bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epoxidation of natural rubber studied by nmr spectroscopy
Authors: Bradbury J. H. , Perera M. C. S. 
Published: April 2003

AbstractEpoxidation of natural rubber with peroxyacids in homogeneous solution (CHCl3, benzene) and in latex occurs without main chain fission or isomerization of the cis configuration. There are two possible modes of addition of oxygen to the double bond, which gives rise to diastereoisomers in dyad structures, as shown by the occurrence of splitting of 13C NMR resonances in 100% epoxidized rubber. In partially epoxidized rubber the 13C NMR resonances of the methylene carbon atoms have been fully assigned using pulse sequences and lanthanide shift reagents, in terms of triad sequences. Resonances in the olefinic region of the spectrum require assignment in terms of pentad sequences whereas those from the oxirane region are much more closely spaced and are assigned using triads. Intensity measurements on the methylene carbon NMR resonances show that the epoxidation reaction is a random process in both homogeneous solution and in latex particles.
Characterization of some poly(methyl methacrylate)s prepared by emulsion polymerization in the presence of burnt mazot boiler deposit (BMBD)
Authors: Moustafa A. B. , Sayyyah S. M. , Badran A. S. , Hassanin M. S. 
Published: April 2003

AbstractThe emulsion polymerization of MMA was studied in water using potassium persulfate as initiator and dodocyl benzene sodium sulfonate as emulsifying agent in the absence and presence of burnt mazote boiler deposit (BMBD). The BMBD has a catalytic effect on the polymerization reaction; its effect on the mean average molecular weights of the obtained polymers was also examined by viscosity measurements. The molecular weight distribution was obtained by thin layer chromatographic analysis. The polydispersity for the obtained polymers was wider when prepared in the presence of BMBD. The apparent activation energy among 65, 75, and 85°C for this system was 13.2 × 104 J/mol and 9.2 × 104 J/mol when the polymerization is carried out in the absence and presence of 0.1 g BMBD/20 mL of the reaction mixture, respectively. The suitable mobile phase was ethylacetate or dimethylformamide as single eluent system. In case of binary eluent systems the mobile phase was benzene + methanol (1:1.4 by volume).
Reaction kinetics of the reaction of terephthalic acid and ethylene carbonates
Authors: Fagerburg David R. 
Published: April 2003

AbstractThe kinetics of the reaction of terephthalic acid with a number of ethylene carbonates in the presence of an amine catalyst were examined. All reactions apparently follow first‐order kinetics; therefore, the solution rate of TPA is not rate‐limiting. With minor adjustments, the mechanism appears to be in accord with that of the model reaction of benzoic acid and ethylene carbonate previously reported. Attack of the carboxylate on the carbonate ring must be the rate‐limiting step. Substituent effects (owing to substituents on the carbonate ring) appear to be mostly steric in nature; surprisingly, ann‐octyl group causes the slowest reaction. Besides being strongly influenced by steric hinderance, the transition state appears to be highly polar. Activation energy (16.0 kcal/mol) and activation entropy (−23.6 cal/deg) are very similar to those of the model reaction.
Polymer crystallization induced by sorption of CO2 gas
Authors: Chiou J. S. , Barlow J. W. , Paul D. R. 
Published: April 2003

AbstractPrevious work has shown that sorption of CO2 at relatively high pressures by glassy polymers reduces their glass transition temperatures and may convert the glass into a rubber under certain conditions. It is shown here that this plasticization by a gas can induce crystallization just as sorption of vapors or liquids is known to do. This point is extensively explored for miscible blends of poly(vinylidene fluoride) and poly(methyl methacrylate) and to a lesser extent for poly(ethylene terephthalate). In some cases, this secondary crystallization process results in small crystals whose melting endotherms are just above the glass transition and are very similar to peaks resulting from heat capacity overshoots, or enthalpic relaxation, caused by sub‐Tg annealing; however, by appropriate techniques peaks arising from these two separate mechanisms can be distinguished. For oriented materials, evidence is shown which demonstrates that the additional crystals formed on CO2 sorption have the same preferential orientation as the original material.
Surface modification of cellulose fibers. II. The effect of cellulose fiber treatment on the performance of cellulose–polyester composites
Authors: Zadorecki Pawel , Flodin Per 
Published: April 2003

AbstractCellulose fibers treated with different coupling agents based on trichloro‐s‐triazine have been evaluated in terms of their reinforcement effect on unsaturated polyesters. The treatment with coupling agents containing double bonds resulted in what we believe to be the formation of covalent bonds between fiber and matrix. This has been compared with a treatment, which can only lead to formation of close interfacial molecular contact by wetting. The tensile properties of composites prepared from treated and untreated fibers were studied before and after exposure to water. It was found that all types of fiber treatment decreased water absorption and the reduction of mechanical properties in wet conditions, but that the degradation at the fiber/matrix interface which occurs from immersion in water and drying could only be avoided through the development of covalent bonds between fiber and matrix. Scanning electron microscopy was used to study the adhesion between fiber and matrix. An explanation of the reduction of mechanical properties of cellulose‐fiber reinforced polymers in wet conditions is proposed.
Modeling the free radical solution and bulk polymerization of methyl methacrylate
Authors: Louie Brian M. , Carratt Gregory M. , Soong David S. 
Published: April 2003

AbstractThis paper reviews our current understanding of the kinetics and mechanisms of free‐radical chain polymerization of methyl methacrylate. A mathematical model previously proposed to describe the bulk polymerization of MMA is here extended to cover solution polymerization. This extended model is validated by comparing its predictions with experimental data over a range of conversions and product molecular weights.
A numerical approach for obtaining nonlinear viscoelasticity parameters of polymeric materials and composites
Authors: Augl Joseph M. , Land David J. 
Published: April 2003

AbstractA least‐squares fitting procedure is developed for application to determine the parameters of the power law for nonlinear creep and recovery behavior of polymeric materials. The nonlinear power law, developed by Schapery from thermodynamic principles, is linearized, and an iterative approach is used to determine the desired parameters. The iteration is stopped after the standard deviation of the calculated points with respect to the fitted points reaches a minimum value. The purpose of this method is to avoid the inherent ambiguities present in the more familiar graphical fitting procedure. In order to study the sensitivity and limitations of an experimental approach for determining the viscoelastic parameters, sets of artificial experimental data points were generated for use as a control. These points were obtained by varying the theoretical functional values with normally‐distributed random numbers within a preset error band.
Two‐resistance mass transfer model for the adsorption of various dyestuffs onto chitin
Authors: McKay G. , Blair H. S. , Gardner J. G. , McConvey I. F. 
Published: April 2003

AbstractThe kinetics of the adsorption of various dyestuffs onto chitin have been studied. The dyestuffs used are Neoland Blue 2G, Eriochrome Flavine A, and Solophenyl Brown 3RL and a number of process variables were considered, such as adsorbent mass and dye concentration. The mass transfer model is based on the assumption of a pseudoirreversible isotherm and two resistances to mass transfer. These are external mass transfer and internal pore diffusion mass transfer. The rate of adsorption of dyestuffs onto chitin can thus be described by an external mass transfer coefficient and a pore diffusion coefficient. The external mass transfer coefficients are 5.0 × 10−5, 5.0 × 10−5, and 1.0 × 10−5 m·s−1 and the pore diffusivities are 3.0 × 10−10 and 4.0 × 10−11 m2·s−1 for Neolan Blue 2G, Eriochrome Flavine A, and Solophenyl Brown 3RL, respectively.
Criteria for rheological compatibility of polymer blends
Authors: Han Chang Dae , Chuang Hsiao‐Ken 
Published: April 2003

AbstractCriteria for rheological compatibility of polymer blends are suggested. The criteria suggested make use of plots of first normal stress difference (N1) against shear stress (σ12), and of storage modulus (G′) against loss modulus (G″). Compatible blend systems considered are (1) blends of two different grades of low‐density polyethylene, (2) blends of poly(vinylidene fluoride) and poly(methyl methacrylate), (3) blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) and polystyrene, and (4) blends of poly(styrene‐co‐acrylonitrile) and poly(styrene‐co‐maleic anhyride). And incompatible blend systems considered are (1) blends of nylon 6 and poly(ethylene‐co‐vinyl acetate) and (2) blends of nylon 6 and an ethylene‐based multifunctional polymer. It has been found that plots of N1 vs. σ12 and G′ vs. G″ give (a) temperature‐independent correlations for both compatible and incompatible blend systems; (b) composition‐independent correlations for compatible blends; (c) composition‐dependent correlations for incompatible blends.
Investigation of thermal degradation of polyethylene–polypropylene‐based grease
Authors: Al‐Sammerrai Dhoaib 
Published: April 2003

AbstractThermal degradation of polyethylene–polypropylene‐based lubricating grease was studied in a differential scanning calorimeter under static air atmosphere, while weight loss with increase in temperature under inert atmosphere of nitrogen gas was recorded thermogravimetrically. The polymer‐based grease exhibited higher thermal stability when compared to that of a soap‐derived multipurpose lubrcating grease based on lithium 12‐hydroxystearate.
Thermal expansion behavior of various aromatic polyimides
Authors: Numata Shun'ichi , Oohara Shuuichi , Fujisaki Koji , Imaizumi Jun'Ichi , Kinjo Noriyuki 
Published: April 2003

AbstractThe thermal expansion behavior for various aromatic polymides was investigated. Usally polymers, including polyimides, have high thermal expansion coefficients (3–6 × 10−5 K−1), compared with metals and ceramics. However, there are some polyimides which have very low thermal expansion coefficients below 1 × 10−5 K−1. This property was observed for the polymides obtained from pyromellitic dianhydride or 3,3′ 4,4′‐biphenyltetracarboxylic dianhydride and aromatic diamines which were constituted of only benzene rings fused at para positions. It was proposed that their low thermal expansion coefficient related to the linearity in their polymer molecular skeltons.
Plastic zones in glassy polymers around cracks approaching a bimaterial interface under small‐scale yielding
Authors: Theotokoglou E. E. , Tsamasphyros G. 
Published: April 2003

AbstractA study of the plastic zones created around the tips of cracks in glassy polymers, under small scale yielding, can be confronted by using the two well‐known pressure‐modified yield criteria and the elastic solution of the problem. There is particular interest in the case of a cracked body reinforced by another more resisting body under plane‐strain conditions. The shapes of plastic zones developed around the tips of the crack subjected to opening mode loadinng conditons are examined as the crack approaches perpendicularly the bimaterial interface. For the study of plastic zones the exact solution derived from Muskhelishvili's complex potentials was used. Moreover, the plastic zones are confronted using either the exact solution or Sneddon's asymptotic expansion.
Thermodynamics of flow‐induced phase separation in polymers. II. The effect of molecular weight distribution
Authors: Vrahopoulou E. P. , McHugh A. J. 
Published: April 2003

AbstractA thermodynamic analysis of flow‐induced phase transformations in polymers is presented. Calculations are based on the assumption that stresses on the polymer coils lower their effective flexibility. This leads to the possibility of a spontaneous liquid separation in which the more concentrated phase contains chains having a lower flexibility relative to those in the more dilute phase. The effects of molecular weight distribution are included, and calculations demonstrate that reducing the flexibility also enhances fractionation in that the more concentrated phase is preferentially enriched with the higher molecular weight fraction of the original polydisperse system. These results offer a quantitative basis for understanding flow‐induced structure formation and phase transformation phenomena in polymers in general and the phenomena of precursor formation and polymer fractionation in flow‐induced crystallization in particular. Application to the latter phenomenon is also discussed.
Glass transition temperature and chain flexibility of 1,2‐polybutadiene
Authors: He Tianbai , Li Bincai , Ren Shoujing 
Published: April 2003

AbstractThe solubility parameter and glass transition temperature of 1,2‐polybutadiene with different 1,2‐unit content have been measured. Tg increases with increasing 1,2‐unit content, whereas no essential change of solubility parameter has been observed. So, it may be concluded that chain flexibility arising from internal rotation about single bond is the sole factor which determines glass transition. Chain flexibility was then studied by computation of energy of rotational isomerization ε and the steric factor ε characterizing hindrance to internal rotation. Finally, the potential barrier to internal rotation U was obtained by correlating δ and ε via Tg. The results are shown in Table VI. σ, ε and U all increase with increasing 1,2‐unit content indicating rising of Tg is a result of increasing chain stiffness. Determination of the solubility parameter of 1,2‐polybutadiene by viscometry with toluene–cyclohexane (similar molar volume) as mixed solvent was examined and proved to be reliable. The exponent α in the Mark–Houwink equation for 1,2‐polybutadiene–toluene system was estimated from the solubility parameter of polymer and solvent according to the method of van Krevelen and Hoftzer16 and found to be 0.725. This value of α was used as a first approximation for the calculation of molecular weights from GPC data. The Mark–Houwink equations finally established for the system, 1,2‐polybutadiene–toluene (30°C) with different 1,2‐unit contents are given in eqs. (8)–(10).
Inverse relaxation in spun yarns
Authors: Nachane R. P. , Hussain G. F. S. , Patel G. S. , Iyer K. R. Krishna 
Published: April 2003

AbstractThis paper presents some experimental data on inverse relaxation exhibited by yarns spun from cotton, polyester, viscose rayon, and jute fibers. Inverse relaxation (IR) is the building up of tension in a viscoelastic material that has been allowed to recover a part of the initial extension it is subjected to. The IR index defined as a measure of the extent of this property has been determined at various levels of extension. A qualitative explanation of the results based on the fiber model proposed by Vitkauskas and Matukonis is also given.
Influence of molecular weight on the ordered state in poly(ethylene terephthalate)
Authors: Rao M. V. S. , Dweltz N. E. 
Published: April 2003

AbstractWAXS, DSC, and IR methods have been employed to follow the crystallization of poly(ethylene terephthalate) as a function of molecular weight. The degree of order, which is a measure of the extent of crystallization, decreased with increasing molecular weight. The degree of reduction in the molecular order with increasing molecular weight differed depending on the technique employed to measure it. Crystallinity indices obtained by x‐ray diffraction methods show an almost linear relationship with molecular weight. The Trans‐Gauche ratio inferred from the IR spectrum tends to decrease at a very rapid rate with increasing molecular weight. The heat of fusion, computed from the melting endotherm in DSC thermograms, shows a smaller but a definite decreasing trend with increasing molecular weight. Besides, the thermograms themselves showed distinct changes related to the molecular weight differences. The results have been discussed in terms of two different possible influencing factors known to affect the crystallization process in almost all polymers. Up to certain molecular weights, random coiling of molecules appears to be the more dominant factor, but in a much higher range of molecular weights, entanglement in the molecular network may become predominant.
Effect of synthesis conditions on the rheological properties of styrene butyl acrylate copolymers
Authors: Garcí‐Rejón A , Rios L. 
Published: April 2003

AbstractThe chemical and physical properties of synthetic polymers depend strongly on the polymerization process. This fact is even more determinant when dealing with copolymers. Styrene/butyl acrylate copolymers were synthesized using an emulsion copolymerization process. The amount of initiator, emulsifier, and transfer agent were varied in a systematic way in order to establish the relationship between polymerization conditions and rheological properties of the molten copolymers. Rheological and molecular weight results show that the different polymerization conditions have important effects on the properties of the final copolymers mainly through the development of different sequence distributions of the monomeric units in the copolymer chain. These results have been interpreted in terms of the kinetic mechanisms that explain the emulsion copolymerization processes. Furthermore, the rheological characterization is used as an additional tool in establishing the different structure of the resulting copolymers.
Polymer swelling 2: A restudy of poly(styrene‐co‐divinylbenzene) swelling in terms of the cross‐link density1
Authors: Errede L. A. 
Published: April 2003

AbstractA very convenient and reliable gravimetric method was developed for measuring swelling of poly(styrene‐co‐divinylbenzene) in particulate form. The method is based on the gravimetric procedure reported earlier2 for monitoring liquid uptake by thin (<0.3 mm) microporous composite films, consisting of swellable particulate (80% by weight) enmeshed in poly(tetrafluoroethylene) microfibers (20%). The swellability S (in milliliter of liquid absorbed per gram of polymer in equilibrium with excess liquid) for six sty‐co‐DVB polymers with crosslink densities ranging from 0.01 to 0.12 was measured in 19 organic liquids. In each study of S as a function of the relationship was given by
where is the average number of carbon atoms in the “backbone” of the polystyrene segments between cross‐link junction, C is the relative swelling power of the liquid, and is the critical cross‐link density above which S is equal to zero.
Studies on fiber properties of sodium hydroxide‐treated and grafted murga fibers—microscopical study
Authors: Samal Bibhuti B. , Mahapatra Lalit M. , Mohanty Trijama R. , Ray Alok R. 
Published: April 2003

AbstractMurga fiber (purified) treated with sodium hydroxide shows crimp. Above 20% NaOH concn no further change in crystallinity is marked. Incorporation of AN onto fiber matrix through grafting has been carried out. The surface is characterized by a scanning electron microscope.
High‐strength–high‐modulus polyimide fibers II. Spinning and properties of fibers
Authors: Kaneda Takaho , Katsura Toshio , Nakagawa Kanji , Makino Hiroshi , Horio Masao 
Published: April 2003

AbstractThe polyimides based on 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) described in Part I of this series were dissolved in p‐chlorophenol and spun into fibers using a coagulating bath of ethanol. The fibers as spun had in general low tenacities and low moduli, but a heat treatment at 300–500°C under tension produced a remarkable increase in strength and modulus, and fibers with a tensile strength of 26 g/den (3.1 GPa) and an initial modulus higher than 1,000 g/den (120 GPa) could be obtained. Thus, the annealed fibers of polyimides are comparable to aramid fibers in mechanical properties. To heating in air and in the saturated steam, the polyimide fibers showed higher resistance than the aramid fibers. The polyimide fibers surpassed the aramid fibers in resistance to acid treatment and ultraviolet (UV) irradiation, but were inferior in resistance to alkali treatment. The annealed fibers of polyimides displayed distinct X‐ray diffraction patterns. The chain repeat distance of 20.5 Å determined on the fibers of polyimide prepared from BPDA and o‐tolidine, and 20.6 Å determined on the fibers of polyimide derived from BPDA and 3,4′‐diaminodiphenyl ether are reasonable when the dimensions of monomeric units and the shapes of the molecular chains are considered. The X‐ray reflections of both polyimide fibers were indexed satisfactorily on the basis of postulated unit cells.
Using disaccharides as a kinetic model for alkaline degradation of celluloses and starches
Authors: Ziderman I. Irving , Belayche Janine 
Published: April 2003

AbstractDegradation kinetics of cellobiose and maltose in hot aqueous solution was determined at pH 9.8 and 13. The positive concentration‐dependence found for the depropagation rate constant of cellobiose indicated that disaccharides decompose more slowly than amyloses under the same reaction conditions, in keeping with a mechanism whereby terminal glucosidic linkages in amylose are also ruptured slowly in an initiation step that is followed by a faster depropagation. Cellobiose termination has a lower activation energy than its depropagation, as does amylose: The opposite result that has been paradoxically ascribed to hydrocellulose is shown to be erroneous. The view that cellobiose does not undergo a chemical stopping reaction appears to be unjustified. The status of a “single‐chain” mechanism for 1,4‐glucan depropagation is discussed, and is considered to occur with cellobiose, maltose, hydrocellulose, and hydroamylose.
Characterization of sorbed water in saponified start–g‐polyacrylonitrile with differential scanning calorimetry
Authors: Rodehed Cenita , Rånby Bengt 
Published: April 2003

AbstractA saponified starch‐polyacrylonitrile graft copolymer containing water was studied using differential scanning calorimetry. The samples had a moisture content in the range of 0‐1.05g water per gram of dry polymer. Molar heat capacity measurements at temperatures higher than 273 K gave partial molar values between those of ice and bulk liquid water. No crystallizable water was detected in samples with water contents lower than 0.44 g/g dry polymer. In samples containing larger amounts of water, both the amount of “bound” uncrystallizable water and the amount of “free” crystallizable water increased linearly. Two melting endotherms were detected, suggesting that the free water could be divided into two components withdifferent melting points (268 K and 274 K, respectively).
Synthesis of IPN‐related materials from solution of polyacrylates
Authors: Takemura Akio , Tomita Bun‐Ichiro , Mizumachi Hiroshi 
Published: April 2003

AbstractIPN‐related materials were synthesized from solution of two acrylate polymers having epoxide. From the dynamic mechanical spectroscopy, it was difficult to distinguish IPN or semi‐IPN from mechanical blend in the case of PEMA/P2EHMA system. But some possibility of IPN phenomenon was observed. In the case of PEMA/PEA system, IPN synthesized from benzene‐chloroform mixed solvent showed phase separation with the matrix of PEMA. IPN synthesized from xylene, however, showed phase separation with the matrix of PEA and the transition due to PEA shifted higher by 5°C than that of homo PEA. From the results, we concluded that PEMA/PEA system synthesized by xylene showed JPN phenomenon.