bluuebunny/crossref_metadata_2025_split huggingface dataset:
Short contribution: A practical alternative to Kubiena boxes for the collection of samples for micromorphological analysis
Authors: Josephs Richard L. , Bettis E. Arthur 
Published: April 2003

AbstractThis note proposes a practical and economical alternative to using Kubiena boxes for the collection of undisturbed soil or sediment samples for micromorphological analysis. The authors promote the use of plastic electrical outlet boxes (gang boxes) that can be purchased at any hardware store for around 20 cents apiece. In addition to availability and low cost, plastic gang boxes are preferred by thin‐section laboratories over that of the aluminum Kubiena boxes because they cause less wear on the thin‐sectioning equipment. As with Kubiena boxes, the samples are impregnated directly in the gang boxes, yet they are more easily and efficiently retrieved, thus facilitating overall sample preparation and insuring a final product of equal or better quality. © 2003 Wiley Periodicals, Inc.
Origin of post‐Minoan caves and volcaniclastic cave fill, Thera (Santorini), Greece
Authors: Ramage Joan M. , Shaw George H. , Hoffman Jeff A. , Johnston Sarah A. 
Published: April 2003

AbstractThe Aegean island of Thera (Santorini) was covered by tephra from its cataclysmic Late Bronze Age (ca. 3600 yr B.P.) eruption. Vertical exposures of the eruptive sequence show secondary, nonvolcanic, circular (in cross section) features composed of stratified sediment. Many are inaccessible from the floors of modern quarries and appear to be caves filled with younger sediment, but show no connection to the land surface. A filled cave was found in the wall of a modern gully outside the modern quarries, and a filled cave was found in a terrace scarp, well above the modern gully. Natural (and probably rapid) incision by gullies into the thick tephra deposit left many locations with lateral access to tephra. Inhabitants from post‐Minoan to recent times excavated tephra for materials and buildings, and caves were subsequently filled by sporadic (possibly seasonal) flood events that deposited sediment. These gullies may have provided access for modern tephra removal that isolated the filled caves high on the modern quarry walls. © 2003 Wiley Periodicals, Inc.
Short contribution: Strategies and techniques in collecting micromorphology samples
Authors: Goldberg Paul , Macphail Richard I. 
Published: April 2003

AbstractMicromorphology plays an important role in understanding the context and formation of archaeological deposits and soils. However, little information about the strategies and considerations for collecting samples for micromorphological analysis has been published. This is especially so for stony or crumbly deposits that are difficult to remove while preserving their undisturbed nature. We present several techniques and strategies to facilitate the collection of micromorphological samples by people with limited experience. © 2003 Wiley Periodicals, Inc.
Thin film melt polymerized single crystals of poly(p‐oxybenzoate)
Authors: Rybnikář František , Liu Jiang , Geil Phillip H. 
Published: April 2003

AbstractThe morphology of poly(p‐oxybenzoate) polymerized from p‐acetoxybenzoic acid (pABA) in constrained thin films at temperatures between 130°C and 315°C for various times is described. Polymerization below the melting point of the monomer, 196°C, occurs by a sublimationrecrystallization‐melting process, with polymerization occuring in the melt. Lamellar crystals, often bilayered, are found that are ca. 100 Å thick as well as single disclination domains. Electron diffraction patterns indicate the presence of either phase I or II in a given crystal, with the unit cell for phase II being proposed; the molecular axes are normal to the lamellae. Polymerization above 200°C results in holes in the lamellae; it is suggested that polymerization also is in the form of lamellae followed by the hole formation as further reaction occurs in the crystalline state, initial “crystal” growth at all temperatures is in the liquid crystalline state.
In situ polymerization of tetraethoxysilane in poly(vinyl acetate)
Authors: Girard‐Reydet Emmanuel , Lam Thanh My , Pascault Jean Pierre 
Published: April 2003

AbstractThe in situ polymerization of tetraethoxysilane (TEOS) in poly(vinyl acetate) (PVAc) yields homogeneous and transparent nanocomposite materials. It was shown that covalent bonds occur between the organic chains and the inorganic clusters, preventing macroscopic phase separation. For an initial amount of TEOS higher than a critical value, gel formation is observed. Up to this critical TEOS content, improved mechanical properties, which persist at high temperatures, are obtained.
Evaluation of unperturbed polymer dimensions from intrinsic viscosity in non‐ideal solvents
Authors: Abdel‐Azim Abdel‐Azim A. 
Published: April 2003

AbstractFor solutions of polystyrene (PS) samples of different relative molecular mass (molecular weight) M and intrinsic viscosities [n] have been measured at 298,15 K in pure toluene (T) and toluene/methanol (MeOH) mixtures. Upon mixing toluene (good solvent (1)) and methanol (nonsolvent (2)), a systematic decrease in the solvation power was obtained. A critical examination of the Stockmayer‐Fixman method for obtaining unperturbed dimensions from intrinsic viscosity measurements has been made. It was found that the unperturbed dimensions were not constant and different from those measured in a theta solvent (T/MeOH mixture having volume fraction of methanol (ϕMeOH) = 0,23). The derived values of unperturbed dimensions were found to increase with increasing Kuhn‐Mark‐Houwink‐Sakurada exponent a. A modified form of the Stockmayer‐Fixman equation is presented. It is suggested that the volume effect be taken into account in a complementary fashion to obtain accurate estimates of unperturbed dimensions from data in active solvents where the mean‐square end‐to‐end distance 〈r2〉 increases at these conditions more rapidly than M. Different viscosity measurements of polystyrene (PS) and poly(N‐vinyl‐2‐pyrrolidone) solutions containing non‐ideal solvents were taken from the literature and found that the newly proposed, though purely empirical equation is valid.
Hydrogen activation in propene polymerization with MgCl2‐supported Ziegler‐Natta catalysts: the effect of the external donor
Authors: Chadwick John C. , Miedema Arjen , Sudmeijer Olof 
Published: April 2003

Abstract13C NMR analysis of relatively low‐molecular‐weight polypropylenes prepared using the catalyst system MgCl2/TiCl4/phthalate ester‐AlEt3‐external Lewis base has revealed the presence of up to around 20% butyl (n‐Bu) chain ends, indicative of regioirregular (2,1‐) monomer insertion followed by chain transfer with hydrogen. The effect of hydrogen on catalyst activity depends on the nature of the external donor, and the results indicate that at least part of the observed increase in catalyst activity in the presence of hydrogen can be ascribed to the regeneration of active species via chain transfer at dormant (2,1‐inserted) sites.
Synthesis and 13C NMR characterization of ethylene glycol/terephthalic acid/hydroxybenzoic acid copolyesters
Authors: Abis Luigi , Po Riccardo , Schimperna Giuliana , Merlo Edoardo 
Published: April 2003

AbstractCopolyesters of terephthalic acid, p‐hydroxybenzoic acid and ethylene glycol were prepared by high‐temperature melt polycondensation, starting from different hydroxybenzoic acid derivatives. Methyl p‐hydroxybenzoate monomers having the hydroxyl either free, etherified with ethylene glycol or esterified with terephthalic acid were used. The chemical structure of the copolyesters obtained was characterized by means of 13C NMR spectroscopy, and chemical shifts were assigned to the respective carbons. The investigation clearly indicates that oxybenzoate units are quantitatively present in the polymer as etherified (on the hydroxyl group) and esterified (on the carboxylic group) with ethylene glycol. Similar analyses were performed on intermediate products formed after the transesterification stage. They point out that at this stage the hydroxyl group is free when starting from methyl p‐hydroxybenzoate, while a noticeable amount of ether is already present when starting from the monomer esterified with terephthalic acid. A reaction scheme encompassing these results and based on the competition between esterification and etherification process of the phenolic hydroxyl is put forward.
Poly(methyl methacrylate)‐block‐poly(ethyl acrylate) by group transfer polymerization: synthesis and structural characterization
Authors: Masař Bohumil , Vlček Petr , Kříž Jaraslav , Kovářová Jana 
Published: April 2003

AbstractPoly(methyl methacrylate)‐block‐poly(ethyl acrylate) (PMMA‐block‐PEA) was synthesized by sequential group transfer polymerization (GTP) in tetrahydrofuran at −30°C using (1‐methoxy‐2‐methyl‐1‐propenyloxy)trimethylsilane (MTS) as an initiator and tetrabutylammonium fluoride monohydrate (TBAF · H2O) as a catalyst. First, the PMMA macroinitiator was prepared in situ in quantitative conversion and its lifetime was at least 15 min. In the second step, an equimolar amount of ethyl acrylate was polymerized with a conversion of 67–88% and PMMA‐block‐PEA with number‐average molecular weight 5000 < M̄n < 11 500 and polydispersity 1,4 < M̄w/M̄n < 2,1 was obtained. The number of chains almost does not change during the polymerization and the initiating efficiency of MTS was in both steps ca. 0,65–0,80. The diblock structure of the copolymer was confirmed by the 13C NMR spectrometric direct proof of the bond‐linking of both blocks and by comparing the DSC behaviour of the copolymer with that of the corresponding blend of the homopolymers. No contamination of the block copolymer with the homopolymers was detected by the analytical methods used for the structural characterizations.
Synthesis and functional analysis of phenyl‐end‐blocked poly(methyl methacrylate) with N,N′‐dimethyl‐N,N′‐bis(phenethyl)thiuram disulfide as a thermal iniferter
Authors: Haque Shah Abdul , Clouet Gilbert 
Published: April 2003

AbstractPhenyl‐end‐blocked poly(methyl methacrylate) was synthesized by bulk polymerization of methyl methacrylate by a new functional iniferter, viz., N,N′‐dimethyl‐N,N‐bis(phenethyl)‐thiuram disulfide by thermal polymerization. The iniferter was synthesized and characterized by elemental analysis, ultraviolet, infrared, 1H and 13C nuclear magnetic resonance (1H NMR and 13C NMR). Some kinetic parameters like rate of polymerization, variation in the molecular weight and transfer constants as a function of iniferter concentration in the temperature range between 55°C and 100°C have been studied. The rate of polymerization increased with increasing temperature but passed through a maximum with respect to the iniferter concentration. The rate did not follow straight‐line behaviour with respect to iniferter concentration as usually found with alkylthiuram disulfides. The chain transfer due to iniferter exhibited the usual temperature dependence, and the activation energy was of the same order of magnitude as for the aliphatic thiuram disulfide. Spectral and thermal analyses of the resultant polymers confirmed the terminal functionalization of the polymer chains.
Polymerizability of methyl α‐substituted acrylates containing methoxycarbonyl groups
Authors: Kudoh Masaki , Akutsu Fumihiko , Odagawa Yoshiyuki , Naruchi Kiyoshi , Miura Masatoshi 
Published: April 2003

AbstractDimethyl 4‐methyl‐1‐pentene‐2,4‐dicarboxylate (3) and trimethyl 4‐methyl‐1‐octene‐2,4,7‐tricarboxylate (4) are not radically homopolymerizable. Dimethyl 1‐hexene‐2,4‐dicarboxylate (5) polymerizes slowly to yield a small amount of oligomers. Homopolymerization of dimethyl 1‐butene‐2,4‐dicarboxylate (6) affords a high‐molecular‐weight polymer. Radical copolymerization of these methyl α‐substituted acrylates (M2) with styrene (M1) was carried out at 60°C using AIBN, and the following monomer reactivity ratios were obtained; 3: r1 = 0,983, r2 = 0,000; 4: r1 = 0,938, r2 = 0,000; 5: r1 = 0,672, r2 = 0,119; 6: r1 = 0,566, r2 = 0,195. The polymerizability of these methyl acrylate derivatives is influenced by the steric effect of the α‐substituents.
Stereocontrol mechanism of an organozinc complex having chair‐type structure in the polymerization of tert‐butylethylene oxide; comparison with propylene oxide
Authors: Tsuruta Teiji , Hasebe Yoshihiro 
Published: April 2003

AbstractA ring‐opening polymerization of racemic tert‐butylethylene oxide (t‐BEO) was carried out with a well‐defined organozinc complex, [CH3OCH2CH(CH3)OZnOCH(CH3)CH2OCH3]2·[C2H5ZnOCH(CH3)CH2OCH3]2 ([Zn‐MP]2,2), as initiator. The 13C NMR analysis showed that the main chain of poly(t‐BEO) is isotactic although the initiation reaction between t‐BEO and [Zn‐MP]2,2 is much less enantioselective compared with the very high selectivity in the propagation stage. In the R,S‐copolymerization reaction of t‐BEO (R/S = 64/36), no change in the optical purity of the residual monomer was observed at any extent of conversion. It was concluded from these results that the enantioselection in the propagation stage at any particular site is perfectly governed by the chirality of the first t‐BEO molecule that entered and reacted at the site of [Zn‐MP]2,2. The mechanism of the stereocontrol processes for the [Zn‐MP]2,2 initiated polymerization of t‐BEO is discussed in comparison with that for the polymerization of propylene oxide.
Assemblies of liquid crystalline polyelectrolytes and amphiphilic compounds
Authors: Ciferri Alberto 
Published: April 2003

AbstractA tentative mechanism of aggregation of amphiphilic molecules to a rigid mesogenic polylelectrolyte is suggested. A basic soluble unit may grow laterally and longitudinally, eventually forming nematic phases and gels. Relevance to self‐assembly of complex biological structures is hypothesized.
Syntheses and ESR spectra of radicals produced in the thermal decomposition of tetraarylsuccinonitriles
Authors: Plaček Jan , Szőcs Ferenc , Braun Dietrich , Skrzek Thomas 
Published: April 2003

AbstractTetraarylsuccinonitriles 2a–e were synthesized via oxidative dimerization of diarylacetonitriles 1a–e in basic media. The thermal decomposition of 2 results in two identical cyanodiarylmethyl radicals 3. Both 1H and 13C NMR analyses of 1a–e and 2a–e and ESR spectra of 3a–e are presented and discussed. The results of ESR measurements provide a plausible explanation for the different reactivity of cyanodiarylmethyl radicals 3a–e in free radical polymerization.
Thermally crosslinked rigid‐rod aramids, 2. Fiber spinning and fiber properties
Authors: Glomm Bernhard , Rickert Christoph , Neuenschwander Peter , Suter Ulrich W. 
Published: April 2003

AbstractFibers of three rigid‐rod aromatic copolymers, produced by polycondensation of 2,2,6,6‐tetraoxo‐1,3,5,7‐tetrahydro‐2,6‐dithia‐s‐indacene‐4,8‐diamine (DSDA), p‐phenylenediamine and terephthaloyl dichloride, were spun from nematic solutions and characterized by wideangle X‐ray‐diffraction (WAXD) measurements and mechanical tests. A post‐spin heat treatment was employed to improve the low degrees of orientation and crystallinity exhibited generally by the untreated fibers. The dominating crystal structures of the copolymers are similar to “modification I” of the well known fibers from poly(p‐phenyleneterephthalamide) (PPTA). Thermally induced crosslinking of the fibers in the solid state was performed simultaneously with post‐spin treatment. The influence of the annealing conditions on the mechanical fiber properties and the molecular order in the fibers was also investigated. All mechanical parameters were time‐dependent, probably due to the generation of stable radicals during heat treatment. The radicals may give rise to chain scission.
Preparation and properties of new photo‐functional polymers, 1. N‐substituted maleimide/styrene copolymers containing pendant para‐nitrobenzyl groups
Authors: Chiang Wen‐Yen , Lu Jin‐Yuh 
Published: April 2003

AbstractA new photo‐functional copolymer was designed by etherification or esterification of poly‐[N‐(4‐hydroxyphenyl)maleimide‐co‐styrene] or poly[N‐(4‐carboxyphenyl)maleimide‐co‐styrene] with p‐bromomethylnitrobenzene using 1,8‐diazabicyclo[5.4.0]‐undec‐7‐ene (DBU) as the base in an aprotic solvent. The chain‐stiffening effect of the N‐substituted maleimide group provided good thermal stability. It was observed that the photosensitivity of the copolymer is enhanced by the addition of a base like tributylamine.
Liquid‐Crystalline side‐chain AB block copolymers by direct anionic polymerization of a mesogenic methacrylate
Authors: Bohnert Robert , Finkelmann Heino 
Published: April 2003

AbstractAB block copolymers with a liquid‐crystalline and an amorphous block are synthesized by anionic copolymerization of 4‐[4‐(4‐methoxyphenylazo)phenoxy]butyl methacrylate (1) with either styrene or methyl methacrylate (MMA). The polymerization of 1 proceeds from polystyrenelithium capped with 1,1‐diphenylethylene to produce polystyrene‐block‐poly(1), while poly(1)‐block‐PMMA is prepared by addition of MMA to the “living” poly(1) anion. A large variety of block copolymers is obtained with narrow molecular weight distribution and definite composition. The mesophase behaviour of these samples is analyzed with respect to the chain length of the liquid‐crystalline block. Electron microscopy of a high‐molecular‐weight polystyrene‐block‐poly(1) provides direct evidence for a microphase‐separated structure composed of spherical polystyrene domains embedded in a liquid‐crystalline matrix. For the corresponding poly(1)‐block‐PMMA, however, electron microscopy indicates no structure, although dynamic mechanical analysis proves microphase separation.
Chromatographic investigations of macromolecules in the critical range of liquid chromatography, 6. Analysis of the methyl methacrylate block in block copolymers of decyl and methyl methacrylate
Authors: Pasch Harald , Augenstein Michael , Trathnigg Bernd 
Published: April 2003

AbstractUsing liquid chromatography at the critical point of adsorption the molar mass and the polydispersity of the individual blocks in block copolymers of decyl and methyl methacrylate are determined. In addition, the total molar mass and the chemical composition of the block copolymers are calculated and compared to data from conventional size exclusion chromatography (SEC) and SEC with coupled density‐refractive index detection. The agreement of the data obtained by the different methods is found to be very good.
Synthesis, properties and biodegradability of polyesters based on 1,3‐propanediol
Authors: Witt Uwe , Müller Rolf‐Joachim , Augusta Josef , Widdecke Hartmut , Deckwer Wolf‐Dieter 
Published: April 2003

AbstractAliphatic homopolyesters and copolyesters based on 1,3‐propanediol and containing terephthalic acid as aromatic compounds and sebacic acid as aliphatic compound were synthesized by condensation in bulk. Intrinsic viscosity and weight‐average molecular weight were measured. Melting temperatures were studied by differential scanning calorimetry. For all polyesters the biodegradability was tested. Test media were inoculated with either municipal compost eluates or decanted sewage sludge. Criteria measured were visible changes, weight loss, and scanning electron microscopy indicating the visible changes of the surface. Compositions of copolyesters were characterized by 13C NMR spectroscopy. As a major result it is concluded that biodegradability depends substantially on the sequential structure of the polymer.
Kinetic and electron paramagnetic resonance studies on radical polymerization. Radical copolymerization of p‐tert‐butoxy‐styrene and dibutyl fumarate in benzene
Authors: Sato Tsuneyuki , Shimooka Sumio , Seno Makiko , Tanaka Hitoshi 
Published: April 2003

AbstractThe copolymerization of p‐tert‐butoxystyrene (1) (M1) and dibutyl fumarate (2) (M2) initiated with dimethyl 2,2′‐azobisisobutyrate (3) was studied in benzene at 60°C kinetically and by means of electron paramagnetic resonance (EPR) spectroscopy. The monomer reactivity ratios were determined to be r1 = 0,18 and r2 = 0,01, indicating that homopropagation of M2 is almost negligible in the copolymerization. The copolymerization system was revealed to involve EPR‐observable propagating polymer radicals under practical copolymerization conditions. The apparent rate constants of propagation (kp) and termination (kt) determined by EPR show a rapid increase in the range from 0,9 to 1,0 of feed composition (f1 = {[M1]/([M1] + [M2])}) of M1. From the relationship between kp and f1 based on Fukuda's penultimate model, the rate constants of propagation of copolymerization were evaluated; k111 = 140 L · mol−1 · s−1, k211 = 4,3 L · mol−1 · s−1, k112 = 778 L · mol−1 · s−1, k212 = 24 L · mol−1 s−1 and k121 = 19 L · mol−1 · s−1, suggesting a pronounced penultimate effect.
Synthèse et caractérisation d'un amorceur azoïque disulfonique. Application à la polymérisation de l'acide acrylique
Authors: Bessière Jean‐Marie , Boutevin Bernard , Loubet Olivier , Piétrasanta Yves 
Published: April 2003

AbstractThe synthesis of a water‐soluble azo initiator was performed in four steps: action of hydrazinium sulfate onto 4‐phenylbutan‐2‐one followed by an addition of hydrogen cyanide onto the azine, then oxydation with bromine and finally chlorosulfonation of the obtained aromatic azo compound. The overall yield of this azo compound was about 40%. The kinetical and thermal parameters were determined by differential scanning calorimetry. The decomposition rate constant (kd) is similar to that of 2,2′‐azoisobutyronitrile (AIBN) but the activation energy (ca. 38 kJ/mol) is lower than that of AIBN. The polymerization with this initiator in aqueous medium has advantages as compared with Fenton's reagent.
Compensating the composition drift in reactivity ratio calculations for copolymerizations carried to high conversions
Authors: Catalgil‐Giz Huceste , Giz Ahmet T. 
Published: April 2003

AbstractThe effect of composition drift on the accuracy of linearised methods of determining the reactivity ratios in copolymerization reactions is calculated. It is shown that, when the reactivity ratios differ widely, even at a very low conversion of 5% the drift causes large errors in the ratios found with these methods. However, by using an appropriate average of the initial and the final monomer ratios, the errors due to the composition drift can be significantly reduced, so that linearised methods with averaging can be used with confidence at moderate (30–50%) conversions.
Synthesis and characterization of new hydrophobic polyurethanes for biomedical applications
Authors: Marconi W. , Martinelli A. , Piozzi A. , Zane D. 
Published: April 2003

AbstractThe synthesis of new segmented polyurethanes containing as chain extender N‐hexadecyl‐2,2‐bis(hydroxymethyl)propionamide (alone or with 1,4‐butanediol at different mole ratios) is described. The degree of hydrophobicity and the glass transition temperatures Tg were found to be proportional to the alkyl chain content of the polymer. Also the amount of bonded albumin is proportional to the alkyl group content of the polymer, and platelet adhesion is remarkably lower for the 100% alkylated polymer (PEUHDA) than for the standard non‐alkylated polyurethane (PEU). This behaviour was confirmed by SEM evaluation, showing a much lower degree of activation of platelets on albuminized PEUHDA films. It was not possible to ascertain with sufficient reliability a different behaviour, with respect to platelet adhesion, of the polymers containing alkyl chains in the range 9 ÷ 50 mol‐%, due to the relatively high error of the evaluation systems.