bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionization of MgCl2 during the formation of α‐olefin polymeryzation catalyst
Authors: Sobota Piotr
Published: March 2011

The examination of the reaction between [MgCl2(THF)2], TiCl4(3), AlCl3, AlEt3, AlEt2Cl and the synthesis and isolation of compounds as crystals and resolution of their structure by the X‐ray method were the subject of our study. It was expected that these investigations would help to understand the behaviour of MgCl2 towards the transition metal and furnish useful relationships to the structure of catalyst active center and to the polymerization mechanism in TiCl4(3)/MgCl2/AlEt3 system. Our studies have revealed that the main difference between the first and higher generations of Ziegler‐Natta catalysts is only the number of active centers.
Steric equivalence between internal and external donors as polymerization stereoregulators: A molecular mechanics study
Authors: Barino Luisa , Scordamaglia Raimondo
Published: March 2011

New models for steric environment of Ti isospecific polymerization sites on MgCl2 microcrystals are presented. They directly involve the presence of a donor molecule in order to obtain chiral activable Ti atoms otherwise belonging to isolated adsorbed TiCl4 molecules or Ti2Cl8 dimers which are lacking the required symmetry. The most important steric features of donor molecules have been obtained through structure‐activity relationships and molecular comparisons, while their adsorption on MgCl2 faces lateral to (001) has been studied through a conformational analysis approach.
Kinetics of olefin copolymerization with heterogeneous Ziegler‐Natta catalysts
Authors: Kissin Yury V.
Published: March 2011

The kinetics of the ethylene/1‐hexene copolymerization reaction with a Ti‐based Ziegler‐Natta catalyst has been studied. Kinetic analysis established the existence of several populations of active centers in the catalyst. The centers differ in two aspects: their ability to incorporate α‐olefin units into copolymer chains (i.e., their reactivity ratios) and the average molecular weights of the polymer chains they produce. The centers of different populations are formed at different rates and have different kinetic stabilities. As a consequence, both the molecular weight distributions of the copolymers and their compositional distributions are relatively broad and change with in time. Two kinds of catalyst poisons were found. The poisons of the first type, arylalkoxysilanes, preferentially deactivate the centers which have the highest ability to copolymerize α‐olefins with ethylene. These poisons decrease the average α‐olefin content in the copolymers and the fraction of their olefin‐rich components. The poisons of the second type, conjugated dienes, preferentially deactivate the centers which have the lowest ability to copolymerize α‐olefins with ethylene. These poisons significantly increase the content of the olefin‐rich components in the copolymers.
Comparative kinetic and active centre studies on magnesium chloride supported catalysts in propylene polymerization
Authors: Tait Peter J. T. , Zohuri G. Hossein , Kells Andrew M.
Published: March 2011

Three different types of high activity magnesium chloride catalysts were prepared and used for propylene polymerization both in the absence and in the presence of external donors. The rates of polymerization were studied as functions of polymerization time, and the effects of methyl paratoluate and diphenyldimethoxysilane as external donors were investigated. Active centre concentrations (C*) were determined using tritiated methanol quenching and 14CO radio‐labelling in order to assess their applicability. A relatively good agreement between values of C* evaluated by the use of these two methods was obtained. The morphologies of the supports, catalysts and polymers produced were studied using scanning electron microscopy. A model involving expanding microreactors is proposed for polymer growth.
Some peculiar aspects of a new catalyst for propene polymerization
Authors: Luciani Luciano , Milani Federico , Zannetti Roberto
Published: March 2011

An investigation was carried out on the preparation of highly disordered samples of MgCl2 (in delta ‐form), starting from different Mg‐alkyls and chlorinating agents.

Successively we studied which kind of silica carrier had to be preferred and which treatment was strictly' necessary to achieve a qualified catalyst precursor showing outstanding performance. Different routes were investigated to support the active, disordered MgCl2 on the silica carrier and then some following ways to complete the catalyst. The final result of this investigation was the synthesis of a catalyst showing the best performance with reference to the parameters of use in every polymerization process.

It has to be e.g. mentioned:

— high yield, referred to the residual content of Mg, Ti and Cl;

— no activity decrease when operating at a very high hydrogen concentration;

— possibility to polymerize also at elevated temperatures;

— very high isotactic index and stereoregular structure, as measured by the NMR technique;

— possibility to reach high MFR (Melt Flow Rate) (up to 400 g IPP/10 min at 230°C, 2,16 kg, ASTM D 1238L);

— outstanding morphology and flowability.
Stereospecific oligo‐ and polymerization with metallocene catalysts
Authors: Kaminsky Walter
Published: March 2011

The regio‐ and stereo‐selectivity of metallocene/methylaluminoxane catalysts was shown to be significantly and rapidly enhanced by substitution of the indenyl ligands and by heterogenization of the zirconocenes. By oligomerization of 1‐butene with optically active metallocenes, it could be shown that there is a small influence from the growing polymer chain on the isotacticity, the overriding factor in every case being the existence of a chiral active centre. Each insertion step increased the stereospecificity, until the maximum value was achieved.
Stereospecific metallocene catalysts: Scope and limits of rational catalyst design
Authors: Spaleck Walter , Aulbach Michael , Bachmann Bernd , Küber Frank , Winter Andreas
Published: March 2011

Structure‐performance relationships in the propene polymerization behaviour of a number of silicon bridged bisindenyl zirconocenes show a rational pattern. Prognosis of the polymerization behaviour of different type structures, however, often fails, which is demonstrated by three examples of new zirconocenes. These include two bisindenyl complexes with two‐membered silicon bridges and one isospecific bridged fluorenyl cyclopentadienyl species. It is thus demonstrated that the scope of a “rational catalyst design” in the field of metallocene catalysts is still limited.
Metallocenes for polypropylene: Polymerization performance and computer modeling
Authors: Burkhardt Terry J. , Murata Masahide , Vaz Roy J.
Published: March 2011

The structures of eleven different metallocenes substituted with either methyl and/or t‐butyl groups were minimized by computer molecular modeling. Using Comparative Molecular Field Analysis (CoMFA), a computer model was generated from the minimized metallocene structures and actual polymerization performance. When the model was tested, a statistically valid correlation of the model's predicted DSC melting point with the observed DSC melting point was found. The model indicates the extent of the steric effect of these alkyl substituents and their influence on the DSC melting point.
The catalysis of the stereospecific butadiene polymerization by Allyl Nickel and Allyl Lanthanide complexes — A mechanistic comparison
Authors: Taube Rudolf , Windisch Heike , Maiwald Steffen
Published: March 2011

A short overview on the general mechanistic principles of the allyl metal complex catalyzed stereo‐specific butadiene polymerization is given. The present state of knowledge on the mechanism of stereoregulation and in the understanding of the catalytic structure reactivity relationships is discussed comparatively for allyl nickel and allyl lanthanide catalysts.
Ring‐opening metathesis copolymerization employing ruthenium‐based metathesis catalysts
Authors: Hillmyer Marc A. , Benedicto Alto D. , Nguyen SonBinh T. , Wu Zhe , Grubbs Robert H.
Published: March 2011

The copolymerization of both high‐ and low‐strain cyclic olefins employing three ruthenium‐based metathesis catalysts is desribed. The effect of the ligand environment as well as the nature of the carbene on the copolymerizations is discussed.
Stereospecific and asymmetric polymerization of 1‐phenyldibenzosuberyl methacrylate with radical and anionic initiators
Authors: Okamoto Yoshio , Nakano Tamaki , Shikisai Yoshifumi , Mori Masatoshi
Published: March 2011

Stereospecific and asymmetric (helix‐sense‐selective) polymerization of 1‐phenyldibenzosuberyl methacrylate (PDBSMA) was performed with radical and anionic initiators. A highly isotactic polymer having triad isotacticity greater than 97% was obtained by radical polymerization with (i‐PrOCOO)2 at 40°C. The radical polymerization of PDBSMA in (+)‐ and (‐)‐menthol gave (‐)‐and (+)‐polymers, respectively, whose optical activity is ascribed to the prevailing one‐handed helical conformation of a polymer chain. The radical copolymerization of PDBSMA with a small amount of an optically active monomer, (+)‐phenyl‐2‐pyridyl‐o‐tolylmethyl methacrylate, afforded an optically active copolymer with the prevailing one‐handed helical structure of PDBSMA sequences. Asymmetric anionic polymerization of PDBSMA was carried out with the complex of N, N′‐diphenylethylenediamine monolithium amide and a chiral ligand, (+)‐1‐(2‐pyrrolidinylmethyl)pyrrolidine in toluene at −78°C. The obtained polymer was highly isotactic and optically active due to nearly 100% one‐handed helical structure.
Recent results on the polymorphic behavior of isotactic polypropylene
Authors: Meille Stefano V. , Ferro Dino R. , Brückner Sergio
Published: March 2011

The more recent results concerning the polymorphic behavior of isotactic polypropylene (iPP) are presented. Specifically contributions on the recently determined γ phase crystal structure, in which non‐parallel chains coexist, and the novel results concerning the β phase are summarized. The new data appear to suggest that the normally occurring α‐phase is in general neither the kinetically favored nor the thermodynamically more stable phase but rather it represents the best compromise between these two criteria. The implications and the open questions arising from the new findings with respect to morphology and polymer crystal growth are considered.
Applications of molecular mechanics to refine and understand polymer crystal structures
Authors: Ferro Dino R. , Ragazzi Massimo , Brückner Sergio , Meille Stefano V.
Published: March 2011

A computational approach to refine and analyze polymer crystal structures is presented, where both intra‐ and intermolecular interactions are simultaneously optimized by minimizing the total crystal potential energy in cartesian coordinates and utilizing a full‐atom force field. The advantages of the present methodology are illustrated through several applications, including very recent results concerning the polymorphism of isotactic polypropylene. Some features of the computer program for molecular mechanics CHAMP, developed in our laboratory, are also described.
Orientation fluctuations in diblock copolymers
Authors: Fytas George
Published: March 2011

Depolarized light scattering and dielectric relaxation spectroscopy reveal pertinent composition fluctuations effects on the orientation dynamics in diblock copolymers near the ordering transition (ODT). The main evidence stems from the broadening of the block relaxation function and collective chain orientation in the disordered state near ODT as well as a slow relaxation process below ODT.
Fluorescence studies of the kinetics of processes in polymers
Authors: Morawetz Herbert
Published: March 2011

Using a stopped‐flow apparatus with fluorescence detection we followed the expansion of poly(methacrylic acid) after a pH jump, the enhancement of fluorescence of Auramine O after association with poly(methacrylic acid), the counterion exchange in ionomer solutions and the dependence of the rate of inter‐polymer reactions on the polymer chainlength. Fluorescence was also used to follow the unfolding of collapsed chains in bulk polymers and counterion diffusion in bulk ionomers.
Polyethylene‐based polyurethane copolymers and block copolymers
Authors: Byrne Catherine A. , Desper C. Richard , Schneider Nathaniel S. , Li Yingjie , Chu Benjamin
Published: March 2011

Low molecular weight hydroxy terminated polyethylene (HTPE) containing on average an ethyl group every 16–18 carbon atoms, and a hydroxy functionality of 2.6, has been used to prepare polyurethane copolymers and block copolymers which have good solvent resistance. The polymers show somewhat complicated thermal behavior, including Tg's at around −40°C due to the HTPE and diffuse endotherms between 40 and 60°C. The simple copolymers, containing only the polyol and a diisocyanate, show infrared evidence for two phases in the case where CHDI (trans‐1,4‐diisocyanatocyclohexane) was used, and poorer phase separation where other diisocyanates were used. Dynamic mechanical spectra show very broad tan delta transitions for the copolymers in the range of ‐9 to −23°C. All the polymers exhibit another transition in the G” curve above room temperature. SAXS reveals a microphase separated structure at 30°C for the simple copolymers which increases in spacing, then disappears in the 60–70°C range. With cooling, the microphase separated structure reappears readily for the CHDI‐based copolymer, while its reappearance shows a hysteresis resulting from rate effects for the other copolymers.
Synthesis of well‐defined macrocyclic block copolymers using living coupling agent method
Authors: Ma Jingjing
Published: March 2011

Macrocyclic poly(styrene‐b‐butadiene) (SB) block copolymers were prepared by coupling a living poly(styrene‐b‐butadiene‐b‐styrene) (SBS) block copolymer using a living coupling agent, 1,3‐bis(1‐phenylethylenyl)benzene (DDPE), or a difunctional electrophile, dimethyldichlorosilane. The living poly(styrene‐b‐butadiene‐b‐styrene) block copolymer was generated from an addition product of sec‐butyllithium and DDPE. A living heteroarmed star block copolymer has been prepared by coupling two moles of monolithium polystyrene with one mole of DDPE followed by reinitiation and polymerization of the butadiene monomer. The dilithium 4‐armed star block copolymer was then coupled using dimethyldichlorosilane to form a cyclic polybutadiene with two attached polystyrene branches.
One‐step synthesis of poly(methacrylic acid) macromonomers and application to soap‐free emulsion copolymerization with styrene
Authors: Ito Koichi , Sabao Kazumasa , Kawaguchi Seigou
Published: March 2011

Allylic sulfides such as α‐(tert‐butylthiomethyl)styrene and α‐(2‐hydroxyethylthiomethyl)styrene worked as effective chain transfer agents in the radical polymerization of methacrylic acid, to afford a one‐step synthesis of water‐soluble macromonomers with the 2‐phenylallyl end groups. The macromonomers were found to be effective, particularly in the partially neutralized form, in emulsion copolymerization with styrene in water, to give stable emulsions with nearly monodisperse, submicron‐sized particles. The microspheres thus obtained are considered to have carboxyl groups densely bound on the surface as a result of an organized copolymerization.
Characterization of network structure in elastomeric materials
Authors: Kohjiya Shinzo
Published: March 2011

There are two types of elastomeric materials, i.e., covalently crosslinked systems (vulcanizates) and thermally reversible systems such as thermoplastic elastomers (TPEs). The analysis of pre–gels was found to be a technique for the characterization of the former. Some results on the network systems are described which include sulfur– and moisture–cured rubbers, filled vulcanizates, a few exotic TPEs, and new hybrid network systems.
Anisotropic thermoset networks based on ring‐forming monomers (cyanate esters and isocyanates)
Authors: Mormann Werner , Zimmermann Jörg
Published: March 2011

Cyanate esters and isostructural isocyanates have been synthesized and investigated in terms of their thermal and phase behaviour. Model cyclotrimers of both were synthesized to study the influence of the triazine rings on the mesophase formation. Liquid crystalline properties (calamitic mesophases) were found only for cyanurates. Polycyclotrimerization of 4‐cyanatophenyl 4‐cyanatobenzoate starts in an isotropic phase with a transition to a mesophase after reaching the gel point. The gel point observed by rheological measurements is temperature‐dependent and probably caused by association of the reactive oligomers as no gel particles are found below the chemical gel point. The gel point of the commercial 2,2‐bis(4‐cyanatophenyl)propane was found at 50 % conversion by the same method. Due to the higher rigidity of the mesogenic cyanate the final conversion is below 100 %, as opposed to the conventional material. Under appropriate conditions isotropic networks can be obtained from the mesogenic monomer, which sets the basis for a quantitative investigation of the influence of liquid crystalline order on physical properties of the thermosets.
Influence of crosslink density and chain flexibility on mechanical properties of model epoxy networks
Authors: Espuche Eliane , Galy Jocelyne , Gérard Jean‐François , Pascault Jean‐Pierre , Sautereau Henry
Published: March 2011

Fully cured epoxy networks having different architectures were prepared by introducing either a monoamine acting as a chain extender or an aliphatic epoxy monomer. As expected an increase in the amount of the difunctional amine leads to a decrease in the crosslink density whereas the introduction of an aliphatic epoxy comonomer leads to more flexible chains between crosslinks. Values of the Young modulus and the dependence of the yield stress as a function of temperature were related to the occurrence and amplitude of secondary relaxations. The fracture toughness at room temperature was clearly associated with the glass transition temperature as a consequence of plastic deformation, rather than with chain scission.
Simulation of polymer network formation: Connectivity considerations
Authors: Galiatsatos Vassilios , Castner Eric S. , Al‐Ghamdi Ali M.S.
Published: March 2011

The issue of connectivity in polymer networks is discussed by employing graph theory. Several topics are addressed, including the theory of rubberlike elasticity and computer simulations of network formation. The formulation of the partition function is reviewed and new applications are presented on the irradiation cure of polybutadiene and the sulfur vulcanization of cis(1,4)‐polyisoprene and cis(1,4)‐polybutadiene.
Microgels 1: Solution polymerization using vinyl monomers
Authors: Graham Neil B. , Hayes Carmel M.G.
Published: March 2011

Theories of gelation predict that the polymerization and copolymerization of polyfunctional monomers having an average functionality of greater than two will form a macrogel. The theories have not been found to accurately predict the degree of reaction at the gel point in the presence of solvents. This paper, the first in a series, explores a concept in which it is postulated that macrogelation in solution in many cases is not the expected outcome and that small and usually soluble internally crosslinked polymer molecules(microgels) will be the product at complete reaction. The monomers methyl methacrylate and diethyleneglycol dimethacrylate were radically copolymerized in various proportions in a range of solvents to test the hypothesis. It was found that, at essentially complete conversion in good solvents below a critical and relatively high concentration, gelation could not be obtained and a general technique for the preparation of “microgels” is thus revealed.
Evolution of crystallinity in photodegraded polyethylene films studied by ft‐raman spectroscopy
Authors: Rull Fernando , Rodriguez Jorge , Alia Jose María , Arroyo Fernando , Edwards Howell
Published: March 2011

FT‐Raman spectroscopic studies of photodegraded polyethylene films have enabled the evolution of the crystallinity process to be measured. Commercial polyethylene films of Mw=90 000 were exposed in a weathering UV‐chamber under known conditions of exposure time and radiant energy. The spectral profiles were modelled using Fourier methods. The relative amounts of the orthorrombic crystalline phase, αc, the amorphous phase, αa and the interphase, αb, were calculated using Raman bands at 1416 cm−1 characteristic of the crystalline phase and the bands at 1080, 1305 cm−1, characteristic of the amorphous phase. The interphase content can be calculated from the relationship αb= 1‐(αc+αa). It was found that the weathering process affects only the relative intensities of the bands attributed to crystalline and amorphous fractions; the crystalline content increases at the expenses of the amorphous fraction. These results are discussed in terms of the changes in the intermolecular forces caused by radiation exposure.
Properties of arylpolyesters with reference to water content
Authors: Rueda D. R. , Viksne A. , Kajaks J. , Balta‐Calleja F. J. , Zachmann H. G.
Published: March 2011

The 4000–2000 cm−1 infrared spectral region from transmission FTIR spectra of films (≈ 220 μm thick) of amorphous poly (ethylene terephthalate) (PET) and poly(ethylene 2, 6‐naphthalenedicarboxylate) (PEN) was analyzed. In addition to the strong bands for the stretching vibration modes of H‐C bonds, the ester‐overtone band at about 3430 cm−1 and a doublet (3630, 3550 cm−1) band, related to absorbed water, appear. The spectra for these materials show significant differences in absorptivity and frequency for the ester overtone band. Real time water sorption/desorption in these films was investigated simultaneously by FTIR spectroscopy and by measurement of weight changes. A linear correlation between the integrated absorbance of the water bands and the relative weight variation of the films was found for these two polymers. Results show that the infrared absorptivity of these bands is identical in both materials and that water molecules are weakly bound to ester groups throughout the films. However, it turns out that the water content is higher in the case of PEN which has a larger specific volume.
Synthetic applications of non‐polymerizable monomers in living carbocationic polymerization
Authors: Fodor Zs. , Hadjikyriacou S. , Li D. , Takacs A. , Faust R.
Published: March 2011

The foundation and methodology of using highly reactive but non‐polymerizable monomers in living cationic polymerizations is introduced. The chemistry and kinetics of 1,1‐diphenylethylene (DPE) addition to living polyisobutylene (PIB) in methyl chloride/n‐hexanes 40/60 v/v at −80°C is reported. Monoaddition occurred even when large excess of 1,1‐diphenylethylene was used. The methanol quenched polymer of the DPE capped PIB carried ‐OCH3 functionality exclusively, suggesting that the diphenyl alkyl chain‐ends are completely ionized, which was confirmed by conductivity studies. By in‐situ functionalization using soft nucleophiles a variety of functional groups were obtained, most notably ester upon reaction with silyl ketene acetal. It was found that the diphenyl carbenium ion is an efficient initiating species for the polymerization of reactive monomers such as vinyl ethers and α‐methylstyrene. The synthesis of PIB based block copolymers was accomplished by sequential monomer addition, using para‐methylstyrene, α‐methylstyrene or isobutyl vinyl ether as the second monomer. It involved capping with DPE, followed by tailoring the Lewis acidity to the reactivity of the second monomer by the addition of titanium(IV) alkoxide, by replacing the Lewis acid with a weaker one or by the use of a common ion salt. PIB‐b‐PMMA was obtained by the combination of living cationic and group transfer (GTP) polymerizations.
Polymerization with metallocene catalysts. Hydrooligomerization and NMR investigations concerning the microstructure of poly(cyclopentenes)
Authors: Arndt Michael , Kaminsky Walter
Published: March 2011

Hydrooligomerizations and polymerizations of cyclopentene were carried out using CS, C2 and C2v symmetric zirconocenes and methylaluminoxane as catalyst. The structure of the hydrotrimers was investigated by one‐ and twodimensional NMR spectroscopy and correlated to the structure of the polymers. The assignments for the 13C‐NMR spectrum of the cis‐1,3‐enchained hydrotrimer made by Collins [3] are corrected. Cis‐1,3‐enchainment of the configurational base units in the poly(cyclopentenes) is confirmed. rac‐[Me2Si(Ind)2]ZrCl2/MAO catalysis features crystalline polymers and the erythrodiisotactic hydrotetramer indicating highly stereoselective insertion. Cp2ZrCl2/MAO and [Ph2C(Fluo)(Cp)]ZrCl2/MAO show none or low stereoselectivity respectively yielding amorphous polymers and both of the diastereomeric hydrotetramers.
Ring‐opening polymerization of lactones by mono(cyclopentadienyl)titanium complexes
Authors: Okuda Jun , Kleinhenn Thomas , König Peter , Taden Insa , Ngo Silvana , Rushkin Ilya L.
Published: March 2011

Mono(cyclopentadienyl)titanium complexes of the general formula Ti(η5‐C5R5)X2OR' were designed as structurally well‐defined mononuclear initiators for the ring‐opening polymerization of four‐, six‐, and seven‐membered lactones. Living pseudo‐anionic mechanism with acyl‐oxygen cleavage is suggested by various NMR spectroscopic studies as well as the isolation of the mono(insertion) products. The nature of the ancillary ligands lead to significant changes in the polymerization activity and is discussed in terms of electronic and steric effects.
Rare earth metal initiated polymerization to give high polymers with narrow molecular weight distribution
Authors: Yasuda Hajime , Ihara Eiji , Morimoto Masakazu , Nodono Mitsufumi , Yoshioka Shiro , Furo Masahito
Published: March 2011

Organolanthanide (III) initiated polymerization of alkyl acrylates gave high molecular weight poly(alkyl acrylate)s with extremely narrow molecular weight distribution in high yield. Molecular weight of the polymers increased linearly with the conversion. Random and block copolymerizations of acrylate monomers (alkyl acrylates and MMA) were successful. For development of olefin polymerization catalystsbased on lanthanide complexes, bulky substituents were introduced into Me2Si bridged Cp rings and they were used as ligands of lanthanide complexes. Tri‐ and divalent lanthanide complexes with such a ligand system showed high activity for olefin polymerization and gave high molecular weight polyolefins.
Copolymerization of 2,2‐dimethyltrimethylene carbonate and cyclic esters
Authors: Keul Helmut , Schmidt Peter , Robertz Bernd , Höcker Hartwig
Published: March 2011

The anionic and/or insertion copolymerization of 2,2‐dimethyltrimethylene carbonate (DTC) with ϵ‐caprolactone (ECL), pivalolactone (PVL) and L‐lactide (LLA) is presented with special emphasis on the copolymerization mechanism. Statistical copolymers are obtained by copolymerization of DTC with ECL and with LLA, while with PVL a block copolymer is obtained. The role of transesterification on the microstructure is discussed.
Synthesis and characterization of “umbrella” shaped polymers
Authors: Wang Fei , Roovers Jacques , Toporowski Paul M.
Published: March 2011

A new strategy has been developed to prepare umbrella polymer, i.e. star polymers with one heteroarm. The synthesis uses living anionic polymerization to prepare a short segment of 1,2‐polybutadiene at the end of a linear polystyrene. The vinyl groups of 1,2‐polybutadiene are hydrosilylated with dichloro(methyl)silane. The umbrella polymer is then formed by nucleophilic displacement of the silicon‐chlorine with 1,4‐polybutadienyllithium. An umbrella polymer with poly(2‐vinylpyridine) arms is prepared in the same way after hydrosilylation with chlorodimethylsilane. The umbrella polymers are characterized by light scattering, size‐exclusion chromatography (SEC), ultraviolet/visible spectroscopy (UV/vis), nuclear magnetic resonance (NMR) and intrinsic viscosity.
Polymerization of monomers containing functional silyl groups. 12. Anionic polymerization of styrene derivatives para‐substituted with pentamethyldisilyl (Si‐Si), heptamethyltrisilyl (Si‐Si‐Si), and nonamethyltetrasilyl (Si‐Si‐Si‐Si) groups
Authors: Hirao Akira , Ando Yushi , Nakahama Seiichi
Published: March 2011

Three styrene derivatives, para‐substituted pentamethyldisilyl (Si‐Si), heptamethyltrisilyl (Si‐Si‐Si), and nonamethyltetrasilyl (Si‐Si‐Si‐Si) groups 1 ‐ 3 were synthesized and polymerized in tetrahydrofuran (THF) at −78°C and in benzene at 40°C. The polymerizations of 1 and 2 in THF were found to proceed without transfer and termination reactions to afford stable living polymers. The Si‐Si and Si‐Si‐Si bonds are found to be completely stable under the conditions. Under the same conditions, novel block copolymers with well‐defined structures were synthesized by sequential addition of 1 or 2 and styrene. By contrast, side reactions occurred during the polymerizations of 1 and 2 in benzene at 40°C, although polymer yields were quantitative. More seriously, polymer was not obtained in the polymerization of 3 both in THF and in benzene. Thus, the effect of chain length of the oligosilyl group is found to be critical in the anionic polymerization of 1 ‐ 3.
Behaviour of differently produced methylalumoxanes in the phase separation with diethyl ether and molecular weight estimations
Authors: Von Lacroix K. , Heitmann B. , Sinn H.
Published: March 2011

Cryoscopic molecular weight estimations and phase separation experiments of differently produced methylalumoxanes showed diverse behaviour. The cryoscopic molecular weight estimations showed higher molecular weights caused by increasing methyl conversion. The average molecular weight in benzene lay between 1000 to 2000 while the solvent 1, 4‐dioxane delivered smaller molecular weights (factor 2 to 4). Molecular weights in trimethylaluminium were similar to those in benzene. In phase separation experiments we obtained an increasing volume portion of lower phase with increasing methyl conversion during production. There was a decisive influence of circulation circumstances at the ice surface and the trimethylaluminium concentration at production according to the behaviour in phase separation experiments.
Ethylene polymerization with metallocene and trimethylaluminumtreated silica
Authors: Lee Dong‐Hee , Shin Sang‐Young , Lee Dong‐Ho
Published: March 2011

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

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

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

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

Paul J. Flory was a pioneer in the development of a quantitative understanding of polymer science and a leader in placing it among the major scientific disciplines. Through his energy, skill and genius, and by the judicious interplay of experiment and theory, he demonstrated that polymers are not the complicated, intractable systems they were thought to be earlier, but are treatable in a rigorous and straight‐forward manner.

From his first scientific paper on polymers in 1936 to his last contributions, published posthumously, in 1986, Paul Flory was involved in shaping a consistent view of polymer science. A unique ability, to perceive the dominant cause in a complex effect and to formulate the action of this most important element of a situation in a simple and straightforward model, made his contributions so helpful and relevant that still today his models are often chosen over later, more refined, more accurate ones – Flory's models and concepts are of penetrating insight and a simplicity that allows all polymer scientists to understand and use them.

Flory was involved in a very broad range of topics: among other topics, he laid the foundation of the understanding of polymerization reactions, illuminated the thermodynamics and hydrodynamics of polymer solutions and through this the nature of the polymer‐solvent interactions and the θ‐state, formulated important models of rubber elasticity, and investigated with excellent success polymeric crystals and liquid crystals. A contribution of great importance was the development of the rotational isomeric state method to the treatment of macromolecules of arbitrary size and structure and for many properties. His achievement was recognized by numerous awards, honorary degrees, and the Nobel Prize in 1974.

Paul J. Flory, born on June 19, 1910, died on September 8, 1985.
The essence of changes in central and eastern Europe. New challenges and limitations
Authors: Diem Tadeusz
Published: March 2011

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

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

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

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

Liquid crystal elastomers can be macroscopically ordered with respect to the director by applying a mechanical field similar to electric/magnetic field effects of low molar mass liquid crystals. Introducing network anisotropy a priori by the synthesis, uniformly aligned nematic or smectic elastomers are available without external mechanical field. These LSCE's combine optical properties of single crystals with entropy elasticity of elastomers.

Due to uniform director orientation without defects, the LSCE's exhibit excellent transparency which makes them applicable for optical elements. Non‐linear optical properties can be easily optimized by attaching suitable I.c.‐moieties to the polymer network. On the other hand, due to the rubber elasticity of the LSCE's, electromechanical effects can be observed, e. g. piezoelectricity of chiral smectic C‐LSCE's.
Viscoelastic properties of liquid crystal polymers: Collective motions and nuclear spin relaxation
Authors: Heaton Nicholas , Reimer Dirk , Kothe Gerd
Published: March 2011

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

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

So far all lattices of regular microdomain structures reported in the literature, either based on binary AB, ABA or ternary ABC block copolymers, can be described using simple symmetry elements like mirror planes, symmetry centers and rotation axes.

The microphase separation in a linear ternary block copolymer consisting of three immiscible components namely polystyrene, polybutadiene and polymethyl methacrylate gives rise to the formation of a chiral supramolecular assembly in which chirality is not defined on a molecular (or macromolecular) level but only by the assembly of the linear triblock copolymer molecules. The polybutadiene (7, 12 wt.‐%) phase forms helical strands surrounding the polystyrene cylinders (25, 26 wt.‐%). This chiral mesoscopic assembly can be recognized unambiguously by transmission electron microscopy.1

Both left‐ and right‐handed helical structures are formed, either on different cylinders but also along the same cylinder. In the latter case helix reversals are observed. The helical morphology has been obtained by casting the block copolymers from various solvents, with different solubilities for the three components. It also does not change with annealing time. This is a strong indication that the helical morphology is the equilibrium structure of the system.

The formation of the helical structure in the present polystyrene‐block‐polybutadiene‐block‐poly(methyl methacrylate) triblock copolymers can be explained on the basis of the theory of block copolymers in the strong segregation limit which was originally developed by Alexander2 and De Gennes3, 4 for lamellar interfaces and extended by Semenov5 to curved (micellar) systems. This approach was successful for the description of symmetric ABC block copolymer systems. The details of the calculations for the helical morphology will be published elsewhere.6
Synthesis of molecular objects: Two‐dimensional polymers
Authors: Stupp S. I.
Published: March 2011

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

Under certain conditions the ring‐opening polymerization of cyclic monomers may be reversed to result in a ring‐closing depolymerization of the respective polymers. This method of “thermodynamic recycling” was explored for a number of examples such as polytetrahydrofuran, polyalkenamers, poly‐ε‐caprolactone, polycarbonates, polysiloxanes and respective blockcopolymers.