bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gradient‐IPN‐modified hydrogel beads: Their synthesis by diffusion–polycondensation and function as controlled drug delivery agents
Authors: Mueller Karl F. , Heiber Sonia J. 
Published: April 2003

AbstractInterpenetrating polymer network (IPN) membranes and gradient–IPN polymers were synthesized by immersing crosslinked, 2‐hydroxyethylmethacrylate copolymer beads which were swollen in polyol in solutions of diisocyanates. Diffusion of reactants and polycondensation take place simultaneously, and the polymer beads are modified by a polyurethane–IPN layer whose thickness and compositional gradient are a function of reaction rate and diffusion rate. When the reaction is fast relative to diffusion, the reaction zone is narrow and the IPN boundary layer is sharp, whereas when diffusion dominates, the reaction zone and the IPN‐modified region becomes broader and more diffuse. A water‐soluble drug imbibed into such gradient‐IPN‐modified hydrogel beads is released over a prolonged time period due to the less permeable IPN barrier and because of a drug‐distribution gradient in the polymer, which follows the polyurethane gradient. Diffusion polycondensation can be considered a special case of interfacial polycondensation, one in which the interface area is expanded into and stabilized by a preformed polymer matrix, which serves as reaction medium.
Shear modulus in closely packed gel suspensions
Authors: Taylor N. W. , Gordon S. H. 
Published: April 2003

AbstractRheological properties and swelling were examined in a series of concentrations of particles of crosslinked polyacrylate gels in water or salt solutions. The modulus during steady shear Gs = 2τ2/P11‐P22 was determined from shear stress τ and primary normal force difference P11‐P22 in a cone‐and‐plate rheometer. Gs was nearly constant with shear rate for the gel particles in the closely packed condition. The dynamic storage modulus G′ determined by ecentric rotating disc rheometry increased with increasing frequency for all concentrations. The apparent equilibrium shear modulus Ge determined by stress relaxation agreed closely at all concentrations and ionic strengths with the corresponding values of Gs, and hence Gs is considered a good estimate of equilibrium shear modulus for this gel material.
An analysis of the moisture‐related properties of hydrolyzed polyester
Authors: Sanders Erin Murphy , Zeronian S. Haig 
Published: April 2003

AbstractAlkaline hydrolysis causes pitting of the surface of polyester (PET) fibers and films and improves their wettability, as indicated by contact angle measurements. The enhanced wettability is due to an increase in either the number or the accessibility of polymer hydrophilic groups to water and/or an increase in the roughness of sample surfaces. The increase of void space in the PET yarn and fabric structure, induced by treatment in aqueous NaOH together with the increased wettability of the fibers, was effective in improving the moisture transport properties of the materials. The NaOH‐treated PET fabrics transported the water further than isolated corresponding yarns, possibly because, in the fabrics, the spaces between the yarns acted as an additional reservoir that permitted further wicking to occur. It is apparent from immersion and equilibrium wicking capacity tests that a hydrophilic topical finish, as well as a change in the yarn/fabric structure and the hydrophilicity of their surfaces can increase the water holding capacity of PET fabric. The moisture regain and water retention values of the samples were determined, and it was found that such tests are not sufficiently sensitive to distinguish between the hydrophilicity of nontreated PET fabrics and that of PET fabrics modified either by application of a topical finish or by NaOH treatment.
The effect of addition of high‐density polyethylene on the crystallization and mechanical properties of polypropylene and glass‐fiber‐reinforced polypropylene
Authors: Gupta A. K. , Gupta V. B. , Peters R. H. , Harland W. G. , Berry J. P. 
Published: April 2003

AbstractHigh‐density polyethylene up to about 30% by weight was melt‐mixed with polypropylene and short‐glass‐fiber‐reinforced polypropylene. The presence of high‐density polyethylene and glass fibers in the polypropylene matrix affects its crystallization characteristics, which were studied with the help of differential scanning calorimetry. The blend and composite samples have a large number of polypropylene domains apparently due to an abundance of surface nuclei; as a result, the tensile strength, tensile modulus, and toughness are enhanced. The temperature dependence of shear modulus and logarithmic decrement indicate that high‐density polyethylene can have plasticizing effect below the glass transition temperature of polypropylene. The scanning electron micrographs of fractured ends show the presence of dispersed domains in the composite samples.
Influence of tacticity on thermal degradation of PVC. V. Relation between the nature of labile conformations and the polyene distribution in the degraded polymer
Authors: Martinez G. , Mijangos C. , Millan J. 
Published: April 2003

AbstractFour poly(vinyl chloride) (PVC) samples, 1, 2, 3, and 4, were prepared in bulk using 2,2′‐azodiisobutyronitrile at 90°C and 60°C and the same initiator together with UV irradiation at 0°C and −50°C, respectively. Fractions were obtained from samples 2,3, and 4 by extracting with acetone, sample 1 being completely soluble in this solvent. The whole PVC's as well as their acetone soluble and insoluble fractions, were characterized by determining the intrinsic viscosity, the osmometric molecular weight, and the tacticity; then they were thermally degraded up to conversion of 0.3% in powder state. The values of degradation rate for both the insoluble fractions and the whole PVC's were in agreement with some prior results on the influence of syndiotactic sequences on propagation step. The soluble fractions proved to be very unstable in comparison with the insoluble, which, despite the lower molecular weight of the former, seems to obey their higher content of isotactic conformations. The fine polyene distribution in the degraded polymers was carried out by UV–visible spectroscopy. The results reveal the occurrence of two different polyene distributions, and allow for the peculiar one of the soluble fractions to be related to polyenes consisting of two sequences of trans conjugated double bonds separated by a single cis double bond. The results clearly shows that there are two mechanisms for initiation of the PVC degradation, depending on whether it occurs by random unstable structures or by the normal GTTG isotactic or TTTG heterotactic triads. Moreover, these two initiation processes are proved to give rise to different types of polyenes, which accounts for the occurrence of two unlike mechanisms of propagation.
Longitudinal growth of polymer crystals from flowing solutions. X. Conditions for continuous growth on the rotor surface
Authors: Torfs J. C. M. , Smook J. , Pennings A. J. 
Published: April 2003

AbstractUltrahigh strength polyethylene fibers can be generated by stress‐induced crystallization from a supercooled solution subjected to Couette flow, usually referred to as the “surface‐growth” process. Under appropriate conditions, continuous fiber production can be realized for a period as long as 19 days, whereas under other circumstances a rapid interruption of the growth process is met. The present investigation deals with the origin of fiber fracture during “surface growth.” The limiting values of process variables required to maintain continuous growth have been established. Interruption of the continuous growth can occur in three different ways: (1) formation of a closed fiberloop around the rotor; (2) limited crystal growth rate; (3) rapid crystallization, leading to depletion of the gel on the rotor surface. The gel layer is being formed by adsorption of long molecules on to the rotor surface and subsequent “reptation,” resulting in a dense entanglement network of these molecules. These factors determine the boundaries of the triangularly shaped domain for continuous growth in a graph of the two main variables, namely the takeup speed and the rotor speed. Furthermore, it was noticed that the introduction of a wedge‐shaped groove in the surface of the Couette rotor leads to a substantial reduction of failure. Continuous growth could be established in the temperature range from 103–125°C when p‐xylene was used as a solvent. For p‐xylene solutions at a crystallization temperature of 110°C and using a teflon rotor of 115 mm diameter, a maximum takeup speed and rotor speed were 16 and 180 mm/s, respectively. Basically the restrictions of the process appeared to be due to the limited rate of crystallization and rate of adsorption of polyethylene molecules on the surface of the rotor.
Longitudinal growth of polymer crystals from flowing solutions. XI. The friction with the rotor surface
Authors: Torfs J. C. M. , Pennings A. J. 
Published: April 2003

AbstractDuring the formation of ultrahigh modulus fibers by the “surface‐growth process,” the takeup stress is the main limiting factor lowering the attainable takeup speeds. This paper presents an investigation into the relative importance of the various factors contributing to takeup force and stress. Equations for force and stress have been derived which appear to agree with measurements. It has been concluded that the major part of the stress stems from the friction with the rotor surface and a smaller contribution arises from the coil deformation due to the flow. The equation for the stress has been employed to compute the maximum takeup speed.
Influence of the oxidizing temperature on the combustion of some well‐known polymeric materials
Authors: Breillat C. , Vantelon J. P. 
Published: April 2003

AbstractThe purpose of this work is to characterize the combustion of little samples of some well‐known polymeric materials, polyethylene, polypropylene, and polystyrene, in an atmosphere of quiescent hot air at different temperatures. The analytical treatment of this problem, which is a heat and mass transfer one with chemical reaction between pyrolysis and oxidizer gases, is based upon the fact that the burning regime is diffusion controlled. A mathematical approach developed from Spalding's theory, taking into account radiative effects, is applied to this model of combustion. Experimental results allow us to determine the apparent heat of combustion of these different materials and to study the evolution of radiative and convective fluxes.
Relationship between electron sensitivity and chemical structure of polymers as EB resists. I. Electron sensitivity of various polyamides
Authors: Ogata Naoya , Sanui Kohei , Azuma Chiaki , Tanaka Hozumi , Oguchi Kiyoshi , Nakada Tomihiro , Takahashi Yoichi 
Published: April 2003

AbstractPolyamides containing double bonds or epoxy groups were synthesized and evaluated as electron beam (EB) resists, in order to find the relationship between electron beam sensitivity and chemical structure of the polyamides. It was found that polyamides containing double bonds, which have good solubility, are easily crosslinked by the electron beam exposure. The sensitivity of a polyamide with 70 mol% of the repeat units containing double bonds was equivalent to that of a 100% unsaturated polyamide which contained double bonds of 100% molar ratios, and thus it is not necessary that the polyamide be a homopolymer of unsaturated repeating units. The polyamides have good physical properties, and are adaptable to dry etching processes.
Mechanisms of rubber abrasion
Authors: Gent A. N. , Pulford C. T. R. 
Published: April 2003

AbstractRates of wear have been determined for several elastomer materials, using a razor‐blade abrading apparatus based on one described by Champ, Southern, and Thomas. Measurements have been carried out at different levels of frictional power input, corresponding to different severities of wear, at both ambient temperature and at 100°C, and both in air and in an inert atmosphere. It is concluded that wear occurs as a result of two processes: local mechanical rupture (tearing) and general decomposition of the molecular network to a low‐molecular‐weight material (smearing). Marked differences were shown by different elastomers. Carbon‐black‐filled natural rubber, SBR (styrene–butadiene copolymer) and EPR (ethylene–propylene copolymer) were particularly susceptible to decomposition and smearing, but for natural rubber and SBR the decomposition process was not observed in an inert atmosphere. It is attributed to molecular rupture under frictional forces followed by stabilization of the newly formed polymeric radicals by reaction with oxygen, if present, or with other polymer molecules, or with other macroradicals. Cis‐polybutadiene and trans‐polypentenamer did not appear to undergo smearing to a significant degree. The reactive radicals formed in these materials by molecular rupture are assumed to undergo rapid addition to other molecules so that the network structure is maintained. Rates of wear have been found to increase with the applied frictional force raised to a power n. The value of n was between 2.5 and 3.5 for unfilled materials at ambient temperature, in agreement with Champ, Southern, and Thomas, who pointed out a general correlation with mechanical fatigue. Filled materials were found to be less sensitive to the frictional force, whether wear took place by tearing or by smearing, having values of the index n of 1.5–1.8. Several observations suggest that wear, even in the absence of smearing, is not fully correlated with mechanical fatigue: the markedly lower wear rates for carbon‐black‐filled materials, the anomalous rankings of unfilled materials, and the relatively small effects of raising the test temperature to 100°C. It is concluded that abrasive wear by small‐scale tearing is not accounted for solely by the crack growth properties of the material but involves other failure processes as well.
Dehydrochlorinated poly(vinyl chloride)‐g‐polystyrene. II. Characterization and physical properties
Authors: Mukherjee A. K. , Gupta Achla 
Published: April 2003

AbstractDehydrochlorinated poly(vinyl chloride)‐g‐polystyrene (DHPVC‐g‐PSt) prepared by free radical grafting was characterized, and some of its physical properties were evaluated. The presence of graft was established by the appearance of new absorption peaks in the IR spectra of the graft copolymer. GPC analysis showed increase in the average molecular weights of the graft copolymer upon increase in the PSt content. Besides, GPC revealed the uniform PSt distribution of DHPVC‐g‐PSt. A marked improvement in the thermal stability of DHPVC‐g‐PSt over that of DHPVC and DHPVC/PSt blends was observed. Graft copolymers with high percent grafting were thermally more stable than even the original PVC. Stress–strain data indicated decrease in yield stress, breaking stress and elongation, along with an increase in the initial modulus, upon increase in PSt content of the graft copolymer.
Semi‐ and fully interpenetrating polymer networks based on polyurethane–polyacrylate systems. I. The polyurethane networks
Authors: Hourston D. J. , Zia Y. 
Published: April 2003

AbstractThe polyurethane networks based on commerical prepolymer, Adiprene L‐100, and trimethylol propane (system 1) and on toluene diisocyanate, polypropylene gylcol, and trimethylol propane (system 2) were prepared and characterized in a number of ways. The materials constitute the first formed networks in a series of interpenetrating polymer networks and semi‐interpenetrating polymer networks to be reported in subsequent papers in this series. System 1 networks were characterized by swelling tests which showed the Mc values to be sensitive to the amount of polyurethane present in the polymerization solvent. Stress–strain, stress–relaxation, and dynamic mechanical analyses wer also conducted. For system 2, Mc was measured, by both the swelling and the Mooney–Rivlin techniques, for materials in which the diol‐to‐triol ratios had been altered. the latter showed C1 increasing as Mc decreased while C2 was small and changed onlyy slightly indicating approximately ideal behavior. These Mc values were about 13 % larger than predicted by swelling.
Structure–property relationship in copolyesters. I. Preparation and characterization of ethylene terephthalate–hexamethylene terephthalate copolymers
Authors: Negi Yuvraj S. , Choudhary Veena , Varma Indra K. , Varma D. S. 
Published: April 2003

AbstractPoly(ethylene terephthalate)‐containing ethylene and hexamethylene residues in the polymer backbone were prepared by melt condensation reaction of dimethyl terephthalate (DMT) and diffrent quantities of ethylene glycol (EG) and 1,6‐hexane diol (H) in the initial monomer feed. Several polyester samples were prepared by varying the mol % of 1,6‐hexane diol with respect to ethylene glycol in the initial monomer feed. These included 0.0 (PET), 2.5 (H1), 5.0 (H2), 7.5 (H3), 10.0 (H4), 12.5 (H5), 15.0 (H6), 17.5 (H7), 20.0 (H8), 50.0 (H9), 80.0 (H10), and 100.0 (H11), respectively. The polymers were characterized by recording IR spectra and intrinsic viscosity measurements. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in air. An increase in mol % of 1,6‐hexane diol resulted in a decrease in melting points and thermal stability of copolymers. PET and copolyesters were spun to fibers by using the melt‐spinning technique. The fibers were drawn to draw ratios 2,3,4, and 5. In case of copolymes, tensile strength decreases slightly with increasing mol % of H whereas % elongation increases. The moisture regain and dye uptake in copolyesters was treatly enhanced as compared to PET.
Photoacoustic study of thermal degradation of polyurethane
Authors: Abu‐Zeid M. E. , Nofal E. E. , Abdul‐Rasoul F. A. , Marafi M. A. , Mahmoud G. S. , Ledwith A. 
Published: April 2003

AbstractPolyurethane rigid foam shows substantial changes in its photoacoustic absorption spectra (PAS) on heating in the presence of air. These spectral changes are due to conjugated structures and quinone–imide formation, formed during degradation. The mechanism of degradation appears to be free radical in nature.
A comparison of physical and mechanical properties of polyimide films containing different metal ions
Authors: St. Clair A. K. , Taylor L. T. 
Published: April 2003

AbstractMetal ions have been incorporated into linear polyimide films in order to improve the potential of these materials for applications in space. Various metals such as Al, Pd, Ag, Au, and Sn in a variety of chemical states were added to a polyamic acid prepared from 3,3′, 4,4′‐benzophenone tetracarboxylic acid dianhydride and 4,4′‐oxydianiline. Films of the metal ion‐filled polyamic acids were prepared and cured to the corresponding polymides by heating at 300°C in air. The cured films were characterized for such properties as glass transition temperature, electrical conductivity, and thermal stability. Modulii and tensile strengths of the metal‐containing polymide films were obtained at both ambient and elevated temperatures. Comparison of the physical and mechanical properties of these polyimide films as a function of metal additive is made.
The simulation of hydrolytic polymerization of ε‐caprolactam in various reactors: A simulation model for the tubular reactor with heat exchanger and its numerical solution
Authors: Tai Kazuo , Arai Yoshihiro , Tagawa Takashi 
Published: April 2003

AbstractA concrete simulation model which deals with the hydrolytic polymerization of ε‐caprolactam (CL) in the tubular reactor (TR) with the heat exchangers (HEx's) was described, and a method for its numerical solution was presented. The numerical calculations were carried out for 13 cases, where the position and number of the HEx's in the TR were varied. The effects of the HEx on the distribution of the temperature in the TR and of the characteristic data of the polymerization (the concentration of CL and number average degree of polymerization) in the TR and at the outlet of the TR were investigated. The results suggested that the HEx positioned at the upper half of the TR and the HEx positioned at the lower half of the TR are effective to narrow the temperature distribution in the TR and to produce the polymer product with narrower molecular weight distribution, respectively.
Synthesis and thermal stability of carborane‐containing phosphazenes
Authors: Fewell L. L. , Basi R. J. , Parker J. A. 
Published: April 2003

AbstractCarborane‐substituted polyphosphazenes were prepared by the thermal polymerization of phenyl‐carboranyl pentachlorocyclotriphosphazene. Successive isothermal vacuum pyrolyses were conducted on the polymer and examined for structural changes by infrared spectroscopy. The degradation products were ascertained by gas chromatography‐mass spectrometric analysis. It was found that the presence of the carborane group improves the thermal stability of the polymer by retarding the ring‐chain equilibrium processes of decomposition.
On the relationship between the thermal properties of modified polyurethane elastomers and the efficiency of antipyrens
Authors: Troev K. , Markova K. , Borisov G. 
Published: April 2003

AbstractA study is made of the relationship between the thermal properties of polyrethane elastomers and the efficiencies of anitpyrens containing phosphorus and some containing both phosphorous and chlorine. It is shown that a ralationship exists between the thermal properties of polyurethane elastomers and the efficiencies of the antipyrens. It is also found that the presence of antipyrens in the molecules of the polyurethene elastomer effects the course of DTA, DTG, and TG curves. This permits antipyren efficiency to be qualitiatively evaluated as well as the antipyren optimal concentration to be determined.
Interrelation between moisture absorption, mechanical behavior, and extent of the boundary interphase in particulate composites
Authors: Theocaris P. S. , Papanicolaou G. C. , Kontou E. A. 
Published: April 2003

AbstractThe influence of moisture absorption on the extent of the boundary interphase in particulate composites is thoroughly studied. It was found that, during the process of moisture absorption there is a variation of the extent of the boundary interphase, closely related to the degradation of the mechanical behavior of the composite, as well as to the percentage amount of moisture absorbed. An explanation of the observed relationship was advanced, based on a theoretical mechanism of absorption. This study complements a previous one, where the observed degradation of the thermomechanical properties of particulate composites due to moisture absorption was shown to be intimately interrelated with the state and extent of the interphase between fillers and matrix.