bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regio‐ and Stereochemistry in Propylene Polymerization Catalyzed with Bis(phenoxy‐imine) Zr and Hf Complexes/MAO Systems
Authors: Makio Haruyuki , Tohi Yasushi , Saito Junji , Onda Mitsuhiko , Fujita Terunori 
Published: October 2003

AbstractEnd‐group analyses of the oligo‐ and polypropylenes produced with bis(phenoxy‐imine) Zr and Hf complexes with methylaluminoxane (MAO) indicate that the polymerization is initiated by two consecutive 1,2‐insertions and is terminated by a β‐H transfer following a 2,1‐insertion. Our data indicate that chain propagation occurs with prevailing 1,2‐regiochemistry but with considerable regioerrors, and with virtually no stereoselectivity.The polymerization of propylene mediated by bis(phenoxy‐imine) Zr and Hf complexes with MAO.magnified imageThe polymerization of propylene mediated by bis(phenoxy‐imine) Zr and Hf complexes with MAO.
New Microphase‐Separated Diblock Copolymers Carrying Semifluorinated Side Groups Prepared by ROMP
Authors: Wewerka Karin , Wewerka Alf , Stelzer Franz , Gallot Bernard , Andruzzi Luisa , Galli Giancarlo 
Published: October 2003

AbstractWe prepared new varied diblock copolymers by ring‐opening metathesis polymerization of functionalized norbornenes and cyclooctene in the presence of Schrock‐type initiators, either [Mo(CHCMe2Ph)(N‐2,6‐iPr2Ph)(OCCH3(CF3)2)2] or [Mo(CHCMe2Ph)(N‐2,6‐iPr2Ph)(OC(CH3)3)2]. The block copolymers were microphase separated and presented the individual phases of each polymer block constituent, that were amorphous/amorphous, amorphous/semicrystalline, or semicrystalline/liquid‐crystalline. One example of such a block copolymer is shown.
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Heterogenization of a Modified Grubbs–Hoveyda Catalyst on a ROMP‐Derived Monolithic Support
Authors: Krause Jens O. , Lubbad Said H. , Nuyken Oskar , Buchmeiser Michael R. 
Published: October 2003

AbstractA ring‐opening metathesis polymerization‐ (ROMP‐) based monolith was synthesized using a Grubbs' first generation catalyst. The living termini were used for surface grafting of norborn‐5‐ene‐2‐ylmethyl hexafluoroglutarate. The free carboxylic acid groups of the graft polymer were converted into the corresponding silver salt and reacted with the Grubbs–Hoveyda catalyst [RuCl2(CH(2‐iPrO)C6H4)(IMesH2)] (IMesH2 = 1,3‐bis(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene) to yield a stable heterogeneous version of this catalyst for use in ring‐closing metathesis (RCM) under continuous flow conditions.The monolith‐supported Grubbs–Hoveyda catalyst.magnified imageThe monolith‐supported Grubbs–Hoveyda catalyst.
α,ω‐Nitroxide‐Capped Polystyrenes and Poly(butyl acrylate)s as Macroinitiators for the Free‐Radical Polymerization of Methyl Methacrylate
Authors: Bothe Marc , Schmidt‐Naake Gudrun 
Published: October 2003

AbstractThe use of a bisaminooxy compound as initiator for nitroxide‐mediated radical polymerization (NMRP) of styrene or n‐butyl acrylate allows the synthesis of α,ω‐nitroxide‐capped polymers. At high temperatures and with the addition of acetic anhydride, it was found that these polymers could be applied as macroinitiators in the free‐radical polymerization of methyl methacrylate. This enables the synthesis of block copolymers with only minor contents of homopolymer.The structure of bis‐TIPNO, the bisaminooxy compound used as an initiator for the nitroxide‐mediated radical polymerization of styrene or n‐butyl acrylate.magnified imageThe structure of bis‐TIPNO, the bisaminooxy compound used as an initiator for the nitroxide‐mediated radical polymerization of styrene or n‐butyl acrylate.
Shape persistence as a concept in the design of macromolecular architectures
Authors: Wegner Gerhard 
Published: October 2003

AbstractShape persistent macromolecules are objects defined by a time independent overall shape. In most cases such macromolecular objects are characterized by an exterior surface structure and an internal architecture giving coherence to the shape and topology. Shape persistent macromolecules are essential to the development of a polymer based nanotechnology and serve as constitutive units of larger scale architectures either via self‐organization or via processes in which they are assembled to give constructs of nanoscale defined patterns.
Dendritic macromolecules at the interface of nanoscience and nanotechnology
Authors: Fréchet Jean M.J. 
Published: October 2003

AbstractAs a result of their unique architecture and structural as well as functional versatility, dendrimers have generated considerable interest in numerous areas of the physical sciences, engineering, as well as the biological sciences. Both their size ‐ in the 1‐10 nm range ‐ and their globular shape resemble those of many proteins suggesting a host of biomimetic and nanotechnological applications. This brief highlight describes some of our recent work with nascent applications of dendrimers as unimolecular nanoreactors, as nanoscale antennae for energy harvesting and transduction, and as nanosized carriers for diagnostic or therapeutic applications. While implementation of some of these applications may still be distant, the impatient critic might remember that new markets are not created overnight as demonstrated by the slow commercial acceptance of many promising molecules and technologies with development frequently extending decades after their initial discovery.
The influence of hydrogen bonds on the globular structure of HP‐copolymers
Authors: Kriksin Yury , Khalatur Pavel , Khokhlov Alexei 
Published: October 2003

AbstractWe present the results of computer modeling of coil‐globule transition of HP‐copolymer which can form hydrogen bonds between some specific monomer units (hydrogen bond units). Langevin dynamics approach is used for the simulation of coil‐globule transition. We study the influence of the number and distribution of hydrogen bond units along primary sequence on the formation of globular conformations.
Polymer modeling: where has it been and where is it going?
Authors: Rigby David , Eichinger B.E. 
Published: October 2003

AbstractThe development of the area of polymer modeling often referred to as molecular modeling has been reviewed from its early beginnings to the present day. Key forces influencing the development include computational power, algorithmic advances and access to computational resources. The desire to apply modeling techniques to predict the properties of increasingly complex polymer‐containing systems, taken in conjunction with a number of current limitations discussed in this brief review, is expected to define in part some essential future developments.
Polymer concepts in microscopically‐viewed phase transition behavior of crystalline polymers
Authors: Tashiro Kohji , Yoshioka Yayoi , Hama Hisakatsu , Yoshioka Akiko 
Published: October 2003

AbstractStructural evolution process in crystalline phase transition, isothermal crystallization from melt and solvent‐induced crystallization has been investigated for crystalline polymers on the basis of the time and/or temperature dependence of small‐angle X‐ray scattering (SAXS), wide‐angle X‐ray scattering (WAXS) and infrared/Raman spectra. As examples of isothermal crystallization study, polyethylene and polyoxymethylene were investigated. As for polyoxymethylene, the time‐resolved infrared spectral measurement clarified the appearance of infrared bands characteristic of folded chain crystal (FCC) in the early stage of crystallization process, followed by the detection of infrared bands characteristic of extended chain crystal (ECC) in a later stage. From the time‐resolved SAXS measurement, the stacked lamellar structure of ca. 14 nm long period was detected at first and it was followed by an appearance of the new lamellae in the amorphous region sandwiched between the original lamellae, resulting in the tightly stacked lamellar structure of 7 nm long period. The timing of detecting the SAXS 14 nm peak was almost the same with the observation of infrared FCC bands and the SAXS 7 nm peak with the infrared ECC band. This correspondency allowed us to speculate that some chains bridging several lamellae became fully extended when the new lamellae were formed in the amorphous region sandwiched between the original lamellae. As a result the ECC‐like structural parts were formed, giving the ECC infrared bands. As other examples, the Brill transition of aliphatic nylons and the solvent‐induced crystallization of syndiotactic polystyrene have been reviewed.
Competing short‐range and long‐range interactions in block copolymers: a role of connectivity in polymer science
Authors: Hashimoto T. , Yamauchi K. , Yamaguchi D. , Hasegawa H. 
Published: October 2003

AbstractWe explored a role of connectivity in polymer science by using two model systems: mixtures of two lamella‐forming block copolymers with short and long chain lengths and triblock terpolymers of polyisoprene‐block‐polystyrene‐block‐poly(vinyl methyl ether). These two systems commonly have enriched competitions or interplays of short‐range segmental interactions and long‐range interactions arising from connectivity between block chains and their packing in the respective domains. The enriched interplays were found to give an intriguing cosurfactant effect for the block copolymer mixtures and interesting two‐step microphase transitions for the triblcock terpolymers.
New developments and directions in the area of elastomers and rubberlike elasticity
Authors: Mark J.E. 
Published: October 2003

AbstractThere are number of important developments in the area of elastomeric polymers, including (i) network chains of controlled stiffness, (ii) model elastomers (including dangling‐chain networks), (iii) fluorosiloxane elastomers, (iv) new thermoplastic elastomers, (v) other new elastomers, (v) bimodal network chain‐length distributions, (vi) cross linking in solution or in a state of deformation, and (vii) gel collapse. Interesting elastomeric composites include those with (i) in‐situ generated ceramic‐like particles, (ii) ellipsoidal fillers, (iii) clay‐like layered fillers, (iv) polyhedral oligomeric silsesquioxane (POSS) particles, (v) porous fillers, (vi) elastomeric domains modifying ceramics, and (vii) controlled interfaces. New characterization techniques are being developed for elastomers, and there have been new developments in elasticity theory and in elastomer processing. Some examples of societal aspects of relevance are (i) synthesis of elastomers in environmentally‐friendly solvents, (ii) biosynthesis, (iii), recyclability, (iv) improved adhesion to tire cords, and (v) better barrier properties in anti‐terrorism clothing. Educational topics include curriculum development, and mobile laboratories for elastomer experiments and demonstrations.
Supramolecular aspects of polymer science: a challenge for solid state NMR
Authors: Spiess Hans Wolfgang 
Published: October 2003

AbstractRecent developments in structural elucidation of supramolecular systems by advanced solid state NMR are described. Special emphasis is placed on hydrogen‐bonded sytems and columnar stacks of aromatic moieties. In imidazole‐based proton conductores spatially separated regions of high and low mobility are identified. In stacks of alkyl‐substituted hexabenzocoronenes maximum charge carrier mobility is observed for crystal‐like stacking of the discs.
Watching macromolecules diffuse at surfaces and under confinement
Authors: Granick Steve , Zhao Jiang , Feng Xie Anne , Bae Sung Chul 
Published: October 2003

AbstractAt the single‐molecule level, this laboratory has been making direct measurements of polymer diffusion at and near surfaces. Parameters of special interest have been to understand (a) the role of molecular weight, N; (b) the role of surface coverage, which may range from dilute to saturated, and (c) the role of the surface, which may range from hard (a silicon wafer) to soft (a supported lipid bilayer), and (d) the use of external fields to direct the transport of small molecules through narrow surface channels that are one macromolecule thick.
Surface mobility in monodisperse polystyrene films
Authors: Kajiyama Tisato , Kawaguchi Daisuke , Tanaka Keiji 
Published: October 2003

AbstractSurface dynamics in monodisperse polystyrene films was examined by lateral force microscopy in conjunction with dynamic secondary ion mass spectroscopy. Glass transition temperature, Tg, at the surface was markedly lower than the corresponding bulk Tg. Also, it was shown that polymer chains present at the surface could diffuse even at a temperature below the bulk Tg. The surface depth, in which molecular motion was activated, was of the order of 5 nm.
Nanostructures formed by combination of nanotube and polymer chain
Authors: Ito Kohzo , Shimomura Takeshi , Okumura Yasushi 
Published: October 2003

AbstractWe have investigated polymeric supramolecular systems of inclusion complexes between molecular nanotube and polymer chains theoretically and experimentally. This system indicates inclusion‐dissociation behavior much sharper than the inclusion complex between cyclic molecule and small compounds. And we propose some functional supramolecules utilizing the combination of the nanotube or nanoring and polymer chains such as insulated molecular wire and topological gel.
Development of multivalent macromolecular ligands for enhanced detection of biological targets
Authors: Levon Kalle , Yu Bin 
Published: October 2003

AbstractMacromolecular conjugates enable simultaneous binding of multiple ligands on one biological entity and these polyvalent interactions can be collectively stronger than the corresponding monovalent ligands. We have synthesized macromolecules and conjugated them with a lectin (Helix Pomatia lectin, HPA), and an antibody, both with shown affinities to certain bacteria. The binding ability was studied by flow cytometry and the results showed that the affinity of the biomolecules was greatly enhanced due to the polyvalent effect.
Optical absorption and photoluminescence properties of the PPV nanotubes and nanowires
Authors: Kim Kyungkon , Jeoung Sae Chae , Lee Jinwoo , Hyeon Taeghwan , Jin Jung‐Il 
Published: October 2003

AbstractWe measured optical absorption and time resolved photoluminescence decay properties of the PPV nanotubes and nanowires which were prepared by CVD polymerization using templates. When compared with bulk PPV films, their nano objects showed different optical properties, long photoluminescence decay time and higher photoluminescence efficiencies.
Self‐amplifying sensory materials: energy migration in polymer semiconductors
Authors: Kuroda Kenichi , Swager Timothy M. 
Published: October 2003

AbstractSignal amplification for ultra‐sensitive detection has been achieved by energy migration in conjugated semiconducting polymeric assemblies. Critical to optimizing this effect is the synthesis of non‐aggregate polymers, the multidimensional directional transport of excited states (excitons), and extending the intrinsic excited state lifetime of conjugated polymers. We developed new water‐soluble non‐ionic conjugated polymers for use in biosensory applications, which can be used to provide highly sensitive/specific ultra‐trace detection that is immune to specificity problems that plauge ionic conjugated polymers.
Macromolecular helicity inversion of poly(phenylacetylene) derivatives induced by various external stimuli
Authors: Maeda Katsuhiro , Morino Kazuhide , Yashima Eiji 
Published: October 2003

AbstractUnique macromolecular helicity inversion of stereoregular, optically active poly(phenylacetylene) derivatives induced by external achiral and chiral stimuli is briefly reviewed. Stereoregular, cis‐transoidal poly(phenylacetylene)s bearing an optically active substituent, such as (1R,2S)‐norephedrine (poly‐1) and β‐cyclodextrin residues (poly‐2), show an induced circular dichroism (ICD) in the UV‐visible region of the polymer backbone in solution due to a predominantly one‐handed helical conformation of the polymers. However, poly‐1 undergoes a helix‐helix transition upon complexation with chiral acids having an R configuration, and the complexes exhibit a dramatic change in the ICD of poly‐1. Poly‐2 also shows the inversion of macromolecular helicity responding to molecular and chiral recognition events that occurred at the remote cyclodextrin residues from the polymer backbone; the helicity inversion is accompanied by a visible color change. A similar helix‐helix transition of poly((R)‐ or (S)‐(4‐((1‐(1‐naphthyl)ethyl)carbamoyl)phenyl)acetylene) is also briefly described.
Supramolecular polymers: from scientific curiosity to technological reality
Authors: Bosnian A.W. , Brunsveld L. , Folmer B.J.B. , Sijbesma R.P. , Meijer E.W. 
Published: October 2003

AbstractSupramolecular polymers[1] are introduced as a new approach to come to materials in which the repeating units are not connected by covalent bonds but by specific secondary interactions. Self‐complementary quadruple hydrogen bonded structures with high association constants are presented as easy to synthesize fragments in supramolecular polymers. Some of the many possibilities of equilibrium polymers are discussed, while it is shown that these supramolecular polymers can obtain materials properties normally only obtained with macromolecules.
Status and dreams of photonics polymer for IT
Authors: Koike Yasuhiro , Ishigure Takaaki , Tagaya Akihiro 
Published: October 2003

AbstractWe have proposed a low‐loss, high‐bandwidth and large‐core graded‐index plastic optical fiber (GI POF) in data‐corn, area. The GI POF enables us to eliminate the “modal noise” problem which is observed in medium‐core silica fibers. Therefore, stable high‐speed data transmission can be realized by the GI POF rather than medium‐core silica fibers. Furthermore, advent of perfluorinated (PF) polymer based GI POF network can support higher transmission than silica fibers network because of the small material dispersion of PF polymer compared with silica. In addition, we proposed a “highly scattering optical transmission (HSOT) polymer” and applied it to a light guide plate of a liquid crystal display backlight. The HSOT polymer backlight that was designed using the HSOT designing simulator demonstrated twice the brightness of the conventional taransparent backlight with sufficient color uniformity. Furthermore, we proposed the two types of zero‐birefringence polymers synthesized by the random copolymerization method and the anisotropic molecule dopant method. Both of the polymers exhibited no orientational birefringence for any orientation of polymer chains.
Quantifying supercritical CO2 dilation of poly(vinylidene fluoride) and poly(vinylidene fluoride‐co‐hexafluoro‐propylene) utilizing a linear variable differential transducer: plasticization and melting behavior
Authors: Shenoy Suresh L. , Fujiwara Tomoko , Wynne Kenneth J. 
Published: October 2003

AbstractMelting behavior of semicrystalline poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride‐co‐hexafluoropropylene) is investigated as a function of supercritical CO2 pressure using a Linear Variable Displacement Transformer (LVDT). The melting temperature (Tm) of both polymers is lowered due to supercritical CO2 plasticization. For PVDF, the maximum lowering of Tm (ΔTm/n=23°C) occurs between 483 and 552 bar. The corresponding value for the copolymer is Δ Tm = 26°C at 552 bar. At higher pressures, hydrostatic effects override plasticization and Tm increases for both polymers. By comparing Tm in N2, a noninteracting gas, the opposing effects of plasticization and hydrostatic pressure on Tm are explored.
Impact of microcellular plastics on industrial practice and academic research
Authors: Suh Nam P. 
Published: October 2003

AbstractMicrocellular plastics (MCP) refer to any plastic with tiny bubbles of less than about 50 microns. It is made by subjecting polymers with a large amount of dissolved gas to a thermodynamic instability so as to nucleate a large number of cells instantaneously. MCP has been extruded and injection molded to make various industrial products. The fundamental theory for design of MCP and the processing methods are reviewed. It also discusses the design of equipment, including the die or mold, for MCP processing. The performance of MCP and the advantages of using MCP are presented. Some of industrial applications are also highlighted.
Lignin: its functions and successive flow
Authors: Funaoka Masamitsu 
Published: October 2003

AbstractPhenolic lignin‐based polymers with structure‐variable function have originally been designed, and a process has been developed for synthesizing them directly from native lignins. The key point of the process is to set up two different solvents, which are immiscible each other, for selective modification and separation of lignin and carbohydrates: hydrophobic solvent for hydrophobic lignin and hydrophilic solvent for hydrophilic carbohydrates. The native lignins, three dimensional network polymers, are subjected to selective modifications at the interface between both phases to give linear type polymers (lignophenols) composed mainly of 1,1‐bis(aryl)propane type units, almost quantitatively. The process provides a new system for successively utilizing lignocellulosics in the molecular level.
The new science of protein mimetics
Authors: Goodman Murray , Cai Weibo , Kinberger Garth A. 
Published: October 2003

AbstractNew chemistries have been developed for de novo protein design. Protein mimetics of different structural and functional properties such as synthetic peptide ligases and Dn symmetrical helical bundles have been reported. The Template‐Assembled Synthetic Protein (TASP) method (as well as the ßMolecular Kit' approach) has also been utilized to prepare protein‐like molecules. Here we report the synthesis of single chain, scaffold (TRIS)‐ and dendrimer‐assembled collagen mimetics composed of the Gly‐Nleu‐Pro sequence where Nleu denotes N‐isobutyl glycine. From the CD spectra and the thermal denaturation studies it can be seen that the collagen mimetics prepared form stable triple helices except the single chain structure. Furthermore, the 162‐residue collagen mimetic dendrimer exhibits enhanced triple helical stability compared to the equivalent scaffold‐terminated structure by an increase in the melting temperature in both H2O and 2:1 ethylene glycol/H2O (4°C and 12°C respectively). The concentration dependence for the melting transition of the collagen mimetic dendrimer was measured from which it was determined that the stabilization effect arises from the intramolecular clustering of the triple helical arrays about the core structure. This ensemble excludes solvent from the interior portion of the array which stabilizes the triple helix cluster.
DNA: beyond the double helix
Authors: Seeman Nadrian C. 
Published: October 2003

AbstractReciprocal exchange can be used to produce DNA motifs based on branching at the level of secondary structure. These motifs can be combined by sticky‐ended cohesion to produce a variety of structures. Stick polyhedra and nanomechanical devices have been produced by self‐assembly from motifs based on branched DNA. Periodic arrays with tunable surface features has also been produced; aperiodic arrangements have been used for DNA‐based computation.
Novel biomaterials derived from deoxyribozyme and NAPzyme
Authors: Okumoto Yasuhide , Fujiki Hiroyoshi , Kawakami Junji , Nakashima Shoji , Nakano Shu‐ichi , Ohmichi Tatsuo , Miyoshi Daisuke , Sugimoto Naoki 
Published: October 2003

AbstractWe report the potential of a small Ca2+‐dependent deoxyribozyme as a novel biomaterial to distinguish RNA foldings. It is found that an immobilized deoxyribozyme using avidin‐biotin interaction cleaves the target site within only single‐stranded RNAs. The RNA cleavage reaction is also detected using the deoxyribozyme SPR sensor chip. Furthermore, we develop a novel NAPzyme (nucleic acid peptide deoxyribozyme) with its RNA cleavage function in the absence of divalent metal ions.