bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular motion and anisotropy in polymers investigated by fluorescence techniques
Authors: Fuhrmann Jürgen , Hennecke Manfred
Published: March 2011

Fluorescence 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

Several 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

Sulfur 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

The 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

The 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

Cyclotetrasiloxanes 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

The 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

Thermal 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

The 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

Three 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

We 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

Small 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

The 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

1H 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

The 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

Cyclic 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

Gel 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

Highly 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

As 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

The 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

A 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

Many 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

The 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.
Polyphosphate chains by addition of oxiranes to phosphoric acid
Authors: Biela Tadeusz , Nyk Andrzej , Kubisa Przemyslaw
Published: March 2011

Addition of diepoxides to the acids of phosphorus provides a new, attractive route to polyphosphates. In order to understand better the mechanism of this reaction and the structure of the products, the model reactions, namely additions of simple oxiranes to the acids of phosphorus, have been studied. It was shown that this reaction is catalysed by the P‐OH groups of the acids. Activation of the oxirane molecule occurs predominantly by formation of the hydrogen bonded species while ionized form of acid plays only a minor role at the studied conditions (1,4‐dioxane solution, 25°C). Reactivity of subsequent P‐OH groups in phosphoric acid increases with increasing degree of substitution by ‐OCH2CH2OH groups. The ratio of the rate constants of formation of mono‐, di‐, and triesters of phosphoric acid is equal to 1/2/4. This has been attributed to the formation of internal hydrogen bonds, involving substituents and the P‐OH groups. The observed order of the rate constants shows that reaction can not be stopped at the diester stage (linear units) and triester species (branched units) are formed fast. However, due to the large difference in the rate of hydrolysis, especially pronounced at basic conditions, triesters of phosphoric acid can easily be converted into the corresponding diesters by simple hydrolysis. Thus, the addition of diepoxides to phosphoric acid, followed by hydrolysis, leads to essentially linear polyphosphate chains.
Zwitterionic chain polymerizations of cyanoacrylates
Authors: Pepper D. C.
Published: March 2011

The lecture reviews recent studies on vinyl and vinylidene compounds, chiefly alkyl cyanoacrylates. It emphasizes the kinetics, especially the distinctive SINT (slow‐initiation‐no‐termination) pattern, and the composite mechanism of initiation by tertiary amines. The need for corroboration of interpretations, clarification of ambiguities and extensions is emphasized.
Model theory of relaxation properties of macromolecules in the nematic LC state
Authors: Gotlib Yuli , Medvedev Grigori , Fridrikh Sergei
Published: March 2011

The continuous and lattice dynamic models of the macromolecules in the LC state are considered. The relaxation properties of polymer chain in the nematic LC state may depend on both the variation of the conformation in the ordered state and on the activation barrier of the molecular field. The calculation and comparison of the longitudinal and transversal relaxation spectra for the continuous and discrete rotameric mechanism of the mobility are performed. For the simplest model of the heterogeneous polymer chain for continuous dynamic models the complicated relaxational behavior with two longitudinal and two transversal branches is manifested. The dynamic properties of the lattice dynamic model with spacer consisting of several bonds are considered.
Zirconocenium cation catalysis of propene polymerization
Authors: Chien James C. W. , Tsai Woei‐Min
Published: March 2011

rac‐Ethylenebis(1‐η5‐indenyl)dimethylzirconium (1) was reacted with triphenylcarbenium tetrakis(pentafluorophenyl)borate (2) to produce in situ the rac‐ethylenebis(indenyl)methylzirconium cation (3). This aluminium‐free catalyst showed propene polymerization activity (A) and stereoselectivity which both increase with the decrease of polymerization temperature (Tp). At very low Tp, 3 behaved as a “single‐site” catalyst. An efficient way to produce such cation is to react ansa‐zirconocene dichloride with 2 in the presence of TEA (=triethylaluminium). A superior cationic catalyst was obtained from rac‐dimethylsilylenebis(1‐η5‐indenyl)dichlorozirconium, 2, and TEA, which polymerizes propene at −20°C(−55°C) with activity of 2×109 (3×108) g polypropene per (mol Zr η mol C3H6 η h) to polypropenes which are 93.8% (99.4%) isotactic with melting temperature Tm = 152.6°C (159.9°C) and viscosity‐average molecular weight Mv = 1.4×105 (2.2×105). The addition of methylaluminoxane lowers the A of the cationic catalyst especially at low Tp. Rigorously speaking, the cation derived from 1 or 3 behaves as a “single site” catalyst only at very low Tp. The use of TEA significantly and unexpectedly enhances the efficiency of the zirconocenium catalyst system.
A theory for concentrated fiber suspensions with strong fiber‐fiber interactions
Authors: Sandstrom Chad R. , Tucker Charles L.
Published: March 2011

A theory is presented for the flow‐induced fiber orientation and stress in fiber‐reinforced polymer composites with planar fiber orientation. The rate of change of fiber orientation is given as a function of the strain rate in the continuum and the probabilistic effects of physical inter‐fiber contacts. The continuum stress is calculated from the stress in the fluid and fibers, where fiber stress is a result of the local disturbance in the fluid velocity field and of the inter‐fiber contact forces. Fiber orientation is described via a probability density function whose transport equation has the form of a standard advection‐diffusion equation with an orientation‐dependent rotary diffusion. This equation is solved using a finite difference scheme and the results are presented.
Supramolecular chemistry — Molecular information and the design of supramolecular materials
Authors: Lehn Jean‐Marie
Published: March 2011

Molecular information expressed through molecular recognition events provides means for directing the spontaneous formation of supramolecular species from complementary components. It may allow the design and engineering of supramolecular materials, in particular of liquid crystalline and of polymeric nature. Thus, supramolecular mesophases have been obtained from molecular recognition‐induced association of suitable subunits. The self‐assembly of complementary ditopic components generates liquid crystalline “polymers” of supramolecular nature; it takes place by a progressive growth revealed by electron microscopy: from nuclei, to filaments, to tree‐like species, to strings and fibers that present helicity induced by the chirality of the subunits. A rich variety of structures and properties may be expected to result from the blending of supramolecular chemistry with polymer chemistry and materials science.
Nitrogen based flame retardants for nitrogen containing polymers
Authors: Horacek H. , Grabner W.
Published: March 2011

The future aspects of Nitrogen based flame retardants in Nitrogen containing polymers are promising, as they contain no other chemical element than already present in the polymers. Sucessful applications are:

* Melamine in Combustion Modified High Resilient Foam

* Melamine in B‐1 rigid foam

* Melamine Cyanurate in Polyamides

* Melamine and Melamine salts in intumescent paints

* Melamine Cyanurate in thermoplastic Polyurethanes.
What is a ‘gel’?
Authors: Almdal Kristoffer , Dyre Jeppe , Hvidt Søren , Kramer Ole
Published: March 2011

Some of the existing definitions of the term ‘gel’ are discussed and shortcomings are identified. A purely phenomenological definition is proposed: a gel is a soft, solid or solid‐like material consisting of two or more components one of which is a liquid, present in substantial quantity. ‘Solid‐like gels’ are further defined in terms of the dynamic mechanical properties.
Synthesis of soluble, liquid crystalline aramids via transition metal π‐Complexation
Authors: Dembek Alexa A. , Burch Robert R. , Feiring Andrew E.
Published: March 2011

An organo‐soluble, liquid crystalline organometallic polymer, (p‐phenyleneterephthalamide)Cr(CO)3 [(PPTA)Cr(CO)3], is prepared by polycondensation of (p‐phenylenediamine)Cr(CO)3 with terephthaloyl chloride. Polarizing optical microscopy of this high molecular weight metallo‐aramid shows a nematic liquid crystalline texture in N, N‐dimethylacetamide (DMAc), demonstrating that metal π‐complexation maintains the lyotropic, rigid‐rod character of PPTA. A PPTA copolymer with 50% of the diamine rings Cr(CO)3 π‐complexed is also soluble and lyotropic in DMAc. Tensile properties of films of the 100% Cr(CO)3 complexed aramid are isotropic in the plane of the film, while those of the 50% complexed analog are highly anisotropic. The organometallic substituent is a site for polymer functionalization: exchange of a carbonyl for a trimethylphosphine ligand, and subsequent polymerization affords the phosphine‐functionalized (PPTA)Cr(CO)2P(CH3)3, which has a much higher critical concentration for liquid crystal formation. Oxidative decomplexation of the Cr(CO)3 group yields the parent PPTA, demonstrating the reversibility of the organometallic modification approach.
Macromolecular metal complexes an overview
Authors: Wöhrle Dieter
Published: March 2011

An introduction to the 5th International Symposium on Macromolecule Metal Complexes (MMC V) is given. Macromolecule metal complexes are classified in two different types of structural arrangements. Examples are exemplarily given from the research in the authors laboratory. Some properties and potential applications are mentioned. Outstanding results described in 24 contributions of main lectures are related to the increasing importance of the field of macromolecular metal complexes.
Thermoreversible gelation with junctions of variable multiplicity
Authors: Tanaka Fumihiko , Stockmayer Walter H.
Published: March 2011

Effect of junction multiplicity on the phase behavior of physical gels is studied with special attention to the interference phenomena between gelation and phase separation. Three important models of the junction multiplicity are detailed, each representing cross‐linking by hydrogen bond, microcrystallization and dipole aggregation. Singularities accompanying the gelation transition are found to be analogous to those of the Bose‐Einstein condensation.
Electrical conductivity of iodine doped pseudo interpenetrating polymer networks
Authors: Frisch H. L. , Chen Z. J. , Chen X.
Published: March 2011

The iodine doped pseudo interpenetrating polymer networks (PIPN's) of both conjugated and non‐conjugated linear polymers in less conducting crosslinked polymer networks may possess modest DC conductivities, σ, of the order of the iodine doped bulk polymers. There is evidence that critical percolation occurs in PIPN's and that these materials possess a quasi‐one dimensional character unlike the iodine doped bulk polymers, e.g. the σ of the iodine doped PIPN's increases from about 120 K to 4 K with decreasing temperature. We provide a simple partial (near and somewhat below room temperature) theory and summarize conductivity and resonance Raman spectroscopic studies.
Polymer chains at the interface of two different phases
Authors: Kosmas M. , Kosmas A.
Published: March 2011

We describe the macroscopic behaviour of polymers at the interface of two different phases in terms of the two average lengths which the chain units obtain at the two phases. The possibility for the units of the same chain to have different average lengths changes the spatial monomeric distribution and all the other macroscopic properties of the polymers compared to those of similar systems in a single phase.
Surface analysis of polymer materials by secondary ion mass spectrometry
Authors: Benninghoven Alfred , Rading Derk
Published: March 2011

Atomic as well as molecular secondary ions are emitted from the uppermost monolayer of a solid during ion bombardment. Mass analysis of these positive and negative secondary ions supplies detailed information on the chemical composition of the bombarded surface. High mass range (> 10,000 u), high mass resolution (m/Δm > 10,000), accurate mass determination (ppm range) and high sensitivity (ppm of a monolayer) are achieved by applying time‐of‐flight (TOF) mass analyzers. TOF‐SIMS has been successfully applied to a wide variety of polymer materials, including polymer blends, chemically or plasma modified surfaces, and plasma polymerization layers. Detailed information on the composition of repeat units, endgroups, oligomer distributions, additives, as well as surface contaminants can be obtained. Basic concepts of TOF‐SIMS will be described and typical analytical examples for the characterization of polymer materials will be presented.
Recent product developments and process monitoring in the field of reactive polymer compounding
Authors: Fritz Hans Gerhard , Cai Quiongying , Bölz Uwe , Anderlik Rainer
Published: March 2011

This contribution aims at the illustration of the potential of reactive blending, hold up polypropylene modification as an example. Formulation rules and process technology to create PP/PA‐alloys and thermoplastic elastomers based on PP/EP(D)M, as well as the property profiles of the resulting products will be described. A separate chapter is dedicated to functionalization of polypropylene by mainchain‐grafting of selected linkage molecules, to widen the range of application of this low‐cost polymer.
Reactive blending of poly(ethylene terephthalate) with ethylene‐propylene rubber
Authors: Yokoyama Koichi , Fujita Yuji , Higashida Noboru , Inoue Takashi
Published: March 2011

A gram‐scale miniature reactor designed for reactive blendind was introduced. A brief review was given on the light scattering method for morphology characterization and the ellipsometric analysis on polymer‐polymer interface. These methods were applied for the reactive blending of poly(ethylene terephthalate) with ethylene‐propylene rubber (70/30 PET/EPR). Compared with non‐reactive system, the reactive one yielded finer dispersion of rubber particles. It showed better stability of particle dispersion during static annealing. The reactive system with thick interface showed higher impact strength than the non‐reactive one having same particle size but thinner interface, suggesting that the thick interface may be a prerequisite to the rubber toughening.
Fundamentals of texturing: Crystallization by heat transfer and flow
Authors: Janeschitz‐Kriegl H.
Published: March 2011

The textures which are obtained in crystallizing materials, are strongly dependent on the processes of casting (flow and heat transfer). It is very important to discern between two extreme limiting cases, viz. the heat conduction controlled processes (occurring with fast crystallizing materials and thick samples) and the nucleation rate controlled processes (occurring with slowly crystallizing materials and thin samples). Clearly, polymer processing must be classified near the latter limiting case. In principle, the mathematical problems were solved by W. Schneider et al. in the course of an Austrian National Working Party. But, the evaluation of the physical data is a cumbersome task. A brief report is given of the (partial) unravelling of the crystallization kinetics of isotactic PP under the influence of shear flow.
Recent advances in molecuar and supermolecuar characterization of cellulose and cellulose derivatives
Authors: Kamide Kenji , Saito Masatoshi
Published: March 2011

Recent advances between 1985 and early 1993 in the following topics of the characterization of molecular structure and molecular properties of cellulose and its derivates (CD) made in the authors' laboratories are briefly reviewed: (1) A theoretical basis of the assignment of carbonyl carbon peaks of 13C NMR spectra on cellulose acetate (CA) was given, especially when the total degree of substitution <> is below 3. (2) Molar fractions of 8 kinds of unsubstituted and partially or fully substituted anhydroglucopyranose units were successfully determined for CA and sodium cellulose sulfate (NaCS). (3) The sequence distribution of substituted and unsubstituted anhydroglucopyranose units along a water–soluble CA chain was evaluated. (4) C6‐substituted (i.e., 6‐O‐acetyl) CA and C2‐ and C6‐substituted CA were synthesized, and the full assignment of the 13C NMR spetrum of the former was given and a new method for evaluating the degree of substitution at C6 position was proposed. (5) By destructing the intramolecular hydrogen bonding, cellulose becomes soluble in aq. sodium hydroxide. The specific supermolecular structure of aq. sodium hydroxide, dissolving mechanism, dissolved state and molecular parameters of cellulose in aq. sodium hydroxide were discussed. (6) The solubility behavior of CA with a wide range of total degree of substitution in solvents including water, acetone/water and acetone is controlled by the distribution of substitution and the supermolecular structure. (7) The existence of O3‐H … O'5 intramolecular hydrogen bonds in a water‐in soluble cellulose derivative with hydrophilic substituent (NaCEC) was confirmed by CP/MAS 13C NMR and deuteration IR method. At a relatively low degree of substitution the solubility of the derivative in water or aqueous alkali was mainly governed by considerable destruction of the intramolecular hydrogen bonds. (8) The persistence length q, evaluated directly by small‐angle X‐ray scattering (SAXS) on CA with different total degree of substitution <> ranging from 0,8 to 2,9 confirmed definitely the conclusion drawn before by Kamide and Saito on the molecular rigidity of CD, especially the effect of <> on q. (9) C6‐substituted CA shows different solubility towards dimethylacetamide and water at 20°C, as compared with C2‐ and C3‐subsituted CA and C2‐, C3‐ and C6‐ substituted CA, whose <> is ca. 0,6.
Polymerization of acetylenes with rare earth coordination catalysts
Authors: Shen Zhiquan
Published: March 2011

The polymerization of acetylene and its derivatives by rare earth coordination catalysts and the characterization of the polymers so obtained in our laboratory are reviewed.

Because of the metallic conductivity possessed by doped polyacetylene and the unique properties such as conductivity (semiconductivity), paramagnetism, migration and transfer of energy and chemical reactivity and complex formation ability often shown by acetylenic polymers, which seem promising as specialty polymers, there has been considerable interest in the polymers of acetylene and its derivatives. A wide variety of catalyst systems have been developed for the polymerization of acetylenes. But there has been no information concerning the use of rare earth compounds as catalysts in the polymerization of acetylene and its derivatives. We for the first time in 1981 have succeeded in the polymerization of acetylene with rare earth coordination catalysts, which in turn is a development based upon earlier work on the diene polymerization using rare earth coordination catalysts(Ref. 1). Using rare earth catalysts, acetylene can be polymerized conveniently into high cis polyacetylene films with metallic sheen at room temperature and phenylacetylene can also be polymerized into high molecular weight, high cis polyphenylacetylene films at ambient temperature. Thus new varieties of polyacetylenes have been developed and a novel family of coordination catalysts consisting of a rare earth compound plus trialkyl aluminum for the polymerization of acetylenes has been exploited. This article reviews our studies on the polymerization of acetylene and its derivatives with rare earth coordination catalysts and on the characterization of the polyacetylenes prepared.
Design of functional polymers based on organic synthesis ‐ novel polymerizations of allene and propargyl derivatives
Authors: Endo Takeshi , Tomita Ikuyoshi
Published: March 2011

This paper describes our recent work dealing with novel polymerization methods of allene and propargyl derivatives. By the radical, cationic, and living coordination polymerizations, polymers bearing exomethylene moieties in the side chain could be obtained. The polymers obtained could undergo the cationic crosslinking reaction. As step‐growth polymerizations, spontaneous copolymerizations, polyadditions with dithiols, and coupling polymerizations using palladium catalyst are also described.
Polymer dispersed liquid crystal display device for projection high definition television application
Authors: Chang S. J. , Chiao S. , Lai W. J. , Lin C. M. , Fuh Andy Y. G.
Published: March 2011

Polymer dispersed liquid crystal (PDLC) is a light scattering material that operates on the principle of electrically modulating the refractive index of the liquid crystal in an optical isotropic, transparent solid. The principle of operation of the PDLC device, the interface requirements between PDLC material and its driving circuit are studied. For high definition television (HDTV) application, a detailed comparison of PDLC vs. twisted nematic/super twisted nematic (TN/STN) display devices will be discussed. It was found that single crystal metal oxide semiconductor field effect transistor (MOSFET) is better than conventionally used thin film transistor (TFT) in driving these PDLC light valves.
Use of noncovalent interactions to form novel liquid crystalline polymeric materials
Authors: Geraldine Bazuin C. , Brandys Frank A. , Eve Tegan M. , Plante Michel
Published: March 2011

A novel concept in polymeric liquid crystalline (LC) materials, via electrostatic grafting or complexation of functionalized mesogens and appropriate polymers, is described. It is applied to three specific systems characterized by side‐chain LC architecture, two of which involve hydrogen‐bonding interactions, the third ionic interactions. In these systems, complexation tends to create greater order in the mesophases present. In the hydrogen‐bonded systems, the transition temperature from the isotropic state tends to decrease compared to that of the functionalized mesogen; in the ionically‐bonded system, the reverse is true. At low concentrations, the mesogens act as plasticizers.
Characterization and flow properties of lyotropic ultrahigh‐molar‐mass polysaccharide mesophases
Authors: Jacobs Alexandra , Kulicke Werner‐Michael
Published: March 2011

The occurrence of lyotropic mesophases in solutions of various polysaccharides, such as non‐ionic schizophyllan and anionic xanthan, was demonstrated by means of polarizing microscopy. In contrast to synthetic polymers where the formation of liquid‐crystalline phases has been attributed to the presence of mesogenic groups in the main‐ or side‐chain, here a helical structure is a prerequisite for the formation of mesophases. It was then shown that the stability of the helix is dependent on the chemical structure and the arrangement of the side groups. Apart from their optical anisotropy, some lyotropic mesophases are distinguished by extraordinary viscous and elastic properties (e.g. maximum behaviour of viscosity). The viscoelastic material functions were determined by rheological methods. A precise characterization of the chemical and steric microstructure should provide information on the ability of polysaccharides to form mesophases. Determination of the chemical microstructure (quaternary polymer) was carried out by 1H NMR spectroscopy after ultrasonic degradation. Low‐ and multi‐angle laser light scattering were employed for the determination of the steric microstructure which indicates an expanded semi‐flexible structure. The experimental results were compared with those from molecular modelling.
New concept for molecular composites
Authors: Ogata Naoya
Published: March 2011

New concept for molecular composites was proposed by in‐situ polymerization of rigid monomers in matrix polymer solutions. When the monomers and the matrix polymers had some affinity interactions such as hydrogen‐bonding or acid‐base interactions, resulting composite materials showed a homogeneously mixed blending to reach molecular composites. Polyimide composites were discussed based on this concept.
Thermotropic liquid crystal polyesters derived from 4,4′‐biphenyldicarboxylic acid and oxyalkylene spacers
Authors: Bello Antonio , Pereña José Manuel , Pérez Ernesto , Benavente Rosario
Published: March 2011

Several polyesters derived from bibenzoic acid and oxyalkylene glycols have been prepared and the ability of formation of mesophases was studied. The phase behaviour was investigated by means of differential scanning calorimetry, wide‐angle X‐ray diffraction and real‐time variable‐temperature small‐angle X‐ray diffraction. A common feature of all the studied polyesters, with ether groups in the spacer, is the inhibited ability for developing three‐dimensional structures, in contrast to the polymers with all‐methylene spacers. Moreover, the latter polymers show a monotropic mesophase behaviour but the former exhibit an enantiotropic transformation. Smectic structures of different types have been detected: The polyester derived from 3,3'‐oxybis(1‐propanol) produces a smectic SA structure, while the polyester from triethylene glycol leads to a smectic SC mesophase. The influence of the spacers on the dynamic mechanical relaxations of these polybibenzoates has been studied and discussed.
Oxidative degradation of water ‐ soluble polyethers by HO• and HO2• generated photochemically: Ft‐ir studies
Authors: Kaczmarek H. , Lindén L.Å. , Rabek J. E.
Published: March 2011

Two water ‐ soluble polyethers, poly(ethylene oxide) and poly(methyl vinyl ether) were UV irradiated in hydrogen peroxide (H2O2) solutions. It has been shown that HO• and HO2• radicals accelerate oxidative degradation of these polymers. Hydroxy (HO•) and probably hydroperoxy (HO2•) radicals can abstract hydrogen from methylene groups in both polymers. As a result of further oxidative reactions, different carbonyl, hydroxy and hydroperoxy groups are formed. A mechanism for the formation of these groups has been proposed.
Controlled copolymer structures via anionic/insertion polymerization of cyclic carbonates
Authors: Höcker H. , Keul H.
Published: March 2011

Cyclic carbonates are polymerized in a ring‐opening fashion by means of anionic and insertion type initiatiors. Different hexacyclic carbonates are copolymerized in a random way when both monomers are added to the initiator simultaneously. Block copolymers are obtained when the monomers are added in sequential way.

With anionic initiators cyclic carbonates are polymerized preferentially as compared with lactones while insertion initiators are less selective.

A special case is the preparation of copolymers of carbonates with lactams. When the polycarbonate is formed first the lactam unit is inserted into carbonate bond to form urethane and ester bonds. Thus, eventually an alternating polyesterurethane is formed with negligible amount of carbonate, amide, and urea units.

Moreover, the anionic ring‐opening polymerization of cyclic carbonates may be combined with vinyl polymerization. In the case of group transfer polymerization a transformation of the active site to the non‐metallic anionic initiation of the cyclic carbonate occurs.