bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crosslinking of poly(arylene ether ketone)s 1. Rheological behavior of the melt and mechanical properties of cured resin
Authors: Chan C.‐M. , Venkatraman S. 
Published: April 2003

AbstractElemental sulfur has been used to crosslink poly(arylene ether ketone)s. Evidence for crosslinking is presented in terms of rheological data of the melt. The effects of crosslinking on mechanical properties have been examined using tensile creep, stress–relaxation, and dynamic‐mechanical properties in torsion. The crosslinking elevates the glass transition temperature (Tg), as measured by the maximum in the loss tangent, and reduces creep strain at temperatures above Tg. A new technique for monitoring cure is also presented. One of the advantages of this method for crosslinking poly(arylene ether ketone)s is that the crosslinking can be carried out both in the solid state and in the melt, the rate being dependent on the temperature (above Tg) of annealing.
The kinetics of solution copolymerization of vinyl chloroacetate with vinyl acetate in a CSTR
Authors: Das Siddhartha , Rodriguez Ferdinand 
Published: April 2003

AbstractThe kinetics of isothermal, solution copolymerization of vinyl chloroacetate (VCLAC) with vinyl acetate (VAC) in methyl isobutyl ketone (MIBK) has been investigated using a continuous flow stirred‐tank reactor (CSTR). The initiator used was 2,2′‐azobis 2,4‐dimethyl valeronitrile (ADVN). Polymerizations were carried out to moderately high conversions, necessitating the use of a modified parameter estimation method to determine the reactivity ratios. The copolymer composition conforms to terminal model kinetics. The values obtained for r1 and r2 are 1.18 and 0.80, respectively, with VCLAC as M1 and VAC as M2. Both values are close to unity indicating random copolymerization. The cross termination factor ϕ strongly depends on the composition of the comonomer feed ratio, implying that the chain‐termination step is possibly diffusion controlled. The variation of ϕ could also be caused by chain transfer to the solvent retarding the reaction rate. Such a possibility is consistent with the observed reduction in the molecular weight of the copolymer in the presence of the solvent. The approach to steady‐state in the reactor was characterized. It was not possible to obtain good agreement between experiment and simulation with a single value of the ϕ factor.
Molecular composites via in situ polymerization: Poly(phenylene terephthalamide)–nylon 3
Authors: Moore D. Roger , Mathias Lon J. 
Published: April 2003

AbstractAll‐polyamide molecular level composites composed of rigid rod and flexible coil polymers were prepared using an in situ polymerization process in which the anion of the rigid rod poly‐(phenylene terephthalamide) (PPTA) was used as the initiator for the anionic polymerization of acrvlamide to form the nylon 3 matrix. The rigid aramid component then serves as the reinforcing agent. This polymerization resulted in both graft and homo‐nylon 3 formation. Composite films prepared using in situ processing showed greatly improved strength and modulus over unmodified nylon 3 with no loss of flexibility. The composites showed aggregation and phase separation of PPTA fibrils at PPTA weight fractions of > 30% as indicated by wide angle X‐ray scattering and electron microscopic analysis. The structure of the PPTA formed is that produced from swelled liquid crystalline solutions, indicating that the in situ process involves polymerization in the liquid crystalline state.
Glass‐reinforced interacting blends of epoxy/polyurethane based on castor oil: Synthesis and characterization. II
Authors: Patel Mayur , Suthar Bhikhu 
Published: April 2003

AbstractMechanical and dielectric properties of rubber mixtures of epoxy/polyurethane based on castor oil loaded with glass fiber is of great interest from a technological point of view. Epoxy resin was prepared from bisphenol A and epichlorohydrin in alkaline medium. Polyurethane was prepared from the hydroxyl group of castor oil reacted with 2,4‐toluene diisocyanate. Elemental analysis and infrared (IR) spectra are presented as evidence for the formation of these materials. A homogeneous solution of epoxy resin and polyurethane was prepared in acetone containing a curing agent 1,3‐propane diamine. The glass‐reinforced laminates were prepared by interacting polymer blends on the glass fiber through compression moulding. Chemical resistance to solvents, flexural strength, izod impact strength, and Rockwell hardness studies on a series of specimens were investigated. It was observed that they behave as tough materials. An attempt was made to study the effect of electrical conductivity by changing the compositions of rubber mixtures during reinforcement with glass fibers. The dielectric constant (E′) dielectric loss (E″), and loss tangent (tan δ) of the specimens and their dependence of temperature was studied.
Chemical modification of poly(2,6‐dimethyl‐1,4‐phenylene oxide) by friedel–crafts reactions
Authors: Percec Simona 
Published: April 2003

AbstractThe chemical modification of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) by electrophilic sulfonylation and acylation of the aromatic structural units has been investigated. A maximum monosubstitution degree of 79.4 has been reached. Higher substitution levels were difficult to achieve because of both a decrease in the remaining position nucleophilicity and steric hindrances. Minor changes in thermal stability and a broadening of the solubility range of substituted PPO compared with the parent PPO have been recorded. Very good permeation properties to gases, better than for PPO, have been detected for the modified structures.
Thermal stability of substituted phenol‐formaldehyde resins
Authors: O'Connor Daniel , Blum Frank D. 
Published: April 2003

AbstractA variety of crosslinked phenol‐, or derivatized phenol‐formaldehyde polymers have been synthesized. The phenol derivatives included o‐ and p‐cresol, p‐nonylphenol, m‐pentadecylphenol, and raw and distilled cashew nutshell liquid. The derivatives were copolymerized with phenol and formaldehyde using sulfuric acid as catalyst to yield novolak‐type prepolymers, which were then cured with hexamethylenetetramine. Thermogravimetric analysis was used to evaluate the thermal stability of the cured resins. It was found that the thermal stability of the resins decreased with increasing amounts of cashew nutshell liquid, with distilled cashew resins being slightly more thermally stable than raw cashew resins. The thermal stability of resins containing substituted phenols with alkyl chains was observed to increase from n‐pentadecylphenol to cresol to phenol. The trend in thermal stability of the resins may be explained on the basis of alkyl groups being less thermally stable than aromatic rings. The amount of hexamethylenetetramine used to cure the prepolymers also influences the thermal stability of the resins. It appears that a level of 10 to 15% hexamethylenetetramine maximizes the thermal stability of the resin.
Optimal periodic control of a continuous “living” anionic polymerization II. New theoretical results
Authors: Frontini G. L. , Eliçabe G. E. , Meira G. R. 
Published: April 2003

AbstractIn a previous publication1, a suboptimal technique was developed to solve the problem of producing polymers with prespecified values of the number‐average chain length and the polydispersity, through “living” anionic polymerizations carried out in continuous stirred‐tank reactors. The solution of that problem involved the periodic operation of the monomer solution feed and of the initiator solution feed, as well as readjustments in their feedstock concentrations. The present work solves the problem directly, without resorting to laborious “optimization‐rescaling” procedures. The objective functional considers not only the polymer quality, but also the required polymer production. Compared with the previous results1, the present solutions are better and obtained with less computational effort. The proposed technique may be applicable to other optimal periodic control problems with nonconventional objective functionals.
Environmental effects and relaxation in natural rubber
Authors: Hakim I. K. , Aziz A. W. , Abd‐El‐Nour K. N. 
Published: April 2003

AbstractThe change in attenuation of longitudinal ultrasonic waves has been measured as a function of frequency and temperature for natural rubber samples loaded with intermediate super abrasion furnace (ISAF) in increasing quantities and vulcanized with N‐oxidiethylene benzotriazol sulfunamid (OBTS) after being subjected to natural aging for 5 years. Three relaxation processes, namely α, β, and γ, were noticed. The activation energy for each process was calculated and the results are discussed. Also, the dielectric constant ε′ and dielectric loss ε″ have been investigated for those samples after being immersed in various water media. The measurements were carried out in the frequency range from 100 Hz up to 100 kHz and at room temperature (∼ 28°C). The results are compared with each other and the differences are interpreted.
Synthesis, characterization, and properties of novel polyisobutylene‐based urethane model networks
Authors: Kennedy J. P. , Lackey J. 
Published: April 2003

AbstractThis paper concerns the synthesis, characterization, and physical properties of novel polyisobutylene (PIB)‐based urethane model networks prepared from diphenylmethane diisocyanate (MDI) and three‐arm star PIBs capped with CH2OH end groups (PIB(CH2OH)3). The PIB(CH2OH)3 starting materials were produced by the inifer method in the M̄n = 13,550–27,000 range. The best networks were obtained with NCO : OH = 1. Solvent extractions showed uncatalyzed network formation to be essentially complete and swelling studies indicated the expected architecture, i.e., M̄c = 2M̄n/3 and virtual absence of dangling chains. Stannous octoate was found to increase the rate of network formation in the absence of side reactions (i.e., allophanate formation), while other catalysts also accelerated undesirable reactions. The effect of molecular weight between crosslinks (M̄c) on network physical properties has been studied in the M̄c = 900–18,500 range. The tensile strength increases with decreasing M̄c up to a limiting value after which it sharply declines. Elongations at break decrease monotonously with decreasing M̄c. Low temperature tensile studies show higher tensile data at −20°C, and, surprisingly, a retention of elongations at break. The Tg's decrease with increasing M̄c's until a plateau is reached at −73°C. Hysteresis is fairly constant and permanent set is constant and low. The PIB‐based urethane networks exhibit excellent hydrolytic stability, negligible moisture absorption, and outstanding heat‐aging stability, far beyond what is expected for a polyurethane. Conceivably the thermal deblocking of the urethane group may be reversible (NHCOOCH2⇌ NCO + HOCH2) because the isocyanate that arises in the highly hydrophobic PIB matrix recombines with the alcohol, and cannot react with moisture as in conventional urethane networks.
Characterization of poly(vinyl alcohol‐co‐vinyl acetate) by the iodine complexation method
Authors: Hirai Toshihiro , Okazaki Akira , Hayashi Sadao 
Published: April 2003

AbstractAnalysis of sequence distribution (SD) in poly(vinyl alcohol‐co‐vinyl acetate) (p(VA‐VAc)) by the iodine complexation method (ICM) was investigated through the formation of a red complex of p(VA‐VAc) with iodine‐iodide. Differential thermal analysis (DTA) has been known to be a measure of SD and the ICM was also suggested to be valid for the SD analysis. ICM can be applied for samples of p(VA‐VAc) rich in VAc‐unit content, in which DTA could not be used. Results of SD analysis on p(VA‐VAc) by 1 NMR spectra were compared with those from ICM, and excellent agreement was found between data. The ICM can be applied as a convenient screening method for SD of p(VA‐VAc) as far as the red‐complex formation is concerned, and was shown to have much wider applicable range than the DTA method.
Mechanism of cold drawing in melt‐spun poly(ethylene terephthalate) fibers
Authors: Napolitano M. J. , Moet A. 
Published: April 2003

AbstractAn investigation has been made into the mechanism of cold drawing in melt‐spun poly(ethylene terephthalate) (PET) fibers. An analysis of the cold‐drawing behavior using wide‐angle x‐ray diffraction, orientation measurements, calorimetric and mechanical techniques was performed. The evidence suggests that the cold‐drawing process involes stress‐enhanced crystallization which occurs in conjuction with incresing orientation of the crystalline and amorphous regions. A degradation in the fiber properties after cold drawing was observed for fibers spun below 1,000 m/min while fibers spun above 1,000 m/min exhibited an improvement in fiber properties with cold drawing. This behavior was explained by the existence of two distinct irreversible deformation micromechanisms for fibers spun below and above 1,000 m/min.
Melt flow and fiber properties of copolyesters
Authors: Hong Zhang , Shengping Li , Honglie Luo 
Published: April 2003

AbstractThe effect of modifying monomer [sodium 3,5‐di(carbonethoxy)benzene sulfonate] contents range from 1.5 to 4.5 mol % on the melt flow and fiber properties of copolyesters (COPET) dyeable with basic dyes was investigated. An Instron capillary rheometer was used to obtain data over shear rates ranging from 10 to 104 s−1 at 265, 275, and 285°C. The COPET's flow properties as a function of temperature, inherent viscosity, melting point, and modifying monomer content were determined. The drawn fibers annealed in oil and air at 80, 110, 130, 150, 175, and 200°C were studied by means of measurements of shrinkage ratio, crystallinity, birefringence, long period, sonic rate, and static state flexibility of molecular chain. All these showed that the large side group, SO3Na in COPET molecular chains causes an increase in chain rigidity and melt viscosity, and a decrease in crystallinity and orientation.
Polymerization of melamine and formaldehyde in homogeneous continuous‐flow stirred‐tank reactors using functional group approach: Part A: Conversion of functional groups
Authors: Kumar Anil 
Published: April 2003

AbstractA comprehensive kinetic model using the functional group approach has been proposed for the polymerization of melamine and formaldehyde. The kinetic model is consistent with the basic chemistry of polymerization and involves five rate constants which have been estimated using the experimental data of Tomita. Homogeneous continuous‐flow stirred‐tank reactors (HCSTRs) have been modelled and the mole balance relations for various functional groups have been written. The performance of HCSTRs is governed by algebraic equations and, for any specified residence time, is found by the method of successive substitution using the Brown's algorithm. The computations show that as long as free formaldehyde is present, the reaction mass would consist predominantly of substituted melamine molecules. However, after formaldehyde is completely reacted, larger oligomers are formed in larger concentrations. On comparison of results with batch reactors, it is found that for the same reaction time HCSTRs yield polymer with higher branching.
Electroinitiated copolymerization of N‐vinylcarbazole and α‐methylstyrene in a mixed biphasic medium
Authors: Sanyal Swati , Nayak Bimbadhar 
Published: April 2003

AbstractThe electroinitiated copolymerization of N‐vinylcarbazole and α‐methylstyrene has been studied using a mixed biphasic system in which formamide together with some added electrolyte has been used as the polar phase and the monomer in bulk form or its solution in a nonpolar solvent as the nonpolar phase. The copolymer has been characterized by elemental analysis, and infrared and nuclear magnetic resonance spectroscopy. Molecular weights obtained from gel permeation chromatography were in the range of 20–25 × 103. Generally the copolymer yield increased with increased applied current density. The effect of various other parameters such as dependence of copolymer yield on concentration of electrolyte and comonomer, temperature, and time of electrolysis have also been examined. The locus of polymerization is the anode compartment and a plausible mechanism based on the electrochemical formation of a radical‐cation and a dication has been suggested.
Adsorption of trypsin onto poly(2‐hydroxyethyl methacrylate)/polystyrene composite microspheres and its enzymatic activity
Authors: Kamei Shigeru , Okubo Masayoshi , Matsumoto Tsunetaka 
Published: April 2003

AbstractPoly(2‐hydroxyethyl methacrylate)/polystyrene (PHEMA/PS) composite microspheres were produced by emulsifier‐free seeded emulsion polymerization for styrene in the presence of PHEMA seed particles. Effects of the surface characteristics of the PHEMA/PS composite microspheres on the adsorption immobilization of trypsin and on its enzymatic activity were discussed. Above 5 mol% of HEMA content, trypsin molecules adsorbed had high activity, 65–100% of the activity of free trypsin. The excellence of the composite microspheres as a carrier for trypsin seems to be closely related with the surface heterogeneity consisting of both hydrophilic and hydrophobic parts.
Dynamic birefringence and dynamic mechanical studies on acrylonitrile copolymers
Authors: Kumar Satish , Mead W. T. , Stein R. S. 
Published: April 2003

AbstractDynamic birefringence and dynamic mechanical studies have been done on (i) acrylonitrile/methyl acrylate copolymer and (ii) rubber‐modified copolymer, in the frequency range of 0.06–5.55 Hz (acrylonitrile/methyl acrylate copolymer only at 0.92 Hz) and temperature range of −85 to +85°C. These studies were made on a computerized dynamic birefringence apparatus. A comparison of the dynamic birefringence and dynamic mechanical properties in the rubber‐modified copolymer reveals a rubber glass transition peak, which is much more pronounced in dynamic birefringence data than in dynamic mechanical data. In addition to the glass transition of the rubber part in the rubber modified copolymer, there is a main transition of the copolymer in the vicinity of 80°C. Before the main transition there is a shoulder in the mechanical and optical loss curves. The reasons for the occurrence of the shoulder are discussed.
Studies on the effects of gamma irradiation on nontoxic PVC formulations
Authors: Saxena Anita , Kalliyanakrishnan V. , Pal S. N. 
Published: April 2003

AbstractThirty‐five PVC formulations were compounded initially from which selected nontoxic formulations were subjected to studies in changes of mechanical, optical, migratory, viscosity, and toxicity properties due to gamma irradiation to 2.5 M rads. Degree of discoloration was found to vary from negligible to intense discoloration after irradiation on the selected samples. The nontoxic character of all samples was retained after irradiation. One formulation (R2) showed excellent radiation resistance and minimum discoloration. Effects of various additives on PVC radiation stability is also discussed.
Pervaporation of organic solvents by poly[bis(2,2,2‐trifluoroethoxy) phosphazene] membrane
Authors: Suzuki Fumio , Onozato Kenji , Yaegashi Hidetami , Masuko Toru 
Published: April 2003

AbstractThe permeation and pervaporation behaviour of water and several organic solvents through poly[bis(2,2,2‐trifluoroethoxy)phosphazene] (PBFP) membrane have been investigated in the temperature range from 42 to 80°C. The steady‐state permeation fluxes of the solvents increased in the following order: methanol > ethanol > benzene > water > cyclohexane. An Arrhenius plot of permeation flux of water suddenly changed in its gradient at about 66–70°C, which corresponds closely to the T(1) transition temperature (75°C) of PBFP studied. Interestingly, in the pervaporation of water‐methanol mixtures, methanol permeated more rapidly through the membrane than did water; however, the pervaporation of water‐ethanol mixtures showed poor permselectivties. In the case of an athermal mixture of methanol and ethanol, the fluxes of methanol and ethanol indicated convex and concave curves, respectively, to the axis of methanol concentration; thus the separation characteristics of this system were slightly better than those of a simple distillation technique. The pervaporation of benzene‐cyclohexane mixtures showed excellent permselectivty enrichment in benzene resulting in a separation factor of 12.
Dielectric behavior of a rubber‐toughened epoxy resin
Authors: Domenici C. , Levita G. , Marchetti A. , Frosini V. 
Published: April 2003

AbstractThe dielectric behavior of amine‐terminated butadiene acrylonitrile rubber/DGEBA epoxy resin bleuds of different formulations has been studied in the temperature range −120–160°C at 10kHz. As indicated by the constancy of the glass transition temperatures of the two components, the degree of segmental mixing was very low or nil, irrespective of cure schedules. The intensity of the α‐relaxation of the rubber was much less than that predicted by the simple series model (lower bound). This has been attributed to incomplete phase separation at gelation. Measurements carried out with a nonreactive rubber support this conclusion. Part of the rubber remains molecularly dispersed within the glassy matrix, thus contributing to the modification of the mechanical properties of epoxy resins brought about by reactive rubbers.
Linear polythioesters. XIII.. Products of polycondensation of isomeric di(mercaptomethyl)–dimethylbenzenes with adipoyl and sebacoyl chlorides
Authors: Podkościelny Wawrzyniec , Szubińska Stanisława 
Published: April 2003

AbstractThe synthesis of a new aliphatic–aromatic polythioesters obtained by polycondensation of 4,5‐di(mercaptomethyl)–1,2‐dimethylbenzene,4,6‐di(mercaptomethyl)–1,3‐dimethylbenzene and 2,5‐di(mercaptomethyl)–1,4‐dimethylbenzene with adipoyl and sebacoyl chloride is described. To define the optimal condition of the process, the polythioester from 2,5‐di(mercaptomethyl)–1,4‐dimethylbenzene and sebacoyl chloride was chosen as a model system and obtained by interfacial polycondensation as well as by low‐ and high‐temperature solution polycondensation. To determine the optimal conditions for polycondensation the following parameters have been studied: kind of organic solvent, concentration of reagents, temperature and time of reaction and, in the case of interfacial polycondensation additional, ratio of aqueous to organic phase, kind and concentration of hydrochloride acceptor, and kind and concentration of catalyst were taken into consideration. The quality of the obtained polycondensates was estimated on the basis of values of the reduced viscosity and yield. The structure of the aliphatic–aromatic polythioesters was determined from elementary analysis, infrared spectra, and X‐ray analysis. Some thermal, mechanical, electrical, and chemical properties as well as molecular weights of obtained polycondensates have been determined.
Graft copolymerization of methoxypoly(ethylene glycohol) methacrylate onto polyacrylonitrile and evaluation of nonthrombogenicity of the copolymer
Authors: Miyama Hajime , Shimada Hiroshi , Fujii Nobuyuki , Nosaka Yoshio , Noishiki Yasuharu 
Published: April 2003

AbstractMethoxypoly(ethylene glycohol) methacrylate was grafted onto polyacrylonitrile in dimethylsulfoxide solution via thioamide formation, where ammonium peroxydisulfate was used as an initiator. Optimum conditions for the graft copolymerization, such as degree of thioamidation of the trunk polymer, feeding concentration of the acrylate and the trunk polymer, and temperature were examined. Also the rate of graft polymerization was found to be proportional to concentrations of the acrylate and the trunk polymer. An increase of the degree of the grafting increased water content of the graft copolymer and decreased interfacial free energy between the copolymer and water. In vivo tests showed that the graft copolymer obtained was highly nonthrombogenic.