bluuebunny/crossref_metadata_2025_split huggingface dataset:
Micellization of amphiphilic block copolymers and use of their micelles as nanosized reaction vessels
Authors: Antonietti Markus , Förster Stephan , Oestreich Sascha 
Published: March 2011

AbstractAmphiphilic block copolymers made by a variety of techniques form in selective solvents micelles of well defined size and shape. We report on the underlying principles of micelle formation, as revealed by light scattering experiments.In addition, we will delineate some applications of these block‐copolymer micelles where we focus on two technological relevant cases, namely the stabilization of polymer particles in low cohesion energy environments as well as the stabilization of metal and semiconductor colloids inside specially functionalized block copolymer micelles. In the latter case, stable hybride materials are obtained where the properties both of the polymer and the inorganic are added in a synergistic way. First data on special catalytic properties, the generation of superparamagnetic materials, and special colloids with optical functionality are presented.
Towards realistic rheological models for polymer melt processing
Authors: Feigl Kathleen , Christian Öttinger Hans 
Published: March 2011

AbstractGreatly needed improvements to rheological models of polymer fluids can best be made by understanding and modifying a model on the molecular level, where the physics governing real fluids are created. For this purpose, stochastic simulations are an indispensible tool. The usefulness of stochastic simulations for kinetic theory models are well‐known. In this paper, we show that the class of Rivlin‐Sawyers, or K‐BKZ, integral models is also subject to a molecular interpretation and can be simulated using stochastic techniques. We also illustrate how an existing molecular model can be modified, resulting in better predictions of viscoelastic behavior. For this we formulate a stochastic simulation of a reptation model modified to account for double reptation and tube‐length fluctuations.
Diffusion in microstructured block copolymer melts
Authors: Lodge Timothy P. , Hamersky Mark W. , Milhaupt Jodi M. , Kannan Rangaramanujam M. , Dalvi Mukul C. , Eastman Christine E. 
Published: March 2011

AbstractForced Rayleigh scattering has been employed to measure tracer and self‐diffusion in block copolymer melts, for both entangled and unentangled systems, and in both the ordered and disordered states. It is shown that entanglements are particularly effective in retarding the motion of copolymers parallel to the interface between microdomains. The mechanisms of “activated reptation” and “block retraction” are proposed for parallel diffusion. The importance of large amplitude composition fluctuations in the disordered state near the ordering transition is also demonstrated, for both copolymer and homopolymer tracers; the results suggest that copolymer tracers are more affected than homopolymers of comparable molecular weight.
Synthesis of unsaturated polyesters from dipotassium salts of cis‐aconitic, itaconic and mesaconic acids and 1, 4‐dibromobutane
Authors: Sepulchre Marie‐Odile , Sepulchre Maurice 
Published: March 2011

AbstractThe polycondensation of dipotassium salts of cis‐aconitic, itaconic and mesaconic acids and 1, 4‐dibromobutane in 1‐methyl‐2‐pyrrolidone at 105°C led in all the cases to the formation of an unsaturated copolyester containing at least three different units: butylene itaconate, butylene mesaconate and butylene citraconate units. At the equilibrium, the relative molar portions of the three units were found to be equal to 36, 59, and 5%, respectively. The polycondensation of the cisaconitic acid salt was accompanied by a decarboxylation reaction which excluded the possibility of preparing unsaturated polyesters with pendant carboxylic acid groups. The study of model reactions carried out with hexyl bromide did not allow us to determine the structure of unexpected units resulting from side reactions occurring only in the polycondensation of cis‐aconitic and itaconic acid salts.
Biodegradation of poly(amino acid)s: Evaluation methods and structure‐to‐function relationships
Authors: Rypáček F. , Pytela J. , Kotva R. , Škarda V. , Cífková I. 
Published: March 2011

AbstractTwo poly(amino acid) systems were studied: (a) poly[N5‐(2‐hydroxyethyl)‐L‐glutamine] (PHEG) derivatives prepared by NCA polymerization; (b) poly‐α,β‐[N‐(2‐hydroxyethyl)‐DL‐aspartamide] (PHEA) derivatives prepared by thermal polycondensation of aspartic acid to racemic polysuccinimide followed by chemical modification reactions. The degradation of polymers by isolated enzymes and homogenate of kidney tissue was studied in vitro and the effect of polymer structure on the rate of degradation and the size of degradation products was evaluated. A PHEA derivative (modified by tyramine residues in 9.6 % of side chains) was accumulated in the lysosomes of kidney cells of rats and the molecular‐weight distribution of the polymer retained inside the lysosomes of living cells and that of the polymer excreted into urine was analysed by a high‐sensitivity size‐exclusion chromatography using the fluorescence and radioactive labelling. While PHEG derivatives were degraded by isolated mammalian enzymes and a tissue homogenate, no significant degradation of PHEA and derivatives was observed, either in vitro, with isolated enzymes and homogenate or in vivo, under a long‐term exposure to the lysosomal enzymes in living cells.
Bulk polymerization of lactides initiated by aluminum isopropoxide. I. Mechanism and kinetics
Authors: Degée Philippe , Dubois Philippe , Jérǒme Robert 
Published: March 2011

AbstractCommercially available Al isopropoxide (Al(OiPr)3) has proved to be an efficient initiator for the bulk polymerization of lactide. The ring‐opening polymerization proceeds through a “coordination‐insertion” mechanism and the selective rupture of the acyl‐oxygen bond of the monomer. Polyester chains are selectively end‐capped with an aluminum alkoxide and an isopropoxy group. Therefore, substitution of Al tris(4‐penten‐1‐olate) for Al(OiPr)3 leads to the formation of macromonomers. In the temperature range from 110 to 150°C, polymerization is “living”, i.e. the molecular weight can be predicted by the initial monomer‐to‐Al molar ratio and the monomer conversion. The narrower polydispersity of poly(L,L‐lactide) compared to the amorphous poly(D,L‐lactide) (M̄w / M̄n 1.3 compared to 1.9, respectively), both prepared in the bulk, is thought to result from the restricted mobility of the crystallized isotactic polyester chains. When the temperature is increased up to 180°C, inter‐ and intramolecular transesterification reactions interfere with chain propagation.
Novel biodegradable ester‐based polymer blends
Authors: Tighe Brian J. , Amass Allan J. , Yasin Mohammed 
Published: March 2011

AbstractWe have found, within the polyester family, interesting and potentially useful patterns of three‐component compatibility. The bacterially produced biodegradable polyester, poly(hydroxybutyrate) (PHB) and its copolymers with hydroxyvalerate (HV) together with polymers such as cellulose acetate butyrate (CAB), polycaprolactone, poly(lactic acid), and a series of high‐molecular‐weight, non‐crystallizable ester‐based plasticisers have been identified as possible candidates in the production of blends in which aspects of performance can be varied with a degree of independence of cost. The compatibility ranges can be conveniently represented in the form of triangular graphs, with the relative weight fraction, or percentage, being represented along each of the three axes. The extent to which the modulation of the physical properties in general, but the stability in various environments in particular, is possible by the formation of three‐component blends, such as those formed between P(HB‐HV), cellulose acetate butyrate and poly(alkylene adipate) plasticisers, is discussed.
Single‐chain single crystals
Authors: Cao Jie , Gu Fangming , Liu Yongjian , Bi Shuguang , Bu Haishan , Zhang Ze 
Published: March 2011

AbstractSingle‐chain single crystals of isotactic polystyrene and poly(ethylene oxide) were studied by using transmission electron microscopy, high resolution electron microscopy, electron diffraction. Single‐chain single crystals were prepared by spreading a dilute solution of polymers on a water surface and collecting the resulting single‐chain particles on copper grids, followed by isothermal crystallization. A statistical analysis of the sizes of single‐chain crystals was found to match with the known molecular weight distribution of original sample, indicating the particles to be composed of single chain. Observation of the morphology and electron diffraction gave evidence of the single crystal nature. Regular‐shaped single‐chain crystals were obtained after isothermal crystallization for a longer time. By close observation, several types of morphologies were found for single‐chain crystals of isotactic polystyrene and poly(ethylene oxide); in addition to the conventional morphologies observed for multi‐chain crystals, new morphologies were observed in both cases. The morphologies of poly(ethylene oxide) were explained according to the crystal structure and twin modes. Tent‐like single‐chain crystals were often observed. Because of the small size of the crystals, they can avoid collapse on the substrate. The crystalline c‐axis of single‐chain crystals were found to orient preferably in the direction normal to the substrate. The investigation of electron diffraction and high resolution electron microscopy revealed that the structure of the single‐chain crystals of isotactic polystyrene is the same as for multi‐chain crystals. A reasonable explanation is given for the unusual resistance to electron irradiation and the missing of lower‐index reflections. Regular periodic stripes were found on the top surface of single‐chain crystal of isotactic polystyrene with an average periodic length in accordance with (220) spacing. In addition, a statistical thermodynamics theory was developed for single‐chain crystal. It is found that the equilibrium dimensions are related to molecular weight and annealing temperature, while the equilibrium melting temperature depends on molecular weight.
Shear mixing and phase diagram shift of polymer blends
Authors: Han Charles C. 
Published: March 2011

AbstractFor a low molecular weight polystyrene/polybutadiene blend, the effect of shear on the suppressing of critical fluctuations and the critical temperature has been studied and is in good agreement with the predictions of Onuki and Kawasaki. By assuming the symmetry of this critical scaling into the two phase region, together with the Taylor theory, the observed (phase separated) droplet break‐up and the formation of string pattern can be explained. The exact shear dependence of Tc(γ) can be obtained by the use of the fluorescence microscope under steady shear.
Morphologies and domain sizes of microphase‐separated structures of block and graft copolymers of different types
Authors: Matsushita Yushu , Noda Ichiro , Torikai Naoya 
Published: March 2011

AbstractWell‐defined block and graft copolymers of different types with different compositions and molecular weights, such as styrene(S)‐2‐vinylpyridine(P) diblock copolymers, SP star‐shaped block copolymers, PSP triblock copolymers, styrene(S)‐isoprene(I) multiblock copolymers of the (SI)n type, ISP triblock copolymers, SPP graft copolymers and their deuterated samples were prepared. Variations of the morphologies with compositions, molecular weight dependences of the lamellar domain sizes and conformations and distributions of block chains in the lamellar domains were studied in the strong segregation limit.Besides typical morphologies such as spherical, cylindrical and lamellar structures, ordered bi‐ and tri‐continuous structures were found between cylindrical and lamellar structures for SP diblock copolymers, PSP and ISP triblock copolymers, respectively. The composition ranges of morphologies are different for the block and graft copolymers of different types.The molecular weight dependences of lamellar domain sizes are about the same, but their magnitudes are not always the same for the block and graft copolymers of different types. These results are well explained by the theories of Helfand‐Wasserman and Semenov.Block chains in lamellae are extended along the direction perpendicular to lamellae, but they are contracted along the parallel direction. The former result is well explained by the theories, but the latter is not. Chains adjacent to the junction points between different block chains are localized near the domain interface, but chains at the free‐ends of block chains are widely distributed in the domain with the maximum at the center of domain.
Spiro linked compounds for use as active materials in organic light emitting diodes
Authors: Salbeck Josef , Weissörtel Frank , Bauer Jacqueline 
Published: March 2011

AbstractSpiro‐linkage of low molecular weight entities as a new structural concept for the design of new active materials for electroluminescent applications is presented. These spiro linked compounds result in nonpolymeric organic glasses with high thermal stability as can be derived from their high glass transition temperatures (Tg), and characterized by differential scanning calorimetry. Blue emitters based on spiro linked oligophenyles are presented. These compounds are soluble in common organic solvents and show high photoluminescence quantum efficiency in the solid state and high morphologic stability with glass transition temperatures up to 250°C. Charge transport materials based on spiro linked versions of 2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole (PBD) for electron transport, and spiro linked versions of triphenyldiamin derivatives (TPD) for hole transport show improved morphologic properties with nearly unchanged electronic properties compared to the parent compounds.High quality amorphous films can be prepared with the spiro compounds by vapor deposition as well as by simple spin coating.
Aromatic polyethers with 1,3,5‐triazine units as hole blocking/electron transport materials in leds
Authors: Fink Ralf , Frenz Carsten , Thelakkat Mukundan , Schmidt Hans‐Werner 
Published: March 2011

AbstractVarious difluoro functionalized aromatic 1,3,5‐triazine monomers were prepared. A series of poly‐(1,3,5‐triazine‐ether)s was synthesized by polycondensation with 4,4′‐(hexafluoroisopropylidene)diphenol. The polymers have excellent thermal stability and are amorphous with glass transition temperatures in the range of 190–250°C. In order to examine the potential to apply these polymers in organic electroluminescent devices, the redox properties were studied by cyclic voltammetry. It was found that the monomers have high electron affinity and reach LUMO values in the range of −2.7 to −3.1 eV. This opens the possibility to utilize 1,3,5‐triazine containing materials as electron injecting/hole blocking layer in LEDs. First LED results are in accordance to these high electron affinities.
Ultrathin organic layers for corrosion protection
Authors: Maege Iris , Jaehne Evelin , Henke Axel , Adler Hans‐Juergen P. , Bram Christian , Jung Christian , Stratmann Martin 
Published: March 2011

AbstractThe adsorption and self‐organisation process of alkyl‐phosphonic acids and phosphoric acid monoalkyl esters on technical aluminium surfaces have been investigated by different surface sensible techniques: Grazing angle FT‐IR‐ spectroscopy, angle dependent XPS and Auger‐ spectroscopy. The aim of these studies was to replace the present technical procedure for pretreatment of aluminum surfaces with Chromate acid in order to improve the corrosion inhibition and the coating adhesion.The ability for self‐assembly is given by substances which have a surface reactive group and a long‐aliphatic or aromatic spacer and a supramolecular order is built‐up between these spacers. The results show that these molecules are able to adsorb spontaneously onto the aluminum surface and subsequently a structured molecular order is formed.These effects were confirmed by industrial linked adhesion and corrosion tests.
Interaction of Linear Polyelectrolytes with Oppositely Charged Lightly Cross‐Linked Networks
Authors: Zezin Aleksander B. , Rogacheva Valentina B. , Kabanov VictoR. A. 
Published: March 2011

AbstractThe processes proceeding at the contact of highly swollen lightly cross‐linked polyelectrolyte networks with aqueous solutions of oppositely charged linear polyions were studied. The reactions under discussion proceed as frontal processes and follow by strong (three orders of magnitude) contraction of the gel sample. The existence of sharp boundary between outer weakly swollen layer which is the reaction product—interpolyelectrolyte complex and the highly swollen inner part which is the initial unconverted gel is characteristic for the process. The kinetics of linear polyions absorption by polyelectrolyte networks and factors controlling the rate of sorption such as chemical structure of polyelectrolytes, nature and concentration of simple salts, pH, temperature were investigated. The “relay‐race” mechanism of linear polyelectrolyte transport was established.
Improvement of adhesive bonding of thermoplastic polymers by different surface treatments
Authors: Zeiler Thomas , Pfeffer Petra , Kürner Marcus , Münstedt Helmut 
Published: March 2011

AbstractInjection moulded samples of six species of thermoplastic polymers were exposed to different surface treatments and successively glued together to form single lap shear joints. Lap shear strength and failure mode of these specimens were examined. The surfaces obtained after treatment were characterized by electron spectroscopy for chemical analysis, contact angle measurements and atomic force microscopy.
Fluorescent molecular rotors as probes for polymers
Authors: Carré Marie‐Christiane , Dorion Catherine , Rebizak Richard , Pla Fernand , Brembilla Alain , Viriot Marie‐Laure 
Published: March 2011

AbstractThe use of a molecular rotor (1,1‐dicyano‐4‐(4'‐dimethylaminophenyl)‐1,3‐butadiene) as a fluorescent probe was proved to be of great interest for the study of polymers. First, the rotor can detect the critical time of the glass effect in the bulk polymerization of MMA into PMMA due to viscosity change, this will allow a better control of the process and is complementary to the information issued from the use of the fluorescent pyrene probe which is sensitive to the gel effect. Second, the cinnamylidene rotor was able to detect the formation of hydrophobic microdomains for cationic amphiphilic polymers in their aggregation modes when they were solubilized in water, both polarity and viscosity changes are playing a role. The possibility of incorporation of various molecular fluorescent rotors in polymers beads was also studied.
The influence of processing conditions on the properties and the degradation of poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)
Authors: Renstad R. , Karlsson S. , Albertsson A.‐C. 
Published: March 2011

AbstractThe influence of melt‐extrusion on the degradation behavior of poly(3‐hydroxybutyrate‐co‐7% 3‐hydroxyvalerate) in a small‐scale compost and in salt media with Aspergillus fumigatus has been studied. The degradation has been monitored by Size Exclusion Chromatography (SEC), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and X‐ray analysis. During the first 9 weeks of composting the degradation proceeds through surface erosion without any significant change in molecular weight or weight crystallinity. After 10 months the weight average molecular weight, Mw, has decreased by approximately 15–50%. It is suggested that degradation mechanism is converted from enzymatic to chemical hydrolysis as the porosity of the samples increases which facilitates water penetration. In addition, the acidic degradation products would accelerate the chemical hydrolysis inside the sample due to lowering of the pH. During degradation in media containing A. fumigatus the sample processed at low temperature exhibited extensive surface degradation and a 12% reduction of the Mw. In contrast the sample processed at high temperature showed an homogeneous surface degradation and no reduction in molecular weight. The differences in degradation are attributed to variations in the initial morphology of the samples caused by the processing conditions. Further investigations are, however, required to separate effects attributed to local differences in the compost environment and the structure of the samples.
Stereochemical aspects of the controlled ring‐opening polymerization of chiral cyclic esters
Authors: Spassky Nicolas , Pluta Christian , Simic Vesna , Thiam Mohamedou , Wisniewski Muriel 
Published: March 2011

AbstractThe stereochemical aspects of controlled polymerization of lactide and β‐butyrolactone are discussed. The physicochemical and thermal properties of these polymers are shown to be depending on the stereochemical structure of the macromolecular chain. Different types of processes involving change of enantiomeric composition in the course of the polymerization reaction are examined in function of different initiators used. The formation of stereocomplexes from stereocopolymers of various enantiomeric compositions is reported.
Cyclic and linear liquid crystalline functionalized polyesters with main‐chain ortho‐linked units. synthesis and characterization of cyclic lc unimers and dimers with “u”‐shaped rigid mesogenic units with alkyl side chains
Authors: Navarro Fernando 
Published: March 2011

AbstractAlthough ortho‐diphenols had not been extensively used in the synthesis of LC esters, a great variety of molecular structures of low and high molecular weight LC esters containing high proportions of these units can be synthesized. In this paper we describe the synthesis and characterization of new series of low and high molecular weight cyclic and linear LC esters with mesogenic “U”‐shaped rigid units with terminal groups which are alkyl chains. Cyclic oligoesters and linear polyesters were formed by the polycondensation of 4,4'‐[1,10‐decamethylenebis(oxy)]bis(cinnamic acid) with monosubstituted catechols which are the alkyl esters of 3,4‐dihydroxybenzoic acid. Although the great importance that concomitant cyclization reactions have in polyesterifications involving high proportions of ortho‐diphenols does not seem to have been considered until now, we have found mat these polyesterifications produced linear polyesters along with high proportions of cyclic oligoesters even when reaction conditions disfavored cyclization. Copolymerization with p‐hydroxybenzoic acid decreased the amount of cyclic oligomers, however it was necessary to copolymerize with proportions of PB higher than 50 mol‐% to get copolyesters with low proportions of cyclic oligomers. As far as we know we describe the first examples of cyclic LC oligoesters and cyclic LC unimers and dimers which display enantiotropic LC mesophases stable over broad ranges of temperature. Cyclic dimers display mesophases whose isotropization temperatures ( > 300°C) are much higher than that of their linear high molecular mass homologues. Cyclic LC unimers and dimers, linear LC polyesters and model compounds were characterized by FAB‐MS, GPC, 1H NMR, DSC and hot‐stage polarized microscopy. All these compounds contain reactive C=C double bonds and can be crosslinked thermally and photochemically. Cyclic unimers and dimers can be polymerized termally to produce high molecular mass polymers.