations, the as‐received samples are also characterized by small‐scale residual stresses that relax out irreversibly at temperatures lower than the glass transition temperature Tg. The systematic study of the influence exercized by the position of a specimen in a given sheet, and, for a given sample, by annealing, thermal cycling, and physical aging on relaxation properties shows that, besides spatially inhomogeneous internal stresses, cross‐linking density, and cluster morphology, marked structural modifications and nonequilibrium processes can occur by heating the polymer above Tg. These phenomena deserve a great deal of consideration because they could be key points for identifying the sources of the troublesome fluctuations of dosimetric response. Relaxation studies thus appear as useful and sensitive tools for a deeper understanding of the performance of CR‐39 polymer as a track recorder.
Preparation of composite membranes via interfacial polyfunctional condensation for gas separation applications
Authors: Chern Yaw‐Terng , Chen Leo‐Wang 
Published: April 2003

AbstractComposite membranes were prepared by interfacial polycondensation of a water‐soluble diamine (4,4′;‐methylene dianiline [MDA] or ethylene diamine [EDA]) with an organic solvent (hexane)‐soluble 1,2,4,5‐benzenetetra acyl chloride (BTAC) on top of a porous polysulfone (PSF) support. For both the poly(BTAC‐MDA) and poly(BTAC‐EDA) composite film systems, the permselectivity of these films increases only slightly with an increasing number of coatings. The poly(BTAC‐MDA) composite membranes are treated at 135°C in a nitrogen atmosphere for 4 h, and they have a high selectivity [α*(CO2/CH4) = 20.51] and permeability [P̄(CO2) = 44.12 Barrer]. This is due mainly to the great chain stiffness of the formed polyimide, which has high selectivity. The high permeability is due to a porous polysulfone support. The trend of the permeability for this composite film is P̄(CO2) > P̄(O2) > P̄(N2) > P̄(CH4). In poly(BTAC‐EDA) composite membranes, the permeation of different gases decreases in the order of P̄(CO2) > P̄(O2) > P̄(CH4) > P̄(N2). As to the composite films being more permeable to CH4 than to N2, this is probably due to the presence of a considerable quantity of aliphatic chains (–CH2–CH2–) in the poly(BTAC‐EDA) composite film caused by its particularly excellent solubility for methane.
Study on ketalization reaction of polyvinylalcohol by ketones. V. The film properties of polyvinylketals obtained by aliphatic ketones
Authors: Nakamura Naofumi , Suzuki Kimihiro 
Published: April 2003

AbstractThe physical and chemical properties of polyvinylketals (PVKL) prepared from seven aliphatic ketones [acetone, methyl ethyl ketone (MEK), methyl n‐propyl ketone (nPK), methyl i‐propyl ketone (iPK), methyl n‐butyl ketone (nBK), methyl i‐butyl ketone (iBK), methyl t‐butyl ketone (tBK)] were studied. The moisture regain and water vapor permeability of PVKL films decrease in the following order: acetone > MEK > nPK > iPK ≒ nBK > iBK > tBK. The contact angle measurements revealed that this order is determined by the surface free energy of films, which depends upon the kind of the original ketones. PVKL (acetone) with low ketalization degree was not soluble in neutral water and had lower moisture regain than PVA. As shown in X‐ray analysis, the molecular orientation was not random, the crystalline part of PVA remaining. Thus, it becomes clear that behavior of PVKL in water is affected not only by the hydrophobicity of film surface, but also by the crystallinity of PVKL.