bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and characterization of poly[(vinylidene fluoride)‐co‐hexafluoropropene]–(dibutyl phthalate) blends
Authors: Marigo Antonio , Marega Carla , Bassi Mattia , Fumagalli Massimiliano , Sanguineti Aldo 
Published: August 2002

AbstractBlends of poly[(vinylidene fluoride)‐co‐hexafluoropropene] with dibutyl phthalate were examined by wide‐ and small‐angle X‐ray scattering, differential scanning calorimetry and dynamic mechanical spectroscopy, in order to study the influence of amount of plasticizer and the crystallization rate on the crystallinity and lamellar morphology of the copolymer.The dibutyl phthalate seems, at least for the cooling and heating rates used, simply to dilute the crystalline phase without affecting the amount of polymer that is able to crystallize. Furthermore, the small‐angle X‐ray scattering technique points out that the plasticizer mostly enters the amorphous phase either outside or inside the lamellar stacks.© 2001 Society of Chemical Industry
Water uptake effects in resins based on alkenyl‐modified cyanate ester–bismaleimide blends
Authors: Hamerton I , Herman H , Rees K T , Chaplin A , Shaw S J 
Published: August 2002

AbstractThe analysis of cured resin blends comprising a commercial dicyanate, bismaleimide and a range of novel alkenyl‐substituted cyanates, to determine the chemical effects of long‐term exposure to water, is reported. The cured resin blends underwent accelerated water uptake by immersion at temperatures of 50 °C and 70 °C, for a period of 14–17 months. The presence of about 10–15% (by weight) of alkenyl‐substituted cyanate in the blend leads to a marked reduction in moisture absorption in comparison with the unmodified bismaleimide/cyanate blend containing a comparable amount of bismaleimide. All samples display non‐Fickian diffusion behaviour at both immersion temperatures, although this is most marked at the higher temperature. Thermogravimetric analysis was performed on alkenyl‐modified neat resin samples before and after the immersion period. The modified samples display thermal stabilities that are indistinguishable from cured resins that have not undergone immersion. Spectroscopy (near infrared Raman and mid‐infrared attenuated total reflectance) was performed on cured resin plaques to determine the sample composition as a function of modifier content. The elemental composition of the samples was also determined before and after the immersion period, and no significant variation in elemental composition was recorded for the modified samples.© British Crown Copyright 2001/DERA. Reproduced with the permission of Her Majesty's Stationery Office. Published for the SCI by John Wiley & Sons, Ltd.
Dielectric relaxation spectroscopy of poly(ethylene terephthalate)
Authors: Pratt Graeme J , Smith Michael J A 
Published: August 2002

AbstractContour maps of dielectric loss tangent within the ranges 0.1 Hz to 3 MHz and −175 °C to +190 °C are presented for a commercial poly(ethylene terephthalate) (PET) in two initial states of crystallinity. Individual absorption regions resemble those for poly(butylene terephthalate) and are attributed to carbonyl‐driven α‐ and β‐relaxation processes and to Maxwell–Wagner–Sillars polarizations. Possible causes are considered for the asymmetry and structure apparent in the α‐peak of partially crystalline PET.© 2001 Society of Chemical Industry
2‐Hydroxyethylmethacrylate carrying uniform porous particles: preparation and electron microscopy
Authors: Tuncel A , Tuncel M , Cicek H , Fidanboy O 
Published: August 2002

AbstractUniform macroporous particles carrying hydroxyl groups have been obtained in the size range 3–11.5 µm by seeded polymerization. For this purpose, uniform polystyrene particles in the size range 1.9–6.2 µm were used as seeds. The seed particles were successively swollen by dibutyl phthalate (DBP) and a monomer mixture comprising styrene, 2‐hydroxyethylmethacrylate (HEMA) and a crosslinker. Two different crosslinkers, divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA), were tested. Size distribution properties together with bulk and surface structures of the particles have been characterized by both scanning and transmission electron microscopy. While EGDMA provides uniform particles with a non‐porous surface, DVB produces uniform particles having a highly porous surface and interior. The comparison of FTIR and FTIR‐DRS spectra shows that the HEMA concentration is higher on the particle surface than within the particle interior. Seed latex size and monomer/seed latex ratios are identified as the most important variables affecting the final particles. Different seed latexes have been tried; the result is that highly macroporous particles with a sponge‐like pore structure both on the surface and in the particle interior have been obtained by use of the seed latex with the largest particles and the lowest molecular weight. An increase in the HEMA feed concentration leads to final particles with a non‐porous surface and a crater‐like porosity in the particle interior. The average pore size significantly decreases with increasing DBP/seed latex and monomer/seed latex ratios.© 2001 Society of Chemical Industry
DSC curing study of catalytically synthesized maleic‐acid‐based unsaturated polyesters
Authors: Simitzis J , Zoumpoulakis L , Soulis S 
Published: August 2002

AbstractUnsaturated polyesters were synthesized based on ethylene glycol and maleic acid as unsaturated dicarboxylic acid, using a variety of saturated acids in the initial acid mixture, without or with different catalysts. The curing of the polyesters produced with styrene was studied using differential scanning calorimetry (DSC) under dynamic‐ and isothermal‐heating conditions. The FTIR spectra of the initial polyesters and cured polyesters were also determined. Curing is not complete at the end of DSC scan and the unreacted bonds were quantitatively determined from the FTIR spectra and by estimation based on literature data. The value of the mean degree of conversion (α) of all double bonds (styrene unit and maleate unit) was approximately α = 0.40. Using an appropriate kinetic model for the curing exotherm of polyesters, the activation energy (Ea), the reaction order (x) and the frequency factor (ko) were determined. Because the kinetic parameters (ie Ea, k, x) affect the kinetics in various different ways, the curves of degree of conversion versus time at various isothermal conditions are more useful to compare and characterize the curing of polyesters. The kinetic parameters are mainly influenced by the proportion of maleic acid in the polyesterification reaction mixture and secondarily by the residual polyesterification catalyst. The degree of conversion of already crosslinked polyesters is greatly increased by post‐curing them at elevated temperature and for a prolonged time.© 2002 Society of Chemical Industry
Preparation of silica‐supported late transition metal catalyst and ethylene polymerization
Authors: Ma Zhi , Sun Wen‐Hua , Zhu Ning , Li Zilong , Shao Changxing , Hu Youliang 
Published: August 2002

Abstract A Correction has been published for this article in Polymer International 51(6) 2002, 561The late transition metal catalyst 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron(II) chloride was supported on silica. Fourier transform infrared spectroscopy, scanning electronic micrograph and X‐ray photoelectron spectroscopy measurements were utilized to examine the process of supporting catalyst on silica and investigate the possible mechanism of support. Furthermore, ethylene polymerizations with the supported catalysts were carried out in various conditions such as different reaction temperatures and Al/Fe molar ratios. The results showed that MAO first reacted with the hydroxyl of silica forming SiOAl bonds and then the catalyst was bridged through MAO on the surface of silica. Compared with homogeneous catalysts, the supported catalysts show some decrease in catalyst activity. However, they can show good activity at a lower Al/Fe molar ratio with MAO as co‐catalyst and give rise to higher molecular weight and melting temperature of the polymer. Better morphology of polyethylene was obtained by a supported catalyst than by its corresponding homogeneous catalyst.The late transition metal catalyst 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron(II) chloride was supported on silica. Fourier transform infrared spectroscopy, scanning electronic micrograph and X‐ray photoelectron spectroscopy measurements were utilized to examine the process of supporting catalyst on silica and investigate the possible mechanism of support. Furthermore, ethylene polymerizations with the supported catalysts were carried out in various conditions such as different reaction temperatures and Al/Fe molar ratios. The results showed that MAO first reacted with the hydroxyl of silica forming SiOAl bonds and then the catalyst was bridged through MAO on the surface of silica. Compared with homogeneous catalysts, the supported catalysts show some decrease in catalyst activity. However, they can show good activity at a lower Al/Fe molar ratio with MAO as co‐catalyst and give rise to higher molecular weight and melting temperature of the polymer. Better morphology of polyethylene was obtained by a supported catalyst than by its corresponding homogeneous catalyst.© 2002 Society of Chemical Industry
Thermochemistry of cyclopentadienylidene (c‐C5H4, C2v, 3B1), cyclopentadienyl radical (c‐C5H5•, C2v, 2B1) and 1,3‐cyclopentadiene (c‐C5H6, C2v, 1A1): a theoretical study by the G2M(RCC,MP2) method
Authors: Nguyen Thanh Lam , Le Trung Ngoc , Mebel Alexander M. 
Published: August 2002

AbstractThe thermochemistry of c‐C5H4 (3B1), c‐C5H5• and c‐C5H6 was investigated at the G2M(RCC,MP2) level. The heat of formation (ΔHof,298), ionization potential (IP), electron affinity (EA) and proton affinity (PA) are respectively, 125.1, 204.4, 42.5 and 230.7 kcal mol−1 for c‐C5H4 (3B1), 63.5, 195.2, 44.9 and 197.2 kcal mol−1 for c‐C5H5• and 32.1, 199.9, 26.0 and 195.2 kcal mol−1 for c‐C5H6. The computed values for the last two molecules are in excellent agreement with available experimental data, with the errors of ±1 and ±2 kcal mol−1 for the heat of formation and the other parameters, respectively. In addition, the heat of formation of c‐C5H4•− is evaluated as 82.0 kcal mol−1, about 10 kcal mol−1 higher than the experimental value. This leads to the suggestion that the experimental ΔHof,298(c‐C5H4•−) value needs to be re‐examined. Copyright © 2001 John Wiley & Sons, Ltd.
AM1 and PM3 studies of some thio analogues of pyrimidine bases in the gas and aqueous phases
Authors: Civcir Pervin Ünal 
Published: August 2002

AbstractHeats of formation, entropies, Gibbs free energies, relative tautomerization energies, dipole moments, and ionization potentials for the tautomers of 2‐thiocytosine, 2,4‐dithiouracil and 2,4‐dithiothymine and their 1‐methyl analogues were studied by using semiempirical AM1 and PM3 quantum‐chemical calculations at the SCF level both in the gas phase and in aqueous solution, with full geometry optimization. The COSMO solvation model was employed for aqueous solution calculations. The calculations show that the thiol‐amino tautomer of 2‐thiocytosine is the most stable in the gas phase whereas the thione‐amino tautomer is the most stable in the aqueous phase. For 2,4‐dithiouracil and 2,4‐dithiothymine, dithione tautomers are the most stable in both phases. The results are in good agreement with available experimental and theoretical results. The entropy effect on the Gibbs free energy of the thiopyrimidine bases is very small and has practically no significance for the tautomeric equilibria of thiopyrimidine bases. The enthalpic term is dominant in the determination of the equilibrium constant. Copyright © 2001 John Wiley & Sons, Ltd.
Synthesis and structural analysis of 1,4‐bis[n‐(N,N‐dimethylamino)phenyl]buta‐1,3‐diynes and charge‐transfer complexes with TCNE
Authors: Gonzalo Rodríguez J. , Lafuente Antonio , Martín‐Villamil Rosa , Martínez‐Alcazar M. Paz 
Published: August 2002

Abstractn‐(N,N‐Dimethylamino)phenylethynes were satisfactorily prepared by a Wittig reaction between chloromethylene(triphenyl)phosphine ylide and the appropriate n‐(N,N‐dimethylamino)benzaldehyde, followed by dehydrochlorination with a strong base. The conjugate dimers 1,4‐bis[n‐(N,N‐dimethylamino)phenyl]buta‐1,3‐diyne were obtained by oxidative dimerization with copper(I) chloride. X‐ray molecular structure analysis of the dimer 1,4‐bis[2‐(N,N‐dimethylamino)phenyl]buta‐1,3‐diyne corroborated the resonance contribution of the o‐dimethylamino substituent, which was confirmed in the solid state by the molecular crystalline packing. Both o‐ and p‐(N,N‐dimethylamino) conjugate dimers develop 1:1 charge‐transfer complexes with TCNE and their structure was identified by NMR, IR and UV–visible spectroscopic data. Differential scanning calorimetric analyses of the 1,3‐diynes showed an irreversible transformation to a thermopolymer as a unimolecular reaction. Copyright © 2001 John Wiley & Sons, Ltd.
Particle formation under monomer‐starved conditions in the semibatch emulsion polymerization of styrene. I. Experimental
Authors: Sajjadi S. 
Published: August 2002

AbstractParticle formation and particle growth compete in the course of an emulsion polymerization reaction. Any variation in the rate of particle growth, therefore, will result in an opposite effect on the rate of particle formation. The particle formation in a semibatch emulsion polymerization of styrene under monomer‐starved conditions was studied. The semibatch emulsion polymerization reactions were started by the monomer being fed at a low rate to a reaction vessel containing deionized water, an emulsifier, and an initiator. The number of polymer particles increased with a decreasing monomer feed rate. A much larger number of particles (within 1–2 orders of magnitude) than that generally expected from a conventional batch emulsion polymerization was obtained. The results showed a higher dependence of the number of polymer particles on the emulsifier and initiator concentrations compared with that for a batch emulsion polymerization. The size distribution of the particles was characterized by a positive skewness due to the declining rate of the growth of particles during the nucleation stage. A routine for monomer partitioning among the polymer phase, the aqueous phase, and micelles was developed. The results showed that particle formation most likely occurred under monomer‐starved conditions. A small average radical number was obtained because of the formation of a large number of polymer particles, so the kinetics of the system could be explained by a zero–one system. The particle size distribution of the latexes broadened with time as a result of stochastic broadening associated with zero–one systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3940–3952, 2001
Diblock copolymers, micelles, and shell‐crosslinked nanoparticles containing poly(4‐fluorostyrene): Tools for detailed analyses of nanostructured materials
Authors: Becker Matthew L. , Remsen Edward E. , Wooley Karen L. 
Published: August 2002

AbstractAmphiphilic core–shell nanostructures containing 19F stable isotopic labels located regioselectively within the core domain were prepared by a combination of atom transfer radical polymerization (ATRP), supramolecular assembly, and condensation‐based crosslinking. Homopolymers and diblock copolymers containing 4‐fluorostyrene and methyl acrylate were prepared by ATRP, hydrolyzed, assembled into micelles, and converted into shell‐crosslinked nanoparticles (SCKs) by covalent stabilization of the acrylic acid residues in the shell. The ATRP‐based polymerizations, producing the homopolymers and diblock copolymers, were initiated by (1‐bromoethyl)benzene in the presence of CuBr metal and employed N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the coordinating ligand for controlled polymerizations at 75–90 °C for 1–3 h. Number‐average molecular weights ranged from 2000 to 60,000 Da, and molecular weight distributions, generally less than 1.1 and 1.2, were achieved for the homopolymers and diblock copolymers, respectively. Methyl acrylate conversions as high as 70% were possible, without observable chain–chain coupling reactions or molecular weight distribution broadening, when bromoalkyl‐terminated poly(4‐fluorostyrene) was used as the macroinitiator. Poly(4‐fluorostyrene), incorporated as the second segment in the diblock copolymer synthesis, was initiated from a bromoalkyl‐terminated poly(methyl acrylate) macroinitiator. After hydrolysis of the poly(methyl acrylate) block segments, micelles were formed from the resulting amphiphilic block copolymers in aqueous solutions and were then stabilized by covalent intramicellar crosslinking throughout the poly(acrylic acid) shells to yield SCKs. The SCK nanostructures on solid substrates were visualized by atomic force microscopy and transmission electron microscopy. Dynamic light scattering was used to probe the effects of crosslinking on the resulting hydrodynamic diameters of nanoparticles in aqueous and buffered solutions. The presence of fluorine atoms in the diblock copolymers and resulting SCK nanostructures allowed for characterization by 19F NMR in addition to 1H NMR, 13C NMR, and IR spectroscopy. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4152–4166, 2001
Formation of pore‐filled microfiltration membranes using a combination of modified interfacial polymerization and grafting
Authors: Childs Ronald F. , Weng Junfan , Kim Marcus , Dickson James M. 
Published: August 2002

AbstractA novel method of fabricating pore‐filled membranes has been developed by coating a hydrophobic polyolefinic microfiltration membrane with polyethylenimine (PEI) to produce a chemically active surface. An evaporative coating technique was used to coat the internal surface of a polyolefinic membrane with PEI in chloroform (CHCl3). The coated PEI was then crosslinked by naphthalene‐1,4‐disulfonyl chloride in carbon tetrachloride (CCl4). The incorporation of the PEI coating changed the properties of the base membrane from hydrophobic to relatively hydrophilic; the nitrogens could be titrated, and the coating could not be washed out. 4,4′‐Azo‐bis(4‐cyanovaleryl chloride), a heat‐sensitive radical source, was incorporated into the coated membrane. The coated membrane, with incorporated azo compound, was heated to 75 °C in the presence of acrylic acid, 4‐(vinylpyridine), or styrene to give the corresponding grafted, pore‐filled membranes. The membranes exhibited hydraulic fluxes and pH valve effects consistent with molecular brushes grafted within the pores of the membranes. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 242–250, 2002
Rare‐earth‐catalyzed alternating copolymerization of carbon monoxide with styrene
Authors: Yao Fanglian , Xu Chunjian , Deng Liandong , Bai Yun , Zhang Jianhui , Sun Jingwu 
Published: August 2002

AbstractRare‐earth acetates were used to catalyze the copolymerization reaction of carbon monoxide and styrene. Cupric acetate, 1,10‐phenanthroline, p‐toluenesulfonic acid, and 1,4‐benzoquinone were also added to the catalyst system. The structures of the copolymers obtained were characterized with IR, 1H NMR, 13C NMR, wide‐angle X‐ray diffraction, and elemental analysis methods. The relationship between the catalytic activity and the catalyst composition was studied in detail. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 642–649, 2002; DOI 10.1002/pola.10147
Nylon–selected topics
Authors: Zimmerman Joseph , Kohan Melvin I. 
Published: August 2002

AbstractElements of the technology of nylon fibers and nylon plastics are reviewed. These include the development of equations to quantify the effects of end‐group imbalance and chain‐ending impurities, the kinetics of the polymerization of caprolactam, the solid‐state polymerization of nylon‐66, and the dependence of fiber tensile strength on molecular weight. This is followed by remarks that include comments on the significance of the amidation equilibrium for melt behavior and estimates of the activation energy of viscous flow, the pyrolysis of nylon, the use of the glass‐transition temperature (Tg) to predict the effect of moisture on properties, and the prospect for new nylons. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2565–2570, 2001
Synthesis and optical and electrochemical properties of novel polyethers containing isolated distyrylbenzene derivatives and side‐aromatic 1,3,4‐oxadiazole chromophores
Authors: Chen Yun , Lai Shiao‐Ping 
Published: August 2002

AbstractNew polyethers (P2, P4) with isolated emitting distyrylbenzene derivatives and pendant aromatic 1,3,4‐oxadiazole chromophores have been prepared by the Horner–Wadsworth–Emmons olefination reaction. Polyethers P1 and P3 without oxadiazole groups have also been synthesized for comparison. The reduced viscosities were about 0.20–0.33 dL/g, and the solubility in organic solvents increased with a number of side methoxy or ethoxy substituents in the distyrylbenzene section. Absorption spectra showed two peaks at 371–388 and 304 nm that corresponded to the π‐π* transition of the conjugated distyrylbenzene derivatives and aromatic oxadiazoles, respectively. The band gaps were at 2.76–2.85 eV, which were calculated from onset absorption in the film state. The photoluminescence (PL) maxima were at 459–469 nm, indicating that they are blue‐emitting materials, and the relative PL quantum efficiencies were 0.62–0.77 and 0.23–0.40 in solution and the film state, respectively. Cyclic voltammetric investigations demonstrated that oxadiazole moieties decrease the barrier of electron injection but also retard hole injection. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2571–2580, 2001
New cholesteric liquid‐crystal epoxy resins derived from 6‐hydroxy‐2‐naphthoic acid
Authors: Espinosa M. A. , Cádiz V. , Galià M. 
Published: August 2002

AbstractLiquid‐crystalline epoxy resins were synthesized from 6‐hydroxy‐2‐naphthoic acid, which was used as a mesogenic component, with phenylhydroquinone or isosorbide and via a further reaction with (6‐bromo‐1‐hexyl)glycidylether, which was used as a flexible spacer. In this way, phenylhydroquinone‐bis‐6‐[6‐(glycidyloxy)hexyloxy]2‐naphthoate (Gly A) and isosorbide‐bis‐6‐[6‐(glycidyloxy)hexyloxy]2‐naphthoate (Gly B) were obtained. Nematic elastomers were obtained by the crosslinking of Gly A with 2,4‐diaminotoluene (DAT) and 1,10‐decanedicarboxylic acid (SA). The liquid‐crystalline behavior was investigated with differential scanning calorimetry, polarizing light microscopy, and X‐ray diffractometry. Cholesteric mesophases were produced by the blending of different ratios of Gly A and Gly B, and these blends were then crosslinked with SA to produce nematic mesophases. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2847–2858, 2001