bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of the thermal degradation of poly(N‐vinyl‐2‐pyrrolidone) by thermogravimetry–FTIR
Authors: Peniche Carlos , Zaldívar Dionisio , Pazos Mercedes , Páz Senen , Bulay Anna , Román Julio San 
Published: April 2003

AbstractThe thermal degradation of poly(N‐vinyl‐2‐pyrrolidone) (PVP) was studied by dynamic thermogravimetric analysis (TGA) in the range 200–600°C under nitrogen and oxygen atmospheres at various heating rates. The apparent activation energy of the degradative process was determined by the application of kinetic treatments, giving an average value of 242 kj/mol in N2, whereas in the presence of oxygen, two trends may be considered: At relatively low temperatures (200–400°C) and degrees of conversion, α, lower than 0.5, we obtained an average value of 199 kj/mol, whereas in the temperature interval 400–600°C with degrees of conversion higher than 0.5, the value of Ea was 306 kj/mol. Isothermal experiments carried out in N2 in the interval 350–400°C gave an average value of Ea = 231 kj/mol, in good agreement with that obtained from dynamic treatments. The FTIR spectra of the volatile compounds evolved in degradation experiments carried out in N2 as well as in the presence of oxygen suggest that PVP is thermally degraded, predominantly, by the release of the pyrrolidone side group and the subsequent decomposition of polyenic sequences. © 1993 John Wiley & Sons, Inc.
The separation of SEC curves of HDPE into flory distributions
Authors: Vickroy V. V. , Schneider H. , Abbott R. F. 
Published: April 2003

AbstractA technique is reported here whereby molecular weight distribution curves from size exclusion chromatography (SEC) obtained on high‐density polyethylene (HDPE) can be deconvolved into a series of Flory‐distribution curves using a commercially available computer software system. Our analysis has shown that five to seven individual Flory distributions describe HDPE with better than a 99.9% degree of fit. We impute from this that upon taking proper precautions, we can consider these HDPE resins to be derived from at least this number of distinct catalyst sites and, furthermore, that modification of the sites will lead to a modification of the resultant resin. © 1993 John Wiley & Sons, Inc.
Modified cyclohexanone–formaldehyde and acetophenone–formaldehyde resins
Authors: Kizilcan Nilgün , Galioğlu Oya , Akar Ahmet 
Published: April 2003

AbstractPreparation of in situ‐modified cyclohexanone‐formaldehyde and acetophenone‐formaldehyde resins with compounds such as diphenols, melamine, and p‐toluene sulfonamide were studied. Modification of acetophenone‐formaldehyde resins with hydroxylamine, semicarbazide, phenylhydrazine, phthalic anhydride, and acetic anhydride was also studied. Melting points, solubilities in organic solvents, and FTIR and NMR spectra of modified resins were determined. © 1993 John Wiley & Sons, Inc.
Preparation and cured properties of novel cycloaliphatic epoxy resins
Authors: Tokizawa Makoto , Okada Hiroyoshi , Wakabayashi Nobukatsu , Kimura Tomiaki , Fukutani Hideo 
Published: April 2003

AbstractPreparation and characterization of novel cycloaliphatic epoxy resins, which are derived from octadienyl compounds, were studied. From a model peracetic acid epoxidation reaction using 2,7‐octadienyl acetate‐1, the structure of the liquid resins is estimated to be mainly terminal epoxides and some amount of inner epoxide depending on the epoxide content. The epoxy resins offer lower toxicity and lower vapor pressure. The reactivity of the resin with acid anhydrides is moderate but faster than that of traditional cyclohexane epoxide‐type resins and slower than that of the glycidyl ester‐type resins. This reactivity was also examined using model compounds. The heat deflection temperature of the hexahydro‐phthalic anhydride‐cured resins is shown to be directly proportional to the number of epoxy groups in the molecules. The flexural strength of the cured resins is nearly equivalent to that of the commercial resins, although the flexural elongation of the resins is larger than that of the rigid cyclohexane epoxide‐type resins. The thermal stability of the cured resins is comparable to typical rigid cycloaliphatic resins; furthermore, high water resistance of the cured resins is suggested to be attributed to the hydrophobic character of the C8 chain by cross‐linking. © 1993 John Wiley & Sons, Inc.
Biocidal polymers active by contact. III. Ageing of biocidal polyurethane coatings in water
Authors: Nurdin N. , Helary G. , Sauvet G. 
Published: April 2003

AbstractPolyurethane coatings prepared from hydroxytelechelic polybutadiene with pendant qua‐ternary ammonium salts (QAS) are able to kill microorganisms, these biocidal polymers were submitted to various ageing conditions. The activity remained constant after exposure to a very high number of bacteria (Escherichia coli). Nevertheless immersion in water caused a slow decrease of activity with time whatever the QAS examined (N+R2R′ with R = Me or Bu and R′ = n‐octyl to n‐hexadecyl). The phenomenon can be analysed in two stages. The first one, short (5–10 days) and limited, is due to the diffusion of a water‐soluble synthesis residue. At the end of this period, the samples are still active and the activity is only due to a contact polymer‐bacteria. The second stage is much slower and is accompanied by a transformation of QAS in amine. This is attributed to an equilibrium between QAS, amine, and alkyl bromide slowly shifted toward the formation of amine because of a weak solubility of alkyl bromide in water. Increasing the lipophilicity and bulkiness of the QAS substituents improves the durability of the biocidal activity. Some samples still exhibit a good activity after more than 1 year of ageing in harsh conditions. © 1993 John Wiley & Sons, Inc.
Structure‐property relationships in polyurethane‐poly(styrene‐co‐acrylonitrile) blends
Authors: Z̆erjal B. , Musil V. , S̆mit I. , Jelčić Z̆. , Malavas̆Ic̆ T. 
Published: April 2003

AbstractBlends of Thermoplastic polyurethane (TPU) and poly(styrene‐co‐acrylonitrile) (SAN) (34% acrylonitrile and 24% acrylonitrile) and polyurethane ionomer (PUI) with SAN (34% acrylonitrile) were prepared in the melt. The structural properties and morphology of the blends were investigated. TPU and SAN blends were immiscible in the composition range 30–70 wt % of TPU or SAN. In TPU‐rich blends, SAN propagates the separation of hard and soft segements in TPU. In SAN‐rich blends, the interaction stage depends on acrylonitrile contents. SEM measurements showed that the blends of TPU/SAN were fine dispersions and clearly showed a continuous and disperse phase, whereas the morphology of the PUI/SAN blends were different. © 1993 John Wiley & Sons, Inc.
Swelling properties of cross‐linked maxillofacial elastomers
Authors: Andreopoulos A. G. , Polyzois G. L. , Evangelatou M. 
Published: April 2003

AbstractSilicone specimens cross‐linked with various amounts of cross‐linking agent were studied in terms of mechanical and swelling behavior. The measured tensile modulus allowed calculation of the average molecular weight between cross‐links (M̄c). Equilibrium swelling data were also used, in combination with the determined M̄c values, to obtain the interaction parameter χ of various silicone–solvent systems at 25°C. Part of this work was also the study of swelling of silicone samples with varying network density in selected solvents such as toluene, ethyl acetate, n‐butanol, and methyl ethyl ketone. © 1993 John Wiley & Sons, Inc.
Poly(vinyl alcohol)/poly(acrylic acid) blends: Miscibility studies by DSC and characterization of their thermally induced hydrogels
Authors: Vázquez‐Torres H. , Cauich‐Rodríguez J. V. , Cruz‐Ramos C. A. 
Published: April 2003

AbstractBinary blends of poly(vinyl alcohol) (PVA) with poly(acrylic acid) (PAA) and polyacrylamide (PAAm) were characterized by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and infrared spectroscopy (IR). Molecular weight, blend composition, and heating time at 150°C were the variables used. Results obtained by DSC indicated that PAA/PVA blends are miscible in the full range of composition. Similarly, TGA traces showed that thermal stability was higher for blends than for pure polymers. Blends of PVA with high molecular weight PAA exhibited a hydrogel behavior after drying at relatively low temperature (100°C), whereas blends containing low molecular weight PAA behaved as hydrogels only after they were heated at 150°C. Hydrogel character was increased for these two PVA/PAA blends with the heating time at higher temperature (150°C). IR spectra revealed that esterification took place in these blends after thermally treated at this temperature. In contrast, addition of glyoxal in combination with heating was necessary to produce hydrogels from PAAm/PVA blends. Furthermore, the crosslinking degree of these hydrogels was estimated from their absorbency values by applying the Flory–Rehner equation. © 1993 John Wiley & Sons, Inc.
Characterization of fractionated LLDPE by DSC, FTIR, and SEC
Authors: Neves Claudio J. , Monteiro Elisabeth , Habert Alberto C. 
Published: April 2003

AbstractSamples of ethylene / 1‐butene copolymer were fractionated according to chemical composition by preparative temperature rising elution fractionation (TREF) in the range of 27–117°C. The resulting fractions were submitted to DSC, SEC, and FTIR analyses. For each fraction, the methyl group content, melting temperature, crystallinity, average molecular weight, and molecular weight distribution were determined. From the results, it was found that the melting tempreature increased linearly with the extraction temperature in the range of low temperatures and remained constant at high temperatures. Similar behavior was observed for crystallinity. It was also verified that the first two fractions showed a higher degree of supercooling than the fractions extracted at higher temperatures. These results were explained by the existence of a heterogeneous intermolecular distribution of comonomer molecules. In a general way, the comonomer units, present at higher concentrations in the low temperature fractions, tended to destroy the crystalline order of the polymer. © 1993 John Wiley & Sons, Inc.
Conducting diblock copolymers with lonic complex/insulator lamellar microdomains
Authors: Ishizu Koji , Yamada Yoshikuni , Saito Reiko 
Published: April 2003

AbstractPoly(styrene‐b‐2‐vinylpyridine) diblock copolymer films with horizontally oriented lamellar microdomains were obtained by the casting method. Poly(2‐vinylpyridine) (P2VP) microdomains were not only quaternized, but were also crosslinked with 1,4‐diiodobutane vapor. Subsequently, ionic complex phases were constructed by an ion‐exchange reaction of quaternized P2VP phases with lithium perchlorate. The element (chlorine and iodine atoms) distributions on the vertical section of the modified films were measured by means of an energy dispersive X‐ray spectrometer. These materials had highly anisotropic conductivity with approximately 6 orders of magnitude. © 1993 John Wiley & Sons, Inc.
Crystal size and minimum enthalpy of crossbreed silk fibers annealed at various temperatures
Authors: Somashekar R. , Urs R. Gopal Krishne 
Published: April 2003

AbstractWide‐angle X‐ray diffraction studies of crossbreed silk fibers and fibers annealed at various temperatures for different periods of time were carried out to evaluate the crystal size and lattice distortion parameters, as these determine the properties of silk fibers. Also, minimum enthalpy for the formation of these fibers has been estimated and compared. © 1993 John Wiley & Sons, Inc.
Determination of diffusion coefficient of water in polymer films by TGA
Authors: Ogawa Toshio , Nagata Toshio , Hamada Yoshikazu 
Published: April 2003

AbstractThis study is concerned with the determination of the diffusion coefficient of water into polymer films using a thermogravimetric analyzer (TGA). First, the sample film in the sample chamber was dried completely by N2 gas supplied by a cylinder. Next, the mixture of air and N2 gas having a given humidity was introduced into the sample chamber of the TGA. The sample weight was recorded as a function of time. The diffusion coefficient was calculated from the initial slope of weight vs. the square root of the time curve. The results were consistent with those obtained using Prager and Long's method. © 1993 John Wiley & Sons, Inc.
New method for measuring poisson's ratio in polymer gels
Authors: Li Yong , Hu Zhibing , Li Chunfang 
Published: April 2003

AbstractA new method for measuring the Poisson's ratio of polymer gels has been proposed and has been experimentally demonstrated. The method is based on different swelling behaviors of free and constrained gels. The Poisson's ratio of polyacrylamide gel, as a function of crosslinker concentration, has been measured using this method and has been found to be sensitive to the amount of polymerization initiator. The results are compared with results determined by other methods. © 1993 John Wiley & Sons, Inc.
Development of a new advanced process for manufacturing polyacetal resins. Part III. End‐capping during polymerization for manufacturing acetal homopolymer and copolymer
Authors: Masamoto J. , Matsuzaki K. , Iwaisako T. , Yoshida K. , Kagawa K. , Nagahara H. 
Published: April 2003

AbstractConventionally, acetal homopolymer or copolymer is obtained by the polymerization of formaldehyde or trioxane, following the end‐capping using acetic anhydride or unzipping of the unstable polymer end fraction. First, Asahi Chemical developed a new process to obtain an end‐capped polymer during polymerization of highly purified formaldehyde using acetic anhydride as the chain‐transfer agent. Use of highly purified formaldehyde and endcapping during polymerization using acetic anhydride as a chain‐transfer agent or an endcapping agent will provide a simple process for manufacturing acetal homopolymer. The polymerization mechanism was confirmed by infrared spectroscopy analysis and proton NMR analysis of the polymer obtained. Second, for the acetal copolymer, purified trioxane was copolymerized with ethylene oxide in the presence of methylal, which gave an endcapped polymer with high thermal stability. Two new intermediates from the initiation reaction of the copolymerization, 1,3,5,7‐tetraoxacyclononane (TOCN) and 1,3,5,7,10‐pentaoxacyclododecane (POCD), were isolated and a new initiation mechanism was proposed. © 1993 John Wiley & Sons, Inc.
Mechanical scission of perfluoropolyethers
Authors: Karis T. E. , Novotny V. J. , Johnson R. D. 
Published: April 2003

AbstractMechanical scission of two typical perfluoropolyethers was investigated: Y, a copolymer of CF(CF3)CF2O, CF2O, and CF(CF3)O, and Z, a copolymer of (CF2)nO, with n = 1,2,3,4. Undiluted polymers were subjected to prolonged shearing in a media mill with ZrO2 particles. A chemical extraction of the polar ZrO2 particles was carried out to collect adsorbed polar scission products. Mechanochemical scission products from both the Y and Z fluorocarbon polymers were identified by 19F‐NMR. A significant amount of CF3CO2− was present after the milling and the primary functional groups formed at scissioned chain ends were CO. A hydrodynamic expression was derived and the maximum extension rate was estimated to be in the range of 5 × 106 s−1. Initial degrees of polymerization were between 20 and 200, well below levels for which flow‐induced scission is expected to occur. Final degrees of polymerization were less than 10, and the scission was noncentral and nonrandom in both polymers. © 1993 John Wiley & Sons, Inc.
Inhibition of bovine serum albumin adsorption by poly(ethylene glycol) soft segment in biodegradable poly(ethylene glycol)/poly(L‐lactide) copolymers
Authors: Hu David Shiaw‐Guang , Liu Hsin‐Jiant , Pan I‐Lung 
Published: April 2003

AbstractThe objective of this study was to investigate the effects of the incorporation of ether linkages into polylactide (PLLA) chains and the time of biodegradation on the behavior of protein adsorption. The content of poly(ethylene glycol) (PEG) in PLLA/PEG copolymers is from 4.4 to 18.3 wt %, and the length of the PEG soft segment is 1000, 2000, and 6000 daltons. The bovine serum albumin (BSA) adsorption onto the biodegradable PLLA/PEG copolymers was carried out using ultraviolet spectroscopy. The surface tension of PLLA and PLLA/PEG was measured using a contact angle. The data show that the incorporation of PEG segments makes the copolymer more polar and, therefore, leads to a reduction of protein adsorption. As the hydrolysis of polymers proceeds, both PLLA and PLLA/PEG turn out to be more polar. However, the initial compositions of degraded PLLA/PEG have a weak influence on the protein adsorption onto its hydrolyzed surface with a substantially long duration of hydrolysis. This phenomenon is attributed to the hydrophobic interaction between polar PLLA/PEG and BSA. © 1993 John Wiley & Sons, Inc.
Investigation of the properties of polyacrylamide‐polyaniline composite and its application as a battery electrode
Authors: Bhat N. V. , Joshi N. V. 
Published: April 2003

AbstractThe composite films of polyacrylamide and polyaniline were prepared by polymerizing aniline using ammonium persulfate as an initiator in an aqueous solution containing polyacrylamide. A film was then cast from this solution. The structural, dynamic mechanical, electrical, and thermal properties of these films have been studied. The infrared spectrum shows the presence of polyacrylamide as well as polyaniline in the composite film. The thermal analysis shows that the composite degrades slower than does the polyacrylamide alone. The dynamic mechanical analysis indicates that there is an increase in the glass transition temperature after the composite formation. The electrical conductivity has been found to increase by more than eight orders of magnitude. These composite films have also been suitably used as electrodes in secondary batteries. © 1993 John Wiley & Sons, Inc.
Photoconductivity and photovoltaic effect of charge‐transfer complex of poly[4‐phenyl‐2,6‐(p‐phenoxy) quinoline] and 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone
Authors: Choi Donghoon , Lee Eun Ju , Kim Kyeong‐Ah , Park Soo Young , Kim Nakjoong 
Published: April 2003

AbstractA new polymer containing a heterocyclic quinoline unit in the main chain, poly[4‐phenyl‐2,6‐(p‐phenoxy) quinoline] (PQ), was synthesized by an acid‐catalyzed self‐condensation reaction. We have found that PQ, which is generally a good insulator itself, can show photoconductivity when doped with an electron acceptor. From the UV‐VIS absorption spectra, we found that PQ can form a charge‐transfer (CT) complex with an electron acceptor, 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). The CT complex of the PQ‐DDQ mixture showed distinct photoconductivity. Employing the DDQ composition ranging from 5 to 10 wt %, the ratio of dark and photoconductivity was calculated to be about 1 : 100 at an applied electric field of 105 V/cm. Additionally, the bilayer sample of PQ/DDQ exhibited a significant photovoltaic effect. The photovoltaic current increased with increasing photointensity. The open‐circuit voltage was measured ranging from 0.4 to 0.7 V and the photovoltaic conversion efficiency was calculated to be 10−3−10−2%. The PQ film treated with DDQ vapor showed a relatively higher photovoltaic effect than that of the sample treated with DDQ solution. © 1993 John Wiley & Sons, Inc.
Water‐sorption and transport properties of Nafion 117 H
Authors: Morris David R. , Sun Xiaodong 
Published: April 2003

AbstractThe density and dimensional changes of Nafion 117 H have been measured as a function of the water content. Swelling of Nafion commences at N (≡ mol ratio water to hydrogen ion) ∼ 1.9. Some anisotropy of dimensional changes was observed. Water‐sorption isotherms obey Henry's Law with a nonzero intercept indicating some water retention. The diffusion coefficient of water in Nafion and the electrical conductivity of Nafion are strong functions of the water content. The latter is exploited for the development of a humidity sensor. © 1993 John Wiley & Sons, Inc.
Preparation and thermal kinetics of poly(imide‐siloxanes)
Authors: Moon Yoon Duk , Lee Young Moo 
Published: April 2003

AbstractThermoplastic poly(imide‐siloxanes) (PISILs) were synthesized from hexafluoroisopro‐pylidene‐2,2‐bis(phthalic acid anhydride) (6FDA), 3,3',4,4'‐benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), and amine‐terminated poly(dimethyl siloxanes) (PDMS) having different molecular weights. Glass transition temperatures of fully cured PISILs ranged from −91 to −48°C. Various kinetic parameters for the thermal decomposition reaction of PISILs were examined by dynamic thermogravimetric analysis (DTGA) at four different heating rates. The degradation path was a kinetically first‐order reaction for PISILs (abbreviated 6FDA‐860, BTDA‐860, and PMDA‐860, respectively) from 6FDA, BTDA, PMDA, and PDMS (Mn = 860 g/mol). The reaction rate constant times the half‐life (k × t1/2) was approximately 0.693. The activation energies for decomposition were in the following order: 6FDA‐860 <BTDA‐860 <PMDA‐860. The lifetime of the highest heat‐resistant PMDA‐860 at about 200°C and at the conversion level of 10% was 6.5 × 105 h or 74 years. Other kinetic factors were also calculated. © 1993 John Wiley & Sons, Inc.
Microstructural effects and the toughening of thermoplastic modified epoxy resins
Authors: Min B.‐G. , Stachurski Z. H. , Hodgkin J. H. 
Published: April 2003

AbstractWe have studied an epoxy resin formulation consisting of the diglycidyl ether of bisphenol‐A (DGEBA), modified with phenolic hydroxyl‐terminated polysulfone (PSF) and cured with an aromatic amine curing agent, diaminodiphenyl sulfone (DDS). A range of microstructures and fracture properties have been obtained by controlling the formulation cure conditions (cure temperature and cure cycle in an isothermal mode). The chemical conversion of the cured resins has been monitored by near‐infrared spectroscopy (NIR). Although only a single material formulation was used, three distinct types of microstructure were identified by scanning electron microscope (SEM) observations on samples prepared at different cure temperatures. Surprisingly, the thermal and fracture properties of the cured samples did not vary noticeably, in spite of the significant microstructure variations. The consistency of these fracture toughness results with cure temperature changes was an unexpected result in the light of our earlier observations of a strong dependence of fracture toughness on cure temperature in neat resin systems. The difference in behavior between neat and modified resins reveals that the fracture toughness of the latter is dependent on a combination of the microstructure and the matrix resin properties. This hypothesis was also supported by an observation of high fracture thoughness in a sample cured in a two‐step process, which we believe is due to the optimum microstructure and matrix resin properties, being achieved separately during precure and postcure, respectively. The increase in fracture toughness values caused by the modification (ΔGIC) was calculated from the fracture toughness values of neat and modified resins, prepared under the same cure conditions, using a proposed theoretical equation. © 1993 John Wiley & Sons, Inc.