bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of orientational relaxation in binary blends of long and short polystyrene chains by fourier transform infrared dichroism and small‐angle neutron scattering
Authors: Hayes Carmel , Mendes Eduardo , Bokobza Liliane , Boué François , Monnerie Lucien 
Published: March 2011

AbstractMeasurements of the local orientational order and average chain anisotropy in non‐uniform polystyrene are reported. Fourier‐transform infrared dichroism spectroscopy has been used to determine the effects of short deuterated chains (Mw = 500 to 188 000) on the orientational relaxation of long entangled chains (Mw = 2 000 000) in bidisperse melts uniaxially deformed above the glass transition temperature. While the long‐chain relaxation is found to be dependent on the short‐chain concentration, the local orientational order of the latter is molecular weight dependent consistent with the classical relaxation theories. The FTIR experiments are also combined with small‐angle neutron scattering measurements which probe the deuterated‐chain anisotropy in the defomed melts. There is evidence, from the combination of the two techniques, that although the short chains possess a negligible local orientational order, there exists an important anisotopy in the short chain distribution in space.
Application of ftir spectroscopy to the study of curing of glass reinforced polyester composites
Authors: Carmen Matías M. , Larena Alicia , De La Ulagares Orden M. , Urreaga Joaquín Martinez 
Published: March 2011

AbstractThe effect of glass fiber reinforcements on the curing behavior of unsaturated polyester commercial resins was investigated by Fourier transform infrared spectroscopy. Two different E‐glass fibers and two commercial resins were employed. The results indicate that both the glass fiber content and the fiber size have a pronounced effect on the ultimate values of the styrene conversion. Some complications found in the infrared analysis of commercial resins are also presented.
Utilization of complex initiators for the controlled polymerization of acrylic and methacrylic esters
Authors: Vlček Petr , Dvořánek Ladislav , Otoupalová Jaroslava , Janata Miroslav 
Published: March 2011

AbstractThe article presents a short overview of the controlled polymerization of (meth)acrylates assisted with Li tert.butoxide as the stabilizer of active centres. The “living” homopolymerizations of 2‐ethylhexyl acrylate, butyl acrylate and allyl methacrylate, and the synthesis of fully‐acrylate block copolymers are given as examples. The reaction conditions always need to be tuned up with respect to the monomer. The stabilizing effect of lithium 3‐methylpentoxide‐3, which seems to be a highly efficient type of the tert.alkoxide stabilizing additive, is briefly shown.
Synthesis of linear and star‐shaped phosphorus‐containing telechelic polymers via living cationic ring‐opening polymerization using a halobenzene/nickel(II) bromide catalyst
Authors: Kadokawa Jun‐ichi , Kobayashi Shiro 
Published: March 2011

AbstractThis paper reports a living cationic ring‐opening polymerization of 2‐phenyl‐1,3,2‐dioxaphosphorinane (a six membered cyclic phosphonite, 1) initiated by a new catalyst system of a halobenzene with NiBr2. The polymerization proceeded in a living nature to produce a poly(phosphinate) 2. The polymerizations of seven‐and five‐membered cyclic phosphonites with this catalyst system are also described. The kinetic analysis of the polymerization of 1, initiated with this catalyst system, has successfully been carried out. The difference of the nature in the polymerizations of five‐, six‐, and seven‐membered monomers is discussed. Syntheses of linear and star‐shaped telechelic polymers using di‐, tri‐, tetra‐, and hexahalobenzenes as a catalyst component are disclosed.
In‐situ polymer blends via chain transfer living polymerization (CTLP)
Authors: Yoon Hae Seong , Kim Kwang Ung , Lee Jonghwi , Lee Youngjun , Hwang Sung Sang , Park Tae Seok , Cho Jaecheol , Kim Jungahn , Inahn Byeong , Char Kookheon , Quirk Roderic P. 
Published: March 2011

AbstractIn‐situ polymer blends of polystyrene (PS)/poly(methyl methacrylate) (PMMA) with controlled and variable different compositions and molecular weights were found to be successfully synthesized by “chain transfer living polymerization (CTLP)” methodology by a combination of size‐exclusion chromatographic analysis, differential scanning calorimetry (DSC), UV/Vis and H NMR spectroscopy, and optical microscopic analysis. The PMMAs prepared in tetrahydrofuran (THF) in the presence of polystyrene exhibit highly syndiotactic stereoregularity (over 70 mol‐%) and a glass transition temperature over 120°C. A dispersed morphology was found even for blends with over 31 vol.‐% of the weight fraction of one component due to the discrepancy in the molecular weights of two components in the PS/PMMA blends. A ternary polymer blend system having PS/PMMA/PS ‐block‐ PMMA can be generated by control of the concentration of fluorene as the chain transfer agent in the CTLP.
Recent advances in the observation of disclinations of main‐chain nematic polymers
Authors: Qian Renyuan , Chen Shouxi , Song Wenhui 
Published: March 2011

AbstractExperimental observation of disclinations of main‐chain nematic polymers is reviewed. The geometry of disclination structure is discussed both from observations of schlieren texture and the theory of curvature elasticity for a two‐dimensional case with equal splay and bend moduli. The effects of non‐equal elastic moduli, the nature of the disclination core and the observation of inversion wails are briefly mentioned. Examples of experimental observation of disclinations of high topological strengths up to S=4 are given. The main experimental methods to map the director field around disclinations are 1) lamellar decoration, 2) band‐texture decoration and 3) surface microcrack decoration. The methods are discussed and compared, and examples illustrated by electron micrographs or photomicrographs are presented.
Polymer modified and stabilized cholesteric liquid crystal materials for flat panel application
Authors: William Doane J. , Yang Deng‐Ke , Pfeiffer Matthias 
Published: March 2011

AbstractPolymer dispersions, even in very low concentrations, can improve the performance of cholesteric liquid crystal materials necessary for their application in flat panel displays. Normal scattering mode, reverse scattering mode and reflective mode cholesteric liquid crystal materials are described. The roll of the polymer in each of these display modes is reviewed as are the unique electro‐optic characteristics of the dispersions.
Electroclinic properties of chiral smectic a liquid crystalline polymers and block copolymers
Authors: Chiellini Emo , Galli Giancarlo , Lagerwall Sven T. , Komitov Lachezar 
Published: March 2011

AbstractThe scope for the synthesis and investigation of chiral smectic A liquid crystalline (LC) polymers and block copolymers is discussed. LC block copolymers can combine the molecular order of liquid crystals and the supramolecular order typical of block copolymers, thus allowing to attain information on mesomorphic responses in restricted geometries. We present a general overview on several aspects of the syntheses and properties of LC block copolymers, specifically those obtained by starting from azomacroinitiators. These materials can exhibit an electroclinic effect, that is an electrically induced molecular tilt, which is characterized by a linear dependence on the applied field and a very fast response time in the paraelectric smectic A phase. The current progress in their potential application in electrooptics is outlined.
Wholly aromatic polyesters derived from 6‐hydroxy‐5‐phenyl‐2‐naphthoic acid and 4'‐hydroxy‐3′ ‐phenylbiphenyl‐4‐carboxylic acid
Authors: Jin Jung‐Il , Huh Seung‐Moo 
Published: March 2011

AbstractTwo series of new wholly aromatic copolyesters were prepared from 6‐hydroxy‐5‐phenyl‐2‐naphthoic acid (HPNA) and 4‐hydroxybenzoic acid (HBA), and 4'‐hydroxy‐3'‐phenylbiphenyl‐4‐carboxylic acid (HPBA) and 4‐hydroxybenzoic acid in varying mole ratio. The polyesters were synthesized in melts using the acetylated monomers. They were characterized for their crystallinity, liquid crystallinity, thermal transitions and thermal stability by wide‐angle X‐ray diffractometry, differential scanning calorimetry, thermogravimetry and on a polarizing microscope. In general, the HPNA copolyesters revealed higher degree of crystal‐Unities and greater melting temperatures than the HPBA copolyesters. This difference is explained by the planar geometry of naphthalene moiety in the HPNA structure. In contrast, the two phenylene rings of the HPBA unit along the backbone may not be coplanar. All of the polyesters appear to be thermotropic.
Orientational phenomena in comb‐shaped liquid crystal polymers induced by laser beam irradiation
Authors: Shibaev Valéry , Kostromin Sergey , Ivanov Sergey , Läsker Lutz , Fisher Thomas , Stumpe Joachim 
Published: March 2011

AbstractAction of the laser illumination on optical properties of liquid crystalline (LC) comb‐shaped acrylic and methacrylic copolymers containing cyanobiphenyl mesogenic groups and azo dye fragments has been studied. Under an illumination the cis‐trans configurational changes of dye fragments take place and reorientation of the side groups towards a direction perpendicular to the electric vector of the actinic light occurs. As a result the photoinduced optical birefringence (δn = 0.05‐0.11) appears. The detailed study of dichrotic and optical properties of polymeric films, kinetics and relaxation of δn, as well as mechanism of orientational transformations during a laser illumination are discussed. The induced optical anisotropy of the films can be changed reversibly by rotating the electric vector of the laser beam in respect to the film that may be used in reversible optical data storage.
Characterization of the chain stiffness for a mesogen‐jacketed liquid crystal polymer: Poly{2,5‐BIS [(4‐Methoxybenzoyl)Oxy] Styrene}
Authors: Wan Xinhua , Zhang Fei , Wu Peiqiang , Zhang Dong , Feng Xinde , Zhou Qi‐Feng 
Published: March 2011

AbstractNarrow‐distribution fractions of poly{2,5‐bis[(4‐methoxybenzoyl)oxy] styrene} ranging in weight‐average molecular weight Mw from 1.1 × 105 to 1.96 × 106 were studied by static light scattering and viscometry in THF at 25 ° C. From Mw and the intrinsic viscosity [ η ] Mark‐Houwink‐Sakurada equation was formulated with K=7.54×10−4 and ≈=0.82. The relation between [ η ] and Mw was analyzed according to Bohdanecky for the Kratky‐Porod wormlike chain, the ranges of the mass per unit length ML and the persistence length q were estimated as 35 nm−1 M<L42 nm<−1 and 11.5 nm <13.5 nm, respectively. The values of ≈ and q indicate that the polymer, though a liquid crystal polymer of the side‐chain type, has wormlike chain in dilute solution as most main chain liquid crystal polymers.
Some reactions of alumoxanes
Authors: Pasynkiewicz Stanislaw 
Published: March 2011

AbstractThe reactions of tetraalkyldialumoxanes (R2Al‐O‐AlR2)n or alkylalumoxane (AlOR)n with acetylacetone, some electron donors (ethers, amines, nitriles) and alcohols were discussed. The structures of alumoxanes were also considered. Despite a lot of studies the structure is not always clear and changes with a change of many parameters such as kind of ligands, synthetic conditions (solvents, reaction temperature, molar ratio of reactants), methods of isolation etc.
Proposals for structure and effect of methylalumoxane based on mass balances and phase separation experiments
Authors: Sinn Hansjörg 
Published: March 2011

AbstractMethylaluminoxane prepared from trimethylaluminium on a surface of ice mainly can be described as [Al4O3(CH3)6]4. This is shown through analysis, phase separation experiments with diethyl ether and molecular weight determinations in benzene, 1, 4‐dioxane, tetrahydrofuran and trimethylaluminium. It is discussed that the reason for forming this ball‐like structure is the saturation of four coordinated Al4O3(CH3)6. This molecule has a cavern which contains a solvent molecule or a molecule of trimethylaluminium. The consequences for the formation of the catalytically active structure together with metallocene are discussed.
How to reduce the ratio mao/metallocene
Authors: Kaminsky W. 
Published: March 2011

AbstractThe optimal ratio of Al/Zr in Metallocene/Methylalumoxane catalysts lies between 5000 to 10000. Bimetallic deactivation reactions and equilibria are responsible for this high excess. Substitution at the cyclopentadienyl or indenyl ligands can decrease the possibility for a hydrogen transfer and deactivation resulting in higher activity, higher molecular weights of the polymers and less excess of MAO. The MAO/metallocene ratio can also be reduced by supporting the metallocene on silica.
Development of a method for the determination of the “free” trimethylaluminum content in methylalumoxane
Authors: Thorn‐Csányi Emma , Dehmel Jörg , Dahlke Barbara 
Published: March 2011

AbstractUltraviolet/visible (UV/VIS) spectroscopic investigation of the reaction between tungsten oxytetrachloride and methylalumoxane (MAO) respectively trimethylaluminum (TMA) resulted in a method for the determination of the amount of “free” TMA in MAO samples. The development of the method of investigation is described.
Metallocenes/methylalumoxanes: A 13C NMR study of the reaction equilibria and polymerization
Authors: Tritto Incoronata , Sacchi Maria Carmela , Locatelli Paolo , Li San Xi 
Published: March 2011

AbstractA study of the reactions of Cp2Ti13CH3CI and Cp2Ti(CH3)2 with AIMe3 (TMA) and/or methylaluminoxane (MAO) and of the 13C 90% enriched ethylene polymerization in situ in the presence of the same catalytic systems has been made by 13C NMR spectroscopy. The NMR data have been compared with the catalytic activity. Active cation‐like species such as Cp2TiMe+CI·[AIMeO]n− and Cp2TiMe+Me·[AIMeO]n− and side products have been identified. The role of “free” and “associated” AIMe3, contained in MAO solutions, has been elucidated.
Metallocene/mao polymerization catalysts supported on cyclodextrin
Authors: Lee Dong‐Ho , Yoon Keun‐Byoung , Huh Wan‐Su 
Published: March 2011

AbstractBy treating cyclodextrin(CD) with methylaluminoxane (MAO such as PMAO or MMAO) or trimethylaluminium (TMA) followed by Cp2ZrCl2, CD/PMAO/Cp2ZrCl2, CD/MMAO/Cp2ZrCl2 and CD/TMA/Cp2ZrCl2 catalysts were prepared. The catalysts were analyzed by 13C‐CP/MAS NMR spectrometer and ICP to examine the structure of catalyst and content of Zr and Al. Ethylene polymerization was conducted with MAO or TMA as cocatalyst. Styrene polymerization was also carried out with α‐CD/MMAO/Cp*TiCl3 and α‐CD/TMA/Cp*TiCl3 catalysts. While the ordinary trialkylaluminium such as TMA as well as MAO can be used as cocatalyst for ethylene polymerization, only MAO could initiate the styrene polymerization with α‐CD supported catalysts.
The role of dormant sites in propene polymerization using methylalumoxane activated metallocene catalysts
Authors: Jüngling Stephan , Mülhaupt Rolf , Stehling Udo , Brintzinger Hans‐Herbert , Fischer David , Langhauser Franz 
Published: March 2011

AbstractPropene polymerization of methylalumoxane (MAO) activated rac‐Me2Si(Benz[e]Indenyl)2ZrCl2 (BI) and rac‐Me2Si(2‐Me‐Benz[e]Indenyl)2ZrCl2 (MBI) was studied to investigate the influence of the ligand substitution pattern and the role of dormant sites. Poly(propene) end group composition as well as regio‐ and stereoirregularities were examined by means of 1H‐ and 13C‐NMR spectroscopy. Dormant sites, resulting from 2, 1‐propene insertion, were reactivated either by β‐hydrogen transfer to propene, yielding 2‐butenyl end groups, or by 1, 2‐insertion of propene, yielding regioirregularities. Propene polymerization in the presence of hydrogen gave n‐butyl end groups and less regioirregularities as expected for hydrogenolysis of such dormant sites. Methyl substitution in 2‐position of the benz[e]indenyl ligand suppressed β‐hydrogen transfer to propene, and increased molecular weight with increasing propene concentration. Also, activation energy increased from 30 kJ/mol (BI/MAO) to 59 kJ/mol (MBI/MAO). For both catalysts activity depended on propene concentration. The order of reaction relative to propene was 1.7.
The interaction of metallocenes with selected activators a contribution to determine the formation of ion pairs
Authors: Gürtzgen Stefan , Rieger Rainer , Uzick Wolfram 
Published: March 2011

AbstractElectric conductivity measurements and 1H‐NMR spectroscopy were performed to get evidence for the formation of ion pairs as key intermediates in the metallocene activation by methylaluminoxane 3 or tris[pentafluorophenyl]boron 2.
Spontaneous copolymerizations in the reactions of electronrich dienes with electrophilic olefins
Authors: Hall H. K. , Padias Anne Buyle 
Published: March 2011

AbstractThe spontaneous thermal reactions of electron‐rich dienes with electrophilic olefins lead to both [4+2] cycloadducts and copolymers. The mechanism proposed for the initiation of the copolymerization involves the formation of a 2‐hexene‐1, 6‐diradical. Structure‐reactivity relationships are discussed.
Herman Mark: Life and accomplishments
Authors: Morawetz Herbert 
Published: March 2011

AbstractThis short outline of Herman Mark's career covers his youth in Vienna, his activity in the army during World War I, his years at the Kaiser Wilhelm Institute in Berlin‐Dahlem where he was mostly concerned with X‐ray crystallography, his career as the director of a research laboratory of high molecular compounds of the IG Farben in Ludwigshafen, his years at the University of Vienna where he designed the first academic curriculum of polymer chemistry and his final years at the Polytechnic Institute of Brooklyn (now Polytechnic University) where he created the first American doctoral program in polymer science. His activity was crucial to the recognition of polymer chemistry as an important scientific discipline and to its international organization. He was equally at home in the academic environment, and as an industrial and government consultant. His crucial scientific contributions included the first crystal structure of a macromolecule, the first derivation of the mechanical property of a fiber from molecular parameters and the statistical theory of rubber elasticity.
From the pioneers till tomorrow
Authors: Bikales Norbert M. 
Published: March 2011

AbstractThe evolution of polymer science has been astounding. Since the early days when Staudinger, Mark and others pioneered the then‐new field, it has grown enormously thanks to a breathtaking collection of talent. A series of major discoveries has taken place since the 1950s, and the number of practitioners has grown impressively. Polymer science is now deeper and broader, and well poised to advance science and benefit society.
Svedberg — Discoverer of the protein macromolecules
Authors: Rånby Bengt 
Published: March 2011

AbstractThe(odor) Svedberg* (1884‐1971), Uppsala University, was the first professor of physical chemistry in Sweden. He started his research in 1904 as a colloid chemist. He prepared inorganic dispersions by electrical discharge through organic liquids, measured particle size and size distribution of colloids by diffusion and sedimentation rates and invented the ultracentrifuge for convection‐free sedimentation of colloidal particles. In 1924 Svedberg applied the ultracentrifuge for studies of haemoglobin in aqueous solution. Unexpectedly he found that the protein was not a gel of associated small molecules. It sedimented as macromolecules of uniform mass (68 000 dalton), i.e. is monodisperse.In subsequent work Svedberg found that other proteins like ovalbumin (from egg white) and haemocyanins from snails and other invertebrates also are monodisperse or contain a few uniform macromolecular components. After extensive studies of soluble protein molecules from a large number of animals and plants, Svedberg classified the species and could trace the relations for the species from the molecular mass of their protein macromolecules.Studies of soluble polysaccharides from bulbs also showed well defined macromolecules of masses that could be related to the various botanical species. Other native substances like cellulose, other wood polysaccharides and starch were found to be of high molecular mass but polydisperse.Svedberg's research in the 1920's and 1930's gave strong experimental support for Staudinger's macromolecular concept although Svedberg, at the time of his own important discoveries, was not influenced by Staudinger. Svedberg's discovery of the protein macromolecules and their uniform molecular mass initiated the macromolecular research in biochemistry.
Research and development activities on polymer for the 21st century in korea
Authors: Kim Un Young , Kim Kwang Ung 
Published: March 2011

AbstractThe polymer industries have been expanded steadily from the beginning of 1970's. Accordingly, the production capacity of commodity plastics reached 5.37 million tons in 1993, which ranked fourth in the world. The market for the engineering plastics is not fully matured yet, but the recent annual increasing rate was higher than 20% for demand and 40% for production. A state of the art for research and development activities on polymer for 21st century in Korea will be briefly reviewed in terms of technology evolution, polymers for electronic industry, for environment, and for energy saving.
Control of living anionic polymerization of (meth)acrylates: Active complex species, macromolecular engineering and possible scaling‐up
Authors: Teyssie Philippe , Bayard Philippe , Jerome Robert , Varshney Sunil K. , Wang Jin‐Shan , Heim Philippe , Vuillemin Bruno 
Published: March 2011

AbstractTailored polymerization of acrylic and methacrylic esters, particularly methyl methacrylate (MMA), has been the topic of a frantic research effort during the last decade. It is the purpose of this paper to present one of the main lines of that quest, and to evaluate its potential versus other new approaches.
Transition metal catalyzed alternating copolymerizations of olefins and co
Authors: Rix F. , Barborak J. , Wagner M. , Tahliani S. , Desimone J. , Brookhart M. , Elder D. 
Published: March 2011

AbstractWell defined Pd(II) catalysts of the type (N′N)Pd(CH3)(Solv.)+ B(Arf)4‐ (Arf = −3, 5‐(CF3)2C6H3) have been prepared for living alternating copolymerizations of olefins with CO. This talk will focus on the mechanistic details of chain growth as elucidated by 1H and 13C NMR spectroscopy, model studies of key migratory insertion steps and synthesis and properties of various copolymers and block copolymers based on styrenes, CH2=CHC6H4X [X = p‐C(CH3)3, p‐OC(O)CH3, p‐OC(O)C‐t‐Bu), p‐NHC(O)(C‐t‐Bu)]. Use of the catalysts based on the C2 symmetric, homochiral ligand 2, 2'‐bis[2‐[4(S)‐(Alkyl)‐1, 3‐oxazolinyl]]propane [Alkyl = CH3, CH(CH3)2] produces a copolymer, 1, with a highly isotactic microstructure and high optical activity in contrast to achiral ligands such as 1,10‐phenanthroline which produce copolymers with predominantly syndiotactic microstructure.
Synthesis and characterization of new aromatic liquid crystalline polyesters having phenyl substituents
Authors: Choi Tae‐Gyu , Chung Sung‐Jae , Huh Seung‐Moo , Yun Yong‐Kuk , Jin Jung‐Il 
Published: March 2011

AbstractTwo different series of new aromatic liquid crystalline (LC) polyesters were prepared from 3‐phenyl‐4, 4'‐biphenyldicarboxylic acid (PBDA) and 1‐phenyl‐2, 6‐naphthalenedicarboxylic acid (PNDA). PBDA and PNDA were polymerized with various aromatic diols such as hydroquinone, substituted hydroquinones, isomeric naphthalenediols and 4, 4'‐biphenol, and the resulting polyesters were characterized by DSC, WAXD, and on a cross‐polarizing microscope for the study of their thermal transition and crystallization properties, and mesophases formed therefrom.