bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phase separation during fast (RIM) poly‐urethane polymerization
Authors: Yang Wenliang P. , Macosko Christopher W. 
Published: March 2011

AbstractPhase separation dynamics during a reaction injection molding process of an elastomeric polyurethane was studied via FT‐IR and rheology. 4, 4′ methylenediphenyl isocyanate and 1, 4 butanediol were mixed with 50 wt% of a 2000 molecular weight poly(proplyene oxide)polyol catalyzed by dibutyltin dilaurate. A small reaction injection molding machine was used to impingement mix the chemicals and inject these directly into a Fourier transform infrared spectrometer or into a rheometer. The reaction conversion was followed by the isocyanate absorbance and the development of inter‐urethane hydrogen bonding was related to phase separation dynamics. Isothermal dynamic mechanical modulus build‐up during reaction was monitored by a thin gap parallel plate geometry subjected to small amplitude oscillation. An optimum reaction temperature was found, below which phase separation prematurely cuts off high molecular weight build up. Above this temperature phase separation is too slow and incomplete; modulus values are lower. Increasing catalyst reduces this optimum temperature.
Molecular motion and anisotropy in polymers investigated by fluorescence techniques
Authors: Fuhrmann Jürgen , Hennecke Manfred 
Published: March 2011

AbstractFluorescence polarization has been used to investigate the correlation between the orientation distribution function odfG of quasi rigid rod fluorescent guest molecules and the odfH of anisotropic host polymer in which the guests are imbedded, e.g. fluorescent molecules incorporated in the non‐crystalline regions of uniaxially stretched polyethylene (LDPE). The orientation correlation between odfG and odfH is discussed with respect to the thickness to length ratio t/1 and the length of the probe molecules. For a rigid rod length around 2 nm there is a linear dependence between the factorizable orientation parameter P2G of odfG and the length of rigid rods at given orientation of LDPE. This behaviour is obtained after correcting the different ratios t/1 of the probes.The variation of probe geometry, i.e. reference length and ratio t/1, gives information not only about the mechanism of orientation but also about the change of rotational mobility depending on size and fluorescence lifetime of the probes. Selecting probes of various length in the lifetime region of 1–6 ns, it results that microregions with reference length larger then 2 nm are rotationally immobile in the non‐crystalline regions of LDPE at ambient temperature.
Some new polyelectrolytes
Authors: Schulz R. C. , Schmidt M. , Schwarzenbach E. , Zöller J. 
Published: March 2011

AbstractSeveral polycations with different charge distributions along the main chain are described: poly(iminohexamethylene), homopolymers and block‐copolymers of 1‐azabicyclo[4. 2. 0] octane, comb‐like polymers on the basis of oxazoline macromonomers. The second part deals with polyampholytes either with random distribution of cationic and anionic units or with block structure.
Novel sulfur containing polymers
Authors: Nuyken Oskar , Reuschel Gerhard , Siebzehnrübl Florian 
Published: March 2011

AbstractSulfur containing polymers were synthesized by the addition of thiols to alkenes and alkynes. Although the polymer formation is explained on the basis of a radical intermediate these processes show typical characteristics of step growth polymerizations. These reactions have been applied for the syntheses of telechelics.
The main elementary events of degradation and stabilization of PVC
Authors: Iván Béla , Kelen Tibor , Tüdös Ferenc 
Published: March 2011

AbstractThe fundamental aspects of PVC degradation and stabilization are discussed. The primary process of thermal degradation (initiation, zip‐elimination of HCl and simultaneous formation of polyene sequences, and termination of unzipping) is reevaluated in the light of results obtained with PVCs containing increased concentrations of labile chlorines. The effect of these defects on thermooxidative stability of the resin is also discussed. It has been shown that results obtained in recent systematic stabilization studies cannot be explained by the widely accepted Frye‐Horst mechanism, i.e., substitution of labile chlorines by stabilizers. A new mechanistic proposition, the reversible blocking mechanism, for the stabilization of PVC is presented, and the effect of stabilizing reactions on the main elementary events of thermal and thermooxidative degradation is described in a unified manner.
The decomposition of potassium persulphate used as initiator in emulsion polymerization
Authors: Okubo Masayoshi , Mori Toshiyuki 
Published: March 2011

AbstractThe decomposition rate of potassium persulphate in various aqueous solutions was measured by isotachophoresis using pure water, sodium dodecyl sulphate (SDS) solution, emulsifier‐free polystyrene emulsion, SDS solution containing acrylamide monomer or an SDS‐containing emulsion polymerization system for styrene. “Free” SDS molecules in the monomolecular dispersed state were found to increase markedly the decomposition rate, whereas those which formed micelles and became adsorbed onto polystyrene particles did not increase it. The acceleration phenomenon in the former case disappeared in the presence of a small amount of monomer.
Anionic ring opening polymerization of cyclotetrasiloxanes with large substituents
Authors: Fish Daryle , Khan Ishrat M. , Smid Johannes 
Published: March 2011

AbstractCyclotetrasiloxanes with large substituents were synthesized by hydrosilylation of 1,3,5,7‐tetramethylcyclotetrasiloxane with CH2=CHCH2X, X being (CH2)2CH3, O(CH2CH2O)3CH3, OCH2epoxy and OCH2‐ benzo‐18‐crown‐6. The tetrasubstituted cycles were homo‐polymerized or copolymerized with octamethylcyclotetrasiloxane in the presence of potassium silanolate to yield polysiloxanes with side chains containing oxirane rings, crown ethers or oxyethylene ligands. In addition to a complex mixture of cycles, about 50 to 80% polymer can be recovered. The copolymer generally contains less of the substituted monomer than the starting monomer feed, but the bulky substituents do not appear to prevent formation of homo‐ or copolymer.
The use of selective deuteration for the sequence specific 1H NMR assignment of larger proteins
Authors: Arrowsmith Cheryl H. , Treat‐Clemons Lynda , Szilágyi László , Pachter Ruth , Jardetzky Oleg 
Published: March 2011

AbstractThe possibility of extending NMR methods for structure determination to larger proteins (MW > 10 kD) depends on the development of isotopic labeling protocols for the simplification of their NMR spectra (isotopic spectral editing). We describe here the successful use of selective deuteration to obtain sequence specific assignments for (thus far) more than 50% of the residues of the trp repressor protein (25 kD). This is the largest protein for which detailed sequence specific assignments have been attempted to‐date.
Thermal ageing of polycarbonate/poly(butylene terephthalate) blends
Authors: Bertilsson H. , Franzén B. , Kubát J. 
Published: March 2011

AbstractThermal ageing of PC/PBT blends and alloys has been studied with dynamic mechanical, calorimetric, and tensile dilatometry tests during creep. The substantial embrittlement occuring in PC/PBT during ageing is tentatively explained in terms of an unusually high densification of the amorphous phase. The phase boundaries have been found to increase in strength during ageing, improving the load bearing properties of the material.
Thermoreversible gelation of solutions of vinyl polymers
Authors: van Den Broecke Ph. , Berghmans H. 
Published: March 2011

AbstractThe thermoreversible gelation of solutions of isotactic poly(methyl methacrylate) is investigated. Amorphous gels can be prepared in l‐butanol by a combination of a liquid‐liquid demixing with an upper critical demixing temperature and a glass transition. Annealing of the demixed solutions above their glass transition temperature TG, results in the formation of a crystalline gel. In oxylene, crystalline gels are formed by a liquid‐liquid demixing with an lower critical demixing temperature and an annealing at room temperature. Very fast gelation is observed to occur far below room temperature in solvents like 2‐butanone.
Ordered structures of stereoregular poly(methyl meth‐acrylates) in solutions studied by spectroscopic methods
Authors: Spêváček Jiří 
Published: March 2011

AbstractThree groups of problems concerning ordered structures in solutions of stereoregular poly(methyl meth‐acrylates) (PMMA) were studied by spectroscopic methods: (i) Self‐aggregation of syndiotactic (s) PMMA in solution was followed by means of NMR and IR spectroscopy; it has been established that double helices are formed during the initial stage of aggregation, and activation and equilibrium thermodynamic parameters (ΔH, ΔS) which characterize the transition coil–double helix in s‐PMMA were determined. (ii) NMR spectroscopy has demonstrated that association in solutions of atactic PMMA proceeds via interactions of stereocomplex type (interaction between m‐diads and r‐tetrads). (iii) It has been found that 13C CP/MAS NMR spectra of crystalline forms of PMMA (prepared from aggregated solutions by solvent evaporation) conform to the double‐helix structure of these systems.
Spinodal demixing, percolation and gelation of biostructural polymers
Authors: San Biagioch P. L. , Bulone D. , Emanuele A. , Madonia F. , Di Stefano L. , Giacomazza D. , Trapanese M. , Palma‐Vittorelli M. B. , Palma M. U. 
Published: March 2011

AbstractWe present a variety of new experiments which concern the self‐assembly of a polymeric network from homogeneous solutions of Agarose, a representative biostructural polysaccharide used for previous studies at our laboratories. They allow deriving a semi‐quantitative phase diagram in the T, C plane. The diagram includes both the spinodal and gelation lines. Below a value of about 2% w/v, concentration is not sufficient for direct gelation; however, quenching of the sol from high temperatures to below the spinodal line initiates the spinodal demixing. The latter generates two sets of regions having respectively, higher‐ and lower‐than‐average polymer concentrations. In the higher‐concentration regions the functional polymer‐polymer interaction (that is, self‐assembly) is favoured. In fact, as in the course of demixing the point representative of higher‐concentration regions reaches the region below the gelation line, gelation is allowed and indeed observed to occur. This evidences the possibly more general role of spinodal demixing (extended to multi‐component systems) as a pathway for specific, local and biofunctional enhancements of concentrations. At very low concentrations (e.g. 10−4 w/v) the kinetics of demixing is still observed to occur, but the set of higher‐concentration regions is no longer percolative. In these conditions, gelation occurs only within each individual region, while the specimen remains free‐running. This illustrates a novel aspect of the notion of non‐gelling concentrations.
Neutron scattering and swelling properties of end‐linked polydimethylsiloxane networks
Authors: Geissler Erik , Hecht Anne‐Marie , Mallam Simon , Horkay Ferenc , Zrinyi Miklós 
Published: March 2011

AbstractSmall angle neutron scattering measurements were performed on polydimethylsiloxane‐toluene solutions and gels at different degrees of swelling. The scattering signal of the gel was decomposed into a solution‐like part and a static part. The thermodynamic information obtained from the solution‐like part of the signal is compared with macroscopic swelling pressure observations.
Elasticity of polymer gels: Effect of solvent quality on the shear modulus of poly(vinyl acetate) networks
Authors: Horkay Ferenc , Zrinyi Miklós , Geissler Erik , Hecht Anne‐Marie 
Published: March 2011

AbstractThe dependence of the shear modulus and of the swelling equilibrium concentration of polyvinylacetate gel homologues in equilibrium with excess isopropyl alcohol is investigated in the temperature range 30≤T≤70°C. At the theta temperature (T=52°C) the volume elastic modulus was also determined and compared with the shear modulus. The results are interpreted in terms of a free‐energy function derived on the basis of the network unfolding hypothesis.
1H and 2H NMR study of chain motion at the poly(dimethylsiloxane)‐filler interface
Authors: Litvinov V. M. , Spiess H. W. 
Published: March 2011

Abstract1H and 2H NMR methods were used to investigate the effect of fillers on the molecular motions in filled poly(dimethylsiloxane). Molecular mobility at the polymer filler interface is strongly different from that outside the adsorption layer. The influence of concentration and type of filler on molecular motions and concentration of the adsorption layer was determined.
Equilibrium processes in linear polydiorganosilanes
Authors: Dement'Ev V. V. , Frunze T. M. , Leites L. A. , Papkov V. S. , Antipova B. A. 
Published: March 2011

AbstractThe synthesis, reactions and structure of linear polydiorganosilanes, including crystalline polydialkylsilane polymers and polydiphenylsilane olygomers with various terminal functional groups are discussed in terms of the equilibrium chemical and structural processes.
The anionic ring‐opening polymerization and copolymerization of cyclic carbonates
Authors: Höcker Hartwig , Keul Helmut , Kühling Steffen , Hovestadt Wieland , Müller Achim Josef 
Published: March 2011

AbstractCyclic carbonates are eligible to ring‐opening polymerization using a wide variety of initiators such as carbanionic or alcoholate species as well as initiators known to be effective for the ring‐opening polymerization of lactones and for the group transfer polymerization of vinyl monomers. Depending on the catalyst, high molecular weight polymers may be obtained in high yields (kinetically controlled regime) or a ring‐chain equilibrium is observed upon end‐biting, back‐biting and transesterification reactions (thermodynamically controlled regime). The polymerizability of the cyclic carbonates is strongly dependent on their structure. Five‐membered cycles generally cannot be polymerized, whereas six‐membered cycles can be polymerized and copolymerized in an ideal manner. The polymerizability of higher cyclics, in particular when containing aromatic ring systems, is highly dependent on the substitution pattern of the aromatics. Since the active species in the polymerization of aliphatic cyclic carbonates was disclosed to be of alcoholate type, a copolymerization with ϵ‐caprolactone is easily achieved, the reactivity of the cyclic carbonate, however, being by far larger than that of the lactone. On the other hand, the copolymerization with pivalolactone exerts a different behaviour, since the active species of the growing pivalolactone chain after a few steps assumes the character of a carboxylate anion which is unable to promote the ring‐opening polymerization of cyclic carbonates. Since carbanionic species may be used as initiators for the ring‐opening polymerization of cyclic carbonates, polystyryl, polybutadienyl, and polyisoprenyl anions may be used as initiators to achieve the corresponding block copolymers. To obtain block copolymers with poly(methyl methacrylate) blocks a group transfer polymerization of the respective acrylate has to be performed, followed by the polymerization of the cyclic carbonate. The latter, however, rather proceeds by a metal‐ free anionic process than by a group transfer process. The ring‐opening polymerization and copolymerization of cyclic carbonates allows the preparation of a broad variety of new polymers with remarkable properties.
Network formation in polyurethanes due to allophanate and biuret formation: Gel fraction and equilibrium modulus
Authors: Dušek Karel , Špírková Miléna , Ilavský Michal 
Published: March 2011

AbstractGel fraction and equilibrium elastic modulus of networks formed from α, ω‐dihydroxypoly(oxypropylene) and bis(4‐isocyanatophenyl)methane (MDI) as a result of side reactions were compared with theoretical predictions based on the theory of branching processes (Macromolecules, 23, 1774 (1990)). If isocyanate is in excess, trifunctional allophanate and biuret groups are formed. The experimental sol fraction can be correlated with theoretical predictions. The resulting networks are rather weak and the measured equilibrium modulus can be correlated with the theoretical values calculated from the concentration of elastically active network chains if the value of the front factor is close to that of a phantom network without a trapped entanglements contribution.
Epoxy resin toughened with thermoplastic
Authors: Gilbert A. H. , Bucknall C. B. 
Published: March 2011

AbstractHighly crosslinked, brittle epoxy resin based on tètraglycidyl‐4,4′‐diaminodiphenyl methane (TGDDM) cured with 4,4′‐diaminodiphenyl sulphone (DDS) is widely used as a matrix material for aerospace composite applications. This work describes how inclusion of a polyetherimide (PEI) thermoplastic rich phase can significantly toughen the resin without a fall in apparent stiffness, which accompanies the more traditional method of rubber toughening. Dynamic mechanical analysis and scanning electron microscopy are used to characterize morphology, while fracture toughness and flexural modulus measurements are also performed on the cured resins. The extent of toughening is found to be dependent upon PEI concentration and test temperature. It is observed that the PEI rich phase toughens through ductile drawing across the faces of the advancing crack tip, and that this is the dominant toughening mechanism in the material.
Specific interaction of desthiobiotin lipids and water‐soluble biotin compounds with streptavidin
Authors: Ahlers M. , Hoffmann M. , Ringsdorf H. , Rourke A. M. , Rump E. 
Published: March 2011

AbstractAs shown for biotin lipids (Ref. 1), the formation of perfect 2‐D crystalline streptavidin domains can also be observed in the plane of desthiobiotin lipid monolayers. The binding constant of streptavidin with desthiobiotin (Ka = 5·1013 mol−1) is lower than that with biotin (Ka = 1015 mol−1) (Ref. 2). By adding free biotin into the subphase a competitive replacement and a detaching of the streptavidin domains from the desthiobiotin lipid monolayer takes place. Streptavidin domains built at receptor lipid monolayers are still functional. As could be shown, there are two biotin binding sites at each protein molecule that are fully accessible to biotin (Ref. 1). This can be proven by the interaction with biotinylated ferritin and fluoresceinated biotin. Further coupling of an anti‐FITC‐antibody can proceed and a second protein layer can be formed. Using a bifunctional biotin linker a second crystalline streptavidin layer underneath the first one can be obtained.
Monte Carlo simulation in polymer physics: Some recent developments
Authors: Binder Kurt 
Published: March 2011

AbstractThe computer simulation of macromolecular materials has to deal with phenomena on length scales from 1Å to 100Å, as well as with time scales ranging over many orders of magnitude, and thus still presents a challenge. With suitably coarse‐grained models which disregard detailed information on chemical structure nevertheless collective phenomena can be described, such as unmixing of polymer blends, mesophase ordering of block‐copolymer melts, “blob formation” in semidilute solutions, etc. Simulations of such models provide a sensitive test of approximate theories and give valuable hints for experiments.
Identification and segregation of materials in mixed waste
Authors: Soler T. Ouintana 
Published: March 2011

AbstractA great amount of plastics are present in waste material, a high percentage of which stem from the family of so‐called “commodities”. Bearing this in mind, it is essential to develop a recycling system in order to avoid the environmental deterioration their presence causes and to reuse materials whose composition enables their recovery. The first problem this paper deals with is the separation of individual polymers before recycling in order to obtain regenerated products of high quality with consequently greater value.The work involves an attempt to use chemical additives as tracers in commonly occurring plastics such as PE, PVC, PP, etc. The tracers must be non‐toxic and must not alter the physical or transformation properties of the plastics. They should be identifiable by simple spectroscopic methods so as to enable physical separation of different polymers prior to recyclying.
Application of segmental interaction energies to miscibility prediction in binary and ternary copolymer solid solutions
Authors: Cowie J.M.G. 
Published: March 2011

AbstractMany binary polymer mixtures, where at least one of the components is a copolymer, are capable of forming miscible blends within certain restricted ranges of compositions of the copolymers. The segmental interaction parameters χij can be determined from many of these systems when the phase boundaries are established, and can be used to predict miscibility in other blends. Determination of χij parameters is illustrated for a number of different copolymer mixtures and the ability to predict and map the miscibility regions in other blends is demonstrated. The technique has been extended to ternary copolymer systems with satisfactory results.
Preparation of polymer‐protected gold/platinum bimetallic clusters and their application to visible light‐induced hydrogen evolution
Authors: Toshima Naoki , Yonezawa Tetsu 
Published: March 2011

AbstractThe dispersions of polymer‐protected gold/platinum bimetallic clusters were easily and reproducibly prepared by refluxing the mixed solutions of tetrachloroaureic(III) acid and hexachloroplatinic(IV) acid in ethanol/water (1/1) at 90 ∼ 95 °C for 2 h in the presence of a protective polymer such as poly(N‐vinyl‐2‐pyrrolidone) (PVP). The gold/platinum bimetallic clusters thus obtained were very small, well dispersed and very stable. The UV‐Vis spectra and the transmission electron micrographs have indicated that each bimetallic particle has an alloy structure consisting of both gold and platinum atoms, and that the surface of the cluster particle is rich in platinum atoms and the inner core in gold atoms. The gold/platinum bimetallic clusters were used as the multi‐electron redox catalysts for visible light‐induced hydrogen evolution from water. The rate of hydrogen evolution depended on the mole ratio of the gold/platinum bimetallic clusters. The bimetallic clusters at the mole ratio of Au/Pt = 2/3 were the most active catalyst. The in‐situ UV‐Vis spectra during the reaction have indicated that the order of the aggregation in the two kinds of metal atoms is very important for structure determination of the Au/Pt bimetallic clusters. The protective polymer PVP plays a role not only in protecting hydrophobic colloidal particles in an aqueous solution, but also in determining the metal composition of the cluster surface.