bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recent developments in living cationic polymerization
Authors: Nuyken Oskar , Kröner Hubertus , Rieß Gisbert , Oh Saehoon , Ingrisch Stefan 
Published: March 2011

AbstractScope and limitation of the vinyl ether polymerization initiated by NR4ClO4(KClO4;LiClO4)/CH3CHI‐OR was discussed. Besides isobutyl vinyl ether (IBVE), N‐vinylcarbazole (NVC) and 2‐chloroethyl vinyl ether (CEVE) were initiated by NR4ClO4/CH3CHI‐OR. These polymerizations exhibited the characteristics of a living polymerization. However, in order to observe narrow molar mass distribution NVC was initiated with CH3CHI‐OR, without salts. Block copolymers were synthesized by the method of sequential monomer addition (NVC, IBVE, CEVE). The PCEVE segment was modified by nucleophilic substitution, which allowed the synthesis of amphiphilic block copolymers.
Polymerization of acrylamide in inverse microemulsions under special conditions
Authors: Bartoň Jaroslav 
Published: March 2011

AbstractIncreasing of Φaw, the volume fraction of the aqueous phase (water + acrylamide) in inverse microemulsion systems toluene / sodium bis(2‐ethylhexyl) sulfosuccinate (AOT) / water / acrylamide (Set A); toluene / AOT / water / acrylamide / sodium dodecyl sulfate (SDS) (Set AD) and toluene / styrene/ AOT / water / acrylamide (Set AS) leads to an increase of the viscosity. The dependence of the viscosity on Φaw in the temperature range 20–45°C is characterized by three maxima (at ΦawΦ25, 45 and 65%). These maxima can be eliminated by an increase of temperature to 50°C (Sets A and AS). The most prominent peak (at ΦawΦ45%) is preserved at 50°C only for systems of Set AD.The acrylamide polymerization behaviour in Sets A and AD is very similar irrespective of the nature of initiator used (dibenzoyl peroxide and ammonium peroxodisulfate). The rate of polymerization is a complex function of Φaw. In the presence of styrene (Set AS) a significant retardation of polymerization was observed. The rate of polymerization increases with increasing Φaw. Viscosity of the inverse dispersion system (Set AD) has no effect on the polymerization rate of acrylamide.
2H NMR studies of oriented bacteriorhodopsin membranes to determine single bond orientations
Authors: Ulrich Anne S. 
Published: March 2011

AbstractFor the structural analysis of oriented polymers and other macromolecular systems, we present a solid state 2H NMR technique capable of measuring the orientations of individual chemical bond vectors with high accuracy. When an immobilized uniaxially oriented sample is aligned along the spectrometer magnetic field direction, the angle between a deuterium‐labelled methyl group and the axis of ordering can be calculated from the spectral quadrupole splitting. However, since positive and negative splittings are indistinguishable, there may be two solutions. We show how these may be discriminated by acquiring additional spectra at different sample inclinations (Ref 1). The analysis of the resulting complex lineshapes is aided by computer simulation, which furthermore allows a characterization of the orientational distribution function of the sample. The 2H NMR method has been developed around the membrane protein bacteriorhodopsin as a biological model system that can be prepared in uniaxially oriented films. The overall orientation and molecular conformation of the retinal chromophore were resolved from the individual orientations of its five labelled methyl groups (Refs 2, 3). Structural changes were detected in an intermediate of the photocycle (M), which provide insight into the mechanism of the protein as a proton pump (Ref 4).
Interfacial interactions and structure of polyolefins
Authors: Lotz Bernard , Wittmann Jean‐Claude 
Published: March 2011

AbstractThe elucidation of structural aspects of polyolefins (isotactic and syndiotactic polypropene and isotactic poly(1‐butene)) oriented by epitaxial crystallization is briefly described. Investigations are performed by a combination of electron and Atomic Force Microscopy. AFM helps assess submolecular details in well defined crystallographic planes selected via the epitaxial crystallization.
Dynamic light scattering method of polymer solutions
Authors: Burchard Walther 
Published: March 2011

AbstractThe main features of dynamic light scattering are briefly outlined. The capability of this method to characterizing molar mass distributions and to distinguishing different molecular architectures is demonstrated with some examples. Special attention is given to the question of internal mobility and the spectrum of relaxation times. Recent results on asymptotic behavior are presented and discussed. Scaling behavior of the first cumulant with respect of space and of the time correlation function with respect of time (shape function) is found. All examples studied so far demonstrate the dynamic scaling of Zimm‐Rouse chains, but the prefactors strongly depend on branching and crosslinking.
Viscoelastic properties of liquid crystalline polymers
Authors: Marrucci Giuseppe 
Published: March 2011

AbstractThe viscoelastic properties of main‐chain liquid‐crystalline polymers are reviewed with an emphasis on the main differences that these materials show with respect to the behaviour of ordinary polymers. The distinction between the anomalies directly arising from the material anisotropy and those which are related to the polydomain structure is also emphasised.
Probe rotation near and below the glass transition temperature: Relationship to viscoelasticity and physical aging
Authors: Ediger M. D. , Inoue T. , Cicerone M. T. , Blackburn F. R. 
Published: March 2011

AbstractReorientation times ťc for two probes in several amorphous polymers near the glass transition temperature Tg are reported. Tg for these polymers ranges from 205 to 459 K. Probe reorientation was measured in the time window from 10−2 to 104 s with a recently developed photobleaching method. ťc for a given probe at the Tgs of the different polymers varies more than three decades. Viscoelastic relaxation times characteristic of the Rouse modes of the matrix polymers are closely related to probe rotation times and thus also not constant at Tg. The characteristic length scale of motions responsible for the glass transition varies significantly for the three polymers studied. Preliminary physical aging results indicate that probe reorientation in polystyrene ages slightly faster than the volume.
Orientation‐dependent interactions in polymer systems: Segmental orientation, miscibility, and self‐organization
Authors: Fukuda Takeshi , Fujimoto Kouji , Murakami Mauro M. , Kawabata Kenji , Miyamoto Takeaki 
Published: March 2011

AbstractThree co‐operative phenomena that are supposed to originate in the orientation‐dependent interactions among polymer segments are discussed and attempted to be interpreted in terms of a common set of polymer models.
Computer simulation and control for product quality in injection molding
Authors: Kamal Musa R. 
Published: March 2011

AbstractThe use of computers in plastics processing has continued to grow in parallel with rapid expansion of computer availability and computing power. One of the main areas of application is in computer simulation of the injection molding process where more demanding applications relate to the simulation of molding of complex‐shaped moldings. Recent development include the use of boundary fitted curvilinear coordinates, the incorporation of fountain flow, and the coupling of crystallization kinetics within the transport equations. Applications in computer control relate to the control of pressure and temperature throughout the injection molding process, self‐tuning control, physically‐based dynamic models, and the control of properties of the molding, e.g. the weight of the article. Recent developments relate to the application of inverse modeling. An example is given of the use of inverse modeling of thermal stresses to predict or optimize thermal or pressure history during molding.
Recent development of the nonlinear optical active material system
Authors: Kim Nakjoong 
Published: March 2011

AbstractNew nonlinear optical active materials have been highlighted to apply them to practical applications since about two decades ago. During this period, a number of materials have been developed and studied in academic and industry field. Particularly, the second‐order nonlinear optical properties are facile to approach in the laboratory. We can consider the possibility of the device application by investigating the macroscopic second‐order nonlinear optical properties using the second harmonic generation and linear electro‐optic study. Nowadays, the absolute value of the nonlinear optical coefficient of organic material overcame the value of conventional inorganic materials due to quick research progress. Therefore, the new organic materials systems showed some promising motives to fabricate the optical device.
Starburstr̀ dendrimers — Nanoscopic supermolecules according to dendritic rules and principles
Authors: Tomalia Donald A. 
Published: March 2011

AbstractConstruction of dendritic macromolecules based on the mimicry of macroscopic branching patterns found in trees is reviewed. From this mimicry, synthetic strategies have been developed for the preparation of precise macromolecular building blocks referred to as Starburstr̀/Cascade dendrimers. These dendrimer constructions involve the amplifications of matter (mass) by organizing monomer units around initiator cores according to geometrically driven mathematical rules and principles. The predictable precision of mass and valency (i.e., number of reactive surface groups) displayed by these dendrimers, as a function of generation, validates their proposed role as fundamental nanoscopic building blocks (i.e., particle sizes of 10 −1000Å). This emerging area of “structure‐controlled polymers” is defining a fourth new major class of macromolecular architecture. Ideal, defect free structures of Starburstr̀ polyamidoamine (PAMAM) dendrimers (e.g., NH3 core; generation = 2.0, MWt. 2,414) have been synthesized in kilogram quantities with overall yields of 60‐70%. The precise masses and surface valencies associated with these dendrimer structures allow one to view these entities as “nanoscopic analogues” to atoms. As such, basic rules of chemical combination between dendrimers to give definite, stoichiometric compositions can be defined much as first noted by Dalton for atoms. The use of these nanoscopic building blocks (i.e., 10–1000Å species) to construct supramolecular/supermolecular structures such as nanoscopic compounds, clusters and macro‐lattices will be reviewed.Registered trademark of Dendritech Inc.
Morphology and strength of high performance main‐chain liquid crystal polymers
Authors: Wegner Gerhard 
Published: March 2011

AbstractThe impact of chain‐length on formation and properties of thermotropic LC‐phases is described for poly(didocecyl‐p‐phenylene). Isotropic, biphasic or anisotropic melts are observed. The zero‐shear viscosity scales as η≈︁Mw2.9 in the isotropic and as η=Mw3.2 in the anisotropic melt. If quenched from the LC‐melt, the material exhibits a smectic superstructure dominated by disclinations. The same feature is seen with the poly(diacetylene) P‐4BCMU crystallized from lyotropic solution. The LC‐phase consists of lamellae the thickness of which scales with the extended chain length. Segregation of the chains allows the lamellae to adapt to the strain field in the vicinity of the core of the disclinations. A banded texture observed when the LC‐phase is subject to shear is resolved by TEM as composed of periodically distorted stacks of lamellae. Small modifications of the chain structure by comonomers has a substantial impact on the mechanical properties. Introducing only 5 mol percent of comonomers with sterically assuming substituents into lyotropic poly(p‐phenylene terephthalamide) improves the compressional strength (Elastica test) of fibers by 25 percent.
Rubber toughening of plastics: Rubber particle cavitation and its consequences
Authors: Bucknall C. B. , Soares V. L. P. , Yang H. H. , Zhang X. C. 
Published: March 2011

AbstractA newly‐developed energy‐based model for cavitation in rubber particles provides a quantitative basis for understanding the factors controlling toughness in rubber‐modified plastics. Cavitation of the rubber is the initial step in the toughening mechanism, and is shown to accelerate yielding of the matrix, either by the formation of dilatation bands or by multiple crazing. Cavitation is thus a strain‐softening effect. However, in some cases the cavitated rubber forms fibrils which become highly stretched as local strains increase, and thus begin to carry a significant fraction of the applied stress. The resulting strain‐hardening ensures that yielding is not limited to a small deformation zone at a crack tip, but spreads outwards.
Modification of metallocene catalysts for olefin polymerization
Authors: Soga Kazuo 
Published: March 2011

AbstractThe metallocene catalyst developed by Kaminsky and Sinn has been demonstrated to permit the synthesis of any kind of stereoregular polymers as well as uniform copolymers with very narrow compositional and molecular weight distributions. The catalyst is, thus, expected to comprise a revolution in the polyolefin industry.More recently, a great deal of research effort has been devoted to modify it for practical applications, which has yielded a new generation of metallocene catalysts.This paper summarizes the results reported so far in the field. Some of our original data will be also reported.
Recent advances in olefin polymerization
Authors: Shiomura Tetsunosuke , Kohno Masahiro , Inoue Norihide , Asanuma Tadashi , Sugimoto Ryuichi , Iwatani Tsutomu , Uchida Osamu , Kimura Shigeru , Harima Shigeru , Zenkoh Hirofumi , Tanaka Eishi 
Published: March 2011

AbstractVarious metallocenes were tested for syndiotactic polymerization of propylene. Reduction in the amount of costly methylalumoxane (MAO) or replacement with the other components was accomplished. Small modifications in the metallocene ligands brought about remarkable differences in the resulting catalysts concerning their storage stability, H2 response as well as stereo‐specificity. Syndiotactic polypropylene (SPP) in the melt state behaves very differently compared to isotactic polypropylene (IPP). The notion that these polymers have different distributions of molecular entanglements are pursued, and verified for the first time. Excellent dispersibility of other olefin polymers in SPP matrix contributed to improve the usefulness of SPP.
Organosilicon polymers with bis‐acetylenic units: Conductivity and ceramisation studies
Authors: Corriu R. , Gerbier P. , Guerin G. , Henner B. 
Published: March 2011

AbstractThe transformation poly[(silylene)diacetylene] into ceramic have been studied and SiC obtained with a quantitative yield: all the silicon atoms present in the starting material are converted into SiC. The key step is the crosslinkage of C4 units into a carbon matrix in which the R1SiR2 moieties are in the vicinity one to each other allowing the quantitative transformation into SiC. The carbon content of the resulting ceramic depends on the nature of R1 and R2 groups. The excess of carbon has been used for the carboreduction of oxides (TiO2, ZrO2, HfO2, etc…) and mixed ceramics with interpenetrating network have been obtained: SiC / TiC, SiC / ZrC, etc… Under nitrogen atmosphere, the ceramisation leads to different systems such as SiC / TiN, SiC / AlN, etc…
Synthesis, characterization, and application of helical polymers
Authors: Okamoto Yoshio 
Published: March 2011

AbstractThis review mainly describes the asymmetric synthesis of optically active polymers with helical conformation. Bulky methacrylates such as triphenylmethyl methacrylate and 1‐phenyldibenzosuberyl methacrylate give one‐handed helical and optically active polymers with almost perfectly isotactic main chain conformation by polymerization with chiral anionic initiators. The radical polymerization and copolymerization of these monomers under chiral conditions also afford optically active polymers with prevailing one‐handed helicity. N, N‐Disubstituted acrylamides also give optically active, helical polymers in the asymmetric anionic polymerization. Optically active polyisocyanates with a prevailing one‐handed helical structure have been prepared in the copolymerization of an achiral isocyanate with a small amount of an optically active isocyanate and also in the polymerization of alkyl and aromatic isocyanates with optically active lithium alkoxide or amide compounds. The existence of a stable helical structure for polychloral has been successfully proved with the helical oligomers of chloral. One‐handed helical polyisocyanides have been prepared by helix‐sense‐selective polymerization of bulky isocyanides and also by the cyclopolymerization of a 1, 2‐diisocyanobenzene derivative with the Pd complex of a one‐handed helical oligomer.
Template‐induced control of stereochemistry for the synthesis of linear vinyl polymers
Authors: Wulff Günter , Gladow Stefan , Kühneweg Bernd , Krieger Stephan 
Published: March 2011

AbstractAsymmetric cyclocopolymerization of judiciously designed bifunctional monomers with a number of common comonomers affords optically active vinyl polymers with main chain chirality. Tacticity and sequence of comonomeric units can be controlled and thus complicated structures built up. Under different reaction conditions the same bifunctional monomer 1 can undergo cyclization involving a 19‐, a 21‐, or an 18‐membered ring. With monomer 3 an 11‐membered ring is formed.
Following the polyisocyanate helix reversal from dilute solution through the liquid crystal and into the solid state
Authors: Green Mark M. , Sato Takahiro , Teramoto Akio , Lifson Shneior 
Published: March 2011

AbstractThe absence of a predetermined helical sense in the polyisocyanates causes the formation of helix reversals which enforce a strong cooperativity for the amplification of chiral effects. The helix reversals though also place a limit on this amplification, a limit which would be eliminated by reducing the helix reversal population. Approaching the liquid crystal state of the polyisocyanates in both dilute and concentrated solutions appears to cause the exclusion of the helix reversals which is consistent with theoretical expectations.Since the linear birefringence of the polyisocyanate solid state precludes optical activity measurements associated with the polymer, we have synthesized hydrogen bonding side chain adapted polyisocyanates which appear by DSC and infra‐red criteria to form equilibrium molecular composites with copolymers of vinyl phenol and styrene. The optical activity properties of these composites may offer a new way to probe polymer motion in the solid state.
Helix change of polypeptides in the solid state as studied by NMR spectroscopy
Authors: Ando Isao 
Published: March 2011

AbstractThe conformational characterization of solid polypeptides has been carried out by means of high‐resolution solid‐state NMR. It has been demonstrated that high‐resolution solid‐state NMR spectroscopy is a very useful means for elucidating the structure of polypeptides and proteins in the solid state.
Biological activities of biodegradable polysaccharide
Authors: Tokura Seiichi , Nishimura Shin‐Ichiro , Sakairi Nobuo , Nishi Norio 
Published: March 2011

AbstractA low toxicity of chitin was demonstrated to be mostly due to biodegradability and the fast metabolization of hydrolysate in animal body. Chitosan, a deacetylated derivative of chitin, is also known to be a biocompatible polymer in spite of a slight immunoadjuvant activity in animal body. Chitosan is easily regenerated to fiber, film, beads and non woven fabrics owing to its high solubility toward diluted aqueous organic acids such as formic acid, acetic acid, glutamic acid and ascorbic acid. The regeneration of chitin was achieved into fibers, gels, porous foams and non woven fabrics following to dissolution of chitin with formic acid or calcium chloride dihydrate saturated methanol. Chitin and its derivatives have been applied as biomedical materials due to remarkable advantages such as antimicrobial activity, acceleration of epidermal cell assembly, low toxicity, and biodegradability.
The molecular dynamics of poly(1, 4‐Trans‐butadiene) in the amorphous state and in an inclusion complex
Authors: Haliloǧlu Türkan , Mattice Wayne L. 
Published: March 2011

AbstractThe molecular dynamics of poly(1, 4‐trans‐butadiene) in the amorphous state at bulk density and in its inclusion complex with perhydrotriphenylene are compared here. The internal motions differ in the two systems, due to the occupation of gauche states at CH2‐CH2 of the amorphous polymer, but the exclusion of gauche states at these bonds in the inclusion complex. This difference in conformational preferences at CH2‐CH2 has consequences for the decay rates for the orientation autocorrelation functions.
Surface modification of biomedical polymers
Authors: Ikada Yoshito 
Published: March 2011

AbstractSurface modification of biomedical polymers by the technique of surface grafting was briefly overviewed, mostly based on our results. It was shown that surface grafting of water‐soluble polymer chains onto polymeric biomaterials was effective in producing mechanically non‐stimulative, blood‐compatible, antibacterial, tissue‐bonding, and cell‐adhesive surfaces. In addition to the improvement of the interfacial biocompatibility, the surface grafting was useful also for obtaining a biofunctional surface such as immunoadsorbent.
The surface and interfacial chemistry of polyimide films
Authors: Coulman D. , Edman J. 
Published: March 2011

AbstractThe surfaces of polyimide films and the structure just below the surfaces have been extensively studied as people have sought to improve and understand the key factors controlling adhesion. Treatments of all types from primers to plasma etching to sand blasting have been evaluated with varying efforts depending on the application. In recent years, the emphasis has been on understanding the chemical and morphological changes effected by these treatments and then correlating chemistry and morphology with adhesion. The picture that emerges is that surface energy alone, as is the case with most polymers, usually is insufficient to predict adhesion to polyimides. Instead, initial bond strength and bond durability, whether with adhesives or metals directly deposited on the film, depend on chemical bonding, diffusion between deposited layers and the polyimide, formation of a micro composite region controlled in part by topography and the viscoelastic properties of the polymer below the surface. Poor viscoelastic behavior frequently is characterized as a weak boundary layer. Recent work has shown that small amounts of organometallics that diffuse to the surface during the film forming process can significantly affect bondability both to adhesives and to vacuum deposited metals. The possible effect of these additives on bond formation, viscoelastic properties, diffusion and topography is under investigation and will be discussed along with an over view of the primary film forming steps that might affect surface chemistry and structure.
New surface improvement techniques for engineering plastics
Authors: Moriuchi Takahiko , Yamamoto Suguru 
Published: March 2011

AbstractSputter etching process and reactive sputter etching process in radio frequency(RF)glow discharge for surface improvement technique of engineering plastics, especially P T F E (polytetrafluoroethylene) were studied. In the case of sputter etching in Ar gas. characteristic cone like structures were developed on the P T F E surface, resulting in improvement of adhesive property. In reactive sputter etching in H2O gas, the P T F E surface changed chemically and showed wettability.