bluuebunny/crossref_metadata_2025 huggingface dataset:
Salt and solvent effects in “living” carbocationic polymerization
Authors: Matyjaszewski Krzysztof , Lin Chih‐Hwa , Bon Angélique , Xiang Jason S.
Published: March 2011

Carbocationic polymerization is strongly affected by medium and salt present in the system. The increase of solvent polarity enhances overall rates of cationic polymerization because it increases the proportion of carbocations in equilibrium with dormant covalent species. Higher solvent polarity might also increase molecular weights due to the reduction of transfer to counterions and may broaden polydispersity by slowing down an exchange between active and dormant species. Added salts may increase the proportion of ionic species by the ionic strength effect. The salts with common ions suppress free ions and lead to a monomodal molecular weight distribution by eliminating free ionic species with long lifetimes. The addition of tetrabutylammonium salts in the polymerization of styrene, initiated by 1‐phenylethyl chloride and catalyzed by tin tetrachloride is a typical example. The special salt effect based on exchange of counterions may enhance or reduce the proportion of ionic species and may accelerate the exchange between active and dormant species, affecting the polymerization rates and polydispersities.
New biomaterials by carbocationic processes
Authors: Kennedy J. P.
Published: March 2011

Well‐defined macromolecular composites have been prepared by living carbocationic polymerization of isobutylene in combination with other conventional techniques. The products were designed for biomedical uses as 1) intervertebral disc replacement, 2) improved impact‐ and fatigue‐ resistant bone cements, 3) delayed drug release reservoirs, and 4) small diameter nonthrombogenic vascular grafts. The syntheses are out‐lined, and the novelty, main characteristics and properties of these unique materials are summarized. The era of designed biomaterials is upon us.
Direct and sensitized photoinitiated cationic polymerization using pyridinium salts
Authors: Yaǧci Yusuf , Schnabel Wolfram
Published: March 2011

Results of polymerization and laser flash photolysis studies concerning the direct and indirect photoinitiation of cationic polymerizations using N‐alkoxy pyridinium and N‐alkoxy quinolinium salts are presented. The indirect action can be based on (a) the generation of carbocations via the oxidation of photochemically produced free radicals and (b) the generation of radical cations via the reaction of electronically excited sensitizers with pyridinium or quinolinium ions. With respect to (a) substituted vinyl bromides were found be an effective source of oxidizable free radicals (vinyl radicals), and regarding (b) singlet or triplet excited states of thioxanthone, anthracene, perylene and phenothiazine, which, in the ground state, strongly absorb light in the 300 to 400 nm range, were found to react rapidly with pyridinium salts.
Polyethers containing stable ionic end‐groups
Authors: Kubisd Przemyslaw , Tadeusz Biedron
Published: March 2011

Polyethers of low and medium molecular weight containing at both ends stable ionic groups (phosphonium ions) were obtained by living cationic polymerization of tetrahydrofuran initiated by difunctional initiator, trifluoromethanesulfonic anhydride, followed by termination with triphenylphosphine. It was shown, that products contain significant quantities of low molecular weight diphosphonium salt; a plausible explanation is presented. Alternative approach to the synthesis of diionically terminated polyethers was based on the conversion of hydroxyl end‐groups of polyether diols, which can be obtained by cationic Activated Monomer (AM) polymerization of e.g. oxiranes, into phosphonium ion end‐groups. Using this approach, poly(ethylene oxide)'s with Mn ranging from 300 to 3400, terminated at both ends with stable ionic groups, were prepared and characterized. Measurements of NMR relaxation times and viscosity measurements provide the evidence for the aggregation of ionic end‐groups. The potential applications of inter‐ and intramolecular aggregation are discussed. It is shown, that intramolecular aggregation of ionic terminal groups in low molecular weight poly(ethylene oxide) leads to cyclic structures resembling crown ethers and showing comparable efficiency for complexing cations.
Stereoregular and conformationally regular oligomers and polymers
Authors: Vogl Otto , Simonsick William J. , Bartus Jan , Qin Meifang , Ute Koichi , Hatada Koichi
Published: March 2011

Configurationally and conformationally regular polymers can now be synthesized based on sterically restrictive considerations. Trihaloacetaldehyde polymerization provided a fertile field for the investigation of the factors for such polymer formations. The convenient ceiling temperature of trihaloacetaldehyde polymerizations allowed the study of the genesis of these polymerizations. Oligomers were prepared by alkoxide initiation, followed by the establishment of the oligomer alkoxide equilibrium and end‐capping. Stereoregularity and conformational regularity were observed in trichloroacetaldehyde (chloral) and tribromoacetaldehyde (bromal) polymerizations. This result was confirmed by solid state magic angle spinning NMR investigations of polychloral, of polybromal as well as of a copolymer of chloral and bromal. Solid state NMR techniques allowed also to investigate copolymers of chloral and aromatic isocyanates. Quantification of the solid state investigation suggests the possibility of a molecular weight estimation of chloral and other insoluble trihaloacetaldehyde polymers by end‐group analysis.
Interactions between ions and free or immobilized ligands. Application of the competition method
Authors: Smid Johannes
Published: March 2011

Application of a competition method to determine affinities of ligands for ionic species in low polarity media is described. A soluble ligand, L, and a network‐immobilized ligand, N, are allowed to interact with the counterion of an ionic chromophore A” according to the reaction NM+A− + L → LM+A− + N (K). K values were determined in toluene and in ether‐type solvents for linear and macrocyclic polyethers and polyamines, as well as for other cation‐complexing agents, by varying either N or L. In solvents such as dioxane, binding constants of M+A− to N can be determined directly. Combined with K values they yield the complex formation constant, KL, of the reaction M+A− + L → LM+A−.
Synthesis of macrocyclic polystyrene‐polydimethylsiloxane block copolymers
Authors: Yin Rui , Amis Eric J. , Hogen‐Esch Thieo E.
Published: March 2011

A series of macrocyclic polystyrene (PS)‐polydimethylsiloxane (PDMS) block copolymers and similar block copolymers was synthesized by sequential polymerization of styrene and hexamethyl cyclotrisiloxane (D3) initiated by a difunctional anionic initiator in THF at −78° followed by coupling with Cl2SiMe2 in very dilute (10−5 – 10−6 M) solutions. Total molecular weights ranged from about 2–85 × 103. The formation of monodisperse macrocyclic block copolymers was indicated by the lower (15–30%) hydrodynamic volume of the rings compared to that of the linear block copolymers. Carbon‐13 and 29Si NMR likewise supported the absence of linear polymer in the macrocyclic block copolymer. The behavior of second virial coefficient A2 of the rings and the linears versus temperature was examined by static light scattering in cyclohexane. Below 20° the A2 for the linear polymer goes negative while that for the cycle remains positive. Dynamic light scattering (DLS) as a function of temperature also reflects that the cyclic polymers remain well solvated even down to 12°C. The DLS autocorrelation functions for the linear triblock however demonstrate the onset of aggregation and phase separation as the temperature is reduced below 20°C.
Role of bimetallic active centres in anionic polymerization of hydrocarbon monomers
Authors: Arest‐Yakubovich Alexander A.
Published: March 2011

Polymerization of hydrocarbon monomers initiated by organometallic compounds of alkali and alkaline earth metals modified by derivatives of other metals of Groups I‐III is reviewed. Various mixed initiators, such as RLi‐RONa, RLi‐RNa, R2Ba‐R3Al, RNa‐R3Al, are discussed in details. It is shown that the presence of a second metal greatly affects the kinetics of elementary steps of chain propagation and chain transfer and also the structure and molecular weight of polymer formed. Active centres in all the systems are complexes containing two or more metal atoms linked by a bridge bond; the addition of a monomer occurs by an insertion either into the “usual” metal‐carbon bond which is external with respect to the polymetal nucleus of the complex or directly into Mt1‐R‐Mt2 bridge bond.
Preparation and properties of isotactic and syndiotactic poly(methyl methacrylate)s, uniform with respect to molecular weight
Authors: Hatada Koichi , Ute Koichi , Kitayama Tatsuki , Nishiura Takafumi , Miyatake Nobuo
Published: March 2011

Highly isotactic (it‐) and highly syndiotactic (st‐) poly(methyl methacrylate)s (PMMAs) uniform with respect to molecular weight (stereoregular, uniform PMMAs) were isolated up to the 100mer from it‐ and st‐PMMAs by supercritical fluid chromatography (SFC) and characterized by NMR and mass spectroscopies. Glass transition temperatures (Tg's) of the uniform it‐ and st‐PMMAs were higher than those of the corresponding PMMAs with MWD and with similar molecular weight on average. The Tg values of the uniform it‐and st‐PMMAs series obeyed the relationship, Tg = Tg∞ ‐ K/M, where M and Tg∞ denote molecular weight and Tg at infinite M, respectively. The reciprocal melting points (1/Tm) of uniform it‐PMMA (degree of polymerization, DP = 28–44), obtained from methanol solutions by evaporating the solvent, increased linearly with increasing 1/DP. Extrapolation of the linear relation to 1/DP = 0 gave the Tm of it‐PMMA with infinite DP; Tm∞ = 171.1°C. Thermal degradation behavior was studied by thermogravimetry and by SFC analysis of degradation products. In gel‐permeation chromatography (GPC) measurements, the it‐50mer eluted faster than the st‐50mer. Calibration curves for it‐ and st‐PMMAs could be obtained using series of the uniform PMMAs. The instrumental spreading factor determined using it‐25mer, it‐50mer, st‐25mer and st‐50mer for our GPC chromatograph was 0.070 ml when the volume of the sample solution was 0.003ml. GPC analysis of a mixture of the it‐ and st‐50mers in tetrahydrofuran indicated formation of a stereocomplex in the solution, and was found quite useful to elucidate the minimum sequence length required for complex formation.
1H and 13C NMR of PMMA macromonomers and oligomers ‐ end groups and tacticity
Authors: Mccord Elizabeth F. , Anton Waifong L. , Wilczek Lech , Ittel Steven D. , Nelson Lissa T. J. , Raffell Keith D. , Hansen Joan E. , Berge Charles
Published: March 2011

1H NMR and 13C NMR have been used to study the end groups and tacticity in PMMA macromonomers and oligomers. These macromonomers are terminated almost exclusively in one vinylidene group per chain. The end group signals from the macromonomers are identified in both the 13C and 1H NMR spectra. The spectra of the purified oligomers (n = 1‐4) were used to aid in assignment. The macromonomers are predominantly syndiotactic, and the tacticity measured is consistent with Bernoullian statistics. The tetramer is a mixture of r and m isomers in a 4:1 ratio. It is shown that T1 experiments can provide a useful method of distinguishing resonances due to low molecular weight impurities from those due to stereochemical or isomeric effects in macromonomers. The absence of internal double bonds was confirmed by isomerizing the vinylidene group of several oligomers and of the macromonomer, and verifying the absence of the isomerized signals in the NMR spectra of the original materials.
NMR spectroscopy of poly(vinyl chloride) defects. 2. 1H and 13C NMR analysis of the terminal vinyl end group, 1,3‐dichlorobutyl end group and chloromethyl branch
Authors: Benedikt George M. , Goodall Brian L. , Rhodes Larry F. , Kemball Alan C
Published: March 2011

We have been able to obtain the 1H NMR subspectra of most of the major saturated end groups in PVC. In order to assign the terminal vinyl (TV) group, CH2CH‐CHCl‐, we synthesized and analyzed the symmetrical model compound 3,5‐dichloro‐1,6‐heptadiene (4) containing a racemic (r) and a meso (m) isomer. They exhibit distinct NMR signals for the vinyl protons, which allowed us to subsequently assign the r diad and the previously unreported m diad terminal vinyl resonances present in very small amounts in commercial PVC. The study of the solvent induced chemical shifts of the vinyl protons in an experimental PVC sample containing an unusually high level of this end group allowed us to further assign it in terms of the terminal rr, rm, mm and mr triads.
Solution and solid‐state NMR analysis of phenolic resin cure kinetics
Authors: Neiss Thomas G. , Vanderheiden Egbertus J.
Published: March 2011

Phenolic condensate resins, produced from the reaction of phenol with formaldehyde, are important components in the chemical industry and have a wide variety of applications. Resins of this type are used in the aerospace industry to produce rocket motor components with strength and rigidity. While methods currently exist (e.g., DMA, DEA, calorimetry) for the examination of phenolic‐based systems during the curing process, none are available to directly measure the functionality and chemical degree of resin advancement during this process. Solution and solid‐state 13C NMR spectroscopy can be implemented to examine the functional group content of the resin. Reactant and product moieties are spectrally resolved in both techniques and can be monitored during resin cure. 1H wide‐line solid‐state NMR can be used to measure the rate of sample curing in situ by monitoring the sample T2 relaxation time as a function of sample heating time. Comparison of these results with the 13C NMR data will establish the degree of resin cure on a functional group basis.
Solid‐state characterization of polysilanes containing the sih bond
Authors: Schilling Frederic C. , Weidman Timothy W. , Joshi Ajey M.
Published: March 2011

Organosilicon hydride polymers show promise for high performance photoresist, dielectric, and optical coating applications. In this report we describe the solid‐state characterization of these silicon‐based polymers prepared by reductive condensation and plasma polymerization methods. The combination of high resolution solid‐state NMR, infrared, and Rutherford backscattering spectroscopies provides a quantitative description of the polymer microstructure. As a result of these studies the effects of polymerization conditions on polymer microstructure can be more readily determined and optimized.
Dynamics of polypropene and propene‐ethylene copolymers at temperatures above ambient
Authors: Zeigler Robert C.
Published: March 2011

Several applications of solid‐state nuclear magnetic resonance (NMR) spectroscopy to studying polyolefin mobility at temperatures ranging from room temperature to above the polymer melt are described. 13C NMR can be used with magic‐angle spinning and high‐power proton decoupling to determine the fraction of mobile polymer in polypropene and to characterize the nature of the polymer chain motions as a function of sample temperature. Similar techniques can be used to characterize the local motions of complex copolymer systems such as heterophasic ethylene‐propene copolymers. The practicality of low‐speed magic angle spinning to observe quantitative high‐resolution NMR spectra of neat, molten polymer samples is also described.
Nuclear spin relaxation times dispersion in disordered polymer systems
Authors: Chu Peter P. J. , Howard J. J.
Published: March 2011

Nuclear spin relaxation reveals a wealth of information concerning motional dynamics and morphology within a polymer system. The conventional breakdown of relaxation into discrete decay components is usually arbitrary and often ambiguous due to strong coupling and spin diffusion between domains. To avoid being limited by pre‐determined models, we have explored the utility of maximum entropy regularization scheme to reconstruct the complete NMR spin relaxation distribution continuum. Case studies showed that the three characteristics of the distribution correlate with various aspects of polymer morphology and with physical properties. These positive results suggested that this approach has the potential of yielding profiles on polymer dynamics and information concerning phonon coupling between domains in complex polymer systems which are not previously accessible. Furthermore, the nondestructive nature of NMR gives this approach an extra advantage over conventional tests for “in‐situ” studies of polymers.
NMR imaging of solid polymers: Strategies for chemical‐shift selectivity
Authors: Hepp Mark A. , Miller Joel B.
Published: March 2011

One reason that the solid‐state imaging field is exciting is because of its potential to provide spatially resolved chemical information from deep inside a solid sample. To achieve this goal, methods are needed which exploit the many NMR parameters to generate image contrast. We describe two strategies for employing the chemical‐shift anisotropy as a contrast mechanism in images of abundant nuclei in solid polymers. We illustrate these approaches with images which map spatial variations of molecular orientation in samples of polytetrafluoroethylene.
Structural characterization of langmuir‐blodgett films of a cellulose derivative by X‐ray photoelectron spectroscopy
Authors: Maaroufi Abdelkrim , Mao Lijun , Ritcey Anna M.
Published: March 2011

The method of variable angle x‐ray photoelectron spectroscopy has been applied to transferred monolayers of a new cellulose derivative. The results support a model for the monolayer in which the cellulose backbone lies flat on the substrate and the sidechains extend perpendicular to the surface. Furthermore, a significant portion of the substrate surface is found to be bare, indicating that the transferred monolayer contains major defects in the form of holes.
Structure and stability of Langmuir‐Blodgett‐Kuhn multilayers containing “hairy‐rod” copolymers
Authors: Foster Mark D. , Vierheller Timothy R. , Schmidt Albert , Mathauer Klemens , Knoll Wolfgang , Wegner Gerhard
Published: March 2011

The microstructure and thermal stability of Langmuir‐Blodgett‐Kuhn multilayers containing rod‐like polyglutamate copolymers having flexible aliphatic side chains have been studied with x‐ray and neutron reflectometry. Upon annealing at 84°C the multilayer structure changes in a manner which is dependent upon the degree of orientation of the rod‐like backbones and therefore upon the flow dynamics of the deposition. A sample deposited with a highly convergent flow loses the bilayer structure induced by deposition, whereas samples with less highly aligned backbones may not undergo this relaxation as readily.
Structure formation of organic multi‐layers
Authors: Isoda Seiji , Hashimoto Shugo , Itoh Toshihiko , Hoshino Akitaka , Kobayashi Takashi
Published: March 2011

Interface structures of C60 and polymeric phthalocyanines (GeOPc and AlFPc) were analyzed by high resolution electron microscopy. C60 was crystallized making its {111} ‐plane parallel to the surface of tetragonal phthalocyanines as on other substrates. This may be due to strong tendency of C60 to make its closed‐pack layer parallel to the surface during crystallization. In addition to this plane orientation, an axial orientation was observed; The <110> and <112> directions of C60 orient along the <110> directions of phthalocyanines. It can be concluded from observations that the lattice‐matching between the corresponding repeating distances of C60 and phthalocyanines is an important factor governing the orientation.
NMR Imaging and materials research
Authors: Blümich B. , Blünder P. , Fülber C. , Scheler U. , Weigand F.
Published: March 2011

The use of nuclear magnetic resonance in materials research is elaborated. While NMR applications to materials are discriminated between rigidly solid, rubbery, and liquid matter, NMR methods are divided into spectroscopy and imaging. The connections between the different material and NMR categories are explained. Particular emphasis is placed on NMR with spatial resolution, which is illustrated by examples from imaging of solid polymers and elastomers.
Surface acidic sites of highly disperse magnesium chloride: IR and ESR spectroscopy studies
Authors: Zakharov V. A. , Paukshtis E. A. , Mikenas T. B. , Volodin A. M. , Vitus E. N. , Potapov A. G.
Published: March 2011

Experimental data obtained by means of some high performance techniques allow to identify and register quantitatively the Lewis acidic sites on the surface of highly disperse magnesium chloride. Carbon monoxide adsorption on magnesium chloride has been studied with the IR diffuse reflectance spectroscopy (IRS‐DR). The interaction of some stable nitroxyl radicals with magnesium chloride has been investigated with the ESR technique.
Asymmetric Markovian analysis of the polymerization mechanism of propene by ziegler‐natta catalysis and external alkoxysilane donors
Authors: Chûjǒ Riichirǒ , Härkönen Mika , Seppälä Jukka V.
Published: March 2011

The formulae for conditional probabilities are derived with the term of NMR triad tacticities for the polymers whose polymerization process is described by an asymmetric Markovian process. The formulae obtained are applied to the polypropylene polymerized by Ziegler‐Natta catalysis with external alkoxysilane donors. For both, unfractionated samples and heptane‐insoluble fractions, four evidences are clarified as follows: Don the transformation from symmetric to (fluctuating) asymmetric sites the transformation of one (hereafter, L) site is much more enhanced than that of the other (D) site, 2) monotonous increase of isotacticity with an increase of the concentration of the donor is due to the increase of pLL, 3) aromatic donors are more effective than aliphatic ones for the improvement of isotacticity, and 4) the improvement of isotacticity after an addition of alkoxysilane is not due to the contribution from both of L and D sites, but the competition between the larger positive contribution from the former and the smaller negative one from the latter.
Symmetrical and lopsided zirconocene pro‐catalysts
Authors: Ewen John A.
Published: March 2011

Me2C[1‐Cp‐9‐Flu]ZrCl2 derivatives with H‐, CH3‐and (CH3)3C‐ substituents β to the Cp bridgehead carbon atom as well as complexes having mono‐ or di‐substituted fluorenyl ligands (R = CH3‐, (CH3)3C‐, CH3O‐, CH3OCH2‐, (CH3)3CC≡C‐, (CH3)2N‐, F‐, and Cl‐) have been investigated as propylene polymerization pro‐catalysts. Steric effects from the β‐Cp substituents determine the iso‐, hemi‐iso‐, and syndio‐specificities of the catalysts. The relative stereospecificities of Me2Si[1‐Cp‐3t‐Bu‐9‐Flu]ZrCl2 and rac‐Me2Si[1‐Ind‐3‐t‐Bu]2ZrCl2 are in accord with molecular models. The more un‐symmetrical the catalysts are the more m and mm stereosequences there are in s‐PP. The m dyads also increase with the concentration of Me2C[1‐Cp‐9‐Flu‐2‐OMe]ZrCl2.
The geometry of the site and its relevance for chain migration and stereospecificity
Authors: Razavi Abbas , Peters L. , Nafpliotis L. , Vereecke D. , Dauw K. Den , Atwood Jerry L. , Thewald Ulf
Published: March 2011

The structurally well characterized members of the family of the bridged metallocene procatalysts with cyclopentadienyl‐fluorenyl ligand framework constitute excellent examples for the investigation of the interrelation between the catalyst geometry and stereospecificity from a dynamic chain perspective. We have thus carefully selected a set of metallocenes, based on the increasing size of their β‐substituents and the choice of Zr and Hf as transition metals. By their application as polymerization catalysts we have been able to investigate the impact of the substituent size on the migratory behavior of the chain and stereospecific control of the corresponding catalysts. Through these investigations it has been demonstrated that the degree of freedom for the chain's lateral displacements, and the frequency of its back and forth migrations, varies largely with and is dependent on the steric bulk of the β‐positioned substituent and to the degree of the geometrical (stereo‐electronic) flexibility of the catalytic site with a given symmetry. It has been inferred from the experimental results that substituents, depending on their voluminosity and spatial expansion, interfer differently with the migratory function of the chain and can bring its migration, temporarily or permanently, to a halt (chain stationary insertion). The ratio of chain migratory insertion to chain stationary insertion and their prevalence in each individual case has the final saying about the degree and the type of the microtacticity of the resulting polymer chains (e.g. syndiotactic, syndiotactic containing isoblock, syndio‐isoblock, isotactic, and isotactic with syndioblock.
AB‐initio molecular dynamics study of metallocene catalysed ethylene polymerisation
Authors: Iarlori Simonetta , Buda Francesco , van Doremaele Gerard , Meier Robert J.
Published: March 2011

Ab‐initio Molecular Dynamics simulations on ethylene insertion in a bridged di(cyclopentadienyl) methylzirconocene have revealed that the entire reaction path starting from the π‐coordinated ethylene‐zirconocene complex up to and including propyl formation takes place in about 150 femtoseconds, which is unexpectedly fast, and suggesting the absence of any significant barrier of activation. Starting from a reactant structure without α‐H agostic interaction, at T=400 K such an interaction evolves during the course of the insertion reaction and before the propyl is formed. The product state exhibits γ‐H agostic interaction.
New catalysts for the polymerization of cyclic olefins
Authors: Goodall Brian L. , McIntosh Lester H. , Rhodes Larry F.
Published: March 2011

Various routes to high Tg thermoplastic materials based on the Ziegler‐Natta catalyzed polymerization of norbornene‐type monomers are described. These routes involve both ring‐opening metathesis polymerization (ROMP) and addition polymerization. New catalysts, and a new catalytically‐active metal (cobalt), for both ROMP and the addition homopolymerization of norbornene‐type monomers are reported.
Regio‐ and stereocontrol in the alternating copolymerization of olefins with carbon monoxide
Authors: Amevor Esther , Bronco Simona , Consiglio Giambattista , Di Benedetto Silvia
Published: March 2011

Strictly alternating copolymers between olefins and carbon monoxide are synthesized using cationic palladium catalysts modified by phosphorus or nitrogen ligands. Basic chelate diphosphines as the ligand allow the regioregular copolymerization of aliphatic olefins thus affording, e.g. in the case of propene, poly(1‐oxo‐2‐methyltrimethylene). Steric control of the copolymerization process towards the production of overwhelmingly isotactic copolymers is possible particularly when using atropisomeric ligands. In the case of styrene as the substrate and for all ligands employed the copolymerization process is regioregular. Prevailing syndiotactic structure is obtained with 1,10‐phenanthroline or 2,2′‐bipyridine as the ligand. Chelate thioether ligands allow the preparation of a completely atactic material. For 4‐tert‐butylstyrene an isotactic structure became accessible by using chiral bisoxazolidines. The prevailing structure of the copolymers of cyclopentene corresponds to a 1,3‐enchainment of the olefin units most probably associated with a prevailing diisotactic structure
The features of syndiotactic polypropylene
Authors: Kakugo Masahiro
Published: March 2011

The mechanism of stereoselectivity of propylene insertion in propylene‐ethylene copolymerization on a CS symmetrical zirconium complex i‐Pr(Cp) (Flu) ZrCl2 catalyst is discussed. Calculation results indicate that not only the β‐carbon in the growing chain end of the polymer but also the substituent of the β‐carbon play an important role in the selectivity of the prochiral face of the next‐coming propylene monomer. The stereoregularity of propylene units connected to an ethylene unit (PPE) in propylene‐ethylene copolymer was observed to be lower than that in propylene sequences (PPP) in the 13C NMR spectrum, which supports the calculation results. Furthermore, the structure and properties of propylene‐olefin (ethylene, 1‐butene, 1‐pentene, 1‐hexene, and 4‐methyl‐1‐pentene) copolymers prepared with the i‐Pr(Cp) (Flu) ZrCl2 catalyst system were studied. Propylene‐1‐butene copolymer exhibits peculiarly lower melting point depression because 1‐butene units enter into the unit cell of the crystal structure of syndiotactic polypropylene.
Syntheses and properties of syndiotactic polystyrene
Authors: Ishihara N.
Published: March 2011

Syndiotactic polystyrene (SPS) is a new crystalline engineering thermoplastic. With a melting point of 270 °C and its crystalline nature, SPS has high heat resistance, excellent chemical resistance and water/steam resistance. Since SPS has excellent dielectric properties, it is useful as a capacitor insulation material. The rate of crystallization is very fast in comparison with isotactic polystyrene (IPS), thus, SPS can be used in a number of forming operations, including injection molding, extrusion and thermoforming.

A system composed of a homogeneous titanium compound and methylaluminoxane (MAO) is an effective catalyst for syndiospecific polymerization of styrene. On the other hand heterogeneous titanium compounds containing halogen make a mixture of isotactic and syndiotactic components. The amount of syndiotactic polystyrene obtained is dependent on the mole ratio of Al to Ti. The result of ESR measurement suggests the Ti3+ species are important as a highly active site for producing syndiotactic polystyrene.

A comparison of the stereoregularities of polypropylene and polystyrene formed by various metallocene catalysts is studied. The (C6H6)2C(η5‐C5H4)(η5‐C9H6)TiCl2/MAO system gives a homogeneous catalyst for the polymerization of propylene giving isotactic rich polypropylene and of styrene to give syndiotactic polystyrene.
Thermodynamics, dynamics and relaxation in glass‐forming liquids ‐ the conformon concept
Authors: Kilian Hanns‐Georg , Beyer Claus , Pietralla Martin
Published: March 2011

Any interpretation of the dynamics in liquids requires understanding of fluctuating collective motions in the stationary limit. To this end, “eigen‐states” are defined, named conformons. Conformons are to be considered as a new type of bosons. Their properties characterize the typical features of the dynamics in disordered systems. Eigen‐energy and “eigen‐entropy” are adjusted to each other to minimize the free energy of each mode (saturation). The whole conformon ensemble exhibits a photon statistics with a broad universal mode spectrum. Analogues of Stefan‐Boltzmann's law and of Wien's displacements law are formulated.

A crucial point of our treatment is that conformons should, in principle, only become excited above a system‐typical temperature To (Vogel‐Fulcher temperature). Equilibrium properties of supercooled liquids are necessarily related to To. Cp/Cv, of the conformon ensemble should, for example, show a typical ΔT3‐dependence (ΔT=T‐To). Experimental data give evidence in support of this behaviour. As a consequence of the excluded volume supercooled liquids already solidify about 30 to 40 degrees above To at least at the quasi‐static glass temperature Tg.

Relaxation in the glass transition regime of glass formers can fully be described if relaxation modes are connected to each conformon. The description covers a set of experiments so different like mechanical and dielectric relaxation or quasi‐elastic light‐ and neutron scattering.
From chemical structure to viscoelastic properties of polymers
Authors: Ngai K. L. , Tsang Kwok Yeung
Published: March 2011

The basic result of the coupling model consists of a cross‐over from exp‐(t/τo) to exp‐(t/τ*)1‐n at a temperature insensitive microscopic time tc. We indicate how this basic result can be derived from chaotic, interacting Hamiltonian systems which include densely packed polymer molecules. Recent quasielastic neutron scattering experiments and molecular dynamics simulations are discussed and the results are shown to support this result as well. An application of the coupling model to find how the viscoelasticity of a polymer depends on the chemical structure of the monomer through the coupling parameter of the local segmental motion is given to illustrate the utility of the model.
Dielectric relaxations in bilayer structures of comb‐like copolymers: Perfluoralkyl and liquid‐crystalline side chains
Authors: Alig I. , Braun D. , Jarek M. , Hellmann G. P.
Published: March 2011

Abstract: A series of comb‐like copolymers and homopolymers containing different liquid‐crystalline and perfluoralkyl side chains was studied by frequency and temperature dependent dielectric measurements. The structure and the phase behaviour of the systems were characterized by X‐ray scattering and differential scanning calorimetry. The dielectric relaxation spectra of these polymers reflect the molecular mobility in bilayer structures formed by the mesogenic or crystalline side chains. By changing temperature it was possible to investigate the molecular motions in the different phases of the copolymers (smectic‐crystalline, smectic‐isotropic, and isotropic). The homopolymer containing perfluoralkyl side chains and all copolymers show a β‐relaxation at low temperatures, which is assigned to local molecular motions. Above the glass transition temperature, all samples exhibit a segmental (α) relaxation with WLF‐like temperature dependence in the activation plots. For the polymers forming LC structures only one relaxation process was detected in all phases, i.e. in the smectic, nematic, and isotropic structure or, in case of the copolymers, in the smectic‐crystalline and smectic‐isotropic double structures. This process was attributed always to the segmental motions, assisted by tumbling motions of the mesogens. The phase transitions are clearly indicated by discontinuities in the dielectric relaxation times and changes in the relaxation strength Δϵ. The dipole reorientations of the mesogens seem to be more restricted by the crystalline layers in the copolymers as by the smectic order of the LC homopolymers.
Triblock copolymers in a selective solvent: Dilute and semi‐dilute solutions
Authors: Lairez Didier , Adam Mireille , Raspaud Eric , Carton Jean‐Pierre , Bouchaud Jean‐Philippe
Published: March 2011

Triblock copolymers polystyrene‐polyisoprene‐polystyrene were studied in dilute and semi‐dilute solutions in a selective solvent, i.e. a non‐solvent for polystyrene and a good solvent for polyisoprene. The mass of the copolymer is equal to 1.6×105g/mol and it contains 70% of polyisoprene. At a concentration C equal to 1.6×10−3 g/cm3 triblock aggregation occurs.

Experiments performed on dilute solutions1 plead in favor of loose and polydisperse aggregates rather than spherical micelles: 1) the form factor of the aggregates shows a smooth decrease at qR<1; 2) internal modes are observed by quasi‐elastic light scattering; 3) specific viscosity measurements show that the internal concentration of unimers and aggregates are identical; 4) the unimer concentration and the aggregation number depend on the copolymer concentration.

In semi‐dilute solutions2 (C>3×10−2 g/cm3), dynamical properties are strongly affected by the temperature. Viscosity and longest relaxation time increase by a factor 105 as the temperature decreases from 50°C to 5°C, whereas the plateau modulus G remains independent of the temperature and proportional to the concentration. Small angle neutron scattering experiments reveal a cubic structure having a unit cell dimension d independent of the temperature and varying as C−1/3 leading to G∼1/d3. Quasi‐elastic light scattering experiments performed on this system show a wide relaxation function extending over 7 decades of time. These results argue for a lattice made of polystyrene nodes linked together by the polyisoprene middle blocks, the dynamics being governed by the glass transition of the nodes.
Mobility op polymer micelles
Authors: Anufrieva Elizaveta V. , Gromova Raisa A. , Lushchik Vanda B. , Nekrasova Tatyana N. , Krakoviak Mark G.
Published: March 2011

The nanosecond mobility of polymer micelles in aqueous solution of poly(N‐propylmethacrylamide) and that of reversed micelles of a surfactant in organic solvents were studied by polarized luminescence. The factors affecting the polymer micelles formation and the effect of polymers solubilized in systems of reversed micelles of a surfactant on their relaxation properties were established.
Structure and dynamics of copoly(oxyethylene‐oxypropylene‐oxyethylene) in o‐xylene/water mixtures
Authors: Chu Benjamin , Wu Guangwei
Published: March 2011

Abstract: The structure and dynamics of supramolecules of a triblock copolymer, copoly(oxyethylene‐oxypropylene‐oxyethylene), also known as PLURONIC L64: PEO13PPO30PEO13, in o‐xylene/water mixtures were studied by means of dynamic light scattering, small‐angle X‐ray scattering and NMR. At low copolymer concentrations, micelles coexisted with unimers and the micellar size increased with increasing amount of water in the mixture. Large aggregates were formed at higher copolymer concentrations. The size and the amount of the large aggregates increased with increasing amount of water in the mixtures, and increasing copolymer concentration. The solubilized water can be classified into free‐water(forming hydrogen bond with water) and bound‐water(forming hydrogen bond with EO units). The environment of EO units changed with the amount of solubilized water. The conformation of the copolymer remained essentially the same before and after micellization and did not change with the amount of solubilized water.
Polyion interchange reactions of interpolyelectrolyte complexes in aqueous solutions and gels
Authors: Kabanov V. A.
Published: March 2011

Cooperative coupling reaction between two opposite charged polyelectrolytes results in formation of polyelectrolyte complexes (IPEC). This reaction is very fast and diffusion controlled.

Whether IPECs formed by linear polyions are soluble or limitary swellable in aqueous media is decided by their composition, namely, by a ratio of oppositely charged polyions as well as by a water phase composition (the nature and the concentration of a simple salt, pH, the presence and the concentration of organic additives etc.).

The most important intrinsic property of IPECs is their ability to participate in interchange (exchange and substitution) reactions with competing polyions. The kinetics and the position of equilibria in these reactions are controlled by the low molecular salt concentration, the nature of small counterions, DP of interaction polyelectrolytes, as well as by their linear charge density.

IPECs can be formed also by interacting linear and opposite charged networks. It is shown that linear polyelectrolytes dissolved in aqueous solution can penetrate unexpectedly fast into oppositely charged cross‐linked polyelectrolyte gels to form “snake‐in‐cage” composites representing IPECs of corresponding polyion segments. It is proved that the mechanism consists in “relay‐race” transfer of linear polyion segments from one segment of the polyelectrolyte network to the other via interpolyelectrolyte exchange reaction. The driving force for the fast transport of linear polyions into the gel is produced by coupling reaction between two polyelectrolytes proceeding on solution/gel interface.
Poly(ether amide) triblock and star block copolymers
Authors: Clark R. J. , Henkee C. S.
Published: March 2011

Triblock and three arm, poly(ether amide) star block copolymers have been synthesized and characterized. Di‐ and tri‐functional amine terminated polyethers were reacted with caprolactam at elevated temperatures to produce the block copolymers. The polyether amines were incorporated at levels ranging from 5%‐40%. Differential scanning calorimetry(DSC) evaluation reveals no reduction in the crystalline melting point of the polycaprolactam end blocks up to 40% polyether incorporation. Dynamic mechanical spectroscopy and FTIR were used to confirm the incorporation of the polyether. A comparison is made between triblock and star block copolymers, and between poly(propylene glycol) and poly(ethylene glycol) polyether midblocks. These block copolymers have improved impact performance as well as a flexural modulus that first increases and then decreases as the amount of polyether is increased in the block copolymer.
Synthesis of homopolymers and block copolymers of methacrylates using a mixed Al/Li alkyl initiator
Authors: Haddleton David M , Muir Andrew V G , O'Donnell John P , Richards Stuart N , Twose David L
Published: March 2011

We report the use of a triisobutylaluminium/tert‐butyllithium initiator in the preparation of living methacrylate homopoloymers and a wide range of methacrylic block copolymers. The system, which we have referred to as Screened Anionic Polymerisation (SAP), is very tolerant of impurities and is effective in hydrocarbon solution with reaction rates such that high molecular weight polymers can be produced at temperatures readily accessible for large scale industrial use. A mechanism for the reaction is proposed based on preliminary spectroscopic evidence.
Polyethylene diblock copolymers: Direct synthesis and morphological analysis
Authors: Drzewinski Michael A.
Published: March 2011

Polystyrene and polybutadiene were block copolymerized with high density polyethylene using a transformation reaction from an anionic to a Ziegler‐Natta type polymerization. Various reaction parameters were investigated and optimized. Efficiencies of conversion of the anionic block to diblock were as high as 33% (100% normalized) consistent with the known 3/1 Li‐R/Ti relationship in the active catalyst species. The activity of the polymeric Li‐R/Ti catalyst with regards to ethylene polymerization was as high as 40 000 grams of polymer/mole Ti. Characterization of the resultant polymers is consistent with diblock copolymer structures but transmission electron microscopy shows distinct differences between the morphological behavior of these materials and the now well established morphological behavior of amorphous‐amorphous diblock copolymers. These differences are readily explained by consideration of the interactions between the competing thermodynamic processes of microphase separation and crystallization.
Network structure of inorganic/organic hybrid gels
Authors: Kajiwara Kanji , Krakovský Ivan , Urakawa Hiroshi , Kohjiya Shinzo
Published: March 2011

Two series of inorganic/organic hybrid gels were prepared by the sol‐gel reaction of triethoxysilyl‐terminated poly(tetramethylene oxide) and tetraethoxysilane. The structure of hybrid gels was observed by small‐angle X‐ray scattering, and the scattered profiles were analysed by assuming a priori the density correlation functions. The results suggest that the hybrid gel is composed of organic‐rich, inorganic‐rich and organic/inorganic mixed regions. The size and structure of respective regions were discussed in terms of the correlation lengths evaluated from the scattering profiles.
Water swelling of polyester networks
Authors: Belan F. , Bellenger V. , Mortaigne B. , Verdu J.
Published: March 2011

The water equilibrium concentration in styrene crosslinked polyesters increases with the temperature; this behaviour has been interpreted in terms of material expansion induced by temperature. We have verified this hypothesis by swelling measurements in water and gravimetric experiments at various temperatures between 30°C and 90°C. Samples were propylene glycol/neopentyl glycol ‐ maleate / isophthalate copolymers crosslinked by styrene.
Synthesis and study of poly(ethylene oxide) membranes obtained from homopolymerization of peo macromonomers
Authors: Schmitt Bertrand , Alexandre Eliane , Boudjema Karim , Lutz Pierre J.
Published: March 2011

Hydrogels were obtained by free‐radical polymerization of bifunctional macromonomers. This reaction can be conducted in water solution or in organic solvent. The kp value is yet strongly depending on the solvent used. The properties of these networks will be compared to those of networks obtained by end‐linking procedures. These materials were also used as a semi‐permeable membrane in the conception of an artificial pancreas.
The peculiarities of physical network formation in carboxyl‐containing poly(dimethylcarbosiloxane)
Authors: Rogovina Lidiya Z. , Vasilev Viktor G. , S. Papkov Vladimir , Shchegolikhina Olga I. , Slonimskii Grigorii L. , Zhdanov Alexandr A.
Published: March 2011

An unusual effect of physical network formation during heating or at room temperature alter previous heating was found for originally liquid poly(dimethylcarbosiloxane) containing 0.5 – 2.5 mol% of side carboxyl groups by means of the measurement of its Theological properties. The reason for this behaviour is supposed to be the predominance of intramolecular hydrogen bonding of COOH groups in original polymer and the intra– to Intermolecular bonds rearrangement during heating. The alternative reason can be the microphase separation with domains of COOH groups. The reversibility of the network is confirmed by the decrease in the elasticity modulus, development of irreversible deformation on further heating and by break‐up of Junctions on the addition of small amounts of polar liquids.
Anisotropic light scattering and rheological study of the physical gelation of atactic polystyrene in carbon disulfide
Authors: Lehsaini Nourdinne , Weill Gilbert , François Jeanne
Published: March 2011

The physical gelation of the solutions of atactic polystyrene (aPS) in carbon disulfide (CS2) is studied by the excess of anisotropic light scattering δHv and by the Theological properties. An abrupt jump of δHv at gelation temperature shows that a part of the chains are stiffened upon gelation. This effect which is independent of aPS molecular weight strongly decreases with concentration. It is well correlated with an abrupt change of the plateau modulus GN which indicates the formation of additional entanglements in the gel phase with respect to the sol. The compatibility of these abrupt jumps with the thermodynamic theories used to interpret the concentration and molecular‐weight dependence of the gelation temperature is discussed.
Microphase separation during the concurrent formation of two polymer networks
Authors: Widmaier Jean‐Michel
Published: March 2011

As a rule, interpenetrating polymer networks (IPNs) are multiphase systems, and the degree of microphase separation is determined by the competition between the chemical kinetics of reaction and the physical kinetics of phase separation. For semi‐IPNs of crosslinked polyurethane and linear polystyrene obtained by a one‐step process, the development of the morphology has been followed by light transmission measurements and by optical microscopy, and finally examined by scanning electron microscopy. When phase separation takes place after gelation, the rather short elastic chains of polyurethane limit the growth of the styrenic phase at a submicroscopic level and the materials thus formed are transparent. On the contrary, when the reaction medium can phase‐separate before gelation of polyurethane, the final morphology results from a superposition of two levels of phase separation: i) a fine dispersion of the components and ii) a gross phase separation of polystyrene noduli surrounded by a polyurethane‐rich shell.