bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of well‐defined comb‐like amphiphilic copolymers with protonizable units in the pendent chains: 1. Preparation of narrow polydispersity copolymers of methyl methacrylate and 2‐hydroxyethyl methacrylate by atom‐transfer radical polymerization
Authors: Liu Ping , Jin Lan , Hu Jianhua , Wang Changchun 
Published: February 2004

AbstractWell‐defined methyl methacrylate (MMA) and 2‐(trimethylsiloxy)ethyl methacrylate (Pro‐HEMA) copolymers were prepared by atom‐transfer radical polymerization(ATRP), using CuCl/2,2′‐bipyridine as catalytic system and p‐toluenesulfonyl chloride as initiator. ATRP process of MMA and Pro‐HEMA was monitored by 1H NMR, and the kinetic curves of the MMA/Pro‐HEMA copolymerization were plotted in terms of the 1H NMR data. At low content of Pro‐HEMA in the feed composition, the copolymerization can be well controlled with the molecular weight, polydispersity and the monomer distribution in the copolymer chain. With the increase of Pro‐HEMA content in the feed mixture, the composition of the final copolymer deviates from the composition of the feed mixture gradually, and gradient copolymers of MMA/Pro‐HEMA can be obtained. Through the hydrolysis process, well‐defined copolymers of MMA/HEMA were obtained from poly(MMA/Pro‐HEMA). Copyright © 2003 Society of Chemical Industry
Kinetics of dehydration–polymerization of aspartic acid and synthesis of polyaspartate catalyzed by potassium bisulfate
Authors: Wang Yaquan , Hou Yongjiang , Zhang Jing , Ruan Gang 
Published: February 2004

AbstractThe dehydration–polymerization kinetics of DL‐ and L‐aspartic acid, either in the absence or presence of KHSO4, from 323 to 573 K, was studied by thermogravimetric analysis (TGA), and the synthesis of polyaspartate through the polymerization of L‐aspartic acid was investigated by a thin‐layer polymerization method. The TGA results revealed that the dehydration–polymerization of both type of aspartic acids proceeds in two steps: first, the loss of one water molecule through the reaction of an amino group of one aspartic acid molecule and a hydroxyl group of another aspartic acid molecule, forming amide bonds, and secondly, the loss of another water molecule through the amide hydrogen and another hydroxyl group, leading to the formation of a succinimide ring. The kinetic parameters of the extrapolated onset temperatures of dehydration—the first and the second maxima—were obtained by a method similar to that of Ozawa–Flynn–Wall. The kinetic results indicate that the dehydration of L‐aspartic acid is slightly more difficult than for DL‐aspartic acid, and that the presence of potassium bisulfate effectively catalyzes the dehydration–polymerization of aspartic acid. In the synthesis of polyaspartate, the product with a weight‐average molecular mass (Mw) of 5000 g mol−1 was obtained in the absence of catalyst. However, in the presence of potassium bisulfate, the products obtained had Mws of up to 7000 g mol−1 Copyright © 2003 Society of Chemical Industry
Evaluation of cross‐linking after accelerated photo‐ageing of silicone rubber
Authors: Virlogeux Fabien , Bianchini David , Delor‐Jestin Florence , Baba Mohamed , Lacoste Jacques 
Published: February 2004

AbstractSilicone formulations based on polydimethylsiloxane (PDMS) were investigated by using a number of analytical techniques. Horizontal attenuated total reflectance Fourier‐transform infrared (HATR‐FTIR) spectroscopy studies have confirmed the stability of these materials towards photo‐oxidation. No significant oxygenated products were detected after 5000 h of accelerated photo‐ageing. However, by using thermoporosimetry, hardness measurements and densitometry, an important vulnerability of these formulations towards the cross‐linking reactions provoked by UV visible radiation was identified. Thermoporosimetry, using the solid‐solid cyclohexane transition as a textural probe, was also used to visualize the profile of cross‐linking inside the materials by calculation of the mesh size distribution in successive slices of 40 µm in thickness. Copyright © 2003 Society of Chemical Industry
Surface‐initiated atom transfer radical polymerization (ATRP) of styrene from silica nanoparticles under UV irradiation
Authors: Liu Peng , Tian Jun , Liu Weimin , Xue Qunji 
Published: February 2004

AbstractDiethyldithiocarbamyl‐modified silica nanoparticles were prepared and used as macroinitiator for the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of styrene under UV irradiation. Well‐defined polymer chains were grown from the nanoparticle surfaces to yield particles composed of a silica core and a well‐defined, densely grafted outer PS layer with a mass ratio of styrene to silica, or percentage grafting, of 276.3% after an UV irradiation time of 5 h. Copyright © 2004 Society of Chemical Industry
Influence of the conformational order of glassy isotactic polypropylene on its crystallization and melting behaviour
Authors: Chen Liang , Wang Yanping , Zhu Xinyuan , Yan Deyue 
Published: February 2004

AbstractThe influence of conformational order of glassy isotactic polypropylene (iPP) on its crystallization and melting behaviour was studied by wide‐angle X‐ray diffraction (WAXD), Fourier‐transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The glassy iPP samples with various conformational orders were prepared by freeze‐drying procedure from very dilute solution. WAXD and FTIR results suggest that although freeze‐dried samples are non‐crystalline, their conformational order is rather high and increases with decreasing concentration of parent solutions. With increasing conformational order of glassy samples, the cold crystallization peak shifts to lower temperature, indicating acceleration of crystallization. At low fusion temperature, the conformational order of melt obtained from freeze‐dried samples is high so that the relaxation time of single‐ and pauci‐chains to re‐entangle is long and the interpenetration between single‐ and pauci‐chain collective particles is slow. However, at high fusion temperature, the interpenetration process can be completed very quickly. Copyright © 2004 Society of Chemical Industry
Adsorption of VO2+ by poly[(tetrafluoroethylene)‐co‐(perfluorovinyl ether)] copolymer grafted with acrylic acid using γ‐irradiation
Authors: El‐Sawy Naeem M 
Published: February 2004

AbstractGrafted films were prepared by the reaction of acrylic acid (AAc) onto poly[(tetrafluoroethylene)‐co‐(perfluorovinyl ether)] copolymer (PFA) using γ‐irradiation by the mutual technique. The grafted copolymer was complexed with the vanadyl group, VO2+, in aqueous solution. The grafted copolymer–metal complexes were examined by infrared and ultraviolet spectrometry, energy‐dispersive spectroscopy (EDS) and X‐ray diffraction (XRD). The amount of vanadium in the grafted films was estimated using EDS. The thermal stability of the films was investigated through thermogravimetric and differential scanning calorimetry measurements. The degree of crystallinity of the grafted and complexed films decreased by treatment with VO2+ ions and also by heating at 300 °C. When heated at a temperature above 300 °C, the grafted chains degraded till they disappeared and the original polymer was almost completely separated. XRD investigation revealed that the metal oxide may be formed as a separate phase with subsequent decrease in the crystallinity of the copolymer. Furthermore, scanning electron microscope (SEM) investigation of the grafted and modified films, both unheated and heated (300 °C), showed changes in the structure and morphology. The tendency of the graft copolymer to adsorb and/or bind to VO2+ from aqueous solution is of promising use in the field of waste treatment of rare metals in the environment. Copyright © 2004 Society of Chemical Industry
Synthesis and characterization of novel optically active poly(imide–urethane)s derived from N,N′‐(pyromellitoyl)‐bis‐(L‐leucine) diisocyanate and aromatic diols
Authors: Mallakpour Shadpour , Shahmohammadi Mohammad Hassan 
Published: February 2004

AbstractN,N′‐(Pyromellitoyl)‐bis‐(L‐leucine) diacid was reacted with ethyl chloroformate in the presence of triethylamine followed by reaction with activated sodium azide and gave N,N′‐(pyromellitoyl)‐bis‐(L‐leucine) diacylazide in high yield. This diacylazide was heated in dry benzene and gave the unstable N,N′‐(pyromellitoyl)‐bis‐(L‐leucine) diisocyanate (5) in quantitative yield. Thus, diisocyanate 5 was generated in situ and polycondensation reaction of this monomer with several aromatic diols, such as 4,4′‐dihydroxybiphenyl, 1,4‐hydroquinone, bisphenol A, phenolphthalein and 1,4‐dihydroxyanthraquinone, was performed in dry toluene under refluxing in the presence of 1,4‐diazabicyclo[2.2.2]octane (triethylenediamine) as a catalyst. The polymerization reactions proceeded within 48 h, producing a series of optically active poly(imide–urethane)s with good yield and moderate inherent viscosity in the range 0.18–0.28 dl g−1. All of the above polymers were fully characterized by infrared spectra, elemental analyses and specific rotation. Some structural characterization and physical properties of these optically active poly(imide–urethane)s are reported Copyright © 2003 Society of Chemical Industry
Polysiloxanes containing crosslinkable diacetylene units in the main chain
Authors: Boileau Sylvie , Bouteiller Laurent , Kowalewska Anna 
Published: February 2004

AbstractThe oxidative coupling of telechelic [2‐(propyn‐1)oxyethyl]oxypropyl‐terminated polydimethylsiloxanes, with the use of copper (I) chloride/TMEDA complex as the coupling catalyst, is described. The results of the studies on the influence of the reaction parameters (the catalyst concentration, the oxygen flow‐rate and the nature of the solvent) are presented. UV curing of the polymers obtained in the course of the oxidative coupling is reported Copyright © 2003 Society of Chemical Industry
Optical properties of plasticized polycarbonate
Authors: Suvorova Anna I , Tchirkova Elena I 
Published: February 2004

AbstractOptical properties of polycarbonate plasticized by pentaerythritol tris(1,1,2,3,3,3‐hexafluoropropyl) ether (HFP), diheptadecyl‐o‐phthalate and pentaerythrityl tetrabenzoate (TBP) have been determined at wavelengths from 300 to 700 nm. X‐ray diffraction analysis, which was used to examine the polymer structure, showed that all the plasticized systems were amorphous. HFP and, especially, TBP impeded crystallization of the polymer. Plasticized polycarbonate films remained transparent over long periods of time even if they were heated at a temperature higher than the polymer glass transition temperature.© 2003 Society of Chemical Industry
New liquid‐crystalline poly(ester amide)s: The role of nitro groups in the phase behavior
Authors: Sandhya K. Y. , Pillai C. K. S. , Sree Kumar K. 
Published: February 2004

AbstractNew hydrogen‐bonded liquid‐crystalline poly(ester amide)s (PEA)s were obtained from 1,4‐terephthaloyl[bis‐(3‐nitro‐N‐anthranilic acid)] (5) or 1,4‐terephthaloyl[bis‐(N‐anthranilic acid)] (6), with or without nitro groups, respectively, through the separate condensation of each with hydroquinone or dihydroxynaphthalene. The dicarboxylic monomers were synthesized from 2‐aminobenzoic acid. The phase behavior of the monomers and polymers were studied with differential scanning calorimetry, polarized light microscopy, and wide‐angle X‐ray diffraction methods. Monomer 5, containing nitro groups, exhibited a smectic liquid‐crystalline phase, whereas the texture of monomer 6 without nitro groups appeared to be nematic. The PEAs containing nitro groups exhibited polymorphism (smectic and nematic), whereas those without nitro groups exhibited only one phase transition (a nematic threaded texture). The changes occurring in the phase behavior of the polymers were explained by the introduction of nitro groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1289–1298, 2004
Extension of the chain‐end, free‐volume theory for predicting glass temperature as a function of conversion in hyperbranched polymers obtained through one‐pot approaches
Authors: Liu Hewen , Wilén Carl‐Eric 
Published: February 2004

AbstractCompared with linear polymers, more factors may affect the glass‐transition temperature (Tg) of a hyperbranched structure, for instance, the contents of end groups, the chemical properties of end groups, branching junctions, and the compactness of a hyperbranched structure. Tg's decrease with increasing content of end‐group free volumes, whereas they increase with increasing polarity of end groups, junction density, or compactness of a hyperbranched structure. However, end‐group free volumes are often a prevailing factor according to the literature. In this work, chain‐end, free‐volume theory was extended for predicting the relations of Tg to conversion (X) and molecular weight (M) in hyperbranched polymers obtained through one‐pot approaches of either polycondensation or self‐condensing vinyl polymerization. The theoretical relations of polymerization degrees to monomer conversions in developing processes of hyperbranched structures reported in the literature were applied in the extended model, and some interesting results were obtained. Tg's of hyperbranched polymers showed a nonlinear relation to reciprocal molecular weight, which differed from the linear relation observed in linear polymers. Tg values decreased with increasing molecular weight in the low‐molecular‐weight range; however, they increased with increasing molecular weight in the high‐molecular‐weight range. Tg values decreased with increasing log M and then turned to a constant value in the high‐molecular‐weight range. The plot of Tg versus 1/M or log M for hyperbranched polymers may exhibit intersecting straight‐line behaviors. The intersection or transition does not result from entanglements that account for such intersections in linear polymers but from a nonlinear feature in hyperbranched polymers according to chain‐end, free‐volume theory. However, the conclusions obtained in this work cannot be extended to dendrimers because after the third generation, the end‐group extents of a dendrimer decrease with molecular weight. Thus, it is very possible for a dendrimer that Tg increases with 1/M before the third generation; however, it decreases with 1/M after the third generation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1235–1242, 2004
Ionomers based on copolymers of alkyl methacrylates with 2‐methacryloylamino‐3‐naphthalene carboxylic acid: Association in solutions studied by steady‐state and time‐resolved fluorescence
Authors: Výprachtický Drahomír , Cimrová Vĕra , Yang Yu , Mikeš František 
Published: February 2004

AbstractMethyl, butyl, and octadecyl methacrylate copolymers with 3‐methacryloylamino‐2‐naphthoic acid (MANA) carrying alkali counterions exhibit two emission bands in highly dilute dioxane, heptane, and toluene solutions. One band (α) has a maximum around 400 nm, and the other (β) has a maximum around 500 nm. The ratio of the intensity of the α band to the intensity of the β band depends on the counterion (Na+, Li+, and Cs+) and the solvent. Varying the MANA content of the copolymer with Na+ counterions increases the relative intensity of the α emission in proportion to the density of MANA residues in the ionomer chain, whereas in chains containing only 0.1% MANA residues, only a β emission can be seen. The α emission is due to associated ion pairs, and the β emission is due to unassociated ion pairs. The shorter the alkyl chain pendant is of the copolymer, the larger the fraction is of the associated ion pairs. The half‐bandwidth of the β emission is much larger than that of the α‐emission band in all cases. The half‐bandwidth decreases in the order Li+ > Na+ > Cs+. The fluorescence anisotropy decays for the α‐ and β‐emission bands are double‐exponential. The longer rotational correlation time and its fractional contribution to the β emission increase with an increasing content of the MANA monomer in the copolymer. The decay anisotropy data are consistent with the shell–core model of ionomers in nonpolar solvents. The fluorescence anisotropy decay of the copolymer of butyl methacrylate with a low content of the nonneutralized MANA (∼ 0.1 mol %) is single‐exponential, and the rotational correlation time of the MANA fluorophore is eight times longer than that of 3‐acetyl‐2‐naphthoic acid methyl ester (0.3 ns) in the same solvent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1243–1254, 2004
Synthesis of an 8‐Benzyl‐4‐(p‐substituted‐benzyl)‐1,4,8‐triazaspiro[4.5]decan‐2‐one Library on SynPhase TMLanterns
Authors: Feliu Lidia , Martinez Jean , Amblard Muriel 
Published: February 2004

AbstractBased on a spiropiperidine motif, a 120 discrete compound library with the general structure 8‐benzyl‐4‐(p‐substituted‐benzyl)‐1,4,8‐triazaspiro[4.5]decan‐2‐one (5) was prepared on SynPhaseTM Lanterns. The spiroimidazolidinone system was formed in one step from N‐benzyl‐4‐piperidone and amino acid amides attached to the solid support through their Nα‐amino group.
A Combination of Different Spectroscopic Techniques to Monitor the “in situ” Solid‐phase Synthesis of Organic Molecules
Authors: Cironi Pablo , Álvarez Mercedes , Albericio Fernando 
Published: February 2004

AbstractThe efficacy, limitations and scope of different spectroscopic techniques to monitor solid‐phase syntheses are discussed. The total solid‐phase synthesis of a natural product derivative, 3,17‐di‐O‐acetyllamellarin U, has been monitored by gel‐phase NMR and HR‐MAS NMR as appropriate. FT‐IR and colorimetric tests also proved to be valuable tools for monitoring the progress of reactions. While the data obtained by FT‐IR provided valuable information on some functional groups, the NMR data provided more specific structural information that allowed the progress of reactions to be monitored. After several reaction steps the “aging” of the resin only allowed the product covalently anchored to the resin to be investigated using an HR‐MAS probe, a situation that severely limited the depth of analysis available.
CoMFA/CoMSIA/HQSAR and Docking Study of the Binding Mode of Selective Cyclooxygenase (COX‐2) Inhibitors
Authors: Chen Haifeng , Li Qiang , Yao Xiaojun , Fan BoTao , Yuan Shengang , Panaye A. , Doucet J. P. 
Published: February 2004

AbstractThe intermolecular interaction between four types of anti‐inflammatory inhibitors (oxazoles, pyrazoles, pyrroles and imidazoles) and COX‐2 receptor was studied. The results of docking suggest that they have similar interaction mechanism. The most active compounds of these four types of inhibitors could both form several hydrogen bonds with residues His90, Arg513, Leu352 and Arg120, and develop hydrophobic interaction with residues Phe518, Leu352 and Leu359. This is consistent with the investigation reported by R. G. Kurumbail et al. (Nature. 1996, 384, 644‐648). A common 3D‐QSAR model could be constructed with these four categories of COX‐2 inhibitors using the method of docking‐ guided conformer selection. The cross‐validated q2 values are found as 0.741 and 0.632 for CoMFA and CoMSIA respectively. And the non‐cross‐validated r2 values are 0.887 and 0.885. 54 inhibitors constitute the test set used to validate the model. The results show that this model possesses good predictive ability for diverse COX‐2 inhibitors. Furthermore, a HQSAR model was used to evaluate the influence of substituents on anti‐inflammatory activity. Compared with the results of previous works, our model possesses significantly better prediction ability. It could help us to well understand the interaction mechanism between inhibitors and COX‐2 receptor, and to make quantitative prediction of their inhibitory activities.
Classical QSAR Modeling of HIV‐1 Reverse Transcriptase Inhibitor 2‐Amino‐6‐arylsulfonylbenzonitriles and Congeners
Authors: Leonard J. Thomas , Roy Kunal 
Published: February 2004

AbstractConsidering the recent interests in the development of novel and potent non‐nucleoside reverse transcriptase inhibitors for the treatment of HIV‐1 infection, anti‐HIV‐1 activity (assayed in MT‐4 cell line) and HIV‐1 reverse transcriptase (RT) binding affinity of 2‐amino‐6‐arylsulfonylbenzonitriles and their thio and sulfinyl congeners (Chanet al., J. Med. Chem.,2001,44, 1866–1882) have been modeled using classical Quantitative Structure‐Activity Relationship (QSAR) tools in an attempt to explore the quantitative contribution pattern of different substituents in the aryl ring to the activities. Different physico‐chemical parameters like hydrophobicity (π), electronic (Hammett σ) and steric (molar refractivityMR) terms have been used along with appropriate indicator and/or integer variables to develop linear free energy related (LFER) model. Additionally, electrostatic potential point charges at different common atoms of the molecules calculated from AM1 optimized energy minimized geometry have also been tried as predictor variables. The models generated were of acceptable statistical quality and predictive potential. The results show that for both response variables, presence of sulfone moiety contributes significantly to the activities. Further, molar refractivity ofmetasubstituents plays a significant role in both the cases: secondmetasubstituents potentiate the activities probably due to enhanced binding (presumably through dispersion interaction) of the ligand with the binding site. Again, presence ofmeta‐trifluoromethyl group at the aryl ring is detrimental for both the activities. Additionally, the anti‐HIV‐1 model shows negative contribution of the steric parameter ofparasubstituents and positive contribution of theortho‐methoxy group.
COREPA‐M: A Multi‐Dimensional Formulation of COREPA
Authors: Mekenyan Ovanes , Nikolova Nina , Schmieder Patricia , Veith Gilman 
Published: February 2004

AbstractRecently, the COmmon REactivity PAttern (COREPA) approach was developed as a probabilistic classification method which was formalized specifically to advance mechanistic QSAR development by addressing the impact of molecular flexibility on stereoelectronic properties of chemicals. In the initial version of COREPA, the probability distributions for only one stereoelectronic parameter at a time were analyzed for the series of chemicals under analysis. To go beyond considering probability distributions of one parameter at a time requires the capability of analyzing a suite of parameters simultaneously for each chemical. This work creates that capability for a multi‐dimensional formulation of the COREPA which is expected to enhance the reliability of the method to discriminate complex patterns. Using probability distance measures such as Kullback‐Leibler divergence and Hellinger distance, the set of parameters are defined that best discriminate activity. The COREPA‐M system automatically identifies the parameters that best discriminates chemicals in groups defined by comparable reactivity endpoints. A detailed Bayesian decision tree is then used for classifying untested chemicals with measures of “goodness of fit” criteria. COREPA‐M is illustrated using the example of modelling binding affinity of chemicals at the aryl hydrocarbon receptor.
Optimization of a Pharmacophore‐based Correlation Vector Descriptor for Similarity Searching
Authors: Fechner Uli , Schneider Gisbert 
Published: February 2004

AbstractThe usefulness of a correlation‐vector based, topological pharmacophore descriptor for similarity searching was examined in matters of three different scaling methods and a fuzzy binning scheme. “Retrospective screening” using twelve different datasets was performed to evaluate the influence of these parameters by means of the enrichment factor. Significant enrichment of active compounds was yielded in this study. Whereas the application of the fuzzy binning scheme did not substantially influence the enrichment factor, we observed significant higher enrichment for individual ligand families with the employment of a specific descriptor scaling method. These results indicate that optimization of individual critical parameters of a well‐established descriptor may be crucial for improved performance in similarity searching and focused library design.