bluuebunny/crossref_metadata_2025 huggingface dataset:
Sequence analysis and kinetic study of the polymerization of 1,4‐bis(hydroxydimethylsilyl)benzene with sir2Cl2
Authors: Newmark Richard A. , Babu Gaddam N.
Published: March 2011

29Si NMR rate studies of the bulk reaction of 1,4‐bis(hydroxydimethylsilyl)benzene (BHB) with dichlorodimethylsilane, dichloromethylphenylsilane, and dichlorodiphenylsilane show a very rapid kinetic equilibrium giving aryl‐SiMe2Cl groups in place of the aryl‐SiMe2OH of the BHB and OH groups in place of Cl in the dichlorosilane. This is followed by a slow condensation polymerization of the 1,4‐bis(chlorodimethylsilyl)benzene with the hydroxy terminated disilane groups. The very rapid initial rates could be followed with 29Si NMR using the INEPT pulse sequence despite the very long 29Si relaxation times. Condensation polymerization is complete within minutes for BHB + SiMe2Cl2, but hours and days are required for the SiMePhCl2 and SiPh2Cl2, respectively, at +22°C. Initial reaction kinetics in the presence of Cr(acac)3 are not identical to those obtained using the INEPT pulse sequence and no relaxation reagent.
Chemically resolved solid state NMR images of polymers
Authors: Cory D. G. , Miller J. B. , Garroway A. N.
Published: March 2011

Polymers are generally spatially heterogeneous, either in terms of morphology or as blends of various components. Solid state NMR imaging provides a means of characterizing both the chemical/morphological composition and its spatial variation. Here we discuss multiple‐pulse line‐narrowing approaches to acquiring high resolution NMR images and how these sequences can be modified so as to be sensitive to the chemical composition of a sample.
NMR imaging of elastomeric polymers
Authors: Koenig Jack L.
Published: March 2011

We have used NMR imaging to determine the dispersion in crosslinking density in complex elastomers both along the chains as well as spatially. Our work has established that the ordinary industrial accelerator systems generate a broad distribution of crosslink densities in rubber articles due to the poor mixing of the solid accelerator/sulfur recipe in the raw rubber. This high inhomogeneity in elastomeric network has an adverse effect on the properties of the elastomer system. In particular, the variation in crosslink density leads to substantial differences in the coefficients of thermal expansion and high internal stresses in the rubber article.
Peels of buckyballs
Authors: Löffler Matthias , Schlicke Benedikt , Schirmer Heike , Schlüter Arnulf‐Dieter
Published: March 2011

The polymer analogous aromatization of double‐stranded Diels‐Alder polymers to give fully unsaturated, all‐carbon ladder polymers by means of dehydration and dehydrogenation is described. The polymers obtained were characterized by solid state 13C NMR spectroscopy.
Speed control for cyclodextrin rings on polymer chains
Authors: Wenz Gerhard , Keller Bruno
Published: March 2011

The inclusion of monomeric α,ω‐diamines and related polymers by cyclodextrins was investigated by 1H NMR spectroscopy. As a result we found, that for both monomers and polymers the rate of the inclusion process largely depends on the degree of protonation of the amino groups of the guest.
Supramolecular formation of triblock copolymers in polar/nonpolar solvents
Authors: Chu Benjamin , Wu Guangwei
Published: March 2011

Triblock copolymers could form supramolecules in either polar or nonpolar solvents at appropriate concentration and temperature ranges or in the presence of additives. The association properties and the structure of supramolecules of PEO‐PPO‐PEO and PPO‐PEO‐PPO (PEO and PPO refer to poly(oxyethylene) and poly(oxypropylene), respectively) triblock copolymers in xylene and/or water were investigated by using light scattering, small‐angle neutron scattering, and small‐angle X‐ray scattering. The association process of aqueous solution or water‐rich ternary systems was entropy driven and temperature played an important role. The additive, e.g., water in the oil‐rich ternary system, played a very important role on the micellization of PEO‐PPO‐PEO, e.g., Pluronic L64, in xylene. The micelles had a core‐shell structure and the micellar shell was rather heavily solvated. At high copolymer concentrations, large aggregates with a lamellar structure was formed and the amount of large aggregates increased with increasing copolymer concentration before gel formation.
Comparison of the supramolecular structures formed by a polymethacrylate with a highly tapered side chain and its monomeric precursor
Authors: Kwon Yong Ku , Danko Craig , Chvalun Sergei , Blackwell John , Heck James A. , Percec Virgil
Published: March 2011

Insight into the supramolecular structure formed by a polymethacrylate with a highly tapered side chain is obtained from parallel X‐ray analysis of oriented fibers of the polymer and its monomeric precursor. The polymer is poly(2‐{2‐[2‐(2‐methacryloyloxyethoxy)ethoxy]ethoxy}ethyl 3,4,5‐tris(p‐dodecyloxybenzyloxy)benzoate) (abbreviated to 12‐ABG‐4EO‐PMA); the monomeric precursor is the hydroxy‐terminated side chain 2‐{2‐[2‐(2‐hydroxyethoxy)‐ethoxy]ethoxy}ethyl 3,4,5‐tris(p‐dodecyloxybenzyloxy)benzoate (12‐ABG‐4EO‐OH). The polymer and precursor both form ordered solid state structures that are converted to columnar hexagonal liquid crystalline (φh) phases at approximately 40°C and 50°C, respectively. The ordered solid state structures consist of ordered hexagonally packed cylindrical columns, in which the monomer units are probably packed with helical symmetry. For the polymer at 25°C, the column diameter is 60.4Å with an axial repeat of 5.03Å containing eight monomer units. For the precursor at 25°C, the column diameter is reduced to 53.5Å, probably due to the absence of the polymer backbone from the center of the column, and the axial repeat is doubled to 10.04Å. The X‐ray data are compatible with a tighter winding of the monomers in a helical structure, but otherwise suggest that there are common features in the stacking of the aromatic groups in the two structures.
Rheology of textured rodlike polymeric systems under shear flow as revealed by brownian dynamics simulation
Authors: Yang Yuliang , Ding Jiandong
Published: March 2011

A Brownian dynamics simulation algorithm has been developed in this paper to study the rheology of rodlike polymers under shear flow. Through the introduction of the Lebwohl‐Lasher potential and consideration of the nearest‐neighbor interaction without mean‐field approximation, the spatial inhomogeneity of the director field, stresses as well as the multiple‐domain effect are automatically included. By this new algorithm, the transient rheological behaviors of textured and untextured (uniformly aligned) rodlike polymeric systems are investigated. The damped oscillations of stresses are reproduced and the negative first normal stress differences are found at the moderate shear rate, all of which agree with the experimental observations in literature very well. Our simulation also demonstrates that the textured initial states only affect the transient responses of stress etc. at early shear stage and that the multiple domains formed during shear flow started from both textured and untextured initial states are essentially the same. The multiple domains are, therefore, the inherent structures resulting from the instability of shear flow, which are not sensitive to the initial textures, and the so‐called multiple domains are conceptually different from the rest textured structures.
Raman spectroscopy of poly[BIS(P‐toluene sulfonate) of 2,4‐Hexadiyne‐1,6‐DIOL] crystals at high pressure
Authors: Webster Simon , Batchelder David N.
Published: March 2011

The resonance Raman spectrum of crystalline poly[bis(p‐toluene sulfonate) of 2,4‐hexadiyne‐1,6‐diol] has been studied as a function of applied pressure to 50 kbar. The Raman bands are observed to shift to higher frequency and change in relative intensity. The origins of these effects are discussed. One of the Raman bands is observed to split into two bands of approximately equal intensity at high pressure. This effect is attributed to correlation field splitting within the unit cell and is possibly the first such observation in a conjugated polymer.
The impact of the discovery of stereoregular polymers in macromolecular science
Authors: Corradini Paolo
Published: March 2011

The paper recalls some aspects of the fascinating history of the discovery by Giulio Natta and his coworkers of the stereospecific polymerization of α‐olefins and of the determination of the structure of synthetic stereoregular polymers.

The most relevant recent advances in the comprehension of the mechanisms regulating their synthesis with heterogeneous supported catalysts and with the newly discovered homogeneous metallocene‐based catalysts are briefly outlined.
Stereoregularity and regioregularity of active centers in propene polymerization
Authors: Kashiwa Norio , Kojoh Shin‐Ichi
Published: March 2011

The relation between stereoregularity of active centers on a MgCl2/TiCl4 catalyst and functions of inside donor (ID) and outside donor (OD) was investigated in the case of ethyl benzoate (EB)/methyl p‐toluate (MPT) as an ID/OD pair. The results indicate that stereregularity depends merely on the amount of MPT supported on the catalyst.

On the other hand, regioregularity of active centers was investigated with a MgCl2/TiCl4/dioctyl phthalate(DOP)‐Et3Al/diphenyldimethoxysilane(DPDMS) catalyst system. Regio‐irregular inserted units were detected only in end groups of PP. It indicates that regio‐irregular insertion leads to dormant centers with respect to propene insertion, though such centers are active for hydrogen transfer.
A mechanistic approach to MgCl2 supported stereospecific propene polymerization: A new model of active sites
Authors: Guyot A. , Spitz R. , Journaud C. , Eisenstein O.
Published: March 2011

A precise description of the active site for heterogeneous stereospecific catalysts for propene polymerization has not been achieved, taking into account the effect of all the components of the catalytic system. A new model is proposed based on the following facts: the active Ti is directly bonded to the support MgCl2; it is bridged with an Al atom of the alkylaluminium; the latter is complexed with the external Lewis base; the more efficient Lewis bases are known to be dialkoxy dialkyl (or aryl) silane containing at least one bulky alkyl group; it is suggested that the two alkoxy groups are complexed, one with the aluminium atom, the second with the titanium atom. The structure of such a site has been built using a Chem 3D software and starting from an octahedral Ti and a bipyramidal Al. Both are bridged with the polymer chain. The silane is located so that each oxygen atom is just above each of the two metal atoms; the bulky alkyl group covers the vacancy of the Ti octahedre being in agostic interaction with the Ti. Such a tight geometry imposes the isospecific coordination of the monomers before its insertion in the polymer chain. The model is flexible enough to allow for the transition state, the insertion of the incoming monomer and the rotation of the new bridge, the driving force being the agostic interaction. The successful replacement of the silane with a diether with 3 carbons atoms in between the oxygen atoms is easily explained by the model, as well as the effect of the structure of the alkoxy and of the alkyl groups of the silane.
The Influence of the growing polymer chain on the catalytic complex in homogeneous ziegler‐natta polymerization: Density functional calculations on model systems TiCI2R+ and ZrCl2R+
Authors: Farina Mario , Fusco Roberto , Longo Luca
Published: March 2011

The influence of the growing chain on the electronic structure of soluble Ziegler‐Natta catalysts was investigated through quantum‐mechanical calculations for model systems MCI2R+ with M = Ti, Zr and R = CnH2n+1 where n = 1–7. The theoretical results show an increase in the energy of the Lowest Unoccupied Molecular Orbital (LUMO) of the cation and a decrease of the transition metal charge in the early stages of polymerization. This behaviour could explain the experimentally observed initial acceleration of the monomer insertion rate as reported in literature for ethylene polymerization with TiCp2CH3Cl·AlCl2CH3 system.
New cationic group 4 metal alkyl complexes
Authors: Tjaden Erik B. , Jordan Richard F.
Published: March 2011

Cationic group 4 metal alkyl complexes containing tetradentate Schiff base ligands, (acen) Zr(R)+ and (F6‐acen) Zr(R)+, are prepared by protonolysis of suitable neutral dialkyl precursors. These complexes display electrophilic behavior and are moderately active ethylene polymerization catalysts in the presence of 1 molar equivalent of AlR3.
New polyolefin elastomers from metallocenes
Authors: Galimberti Maurizio , Martini Emilio , Piemontesi Fabrizio , Sartori Franco , Camurati Isabella , Resconi Luigi , Albizzati Enrico
Published: March 2011

In this paper, new polyolefin elastomers, obtained from metallocene based catalytic systems, are presented. The potentialities of metallocenes for the preparation of polyolefin elastomers are discussed with reference to the traditional vanadium and titanium based catalysts. The role played by a Ziegler ‐ Natta catalyst, either stereospecific or aspecific, is discussed.
Metallocene ion pairs: A direct insight into the reaction equilibria and polymerization by 13C NMR spectroscopy
Authors: Tritto Incoronata , Sacchi Maria Carmela , Locatelli Paolo , Li San Xi
Published: March 2011

The reaction equilibria of Cp2Ti13CH3Cl and Cp2Ti(CH3)2 with AlMe3 (TMA) and/or methylaluminoxane (MAO) have been investigated by 13C NMR. Several adducts have been identified. A study of the 13C 90% enriched ethylene polymerization in an NMR tube in the presence of the above catalytic systems, in the most experimentally significant conditions, and a comparison of the NMR data with the catalytic activity have been made as well. It has been shown that: i) some species are side products, inactive for addition ethylene polymerization; ii) active cation‐like species such as Cp2TiMe+Cl·[AlMeO]n‐ and Cp2TiMe+Me·[AlMeO]n‐ are formed in titanocene‐MAO systems. Concerning the role of AlMe3, contained in MAO solutions, it has been shown that: a) AlMe3 is mainly bound to MAO; b) if some “free” AlMe3 exists in solution it is not the actual cocatalyst in the metallocene‐MAO based catalytic systems; c) the amount of AlMe3 influences either active or inactive species.
Cationic zirconium benzyl complexes as catalysts for olefin polymerization: A comparison among dicyclopentadienyl, monocyclopentadienyl and Cp‐free derivatives
Authors: Pellecchia Claudio , Pappalardo Daniela , van beek§ Johannes A. M.
Published: March 2011

Cationic zirconium complexes of formula [Cp2ZrBz]+, [Cp'ZrBz2]+, or [ZrBz3]+ (Cp = η5‐C5H5, Cp' = Cp or η5‐C5Me5, Bz = CH2C6H5) have been tested as catalysts for the polymerization of ethylene and α‐olefins. The catalyst performances have been compared with regard to polymer productivities, molecular weights and stereoregularities, and tentatively correlated to the structure of the ionic active species.
Mechanism of syndiotactic‐specific polymerization of styrene
Authors: Zambelli Adolfo , Pellecchia Claudio , Proto Antonio
Published: March 2011

Perusal of literature data and some new results concerning syndiotactic‐specific polymerization of styrene suggest a reaction mechanism accounting for the steric control. Key features of the proposed mechanism are stereorigid ηn coordination of the growing chain end and diastereoselective coordination of the monomer imposed by direct interactions with the ancillary ligand of the metal complex, a pseudotetrahedral chiral Ti(III) or Zr(III) cation, which inverts its configuration after every syndiospecific insertion step.
Influence of monomer structure on chemo‐ and stereoselectivity of 1,3‐diene polymerization
Authors: Ricci Giovanni , Porri Lido , Giarrusso Antonino
Published: March 2011

MAO/CpTiCl3 is an active catalyst for the polymerization of various types of 1,3‐dienes. Butadiene, (E) ‐ and (Z) −1,3‐pentadiene, (E) −2‐methyl‐1,3‐pentadiene and 2,3‐dimethylbutadiene yield, at room temperature, polymers with a cis‐1,4 or a mixed cis/1,2 structure. 4‐Methyl‐1,3‐pentadiene and (E,E) −2,4‐hexadiene give, respectively, a 1,2 syndiotactic and a trans‐1,4/1,2 polymer. MAO/CpTiCl2·2THF and MAO/(CpTiCl2)n are less active than the CpTiCl3 catalyst, but give the same type of polymers. A change of stereospecificity with temperature was observed in the polymerization of (Z)‐1,3‐pentadiene: a cis‐1,4 isotactic polymer was obtained at +20°C, and a crystalline 1,2 syndiotactic polymer at −20°C. This effect was attributed to a different mode of coordination of the monomer, which is cis‐η4 at +20°C and may be trans‐η2 at −20°C. Results obtained with catalysts from CpTi(OBu)3 and Ti(OBu)4 are reported for comparison. An interpretation is given of the formation of cis‐1,4 isotactic poly(2‐methylpentadiene) and of 1,2 syndiotactic poly(4‐methylpentadiene), as well as of syndiotactic polystyrene.
Copolymerization kinetics of ethylene and carbon monoxide in the presence of palladium complexes
Authors: Gennadii P. Belov , Oleg N. Golodkov , Zinaida M. Dzhabieva
Published: March 2011

The copolymerization kinetics of ethylene and carbon monoxide has been studied for the catalysts: Pd(C5H7O2)2‐P(C6H5)3‐p‐CH3C6H4SO3H in the medium of acetic acid (system A), and Pd(CH3COO)2‐CF3COOH ‐ (C6H5)2P(CH2)nP(C6H5)2(system B), where n=1−6, in the medium of methyl alcohol. The cationic palladium(II) ‐diphosphine complexes: (Dppp)2Pd(CF3COO)2 (I) and [(Dppp) Pd(μ‐OH)2Pd(Dppp)] (CF3COO)2 (II) have been synthesized and investigated by IR, electrospray mass spectrometry and elemental analysis methods. A comparative study of the copolymerization kinetics in the presence of these complexes and system B has been carried out.
Catalysis and the unipol® process in the 1990s
Authors: Karol Frederick J.
Published: March 2011

Developments in the UNIPOL® process for polyethylene, FLEXOMERS®, EPR/EPDM, and polypropylene continue to demonstrate the broad versatility and scope of the process. The potential of catalyst technology to provide dramatic new opportunities in the gas phase remains high. Selection of the appropriate catalyst with control of ligand environment at the active site will provide the basis for improved process operations and unique product opportunities.
The spherilene process: Linear polyethylenes
Authors: Covezzi Massimo
Published: March 2011

The Spherilene process associates to a low cost gas phase technology the flexibility in the product mix. New grades, HP‐LLDPE, offer a better benefit/cost balance.
Statics and dynamics of dense polymer systems studied by monte carlo simulation
Authors: Binder Kurt
Published: March 2011

Monte Carlo simulations of coarse–grained models of macromolecules offer a unique tool to study the interplay between coil conformations, thermodynamic properties, and chain configurational relaxation and diffusion.

Two examples are discussed where the chain conformation strongly differs from a gaussian coil: (i) collapsed chains in a bad solvent, where anomalous diffusion occurs in the Rouse limit and the relaxation time increases at least with the third power of chain length. (ii) Expulsion of a chain from a semidilute polymer brush. The initially stretched chain contracts to a gaussian coil and the center of mass moves outward with constant velocity until it reaches the region of the “last blob” where crossover to diffusive behavior occurs.
The dynamics of polymer melts as seen by neutron spin echo spectroscopy
Authors: Ewen Bernd , Richter Dieter
Published: March 2011

Using the neutron spin echo spectroscopy, the internal segmental diffusion of chain molecules in polymer melts and concentrated solutions was studied. These investigations show that beyond a characteristic length dt and after a cross over time τe(dt) the segmental diffusion of the single chains is strongly impeded and deviates from the Rouse dynamics. dt is polymer specific and depends on the temperature as well as on the polymer concentration.

Within the framework of the reptation concept, where dt is identified with the mean distance between intermolecular entanglements or with the tube diameter, the microscopically determined dt‐values agree quite well with those derived from related macroscopic measurements of the plateau modulus. A similar good agreement is also found with respect to the segmental friction coefficients obtained either from the Rouse regime of the NSE spectra or from Theological data of corresponding short chain systems, where entanglements are not yet effective.
Dielectric relaxation and intramolecular mobility in LC polymers
Authors: Borisova T.I
Published: March 2011

Intramolecular motion and mechanisms of local mobility were considered in linear polyesters, Including thermotropic systems, on the base of experimental results of dielectric absorption research. In some cases the role of molecular motion in the formation of the mesomorphic structure is established.
Synthesis and ordering of two‐dimensional polymers
Authors: Stupp Samuel I.
Published: March 2011

The work to be discussed in this lecture departs from the usual focus of polymer science on linear chains and explores the “bulk” synthesis and properties of polymer molecules that can be considered shape‐persistent molecular objects. Shapes that are particularly interesting are those not common in the conformational space of linear chains, for example, two‐dimensional polymers shaped as plates or discs and macromolecules shaped as cylinders or parallelepipeds. The lecture focuses on a molecular object which is a rigid and internally anisotropic two‐dimensional polymer with planar dimensions greater than its thickness. The shape‐granting skeleton of this two‐dimensional polymer is built by covalent bonds. We have so far developed three different strategies for their bulk synthesis, all involving systems in which reactive oligomers organize spontaneously into the necessary planar assemblies to form the object. In one strategy molecular recognition events such as homochiral interactions play a key role in the formation of the two‐dimensional flat polymers /1/. A different methodology relies on 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. In these two last strategies the layered rodcoils or hairpins react to form the covalent backbones necessary to grant shape to the object. A computer simulation relevant to the experimental system suggests that large two‐dimensional polymers can be formed by extremely short backbones. The lecture will also describe examples of unique properties in advanced materials that could emerge from these rigid two‐dimensional objects. These examples include. materials with self‐organized surfaces of high chemical definition and temporal stability, self assembling membranes, molecular reinforcement, and films with remarkably stable electrical or optical properties.
Fullerene grafted amine‐containing polymers
Authors: Patil Abhimanyu O. , Schriver George W.
Published: March 2011

We have covalently attached fullerenes to amine containing flexible hydrocarbon polymers such as amino‐ethylene propylene terpolymer (EPDM‐amine) to obtain novel fullerene functionalized polymers. These materials are soluble in solvents such as heptane or tetrahydrofuran (THF), in which the fullerene is essentially insoluble. The reaction of the fullerene and polymer was followed by infra‐red spectroscopy and viscosity measurements. Thermogravimetric analysis (TGA) scans of EPDM‐amine and Fullerene reacted EPDM‐amine show that the fullerene grafted polymer is thermoxidatively more stable than the original polymer. Furthermore, the fullerene grafted polymer could be reacted further with primary‐tertiary diamines to obtain novel polymers in which the fullerene acts as a bridging group for attaching polar functional groups to nonpolar hydrocarbon polymers.
“Living” free radical graft copolymers I: Preparation and properties
Authors: Roha Max , Wang Hsin‐Ta , Harwood H. James , Šebenik Anton
Published: March 2011

Polymers substituted with thio groups are useful for the photochemical synthesis of graft copolymers. Such copolymers have been prepared by the initial conversion of backbone polymers containing chlorinated substituents into polymers containing diethyldithiocarbamate (TC), isopropyl xanthate (IX) or mercaptobenzothiazole (BT) functionality. The photochemical reaction of monomers with these products produced graft copolymers. A variety of halogenated polymers were investigated as starting materials for these syntheses, including poly(vinyl chloride), chlorinated polyvinyl chloride), chlorinated polyethylene, chlorobutyl rubber and neoprene. Characteristics of the grafting reactions, including “pseudo‐living” behavior and tandem grafting aspects, were investigated. Glass transitions of the grafted polymers were found to vary uniformly with composition for most of the grafted products.
Toughness of polymeric networks: The limited importance of crosslink density
Authors: Nusselder Jan Jaap H. , Bos Harriëtte L.
Published: March 2011

Four series of polymeric model networks were prepared with bimodal chain length distribution between crosslink points and two types of dangling chains as network defects. In the last series the crosslink density was changed without a large change in the chemical composition. The fracture toughness of those networks were compared with that of the defect–free networks.

The fracture toughness of the various networks is surprisingly little influenced by the introduction of defects. Neither bimodality, nor dangling chains, nor a high sol fraction alters the toughness of the network. A good correlation between KIc and the weight fraction of polyether is observed. A much smaller dependence of KIc on the strand density can be deduced. The yield stress is high and approximately invariant for all systems studied.

It is concluded that the toughness of a polymeric network does not seem to be influenced by its perfection and only to a small extent by its degree of crosslinking.
Rubber‐ and thermoplastic‐modified polymer networks. Phase separation process induced by polymerization and polycondensation
Authors: Pascault Jean‐Pierre
Published: March 2011

Polymer blends based on thermosets are very useful for many applications (toughened plastics, adhesives, composites, polymer‐dispersed liquid crystals). Generally, at curing temperature, Ti, the initial mixture of monomer(s) and additive is homogeneous. The dispersed phase results from the phase separation induced by polycondensation or polymerization of the monomer(s). The process can be looked upon as a «chemical quench» because the chemical reaction drives the change in free energy. The role of chemistry is principally to try to control the morphologies; some trends are given in this publication.
Entanglement effects in model polymer networks
Authors: Everaers Ralf , Kremer Kurt , Grest Gary S.
Published: March 2011

Many fundamental questions for the understanding of polymer networks are more suitably addressed by current computer simulations than by experiments. Details of the microscopic topology, such as the elastically active cluster or loop entanglements, can be identified as well as controlled. In particular, it is possible to isolate and quantify their effects on macroscopic observables such as the elastic modulus. The constraints due to connectivity and conserved topology are more clearly present for networks than for melts. Already for strand lengths between crosslinks which are relatively short, the effect of the conserved topology is important. The mode relaxation in a network is significantly different from that of a melt. For weakly crosslinked systems the melt entanglement length is the relevant scaling parameter. The elastic modulus of a long chain network under ideal conditions reaches an asymptotic value which is about 2.2 times smaller than the prediction of an affine model for a network made of strands of the melt entanglement length. An analysis of the stress reveals that in the linear regime the contribution from the excluded volume is dominant compared to that from the connectivity along the strands. For larger elongations, however, the non‐linear elastic response is dominated by the chemically and topologically shortest paths through the system, where chemical crosslinks and topological entanglements between meshes of the network play a similarly important role.
Toughening of highly cross‐linked polycyanurates with epoxy‐ and phenol‐terminated butadiene‐acrylonitrile rubbers
Authors: Uhlig Christoph , Bauer Jörg , Bauer Monika
Published: March 2011

Polycyanurate from dicyanate of bisphenol A was modified with epoxy‐ and phenol‐terminated butadiene‐acrylonitrile rubbers. Rubber‐resincopolymerisation was followed by multiple‐detection gel‐permeation chromatography (GPC). It was found that both the epoxy‐terminated and phenol‐terminated rubbers react with the cyanate and thus are covalently bound with the polycyanurate network. The influence of rubber content, acrylonitrile content and type of end group on phase structure was investigated using dynamic mechanical analysis. Fracture toughness was measured for these modifications.
Phase equilibria in polymer/solvent systems VII swelling pressure and swelling equilibrium between gaseous or liquid phases and a gel in a multicomponent system
Authors: Borchard Werner
Published: March 2011

Differential equations for swelling pressure and swelling equilibria in two‐phase systems consisting of many components have been derived. The result includes simple equilibria of gaseous or liquid solvent and a gel which are known from the literature.
Properties of networks based on poly(alkylene glycol) diacrylates
Authors: Priola A. , Bongiovanni R. , Gozzelino G. , Ferrero F. , Malucelli G.
Published: March 2011

Three series of poly(alkylene glycol) diacrylates, namely poly(ethylene glycol), poly(propylene glycol) and poly(tetramethylene glycol) α,ω‐diacrylates have been prepared by acryloylation of the corresponding bis‐OH‐terminated oligomers. Their MW was in the range 200–1000 and their acrylic functionality was close to two. They were subjected to UV curing as thin films obtaining, by FTIR analysis, complete terminal double bond conversion in all cases with the exception of the lowest MW oligomers. Thermal and mechanical properties of the networks were investigated by means of DSC, TMA and DMTA analyses. Concerning the PPGDA oligomers, products totally amorphous and rubbery were obtained; PEGDA and PTMGDA oligomers gave similar amorphous structures with the exception of the highest MWs which showed partial crystallinity. By means of thermal and DMTA measurements, Tg values and E' moduli were obtained and correlated to the MW of the oligomers used. In particular, Tg values, as function of the crosslinking density, agreed with those calculated by the Nielsen equation for the three series investigated. The equilibrium swelling in water was determined for various networks as a function of the MW of the oligomers. The values obtained were compared and discussed in terms of the solubility parameters and the crosslinking density of various structures.
Comparative analysis of polymer network formation processes via polycondensation and polymerization
Authors: Rozenberg Boris A. , Irzhak Vadim I.
Published: March 2011

Some comparative characteristics of the polycondensation and polymerization kinetic features of network formation are discussed. It is shown that just kinetic features of the polymer formation determine topological and supermolecular structures of the forming polymer network.
Acetylene‐terminated resins: Mechanism of thermal polymerization and properties of cured polymers
Authors: Florence Marie , Loustalot Grenier
Published: March 2011

The polymerization kinetics and mechanisms of model compounds (mono‐ and difunctional) characteristic of prepolymers of ATR (acetylene‐terminated resins) have been studied by HPLC, FTIR, UV, NMR (liquid and solid) and HPLC in the temperature range of 150–220°C.

Using monofunctional compounds, we were able to show that the thermal polymerization of acetylene functions is not a simple reaction. Initially, the majority of compounds formed have a low polymerization degree, followed by the formation of species with higher and progressive polymerization degrees.

Spectroscopic techniques such as NMR and FTIR lead to the unambiguous determination of reaction conversion up to 95% in the case of bifunctional prepolymers. The understanding of network structures, on the other hand, is more delicate in polyaromatic systems, since the chains formed are very similar to the basic skeleton of the prepolymer.

The kinetic curves obtained isothermally between 150–220°C have shown that while kinetic monitoring of the disappearance of the first 90% of ethynyl functions poses no particular problems, there is a considerable uncertainty for the last 10%, regardless of the technique chosen.

We have demonstrated that me thermal properties are dependent on the molecular weight and the structure of the polymer.
Use of phase diagrams in the analysis of polymer network formation
Authors: Williams Roberto J. J. , Riccardi Carmen C.
Published: March 2011

A conversion ‐ temperature ‐ transformation (CTT) diagram was used to analyze several non‐isothermal processes of polymer network formation: a) range of heating rates where reliable kinetic information can be obtained; b) a novel process involving part of the cure in the glassy state; c) phase separation in rubber‐modified epoxies cured in heated molds.
Microscopic structure and viscosity behaviours of ion‐complexed polymer gels
Authors: Shibayama Mitsuhiro , Ikkai Fumiyoshi , Nomura Shunji
Published: March 2011

Poly(vinyl alcohol)‐Congo Red (PVA‐CR) complexes in aqueous solutions have a unique sol‐gel transition behaviour. At an appropriate PVA concentration, a sol‐gel‐sol‐gel type reentrant transition takes place with increasing CR concentration. The microscopic structure and Theological properties of these complexes were investigated by small‐angle neutron scattering (SANS) and viscometry.
Fatigue crack growth in crosslinked polymers
Authors: Fischer Michael , Martin Denis , Pasquier Maurice
Published: March 2011

Do crosslinks between the molecular chains of a glassy polymer impede the growth of fatigue cracks? Three polymers H, M, and L of equal chemical composition but differing in crosslinking densities were prepared by the polyaddition reaction of stoichiometric mixtures of 1,4‐butanediol diglycidyl ether, N,N'‐dimethylethylenediamine, and 1,4‐diaminobutane. The growth of the fatigue cracks under cyclic loading (2 Hz) was studied in the glassy polymers at ‐100°C and ‐60°C with the help of strain gauges bonded to the back side of the compact tension specimens. Crack growth rate da/dN ranged from a few nm to 10 μm depending on the stress intensity amplitude K̂1/2 at the crack tip. Log (da/dN) plotted against K̂1 revealed a linear relationship in accordance with the model calculation. The slopes, m, of the straight lines characterizing the fatigue crack growth were found to scale with M̄‐1/2 in the case of the studied polymers. (M̄c: average molar mass of chain segments between crosslinks). Glassy polymers with a low degree of crosslinking are less prone to fatigue crack growth than are the more tightly crosslinked polymers, as shown by the presented examples.
Hydrogen bonded polymer blends and the design of miscible polymeric antioxidants
Authors: Coleman Michael M. , Yang Xiaoming , Stallman John B. , Painter Paul C.
Published: March 2011

The relative magnitude of the equilibrium constants describing self‐association versus inter‐association is an important factor in determining the phase behavior of polymers that hydrogen bond. In studies of sterically hindered phenolics we have found that poly(2,6‐diisopropyl‐4‐vinylphenol) (PDIPP) only moderately self‐associates, but strongly inter‐associates with polymers containing groups such as ester carbonyls, ether oxygens, and the like. PDIPP is miscible with polytetrahydrofuran (PTHF) and simultaneously acts as an efficient polymeric antioxidant. This result points the way to the design of specific miscible polymeric antioxidants for polar polymers.
Structure and interactions in homopolymers and blends as studied by the methods of vibrational and nmr spectroscopy
Authors: Dybal Jiîí , Straka Jaroslav , Schneider Bohdan , Schmidt Pavel
Published: March 2011

The combination of IR, Raman and NMR spectroscopy was used in the study of the blends of semicrystalline and amorphous polymers with considerably different strength of intermolecular interactions: poly(ϵ‐caprolactam)/polystyrene (PCL/PS), poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) and poly(N‐methyllaurolactam)/poly(4‐vinylphenol) (PNMLL/PVPh). In the vibrational and NMR spectra of the blends composed of non‐interacting polymers (PCL/PS) and weakly interacting polymers (PEO/PMMA), no band changes were observed which would indicate changes of the conformational structures. 1H NMR relaxation of the PCL and PS components in the blends is the same as in the respective homopolymers similarly treated. In the blends of weakly interacting polymers (PEO/PMMA), the crystallinity of PEO is influenced by the presence of PMMA and is negligible in the blends with less than 30 wt.‐% of PEO. The rotating‐frame spin‐lattice relaxation time for protons TH1p of PMMA indicates close contact of the PMMA and PEO chains. In the blends PNMLL/PVPh with strong hydrogen‐bonding interactions, both components are intimately mixed on a scale of 3–4 nm and significant shifts of some bands both in vibrational and in NMR spectra reveal changes of structure.
Epoxy resins and epoxy blends studied by near infra‐red spectroscopy
Authors: Chabert B. , Lachenal G. , Vinh Tung C.
Published: March 2011

The cure and the final network of epoxy resins have been investigated by numerous techniques, nevertheless a clear understanding of this network structure has not yet been achieved. FTIR analysis of polymeric materials provides highly precise measurements that are widely interpretable in terms of chemical structure. Yet the high absorption of fundamental bands requires careful sample preparation to reduce the thickness of the sample or special reflection techniques are needed. Furthermore, the occurrence of overlapping bands for epoxy resin (N‐H and O‐H vibrations in the 3000 cm−1 region) renders the quantitative analysis in the region mid IR particularly difficult. However, the overtone and combination bands are 10–100 times weaker than the fundamental ones and are observed in near infrared (NIR) region. Longer pathlengths than Mid IR ones can be used allowing transmission analysis of thick samples (1‐20 mm) without special preparation. NIR absorption bands have different intensities depending on the anharmonicity of vibrations. The strongest absorption bands are due to protons connected to carbon, nitrogen, oxygen. Hydrogen bonding due to inter‐ and intramolecular interactions can cause band broadening, peak position shifts and intensity variations. NIR spectroscopy is therefore a useful technique to investigate polymeric materials and was used to study the cure reactions of various epoxy resins cured with amine hardener. Using different NIR techniques (reflectance, transmission and microscopy) we will briefly present some results concerning hydrogen bonding between epoxy and amine hardener before curing, epoxy resins, glass/epoxy composites and epoxy/PES (polyethersulfone) blends.
Ir‐ spectroscopy of hydrogen bond as a method of analytical determination of physical network in poly(ether urethane)s
Authors: Strikovsky Alexander G. , Zharkov Vadim V. , Letunovsky Mihail P.
Published: March 2011

The equilibrium association of urethane groups in a series of 4, 4′ ‐ diphenylmethane diisocyanate (MDI)/polypropylene oxide) (PPO) based poly(ether urethane) elastomers (PUE) was studied on the basis of IR‐spectroscopy data. The concentration of associates containing 2,3 and 4 urethane groups is calculated, which permits immediate monitoring of changes in PUE mechanical properties using the model of a physically cross‐linked polymer.
Ftir study of hydrogen bonding and phase behaviour in poly(vinylpyridines)/poly(ethylene‐CO‐vinyl alcohol) blends
Authors: Isasi José R. , Cesteros Luis C. , Katime Issa A.
Published: March 2011

The specific interactions between polyvinylpyridines and ethylene‐vinyl alcohol copolymers of different compositions have been studied by Fourier transform infrared spectroscopy (FTIR). Hydrogen bonding between both polymer components leads to significant spectral modification in pyridine rings spectral bands. Minor modifications in other spectral modes have been also detected. The spectral results indicate at least three competing equilibria processes in the blends: hydroxyl‐hydroxyl copolymer self‐association and hydroxyl‐pyridine interassociation. Painter‐Coleman association model was successfully applied and the phase diagram for these systems has been predicted.
A simple method of calculation of vibrational spectra of long‐chain aliphatic compounds and their urea adducts
Authors: Puchkovskaya Galina A. , Sekirin Igor V. , Aryutkina Natalya L.
Published: March 2011

A semi‐quantitative method for calculation of the LCAC's and their urea adducts vibrational spectra based on simple model Hamiltonian on the basis corresponding to excitations of fragments forming the studied system is proposed. A comparison with experimental spectra of LCAC's with different terminal groups and in different phase states is performed. It is shown that the effect of the built‐in incommensurability of polymethylene chain and urea lattice in adducts must manifest itself as additional broadening of some bands in the vibrational series of polymethylene chain. The manifestation of possible resonance of “host” and “guest” vibrations has also been analyzed.
NMR study of ordering in liquid crystalline solution of polybenzylglutamate of various molecular mass
Authors: Khachaturov A. S. , Koltsov A. I. , Roth H. , Shabsels B. M.
Published: March 2011

1H and 2H NMR spectra of fractionated poly‐γ‐benzyl‐L‐glutamate solutions are recorded at various temperatures. NMR signals of both these nuclei of solvent molecules (mixture of CD2Cl2 and CH2Cl2) appear to be doublets. Their splitting (30‐130 Hz for protons and 200–600 Hz for deuterons) reduces when the polymer molecular mass grows. As the splitting is proportional to degree of orientation of solvent and solute molecules, it means that longer macromolecules are less oriented than shorter ones. One can explain such behavior in terms of persistent chain model, since the bended rods of less length can be better oriented along the director.
Towards the selective synthesis of macrocyclic vinyl polymers of controlled size
Authors: Deffieux Alain , Schappacher Michel , Rique‐Lurbet Laurence
Published: March 2011

A new strategy for the synthesis of vinyl type macrocyclic polymers of controlled molecular weight and molecular weight distribution has been investigated. It involves the direct coupling of an α‐ω‐heterodifunctional linear polymer precursor previously prepared by living polymerization. The cyclization is achieved under high dilution, by an appropriate activation of one of the polymer‐ends in order to allow its reaction with the other end function. Its application to the preparation of polystyrenes and poly(vinyl ether)s with a macrocyclic structure, as well as ring closure mechanisms in the presence of different cyclization agents are reported.
Rheological behavior of comb‐shaped mesophase polymers and their modifying role in the blends with thermoplastics
Authors: Plate N. A. , Talroze R. V. , Rogunova M. A. , Zubarev E. R.
Published: March 2011

Most of the polymers with mesogenic groups in side‐ or main‐chains are liquid‐crystalline in nature. One can observe a lot of similarities in the mesophase structure types, orientational order parameter, anisotropy of optical, electrical and magnetical properties of polymer and low‐molecular‐weight liquid crystals. At the same time the presence of backbones contributes some peculiarities and limitations to their behavior.
Micro‐composite systems by in‐situ formation of liquid crystal polymers in commodity polymers
Authors: An Jeongwoong , Ichikawa Tsuneko , Ogata Naoya
Published: March 2011

In‐situ formation of polyimide was carried out in solution of copolymers derived from styrene and 4‐vinylpyridine. The in‐situ formed polyamic acid formed a strong hydrogen‐bonding with pyridine moiety of the copolymers, resulting in homogeneous solutions. Cast films obtained from the solutions were clear and transparent without phase separations, and mechanical properties of the films were much stronger than those of films from the original copolymers. In‐situ polymerization of acrylamide in poly(styrene) was carried out by anionic polymerization to form Nylon 3 which was dispersed in poly(styrene) as fine particles, and mechanical properties of the poly (styrene) were greatly improved.
Polymorphism and structure in different kinds of liquid crystal polymers and copolymers
Authors: Hardouin F.
Published: March 2011

We report a short outline of chain‐conformation informations obtained by small angle neutron scattering (SANS) studies of different kinds of Liquid Crystalline Polymers (LCPs). We conclude that in the nematic phase the prolate shape of the chains are directly connected to the orientational order and the magnitude of the chain extension strongly depends on molecular parameters relative to the coupling mesogen‐chain. The behavior is markedly different when the backbone anisotropy is oblate shape due to the chain confinement between the smectic layers.
Smectic liquid single crystal elastomers
Authors: Finkelmann H. , Benné J. , Semmler K.
Published: March 2011

In the liquid crystalline (I.c.) state the backbone of l.c‐polymers has to adapt an anisotropic conformation that is consistent with the I.c.‐phase structure. For macroscopically uniformly aligned samples this anisotropic backbone conformation can be obtained by applying a suitable mechanical field on chemically crosslinked I.c‐polymers. Introducing the network anisotropy a priori by synthesis, stable macroscopically aligned I.c.‐networks can be realized. We have called these networks Liquid Single Crystal Elastomers (LSCE) because their physical properties resemble that of organic or inorganic single crystals.
Side chain liquid crystalline polymers: Electric field effects and nonlinear properties
Authors: Gonin Dominique , Guichard Bertrand , Noël Claudine , Kajzar François
Published: March 2011

Side chain liquid crystalline polymers offer unique advantages as a new class of organic materials with potential for nonlinear optical response. Synthesis of a number of cyanobiphenyl‐based side chain polymers was carried out employing the concept of having the cyanobiphenyl species serve concomitantly as both the linear optical chromophore and the mesogenic moiety in the polymer. The thermal behavior of these polymers was studied by DSC, optical microscopy and X‐ray diffraction. Thin polymeric films were spin coated and electric field poling measurements were carried out as a function of temperature. The second harmonic (SH) coefficients d33 and d31 were measured by Maker fringe analysis and compared with the values predicted by molecular statistical models. The results showed that one can gain in net polar ordering by starting with a liquid crystalline system. The enhancement in d33 when < P<2 > = 0,6 was found to be a factor of 2,3‐3,3 over the isotropic case ( P<2 > = 0). The relaxation process was investigated. Both the presence of liquid crystal character in the material and the temperature at which the films were stored below Tg appeared important in determining the thermal stability of the SH coefficients.
Recent development in heterogeneous metallocene catalysts
Authors: Soga Kazuo , Arai Takashi , Nozawa Hiroshi , Uozumi Toshiya
Published: March 2011

The synthetic methods of heterogeneous metallocene catalysts reported so far in academic journals are summarized together with their catalyst performance. Some of our new results in this field are also described in brief.