bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metallocenes for polypropylene: Polymerization performance and computer modeling
Authors: Burkhardt Terry J. , Murata Masahide , Vaz Roy J. 
Published: March 2011

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractStereospecific 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

AbstractThe 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

AbstractA 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

AbstractDepolarized 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

AbstractUsing 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

AbstractLow 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

AbstractMacrocyclic 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

AbstractAllylic 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

AbstractThere 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

AbstractCyanate 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

AbstractFully 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

AbstractThe 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

AbstractTheories 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

AbstractFT‐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

AbstractThe 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

AbstractThe 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

AbstractHydrooligomerizations 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

AbstractMono(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

AbstractOrganolanthanide (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

AbstractThe 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

AbstractA 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

AbstractThree 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

AbstractCryoscopic 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.