bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ethylene polymerization with metallocene and trimethylaluminumtreated silica
Authors: Lee Dong‐Hee , Shin Sang‐Young , Lee Dong‐Ho 
Published: March 2011

AbstractTo prepare supported catalyst for ethylene polymerization, silica was treated with trialkylaluminum (AIR3) followed by supporting Cp2ZrCl2. Partially hydrated silica (H‐SiO2) was chosen for reaction with AIR3 to prepare catalyst precursor. The H‐SiO2/ AIR3 / Metallocene catalyst system could effectively catalyse ethylene polymerization even with common alkylaluminums as cocatalyst. The catalytic activity of supported catalyst depended on H2O content of silica. H2O/(CH3) 3Al ratio, metallocene and cocatalyst. The analysis data of silica surface by BET and CP MAS 13C NMR revealed that the catalyst precursor prepared from the reaction between H‐SiO2 and (CH3) 3Al was methylaluminoxane (PMAO) supported on silica with high surface area and reduced pore size.
Synthesis of well defined polymers by controlled radical polymerization
Authors: Matyjaszewski Krzysztof , Gaynor Scott , Greszta Dorota , Mardare Daniela , Shigemoto Takeo 
Published: March 2011

AbstractControlled radical polymerizations can be achieved by using either unimolecular or bimolecular exchange between growing radicals and dormant chains. Dormant chains can be represented as either covalent species or organometallic compounds. Systems based on alkoxyamines, organochromium, organoaluminum compounds, and alkyl iodides are discussed in detail. In many systems, straight semilogarithmic plots indicate a constant number of growing radicals. A linear increase of molecular weights with conversion indicates a constant number of chains capable of growth but being predominantly in the dormant state. Some of these systems can be used in the synthesis of block copolymers and for end‐functionalization.
Grain boundary defects in block copolymer systems: Bulk and thin film results
Authors: Carvalho Bruce L. , Lescanec Robert L. , Thomas Edwin L. 
Published: March 2011

AbstractOrdered periodic morphologies are the hallmark of most discussions of the microphase‐separated state in block copolymer systems yet actual materials contain a myriad of defects. Perhaps the most important of these defects are those which constitute the regions between ordered grains. Transmission electron microscopy (TEM) is used to investigate the grain boundary morphology of diblock copolymers in both bulk and thin film geometries. These experiments show that constant mean curvature (CMC) surfaces are often useful descriptors, not only for the equilibrium morphology of microphase‐separated copolymers, but also for the microphase‐separated morphology within grain boundaries.
Adsorption of hydrophilic‐hydrophobic block copolymers on silica from aqueous solutions
Authors: Sikka Mohan , Schneider Jim , Tirrell Matthew , Amiel Catherine 
Published: March 2011

AbstractAdsorption of a water‐soluble diblock copolymer, poly(t‐butylstyrene)‐sodium poly(styrene sulfonate) (PtBS‐NaPSS), on silica surfaces in aqueous solutions was studied using ellipsometry and atomic‐force microscopy (AFM). Molar masses of 87 000 and 160 000 g/mol were used. The block copolymers used were compositionally asymmetric, with large, hydrophilic, PSS blocks and small, hydrophobic, PtBS blocks. Adsorption could not be observed in pure water without added salt. When the NaCl concentration was increased to 1 mol/L, adsorption could be readily observed. The measured adsorbed amount at long times was significantly larger for the 87 000 diblock compared with that for a polyelectrolyte homopolymer of comparable molecular size, demonstrating the role played by the uncharged block in anchoring the diblock at the solid surface. The kinetics of adsorption showed a two‐stage process, an initial diffusion‐limited stage, followed by a slower buildup of surface coverage in a brush‐limited stage. The number density of molecules at the surface was smaller for the higher molecular weight species, in agreement with simple scaling arguments.
Paul J. Flory
Authors: Suter U. W. 
Published: March 2011

AbstractPaul J. Flory was a pioneer in the development of a quantitative understanding of polymer science and a leader in placing it among the major scientific disciplines. Through his energy, skill and genius, and by the judicious interplay of experiment and theory, he demonstrated that polymers are not the complicated, intractable systems they were thought to be earlier, but are treatable in a rigorous and straight‐forward manner.From his first scientific paper on polymers in 1936 to his last contributions, published posthumously, in 1986, Paul Flory was involved in shaping a consistent view of polymer science. A unique ability, to perceive the dominant cause in a complex effect and to formulate the action of this most important element of a situation in a simple and straightforward model, made his contributions so helpful and relevant that still today his models are often chosen over later, more refined, more accurate ones – Flory's models and concepts are of penetrating insight and a simplicity that allows all polymer scientists to understand and use them.Flory was involved in a very broad range of topics: among other topics, he laid the foundation of the understanding of polymerization reactions, illuminated the thermodynamics and hydrodynamics of polymer solutions and through this the nature of the polymer‐solvent interactions and the θ‐state, formulated important models of rubber elasticity, and investigated with excellent success polymeric crystals and liquid crystals. A contribution of great importance was the development of the rotational isomeric state method to the treatment of macromolecules of arbitrary size and structure and for many properties. His achievement was recognized by numerous awards, honorary degrees, and the Nobel Prize in 1974.Paul J. Flory, born on June 19, 1910, died on September 8, 1985.
The essence of changes in central and eastern Europe. New challenges and limitations
Authors: Diem Tadeusz 
Published: March 2011

AbstractThe principles of transformation of central and eastern European countries into democracies and free‐market driven economy has been analyzed mainly on the example of Poland. The actual political status and economical development has been described by comparative analysis of situations in the region. The legal framework and role of basic financial institutions; central bank, security commission, stock exchange and other institutions forming the environment of the competitive society has been characterized. The process of privatization, with emphasis on the foreign investment in conjunction with the development of basic branches of industry has been described., The actual status, condition and perspectives for international cooperation in the area of polymer industry, including research and development, would be presented.
Macromolecular architecture for the twenty first century‐new products from old monomers
Authors: Webster Owen W. 
Published: March 2011

AbstractDue to the high entry costs for new monomers, polymer products for the 21st century will mainly consist of the monomer mix we have now. The demand for new properties will therefore have to be satisfied by changes in macromolecular architecture. Examples which are discussed include: Block polymers (AB, ABA, (AB)n, ABC, tapered), star polymers (rigid, block, fexible), ladder polymers, graft or comb polymers (from macromonomers), hyperbranched polymers, hypercrosslinked polymers, sequential copolymers. and starburst dendrimers. In addition, control of chain stereo chemistry will increasingly come into play. Synthetic techniques for obtaining these architectural forms are discussed as well as, potential uses for these new products.
Controlled polymerization reaction with new catalyst: Design of metalloporphyrin‐acid systems for monomer activation
Authors: Inoue Shohei , Aida Takuzo , Kinugawa Masashi , Isoda Masanori , Takeuchi Daisuke 
Published: March 2011

AbstractMetalloporphyrin initiator coupled with an appropriate organometallic Lewis acid catalyst could make possible the first example of living anionic polymerization of oxetane. Lewis acid built‐in metalloporphyrins were designed as a new highly active catalyst/initiator system. The concept of monomer activation by Lewis acid was extended to the use of appropriate protonic acid.
New methods of C‐C and C‐O bond formation in the synthesis of conjugated polymers
Authors: Klapper M. , Müllen K. 
Published: March 2011

AbstractNew synthetic developments towards polymers containing aromatic building blocks in the polymer backbone are described. The synthesis of polyphenylene‐related systems with an improved solubility due to their alkyl substitution is discussed. Via bridging of the phenylene rings a twisting of the aromatic subunits is avoided and the conjugation improved. This concept is extended to ribbon‐type polymers containing 6‐ or 6‐ and 5‐ membered rings. It is demonstrated that during a polycondensation process anthracene can be incorporated into various polymers via C‐O bond formation as well as via C‐C connection. Cycloaddition reactions are presented, allowing for modification and grafting of these polymers. Additionally, the use of anthracene derivatives as initiators in homo and block copolymerisation is shown.
Liquid single crystal elastomers (lsce) ‐ mechanical optical and electric properties
Authors: Finkelmann H. 
Published: March 2011

AbstractLiquid crystal elastomers can be macroscopically ordered with respect to the director by applying a mechanical field similar to electric/magnetic field effects of low molar mass liquid crystals. Introducing network anisotropy a priori by the synthesis, uniformly aligned nematic or smectic elastomers are available without external mechanical field. These LSCE's combine optical properties of single crystals with entropy elasticity of elastomers.Due to uniform director orientation without defects, the LSCE's exhibit excellent transparency which makes them applicable for optical elements. Non‐linear optical properties can be easily optimized by attaching suitable I.c.‐moieties to the polymer network. On the other hand, due to the rubber elasticity of the LSCE's, electromechanical effects can be observed, e. g. piezoelectricity of chiral smectic C‐LSCE's.
Viscoelastic properties of liquid crystal polymers: Collective motions and nuclear spin relaxation
Authors: Heaton Nicholas , Reimer Dirk , Kothe Gerd 
Published: March 2011

AbstractTransverse deuterium (2H) nuclear spin relaxation experiments have been performed on a 2H labelled main chain liquid crystal polymer. Relaxation rates are determined as a function of temperature and pulse frequency using a modified Carr‐Purcell‐Meiboom‐Gill pulse train. The results are analysed in terms of a hydrodynamic model for fluctuations of the liquid crystal director. Analytic expressions are employed which relate the transverse spin relaxation rate to the anisotropic viscoelastic parameters of the polymer and allow estimates to be obtained for the effective viscosity and average elastic constant of the polymer. The molecular weight dependence of the viscoelastic parameters has been investigated and is found to be consistent with theoretical predictions for highly extended liquid crystal polymers.
Towards mechanically‐linked polymers
Authors: Preece Jon A. , Stoddart J Fraser 
Published: March 2011

AbstractThis short review describes the progress which is being made towards the self‐assembly of mechanically‐linked polymers. A new concept in polymer synthesis ‐ self‐assembly ‐ is demonstrated to have the potential to create novel high molecular weight polymers which possess repeat units that do not just consist of a main chain backbone built up of entirely covalent bonds, but are constructed of mechanical linkages comprised of catenane and rotaxane motifs.
Chiral helical nanostructures based on amorphous abc‐triblock copolymers
Authors: Stadler Reimund , Krappe Udo , Voigt‐Martin Ingrid 
Published: March 2011

AbstractSo far all lattices of regular microdomain structures reported in the literature, either based on binary AB, ABA or ternary ABC block copolymers, can be described using simple symmetry elements like mirror planes, symmetry centers and rotation axes.The microphase separation in a linear ternary block copolymer consisting of three immiscible components namely polystyrene, polybutadiene and polymethyl methacrylate gives rise to the formation of a chiral supramolecular assembly in which chirality is not defined on a molecular (or macromolecular) level but only by the assembly of the linear triblock copolymer molecules. The polybutadiene (7, 12 wt.‐%) phase forms helical strands surrounding the polystyrene cylinders (25, 26 wt.‐%). This chiral mesoscopic assembly can be recognized unambiguously by transmission electron microscopy.1Both left‐ and right‐handed helical structures are formed, either on different cylinders but also along the same cylinder. In the latter case helix reversals are observed. The helical morphology has been obtained by casting the block copolymers from various solvents, with different solubilities for the three components. It also does not change with annealing time. This is a strong indication that the helical morphology is the equilibrium structure of the system.The formation of the helical structure in the present polystyrene‐block‐polybutadiene‐block‐poly(methyl methacrylate) triblock copolymers can be explained on the basis of the theory of block copolymers in the strong segregation limit which was originally developed by Alexander2 and De Gennes3, 4 for lamellar interfaces and extended by Semenov5 to curved (micellar) systems. This approach was successful for the description of symmetric ABC block copolymer systems. The details of the calculations for the helical morphology will be published elsewhere.6
Synthesis of molecular objects: Two‐dimensional polymers
Authors: Stupp S. I. 
Published: March 2011

AbstractThroughout this century polymer science has studied the linear chain and its architectural derivatives which include familiar forms such as the branched chain and the three dimensional network. Other derivatives with unique properties have been investigated more recently and include macromolecular rings, dendrimers, stars, combs and ladders. The objective of this work is to depart from the focus on linear chains and explore the “bulk” synthesis and properties of polymer molecules that can be considered molecular objects. Ideal molecular objects should be macromolecules with well defined shapes that persist as systems transform reversibly from solids to melts or solutions. The limited access to conformational space which is required in order to define and maintain shape in liquid and solid states of the system is an unusual molecular characteristic in common polymers. Our ability to create such objects through bulk reactions of reasonable scale will undoubtedly extend the current boundaries of polymer science and technology. Shapes that are particularly interesting are those not common in the conformational space of linear chains, for example, two‐dimensional polymers shaped as plates and macromolecular bundles shaped as cylinders or parallelepipeds. The molecular object to be discussed in this lecture is a rigid and anisotropic two‐dimensional polymer with planar dimensions greater than its thickness and a shape‐granting skeleton built by covalent bonds. We have so far developed three different strategies for their synthesis, all involving systems in which reactive oligomers organize spontaneously into the necessary planar assemblies to form the object. In one strategy molecular recognition driven by homochiral interactions plays a key role in the formation of two‐dimensional polymers.1 A different methodology relies on entropy‐driven nanophase separation in rodcoil block molecules in which a rigid segment is covalently bonded to a flexible one sharing the same backbone. The third strategy involves the folding of oligomers into hairpin structures which self assemble into two‐dimensional liquids. The lecture will also describe examples of unique properties that could be achieved in materials containing these rigid two‐dimensional objects. These examples will include bulk materials with self‐organized surfaces and also remarkably stable nonlinear optical properties.
Ring‐opening polymerization and depolymerization in respective polymers
Authors: Höcker Hartwig , Keul Helmut 
Published: March 2011

AbstractUnder certain conditions the ring‐opening polymerization of cyclic monomers may be reversed to result in a ring‐closing depolymerization of the respective polymers. This method of “thermodynamic recycling” was explored for a number of examples such as polytetrahydrofuran, polyalkenamers, poly‐ε‐caprolactone, polycarbonates, polysiloxanes and respective blockcopolymers.
Electro‐optical properties and nonlinear response of side chain liquid crystalline polymers
Authors: Gonin D. , Guichard B. , Noël C. , Kajzar F. 
Published: March 2011

AbstractAmong the NLO processes that have been studied, one of the most visually dramatic is the frequency doubling. In the field of optical information storage this process can provide the conversion of near‐infrared laser light from diode lasers into deep blue light. Compared to the more traditional inorganic NLO materials, polymers with polarizable aromatic pendant side groups are increasingly being recognized as the materials of the future. Recently it has been pointed out that the axial ordering spontaneously present in nematic and smectic A polymers can be used to enhance field‐induced polar ordering by elongating the orientational distribution function along the electric field direction. Depending on the value of the microscopic order parameters <P>2 and <P>4, the performance may be improved by a factor of 1 to 5 by using LCPs instead of ordinary amorphous polymers for SHG.1‐4)Interesting results have been obtained for copolyethers prepared by chemical modification of polyepichlorohydrin with classical 4‐cyano‐4'‐hydroxybiphenyl mesogenic group which possesses NLO properties itself.5‐8) These copolyethers afford the opportunity to fine‐tune the polymer properties by varying the concentration of the mesogenic side groups. As the concentration is increased, we move from a purely isotropic polymer to a nematic polymer. Spin‐coated films have been activated using the corona poling technique and the order parameters <P>2 have been determined from optical absorption spectra. The second harmonic coefficients d33 and d31 have been measured and compared with different statistical models. In view of the great practical importance, characterization of the wavelength dispersion has been carried out. It agrees well with the two‐level approximation model. The dynamics of optical SHG has been investigated. It has been shown that both the presence of LC character in the material and the temperature at which the films are stored below Tg are important in determining the stability of the SH coefficients.A polyacrylate and a polymethacrylate bearing the same 4‐cyanobiphenyl‐based side groups have also been studied.7‐8) Of particular interest is the fact that the former is nematic while the latter is purely isotropic at rest, the addition of a methyl group to each structural unit of the polyacrylate backbone creating a higher conformational barrier to mesogen packing. Studies of the temporal and thermal characteristics of the poling process have been performed to:•understand and control the poling process with the intention of maximizing poling induced nonlinearity and stability.•elucidate the influence of the polymer backbone, our data including the use of the same mesogenic unit attached to increasing flexible backbones (e.g. polymethacrylate and polyether).•establish if, in the isotropic cases, noticeable axial order can be induced by the poling field, especially when the system is pulled through nematic/isotropic transition by the electric field.
Self‐assembly via a complex phase transition in mixtures of polystyrene‐block ‐polybutadiene block copolymer and poly(methyl vinyl ether)
Authors: Hashimoto Takeji , Izumitani Tatsuo , Oono Katsuaki 
Published: March 2011

AbstractThe self‐assembly of a binary mixture of polystyreneblock‐polybutadiene (SB) and poly(methyl vinyl ether) (PVME) was studied by transmission electron microscopy and time‐resolved light scattering. The self‐assembly studied involved first microphase separation, in which a microdomain structure composed of polybutadiene block chains (PB) was formed in a matrix composed of polystyrene block chains (PS) and PVME homopolymers, and subsequently macrophase separation of the PVME from the microdomain phase of SB. The microphase separation was induced in a film preparation process using a solution cast method at room temperature. The macrophase separation was induced by rapidly heating the film specimens to above a critical temperature where PVME and PS undergo spinodal decomposition (SD). This complex phase transition, involving microphase separation followed by macrophase separation, was found to generate a superlattice structure (or a modulated structure) with two characteristic spacings: Amacro associated with the SD and Amicro associated with the microphase separation, both being generally time‐dependent. The growth of the “macrodomains” was found to be pinned at Amacro ˜ 840 nm due to the elastic effect of the microdomain structure. The microdomain structure with Amicro ˜ 57 nm was found to undergo a morphological transition (a transition between two ordered phases of block copolymers) as a consequence of the local composition change of the two polymers induced by the SD.
Nematic, smectic and columnar phases of main‐chain liquid crystal polyethers
Authors: Ungar Goran , Zhou Jianping , Percec Virgil , Chu Peihwei 
Published: March 2011

AbstractA number of interesting thermotropic mesophases and transitions occur in main‐chain polyethers and copolyethers based on aliphatic spacers and various semi‐flexible mesogens of the general 1‐(4'‐hydroxyphenyl)‐2‐(2‐R‐4‐hydroxyphenyl)ethane (RBPE) or 1‐(4'‐hydroxybiphenyl‐4‐yl)‐2‐(4‐hydroxyphenyl)propane (TPP) type. The unusual effects described here are (i) nematic‐nematic transition, (ii) smectic‐B (crystal‐B) phase and its shear‐induced orientation, (iii) calamitic columnar phase, and (iv) nematic‐columnar phase sequence.
Optical rheometry of multicomponent polymer liquids
Authors: Fuller Gerald G. 
Published: March 2011

AbstractRecent advances in optical rheometric techniques are described, and applications of the methods are presented that motivate their use in elucidating the structure and dynamics of complex, polymeric liquids. Spectroscopic methods, such as infrared dichroism and 2‐dimensional Raman scattering, which provide information concerning bond‐level orientation dynamics are presented. In addition, the combination of birefringence and stress measurements is demonstrated to be capable of extracting the component dynamics in some multicomponent systems. Examples of the use of these methods include orientation in block copolymers and compatible blends.