bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct modification for non‐conforming elements with drilling DOF
Authors: Choi Chang‐Koon , Lee Tae‐Yeol , Chung Keun‐Young 
Published: October 2002

AbstractA unified approach to eliminate the undesirable lockings in distorted meshes for both non‐conforming quadrilateral membrane and hexahedral elements with drilling (or rotational) degrees of freedom is presented. The direct modification scheme is utilized in the formulation of non‐conforming modes to improve the general behaviour of isoparametric‐based elements. It is shown that the direct modification is very effective in eliminating the locking and this improvement of element behaviour may be doubled if the selective integration scheme is used simultaneously. To verify the validity of elements formulated by the proposed schemes and to evaluate their effectiveness, several numerical tests are carried out. The combined use of additional non‐conforming modes with the direct modification method and the selective integration technique plays an important role to improve the behaviour of elements, especially for distorted mesh cases. Test results also show that the results for both non‐conforming quadrilateral membrane and hexahedral elements obtained by the proposed schemes are equally satisfactory. Copyright © 2002 John Wiley & Sons, Ltd.
Mesh‐independent p‐orthotropic enrichment using the generalized finite element method
Authors: Duarte C. A. , Babuška I. 
Published: October 2002

AbstractThis paper is aimed at presenting a simple yet effective procedure to implement a mesh‐independent p‐orthotropic enrichment in the generalized finite element method. The procedure is based on the observation that shape functions used in the GFEM can be constructed from polynomials defined in any co‐ordinate system regardless of the underlying mesh or type of element used. Numerical examples where the solution possesses boundary or internal layers are solved on coarse tetrahedral meshes with isotropic and the proposed p‐orthotropic enrichment. Copyright © 2002 John Wiley & Sons, Ltd.
Enantiomerization of bridged 1,1′‐binaphthyls
Authors: Yi Ren , Hoz Shmaryahu 
Published: October 2002

AbstractThe activation energy for the isomerization of 1,1′‐binaphthyl in which positions 2 and 2′ are bridged at by an —O—CH2—O— unit was calculated at various computational levels. AM1 gave good agreement with the experimental results. The transition‐state structure was found to be entirely different from that calculated for the non‐bridged parent compound: whereas the latter has C2 symmetry, the former has C
s symmetry. The C
s symmetry transition state for the non‐bridged parent compound was also located and found to be ca 6 kcal mol−1 higher than the C2 one. However, in the bridged compound, the inclusion of the bridge counterbalanced this by raising the energy of the ground state, leaving the activation energy essentially unchanged. The isomerization of optically active bridged 1,1′‐binaphthyls bearing linear polyphenyl rods of varying length, at positions 6 and 6′, was recently employed as a probe to gain information on the effect of rubber and glassy polymers on reaction rates. The model showed that the rod segments of these molecules traverse long distances in order to reach the transition state, which was consistent with a strong rod length dependence on racemization of the bridged binaphthyls in the glassy state. However, the present results demonstrate an unexpected twisting motion in the racemization process, suggesting that the appended oligophenyl rods are displaced to about half the distance previously expected. This may contribute in part to the experimental observation in the rubbery state where the microviscosity affects the racemization as a function of the appended rods far less than expected. AM1 results also gave reasonable agreement with the experimental ponderal effect consistent with the prior conclusion of force constant independence of rod length for twisting about the 1,1′ bonds. Copyright © 2002 John Wiley & Sons, Ltd.
Structural studies on sulfonylbicyclo[n.2.0]alkan‐1‐ols
Authors: Healy Peter C. , Loughlin Wendy A. , McCleary Michelle A. , Pierens Gregory K. , Rowen Catherine C. 
Published: October 2002

AbstractThe structures of a series of sulfonylbicyclo[n.2.0]alkan‐1‐ols (n = 3–6) 1–6 were determined by single‐crystal x‐ray diffraction. A survey of the Cambridge Structural Database and Monte Carlo conformational searches using MacroModel were performed. Compounds 1, 3 and 4 show intramolecular hydrogen bonding. Compound 2 is stabilized by three‐centered ‘bifurcated’ intra‐ and intermolecular hydrogen bonds between the hydroxyl proton and the sulfone oxygens. Compounds 5 and 6 are stabilized by intermolecular hydrogen bonds formed between the trans 1‐hydroxy and sulfonyl moieties. In compounds 1–6, the degree of cyclotorsion of the four‐ five‐, six‐, seven‐ and eight‐membered rings adjacent to the bond between the bridgehead atoms C1 and C4 is reflected in the magnitude about the exterior angles about C1 (C2—C1—Cx) and C4 (C3—C4—C5). The six‐membered ring systems of 2, 5 and 6 showed noteworthy increases in the C5—C4—C1—Cx and C3—C4—C1—C2 torsion angles, and this was attributed to the conformational constraints of the pseudo‐chair conformation of the six‐membered ring. Similar conformational structure effects were observed in the modeled structures 1a–6a to those observed for the x‐ray structures 1–6. Copyright © 2002 John Wiley & Sons, Ltd.
Molecular polarizability of fullerenes and endohedral metallofullerenes
Authors: Torrens Francisco 
Published: October 2002

AbstractThe interacting induced dipoles polarization model implemented in our program POLAR is used for the calculation of the molecular dipole
µ and tensor quadrupole $\overline{\overline{{\mit \Theta}}}$ moments and also the dipole–dipole polarizability $\overline{\overline{\alpha}}$. The method is tested with Sc
n, C
n (fullerene and graphite) and endohedral Sc
n@C
m clusters. The polarizability is an important quantity for the identification of clusters with different numbers of atoms and even for the separation of isomers. The results for the polarizability are of the same order of magnitude as from reference calculations performed with our version of the program PAPID. The bulk limit for the polarizability is estimated from the Clausius–Mossotti relationship. The polarizability trend for these clusters as a function of size is different from what one might have expected. The clusters are more polarizable than what one might have inferred from the bulk polarizability. Previous theoretical work yielded the same trend for Si
n, Ge
n and Ga
nAs
m small clusters. However, previous experimental work yielded the opposite trend for Si
n, Ga
nAs
m and Ge
nTe
m larger clusters. At present, the origin of this difference is problematic. One might argue that smaller clusters need not behave like those of intermediate size. The high polarizability of small clusters is attributed to dangling bonds at the surface of the cluster. In this respect, semiconductor clusters resemble metallic clusters. Copyright © 2002 John Wiley & Sons, Ltd.
Solvolyses of naphthoyl chlorides. Solvent effect and Grunwald–Winstein correlation analyses with YxBnCl scales
Authors: Liu Kwang‐Ting , Hwang Patty Y.‐H. , Chen Hun‐I 
Published: October 2002

AbstractThe solvolyses of 1‐naphthoyl (2), 2‐naphthoyl (3), 4‐methyl‐1‐naphthoyl (4) and 6‐methoxy‐2‐naphthoyl (5) chlorides in a variety of solvents were studied, and correlation analyses by using the single‐ and dual‐parameter Grunwald–Winstein equations were examined. An excellent linear relationship (R = 0.995) for 4, log (k/k0) = 0.733YxBnCl + 0.269NOTs, was observed. An SN1‐like mechanism with decreasing extent of nucleophilic solvent participation was found in the solvolysis of 2 and 4. 2‐Naphthoyl chloride is likely to have a mechanism at the borderline of SN1‐like dissociation and an addition–elimination process. 6‐Methoxy‐2‐naphthoyl chloride shows more SN1‐like character than 3 and is associated with nucleophilic solvent intervention more pronounced than that for 2 and 4. The applicability and the advantages of using the YxBnCl scale for different types of substrates are discussed. Copyright © 2002 John Wiley & Sons, Ltd.
Correlation of the rates of solvolyses of cinnamyl chloride
Authors: Koo In Sun , An Sun Kyoung , Yang Kiyull , Lee Ikchoon , Bentley T. William 
Published: October 2002

AbstractSolvolytic rate constants (k) at 25 °C are reported for solvolyses of cinnamyl chloride (1) in binary mixtures of water with acetone, ethanol, methanol, methanol‐d and 2,2,2‐trifluoroethanol (TFE), and also in TFE–ethanol mixtures; product selectivities (S) are reported for aqueous ethanol and methanol: S = [ether product]/[alcohol product] × [water]/[alcohol solvent]. A good correlation observed between log k and the parameter YCl (solvent ionizing power) is improved only slightly by additional parameters (N for solvent nucleophilicity and/or I, an aromatic ring parameter). Rate ratios in solvents of the same YCl value but different nucleophilicities provide measures of the minimum extent of nucleophilic solvent assistance, and the value of 1.48 for [k40EW/k97TFE]
Y (EW = ethanol–water) is consistent with an essentially SN1 reaction mechanism. A linear relationship between 1/S and molar ratio of solvent was derived theoretically and validated experimentally for solvolyses of the above substrate from water up to 75% alcohol–water. The dependence of S on solvent composition and the absence of rate depression in the presence of added chloride anions are explained by product formation via a contact ion pair. Copyright © 2002 John Wiley & Sons, Ltd.
The intramolecular hydrogen bond and intrinsic proton affinity of neutral organic molecules: N,N ′,N ″‐tris (3‐aminopropyl)guanidine and some related systems
Authors: Kovačević Borislav , Glasovac Zoran , Maksić Zvonimir B. 
Published: October 2002

AbstractMultiple aminopropyl substitutions of the initial N,N′,N″‐trimethylguanidine lead to high intrinsic absolute proton affinities (APA) and basicities culminating in APA = 268.4 kcal mol−1 (1 kcal = 4.184 kJ) in N,N′,N″‐tris(3‐aminopropyl)guanidine (9). The reason behind a high proton affinity is identified as a strong cationic resonance in the central guanidine moiety and the strength of the intramolecular hydrogen bonding (IMHB), which is enhanced upon protonation. A cooperative IMHB effect in 9 and 9H
+ realized by three N(sp3)H···N(sp3) H‐bridges is estimated to be as high as 14.7 and 33.0 kcal mol−1, respectively. It follows that the IMHB effect contributes 18.3 kcal mol−1 to the absolute proton affinity of 9, which is a respectable amount. The basicity of 9 in acetonitrile is estimated to be very high, as evidenced by the corresponding pKa = 28.8. A derivative of 9, N,N′,N″‐tris(3‐dimethylaminopropyl)guani‐dine (10), assumes an even higher superbasic proton affinity of 275 kcal mol−1 due to an additional relaxation effect caused by the methyl groups. The corresponding pKa(MeCN) = 29.4. Copyright © 2002 John Wiley & Sons, Ltd.
Keto–enol tautomerism of β‐ketoamides and characterization of a sterically crowded α‐amido‐β‐ketoamide
Authors: Sung Kuangsen , Wu Ru‐Rong , Sun Shu‐Yi 
Published: October 2002

AbstractAn α‐amido‐β‐ketoamide (1) and two α‐alkyl‐β‐ketoamides (2 and 3) were prepared and characterized, and their keto–enol tautomerism was studied by H/13C NMR spectroscopy. Both α‐alkyl‐β‐ketoamides 2 and 3 are in the keto form in CDCl3, and their enol forms cannot be detected by 1H/13C NMR spectroscopy, whereas the α‐amido‐β‐ketoamide 1 shows both keto and enol forms in CDCl3 with an experimental KE of 0.70 at 298 K. Copyright © 2002 John Wiley & Sons, Ltd.
Thermoresponsive properties of porous poly(N‐isopropylacrylamide) hydrogels prepared in the presence of nanosized silica particles and subsequent acid treatment
Authors: Serizawa Takeshi , Wakita Kazuaki , Kaneko Tatsuo , Akashi Mitsuru 
Published: October 2002

AbstractPorous poly(N‐isopropylacrylamide) hydrogels were prepared by the free‐radical polymerization of its monomer and a suitable crosslinker in the presence of spherical silica particles of different sizes (74 and 1600 nm) and by the subsequent acid extraction of silica. The yields were 81–83%, and the yields were not affected by the silica content. Scanning electron microscopy observations revealed the porous structure of the hydrogels. Porous and nonporous hydrogels showed volume phase transitions from swelling states to deswelling states at approximately 30 °C, as analyzed by the ratio of the diameter of cylinder‐shaped hydrogels to that of the glass tube used for the hydrogel preparation at the corresponding temperature. Deswelling, which was analyzed by rapid changes in the temperature of the aqueous media from 20 to 40 °C, was facilitated by decreased silica particle size and increased silica content. The deswelling rate constant of the hydrogel prepared with 74‐nm silica at 10 v/v % (silica/solvent) was more than 1500 times greater than that of conventional hydrogels. Swelling was similarly analyzed through changes in the temperature from 40 to 20 °C and was independent of the pore structure. The deswelling–swelling cycle was repeatable with reasonable reproducibility. Moreover, the mechanical strength of the porous hydrogels was significantly maintained compared with that of conventional nonporous hydrogels. This method produced thermoresponsive hydrogels of suitable mechanical strength and remarkable deswelling properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4228–4235, 2002
Synthesis and characterization of new organosoluble and gas‐permeable polyimides from bulky substituted pyromellitic dianhydrides
Authors: Kim Yun‐Hi , Ahn Seong‐Kuk , Kim Hyung Sun , Kwon Soon‐Ki 
Published: October 2002

AbstractTwo new pyromellitic dianhydrides, 1,4‐bis(4′‐t‐butylphenyl) pyromellitic dianhydride and 1,4‐bis(4′‐trimethylsilylphenyl) pyromellitic dianhydride, were synthesized via Suzuki coupling, oxidation, and dehydration. A series of new organosoluble polyimides were prepared from the obtained pyromellitic dianhydride and various aromatic diamines by the conventional polycondensation reaction followed by chemical imidization, as well as high‐temperature, one‐step polymerization. The structures of the dianhydrides and polymers were identified with various spectroscopies. The inherent viscosities of the resulting polymers were 0.62–1.89 dL/g. The synthesized polyimides showed good solubility in various organic solvents such as N‐methyl‐2‐pyrrolidinone, N,N‐dimethylacetamide, and p‐chlorophenol. These polymers had glass‐transition temperatures of 230–260 °C. Thermogravimetric analysis showed that all the polymers were stable, with 10% weight losses recorded above 490 °C in nitrogen. The polyimide films had good mechanical properties and high oxygen permselectivity to nitrogen. The oxygen permeability coefficient (P) and the permselectivity of oxygen to nitrogen (P/P) of the films were 13–56 barrer and 3.7–5.5, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4288–4296, 2002
Synthesis of new hydrolyzable polyurethanes from L‐gulonic acid‐derived diols and diisocyanates
Authors: Yamanaka Chiaki , Hashimoto Kazuhiko 
Published: October 2002

AbstractNew polyurethanes with lactone groups in the pendants and main chains were synthesized by the polyaddition of two kinds of L‐gulonolactone‐derived diols (2,3‐O‐isopropylidene‐L‐gulono‐1,4‐lactone and 5,6‐O‐isopropylidene‐L‐gulono‐1,4‐lactone) with hexamethylene diisocyanate and methyl (S)‐2,6‐diisocyanatohexanoate and by the subsequent deprotection of isopropylidene groups. They were hydrolyzed more quickly than the polyurethane derived from methyl β‐D‐glucofuranosidurono‐6,3‐lactone in a phosphate buffer solution, the pH value of which was 8.0, at 27 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4158–4166, 2002
Preparations of regioselectively methylated cellulose acetates and their 1H and 13C NMR spectroscopic analyses
Authors: Karakawa Makoto , Mikawa Yuji , Kamitakahara Hiroshi , Nakatsubo Fumiaki 
Published: October 2002

AbstractSeven possible regioselectively methylated cellulose acetates (RS‐MCAs)—2,3,6‐tri‐O‐methyl cellulose acetate, 3,6‐di‐O‐methyl cellulose acetate, 2,6‐di‐O‐methyl cellulose acetate, 2,3‐di‐O‐methyl cellulose acetate, 6‐O‐methyl cellulose acetate, 3‐O‐methyl cellulose acetate, and 2‐O‐methyl cellulose acetate—were prepared for the first time from chemically synthesized cellulose derivatives obtained by cationic ring‐opening polymerization and then were analyzed by 1H and 13C NMR spectroscopy. The chemical shifts of ring protons and carbons were influenced by substituent groups (methyl or acetyl) and clearly reflected the pattern of substituent distribution in anhydroglucose units. These data may conveniently be used for the determination of the substituent distribution of methyl cellulose. The synthesized RS‐MCAs also may be used for the elucidation of the structure–property relationship. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4167–4179, 2002
Poly(ester urethane)s with polycaprolactone soft segments: A morphological study
Authors: Kloss Juliana , Munaro Marilda , De Souza Gabriel Pinto , Gulmine Joseane Valente , Wang Shu Hui , Zawadzki Sonia , Akcelrud Leni 
Published: October 2002

AbstractTwo series of poly(ester urethane)s were prepared, containing polycaprolactone (PCL) as the soft segment with molecular weights of 530 and 2000. In each series, the soft‐segment/hard‐segment ratio was varied, and the morphological changes were monitored with differential scanning calorimetry, dynamic mechanical thermal analysis, wide‐angle X‐ray scattering, and scanning electron microscopy techniques. The polyurethanes with longer PCL segments retained their crystallinity, whereas those with shorter PCL segments did not. A morphological model is proposed, in which a continuous PCL‐rich matrix contains both PCL crystallites and domains of urethane hard segments. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4117–4130, 2002
Perfluoropolyether alkyl diesters: Structure effects of the alkyl group on the kinetics of the hydrolysis reactions
Authors: Tonelli Claudio , Di Meo Antonella , Barchiesi Emma 
Published: October 2002

AbstractA series of perfluoropolyether bis‐carboxylic esters was synthesized and their hydrolytic stability investigated. Their formula is ROOCCF2O(CF2CF2O)p(CF2O)qCF2COOR, where p/q = 1.07 and p + q = 2.94. The alkyl group, R, varied both in terms of steric hindrance and electron‐withdrawing ability. Kinetic and thermodynamic data were obtained under homogeneous conditions and compared to a fully hydrogenated ester having a closely related structure CH3(CH2)3OOCCH2O(CH2CH2O)nCH2COO(CH2)3CH3, where n̄ = 10.6. Neutral ester hydrolysis (NEH) conditions were selected with methyl ethyl ketone as a solvent and a 3–4:1 water/ester ratio. The course of the reaction was monitored by 19F NMR or 1H NMR (when R = CH3CH2). Results indicated that the hydrolysis of fluorinated esters, with alkyl aliphatic substituents, is governed by steric hindrance of the substituents. Two distinctive kinetic regimes were observed. The first one, at low conversion, was characterized by lower kinetic constants and related to true NEH conditions. The second regime appeared at higher conversion when acidic autocatalysis dictated the reaction behavior. This is the only observed mechanism when esters more sensitive to the hydrolysis are considered. In these cases, polar factors prevail over steric considerations. Finally, all fluorinated esters of the class (I) showed a much higher reactivity than the hydrogenated ester whose hydrolysis took place only in the presence of a strong acidic catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4266–4280, 2002
Effect of introduction mode of hydroxyl functionality on morphology and film properties of cycloaliphatic diepoxide crosslinkable core‐shell latex
Authors: Teng Ganghua , Soucek Mark D. 
Published: October 2002

AbstractThree series of core‐shell hydroxyl‐functionalized latexes were synthesized and then crosslinked with a cycloaliphatic diepoxide. The same amount of hydroxyl functional monomer was added during the core stage, shell stage, or partitioned equally between the core and the shell. The morphology of the latexes was examined with transmission electron microscopy and contact‐angle measurement. The stress‐strain behavior, viscoelastic properties, and water adsorption were evaluated for the latex films as a function of hydroxyl location. The location of hydroxyl groups within latex particles appeared to be dependent on the introduction mode of hydroxyl functional monomers. The introduction of hydroxyl groups during the shell polymerization resulted in a higher crosslinking density but a lower Tukon hardness and tensile properties. Not surprisingly, distribution of hydroxyl groups in both core and shell polymerization provided the lowest water adsorption and impact resistance as well as the highest tensile elongation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4256–4265, 2002
Synthesis and crosslinking of a series of dimeric liquid‐crystalline diglycidylester compounds containing imine groups
Authors: Ribera D. , Mantecón A. , Serra A. 
Published: October 2002

AbstractWe used readily available commercial reagents and well‐known procedures to synthesize a series of aromatic imine mesogenic diglycidylester compounds with dimeric architectures. The compounds obtained were characterized by spectroscopic techniques. Their liquid‐crystalline behavior was examined by differential scanning calorimetry, hot‐stage polarized optical microscopy (POM), and wide‐angle X‐ray scattering (WAXS) and related to the different structures that varied in the length of the central spacer. All the compounds exhibited nematic mesophases with the exception of the dimer with a three‐methylene central spacer that did not reveal liquid‐crystalline character. We investigated the crosslinking of the synthesized compounds and obtained liquid‐crystalline thermosets (LCTs) with several primary aromatic diamines in stoichiometric ratios or a tertiary amine as a catalyst. The curing processes were measured by calorimetry, and the thermal stability of the LCTs was evaluated by thermogravimetry. The ordered character of the LCTs was confirmed by POM and WAXS. Finally, the mechanical characterization of the LCTs obtained was examined by dynamic mechanical thermal analysis. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4344–4356, 2002
Conducting graft copolymers of poly(3‐methylthienyl methacrylate) with pyrrole and thiophene
Authors: Çi̇rpan Ali , Alkan Selmi̇ye , Toppare Levent , Hepuzer Yeşi̇m , Yağci Yusuf 
Published: October 2002

AbstractA thiophene‐functionalized methacrylate monomer (3‐methylthienyl methacrylate) was synthesized via the esterification of 3‐thiophene methanol with methacryloyl chloride. The methacrylate monomer was polymerized by free‐radical polymerization in the presence of azobisisobutyronitrile as the initiator. Graft copolymers of poly(3‐methylthienyl methacrylate) (PMTM2) and polypyrrole and of PMTM2 and polythiophene were synthesized by constant‐potential electrolyses. p‐Toluene sulfonic acid, sodium dodecyl sulfate, and tetrabutylammonium tetrafluoroborate were used as the supporting electrolytes. PMTM2‐coated platinum electrodes were used as anodes in the polymerization of pyrrole and thiophene. Moreover, the oxidative polymerization of poly(3‐methylthienyl methacrylate) (PMTM1) was studied with FeCl3 as the oxidant. The self‐polymerization of PMTM1 was also investigated by galvanostatic electrolysis both in dichloromethane and in propylene carbonate. The structures of PMTM1 and PMTM2 were investigated by several spectroscopic and thermal methods. The grafting process was elucidated with conductivity measurements, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy studies. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4131–4140, 2002