bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereospecific polymerization and chiral initiation, chiral crystallization and chiral nucleation
Authors: Qin Meifang , Bartus Jan , Vogl Otto 
Published: March 2011

AbstractHelical macromolecules which are configurationally and conformationally specific can now be synthesized. Monomer structures must be selected that demand spacial restriction for monomer addition. High specificity of monomer addition during polymerization has parallels in crystallization of some inorganic salts from aqueous solution. Initiation of highly specific polymerizations with chiral initiators give helical polymers with substantial one‐handedness. Nucleation of certain inorganic salts with chiral nucleating agents, the enantiomers of the salts produce enantiomerically pure chiral salts.
Supramolecular chemistry of cascade polymers: Construction, molecular inclusion, and inorganic connectivity
Authors: Newkome George R. , Güther Ralf , Cardullo Francesca 
Published: March 2011

AbstractThe construction of cascade polymers with novel properties is discussed. A flexible amide‐based cascade architecture facilitates changes of the molecular hydrodynamic radius as a function of environmental pH, provided that the periphery is coated with ionizable functional groups (e.g., carboxylic acids or amines). Thus, it is possible to expand or contract the internal void domains within these cascades. By extension of the heteroatom connectivity, we have prepared a novel multifunctional molecule possessing a predetermined spherical morphology, that utilizes a ruthenium(II) metal center coordinated to two different orthogonal 2,2':6',2″‐terpyridine moieties to build the arm(s) of the cascade polymer. This technology permits the placement of multiple metal complexes at predetermined internal sites within the hydrophilic‐surfaced MicellaneTM framework. The combination of these two strategies to build cascade polymers allows the creation of an unsymmetrical bolaamphiphile constructed from two separate and distinct macromolecules. We are able to build cascade molecules either with a terpyridine unit inside or outside the polyamide sphere. The use of a connecting ruthenium(II) center allows the specific formation of a stable complex between the discrete cascade polymers.
Chirality and dendrimers; the issue of chiral recognition at the nanoscopic level
Authors: Kremers John A. , Meijer E. W. 
Published: March 2011

AbstractThe synthesis and characterization of two chiral dendrimers, 1 and 2, in their racemic form is presented. The chirality is based on the construction of four constitutionally different, but chemically resembling, branches to an achiral core. A multi‐substituted pentaerythritol derivative is used as core and Fréchet's aromatic‐ether dendritic wedges of different generation are used as branches. The synthetic approach makes use of the consecutive attachment of the four branches by selective deprotection of the core. Both chiral dendrimers of different size have been synthesized from the same precursor. 1H‐NMR Spectroscopy indicates an overall chiral shape for 1, while for both 1 and 2 stratified structures are observed. Several attempts to resolve both dendrimers have not been successful so far, giving rise to a discussion on the degree of chirality in these dendrimers of nanometer dimensions.
Microbial synthesis, physical properties, and biodegradability of polyhydroxyalkanoates
Authors: Doi Yoshiharu 
Published: March 2011

AbstractPoly((R)‐3‐hydroxybutyrate), P(3HB), is produced by Alcaligenes eutrophus from fructose or butyric acid. The kinetics and mechanism of P(3HB) biosynthesis are presented. Four types of copolymers, poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), poly (3‐hydroxybutyrate‐co‐3‐hydroxypropionate), poly (3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), and poly (3‐hydroxybutyrate‐co‐4‐hydroxybutyrate), are produced by several bacterial strains from various carbon substrates. These microbial polyesters are biodegradable thermoplastics whose physical properties can be regulated by varying the molecular structure and composition of copolymers.
Recent advances in the field of lactic acid/glycolic acid polymer‐based therapeutic systems
Authors: Vert Michel , Li Suming , Garreau Henri 
Published: March 2011

AbstractThe mechanism of degradation of bioresorbable lactic acid‐ and glycolic acid‐based aliphatic polyesters (PLA/GA) is still far from being totally understood although a majority of authors agree to consider in vivo degradation as essentially hydrolytic. In the past years, we have shown that hydrolysis of large size devices is heterogeneous, i.e. faster inside than at the surface because of reaction‐diffusion phenomena involving acid‐catalyzed ester cleavage reactions and water‐soluble macromolecular fragments. The proposed mechanism is recalled together with some direct or indirect consequences, namely induced crystallization at body temperature, size‐ and formulation‐dependence of the degradation rates. From these features, one can conclude that it is now possible to increase or decrease the degradation rate and to turn on or off heterogeneous degradation by using accelerating or braking factors, however, accurate piloting of the hydrolytic degradation of PLA/GA is still not feasible.
Hydrophilic‐hydrophobic interpenetrating polymer networks and dicyanate‐based semi‐ipn materials
Authors: Kim Young Duk , Lee Bong Keun , Jeon Eun Jin , Shin Yong Cheol , Kim Sung Chul 
Published: March 2011

AbstractHydrophilic‐hydrophobic IPN materials of poly(acrylic acid)‐poly(styrene‐co‐acrylonitrile) were synthesized and the pervaporation characteristics of the IPN membranes were evaluated for the separation of ethanol/water mixture. Hydrophilic‐hydrophobic IPN materials of polyurethane‐polystyrene were synthesized and the blood compatibility of the IPN's were measured for the biomedical application. Dicyanate‐engineering plastics semi‐IPN's were prepared and the morphology and mechanical properties were evaluated for the high temperature composite matrix materials.
Mechanical and morphological investigations of reactive polysulfone toughened epoxy networks
Authors: Yoon Tae Ho , Priddy Duane B. , Lyle Gregory D. , McGrath James E. 
Published: March 2011

AbstractThe diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin was toughened by aminophenyl functional reactive polyethersulfones (R‐PES) or by t‐butyl terminated non‐reactive polyethersulfones (T‐PES). The molecular weights of PES were controlled to afford 5,000 to 20,000 g/mole and loadings were also varied from 5 to 30 wt.%. Epoxy networks cured with 4, 4'‐diaminodiphenylsulfone (DDS) were subjected to Tg determinations, plane strain fracture toughness (K1C) measurements, chemical resistance tests and morphological studies by SEM. Very significantly improved K1Cfracture toughness was obtained with reactive PES toughening without loss of chemical resistance, while non‐reactive PES blended epoxy resins exhibited only slightly improved fracture toughness but poor chemical resistance. It was possible to load up to 30 wt.% of PES without utilizing solvent and the maximum K1Cfracture toughness with R‐PES was around 2.2 MPa‐m 0.5, which was equivalent to the neat thermoplastic resin. Ductile fracture of the PES phase is suggested as a major toughening mechanism and this is highly dependent of the excellent adhesion developed between the PES and epoxy phases due to the chemical bonds. The systems demonstrated that chemical resistance of thermosets can be combined with the tough characteristics of thermoplastics.
Recent developments in the radiation chemistry of elastomers
Authors: Bremner T. , Hill D. J. T. , O'Donnell J. H. , Perera M. C. S. , Pomery P. J. , Whittaker A. K. 
Published: March 2011

AbstractThe radiation chemistry of several elastomers has been reviewed, including that of polybutadiene, polyisoprene, polyisobutylene, halogenated rubbers, ethylene‐alkene copolymers and a range of polyurethanes. The properties investigated include the yields of volatile products and radicals and the new chemical structures formed on radiolysis. The roles of double bonds and hetero‐atoms, such as chlorine, in the radiation chemistry of the elastomers has also been discussed.
Networks of rigid molecules
Authors: Müller‐Nedebock Kristian K. , Aharoni Shaul M. , Edwards Sam F. 
Published: March 2011

AbstractNetworks of rigid molecules do not fit into the paradigm of classical theories of rubber elasticity. Some experimental properties of rigid polyamide networks are summarised, and the basis for a theoretical understanding of such systems is discussed and elaborated in terms of the properties such as the existence of several conformational states and twist of such network elements.
Poly(styrene‐co‐p‐(hexafluoro‐2‐hydroxy‐2‐propyl)‐styrene) blends with syndiotactic and/or isotactic poly(methyl methacrylate)
Authors: Luo Dexin , Kwei T. K. , Pearce Eli M. 
Published: March 2011

AbstractA modified polystyrene, poly(styrene‐co‐p‐(hexafluoro‐2‐hydroxy‐2‐propyl)styrene) (FPS), was blended with syndiotactic and/or isotactic poly(methyl methacrylate) (PMMA) in toluene. Blends were prepared under different conditions to control the self‐aggregation of the PMMA segments. The formation of hydrogen bonding and the attendant changes in the aggregation or crystallization of PMMA segments were determined in the solid state by means of FTIR and DSC. The results indicate that for the binary blends, the aggregation of PMMA segments is diminished by hydrogen bonding interaction with either s‐PMMA or i‐PMMA, and that the interaction is stronger with the s‐PMMA blends. For the ternary blends, FPS/s‐PMMA/i‐PMMA, the preference for stereocomplexation in the system with hydrogen bonding may be attributed to the “kink‐nucleated” mechanism, which needs relatively short chain lengths of PMMA segments. Regardless of the order of addition of the components, the formation of crystalline stereocomplexes of s‐ and i‐PMMA could be readily detected. Therefore, the miscibility of the polymer blends is dependent on the competition between the self‐aggregation of the s‐ or i‐PMMA segments, stereocomplexation and the hydrogen bonding interaction of PMMA segments with FPS.
Ion conduction in poly(crown ethers), polyglucosan gels and macroporous polyethylene films
Authors: Cowie J.M.G. 
Published: March 2011

AbstractMuch work has been reported on ion conduction in solid solutions of salts dissolved in linear and comb‐branched poly(ethylene oxide) analogues. There appears to be a limit to the conductivity levels achieved in such systems, and conductivity values rarely exceed σ ∼ 10−4 Scm−1 at room temperature. To overcome this there has been a move towards more mobile plasticized systems and polymer gel electrolytes are receiving some attention. Gels prepared from N‐methyl‐2‐pyrrolidinone/LiCl and polyglucosans such as cellulose and amylose have been studied and show some promise with ambient σ Ge; 10−4 Scm−1. Macroporous polyethylene has also been used to support fluid polyethylene glycol/salt systems, but these only reached σ ≥ 10−5 Scm−1 at ambient temperature.Comb‐branch polymers with crown ethers provide systems with respectable room temperature conductivities of between 10−4 and 10−5 Scm−1, but these might be improved if the crown ethers could be arranged in regular channels. Ways to achieve this are briefly discussed.
The solubility and transport properties of small molecules in polymers — A modeling approach
Authors: Suter U. W. 
Published: March 2011

AbstractThe molecular mechanisms acting in the transport of “guest” molecules through polymeric solids still pose considerable difficulty: despite a manifest technological demand there has been a considerable lack of fundamental understanding of the mechanisms underlying the solubility and diffusion of even the smallest molecules in macromolecular substances. It is well known that the transport coefficients of low‐molar‐mass substances in polymers are strongly dependent on a number of factors, prominent among them the chemical structure of macromolecules. Nevertheless, the models applied for interpretation of transport of small molecules through macromolecular systems have been usually of a rather unspecific nature.Recently, modeling of the transport of gases through polymers in atomistic detail has been rather successful in elucidating the mechanisms as well as in predicting, without adjustable parameters, the transport coefficients. For the solubility, the quantitative estimate is rather rough since the estimation of the free energy of residence of guest molecules in a host matrix is plagued by the usual inaccuracies, the topological information is accurate, however; on the other hand, it is possible to estimate the diffusion coefficient to within a factor or ca. 2–5 over the entire range investigated (105 < D/(cm2/s) 10< −10).Mechanistically, one can state that the interstitial unoccupied column in the polymer can accommodate gas molecules with only small effects on the matrix. The solubility isotherm follows Fermi‐type statistics as long as the solute concentration is not too high. The gas transport through polymers occurs by a hopping mechanism in a matrix of macromolecular material that executes rapid thermal motion not coupled to large‐scale changes in the polymer. Consequently, the mechanism for gas transport in glasses and melts (or rubbers) is the same. On a short time scale, typically for times between 1013s and ns (or more), the diffusion is anomalous, due to the interstitial structure of the polymer. Einstein diffusion occurs only on time scales that are significantly longer (sometimes up to ms).
Preparation of polysaccharide derivatives and their chiral recognition mechanism
Authors: Okamoto Yoshio , Yashima Eiji 
Published: March 2011

AbstractSeveral new phenylcarbamate derivatives of cellulose and amylose having fluoro and methyl groups or 4‐trimethylsilyl substituent on the phenyl groups were prepared and their chiral recognition abilities as chiral stationary phases for HPLC were evaluated. These derivatives are soluble in chloroform and exhibit chiral discrimination in 1H NMR spectroscopy. Based on the above results and molecular mechanics calculation of interaction energies between the derivatives and enantiomers, the mechanism of chiral discrimination is discussed.
Molecular characteristics of functional polysaccharides
Authors: Norisuye Takashi 
Published: March 2011

AbstractThe molecular characteristics of sodium hyaluronate and amylose in various solvents are discussed by summarizing our recent studies. Data for the intrinsic viscosity and the radius of gyration are analyzed on the basis of the wormlike or helical wormlike chain, with excluded‐volume effects taken into account by the Yamakawa‐Stockmayer‐Shimada theory. The unperturbed hyaluronate molecule in 0.2 M or 0.5 M aqueous NaCl is shown to behave like a wormlike chain with Kuhn's segment length of about 8 nm. Amylose in the unperturbed state is more flexible, regardless of the kind of solvent, its stiffness parameter being about one half that for the hyaluronate chain, but it assumes an irregular helical conformation similar to what is predicted by conformation analysis.
Gelation and its relevance to the function of polysaccharides
Authors: Mimura Mitsuru , Urakawa Hiroshi , Kajiwara Kanji , Kitamura Shinichi , Takeo Kenichi 
Published: March 2011

Abstract(1→4)‐α‐ and (1→4)‐β‐D‐linked glucosidic oligosaccharide chains were generated by the Monte Carlo method, and the scattering from the systems composed of simulated chains was calculated to compare with the results of small‐angle X‐ray scattering from the oligosaccharides in aqueous solution. By extending the simulation to a longer chain, a single chain conformation of (1→4)‐α‐ and (1→4)‐β‐D‐linked polysaccharides was evaluated. On the basis of the simulation, the suprastructure of (1→4)‐α‐ and (1→4)‐β‐D‐linked polysaccharides and their gel formation mechanism were discussed in some detail by analyzing the small‐angle X‐ray scattering from the aqueous solutions of (1→4)‐α‐ and (1→4)‐β‐D‐linked polysaccharides.
Preparation of new types of temperature‐responsive cellulose derivatives
Authors: Miyamoto Takeaki , Long Mingfang , Donkai Nobuo 
Published: March 2011

AbstractThis paper reviews briefly our preliminary results concerning thermoplastic hydrogels and thermotropic aqueous gels from cellulose. Several kinds of thermoplastic hydrogels and thermotropic aqueous gels were prepared from cellulose and their thermal properties were examined. The former aims at preparing water‐insoluble cellulose derivatives having a high water absorbency and a thermal flow temperature of approximately 130°C, while the later aims at preparing water‐soluble cellulose derivatives which show a solubility behavior similar to that of synthetic polymers with a lower critical solution temperature (LCST) in aqueous solution. The results will be discussed in terms of the chemical structure of the prepared derivatives and their substituent distributions along the cellulose chain.
Novel pharmaceutical applications of polysaccharides
Authors: Franz Gerhard , Alban Susanne , Kraus Josef 
Published: March 2011

AbstractThe role of chemically characterized polysaccharides will be discussed in view of their immunostimulating activities. A possible correlation of fungal β‐1.3/1.6‐glucans differing in the branching pattern is demonstrated with in vivo tumor models. In a second part the possible role of sulfated polysaccharide structures as anticoagulating compounds is again correlated with polysaccharide structures and sulfate substitution pattern of these biopolymer derivatives.
Novel drug delivery system by chitin derivative
Authors: Tokura Seiichi , Nishi Norio , Takahashi Kiyohisa , Shirai Akihiro , Uraki Yasumitsu 
Published: March 2011

AbstractA porous chitin foam was regenerated from chitin dope in calcium chloride dihydrate saturated methanol. The porous chitin foam was shown to have cationic property, because chitin foam tended to adsorb anionic dyes through ionic binding and hydrophobic interaction. A pendant type of polymeric drug was prepared applying peptide spacer composed of phenylalanine at amino end and two step hydrolyses of polymeric drug were shown to release active drug at the final step using lysozyme and chymotrypsin in vitro.
Antiviral activity of polysaccharides against infection of tobacco mosaic virus
Authors: Sano Yoh 
Published: March 2011

AbstractIn the course of searching for antiviral substances to tobacco mosaic virus (TMV), it was found that polysaccharides have a high inhibitory activity against TMV infection. The leaves of Xanthi NN tobacco were rubbed with the mixtures of TMV and polysaccharides such as chondroitin sulfate C‐ and A‐ types. The addition of polysaccharides to the inoculum solution greatly reduced the number of local lesions formed on the inoculated leaves. Here the polysaccharide did not completely prevent virus entry into the leaves and the virus particles may penetrate and multiply in leaves without forming lesions. Although the electron micrograph showed that the virus suspension was almost monodisperse, the addition of polysaccharides caused TMV to form large raft‐like aggregates. The TMV solution became turbid after the addition of a large amount of polysaccharides. A threshold concentration of polysaccharides exists for virus precipitation, which is independent of the virus concentration. The size of polysaccharide at the threshold concentration agreed well with that obtained by light scattering method. The strength of the interaction between TMV and polysaccharides was found to be related to the degree of inhibitory activity of polysaccharides.
Polymers for medical uses
Authors: Höcker Hartwig 
Published: March 2011

AbstractA brief survey of biomaterials and of the approaches to modify their surface is given. By means of specific examples of polymers and polymer blends the chemical modification of the surface by means of wet‐chemical processes as well by plasma treatment and the consequences for endothelial cell proliferation, fibronectin adsorption, hydrophilicity, surface tension and zeta‐potential are described. The results are correlated with standard parameters of measuring hemocompatibility and a compatibility window is indicated.
The state of water in swollen polymers
Authors: Rault Jacques 
Published: March 2011

AbstractIt is shown that by low frequency measurements in hydrophilic polymers only one state of water is observed. Water behave as a classical plasticizer and ice melting in polymer is similar to ice melting in binary simple mixture. The non crystallizable water in these systems is explained by the Tg regulation effect. In oriented swollen polymers, only one state of water is observed in the time scale ∼ 1/ωq = 10−5 s by deuterium NMR. This technique gives information on the mean orientation of D2O molecules in the oriented polymer and on the fraction of mobile water molecules. The concept of bound and unbound water is not relevant for explaining the DSC and D‐NMR results.
Use of hydrogels as corneal inlays for refractive surgery
Authors: Laroche Laurent , Honiger Jiri. E. , Borderie Vincent 
Published: March 2011

AbstractA novel hydrogel has been used for intracorneal implantation, in order to correct refractive errors of the eye. Our hydrogel is a polyanionic copolymer of acrylonitrile and sodium methallylsulfonate material (AN 69, made by HOSPAL, France). We describe here its formation, chemico‐physical and biological properties (in vitro and in vivo), and its biomechanical behaviour when implanted into the cornea.
The study of stabilizer action modes by means of time‐resolved techniques: Intermediate radical cations
Authors: Brede Ortwin 
Published: March 2011

AbstractIn organic systems, radiation‐ and photo‐induced electron transfer reactions result in the first step in the formation of radical cations. With pulse radiolysis and laser photolysis experiments radical cations of phenols could be indirectly characterized whereas radical cations of sterically hindered amines (HALS compounds) could be directly observed.
Copolymerization and copolymers of brominated phenylmaleimides with some vinyl monomers
Authors: Janović Zvonimir 
Published: March 2011

AbstractThe kinetics of the free radical copolymerization in solution of N‐(4‐bromophenyl)maleimide (MBPMI), N‐(2, 4‐dibromophenyl)maleimide (DBPMI) and N‐(2, 4, 6‐tribromophenyl)maleimide (TBPMI) with styrene (St), methyl acrylate (MA), methyl methacrylate (MMA) and acrylonitrile (AN) at low and high conversions were described. Some characteristic properties of the copolymers obtained, particularly their thermal behaviour were also presented.
Plasma modification of polymer surfaces
Authors: Friedrich Jörg , Unger Wolfgang , Lippitz Andreas 
Published: March 2011

AbstractTo avoid chemical destructions of macromolecules at the polymer surface and to obtain maximum improvement in adhesion properties the short‐time exposure to plasma is a good choice. Enhanced quality of surface functionalization can be reached by chemical conversion of plasma introduced functional groups. Additionally, molecular and supermolecular orientations of the macromolecules and their re‐arrangement by plasma exposure influence the adhesion properties of polymers. Atmospheric pressure plasma is generally suitable for high‐speed surface modification of polymers.
Metalloporphyrin catalysts for living and immortal polymerizations
Authors: Inoue Shohei , Sugimoto Hiroshi , Aida Takuzo 
Published: March 2011

AbstractThe living polymerization of methyl methacrylate with aluminium porphyrin (1) proceeded dramatically rapidly at room temperature in the presence of sterically crowded organoaluminium compounds such as methylaluminium ortho‐substituted diphenolates (3a − 3g), bis(triphenylmethanolate) (4a), and triphenylaluminium, where undesired reaction between the growing species and the Lewis acids was sterically suppressed. On the basis of this Lewis acid ‐ assisted high‐speed living polymerization, various monomers such as ethyl, propyl, butyl, and dodecyl methacrylates, methacrylonitrile, and 1,2‐epoxypropane were polymerized very rapidly with the aluminium porphyrin ‐ Lewis acid systems.