bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scope and limitations of 1,1‐diphenylethylene chemistry in anionic polymer synthesis
Authors: Quirk Roderic P. 
Published: March 2011

AbstractThe scope and limitations of the addition reactions of simple and polymeric organolithium compounds with substituted 1,1‐diarylethylenes to prepare in chain‐ and chain‐end functionalized polymers is presented. The application of this general living functionalization reaction for the preparation of ω‐functionalized polymers is illustrated for hydroxyl, carboxyl, dimethylamine, and primary amine groups, as well as for the fluorescent naphthalene and pyrene labels. The use of this chemistry to prepare functionalized initiators is described, as well as the copolymerization of substituted 1,1‐diphenylethylenes with monomers to prepare in‐chain functionalized polymers with alternating structures.
Helix‐induced asymmetric polymerization
Authors: Yu Bin , Ding Meng‐Xian , Wang Yue‐Chuan , Hu Hui‐Zhen , Wang Fo‐Song 
Published: March 2011

AbstractAsymmetric polymerization could be induced by an already formed optically active living prepolymer with one‐handed screw sense helix conformation. The usually formed anionic active centre on the prepolymer could be changed to cationic, radical and even of Ziegler‐Natta type. These living prepolymers with various kinds of active centre were all effective to induce a consequent asymmetric polymerization of a monomer which may be other than that in the prepolymer, to afford an optically active helical chain with the same screw sense as that of the prepolymer. Eight monomers have been used in the work. Optical rotation, circular dichroism and gelpermeation chromatography have been taken to prove the helix‐induced asymmetric polymerization.
Organic‐inorganic polymer hybrids
Authors: Saegusa Takeo , Chujo Yoshiki 
Published: March 2011

AbstractThe present article describes a group of new materials by the combination between organic polymer and silica gel, one of typical inorganic substances. Characteristics of these materials exist in the dimension of blending of the two components, i.e., blending at the molecular level dispersion. The new materials are transparent glassy ones, which are well expressed by a word of “Hybrid”. The hybrids are readily prepared by the sol‐gel reaction of Si(OEt)4, the precursor of silica gel, in the presence of an organic polymer which consists of a repeating unit containing ‐N(R)‐C(=O)‐ group (R=hydrogen or alkyl), i.e., N‐alkyl or N,N‐dialkyl substituted carboxyl amide, urea and urethane groups. Hydrogen‐bond between the above group of organic polymer component and silanol group which is a key intermediate of the sol‐gel reaction plays an important role to form a homogeneous transparent material. The formation of hydrogen bond has been established by FT‐IR spectrum, i.e., the shift of vC=O absorption. Calcination of the transparent hybrid produces another interesting material of highly porous silica gel. At a higher temperature, e.g. 600°C, the organic polymer is decomposed but the framework of silica gel remains unchanged. Thus, the space which organic polymer occupies becomes a pore. The new porous silica gel is characterized by a high surface area of inner surface (∼ 810 m2/g) and a pore size of diameter around 20 Å.
Synthesis and characterization of thermotropic poly(alkylene fumarates)‐block‐poly(arylene fumarates)
Authors: Galcéra Thierry , Fradet Alain , Maréchal Ernest 
Published: March 2011

AbstractThermotropic poly(2,2′‐oxydiethylene fumarate)‐block‐poly(2‐methyl‐1,4‐phenylene fumarate) C is synthesized by interfacial polycondensation of α,ω‐dichlorocarbonyl‐poly(2,2′‐oxydiethylene fumarate) and fumaroyl chloride with 2‐methyl‐1,4‐dihydroxybenzene. A study of each block is carried out on the corresponding homopolymers as models of flexible A and rigid B blocks. Copolymer C and models are characterized by 1H and 13C NMR, I.R. spectroscopy, SEC, DSC, TGA, X‐Ray diffractometry and electron microscopy. A phase segregation is observed in C when B content is above 50%. Copolymer C exhibits a nematic mesophase and can be crosslinked.
Recent advances in the chemistry of aromatic cyclic oligomers
Authors: Brunelle Daniel J. 
Published: March 2011

AbstractDevelopment of an efficient and convenient means for preparation of aromatic cyclic oligomeric carbonates has made these materials available for a wide range of polymerization and processing studies. Building on the workbased on bisphenol A cyclics, recent efforts have concentrated on the preparation of new cyclics which afford polymers with properties substantially different from bisphenol A polycarbonate. Cyclic systems have been developed which lead to polycarbonates with improved solvent resistance, either through cross‐linking or via crystallization. Polycarbonates with both high or low glass transition temperatures have also been achieved.
Synthesis of well‐defined all‐acrylic graft copolymers
Authors: Sheridan M. S. , McGrath J. E. 
Published: March 2011

AbstractWell defined all‐acrylic graft copolymers have been synthesized using the macromonomer technique. Poly(methyl methacrylate) (PMMA) macromonomers of controlled molecular weight and narrow molecular weight distribution have been synthesized by group transfer polymerization (GTP) using a protected hydroxyl functional initiator. These macromonomers were quantitatively functionalized with a polymerizable acrylic and group and copolymerized under free radical conditions with 2‐ethylhexyl acrylate (2EHA) to form the desired well defined graft copolymers in high yields. The macromonomers and the copolymers have been characterized by a variety of spectroscopic, chromatographic and thermal analysis methods. Transparent, multiphase materials with glass transition temperature (Tg) values of approximately ‐65 °C and 115 °C were obtained. The reaction conditions necessary to generate these materials most effectively have also been investigated and are described herein.
Block and graft copolymers based on cationic ring‐opening polymerizations
Authors: Goethals Eric J. , Toncheva Veska , Hosteaux Fried'l , Walraedt Saskia , de Clercq Ronny 
Published: March 2011

AbstractThe highly living character of a number of cationic polymerizations has been used to synthesize new, well defined, segmented copolymers. This has been achieved by sequential monomer additions, by grafting reactions, by macromonomer copolymerizations as well as by transfer to polymer. In the present report, a number of examples of such polymers will be presented. The new materials are based on tetrahydrofurane (THF), alkyloxazolines (ROx), cyclic amines, cyclic acetals and cyclic sulfides.
Synthesis and applications of acid‐labile acrylic polymers
Authors: Hertler W. R. , Sogah D. Y. , Raymond F. A. , Bauer R. D. , Chang C. T. , Taylor G. N. , Stillwagon L. E. 
Published: March 2011

AbstractA variety of acrylic and methacrylic acetal esters were synthesized by reaction of unsaturated carboxylic acids with vinyl ethers. The acetal esters were converted by radical polymerization and GTP to acid‐labile homo‐ and copolymers. Coatings of these polymeric acetal esters containing photosensitive acid‐generating compounds are useful in image‐formation through chemical amplification. Thus, poly(tetrahydropyranyl methacrylate‐co‐benzyl methacrylate) can be used in positive working deep UV microlithography. Poly(tetrahydropyranyl acrylate), coated in a thin layer over a tacky elastomer, provides a high resolution, water‐developable negative working tonable composition. Several polymeric and nonpolymeric acetal esters can be used for positive working electrostatic imaging through changes in electrical conductivity.
Interaction of poly(N‐isopropylacrylamide) with perfluorooctanoic acid in aqueous solution
Authors: Schild Howard G. , Tirrell David A. 
Published: March 2011

AbstractInteraction of poly(N‐isopropylacrylamide) (PNIPAAM) with perfluorooctanoic acid (PFOA) was explored in aqueous solution. Increasing concentrations of PFOA were observed first to depress slightly the lower critical solution temperature (LCST) then to elevate it at concentrations greater than ca. 2.5 mM. At concentrations >ca. 3.5 mM, the LCST transition could not be detected by either microcalorimetry or cloud point measurements. PNIPAAM appeared to promote the micellization of PFOA. Pinacyanol dye experiments were ambiguous, but the aggregation concentration reported by surface tension measurements was clearly depressed upon addition of PNIPAAM.
Scanning simulation procedures for calculation of the entropy, the pressure and the chemical potential of many‐chain systems
Authors: Meirovitch Hagai 
Published: March 2011

AbstractUsing the scanning and the hypothetical scanning methods we study a system of many chains with excluded volume contained in a “box” on a square lattice. With these methods the sampling probability P of a configuration can be calculated and therefore the entropy S is known (S ∼ ln P) without the need to resort to thermodynamic integration. Thus, the pressure and the chemical potential can be calculated with high accuracy directly from the entropy using standard thermodynamic relations. The computer simulation results are compared to the approximate theories of Flory, Huggins, Miller and Guggenheim and to the recent improved theories of Freed and co‐workers.
Statistical correlation between configuration‐dependent properties of polymer chains
Authors: Galiatsatos Vassilios 
Published: March 2011

AbstractA new methodology for formulating the averages of elements of generator matrices is presented. Incorporation of this technique to the Rotational Isomeric State (RIS) model allows the efficient generation of the higher and mixed moments of any conformation‐dependent physical property of a polymer chain. The computational technique is based on symbolic manipulation of the generator matrix elements which are treated as character strings. Successful application of the technique is demonstrated by calculating the correlation coefficient between the dipole moment and the end‐to‐end distance of polymer chains with symmetric rotation potentials and in the independent bond rotation approximation. It is shown that the correlation heavily depends on the orientation of the bond dipole moment vector orientation.
A comparison of different methods for the calculation of the chemical potentials of polymer systems
Authors: Kumar Sanat K. 
Published: March 2011

AbstractIn an earlier publication we had presented a Monte Carlo method to calculate the incremental chemical potential between a chain of length v and one of length v+1 at any density. (Ref.9) In this paper we begin by formally proving that the chemical potential of a whole chain of length v can be obtained by sequentially summing the incremental chemical potentials of all chains whose lengths are smaller than v under the same conditions. We then compare the numerical value of chain chemical potentials computed in this fashion to those obtained by inserting whole chains into the simulation cell following the configurational bias procedure proposed by Smit and Frenkel. (Ref.5) It is found, for the two cases considered here, that the results obtained from the two different calculations agree within simulation uncertainty, thus verifying the validity of the proposed arguments.
On the statistics of dense, disordered assemblies: Equilibrium and dynamics
Authors: Simha Robert 
Published: March 2011

AbstractWe consider implications of a lattice model which operates with a vacancy fraction h as a measure of structural disorder. Consequences for the configurational thermodynamics of one‐ and multicomponent systems and their phase equilibria are briefly indicated. The principal topic is the glassy state under steady state conditions, as well as the kinetics of relaxational processes toward equilibrium. The central role of the h‐function in its dependence on variables of state is made evident among others by the connection between equation of state and thermo‐elastic properties. Moreover, a dynamics of volume relaxation can be treated by means of a corresponding theory for the h‐function. Applications of this theory to isothermal annealing below the glass temperature Tg, the response to a constant cooling rate of the melt through the transition zone, and the computation of a complex compression modulus are reviewed. The implications of vacancy cluster distributions for the analysis of positron spectroscopy are pointed out. Finally we indicate the basis for the development of correlations between Tg and structural parameters.
Stress/strain analysis of polymeric materials by molecular dynamics simulations
Authors: Qian Caibao , Ludovice P. J. 
Published: March 2011

AbstractMechanical properties number themselves among the most important properties of any polymeric material used in engineering applications. The Molecular Mechanics approach has been used to calculate the mechanical moduli of various polymers, but this approach has the limitation of requiring experimental densities and neglecting both entropy contributions and local volume fluctuations which can be significant in condensed phase polymers such as glasses and melts. Although constant stress molecular mechanics can provide an estimate of the bulk density, constant stress molecular dynamics (CSMD) can overcome all these limitations. However, CSMD is limited by an inherently short simulation time scale. CSMD was used to calculate the bulk moduli, Young's moduli and density of various amorphous polymers, including: polyethylene, poly(propylene), polystyrene, poly(vinyl chloride), poly(ethylene terephthalate), poly(butylene terephthalate), nylon 6, poly(methyl methacrylate), polydimethylsiloxane, bisphenol‐A polycarbonate, poly(phenylene sulfide). Results indicate that CSMD is a useful tool in characterizing mechanical properties of amorphous polymers despite this time scale limitation.
Conformational and dynamic effects of pendant‐PEK chains on rigid‐rod polymers by molecular dynamics simulation
Authors: Trohalaki Steven , Dudis Douglas S. 
Published: March 2011

AbstractMolecular dynamics simulations were performed with models of a single‐component ‘hairy‐rod’ molecular composite composed of flexible meta poly(aryl ether ketone) (mPEK) chains (the ‘hairs’) grafted to a poly(p‐phenylene benzobisthiazole) (PBZT) rigid‐rod backbone. The molecular‐composite concept, conceived to circumvent solubility problems and improve compressive strength of PBZT, relies on an even distribution of rods in a coil‐like matrix. Two‐molecule simulations show that the pendant mPEK chains associate with the rods causing large bends in the rod backbone. Simulations of bulk systems imply that the mPEK chains greatly reduce the correlation of rod orientation without altering rod spacing. Radial distribution and orientation correlation functions as well as correlation volumes are computed.
Monte Carlo methods for polymer chains in two ‐ dimensional geometries (polymers at surfaces and interfaces)
Authors: Binder Kurt 
Published: March 2011

AbstractCoarse‐grained models of polymers at interfaces can be defined such that their treatment by Monte Carlo simulation is most convenient and efficient for the problem at hand. This simulation strategy is briefly illustrated with three examples: (1) The orientational ordering of rigid rod‐like polymers grafted to a surface, where “table methods” can be used, applying a fine discretization of the angles describing rod orientation. (2) Surface enrichment of one species in a polymer blend is treated by a semi‐grand‐canonical technique. (3) The number of configurations and structure of a star polymer attached with its center to a wall is studied by a “growth technique” generalizing simple sampling methods.
Prediction of structure and properties of end‐linked networks
Authors: Rolfes H. , Stepto R.F.T. 
Published: March 2011

AbstractRate theory has been developed for RA2+RB4 polymerisations including intramolecular reaction and the general behaviour of RA3, RA and stoichiometric RA2+RB3 and RA2+RB4 polymerisations compared regarding the moduli of networks formed at complete reaction. The predictions for RA2+RB3 and RA2+RB4 polymerisations are used to analyse existing experimental data on gel points and moduli in polyurethane polymerisations and networks. By fitting experimental gel points, improved predictions of moduli at complete reaction are achieved.
Cooperative motion in amorphous polymers; application to the study of free‐radical migration in solids
Authors: Tiňo Jozef , Urban Ján , Klimo Viliam , Klimová Marta 
Published: March 2011

AbstractA Monte Carlo method has been used for studying the effect of the motion of some submolecular structures on the migration of radical centres and on the free‐radical decay and its dependence on density. Motions of crank, crankshaft, kink, and double kink type are considered. A cooperative type of motions is also taken into account. The results show that cooperative motions support diffusion of radical centres and thus also the free‐radical decay but, at higher densities, the cooperation of motions is restricted. The density of the system, where the decay of radicals is followed, affects the rate of the decay, its increase causes radical decay retardation. This is in line with the high pressure effect, which also retards the radical decay rate.
Microstructure of copolymers by statistical modeling of their mass spectra
Authors: Montaudo Maurizio S. , Montaudo Giorgio 
Published: March 2011

AbstractA novel method for the determination of the microstructure of copolymers is presented here. Statistical modeling of the mass spectral intensities of copolymers has been used to derive information on the distribution of monomers along the copolymer chain, and an automated procedure to find the composition and the sequence of the copolymers analyzed has been developed.
Heterogeneous Ziegler‐Natta catalysts: On going progress for the polyolefin industry
Authors: Zucchini Umberto 
Published: March 2011

AbstractA great deal of research and development efforts in Ziegler Natta catalysis has been put within the last ten years into the polyolefin industry. The exploitation of new catalysts, the introduction and consolidation of advanced polymerization process technologies and, finally, the development of a broader range and of a better tailoring of product grades, have made the polyolefin market an expression of a young, dynamic, technology‐driven industry. In this context heterogeneous catalysts have played a key role. Many drawbacks of the catalysts of the previous generation have been overcome. However some problems have still to be solved in order to both further improve catalyst performance and reduce the residual areas of empiricism in catalyst design and manufacture.
Role of ion‐pair equilibria in homogeneous Ziegler‐Natta olefin polymerization catalysis
Authors: Eisch John J. , Pombrik Sofya I. , Zheng Guo‐Xiu 
Published: March 2011

AbstractBy means of a multinuclear NMR study of the complexes formed between AlCl3 and either Cp2TiCl2 or Cp2Ti(CH2SiMe3)Cl in methylene chloride solution, isomeric forms of the resulting 1:1 complexes have been detected. The influence of temperature, concentration, ratio of the titanocene chloride to aluminum chloride and nature of the solvent upon the 1H, 13C and 27Al NMR spectra has been investigated. The spectral changes caused by the foregoing factors give compelling evidence for a equilibrium in such Cp2Ti(R)Cl · AlCl3 complexes (R = Cl, CH2SiMe3) between contact ion pairs, Cp2TiR · Cl · AlCl3, and solvent‐separated ion pairs, Cp2TiR+ AlCl4−. Upon experimental variations in temperature, concentration, solvent and ratio of RnAlCl3−n to the titanium catalyst, the polymerization activity of the catalyst system towards ethylene was markedly altered. Such changes in activity support the conclusion that the most active sites for polymerization in such systems are the solvent‐separated ion pairs.
Chemistry of new electrophilic metal ALKYL compounds
Authors: Crowther Donna J. , Jordan Richard F. 
Published: March 2011

AbstractThe reaction of the neutral carborane C2B9H13 with Cp*M(CH3)3 (M = Zr (a), Hf (b); Cp* = η5‐C5Me5) yields [Cp(C2B9H11)M(CH3)]n (3a, b). Complexes 3a, b form THF adducts Cp*(C2B9H11)M(CH3)(THF) 4, insert 2‐butyne to yield Cp*(C2B9H11)M{C(Me=CMe2} 5, and undergo methane elimination upon thermolysis to yield methylene‐bridged complexes [Cp*(C2B9H11)M]2(μ‐CH2) (6). These chemical studies, and companion structural and theoretical studies establish that 3a, b are neutral analogues of the cationic Cp2M(R)+ species (1; Cp = η5‐C5H5) and Cp2M(R)(L)+ (2) which are believed to be active in Cp2MX2‐based Ziegler catalysts. Despite the lower metal charge, 3–6 exhibit characteristic “electrophilic metal alkyl” properties including agostic M‐H‐C and M‐H‐B interactions, high insertion and intramolecular C‐H activation reactivity, and high ethylene polymerization and propene oligomerization activity. These observations suggest that the key requirement for high insertion/polymerization activity in metallocene systems is high metal unsaturation (i.e. two empty metal‐centered orbitals) rather than charge.
Ti complex catalysts including thiobisphenoxy group as a ligand for olefin polymerization
Authors: Miyatake Tatsuya , Mizunuma Kooji , Kakugo Masahiro 
Published: March 2011

AbstractTitanium complexes were prepared by the reaction of 2,2′‐thiobis(6‐tert‐butyl‐4‐methylphenol) (TBP) with TiCl4 or Ti(OPri)4. These complexes in combination with methyalumoxane as cocatalyst are highly active towards ethylene and propene, giving polymers having high molecular weights. The polymerization activities for ethylene and propene are comparable to those of Cp2ZrCl2‐MAO catalyst. Polypropylene obtained had extremely high molecular weight (Mw>6 million) and low regioregularity (30% of head‐to‐head and tail‐to‐tail linkages). Highly syndiotactic polystyrene was obtained with these catalysts with activity up to 27 kg polymer per g Ti and hour. Copolymerization of styrene with ethylene gave highly alternating copolymer with isotactic styrene units. These catalysts are also active toward both conjugated and nonconjugated dienes such as butadiene and 1,5‐hexadiene. Polybutadiene had mainly cis‐1,4‐structure (98%). The structure of poly(1,5‐hexadiene) is rather complicated, which is quite different from that prepared with heterogeneous TiCl3 catalysts.
Carbon‐carbon linkage of ethene by nickel‐chelate complexes
Authors: Keim Wilhelm 
Published: March 2011

AbstractResults will be described oligomerizing/polymerizing ethene. Using nickel catalysts in combination with P‐O‐bidentate (chelate) ligands ethene can be converted to high molecular weight polyethylene. The use of chelate ligands is essential, and emphasis is given to the importance of bidentate chelates.
Recent advances in the field of diolefin polymerization with transition metal catalysts
Authors: Porri Lido , Giarrusso Antonino , Ricci Giovanni 
Published: March 2011

AbstractRecent advances in the field of catalysis for 1,3‐diene polymerization and in the interpretation of the polymerization mechanism are examined. Catalysts prepared from methylaluminoxanes and soluble transition metal compounds are in general more active than the analogous systems prepared from AlR3. With some catalysts, however, (e.g. lanthanide systems) a high activity is obtained only when transition metal compounds containing preformed metal‐carbon bonds are used. Methylaluminoxanes affect also the stereospecificity of the polymerization. Active and stereospecific systems are obtained from monocyclopentadienyl derivatives of Ti and aluminoxanes. Recent views on the factors that determine stereospecificity are examined. Schemes are presented for the formation of iso‐ or syndiotactic polymers, with 1,2, cis‐1,4 or trans‐1,4 structure, from various dienes.