bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multi‐Compartment Unimolecular Micelles from (ABC)n Multi‐Arm Star Triblock Terpolymers
Authors: Stavrouli Nikoletta , Triftaridou Aggeliki I. , Patrickios Costas S. , Tsitsilianis Constantinos 
Published: March 2007

AbstractFour linear and four star equimolar terpolymers based on non‐ionic hydrophilic methoxy hexa(ethylene glycol) methacrylate, ionizable hydrophilic 2‐(dimethylamino)ethyl methacrylate and neutral hydrophobic methyl methacrylate were synthesized using group transfer polymerization and investigated in aqueous dilute solutions. It was found that the (ABC)n multi‐arm star terpolymers formed unimolecular micelles comprising three centrosymmetric compartments. The position of each compartment could be determined by the block sequence (ABC, ACB or BAC) at will. On the other hand, the ABC linear counterparts formed loose associates with very low aggregation numbers. It was shown that the polymer architecture (linear versus star) greatly affected the micellization phenomena of the terpolymers in selective media.magnified image
Microwave‐Assisted Aqueous Polyimidization Using High‐Throughput Techniques
Authors: Dao Buu N. , Groth Andrew M. , Hodgkin Jonathan H. 
Published: March 2007

AbstractHigh‐throughput methodology, as used in pharmaceutical drug discovery, was successfully applied to high performance polyimide development. Using a Biotage® microwave reactor fitted with a flask handling robot and a high‐throughput approach, we have optimized a copolyimide material with high Tg, yet maintaining solution processability. Additionally, the development time for this material has been reduced from months to just weeks. The polyimide was produced using combinations of the monomers 4,4′‐ODA, 6‐FDA and PMDA. The optimal combination was found to be 2:1:1 of 4,4′‐ODA/6‐FDA/PMDA with a molecular weight (MW) of 31 500 and Tg of 347 °C. The resulting polymer can be solution‐cast into strong, flexible membranes for solution and gas phase separations.magnified image
Self‐Assembly of Large Multimolecular Micelles from Hyperbranched Star Copolymers
Authors: Hong Haiyan , Mai Yiyong , Zhou Yongfeng , Yan Deyue , Cui Jun 
Published: March 2007

AbstractThis work focused on the synthesis and aqueous self‐assembly of a series of novel hyperbranched star copolymers with a hyperbranched poly[3‐ethyl‐3‐(hydroxymethyl)oxetane] (HBPO) core and many linear poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) arms. The copolymers can synchronously form unimolecular micelles (around 10 nm) and large multimolecular micelles (around 100 nm) in water at room temperature. TEM measurements have provided direct evidence that the large micelles are a kind of multimicelle aggregates (MMAs) with the basic building units of unimolecular micelles. It is the first demonstration of the self‐assembly mechanism for the large multimolecular micelles generated from the solution self‐assembly of hyperbranched copolymers.magnified image
Direct Metallization of Gold Nanoparticles on a Polystyrene Bead Surface using Cationic Gold Ligands
Authors: Lee Jun‐Ho , Kim Dong Ouk , Song Gyu‐Seok , Lee Youngkwan , Jung Seung‐Boo , Nam Jae‐Do 
Published: March 2007

AbstractGold nanoparticles are formed to cover the surface of sulfonated‐polystyrene (PS) beads by the in‐situ ion‐exchange and chemical reduction of a stable cationic gold ligand, which makes it different from the physical adsorption or multiple electroless metallization methods. PS beads are synthesized by dispersion polymerization with a diameter of 2.7 µm, and their surface is modified by introducing sulfonic acid groups (SO) to give an ion exchange capacity of up to 2.25 mequiv. · g−1, which provides 1.289 × 1010SOper bead. Subsequently, the anionic surface of the PS beads is incorporated with a cationic gold ligand, dichlorophenanthrolinegold(III) chloride ([AuCl2(phen)]Cl), through an electrostatic interaction in the liquid phase to give gold nanoparticles (ca. 1–4 nm in diameter) formed on the PS surface. Assuming that approximately three SOgroups interact with one [AuCl2(phen)]+ion in the ion‐exchange process, the gold coverage on a PS bead is estimated as 12.0 wt.‐%, which compares well with the 16.8 wt.‐% of gold loading measured by inductively coupled plasma–mass spectrometry. Because of the adjustable IEC values of the polymer surface and the in‐situ metallization of Au in the presence of S atoms, both of which are of a soft nature, the developed methodology could provide a simple and controllable route to synthesize a robust metal coating on the polymer bead surface.magnified image
Effect of the Molecular Weight of AB Diblock Copolymers on the Lamellar Orientation in Thin Films: Theory and Experiment
Authors: Potemkin Igor I. , Busch Peter , Smilgies Detlef‐M. , Posselt Dorthe , Papadakis Christine M. 
Published: March 2007

AbstractWe propose a theoretical explanation of the parallel and perpendicular lamellar orientations in free surface films of symmetric polystyrene‐block‐polybutadiene diblock copolymers on silicon substrates (with a native SiOx layer). Two approaches are developed: A correction to the strong segregation theory and a qualitative analysis of the intermediate segregation regime. We show that the perpendicular orientation of the lamellae formed by the molecules of high molecular weight is stabilized by A–B interfacial interactions. They are weaker in the case of the perpendicular orientation of the lamellae, whereas the surface tension coefficient of the A–B interface decreases with the increase of the molecular weight.magnified image
Color Change of Electrospun Polystyrene/MEH‐PPV Fibers from Orange to Yellow through Partial Decomposition of MEH Side Groups
Authors: Chuangchote Surawut , Srikhirin Toemsak , Supaphol Pitt 
Published: March 2007

AbstractThe present contribution reports the electrospinning of PS/MEH‐PPV fibers with average diameters ranging from 0.165 to 1.190 µm from solutions of PS/MEH‐PPV (PS/MEH‐PPV = 7.5:1, w/w) in 1,2‐dichloroethane. With the addition of pyridinium formate (PF), a volatile organic salt, to the PS/MEH‐PPV solution, the electrospinnability of the resulting solution is enhanced significantly. Both the fiber diameters and the number of fibers are found to increase, while the number of beads is found to decrease with increasing applied electrical potential, the addition of PF, and increasing aging period of the spinning solution after PF addition. FT‐IR analysis shows that ≈15% of the MEH side groups are removed from the MEH‐PPV component in the fibers obtained from the solution that is left to age for 1 month after PF addition, which corresponds well to the loss of mass of ≈7% as observed by thermogravimetric analysis. As a result, partial decomposition of the MEH side groups should be responsible for the observed yellow emission color of the PS/MEH‐PPV fibers obtained from the same solution.magnified image
Exploring Microfluidic Routes to Microgels of Biological Polymers
Authors: Zhang Hong , Tumarkin Ethan , Sullan Ruby May A. , Walker Gilbert C. , Kumacheva Eugenia 
Published: March 2007

AbstractPolymer microgels in the size range from several micrometers to hundreds of micrometers are used in the pharmaceutical, cosmetics, nutrition, pesticide, and food industries, as well as in the encapsulation of cells. To date, a broad range of strategies for the generation of polymer microgels exist, however, these methods involve multistage processes, do not utilize biocompatible components or do not allow precise control of the dimensions and internal structure of the microgels. Recently, microfluidic strategies for the production of polymer particles have offered precise control over the shapes, morphologies, and size distributions of polymer colloids. This paper discusses the most recent results obtained by the authors in the area of the microfluidic production of biopolymer microgels. It provides a brief review of the microfluidic methods for the continuous synthesis and fabrication of microgels, sets the criteria for the successful microfluidic generation of biomicrogels, and describes two methods for the preparation of microgels by microfluidic means. The article concludes with a summary and an outlook.magnified image
Novel Acid‐Labile, Thermoresponsive Poly(methacrylamide)s with Pendent Ortho Ester Moieties
Authors: Huang Xiaonan , Du Fusheng , Ju Rong , Li Zichen 
Published: March 2007

AbstractNovel acid‐labile, thermoresponsive methacrylamide‐based (co)polymers with pendent ortho ester groups were prepared by free radical polymerization of N‐(2‐methoxy‐1,3‐dioxan‐5‐yl) methacrylamide (NMM) and N‐(2‐ethoxy‐1,3‐dioxan‐5‐yl)methacrylamide (NEM). These polymers are both thermoresponsive and acid‐sensitive in aqueous solution, which was proved by transmittance measurements, fluorescence, and 1H NMR spectroscopy. The LCSTs of the (co)polymers were shifted to higher temperature by increasing the content of the more hydrophilic NMM units. All of these polymers can be hydrolyzed under acidic condition and the hydrolysis rate increased with the decrease in the pH value.magnified image
Complex Macromolecular Architectures by Reversible Addition Fragmentation Chain Transfer Chemistry: Theory and Practice
Authors: Barner Leonie , Davis Thomas P. , Stenzel Martina H. , Barner‐Kowollik Christopher 
Published: March 2007

AbstractReversible addition–fragmentation chain transfer (RAFT) chemistry can be effectively employed to construct macromolecular architectures of varying topologies. The present article explores the principle design routes to star, block, and comb polymers in the context of theoretical design criteria for the so‐called Z‐ and R‐group approaches. The specific advantages and disadvantages of each approach are underpinned by selected examples generated in the CAMD laboratories. In particular, we demonstrate how the modeling of full molecular weight distributions can be employed to guide the synthetic effort. We further explore the theory and practice of generating amphiphilic block copolymer structures and their self‐assembly. In addition, the article foreshadows how modern synthetic techniques that combine RAFT chemistry with highly orthogonal click chemistry can be employed as a powerful tool that furthers the enhancement of macromolecular design possibilities to generate block (star) copolymers of monomers with extremely disparate reactivities. Finally, the ability of RAFT chemistry to modify the surface of well‐defined nano‐ and microspheres as devices in biomedical application is detailed.magnified image
Kinetic Aspects of RAFT Polymerization
Authors: Vana Philipp 
Published: March 2007

AbstractIn this short review, selected experimental approaches for probing the mechanism and kinetics of RAFT polymerization are highlighted. Methods for studying RAFT polymerization via varying reaction conditions, such as pressure, temperature, and solution properties, are reviewed. A technique for the measurement of the RAFT specific addition and fragmentation reaction rates via combination of pulsed‐laser‐initiated RAFT polymerization and µs‐time‐resolved electron spin resonance (ESR) spectroscopy is detailed. Mechanistic investigations using mass spectrometry are exemplified on dithiobenzoic‐acid‐mediated methyl methacrylate polymerization.
Synthesis of Poly(methyl acrylate) Grafted onto Silica Particles by Z‐supported RAFT Polymerization
Authors: Zhao Youliang , Perrier Sébastien 
Published: March 2007

AbstractRAFT polymerization of methyl acrylate (MA) mediated by silica‐supported 3‐(methoxycarbonyl‐phenyl‐methylsulfanylthiocarbonylsulfanyl) propionic acid (Si‐ MPPA) and 3‐(benzylsulfanylthiocarbonylsulfanyl) propionic acid (Si‐BSPA) was investigated. The molecular weight and polydispersity of grafted polymeric chains and the grafted chain transfer agent (CTA) efficiency (Ge) were strongly dependent on the types and loading of Si‐CTAs and free CTA used in solution. Under similar reaction conditions, the graft polymerization mediated by Si‐MPPA was better controlled than that using Si‐BSPA. The introduction of a free CTA in solution during Si‐MPPA mediated polymerization could significantly decrease the polydispersity of free and grafted polymeric chains and enhance the grafted CTA efficiency, and longer polymeric chains could be grafted onto silica support when Si‐MPPA with a higher CTA loading was used to mediate the polymerization. In all cases, the RAFT polymerization using 2‐(2‐cyanopropyl) dithiobenzoate (CPDB) as a free CTA could afford well‐defined grafted PMA and significantly increased Ge value, while the polymerization rate was also decreased.
Verdazyl‐Mediated Polymerization of Styrene
Authors: Teertstra Steven J. , Chen Eric , Chan‐Seng Delphine , Otieno Peter O. , Hicks Robin G. , Georges Michael K. 
Published: March 2007

AbstractAttempted controlled polymerizations of styrene, conducted in the presence of either 1,3,5‐triphenyl‐6‐oxoverdazyl or 1,5‐dimethyl‐3‐phenyl‐6‐oxoverdazyl radicals initiated with benzoyl peroxide or 1,1′‐azobis(cyclohexanecarbonitrile) were universally unsuccessful regardless of the reaction temperature and the initiator/verdazyl molar ratio. No improvement was observed using a verdazyl‐terminated styrene initiator adduct prepared by an exchange reaction between a styrene‐TEMPO alkoxyamine and a 1,3,5‐triphenyl‐6‐oxoverdazyl radical. However, controlled polymerizations of styrene were achieved at 125 °C using a styrene‐verdazyl adduct containing the 1,5‐dimethyl‐3‐phenyl‐6‐oxoverdazyl radical. Polydispersity indexes remained low throughout the polymerizations and plots of number average molecular weight ($\overline M _{\rm n}$) versus time were linear. However, the actual $\overline M _{\rm n}$ values were considerably lower than theoretical, an unexpected result that is under investigation.
Germanium‐ and Tin‐Catalyzed Living Radical Polymerizations of Styrene and Methacrylates
Authors: Goto Atsushi , Zushi Hirokazu , Hirai Norihiro , Wakada Tsutomu , Kwak Yungwan , Fukuda Takeshi 
Published: March 2007

AbstractSummary: Ge and Sn (non‐transition‐metal) catalyzed living radical polymerizations were developed. Low‐polydispersity (Mw/Mn ∼ 1.1–1.3) polystyrenes, poly(methyl methacrylate)s, poly(glycidyl methacrylate)s, and poly(2‐hydroxyethyl methacrylate) with predicted molecular weights were obtained with a fairly high conversion in a fairly short time. The pseudo‐first‐order activation rate constant kact for the styrene/GeI4 (catalyst) system was large enough, even with a small amount of GeI4, to explain why the system provides low‐polydispersity polymers from an early stage of polymerization. The retardation in the polymerization rate observed for the styrene/GeI4 system was kinetically proved to be mainly due to the cross‐termination between the propagating radical with GeI. Attractive features of the Ge and Sn catalysts include their high reactivity hence small amounts (1–5 mM) being required under a mild condition (at 60–80 °C), high solubility in organic media without ligands, insensitivity to air hence sample preparation being allowed in the air, and minor color and smell. The Ge catalysts may also be attractive for their low toxicity.
Designing Organic/Inorganic Colloids by Heterophase Polymerization
Authors: Bourgeat‐Lami Elodie , Herrera Norma Negrete , Putaux Jean‐Luc , Perro Adeline , Reculusa Stéphane , Ravaine Serge , Duguet Etienne 
Published: March 2007

AbstractPolymer/silica and polymer/Laponite nanocomposite colloids with various morphologies have been elaborated through emulsion polymerization using a polymerizable organosilane (route I) and a methyl methacrylate‐terminated macromonomer (route II) as coupling agents. Depending on the synthetic strategy and on the nature of the mineral particles, either core‐shell, raspberry‐like, multipod‐like, currant bun or inverted core‐shell morphologies (the mineral forming the shell) were achieved. Beyond the control of particle shape, we have demonstrated that some of the polymerizations exhibited particular kinetics behaviors which could be correlated to the mechanism of formation of the composite particles. Interestingly, conversion versus time curves of a series of soap free polymerizations performed in the presence of the macromonomer showed a significant increase in the polymerization rate with increasing the inorganic particles concentration. Characterization of the composite latexes by transmission electron microscopy showed that the mineral was located at the surface of the latex spheres and participated therefore to their stabilization. The higher the amount of inorganic particles, the lower the particles size and the higher the polymerization rate.
Spectral resolution analysis of resonant grating waveguides
Authors: Delmdahl R. F. , Spiecker G. , Bader M. A. , Selle A. 
Published: March 2007

AbstractA high spectral resolution analysis of narrowband reflection filters based on resonant grating waveguide structures is presented. A tunable high‐performance dye laser with ∼0.15 cm‐1 line width and a beam analyzing system consisting of three simultaneously controlled CCD cameras were used to investigate grating waveguide resonances at wavelengths ∼694 nm and ∼633 nm. A reflectivity of 91 % and a line width of ∼0.3 nm were measured and theoretically modeled for a resonant reflection filter specifically designed for the ruby laser wavelength 694.2 nm. A resonance shift of several nanometers was observed for a second grating waveguide structure in the region of the helium‐neon laser emission wavelength 632.8 nm by changing the sample temperature. We discuss the potential of grating waveguide devices combining the narrow line width and the tunability of the resonant response as promising candidates for implementation in innovative concepts for reflection filter and sensor applications.
Broadband proton‐decoupled proton spectra
Authors: Pell Andrew J. , Edden Richard A. E. , Keeler James 
Published: March 2007

AbstractWe present a new method for recording broadband proton‐decoupled proton spectra with absorption mode lineshapes and substantially correct integrals; in both these respects, the new method has significant advantages over conventional J‐spectroscopy. In our approach, the decoupled spectrum is simply obtained from the 45° projection of the diagonal‐peak multiplets of an anti z‐COSY spectrum. This method is straightforward to apply, and does not require any unusual data processing. However, there is a significant reduction in sensitivity when compared to a conventional proton spectrum. The method is demonstrated for typical medium‐sized molecules, and it is also shown how such a decoupled spectrum can be used to advantage in measurements of diffusion constants (DOSY), the measurement of relaxation parameters, and the analysis of complex mixtures. Copyright © 2007 John Wiley & Sons, Ltd.
A quantitative application of the J‐based configuration analysis method to a flexible small molecule
Authors: Sharman Gary J. 
Published: March 2007

AbstractAn example of the use of the J‐based configuration analysis method to determine relative stereochemistry of a small molecule related to reboxetine is described. This study was complicated by the fact that the molecule did not exhibit J‐couplings and NOEs consistent with a single conformation, but rather an ensemble average. A quantitative fitting procedure using predicted couplings and NOEs from all possible conformers was used. This gave a clear indication of the stereochemistry, and the populations of the conformers involved. Copyright © 2007 John Wiley & Sons, Ltd.
Unambiguous NMR spectral assignments of salvinorin A
Authors: Giner José‐Luis , Kiemle David J. , Kutrzeba Lukasz , Zjawiony Jordan 
Published: March 2007

AbstractThe complete assignments of the 1H and 13C NMR spectra of the hallucinogenic neoclerodane diterpenoid salvinorin A were determined in three different NMR solvents using HSQC, HMBC and COSY. Solvent systems are described that allow the resolution of all 1H signals. Virtual coupling was observed for the protons at C‐2, C‐3 and C‐4 in the 600 MHz 1H spectrum in CDCl3. The complete assignments of the 1H and 13C NMR spectra of salvinorin B are also reported. Copyright © 2007 John Wiley & Sons, Ltd.
Optimizing sensitivity and resolution in time‐shared NMR experiments
Authors: Pérez‐Trujillo Miriam , Nolis Pau , Bermel Wolfgang , Parella Teodor 
Published: March 2007

AbstractAn improved approach to optimize the overall sensitivity and the resolution requirements in the indirect dimension of 13C/15N time‐shared (TS) NMR experiments is presented. A different data sampling acquisition procedure is applied for 13C and 15N in the indirect dimension, and a proper data recombination before conventional data processing allows a customized adjustment of spectral widths, number of scans and number of increments individually for 13C and 15N. The major benefit is an important improvement on the detection limits of the TS experiment that overcomes the lower sensitivity of 15N over 13C at natural abundance. We evaluate such enhancements from 2D TS‐HMBC experiments recorded on a nitrogen‐containing synthetic azole derivative of pharmaceutical interest. Copyright © 2007 John Wiley & Sons, Ltd.
Synthesis and structure of some azo coupled cyclic β‐enaminones
Authors: Šimůnek Petr , Lusková Lucie , Svobodová Markéta , Bertolasi Valerio , Lyčka Antonín , Macháček Vladimír 
Published: March 2007

AbstractThe reaction of 3‐phenylaminocyclopent‐2‐en‐1‐one with 4‐methyl, 4‐methoxy and 4‐chlorobenzenediazonium tetrafluoroborates was used to prepare the azo coupling products 3a‐c. It was found that these compounds are present in both CDCl3 solution and solid phase practically exclusively as (E)‐3‐phenylamino‐2‐(4‐subst.phenyldiazenyl)cyclopent‐2‐en‐1‐ones with NH···N intramolecular hydrogen bond. The substitution of the phenyl residue of the diazonium salt has no effect on the position of the tautomeric equilibrium. On the other hand, the compounds 4a, b formed by the reaction of 3‐phenylamino‐1H‐inden‐1‐one with 4‐methylbenzene‐ or benzenediazonium tetrafluoroborates exist in CDCl3 solution and in solid phase as hydrazone compounds. In the solution they occur as a mixture of three forms, out of which two were identified as E/Z isomers with different types of hydrogen bonds. Compound 5 formed by the reaction of 3‐amino‐5,5‐dimethylcyclohex‐2‐en‐1‐one with 4‐methoxybenzenediazonium tetrafluoroborate is converted into a stable hydrochloride 5·HCl on standing in CHCl3 solution; this product exhibits a high degree of delocalization of the positive charge. Its structure was studied by means of X‐ray. Copyright © 2007 John Wiley & Sons, Ltd.
NMR studies of the conformational effect of single and double 3′‐S‐phosphorothiolate substitutions within deoxythymidine trinucleotides
Authors: Jayakumar Hannah K. , Buckingham Joanne L. , Brazier John A. , Berry Neil G. , Cosstick Richard , Fisher Julie 
Published: March 2007

AbstractNMR spectroscopy has been used to investigate the conformational effects of single and two consecutive 3′‐S‐phosphorothiolate modifications within a deoxythymidine trinucleotide. The presence of a single 3′‐phosphorothioate modification shifts the conformation of the sugar ring it is attached to, from a mainly south to north pucker; this effect is also transmitted to the 3′‐neighbour deoxyribose. This transmission is thought to be caused by favourable stacking of the heterocyclic bases. Similar observations have been made previously by this group. When two adjacent modifications are present, the conformations of the attached deoxyribose rings are again shifted almost completely to the north, however, there is no transmission to the 3′ deoxyribose ring. Base proton chemical shift analysis and molecular modelling have been used to aid elucidation of the origin of this feature. The observation for the dimodified sequence is consistent with our previously reported results for a related system in which spaced modifications are more thermodynamically stable than consecutive ones. Copyright © 2007 John Wiley & Sons, Ltd.