bluuebunny/crossref_metadata_2025_split huggingface dataset:
A general equation in polycondensation
Authors: Changren Zhou 
Published: April 2003

AbstractIn polycondensation, we define F and f to be the true and effective average functionalities of the reaction system, respectively. The value of Q relates to the functionality and quantity of the nonbifunctional monomer. If there is monofunctional monomer in the reaction system, the value of Q may be less than 0. If the ring‐closure reaction in a system can be neglected, the relation among the molecular weight, the component of the reaction system, and the reaction extent of functional groups can be represented by the following equation: P = (F − Q − 2/xn)/f. The equation may be used in line, branching, and cross‐linking polycon‐densations without any restrictional conditions. According to Carothers, the gelation point Pc can be estimated by the following equation: Pc = (F − Q)/f. All relations among the molecular weight of the polymer, the component of the reaction system, and the reaction extent of the functional group can be replaced by the new equation. Only the Flory equation that is used to estimate Pc cannot be replaced by the new equation.
Carbonization behavior of polyimide films with various chemical structures
Authors: Inagaki M. , Ibuki T. , Takeichi T. 
Published: April 2003

AbstractSix kinds of polyimide films with different molecular structures were synthesized and carbonized up to 1100°C. The carbonization behavior of polyimides was followed by measuring the changes in weight, size, and electrical conductivity. Pyrolysis gases evolved on the way to carbonize up to 1000°C were analyzed by gas chromatography.All films showed appreciable shrinkage and became a black color above 500°C. No cracks and pores were observed on the films heated up to 1100°C, even under the scanning electron microscope. A large weight decrease of 35–50% was observed in a narrow temperature range from 500 to 650°C, which seemed to be due to the departure of CO groups as either CO or CO2. An additional weight decrease occurred gradually above 800°C, due to N2 departure. A remarkable increase of electrical conductivity along the film surface, more than 2 orders, was observed with the increase in heat‐treatment temperature. The polyimide film with a flat molecular structure (PMDA/PPD) gave the highest conductivity: 3.7 × 102S/cm.
Dielectric relaxation during isothermal curing of epoxy resin with an aromatic amine
Authors: Koike Tsuneo 
Published: April 2003

AbstractThe isothermal curing behavior of an epoxy resin system has been monitored by a dielectric measurement whose sensor consisted of a vertical parallel‐plate cell based on a three‐terminal method. The materials used in the isothermal cure were the diglycidyl ether of bisphenol‐A (DGEBA), which was purified from Epon 825 by recrystallization, and 4,4′‐diamino diphenyl methane (DDM). A dielectric relaxation was observed during each isothermal cure at temperatures of 70,80,90, and 100°C, which were below the glass transition temperature (Tg) of the reactive DGEBA–DDM system at the gel point. The relaxation is considered to be caused by the transformation from a liquid state to an ungelled glassy state as a result of an increase in molecular weight because gelation followed by a rubbery state did not exist in the temperature range studied. The dielectric relaxation for the DGEBA–DDM system fits the empirical model of the Havriliak–Negami equation. The Tg of the DGEBA–DDM system, which was estimated from the dielectric relaxation time, agreed with the one experimentally determined by differential scanning calorimetry (DSC).
Synthesis and properties of acrylonitrile‐EPDM‐4‐chlorostyrene graft copolymer
Authors: Park Duck‐Jei , Lee Neung‐Ju , Ha Chang‐Sik , Cho Won‐Jei 
Published: April 2003

AbstractGraft copolymerization of acrylonitrile (AN) and 4‐chlorostyrene (4‐Clst) onto ethylene–propylene–diene terpolymer (EPDM) was carried out using benzoyl peroxide as initiator. The effects of EPDM content, initiator concentration, solvent, mole ratio of 4‐Clst to AN, reaction time, and reaction temperature on the graft copolymerization were examined. It was found that the light resistance, weatherability, and thermal stability of the acrylonitrile–EPDM–4‐chlorostyrene graft copolymer were considerably better than those of acrylonitrile–butadiene–styrene copolymer.
Pultruded fiber‐reinforced poly(methyl methacrylate) composites. II. Static and dynamic mechanical properties, environmental effect, and postformability
Authors: Ma Chen‐Chi M. , Chen Chin‐Hsing 
Published: April 2003

AbstractThis paper presents a novel process developed to manufacture poly(methyl methacrylate) (PMMA) pultruded composite. The mechanical, thermal, and dynamic mechanical properties, environmental effect, postformability of various fiber (glass, carbon, and Kevlar 49 aramid fiber) reinforced pultruded PMMA composites have been studied. Results show mechanical properties (i.e., tensile strength, specific tensile strength, tensile modulus, and specific flexural strength) and thermal properties (HDT) increase with fiber content. Kevlar fiber/PMMA composites possess the highest specific tensile strength and HDT, carbon fiber/PMMA composites show the highest tensile strength and tensile modulus, and glass fiber/PMMA composites show the highest specific flexural strength. Pultruded glass‐fiber‐reinforced PMMA composites exhibit good weather resistance. These composite materials can be postformed by thermoforming under pressure, and mechanical properties of postformed products can be improved. The dynamic shear storage and loss modulus (G′, G″) of pultruded glass‐fiber‐reinforced PMMA composites increased with decreasing pulling rate, and their shear storage moduli are higher than those of pultruded Nylon 6 and polyester composites.
Plasma polymerization of organoisothiocyanates. I. Characterization of deposition process and deposited materials
Authors: Czeremuszkin G. , Wróbel A. M. , Kryszewski M. 
Published: April 2003

AbstractThin polymer films were produced from methyl‐, n‐propyl‐, allyl‐, and phenyl isothiocyanates in an RF plasma, induced in an electrodeless flow system. The deposition rate of polymer film as well as its composition was found to be dependent on the substrate position in the reactor tube. The distinct effect of the monomer structure and the monomer saturated vapor pressure on the polymer deposition rate suggest a molecular nature for the plasma polymerization process and an important role for adsorption in the deposition process, respectively. The surface free energy data, evaluated by contact angel measurements, reveal the polar character of the organoisothiocyanate plasma polymers. The polar component of the surface appears to increase with the sulfur concentration in the polymer film.
Crosslinking of poly(vinyl chloride) with bismaleic compound. II. Rheological behavior and mechanical properties of crosslinked PVC
Authors: Zhou Dafei , Chen Minwei 
Published: April 2003

AbstractIn this study the rheological behavior of crosslinking PVC was studied. We carefully probed the effects of styrene and initiators on crosslink course and further verified PVC's crosslink mechanism suggested previously. St as auxiliary crosslinker was very important for PVC crosslink, no matter whether at lower temperature or at higher temperature, in the absence of initiator or in the presence of initiator. With higher decay temperature cumvl hydroperoxide (CHP) was a very appropriate initiator for PVC crosslinking. By controlling technological conditions, the crosslinked PVC with different cross density was obtained. We found that PVC with THF‐insoluble fraction of about 7% had the best tenacity and maximum breaking energy. The tensile strength would increase as the gel‐fraction content increased. By citing T. Kurauchi's ROF toughening theory, we satisfactorily explained the good ductility of crosslinked PVC with low cross density and the high fragility of over‐crosslinked PVC. Because the motion of segments is hindered in thoroughly crosslinked PVC, its glass transition was so weak that we hardly found out Tg.
Injection‐moulded blends of a thermotropic liquid crystalline polymer with polyethylene terephthalate, polypropylene, and polyphenylene sulfide
Authors: Seppälä Jukka , Heino Markku , Kapanen Camilla 
Published: April 2003

AbstractThe properties of various blends of a polyester‐type thermotropic liquid crystalline polymer (LCP) with polyethylene terephtalate, polypropylene, and polyphenylene sulfide were investigated. The polymers were blended in a twin screw extruder after which samples were injection moulded. The mechanical properties, morphology, and thermal properties of the blends are discussed.
Effect of molecular architecture on microstructural characteristics in some polysiloxaneimide multiblock copolymers
Authors: Samseth Jon , Mortensen Kell , Burns Janet L. , Spontak Richard J. 
Published: April 2003

AbstractEfforts to correlate molecular characteristics with microstructural dimensions in microphase‐separated diblock and triblock copolymers have been very successful, resulting in relationships that can be utilized to design materials with a specific microstructure and, consequently, with particular thermomechanical properties. However, similar efforts in the arena of multiblock copolymers have not been nearly as extensive, despite the increasing interest and diversity of this class of materials. In the present work, energy‐filtered electron microscopy (EFEM) and small‐angle neutron scattering (SANS) are used in a complementary fashion to probe the phase behavior of a series of three polysiloxaneimide (PSI) multiblock copolymers with different molecular architectures. Despite their relatively short segment lengths, all three materials exhibit signs of microphase separation at ambient temperature. SANS data are obtained from chemically unaltered materials and are subsequently interpreted with the Teubner‐Strey model for microemulsions. Resultant microstructural dimensions are in good agreement with those measured from EFEM micrographs. Additional insight into the intramolecular sequencing of each copolymer is obtained from scaling relationships.
Mechanisms of antioxidant action: Nature of transformation products of dithiophosphates. II. Antioxidant action of thiophosphoryl disulphides
Authors: Al‐Malaika S. , Coker M. , Smith P. J. , Scott G. 
Published: April 2003

AbstractThe nature of transformation products of high‐temperature reactions of thiophosphoryl disulphides with hydroperoxides in the absence and presence of oxidisable substrates and the role of the disulphide in the overall antioxidant mechanism was investigated using a range of techniques such as oxygen absorption, 31P nuclear magnetic resonance (NMR), gas‐liquid chromatography (GLC), and peroxide determination. The major transformation products of the above oxidation reactions were found to be the thio and thiono‐phosphoric acids, in addition to mono and polysulphides. At high molar ratios of peroxide to disulphide (>10), these oxidation products are the main catalysts for peroxide decomposition, while at lower ratios the disulphide itself was found to play a major role in the antioxidant mechanism.
Deformation processing of PMMA into high‐strength fibers
Authors: Buckley C. A. , Lautenschlager E. P. , Gilbert J. L. 
Published: April 2003

AbstractPoly(methyl methacrylate) was drawn into fibers by melt extrusion followed immediately by a transient temperature drawing process. By varying five processing variables, fibers ranging from 0.635 mm to 25 μm in diameter were produced. Heat‐induced relaxation of the aligned structure was used to determine the draw ratio of the resultant fibers and therefore the degree of polymer chain alignment imposed by the deformation process. The resulting changes in length and diameter were measured and it was found that draw ratios of 5–20 had been achieved under the varying processing conditions. It was also observed that fiber diameter immediately after drawing is a good predictor of the degree of orientation present in the fiber irrespective of the processing conditions. To test the effect molecular orientation has on material properties, fibers with varying degrees of orientation were tested in tension. As expected, increasing alignment resulted in increasing tensile strength. The maximum observed true ultimate tensile strength was 225 ± 53 MPa and was seen in fibers with a draw ratio equal to 18.7 ± 4.5. Fibers with a lower degree of alignment, while not as strong in tension, exhibited significantly increased ductility. True strains of as high as 25% were observed.
Preparation of negative photoreactive polyimide and its characterization
Authors: Li Zuobang , Zhu Pukun , Wang Lixin 
Published: April 2003

AbstractIn this article, a polyimide precursor was synthesized from oxydianiline and a diacid chloride. This diacid chloride was prepared by the reaction of thionyl chloride with a diacid, which resulted from the reaction of pyromellitic dianhydride with cinnamyl alcohol in N‐methylpyrrolidone (NMP). The photoresist, made from the above polyimide precursor, was spincoated onto silicon wafers, prebaked, and then exposed to UV light with a high pressure Hg lamp. The pattern generation process was also investigated. The appropriate conditions of the photolithographic procedures, involving photoresist compounding, spin coating, prebaking, exposure, development, rinse, postbaking, etc., were determined. The experimental results show that the photoresist exhibited excellent thermal stability and adequate photosensitivity.
Darzen's glycidic ester condensation reaction on poly(N‐vinyl pyrrolidone)
Authors: Devarajan R. , Arunachalam V. , Kumaraswamy M. D. K. , Tajuddin I. , Joghee T. 
Published: April 2003

AbstractAbout 38% conversion of carbonyl groups into epoxy functions in the molecular chain of poly(N‐vinyl pyrrolidone) using chloracetamide results in the decreased viscosity of the product. De‐epoxidation of the epoxy groups introduced shows the most contributing factor towards decreased viscosity is epoxy function.
Preparation and properties of rigid polyurethane foams containing modified cornstarches
Authors: Cunningham R. L. , Carr M. E. , Bagley E. B. 
Published: April 2003

AbstractRigid polyurethane foams were prepared containing 20% (based on weight of polyol) unmodfied or modified cornstarches. The cornstarches had been modified by breeding or conversion methods and included waxy, acid‐modified waxy, malto‐dextrin, and canary dextrin. Due to its more favorable role as an extender, canary dextrin was added to additional foam formulations at 10–40%. Foams containing dextrins responded to compressive stress as control foams with yield points before 10% deformation. Foams filled with the unmodified or waxy cornstarches did not give clearly defined yield points and were measured at 10% deformation. After 14 days under 70°C and ambient conditions, volume increases for the filled foams were 4.0–7.1% vs. 4.6% for the control. The foams filled with canary dextrin increased in volume 4.3%. With the addition of 40% canary dextrin, the volume increases for the foams were 4.4% under thermal conditions and 4.5% under humid conditions (38°C and 98% relative humidity). Under humid conditions for 14 days, the foams containing canary dextrin increased in weight as dextrin content increased (1.5, 3.2, 3.4, and 7.6% with 10, 20, 30, and 40% dextrin, respectively). with 40% canary dextrin in the foams, thermal conductivity was 0.0235 vs. 0.0242 W/mK (0.163 vs. 0.168 Btu in/ft2h°F) for the control.
Chemical interaction between epoxidized natural rubber and silica: Studies on cure characteristics and low‐temperature dynamic mechanical properties
Authors: Varughese Susy , Tripathy D. K. 
Published: April 2003

AbstractThe unusual reinforcement mechanism exhibited by silica in epoxidized natural rubber (ENR) may be attributed to the specific chemical interaction or the chemical cross‐linking taking place between silica and the epoxy groups while heating the mix. Evidence for the higher interaction is established through rheometric studies conducted at 180°C and changes in the dynamic mechanical characteristics studied over a wide temperature range using a dynamic viscoelastometer for the heated and unheated silica‐filled mixes.
Effect of coupling agents on the mechanical properties of mica/epoxy and glass fiber/mica/epoxy composites
Authors: Bajaj P. , Jha N. K. , Kumar R. Ananda 
Published: April 2003

AbstractThe effect of coupling agents, two silane and one zirconate, on the mechanical properties of mica/epoxy and glass fiber/mica/epoxy composites has been investigated. The results showed that tensile modulus and flexural strength and modulus values were improved by the surface treatment of the coupling agents. The property retention was also found to be better in the case of coupling agent‐treated mica/epoxy samples after boiling in water for 2h. In the case of glass fiber/mica/epoxy composites, the flexural modulus and interlaminar shear strength values improved with increase in mica content, but the effect of coupling agents was not pronounced.
Pyrolysis kinetics of highly crosslinked polymethylsiloxane by TGA
Authors: Li Dong , Hwang Sun‐Tak 
Published: April 2003

AbstractThe pyrolysis kinetics of highly crosslinked polymethylsiloxane (PMS) was investigated by thermogravimetric analysis (TGA) under both isothermal and elevated temperature conditions with several environmental gases, such as oxygen, nitrogen, air, and helium. A non‐chain‐scission mechanism composed of initiation, propagation, and termination was proposed to interpret the thermal degradation of highly crosslinked PMS. The mechanism was verified by the experimental results under isothermal conditions. The activation energy of initiation, Ei, was about 20–30 kcal/mol and the activation energy of propagation, Ep, was about 4–6 kcal/mol. These activation energies were found to be different for different gases. The activation energy of initiation for PMS in an aggressive atmosphere, such as oxygen, was lower than that in an inert atmosphere, such as nitrogen. But the activation energy of propagation for PMS was higher in an active environment than in an inert one. There were no direct conclusions about the thermal degradation of highly crosslinked PMS at elevated temperature. Based on thermogravimetric experiments, it is suggested that a pyrolysis process be conducted with a rate of temperature increase less than 10°C/min for preparing the silicon base inorganic membrane.
Permeation and separation characteristics of alcohol–water mixtures through poly(dimethyl siloxane) membrane by pervaporation and evapomeation
Authors: Uragami Tadashi , Morikawa Takeshi 
Published: April 2003

AbstractPermeation and separation characteristics for aqueous alcoholic solutions such as methanol/water, ethanol/water and 1‐propanol/water were studied using a poly(dimethyl siloxane) membrane by pervaporation and evapomeation. Poly(dimethyl siloxane) membrane preferentially permeated alcohol from aqueous alcoholic solutions in both methods. The concentration of alcohol in the permeate by evapomeation was higher than that by pervaporation. However, the permeation rate for the former method was smaller than that for the latter method. In evapomeation with a temperature difference between the feed solution and the membrane surroundings, when the temperature of the membrane surroundings was kept constant and the temperature of the feed solution was raised, both the permeation rate and the permselectivity for ethanol increased with increasing temperature of the feed solution. On the other hand, as the temperature of the feed solution was kept constant and the temperature of the membrane surroundings was changed, the permeation rate decreased, but the permselectivity for ethanol increased remarkably with dropping temperature in the membrane surrounding. Under permeation conditions of a feed solution of 40°C and a membrane surrounding temperature of −30°C in evapomeation, an aqueous solution of 10 wt % ethanol in the feed was concentrated to about 90 wt % in the permeate. The permselectivity for alcohol was in the order of methanol <ethanol <1‐propanol. The above permeation and separation characteristics are discussed from the viewpoint of the physicochemical properties of the poly(dimethyl siloxane) membrane and the permeating molecules.
Rheology of HTPB propellant. I. Effect of solid loading, oxidizer particle size, and aluminum content
Authors: Muthiah Rm. , Krishnamurthy V. N. , Gupta B. R. 
Published: April 2003

AbstractComposite solid propellants based on hydroxyl‐terminated polybutadiene (HTPB) have become the workhorse propellants in the present‐day solid rocket motors. The other major ingredients of a composite propellant are the crystalline oxidizer and metallic fuel. As the solid loading of such propellants is as high as 86–90%, their rheological behavior is very complex. The propellant slurry needs to have reasonably low viscosity and a long pot life for better casting and, hence, for a defect‐free rocket motor. The primary factors affecting the solid propellant viscosity are solid content, particle size, shape, and distribution. The present study concerns the variations of solid loading from 80 to 89% at constant aluminum cotent, variation of aluminium from 0 to 22% at constant solid loading, and the coarse‐to‐fine ratio of the oxidizer. The plots of yield stress, consistency index, pseudoplasticity index, and thixotropic index at different time intervals are drawn for all these parametric changes. Based on these rheological studies, the optimum ratio of oxidizer coarse‐to‐fine ratio, aluminum content, and level of solid loading have been determined.
Damage evolution in flexible polyurethane foams
Authors: Kau C. , Huber L. , Hiltner A. , Baer E. 
Published: April 2003

AbstractMicrocrazing in the struts of flexible polyurethane foams was discovered during compressive deformation and observed directly in the scanning electron microscope. Attributed to this phenomena was the decrease in stress at maximum compression and the intensity of acoustic emission during compressive cycling. The higher content of styrene–acrylonitrile (SAN) copolymer in these foams resulted in higher modulus, more severe microcrazing, an increase in acoustic emission activity, and a decrease in the stress at maximum compression as cycling progressed.
Photoconductivity of poly((E,E)‐[6.2]paracyclophane‐1,5‐diene) and its complex with TCNE
Authors: Ulański J. , Kubacki J. , Głowacki I. , Kryszewski M. , Glatzhofer D. T. 
Published: April 2003

AbstractSteady‐state photoconductivity measurements carried out for poly((E,E)‐[6.2]‐paracyclophane‐1,5‐diene) pure and sensitized with tetracyanoethylene show that doping causes a significant increase of the photoconductivity. This is due to an increase of both the hole mobility and the photogeneration efficiency. The shape of the spectral characteristic is explained by the possible existence of two paths for charge‐carrier photogeneration connected with absorption of the light by the cyclophane unit for shorter wavelengths or by CT complex for longer wavelengths. For an electric field lower than 106 V/m, the photocurrent exhibits an ohmic field dependence, and for higher fields, it becomes proportional to F1.5.