bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and transport properties of thin film composite membranes. I. Synthesis of poly(phenylene oxide) polymer and its sulfonation
Authors: Huang R. Y. M. , Kim J. J.
Published: April 2003

The synthesis of sulfonated poly(phenylene oxide) polymer was investigated. The poly(phenylene oxide) was synthesized through oxidative coupling from 2,6‐dimethyl‐phenol with copper (I) chloride‐pyridine catalyst and sulfonated using chlorosulfonic acid. The effects of catalyst concentration, solvent, and other experimental variables on the kinetics of the polymerization of poly(phenylene oxide) and its subsequent sulfonation are reported in detail.
Synthesis and characterization of BDSDA/APB polyimide
Authors: Burks Harold D. , St. Clair Terry L.
Published: April 2003

A novel linear aromatic polyphenylene ethersulfideimide (BDSDA/APB) has been synthesized. Its physical, mechanical, thermal, and flow properties and its resistance to some of the more commonly used solvents were determined. The results of these property evaluations indicate this polymer system can be processed via conventional thermoplastic techniques. It has been molded, used as a resin, and cast into thin films and, accordingly, may have a wide variety of applications. Its molecular weight was varied by endcapping with phthalic anhydride. Over the M̄n range 14,000–45,000 the apparent viscosities and GIc values varied only slightly. However, a change in M̄n from 14,000 to 8700 resulted in a dramatic decrease in the apparent viscosity at both 250°C and 280°C. The GIc values for these same molecular weight materials decreased in a like manner as the M̄n decreased, indicating tradeoffs can be made between process optimization and final mechanical properties when polymer systems are developed.
Thermal stability, fractionation, and chemical modification of chlorinated rubbers. I. Infrared and 13C‐NMR study of the structure of chlorinated natural rubber modified under various experimental conditions
Authors: Makani Siku , Brigodiot Maryvonne , Maréchal Ernest , Dawans François , Durand Jean‐Pierre
Published: April 2003

The structure of chlorinated natural rubber (CR) was studied by infrared and NMR spectroscopy. It was shown that the structure proposed by Troussier (thèse de Docteur‐Ingénieur, Lyons, 1954) does not fit the 13C‐NMR characteristics of this compound. CR was fractionated and each fraction was characterized. The thermal stability of CR and the evolution of its structure in various experimental conditions was studied by NMR.
Mechanical properties of paper sheets prepared from partially cyanoethylated wood pulp
Authors: El‐Shinnawy Nabila A. , El‐Kalyoubi Samira F.
Published: April 2003

Cyanoethylated of wood pulp was carried out at different conditions including acrylonitrile concentration, time, and temperature of the reaction. Some mechanical properties of paper sheets prepared from the cyanoethylated wood pulp were examined. Cyanoethylated paper sheets acquired higher breaking length, fold number, and burst factor than the untreated paper sheets irrespective of the conditions used for cyanoethylation. On the other hand, the tear factor of cyanoethylated paper sheets was generally lower than that of the untreated control through under certain conditions cyanoethylation brought about substantial improvement in tear factor. The water retention value and beating time are decreased depending upon the condition of cyanoethylation used.
Crosslinkable polyamide–imides
Authors: Serna Felipe J. , De Abajo Javier , De La Campa José G.
Published: April 2003

A series of polyamide–imides were prepared from aromatic diamines and substituted isophthaloyl chlorides containing unsaturated imide rings. Aromatic polyamides from isophthaloyl chloride were also prepared for comparison. The polyamide‐imides gave enhanced solubility compared to the aromatic polyamides and there was no deterioration in thermal stability orTg. The PAIs were crosslinked by heating at 280°C/4 h under nitrogen. After this heat treatment all the PAIs became insoluble and their mechanical properties increased substantially; their thermal behavior, as measured by DSC and TGA, changed as a function of their chemical structure.
Thermal decomposition behavior of poly[3,3‐bis(ethoxymethyl) oxetane] and related polyethers
Authors: Jones R. B. , Murphy C. J. , Sperling L. H. , Farber M. , Harris S. P. , Manser G. E.
Published: April 2003

The thermal decomposition behavior of poly[3,3‐bis(ethoxymethyl)oxetane] (polyBEMO) was examined and compared to the decomposition of poly(ethylene oxide) (PEO) and poly(tetramethylene oxide) (polyTHF). Differential scanning calorimetric (DSC) studies as a function of heating rates and at constant temperature as a function of time yielded activation energies of 45–50 kcal/mol, characteristic of polyether decomposition. First‐order decomposition kinetics were found. The reaction is endothermic, with a heat of decomposition of 18.6 kcal/mol. Effusion mass spectroscopy on polyBEMO showed major peaks at 112, 140, 168, and 174 amu. A mechanism is proposed in which the thermal scission of the ether bonds in both the polymer chain and in the appendanges initiates the decomposition. The main decomposition reaction for polyBEMO can be written as
magnified image
where the appendages and main chain are cleaved in an unknown order.
Open‐cell flexible polyurethane foams: Comparison of static and dynamic compression properties
Authors: Shuttleworth R. W. , Shestopal V. O. , Goss P. C.
Published: April 2003

Dynamic stress–strain diagrams of polyurethane packaging foams have been obtained from free fall drop tests. The dynamic curves become higher as the deformation rates increase. An equation is proposed to describe the stress–strain dependence for different deformation rates. The model of filament buckling explains the form of the observed stress–strain dependence and phenomena related to repeated loading of the foam.
The viscoelastic properties of rubber–resin blends. I. The effect of resin structure
Authors: Class J. B. , Chu S. G.
Published: April 2003

Blends of elastomers with the proper concentration of appropriate low molecular weight resins exhibit performance as pressure sensitive adhesives. Viscoelastic properties, which may be related to adhesive performance, were measured on 1:l blends of rubber and resin using a mechanical spectrometer. Significant differences in viscoelastic properties were observed depending upon the resin structure. On plots of G′ and tan δ vs. temperature, the addition of a compatible resin produces a pronounced shift of the tan δ peak to a higher temperature and reduces the modulus in the rubbery plateau. An incompatible resin results in a minor shift in the tan δ peak of the elastomer along with the appearance of a second peak at higher temperature, attributed to a second phase which is predominantly resin. Also, the modulus is increased in the rubbery plateau. A polystyrene resin, Mw about 900, is shown to be incompatible with natural rubber but compatible with styrene–butadiene rubber. A cycloaliphatic poly(viny1 cyclohexane) resin, Mw about 650, prepared by hydrogenating the polystyrene resin, is compatible with natural rubber, but incompatible with styrene‐butadiene rubber. An alkyl‐aromatic poly(tert‐butylstyrene) resin, Mw about 850, which is intermediate in aromaticity between the aromatic polystyrene resin and the cycloaliphatic poly(viny1 cyclohexane) resin, is compatible with both natural rubber and styrene‐butadiene rubber. Therefore, the structure of the resin is very important in adjusting the viscoelastic properties of a rubber–resin blend to achieve pressure sensitive adhesive performance.
Thermal degradation of liquid polysulfide polymers: Pyrolysis–GC–MS and thermogravimetric studies
Authors: Rao M. Rama , Radhakrishnan T. S.
Published: April 2003

The thermal decomposition of Thioped, a liquid polysulfide polymer based on dichloroethyl formal, was studied using pyrolysis–GC–MS. The nature and composition of the products of pyrolysis at 358 and 485°C are given. A striking feature of the product analysis is the presence of several disulfide compounds only at the higher decomposition temperature. The pyrolysis‐GC of other liquid polysulfide polymers (LP‐2, LP‐32, LP‐3, and LP‐33) showed that molecular weight had only marginal effect on the product composition. Ionic and radical mechanisms were considered to account for the product formation. Isothermal and dynamic thermogravimetric studies were carried out to differentiate between the two mechanisms. The results were found to be in agreement with a free radical mechanism, with cleavage of the formal CO linkage as the preferred mode of initiation. The overall activation energy for the decomposition was found to be 190 kJ mol−1.
A study on graft copolymerization of methyl methacrylate onto jute fiber
Authors: Tripathy S. S. , Jena S. , Misra S. B. , Padhi N. P. , Singh B. C.
Published: April 2003

A kinetic study of the graft copolymerization of methyl methacrylate onto jute fiber using KMnO4–malonic acid redox initiator system has been made. Effects of the concentrations of malonic acid, monomer, and KMnO4 on graft yield have been studied. Besides, the effects of temperature, acid, and reaction medium, some inorganic salts on graft yield have been investigated. The most remarkable features of the investigation include the proposition of a mechanism, derivation of rate expression for the grafting process, and characterization of the grafted fiber by thermogravimetric analysis.
Protection of wood surfaces against photooxidation
Authors: Hon David N.‐S. , Chang Shang‐Tzen , Feist William C.
Published: April 2003

Protection of wood surfaces against photoinduced oxidative degradation can be achieved by using effective coating agents. Several penetrating chemical agents, such as triol‐G 400, PEGG 400, and 1‐octadecanol, were shown to provide good protection for wood surfaces against discoloration during ultraviolet irradiation. In addition, wood surfaces coated with clear film‐forming finishes, such as homo‐ and copolymers of 2‐hydroxy‐4 (3‐methacryloxy‐2‐hydroxy‐propoxy) benzophenone, exhibited outstanding performance into inhibiting discoloration and surface deterioration. Infrared and ultraviolet absorption spectra and scanning electron microscopy studies revealed that the clear polymeric coatings containing an internal UV absorber were very stable and resistant to photooxidation. Possible chemistry and mechanisms of protection of wood surfaces provided by these polymeric coating systems are discussed.
Structure–property relationships of thermally bonded polypropylene nonwovens
Authors: Wei K. Y. , Vigo T. L. , Goswami B. C.
Published: April 2003

The effect of fiber structure and morphology on the resultant mechanical and low load deformation properties of thermally bonded nonwoven polypropylene fabrics has been studied. Commercially available staple polypropylene fibers varying in linear density and draw ratio (Herculon and Marvess staple fibers) were used in this study. The orientation of these fibers was characterized by birefrigence measurements. Differential scanning calorimetry measurements were made to determine the heat of fusion and melting point of fibers. Experiments confirm that tensile strength and stiffness of the fabrics correlate with this fiber structure. Under the same bonding conditions fabrics made from fibers with low draw ratios show higher tensile strength and stiffness than do fibers with high draw ratios. The mechanical properties of fabrics were found to be greatly affected by the thermal bonding temperature. The tenacity and flexural rigidity of fabrics made from poorly oriented fibers show higher values than those made from highly oriented fibers. The shrinkage of the fabrics was observed to increase with increasing bonding temperature in both machine and cross machine directions. The changes in fabric thickness due to the thermal bonding are considerably lower for poorly oriented fibers.
Glass transition in aliphatic polyamides
Authors: Botta A. , de Candia F. , Palumbo R.
Published: April 2003

The glass transition temperature is analyzed in polyamide systems characterized, owing to their chemical composition, by the absence of hydrogen bonds. The physical behavior exhibited by these systems is similar to that observed in conventional aliphatic polyamides, suggesting that, besides the hydrogen bonds, the amidic group itself plays a specific and important role in determining the polymer physical behavior generally and, in particular, the glass transition mechanism. It is surmised that this role is connected with the polar and rigid character of the amidic group, affecting chain‐chain interactions and chain mobility.
Blends of nylon 6 with an ethylene‐based multifunctional polymer. II. Property–morphology relationships
Authors: Chuang Hsiao‐Ken , Han Chang Dae
Published: April 2003

The tensile properties and impact strength were measured of the three blend systems, nylon 6/CXA 3101, nylon 6/Plexar 3, and nylon 6/EVA, which had been prepared using a twinscrew compounding machine. Scanning electron micrographs (SEM) of the fracture surfaces show that the domain size of the dispersed phase is much smaller in the nylon 6/CXA 3101 blends or nylon 6/Plexar 3 blends than in the nylon 6/EVA blends. This is attributed to the presence of a graft copolymer, formed by chemical reactions between carboxyl or anhydride groups present in the CXA 3101 (or Plexar 3) and the amino end groups of the nylon 6, at the boundaries of the dispersed and continuous phases. The SEM analysis of the fracture surfaces shows that no discrete particles are exposed on the fracture surface of either the nylon 6/CXA 3101 blends or nylon 6/Plexar 3 blends, supporting the theory that a graft copolymer, formed during melt blending, helped the discrete particles adhere to the continuous matrix.
The differential viscometer. II. On‐line viscosity detector for size‐exclusion chromatography
Authors: Haney Max A.
Published: April 2003

The new technique of differential viscometry measures directly the specific viscosity of a solution by subtracting the contribution of solvent in a balanced capillary bridge. The present work adapts the differential viscometry principle to the design of a viscosity detector for use in size‐exclusion chromatography. It is shown that the resulting viscosity detector possesses excellent sensitivity and baseline stability with a minimum detectable specific viscosity of 2.7 × 10−5. The viscosity detector can be operated together with a refractive index detector to determine the intrinsic viscosity of polymer solute fractions as they elute from the SEC column. The bandspreading of the viscosity detector is compared to the refractive index detector by measuring the peak width of a compound having a single discrete molecular weight. The peak width at half‐height was 0.29 mL for the viscosity detector and 0.25 mL for the refractive index detector.
Durability of radiation‐sterilized polymers. I. Estimation of oxidative degradation in polymers by chemiluminescence
Authors: Yoshii Fumio , Sasaki Takashi , Makuuchi Keizo , Tamura Naoyuki
Published: April 2003

In relation to sterilization of medical supplies, the degree of degradation by γ‐ray and electron beam irradiations of homopolypropylene (HP), copolypropylene (CP, coplymer including 6% of ethylene unit) and polymethylpentene were compared, and chemiluminescence (CL) of irradiated polymers were measured. HP degraded extremely around the sterilization dose (2.5 Mrad) by either γ‐ray or electron beam irradiations. In the case of CP and polymethylpentene, stabilities of polymers far differed between γ‐ray and electron beam irradiations. The polymethylpentene was more stable than the polypropylenes against irradiation. The counts of CL emitted by recombination of peroxy radical (ROO ·) increased with increasing dose, reflecting degrees of oxidation of polymers. The degradation of polymers was independent of irradiation sources, rather it depended on the degree of oxidation. It was found that CL analysis are favorable for estimation of degradation in irradiated polymers.
Epoxidation of natural rubber studied by nmr spectroscopy
Authors: Bradbury J. H. , Perera M. C. S.
Published: April 2003

Epoxidation 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

The 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

The 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

Previous 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

Cellulose 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

This 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

A 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

The 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

Criteria 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

Thermal 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

The 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

A 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

A 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

The 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

This 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

WAXS, 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

The 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

A 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

Murga 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

The 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

Degradation 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

A 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

IPN‐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.
Water permeation through elastomer laminates. IV. NBR/EPDM
Authors: Aminabhavi Tejraj M. , Manjeshwar Lata S. , Cassidy Patrick E.
Published: April 2003

The recent considerable interest in the transport and solubility properties of low‐molecular weight penetrants in elastomers arises largely because a number of important practical applications depend wholly or in part on such phenomena. These applications include various protective coatings, packaging materials, selective barriers for the separation of gas and liquid mixtures, biomedical devices, marine applications, etc. The behavior of small molecules in elastomers is strongly dependent on elastomer structure and morphology and any additives to the polymer; therefore, small molecules can be used as very sensitive probes to explore a polymer matrix, especially to gain information about its end applications.
The effect of molecular structure on the gas transmission rates of aromatic polyimides
Authors: Sykes George F. , St. Clair Anne K.
Published: April 2003

A series of high‐molecular weight condensation polyimides was evaluated to determine the effect of polymer molecular structure on the transmission rate of oxygen, carbon dioxide, and water vapor. The polyimide films were prepared from either 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) or pyromellitic dianhydride (PMDA) with various diamines. The study shows that molecular structure had a strong influence on gas transmission rates with results for some films varying three orders of magnitude from that of other polyimide films. In general, the BTDA series of polyimides had overall lower gas transmission rates than the PMDA‐derived series. Polymers prepared with meta‐oriented diamines characteristically displayed lower gas transmission than those prepared with para‐oriented diamines.
Semi‐ and fully interpenetrating polymer networks based on polyurethane‐polyacrylate systems. X. Polyurethane‐poly(ethyl acrylate) interpenetrating polymer networks
Authors: Hourston D. J. , Huson M. G. , McCluskey J. A.
Published: April 2003

A series of polyurethane‐poly(ethyl acrylate) interpenetrating networks (IPNs) containing 40 wt% polyurethane were prepared, in which the cross‐link density of the polyurethane component was varied by altering the ratio of diol/triol. Decreasing the molecular weight between crosslinks from 9500 to 1200 g/mol brought about an increase in the tensile strength accompanied by a decrease in elongation at break. The tensile properties of the IPNs are, however, poorer than those of the equivalent polyurethane homopolymers. Electron microscopy showed that the polyurethane was present as distinct phases, connected by a cellular fine structure, in the poly(ethyl acrylate) matrix. Dynamic mechanical analysis as well as sonic velocity studies gave results which were consistent with this morphological picture.
Characterization of acidic groups in oxycelluloses IV. Effect of accelerated aging on yellowing as well as carboxyl groups and lactones in pulp
Authors: Achwal W. B. , Murali Radha
Published: April 2003

Bleached bamboo pulp as well as two oxypulps were subjected to accelerated aging by heating as well as steaming, and the yellowing or color reversion was studied. The yellowing is increased by the presence of free carboxyl and the reducing groups in oxycelluloses. The again treatments were found to cause an increase in free carboxyl groups accompanied by a reduction in copper number. A differentiation between free carboxyl and various lactone groups in oxidized and also aged samples was carried out based on the variation in their reaction rates with KI/KIO3 solution, and the characteristic acidic group spectrum showed that on steam again the fastreacting lactones are lost.
Distribution of end groups and comonomer of the acrylonitrile‐vinyl acetate copolymer
Authors: Ito Seiichi , Okada Chiharu , Kamada Kensuke
Published: April 2003

The number average molecular weight and strong acid end groups (SAG) of fractionated polymers were measured for the acrylonitrile‐vinyl acetate copolymers (93:7 in weight), which were prepared by continuous polymerization in aqueous medium with the persulfate‐bisulfiteion redox system. Average number of SAG per polymer molecule was nearly 1 for fractionated portions of the polymers prepared under the polymerization conditions of water/monomer ratio in the range 4.0–2.5 in weight. No marked difference existed in comonomer content in fractions of these polymers. For unfractionated polymers prepared under the conditions of water/monomer ratio varied from 4.0 to 1.75, average number of SAG was roughly 0.8–1. The proportion of sulfoxy end groups to SAG was estimated to be roughly from 0.5 to 0.6 and increased slightly with increased bisulfite/persulfate ratio. Based on the above results, disproportionation and transfer to bisulfite‐ion are considered to be the main processes of termination of polymer radicals in the studied range of polymerization conditions.
Mechanisms of antioxidant action: Tellurium dithiocarbamates as antioxidants for polypropylene
Authors: Abed‐Ali S. , Ahmed M. A. K. , McWhinnie W. R. , Scott G.
Published: April 2003

The tetrakis (dialkyldithiocarbamato)tellurium(IV) complexes are highly effective thermal antioxidants and melt stabilizers for polypropylene and the evidence suggests that they are converted to the bis(dialkyldithiocarbamato)tellurium(II) complexes and the corresponding dithiocarbamoyl disulfides during processing. The Te(IV) complexes are also effective photoantioxidants and their activity increases with increasing processing time. The bischelates are in general less effective when used alone.
Hydrogels based on graft copolymers of collagen synthesis
Authors: Amudeswari S. , Reddy C. Rami , Joseph K. Thomas
Published: April 2003

Graft copolymerization of 2‐hydroxyethyl methacrylate in combination with hydrophobic monomers onto soluble collagen was employed in the synthesis of hydrogels. The hydrogels were formed by simultaneous graft copolymerization and crosslinking. In order to study the effect of various crosslinking agents on the water retention character of the hydrogels, three different crosslinking agents, namely, N,N′‐methylene bis acrylamide, 1,4‐butanediol dimethacrylate, and hexamethylene urethanediacrylate were used. Hexamethylene urethanediacrylate crosslinked systems require a minimum amount of crosslinking agent to attain maximum water content in comparison to the other systems.
Adsorption behavior of heavy metal ions on cellulose graft copolymers
Authors: Okieimen Ebhodaghe F. , Ebhoaye Justus E.
Published: April 2003

The adsorption behavior of cadmium, copper and lead ions on holocellulosic materials containing various levels of polyacrylonitrile and poly(acrylic acid) grafts was examined. The amount of metal ions adsorbed per gram of the modified cellulosic substrate depended on the metal ion type, the nature and level of the incorporated graft polymer. In all cases grafting increased the metal ion‐binding capacity of the cellulosic materials (by up to 50% for Cu (II) ions). The influence of temperature and initial metal ions concentration on the sorption behavior of the metal ions on the composite materials was investigated.
The effect of processing conditions on structure evolution in melt spun poly(ethylene terephthalate) fibers
Authors: Napolitano M. J. , Moet A.
Published: April 2003

An investigation has been made into the structural evolution in poly(ethylene terephthalate) fibers as a function of wind‐up speed (WUS) and quench air temperature (QAT). Analysis of the mechanics and mechanisms of cold drawing reveals that the fiber structure is heterogeneous. Evidence from differential scanning calorimetry (DSC) and density measurements indicates the presence of crystallites which are imperfect according to wide‐angle diffraction (WAXD). Increased thread‐line stress (higher WUS and higher QAT) appears to induce larger and more oriented crystallites in a progressively oriented matrix. A radially layered structure is disclosed from high resolution scanning electron microscopy (SEM) micrographs.