bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress‐optical properties of bimodal polymer networks
Authors: Subramanian P. R. , Galiatsatos V. 
Published: March 2011

AbstractThe optical properties of bimodal poly(dimethylsiloxane) (PDMS) networks were studied with special emphasis on the non‐linear stress optical properties exhibited by these materials. In particular the effect of chain length, and junction functionality on the strain induced birefringence was investigated. It is shown that for the non‐linear properties to clearly manifest themselves a critical concentration of short chains is essential and that the junctions are tetra‐functional. However, all bimodal compositions studied were found to exhibit a non‐linear variation of birefringence with strain irrespective of the junction functionality. The optical properties of the unimodal networks were found to vary linearly with stress and strain as expected. The transition from non‐linear to linear optical behavior on increasing the molecular weight of the short chains is also established.
A rheological study of latex polystyrene‐based model systems
Authors: Nemirovski Naum , Narkis Moshe 
Published: March 2011

AbstractLatex two‐phased polystyrene blends have been produced by three different mixing routes. Polystyrene (PS) and lightly crosslinked polystyrene (XPS) latices were either mixed, or else used as seeds in two‐stage polymerizations. This resulted in different microstructures by each of the procedures, leading to different rheological behaviors. Latex PS/XPS systems flow at every composition studied. Activation energies are independent of XPS content, and of the same order of magnitude as PS. Power‐law relaxation has been observed for the physically blended system in the terminal region. This has been attributed to the formation of a “continuous” XPS network in the range 60–100% XPS.
The elasticity of nematic networks
Authors: Bladon P. , Warner M. 
Published: March 2011

AbstractNematic rubbers are composed of crosslinked polymer chains with stiff rods either incorporated into their backbones or pendant as side chains. When nematic effects axe strong, such rubbers exhibit discontinuous stress‐strain relationships and spontaneous shape changes. We model such a rubber using Gaussian elasticity theory, including the nematic interaction via a mean field. Results are presented for the cases of uniaxial extension and compression. Under uniaxial extension the rubber can undergo a first order phase transition to a uniaxial nematic phase. Under uniaxial compression first or second order transitions are possible to genuinely biaxial nematic states with biaxial strains. When nematic effects are very small (i.e. T >> Tc where Tc is the nematic‐isotropic phase transition temperature of the rubber) we postulate that the model is a good approximation to a conventional, non‐nematic elastomer, and fit our model to data from an isoprene rubber.
Dendritic analogues of engineering plastics ‐ a general one‐step synthesis of dendritic polyaryl ethers
Authors: Miller Timothy M. , Neenan Thomas X. , Kwock Elizabeth W. , Stein Susan M. 
Published: March 2011

AbstractThe first general single‐step route to dendritic or cascade polyaryl ethers analogous to common linear polyaryl ethers is described. The sodium salts of four AB2 monomers each containing a single phenolic hydroxyl group and two aryl fluorides activated toward nucleophilic substitution by carbonyl, sulphonyl, or tetrafluorophenyl moieties are shown to polymerize in hot N, N‐dimethylacetamide. The products are high molecular weight polymers (7000 < Mn < 36000), have narrow polydispersities (1.50 < Mw/Mn < 4.50), and are highly soluble in organic solvents. The molecular weights of two of the polymers increase with monomer concentration. The polymers are thermally stable (500 °C under N2) and have glass transition temperatures ranging from 135 to 231 °C.
Structural rigidity control in arborescent graft polymers
Authors: Gauthier Mario , Möller Martin , Burchard Walther 
Published: March 2011

AbstractSuccessive chloromethylation‐anionic grafting sequences on polystyrene have led to well‐defined hyperbranched macromolecules. Polymers with branching functionalities f > 5000 and molar masses over 107 g/mol were thus prepared while maintaining a ratio of mass‐ to number‐average molar masses Mw/Mn = 1,1‐1,3. Three series of styrene polymers were prepared by varying the density of grafting sites along the chain, resulting in controllable stiffening of the molecular structure. Characterization of the branched molecules by size‐exclusion chromatography/low‐angle laser light scattering and light scattering confirmed a geometric increase in molar mass for successive generations, and a low ratio of mass‐ to number‐average molar masses. Static and dynamic light scattering experiments showed that the molecules behave like hard spheres in dilute solutions. Measurements in the semidilute range, however, showed a progressive structural stiffening effect as the branching density increases.
Large‐scale production of polypropylenimine dendrimers
Authors: De Brabander‐Van Den Berg E.M.M. , Nijenhuis A. , Mure M. , Keulen J. , Reintjens R. , Vandenbooren F. , Bosnian B. , De Raat R. , Frijns T. , v.D. Wal S. , Castelijns M. , Put J. , Meijer E. W. 
Published: March 2011

AbstractThe synthesis and characterization of a new series of polypropylenimine dendrimers is reported. Using a repetition of the sequence of a Michael addition to a primary amine, followed by a heterogeneously catalyzed hydrogenation, ultra‐pure polypropylenimine macromolecules with molecular weights up to 6912 are synthesized. The reaction sequence allows the preparation of these dendrimers at very large scales, whilst the availability of a simple purification in the sequence affords ultra‐pure samples. The polypropylenimine dendrimers are fully characterized; apart from the first 0.5 generation they are all oils, possess a Tg in the range from −90 to −40 °C, are unexpectedly stable, and their intrinsic viscosity drops after generation 4.
Towards the self‐assembly of polyrotaxanes
Authors: Sun Xiaoqiang , Amabilino David B. , Ashton Peter R. , Parsons Ian W. , Fraser Stoddart J. , Tolley Malcolm S. 
Published: March 2011

AbstractThe self‐assembly of a number of rotaxanes, pseudorotaxanes, and a pseudopolyrotaxane based on the π‐electron deficient cyclobis(paraquat‐p‐phenylene)d̊ and threads and dumbbell components composed of π‐electron rich hydroquinone rings incorporated symmetrically within polyether chains terminated in the case of the rotaxanes by adamantoyl stoppers.
Towards tobacco mosaic virus‐like self‐assembled supramolecular architectures
Authors: Percec V. , Heck J. , Johansson G. , Tomazos D. , Ungar G. 
Published: March 2011

AbstractThis paper discusses the molecular design of selected examples of structural units containing taper shaped exo‐receptors and various crown ether, oligooxyethylenic, and H‐bonding based endo‐receptors, which self‐assemble into cylindrical channel‐like architectures via principles resembling those of tobacco mosaic virus (TMV). The ability of these structural units to self‐ assemble via a delicate combination of exo‐and endo‐recognition processes will be presented. A comparison between various supramolecular (generated via H‐bonding, ionic, and electrostatic interactions) and molecular “polymer backbones” will be made. The present limitations concerning the ability to engineer the structural parameters of these supramolecular channel‐like architectures and some possible novel material functions derived from them will be briefly mentioned.
Self‐assembly of main chain liquid crystalline polymers via heteromeric hydrogen bonding
Authors: Alexander C , Jariwala C P , Lee C M , Griffin A C 
Published: March 2011

AbstractComplexation between pyridines and carboxylic acids is driven by hydrogen bonding. This simple, single hydrogen bond is shown to be capable of serving concomitantly as both the agent of liquid crystallinity and as the coupling bond generating an extended linear chain structure. Three such complexes made from an aromatic diacid and three structurally different bis pyridyls were prepared. In each case the association complex self‐assembles into an organized liquid crystalline phase. Discussion of this complexation as a step‐growth polymerization process is presented along with an examination of the suitability of various methods for characterizing these materials.
Hybrid thermotropic liquid‐crystalline block copolymers
Authors: Chiellini Emo , Galli Giancarlo , Angeloni Amino S. , Laus Michele , Bignozzi Maria Chiara , Yagci Yusuf , Serhatli Ersin I. 
Published: March 2011

AbstractA new approach to the preparation of two classes of block copolymers containing liquid‐crystalline segments is reported. Copolymers 1 and 2 are constituted by polytetrahydrofuran and side‐chain liquid‐crystalline polymethacrylate blocks, whereas block copolymers 3 consist of polystyrene and main‐chain liquid‐crystalline polyester blocks. The synthetic procedures leading to copolymers 1‐3 are extremely versatile and can be used to prepare a great variety of block copolymer architectures. In both copolymer classes the chemically different blocks are strongly segregated in the solid and melt phases and undergo individual phase transitions. The mesophase transition temperatures of the liquid‐crystalline blocks are very similar to those of the corresponding homopolymers, and their enthalpies are directly proportional to the content of the liquid‐crystalline block.
Synthesis of planar poly(p‐phenylene) derivatives for maximization of extended π‐conjugation
Authors: Tour James M. , Lamba Jaydeep J. S. 
Published: March 2011

AbstractDescribed is the synthesis of a ladder polymer with a poly(p‐phenylene) (PPP) backbone. The main PPP backbone was synthesized via palladium‐catalyzed coupling of an arylbis(boronic ester) with an aryl dibromide. Imine bridges, formed by exposure of the polymer to trifluoroacetic acid, are used to force the consecutive units into planarity. The bridging units are sp2 hybridized thus allowing for greater π‐electron flow between the consecutive phenyl units by lowering the band gap between the hydroquinoidal and the quinoidal forms of the phenylene backbone. When the bridges are n‐dodecyl substituted, the fully planar structures (with Mn < 5 000) are soluble in hot chlorobenzene from which flexible free standing films can be cast. The n‐butyl substituted polymers and the higher molecular weight n‐dodecyl substituted polymers are soluble in CH2Cl2/trifluoroacetic acid mixtures. The optical spectra of the planar systems are compared to that of the parent nonplanarized polymers, some analogous planar oligomers, and oligo(p‐phenylenes).
Thermodynamics of polymer blends
Authors: Koningsveld Ronald 
Published: March 2011

AbstractThe general principles of thermodynamic equilibrium in binary liquid systems are reviewed briefly, and extended to quasi‐binary mixtures of polydisperse polymers. Molecular models allowing actual phase behaviour to be discussed in terms of molecular parameters are exposed to data on the system polystyrene/polyvinylmethylether. Disparity in size and share between the repeating units must be introduced to obtain reasonable agreement between theory and experiment. The neccessary introduction of the molar‐mass distribution detracts from this agreement which makes clear that other aspects exist that must be taken into account. For example, cross association between repeating units has a marked effect on phase behaviour. Blends are subject to two kinds of thermodynamic aging which lead either to considerable mutual solubility in supposedly immiscible blends, or to metastable equilibria transforming into states of lower Gibbs energy. In both cases physical proerties of the blend will change with time.
PC/ABS blends: Compatibilization and mechanical behaviour
Authors: Greco Roberto , Dong Lisong 
Published: March 2011

AbstractPC/ABS(M) blends, encompassing the whole composition range between pure PC and ABS(M), were prepared by melt‐mixing in a Brabender‐like apparatus. Thermal, mechanical and impact tests were performed on compression moulded specimens. Inward Tg shifts were detected for PC and ABS(M) in the blends with respect to pure PC and ABS(M) values, indicating an interaction between the component domains. This finding was confirmed by the comparison of the experimental tensile moduli with the Kernels model predictions, showing an evidence of a good adhesion between the phases. A synergistic effect was observed for the impact strength as well as for the maximum stress at an ABS(M) blend content of about 25 weight %. All the results are interpreted on the basis of an interlayer existing at the boundary between the PC and ABS phases. A preliminary investigation on the influence of the ABS internal composition, keeping constant all the other conditions (mixing, processing, specimen preparation), was carried out as well. Differences in the properties of PC/ABS(M) and PC/ABS(B) blends are thoroughly discussed. The compatibility between PC and ABS domains seems to be scarcely influenced by such a parameter in these blends.
Reactive blending of bioaffine polyesters through free‐radical processes initiated by organic peroxides
Authors: Immirzi Barbara , Malinconico Mario , Martuscelli Ezio , Volpe Maria G. 
Published: March 2011

AbstractReactive polymer blending of poly(β‐hydroxybutyrate) (PHB) and its valerate copolymers (PHBV) are reported, following two different methodologies, namely polymerization of rubber inclusions in the preformed matrix or reactive melt blending of preformed polymers. As second phase, poly(butyl acrylate) (PBA) and polycaprolactone (PCL) are used. The results of spectroscopic, thermal, mechanical and morphological analysis indicate the existence of chemical interactions between the blend components. Such interactions are also responsible of a drastic change in the morphology.
Intercrosslinked polymer networks by simultaneous curing of unsaturated polyesters and bismaleimide resins
Authors: Abbate M. , Di Liello V. , Martuscelli E. , Musto P. , Ragosta G. , Scarinzi G. 
Published: March 2011

AbstractThe modification of an unsaturated polyester resin by incorporating a second co‐reactive monomer as a thermosetting bismaleimide is described The bismaleimide was readily dissolved in the uncured polyester matrix up to a concentration of about 20% wt. FTIR isothermal measurements indicated that the kinetics and the mechanism of the curing process were strongly affected by the presence of the bismaleimide. The resulting inter‐crosslinked network showed a gradual enhancement of the elastic modulus in a wide range of temperatures by increasing the bimaleimide amount in the system. This enhancement was obtained without altering the intrinsic toughness of the matrix.
The reactor granule technology: A revolutionary approach to polymer blends and alloys
Authors: Galli P. 
Published: March 2011

AbstractThe new plastic materials frontier in general and in thermoplastic polyolefins in particular developed in the last years and into next century are and will be represented by polymer alloys. The new trend in polymer alloy is to obtain them from monomer directly in the reactor, replacing the polymer blends previously made by mechanical melt extrusion of preformed polymers. It discloses new opportunities in term of properties together with better economics. The reactor granule technology developed by Himont/Montecatini produces spherical form alloys that are a synergistic combination of morphological, chemical, rheological and thermomechanical properties, by which the polymer finds many applications not previously suitable for polypropylene or polyethylene. In reactor granule technology the multimonomer random and heterophasic copolymers can be produced primarly within the granule enclosed by a solid polymer skin free from sticky nature, typical of polymers obtained by gas‐phase technology and causing many problems like particles agglomeration and fouling.
Blends of natural and synthetic polymers: A new route to novel biomaterials
Authors: Giusti Paolo , Lazzeri Luigi , Barbani Niccoletta , Lelli Letizia , De Petris Silvano , Cascone Maria G. 
Published: March 2011

AbstractBlends of natural and synthetic polymers were studied for potential applications in the biomedical field. Collagen and hyaluronic acid were mixed in aqueous solution with poly(vinyl alcohol) and poly(acrylic acid). The properties of the blends were studied by differential scanning calorimetry and dynamic mechanical thermal analysis. Some methods were also investigated to enhance the miscibility of the polymers in these blends.
Diffusion of spherical micronetworks in polymer diluent systems and melts studied by dynamic light scattering techniques
Authors: Bartsch Eckhard , Frenz Volker , Renth Falk , Sillescu Hans 
Published: March 2011

AbstractSpherical polystyrene (PS) micronetworks can be prepared in microemulsion with bulk radii of 5–60 nm and different cross‐linking densities. The diffusion of these PS spheres has been studied in polymer diluent systems ranging from dilute solutions to plasticized melts by using forced Rayleigh scattering and photon correlation spectroscopy. On increasing the PS concentration, a colloid glass transition is observed at a volume fraction ΦC ≈ 0.64 of the swollen spheres. At higher concentration inside the “colloid glass” state the sphere diffusion is slowed down and becomes very complex but can be observed up to the limit of a melt of collapsed spheres.
Polarized and depolarized dynamic light scattering of concentrated polystyrene solutions
Authors: Brown Wyn , Nicolai Taco 
Published: March 2011

AbstractPolarized and depolarized dynamic light scattering have been used to examine the dynamics of concentrated polystyrene solutions in dioctyl phthalate and toluene. Time‐temperature superposition of the depolarized intensity correlation functions gave master curves covering more than 10 decades on the time scale. Polarized correlation functions are resolved into relaxational and diffusive components having different temperature dependences. When the relaxation rate of the concentration fluctuations approaches the reorientational relaxation rate, the concentration fluctuations become q‐independent i.e. the diffusional relaxation is rate‐determined by the backbone mobility. With a small molecule solvent as toluene, however, a part of the concentration fluctuations relaxes faster than the orientational relaxation, i.e., the diffusion occurs in the free volume within the “frozen” network.
Static and dynamic scattering from cyclic diblock copolymer chains in solution
Authors: Borsali Redouane , Benmouna Mustapha 
Published: March 2011

AbstractThis work discusses the static and dynamic scattering properties of (A‐B)r ring diblock copolymer chains in the semi‐dilute solutions. The case of a symmetric diblock is considered in details. The results show substantial differences with respect to linear diblock copolymers. This is mainly due to the effect of connectivity of the chain extremities A and B leading to different conformations for both types of architectures. The additional entropic interaction in cyclic chains induces a decrease of the elastic scattering intensity and a shift of the location of its maximum to a higher q value. As for the dynamics, the fact that the two extremities are connected speeds up the frequency of the interdiffusion mode and shifts its minimum to higher q value. A discussion of hydrodynamic interactions is also included.
The zeolate ligand; zeolite encapsulated semiconductor nanomaterials
Authors: Ozin Geoffrey A. , Steele Mark R. 
Published: March 2011

AbstractConsolidation of the results of structural, spectroscopic and kinetic studies of a range of intrazeolite guests and their reactions have led to the development of the “crown ether‐zeolite ligand analogy” and the concept of the “zeolate” as a macrospheroidal or macrocylindrical multidentate anionic ligand. This view of a zeolite cavity or channel as a collection of interconnected aluminosilicate crown ether‐like building blocks, permits a coordination chemistry approach to the understanding of metal‐ligand bonding (capping, anchoring, complexing, stabilizing and structure‐directing phenomena) in a variety of zeolite guest‐host inclusion systems. In this paper we focus attention on the role that the zeolate ligand plays in the organization of semiconductor precursors and their assembly to semiconductor nanoclusters with particular reference to II‐VI nanomaterials.
Polymeric porphyrin and metalloporphyrin assemblies in bulk solution
Authors: Fuhrhop Jürgen‐Hinrich , Bindig Uwe , Demoulin Corinna , Rosengarten Bianca , Siggel Ulrich 
Published: March 2011

AbstractSome water‐soluble porphyrins aggregate in aqueous media to form fibrous assemblies. When polynucleotides are used as matrices, porphyrin monomers are aligned at the periphery or intercalated. Porphyrin‐porphyrin interactions hardly occur. Metal‐metal or metal‐ligand‐metal interactions have been observed in oxo‐oligomers, pyrazine‐bridged dimers and radical dimers. β‐Substituted metallo‐porphyrins, however, form no polymers. The only linear polymerization, which has so far been observed in molecular asemblies, occurs with amphiphilic porphyrin amides, amines and carboxylates and their metal complexes in water and of bacteriochlorophyll in DMF/water. These compounds form long‐lived high molecular weight micellar, inverse micellar and vesicular fibers spontaneously in aqueous media. The porphyrin fibers in water are about 4‐6 nm thick and up to several of μm long.
Metal coordination by natural biomacromolecules
Authors: Reedijk Jan 
Published: March 2011

AbstractAn overview is presented of the role of metal ions in living systems, with special attention to the coordination of the metal ions to the ligands in biologically occurring macromolecules. After a discussion of the commonly occurring ligands in biological systems, the several roles of the metal ions will be discussed (storage & transport, structure generation & stabilisation, catalysis and roles as drugs).
O2/n2‐separation by polymer‐bound cobalt complexes
Authors: Nishide Hiroyuki , Suzuki Takayuki , Soejima Yuji , Tsuchida Eishun 
Published: March 2011

AbstractFacilitated or complexation‐mediated transport of oxygen in the solid membrane containing a fixed carrier was described, by using the polymer‐bound cobalt Schiff's base chelate (CoS) and cobaltporphyrin (CoP). α3 β‐Substituted cobaltporphyrin derivatives were synthesized: The oxygen‐binding reaction to cobalt was affected by the cavity structure on porphyrin, i.e., unbulky amido‐substituted groups such as acetylamido‐ and acrylamido‐substituents enhanced oxygen‐binding and ‐dissociation rate constant or provided an oxygen‐binding pathway. Oxygen transport through the membranes of these polymer‐bound CoP derivatives was selectively augmented due to the rapid and reversible oxygen‐binding. Diffusion constants via the fixed CoPs correlated to the characteristics of oxygen‐binding reaction.
A critical overview of the catalytic potential of zeolite supported metal complexes
Authors: De Vos D. E. , Thibault‐Starzyk F. , Knops‐Gerrits P. P. , Parton R. F. , Jacobs P. A. 
Published: March 2011

AbstractThis paper reviews some important items for the design of new zeolite‐metal complex supramolecules. After an overview of the synthesis methods for these systems, complexation reactions inside zeolites are discussed in detail. The last part is focused on the effects of encapsulation on the reactivity of the complexes.