bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave dielectric and mechanical behavior of foams from polystyrene and poly(methyl methacrylate) blends
Authors: Chaki Tapan K. , Bandyopadhyay P. C.
Published: April 2003

Foams have been generated from blends of polystyrene and poly(methyl methacrylate) under identical conditions of solvent–nonsolvent ratio, impregnation time, and heating period. Scanning electron micrographs of copper‐coated fractured surfaces of the samples reveal a distinct transition in their structures from a more or less homogeneous cell‐size distribution with prominent grain boundaries to complete lack of foaming and cellularity through random dispersions of spherical poly(methyl methacrylate) inclusions in polystyrene‐foam matrix. Dielectric measurements have been made on test specimens at 9.375 GHz X‐band microwave frequency by the method of Smith and Hippel modified by Dakin and Works. Percent porosity is the least at 20 wt% of polystyrene while foam density linearly decreases with percent porosity. Dielectric constant is linear in foam density on direct and semilog scales (passing through unity and zero, respectively), in blend composition and also in percent porosity. Dielectric constant increases with increase of foam density or weight percent of polymethyl‐methacrylate and decreases with increase of percent porosity. The dielectric constant is, however, nonlinear in volume fraction of polystyrene on both direct and semilog scales, obeying Weiner's inequalities. The logarithmic law of Lichtenecker and Rother with an empirical factor 0.8276 in the index fits the data best. Specific polarization is minimal at 60 wt% of polymethyl methacrylate. The calculated Bottcher‐Bruggleman plot based on the interacting spherical particle model is found to be of limited applicability. This is explained on the basis of long‐range intra‐ and intermolecular dipole–dipole interactions. The pattern of the change of dielectric loss tangent (tan δ), lying in the range 0.150–0.045 and attaining a minimum at 20 wt% polystyrene, has similarly been explained in terms of α and β relaxations due to conformational rearrangements and steric hindrances of rotations. The compressive strength measured as a function of composition shows that the reinforcement depends on an optimization between the degree of cellularity and packing.
Transport of swelling penetrants in glassy polymers: Influence of convection
Authors: Sarti G. C. , Gostoli C. , Riccioli G. , Carbonell R. G.
Published: April 2003

The transport of a solute by diffusion into a glassy polymer can lead to swelling of the material. For certain types of polymers, a sharp interface is formed between the swollen region and the glassy core. When the density of the swollen material is much smaller than the density of the glass, a significant convective mass‐average velocity is generated within the sample. Previous models have neglected the role this convection plays in solute transport and in the proper calculation of the sample dimensions as a function of time. In this paper, we study the contribution of convective terms to the solute transport process, including the motion of the swollen polymer/solution interface. We also compute the eulerian strains that result from the calculated velocity fields and the stresses that would be generated if a linear viscoelastic model is used as a constitutive equation relating the stress to the strain. We show that serious errors can be generated in the calculations if convective terms are neglected. Furthermore, a comparison of the strains and stresses acting on the polymer with those acting on the mixture of solute and polymer shows that they can be significantly different. The stresses and strains acting on the polymer alone offer the most rational physical picture of the material deformation.
Water extraction of polyethyloxazoline from miscible and immiscible polymer blends
Authors: Pfenning J.‐L. G. , Keskkula H. , Paul D. R.
Published: April 2003

Blends of water‐soluble polyethyloxazoline (PEOx) with a series of hydrophobic styreneacrylonitrile copolymers (SAN) of varying AN contents were immersed in water to determine the kinetics of water swelling and the extent of PEOx extraction. Copolymers containing 25 and 40% by weight of AN form miscible blends with PEOx; those containing higher and lower amounts of AN form immiscible mixtures with PEOx. A high degree of PEOx extraction was observed for the immiscible blends as expected, whereas surprisingly little PEOx was extracted from the miscible blends over periods up to 2 years in spite of a high degree of water swelling. Similar behavior has been noted for other blends of hydrophobic and hydrophilic polymers. In the present system, thermal analysis revealed that the sorption of large amounts of water induces a microphase separation of the two miscible polymers to form microdomains of SAN in which, evidently, segments of PEOx are entrapped to form physical cross‐links that preclude disintegration of the sample and extraction of the PEOx whose phase is highly swollen by the sorbed water. It is proposed that a similar situation probably occurs for other blend systems exhibiting such behavior.
The gamma‐ray‐induced crosslinking of polyacrylamide
Authors: Burillo S. Guillermina , Ogawa Takeshi
Published: April 2003

The gamma‐ray‐induced crosslinking of polyacrylamide was carried out under various conditions. The molecular weight of the polymer before inrradiation was found to be the most important factor for crosslinking. When polymers have low molecular weights such as 80,000, the intensity of radiation, the external pressure applied, and the water content of the polymer powder became important for crosslinking. Although the polycrylamide hydrogel can be obtained directly by irradiating the monomer, it was obtained more conveniently by the irradiation of monomer—polymer mixtures. The hydrogels obtained by the radiation with a dose of over 50 kgray, absorb water by 1000–1500 wt %.
Miscible ternary blends containing polycarbonate, SAN, and aliphatic polyesters
Authors: Shah V. S. , Keitz J. D. , Paul D. R. , Barlow J. W.
Published: April 2003

Ternary blends comprising polycarbonate, (PC), poly(styrene‐co‐acrylonitrile) (SAN), and a polyester, either poly(1,4‐butylene adipate) (PBA), poly(1,4‐cyclohexanedimethylene succinate) (PCDS), or poly(ε‐caprolactone) (PCL), were found to be miscible based on the presence of a single glass transition temperature at many compositions. For all systems, the addition of just 1% by weight polyester resulted in a miscible blend for SAN/PC ratios of 1/1 and 3/1, and a region of immiscibility was generally observed for PC‐rich compositions with low polyester content. The melting point depression of PCL in the ternary and in binary mixtures was studied to obtain interaction parameters for the PCL/PC, PCL/SAN, and SAN/PC binaries. These parameters were used to calculate the locus of compositions which mark the boundary between single‐ and multiple‐phase behavior. Agreement between the calculated and experimental boundary was only fair. PCDS was found to be the most efficient of the three polyesters studied for solubilizing PC and SAN. SAN copolymer containing 25% acrylonitrile (AN), was found to be more easily solubilized in PC by PCDS than SAN containing 13% AN.
Reaction and diffusion of reactive disperse dye in nylon 6
Authors: Morita Zenzo , Saito Takayuki , Motomura Hiromi
Published: April 2003

The diffusion of a reactive disperse dye with a vinylsulfonyl group accompanied by simultaneous reaction with the amino end groups in nylon 6 was examined by the method of cylindrical film roll at 70°C and pH 2.2–8.0. The experimental diffusion profiles of the active and fixed species of the dye in nylon 6 were confirmed to be described by the diffusion equation accompanied by the chemical reaction with substrate taking the limited amount of the end groups into account, where the active species of dye were assumed to react only with the free base of amino end groups. The completion of the reaction with the amino end groups was observed in the first layer from the surface at pH 6.0–8.0. The value of diffusion coefficient was constant (8.0 × 10−10 cm2/s) at all the pH's. The product of the second‐order rate constant, k2, of reaction of the dye and the dissociation constant, Ka, of the amino end groups was constant (k2Ka = 4.0 × 10−9 s−1) at pH 2.2–8.0. The k2 values of the reaction with various substrates for vinylsulfonyl and monochlorotriazinyl‐reactive dyes were compared and the practical dyeing conditions were discussed.
Hydrolytic stability of single‐package silicone sealant
Authors: Gan L. M. , Ong H. W. K. , Tan T. L. , Chan S. O.
Published: April 2003

Stability of a commercially available single‐package silicone sealant has been investigated under different water immersion temperatures. The study involved water sorption, weight loss, thermal stability, and strength reduction. It is believed that the deterioration of silicone sealant was due to the combined effects of leaching, water swelling, and hydrolysis. Water uptake of about 2% was crucial for its hydrolytic degradation, especially at higher temperatures.
Effect of water on the strength of filled polychloroprene vulcanizates
Authors: Hinkley Jeffrey A. , Holmes Brenda S.
Published: April 2003

Three commercial rubber compounds used in marine applications were immersed in water or in 3.5% NaCl solution for up to 250 days. Tear strengths, measured with the “trousers” test piece, decreased in the order dry > salt water exposed > fresh water exposed, and changes of up to 50% were seen. Tensile strengths also decreased, but not always in the same proportion, suggesting a possible change in structure of the voids which initiate fracture. Results are discussed in terms of osmotic swelling and extraction of rubber components.
Preparation of new hydrophilic poly‐vinylpyridine beads and their application to immobilization of urease
Authors: Sugii A. , Ogawa N. , Matsumoto M.
Published: April 2003

Macroporous hydrophilic poly‐vinylpyridine beads were prepared by suspension copolymerization of 4‐ (or 2‐)vinylpyridine and hydrophilic cross‐linking agents, such as ethylene glycol dimethacrylate (1EG) and tetraethylene glycol dimethacrylate (4EG), and their physical properties were studied. Immobilized enzymes were obtained by adsorption of urease on vinylpyridine polymers and commercially available hydrophobic polymers. The poly‐4‐vinylpyridine resin crosslinked with 4EG (degree of crosslinkage, 25%) showed higher water regain, larger average pore radius, and the highest adsorption of urease. Leakage of urease from immobilized urease was scarcely observed in the buffer solution used. The hydrophilicity and hydrophobicity of support affected markedly the enzymatic reaction of the immobilized enzyme. As one of the applications of the polymer‐supported urease, blood urea nitrogen in human sera was determined.
Diffusion of a volatile liquid in polychloroprene rubber
Authors: Lawandy S. N. , Helaly F. H.
Published: April 2003

The penetration rate of chloroform (highly volatile solvent) in chloroprene rubber vulcanizate, based on different carbon black type and loading, has been studied. The results relevent to carbon black loading have shown an increase in the penetration rate with the increase in loading percentage. Other factors affecting the penetration rate, such as particle size and aggregate structures of carbon black, have shown some confusing results, such as the decrease in penetration rate with the increase of particle size and the decrease in penetration rate at a higher degree of equilibrium volume swelling. These results were attributed to the wrinkles formed at the surface of the rubber at these high equilibrium swellings.
Application of statistical experimental design in Ziegler–Natta polymerization of butadiene
Authors: Ho F. K. W. , Hsu C. C. , Bacon D. W.
Published: April 2003

The results of butadiene polymerization initiated with CoCl2· 4Py/Et2AlCl/H2O are presented. The effectiveness of statistical experimental design techniques is demonstrated in identifying the individual and joint effects of polymerization variables on rate constants, molecular weights, and polydispersity. The proposed conversion model, representing polymerization with instantaneous initiation and bimolecular termination, was found to provide an adequate representation of experimental conversion data. Evidence indicates that water is not only directly involved in the initiation reaction but also plays an important role in the chain transfer reaction.
Kinetics of 1‐hexene polymerization
Authors: Dandge D. K. , Heller J. P. , Lien C. , Wilson K. V.
Published: April 2003

Kinetics of 1‐hexene polymerization was studied by following the amount of unreacted monomer using gas chromatography. The Ziegler‐Natta catalyst system used was comprised of TiCl4‐AlEt3 with Al: Ti ratio of 0.85. The sampling and monomer analysis techniques developed can be applied to study the kinetics of higher α‐olefins polymerizations, in general. Also, with minor modifications in this technique, a precise profile of molecular weight can be obtained during polymerization.
Peroxide‐initiated crosslinking of polypropylene in the presence of p‐benzoquinone
Authors: Chodák I. , Lazár M.
Published: April 2003

Crosslinking of polypropylene was investigated when initiated by thermal decomposition of organic peroxides. p‐Benzoquinone was found to be an effective coagent of crosslinking. The efficiency of benzoquinone is about 5 times higher than that of polyfunctional monomers. Almost complete crosslinking of polypropylene can be reached at proper conditions.
Cocrystallization and miscibility studies of blends of ultrahigh molecular weight polyethylene with conventional polyethylenes
Authors: Kyu Thein , Vadhar Parimal
Published: April 2003

Ultrahigh molecular weight polyethylene (UHMWPE) was mechanically mixed with conventional polyethylenes (LLDPE, HDPE, and LLDPE) using an internal mixer. Rheological studies of these blends suggest that UHMWPE seems to be miscible with LLDPE, HDPE, and LDPE in the melt state. Yield characteristics are observed in all blend systems, particularly in high UHMWPE blend compositions. Differential scanning calorimetry and small‐angle light scattering studies show that cocrystallization takes place in the blends of UHMWPE/LLDPE and UHMWPE/HDPE blends. However, separate crystals are formed in UHMWPE/LDPE. The formation of separate crystals may be attributed to long chain branching of conventional low‐density polyethylene. Tensile properties of the former two blends vary almost linearly with blend compositions, while deviations are seen in the latter UHMWPE/LDPE blends.
Graft copolymerization with new class of acidic peroxo salts as initiators. I. Grafting of acrylamide onto cotton–cellulose using potassium monopersulfate, catalyzed by co(II)
Authors: Sahoo Prafulla K. , Samantaray Himansu S. , Samal Rajani K.
Published: April 2003

Graft copolymerization of acrylamide (AM) onto cotton–cellulose has been studied using a new class of acidic peroxo‐salt “potassium monopersulfate” as initiator catalyzed by Co(II). It is observed that the graft yield is influenced by the reaction time, temperature, and concentrations of the monomer, catalyst, initiator, at fixed weight of the polymer. Maximum graft yield (30.8%) is obtained at 40°C under nitrogen atmosphere for the concentrations of monomer 1.2M; initiator 4.83 × 10−3M; Co(II) 5 × 10−4M for 4 h of reaction time. The graft copolymers after proper purification have been subjected to IR analysis, testing of their water‐retention properties, rot resistance, tensile properties, and behavior towards acids and alkalies. The results of such analysis are compared with the base. Suitable mechanism for the graft copolymerization is suggested and grafting rate has been evaluated.
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

Elemental 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

The 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

All‐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

Mechanical 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

The 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

A 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

In 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

The 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

This 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

Analysis 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

An 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

The 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

A 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

The 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

Poly(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

Dynamic 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

Thirty‐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

The 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

The 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

The 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

Methoxypoly(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.
The immobilization of enzymes onto hydrolyzed polyethylene‐g‐co‐2‐HEMA
Authors: Beddows C. G. , Gil M. H. , Guthrie J. T.
Published: April 2003

A study of the immobilization of trypsin and other enzymes onto hydrolyzed poly(2‐hydroxyethyl methacrylate)‐g‐co‐polyethylene using hydroxyl and carboxyl activating agents has been undertaken. Some emphasis was placed on the immobilized trypsin system which involved examination of the variation of (i) the extent of hydrolysis of the graft copolymer, (ii) the concentration of activating agent, and (iii) the temperature of coupling. With the trypsin system, an increase in carbodi‐imide concentration gave an increase in the amount of protein immobilized but a marked decrease in the retention of enzymic activity. Comparison of the behavior of the free with the immobilized enzyme showed that satisfactory yields were obtained and the immobilized system has an extended pH profile and good stability and thus would have broad applicability. The kinetic factors were examined further, and the role of the graft copolymer chains in the immobilized system is discussed.
Characterization of styrene–methyl methacrylate–n‐butyl acrylate terpolymers. I. Average diad concentration determined by 1H‐NMR
Authors: Kobayashi Minoru
Published: April 2003

The average diad concentrations of methyl methacrylate (MMA) unit, P2{MiMj}, of the title terpolymer prepared by radical polymerization with various conversions were studied by 1H‐NMR measurements. Several methoxy proton peaks of MMA resolved by the diamagnetic shielding effects of styrene were assigned to the individual microstructures of MMA‐centered triads. The P2{MiMj} were determined from these peak ratios according to the terminal copolymerization model and the Ham's assumption of statistical simplification for a multicomponent copolymer (P2{MiMj} = P2{MjMi}), The observed values, P2{MiMj}, agreed with the values calculated from the monomer reactivity ratios for each conversions, and agreement with the copolymerization theory was evident.
Effect of flaw size on tensile rupture and morphology of fracture surface of synthetic rubbers with special reference to rocket insulator compound
Authors: Deuri A. Saha , Bhowmick Anil K.
Published: April 2003

Studies on tensile strength of polybutadiene (BR) and ethylene–propylene diene rubber (EPDM) having a wide range of flaw sizes have been carried out under both normal and aging conditions. A similar study has been done for a solid propellant rocket insulator compound, based on EPDM. The morphology of tensile fracture surface has also been reported in each case in order to understand the mechanism of rupture. Unlike NR, EPDM, and BR gum vulcanizates, both unaged and aged, show no critical cut length (lc). lc may be defined as the cut length at which the strength decreases abruptly (sometimes there is a drop of a factor of 3 or more, at lc). However, the insulator compound, based on EPDM, exhibits a definite lc in the region of 1.5–1.7 mm. This arises because of anisotropic effect of asbestos fibers. Scanning electron microscopic studies show that the mechanisms of rupture of EPDM and BR gum vulcanizates are similar throughout the whole range of precuts. It occurs through a tearing process originated from the given precut at the center of the samples. A quantitative relation between tensile strength and distance between crack lines/tear lines has also been found. Though insulator compound shows a definite lc, similar fracture surface has been observed over the entire range of flaw sizes.
Preparation of photoresist polymer by a photoreactive monomer containing N,N‐diethyldithiocarbamate group
Authors: Yamashita Keiji , Nakano Akio , Tsuda Kazuichi
Published: April 2003

A novel photosensitive monomer with a pendant photoreactive diethyldithiocarbamoyl group, VBDC, was synthesized and copolymerized with some vinyl monomers by AIBN. The copolymers obtained have efficient photocrosslinking abilities, and are thermally stable. Therefore, there was no loss of dithiocarbamoyl group during radical polymerization, and the polymerization proceeded through vinyl group. The degree of photocrosslinking was proportional to the concentration of the photosensitive group, but photosensitivity of the polymer was not. Water‐soluble photoreactive copolymers, VBDC with AAm or MA, were also prepared. AAm copolymer has a good photosensitivity by only 3 mol % VBDC incorporation. Photocrosslinking yields of these polymers depend on the viscosity of original polymers except in the case of low concentration of VBDC. The relation between copolymer composition and glass transition temperature was also investigated. From the investigation of Tg, it was concluded that the copolymer structure largely affected on ΔTg. The mechanism of photocrosslinking was studied by photodecomposition of benzyl N, N‐diethyldithiocarbamate, and the result that the decreases of sulfur content clearly related to photocrosslinking points was also obtained.
Gas transport in poly(vinyl cyclohexanecarboxylate)
Authors: Hirose Takuji , Mizoguchi Keishin , Kamiya Yoshinori
Published: April 2003

Low‐pressure gas permeation measurements were performed on poly(vinyl cyclohexanecarboxylate) to evaluate its transport characteristics. The transport data of CO2, O2, N2, He, and Ar, were presented as a function of temperature ranging from 15 to 85°C. The apparent transport parameters were determined by the time lag method above and below the glass transition temperature and they were compared with other polymers of similar chemical structures. The side chain of the polymer has a bulky cyclohexyl group, which seemed to increase gas diffusivity. The activation energy for diffusion seemed to be related with the polarity of side chain. The relationships between gas diffusivity, physical properties, and chemical structure were qualitatively discussed in comparison with the data on poly(vinyl benzoate) and poly(vinyl acetate).
Direct pyrolysis mass spectrometry of chlorine‐containing polymers using capillary GC/MS
Authors: McGuire Jeffrey M. , Bryden Charles C.
Published: April 2003

A direct pyrolysis mass spectrometric technique has been developed and applied to several chlorine‐containing polymers. The capillary column in the gas chromatograph has been replaced by uncoated fused silica tubing to avoid the problem of column degradation induced by the polymer pyrolyzates. Under appropriate conditions, the pyrolysis mass spectra were found to be highly reproducible and to serve as “fingerprints.” The technique can be readily applied to carbon‐black‐filled, crosslinked elastomers, as well as polyblends and composites. The quantitative aspects of the technique have also been addressed.
Measuring and modelling the transition layer during the dissolution of glassy polymer films
Authors: Krasicky P. D. , Groele R. J. , Rodriguez F.
Published: April 2003

The technique of laser interferometry is now used routinely by the microelectronics industry for the measurement of the dissolution rates of thin polymer films. In addition to the rate of dissolution, laser interferometry can also provide quantitative information on the thickness of the transition layer between the dissolving glassy polymer and the liquid solvent. This paper describes how observed patterns of reflected light intensity may be analyzed to calculate the thickness of the transition layer for polymers that dissolve with little or no swelling. The technique requires knowledge of the shape of the concentration profile in the transition layer. However, by assuming various simple model profiles one may obtain a reasonable estimate. Experimental measurements of poly(methyl methacrylate) (PMMA) films dissolving in methylethyl ketone indicate transition layers of thicknesses 0 to 0.1 μm for PMMA of molecular weights Mw = 37,000 to 1,400,000.
Separate or simultaneous immobilization of glucose oxidase and peroxidase on latex particles and their function
Authors: Kawaguchi Haruma , Koiwai Naoko , Ohtsuka Yasujii
Published: April 2003

Glucose oxidase and peroxidase were immobilized individually or simultaneously on aminated latex particles by using sodium meta‐periodide and borohydride. The amount of immobilized enzymes and their activity depended on the surface potential of particles and the surface density of their own, respectively. In the simultaneous immobilization of two enzymes, the predominant immobilization of peroxidase is attributed to higher carbohydrate content in peroxidase compared with that in glucose oxidase. Simultaneously immobilized enzymes worked better in the determination of glucose than the mixture of separately immobilized ones because of the close proximity of the two enzymes.