bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of polymer surfaces using scanning force microscopy (SFM) “a new direct look on old polymer problems”
Authors: Grim P.C.M. , Brouwer H. J. , Seyger R. M. , Oostergetel G. T. , Schutter W.G. Bergsma , Arnberg A. C. , Güthner P. , Dransfeld K. , Hadziioannou G.
Published: March 2011

In this contribution, the general concepts of force microscopy will be presented together with its application to polymer surfaces (Ref.1). Several examples will be presented to illustrate that force microscopy is a powerful and promising tool for investigation of (polymer) surfaces, such as the imaging of polymer single crystals and the surface structure of thin films of piezo‐ and pyroelectric block copolymers. Individual molecules were resolved in the case of polytetrafluoroethylene and double‐stranded circular DNA, without any particular surface treatment.
Interfacial dynamic properties of polymer films
Authors: Yu Hyuk
Published: March 2011

Many vinyl homopolymers are surface active by virtue of their side chains being hydrophilic while backbone hydrocarbon structure being hydrophobic, thus they form remarkably stable monolayers. We report here the studies of collective dynamics of these monolayers and thin films with the technique of surface light scattering by the spontaneous capillary waves on the air/water and oil/water interfaces. The dynamics are represented by the viscoelastic parameters of the lateral dilational mode, which couples efficiently with the transverse mode in the case of air/water interface.
Dynamic light scattering by weakly ionized gels: Effects of inhomogeneities and non‐ergodicity
Authors: Candau Sauveur Jean , Moussaid Abdellatif , Munch Jean‐Pierre , Schosseler François
Published: March 2011

Small angle neutron scattering and light scattering experiments have been performed on partially neutralized poly(acrylic acid) solutions and gels. The structure factor obtained from small angle scattering and static light scattering reveals the absence of significant contribution from large scale inhomogeneities in the gels as soon as the ionization degree exceeds 9·10−3. The comparison of the time and ensemble averages of the autocorrelation function of scattered light intensity shows that the gels behave with respect to that experiment as ergodic media.
Mesomorphic ordering of polymers
Authors: Skoulios Antoine
Published: March 2011

Depending upon their chemical architecture, polymers may give rise to well ‐ ordered mesomorphic phases. A few typical examples of mesomorphic polymers (block copolymers, polysoaps and side‐chain liquid ‐ crystalline polymers, rigid‐chain polymers) will be considered. Their structure will be described as determined by x‐ray diffraction.
Biosynthesis of new polymers of controlled molecular structure
Authors: Dougherty Michael J. , Kothakota Srinivas , Krejchi Mark T. , Zhang Guanghui , Mason Thomas L. , Tirrell David A. , Fournier Maurille J.
Published: March 2011

This paper describes the use of artificial genes to direct bacterial synthesis of new polypeptides of precisely defined molecular structure. This approach has been applied to three problems in polymer chemistry and physics: i) control of chain folding in crystalline polymers, ii) biosynthesis of polypeptides containing unnatural amino acids, and iii) preparation of monodisperse helical polymers.
The role of amine in vinyl radical polymerization
Authors: Feng Xin‐De
Published: March 2011

Advances of radical initiation systems and their initiation mechanisms in vinyl polymerization through peroxycompound and amine systems as well as photo‐induced charge transfer initiation in the presence of amine are briefly reviewed which is concerned with some generalization regarding to the role of amine in the form of aminium radical in such vinyl radical polymerization.
The role of ceric ion in vinyl polymerization and graft copolymerization
Authors: Qiu Kun‐Yuan
Published: March 2011

Six kinds of new ceric ion redox initiation systems for vinyl radical polymerization and two kinds of macromolecule graft copolymerization by ceric ion have been briefly reviewed in this paper. The initiators include ceric ion/acetanilide, ceric ion/alkyl phenylcarbamate, ceric ion/4‐methoxysuccinyltoluidine, ceric ion/aliphatic aldehyde, ceric ion/aromatic aldehyde, ceric ion/diketone systems. Macromolecules such as poly(ether‐urethane) and macromolecules having active pendant groups were selected for graft copolymerization with acrylamide initiated by ceric ion.
Synthesis and characterization of polymers from itaconic acid derivatives
Authors: Otsu Takayuki , Watanabe Hiroyuki , Yang Jian‐Zhong , Yoshioka Masahiro , Matsumoto Akikazu
Published: March 2011

Some itaconic acid derivatives were prepared and polymerized, in which itaconic acid (IA), β‐monoalkyl itaconates (mRI), dialkyl itaconates (DRI), N‐substituted itaconamates (IAE), itaconamides (IAm), itaconic anhydride (IAn), N‐alkylitaconimides (RII), and N‐(alkyl‐substituted phenyl)itaconimides (RPhII) are included. The polymerization reactivity was examined, and discussed in relation to the structure of the monomers. The structure and some properties of the resulting polymers were investigated. Some citraconic acid (CA) and mesaconic acid (MA) derivatives were also polymerized, and their reactivities were compared with the corresponding IA derivatives.
The kinetics and compartmentalization of seeded emulsion polymerization of styrene with a series of seeds of different size
Authors: Fu Shoukuan , Qian Yu , Bai Feng , Yu Tao
Published: March 2011

The Interval II kinetics and compartmentalization effect of emulsion polymerization of styrene with the seeds of five radii (r=40.2, 51.3, 76.5, 99.7 and 252.0 nm) have been studied. The kinetic parameters, i.e., the rate coefficients ρ, K and C which refer, respectively, to the entry of free radicals into latex particles, the exit of free radicals from the particles and the bimolecular termination of free radicals within the particles; nss and nss(thermal), the average number of free radicals per particle in the steady state and in the thermally induced background polymerization, respectively, are obtained. The propagating rate coefficient kp, the termination rate coefficient kt, as far as possible, are calculated in the runs.

From this work, it can be concluded that the kinetic behavior, the kinetic parameters and the compartmentalization effect of emulsion polymerization are greatly influenced by the latex particle size.
Kinetics of polymeric network synthesis via free‐radical mechanisms ‐ polymerization and polymer modification
Authors: Zhu Shiping , Hamielec Archie
Published: March 2011

The kinetics of polymeric network formation via free radical mechanisms is an attractive research area because there are many phenomena which are not well understood and in addition, the commercial potential for crosslinked systems is great. Recently, a large research/development program was initiated at the McMaster Institute for Polymer Production Technology (MIPPT) to investigate the fundamentals and applications of polymeric network, in particular, the kinetics of synthesis via free‐radical mechanisms and network characterization. The research on crosslinking involved both theoretical developments and experimentation. Herein is provided a comprehensive summary of this work.

In the experimental polymerization, two comonomers, methyl methacrylate (MMA) / ethylene glycol dimethacrylate (EGDMA) and acrylamide (AAm) / N,N‐methylene bisacrylamide (Bis), as model systems were studied in considerable detail. Measurements included: monomer conversions, radical concentrations, sol/gel fractions, crosslink densities (equilibrium swelling and swollen‐state 13C‐NMR) over the entire range of divinyl monomer levels as a function of polymerization time. In the polymer modification, high density polyethylenes were crosslinked using peroxides and γ‐radiation. For this system, crosslinking and chain scission occur simultaneously.

In the theoretical studies, it was shown that in general, network formation by free‐radical mechanisms is highly irreversible requiring that the classical equilibrium gelation theories after Flory/Stockmayer be generalized. The general model which was developed using the pseudo‐kinetic rate constant method predicts the existence of a crosslink density distribution (crosslink density of a primary polymer chain depends on its birth time) with a variance which can vary widely depending on network synthesis conditions.
Studies on molecular weight of poly ((vinylidene chloride)‐co‐(vinyl chloride)) in the suspension process
Authors: Liu Long‐Xiao , Weng Zhi‐Xue , Huang Zhi‐Ming , Han Dong‐Lin , Pan Zu‐Ren
Published: March 2011

Various factors affecting the molecular weight of poly ((vinylidene chloride)‐co‐(vinyl chloride)) were studied in the paper. Mathematical models correlating intrinsic viscosity of the copolymer with concentrations of 1,2‐dichloroethane and initiators, and temperature were proposed and may be used to control the molecular weight of the copolymer.
Non‐steady state model for free radical polymerization
Authors: Yan Deyue , Feng Jing
Published: March 2011

The non‐steady state theory for the kinetics of free radical polymerization taking no account of gel‐effect is reviewed. Considering the facts that the monomer consumption in chain propagation is much higher than that in chain initiation and the rate constant of chain termination is much larger than that of chain propagation or transfer, a few very close approximations are introduced to solve the set of kinetical differential equations of free radical polymerization. The expressions for various molecular parameters, such as the molecular size function, the number‐ and weight‐average degrees of polymerization and the dispersity, are derived. In accord with the non‐steady state theory, the curves of free radical decay with reaction time or monomer conversion and the molecular parameters mentioned can be predicted from the reaction conditions. Several numerical examples are given.
Stereochemical control in homogeneous Ziegler‐Natta catalysts
Authors: Chien James C. W.
Published: March 2011

Racemic ethylenebis(η5‐indenyl)zirconium dichloride (Et[Ind]2ZrCl2) activated with methylaluminoxane (MAO) catalyzed propylene polymerization with varying degree of stereochemical control which decreases greatly with the increase of Tp (temperature of polymerization). The PP&s are characterized by low melting temperature (Tm), high solubility, and prefers to crystallize in the γ‐modification. The catalytic activity of Et[Ind]2ZrCl2/MAO becomes very small with the lowering of Tp. Very active and highly stereoselective cationic metallocene alkyl, Et[Ind]2Zr+(CH3), was produced by the reaction of Et[Ind]2Zr(CH3)2 with Ph3C+B(C6F5)4−. Comparison of this system with the Et[Ind]2ZrCl2/MAO catalyst showed that in the latter case a quarter of the Et[Ind]2ZrCl2 was converted by MAO to Et[Ind]2Zr+CH3 at room temperature but less than 0.14% of the Zr was so activated at −20°C. The Et[IndH4]ZrCl2/MAO catalyst was shown to have two kinds of catalytic species one with high propagation rate constant (kp) and stereoselectivity and another with low kp and poor stereoselectivity. The very narrow molecular weight distribution of the PP produced may be attributed to the fact that the different types of active species have comparable kp/ktrA, the latter is the rate constant of transfer. Non‐symmetric, rac‐[anti‐ethylidene(1‐η5‐indenyl)(1‐η5‐tetramethylcyclopentadienyl)‐Ti‐Cl2 and ‐(CH3)2 have been synthesized and structures determined. The complexes provide dissimilar steric environment to propagating chains to produce crystalline‐amorphous multiblock thermoplastic elastomeric PP. The polymerization process here involves a two‐state propagation mechanism.
Copolymerization of propene with high‐1‐olefin using a MgCl2/TiCl4 catalyst
Authors: Yang Shi‐Ling , Xu Zhi‐Kang , Feng Ling‐Xian
Published: March 2011

Copolymerization of propene and 1‐olefins including 1‐octene, 1‐decene, 1‐dodecene, 1‐tetradecene, and 1‐hexadecene were studied with the catalyst system MgCl2/TiCl4‐Al(i‐Bu)3. It was found that the polymerization productivity and the consumption rate of propene are improved significantly in the presence of the comonomer. The total productivity of propene/1‐olefin copolymerizations decreases as follows: 1‐octene> 1‐decene>1‐dodecene>1‐hexadecene>1‐tetradecene. The reactivity ratios were estimated from the copolymerization results. 13C NMR was used to characterize the microstructures of propene/1‐octene copolymer. Finally, the oxygen enrichment behavior of propene/1‐octene copolymer was investigated.
Scope and limitations of 1,1‐diphenylethylene chemistry in anionic polymer synthesis
Authors: Quirk Roderic P.
Published: March 2011

The 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

Asymmetric 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

The 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

Thermotropic 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

Development 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

Well 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

The 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

A 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

Interaction 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

Using 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

A 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

In 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

We 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

Mechanical 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

Molecular 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

Coarse‐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

Rate 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

A 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

A 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.
New Ziegler–Natta polymerization catalysts and new polymers
Authors: Corradini Paolo
Published: March 2011

Models for the explanation of the stereospecific behaviour of Ziegler‐Natta catalysts, homogeneous and heterogeneous, are discussed. Structural data on new types of stereoregular polymers, obtained with homogeneous catalysts, are reported.
Heterogeneous Ziegler‐Natta catalysts: On going progress for the polyolefin industry
Authors: Zucchini Umberto
Published: March 2011

A 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

By 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

The 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

Titanium 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

Results 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

Recent 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.
Anionic polymerization methods: An efficient tool for the synthesis of tailor‐made macromolecules
Authors: Rempp Paul , Lutz Pierre
Published: March 2011

The criteria of livingness, as applied to anionic polymerizations, are discussed. A number of restrictions have to be taken into consideration, if anionic polymerizations are to be applied to the synthesis of model polymers, Several examples of synthesis of tailor‐made polymers via anionic polymerization are presented, namely end‐functionalizations, chain extensions, end‐to‐end cyclizations, block copolymer synthesis, grafting processes, methods to make star polymers. In each case the reliability of the methods is discussed thoroughly.
Comparison of living polymerization mechanisms. Acrylates and carbocationic polymerization
Authors: Pugh Coleen , Matyjaszewski Krzysztof
Published: March 2011

The concept of a living polymerization is critically discussed. A system ranking various classes of “livingness” is proposed, and the importance of determining the real values of ktr/kp and kt/kp ratios is expounded. New living systems, including carbocationic polymerization and group transfer polymerization of acrylates are compared with classic ionic systems. The mechanism of propagation and the nature of the true active species are similar in both new and classic polymerizations. The role of various components which improve the “livingness” of the polymerizations is discussed and explained by dynamic equilibration between dormant and active species and suppression of side reactions.
Structures of (ester) enolates and related compounds
Authors: Boche Gernot , Harms Klaus , Marsch Michael
Published: March 2011

The side reactions in the anionic polymerization of (meth)acrylates initiated by organolithium compounds raise the question about favorable interactions between organolithium and carbonyl compounds in general and in this polymerization reaction. The results of several crystal structures of lithium(sodium) (ester) enolates without or with other molecules clearly demonstrate the favorable formation of homo‐ and mixed aggregates, respectively. It is also shown how different gegenions (ZnBr+, R4N+, etc.) influence the overall structure and the structure of the anion.
Kinetics and stereoregulation in the isotactic‐specific and living polymerization of methyl methacrylate
Authors: Kitayama Tatsuki , Fujimoto Nobutaka , Hatada Koichi
Published: March 2011

Kinetic studies on the isotactic‐specific living polymerization of methyl methacrylate with t‐C4H9MgBr were carried out in toluene at −78°C and the kinetic orders with respect to the monomer and initiator were found to be unity. Propagation rate in the early stage of polymerization and the initiation rate were studied by kinetic measurement and analysis of oligomer distribution. The rate constants for the propagation of the unimer (k1), dimer (k2), and trimer anions (k3) were found to be in the following order; k1 >> k2 > k3. 13C NMR spectra of the oligomer anions indicated the coordination of penultimate and antepenultimate ester groups to Mg counterion. Possible mechanism for stereoregulation in the early stage of polymerization was discussed.
Poly(ethylene oxide) gel as a novel polymerization medium anionic polymerization of methyl methacrylate
Authors: Tsvetanov Ch.B. , Novako Ch.P. , Dotcheva D.T. , Gitsov I.
Published: March 2011

Crosslinked poly(ethylene oxide)‐(PEO‐N) is used as a novel medium for the anionic polymerization of methyl methacrylate (MMA) initiated by t‐BuOK and ethyl‐α‐lithioisobutyrate (α‐LiEtIB) in toluene. Comparative studies with linear poly(ethylene oxide)‐(PEO‐L) are performed as well. It is found that PEO‐N effectively binds both initiators, and the polymerization process takes place mainly in the gel phase. PEO‐N accelerates the polymerization process initiated by t‐BuOK enabling the formation of high‐molecular‐weight polymers with high yields. Part of poly(methyl methacrylate)‐(PMMA) remains in the gel particles yielding semi‐interpenetrating networks with amphiphilic properties. PEO additives do not influence profoundly the course of the polymerization, initiated by α‐LiEtIB. The influence of PEO‐N on the proceeding of the polymerization is discussed in some detail.
Thermolytic behaviour of polybutadienyllithium and polystyryllithium in ethylbenzene at high concentrations
Authors: Schué F. , Aznar R. , Sledz J. , Nicol P.
Published: March 2011

The polymerization of butadiene and styrene with lithium and lithium alkyls has been extensively studied. The kinetics and mechanism of the pyrolysis of alkyllithium compounds has also been investigated thoroughly. The mechanism of these elimination reactions is conveniently elucidated by manometric methods, and mechanistic interpretations have been proposed. However, there are less published accounts of the thermal stability of polymer‐lithium systems. There is a need to have kinetic data describing the thermal termination of “living” polymers at lithium concentrations approaching those of commercial polymerization systems. This paper will discuss the thermal stabilities of concentrated solutions in ethylbenzene of polystyryllithium and polybutadienyllithium.
Mechanism of anionic (ionic) polymerization of acetylene monomers
Authors: Kobryanskii Valery M.
Published: March 2011

Polymerization of phenylacetylene in presence of butyllithium has been studied. It is shown that the process of polymerization is accompanied by the appearance and growth of the ESR signal. The model of anionic polymerization is suggested according to which formation of low‐molecular‐weight polyphenylacetylene is caused by the destruction of the active centers by means of electron transfer from active center to the conjugated chain. The assumption is made that electron transfer from conjugated chain to an active center may also be a fundamental reaction limiting the chain length in cationic polymerization of acetylene monomers. The kinetic scheme of ionic polymerization of acetylene monomers with consideration of electron transfer is analyzed and molecular weight distribution functions are obtained with good agreement between the calculated parameters and experiment. It is shown that one of the ways of obtaining high‐molecular‐weight polyacetylenes in ionic polymerization is the formation of donor‐acceptor complexes with a polyene chain in the process of the chain growth. The formation of complexes exchanges parameters of electron structure of the polyene chain and decreases the rate of the electron transfer reactions.
Mechanistic aspects of group transfer polymerization
Authors: Quirk Roderic P. , Ren Jie , Bidinger Gregory
Published: March 2011

The experimental evidence supporting the involvement of enolate anions in group transfer polymerization(GTP) is reviewed. The results of silyl group exchange studies between living silyl ketene acetal‐ended oligomers under typical GTP conditions are discussed. It is concluded that the observations of significant amounts of silyl group exchange in the presence of polymerizing monomer are not consistent with the originally proposed “associative mechanism” based on the GTP Criterion which precludes intermolecular silyl group exchange.
Mechanism of GTP: Can all of the available data be accommodated?
Authors: Webster Owen W.
Published: March 2011

Group transfer polymerization (GTP)a of acrylic monomers is a living system mediated by a trialkylsilyl capped growing chain end. The fact that it operates at temperatures as high as 100° C differentiates GTP from living anionic polymerization, which at best operates at 25° C for hindered methacrylates. To accommodate all of the mechanistic data available it appears that at least two mechanistic pathways are required: an associative process for mild nucleophilic catalysts and a dissociative process for strong nucleophilic catalysts.
Polymer devolatilization: State of the art
Authors: Astarita Gianni , Maffettone Pier Luca
Published: March 2011

The current state of the art on polymer devolatilization is reviewed. After a brief description of existing processes, two aspects of the problem are taken into consideration: modeling and optimization of actual processes, and physicochemical data needed for analysis. It is shown that, while many of the available models concentrate on the fluid mechanics involved and on mass transfer, heat transfer may well be the rate determining phenomenon. Values of the relevant physicochemical parameters may range over several orders of magnitude within any given process, and the availability of reliable data over the ranges of interest is in general significantly less good than would be needed for reliable analysis.
Numerical evaluation of a method for determining extensional viscosity of fluids using contraction flow analysis
Authors: Davies A. R. , Farah I. M. , Rides M. , Thomas K.
Published: March 2011

We report an evaluation of the use of Binding's method (Ref 11) for determining extensional viscosity values from capillary die rheometry entrance pressure drop data. A constitutive relation defining the fluid's rheological behaviour is first postulated, from which the pressure drop in a contraction region is calculated by numerical simulation for a range of flow rates. Extensional viscosity estimates are then made from the simulated pressure drop data using Binding's method, and these estimates are compared with the exact extensional viscosity determined from the constitutive relation. A highly accurate augmented spectral method is used to perform the numerical simulation. The Binding estimates obtained are good for certain types of fluid, but poor for others. A simple empirical correction of the Binding method, however, is found to give good agreement in all the cases studied.
Influence of the chemorheology of toughened epoxy matrices on the processing behavior of high performance composites
Authors: Kenny Jose M. , Oplicki Marica
Published: March 2011

The rheological and kinetic behavior of a new commercial toughened epoxy matrix is characterized through a complete experimental program. The kinetic behavior of the thermosetting resin is described by applying a new empirical model, accounting for autocatalytic and difussion control effects. The rheological model uses the kinetic information and describes the matrix viscosity as a function of temperature and degree of reaction using only three fitting parameters. The complete model is verified through calorimetric and rheological tests performed at different temperatures (isotherms) or heating rates (dynamic tests); or under more complex conditions simulating the processing conditions during autoclave lamination. Finally the chemo‐rheological model is considered as a part of a master model describing the complete processing behavior of thermoset matrix composites. The use of the master model in control and optimization algorithms is also illustrated.
Extrusion computations in three dimensions
Authors: Tanner R.I. , Beverly C.R.
Published: March 2011

The present paper considers the problem of predicting extrudate shapes from asymmetrical dies for Newtonian and non‐Newtonian fluids. The flow is fully three‐dimensional and an exploration of finite elements and boundary elements is made with a view to finding accurate, stable and economical schemes. A number of finite elements are compared and we conclude that some of the Fortin elements are most useful on the grounds of computational overhead and solution accuracy. These have been used to investigate some symmetrical (square dies) and asymmetrical (unequal lip) planar and general L‐shaped die flows for Newtonian fluids. The question of predicting regions of plug flow is addressed for materials with a yield stress in the three‐dimensional case. Finally, we show that an unconstrained extrudate may, in absence of gravity, describe a helix in space as the most general result.