bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of network models to physical gels
Authors: Clark Allan H. , Nishinari Katsuyoshi , Ross‐Murphy Simon B. , Watase Mineo
Published: March 2011

There are a number of physical models which describe properties of physical gels, such as the time dependence of viscoelastic properties, stress‐strain dependence, and the concentration dependence of gel(ation) time and of gel modulus. One of the latter, due to ourselves, has been useful for fitting data for a number of systems including PVC and gelatin gels. However one of its limitations is that it has three “molecular” parameters, and only infrequently can these be estimated from independent experiment. In some cases a better way of testing the model's viability is to compare data concurrently for different concentrations and molecular weights in a surface fit. This paper reviews earlier work and illustrates the extended technique applied to new data for agarose and PVA gels.
Swelling and fractal heterogeneities in networks
Authors: Vilgis T. A. , Sommer J.‐U. , Heinrich G.
Published: March 2011

In this paper we revisit old swelling data on polymer networks that have not been interpreted theoretically on a closed molecular basis. If the osmotic pressure of the swollen network is compared to the osmotic pressure of the corresponding uncrosslinked solution unsolved problems appear, when the relative osmotic pressure is plotted against the degree of swelling, i.e. the deformation due to swelling. A significant maximum appears which cannot be explained by any of the recently derived elastic models, such as junction constraint or other entanglement models. It is suggested in this paper that the maximum is a consequence of structural heterogeneities of fractal nature. If such fractal heterogeneities are assumed a strong maximum in the relative osmotic pressure can be reproduced. The physical reason is the different thermodynamic behavior of uncrosslinked linear chains and crosslinked self‐similar (non‐linear) polymers. The conclusion is supported by numerical (Monte Carlo) simulations.
Microgels ‐ colloidal models for the cross‐linked state
Authors: Antonietti Markus
Published: March 2011

This article describes the synthesis of various types of microgels with different cross‐linking topologies. The swelling data of the standard systems can be fitted with non‐affine theories of rubber elasticity. Light scattering shows the existence of long‐range swelling heterogeneities. The dynamic mechanical behaviour shows some peculiarities, e.g. small spherical microgels show viscous flow.

Besides statistically cross‐linked systems, critically cross‐linked as well as macroporous systems can be made. The critical systems exhibit a fractal structure scaling which depends on synthetic conditions. This dependence agrees well with the different dynamic percolation theories. On the other hand, no clear relation between structure scaling and the observed dynamic behaviour can be found.

A qualitative scheme which explains various effects observed during cross‐linking of microgels is presented.
Dynamics of junction point motions in model network polymers
Authors: Shi Jiefeng , Dickinson L. Charles , MacKnight William J. , Chien James C.W.
Published: March 2011

31P solid‐state exchange 2D NMR and spin‐lattice relaxation times (T1P) have been used to investigate the motion of a crosslink unit in model networks. The networks were formed from tris(4‐isocyanatophenyl) thiophosphate with telechelic poly(propylene glycol) or poly(tetrahydrofuran). From the variation of the 2D NMR pattern with temperature and mix time, the motion of the crosslink is identified as Brownian reorientational diffusion. Good simulations of the spectra were obtained using the Williams‐Watts distribution of correlation times. The temperature dependence of the crosslink motion follows the WLF equation. The parameters derived from the NMR data are sufficient to describe the temperature dependence and breadth of both the dielectric and mechanical loss associated with the glass transition. The T1P relaxation data fitted equally well to the Cole‐Cole or the Williams‐Watts relaxation functions. The motion of the crosslinks can be described quantitatively by the activation energies and the coupling parameters.
Comparison of irreversible and reversible cluster formation
Authors: Weißmüller Max , Merkle Gerhard , Burchard Walther
Published: March 2011

Covalent and reversible cluster molecules were synthesized by an A3B2 type gelation. Crosslinking of three‐arm hydroxyl‐terminated star polymers with 2,4‐toluenediisocyanate gave branched polymers, while the reversible analogue was made by crosslinking of tertiary amine‐terminated star polymers with bis(4‐hydroxy‐3,5‐dinitrophenyl) adipate. Gelation process was followed by static and dynamic light scattering. The extent of reacted groups was measured with UV spectroscopy. Growth of the covalent clusters could be described in terms of percolation scaling laws. The experimental gel point (POH, cr = 0.70) was shifted significantly from the theoretical predicted gel point (POH, cr = 0.50), indicating extensive ring formation during the gelation. The reversible endlinking reaction gave no macroscopic gelation, though increase of the cluster dimensions was observed. Ring formation proved to be an important side reaction in both cases; however, the ring formation ability seems to change in a different manner during the course of a gelation.
The influence of network structure on the macroscopic mechanical properties of crosslinked polymers
Authors: Kausch H. H. , Fan LU A. , Cantwell W. J. , Szöcs F.
Published: March 2011

Neat and rubber‐toughened epoxy resin systems EPN/BA and EPN/DDS with significantly different crosslink densities and glass transition temperatures were tested under widely different experimental conditions ranging from impact to long‐term loading. The resulting deformation mechanisms were examined in order to ascertain the effects of network structure and toughening modifiers. Different toughening mechanisms were observed in low‐ and high‐crosslink‐density epoxy systems, modified with the same core‐shell rubber particles.
Polymer networks in dentistry
Authors: Lindén L.Å. , Rabek J. F. , Adamczak E. , Morge S. , Kaczmarek H. , Wrzyszczynski A.
Published: March 2011

Polymer networks applied in clinical dentistry can be divided into two groups: (i) hard, solid two‐and threedimensional crosslinked structures formed during photo‐curing of dental polymeric filling compositions, and (ii) soft, hydrogel‐type of networks based on polymeric ionic complexes, used for the tightening of microchannels in teeth.

The first group is based on crosslinked di‐ and trifunctional monomers, and on solid poly(acrylic acid) ‐ inorganic glasses (“glass ‐ ionomer cements”) This group has found wide clinical applications, in spite of many disadvantages such as susceptibility towards hydrolytic, mechanical. bio‐ and enzymatic degradations, and contents of toxic, allergenic and mutagenic components.

The second group, the soft‐hydrogel type of networks, has been investigated and developed at our institute in order to tighten channels in teeth. The microchannels, with a diameter of 30–200Å in enamel and 1–3 μm in dentine, are filled with a loose, native bio‐hydrogel of protein origin. Hydrogels have the ability to swell in water of biological fluids present in the oral cavity, and can retain a significant fraction of fluid within the structure. Decreasing pH below 5.5 causes a slow dissolution of the hydroxyapatite crystals in the walls of the microchannels with a consequent widening of their lumens. Metabolites and toxins from microorganisms, which are always present in the oral cavity, can penetrate into these enlarged channels and cause inflammatory reactions in the underlying pulp tissue. In order to decrease fluid flow and inhibit penetration of microorganisms, but still allow diffusion of ions and water, we have developed and tested polymeric hydrogels based on poly(acrylic acid) and metal salts, and chitosan, which can be formed directly in the micro‐channels of dental hard tissues.
FT‐NIR Spectroscopy of some long‐chain fatty acids and alcohols
Authors: Ozaki Yukihiro , Liu Yongliang , Czarnecki MirosłAw A. , Noda Isao
Published: March 2011

Fourier‐transform (FT) near‐infrared (NIR) spectroscopy has proved to be a powerful technique in investigating structure and thermodynamic properties of long‐chain fatty acids and alcohols. In order to extract useful information from the NIR spectra, bands due to the second as well as first overtones of OH‐stretching modes of the monomeric forms were employed. It has been also found that two‐dimensional (2D) NIR correlation spectroscopy can accentuate useful information often obscured in the complicated NIR spectral data set.
Dynamic ft‐ir spectroscopy of polymer films and liquid crystals
Authors: Gregoriou Vasilis G. , Palmer Richard A.
Published: March 2011

The use of continuous‐scan and step‐scan Fourier transform infrared (FT‐IR) spectroscopic techniques to study the dynamics of the response of polymer films and liquid crystals to external perturbations is described here. The first application of dynamic stepscan FT‐IR deals with the response of various polymer films to sinusoidally modulated tensile strain. In these experiments, a small amplitude sinusoidal stress is applied to a polymeric film and the transition dipole responses are monitored as a phase lag with respect to the external perturbation. The degree of deformation is small enough to cause only linear reversible responses to the sample. The main advantage of the technique is that it can provide valuable information at the molecular level that can be used to interpret the macroscopic properties of the polymeric material under investigation. Results for heterogeneous polymers include semicrystalline high density/low density polyethylene blends and the micro‐phase separated copolymer Kratonr̀ are presented. In addition, continuous‐scan stroboscopic FT‐IR was used to explore the submolecular (functional group) contributions to the reorientation dynamics of the liquid crystal director in response to pulsed (DC) electric fields. For the nematic liquid crystal molecules, 4‐pentyl‐4'‐cyanobiphenyl (5CB) and 4‐pentyl‐4'‐cyanophenylcyclohexane (5PCH), the individual response of the rigid and floppy parts was examined.
The dynamics of glass‐forming polymers in the microscopic‐mesoscopic time scale. A quasielastic neutron scattering phenomenological approach
Authors: Colmenero J.
Published: March 2011

The dynamics of three glass‐forming polymers, PVC, PB and PI, has been investigated by time of flight (TOF) neutron scattering in a time scale from 10−13s to 1011s looking for the crossover from microscopic dynamics to segmental dynamics (α relaxation). A new analysis procedure has been applied to TOF data in order to separate harmonic vibrational and relaxational contributions. Due to the involved assumptions, this procedure can be considered only as a first approximation adequate for the case of “fragile” systems (in the Angell's meaning) like the polymers here investigated. The behaviour obtained was the same for the three polymers studied. The intermediate scattering function corresponding to the relaxational dynamics, Io(Q,t), shows two different dynamical regimes separated by a crossover time tc (≈ 2 ps), which hardly depends on Q (momentum transfer) and temperature. At t < t<c, Io(Q,t) displays a Debye‐like behaviour (exponential decay). The activation energy found for the relaxation time corresponding to this regime was in the range of 2–5 Kcal/mol, i.e., in the range of the activation energy for local conformational transitions in isolated macromolecular chains. At t > tc and, at least at high temperature, Io(Q,t) shows a Kohlrausch‐Williams‐Watts (KWW) behaviour similar to the obtained one by means of backscattering neutron techniques in the mesoscopic time scale (10−11s to 10−7s) and dielectric measurements in the macroscopic time scale (10−7s to 10°s). This KWW regime can be associated to the segmental dynamics involved in the α relaxation. A phenomenological interpretation is outlined. In this framework, the Debye‐like regime is interpreted to be the segmental dynamics free from intermolecular hindrances. Therefore, tc should be the time at which intermolecular interactions start to play a significant role concerning to the segmental dynamics. This interpretation recalls some of the basic ideas of the so called “Coupling‐Model” proposed a long time ago by Ngai.
A comparison between PA‐FTTR and FT‐Raman spectroscopies in the structural analysis of annealed injected‐moulded poly (ethylene terephthalate)
Authors: Quintanilla Luis , Rodríguez‐Cabello José Carlos , Merino Juan Carlos , Pastor Jose María
Published: March 2011

With the introduction of the Fourier Transform technique in Raman spectroscopy (FT‐Raman) and the development of new methods in FTIR, such as FTIR with photoacoustic detection (PA‐FTTR), vibrational spectroscopy has been launched into a new era of application in polymer chemistry and physics. This work provides a comparative study between PA‐FTIR and FT‐Raman techniques in which the potentials and limitations of these two methods are investigated by following and analyzing structural variations that take place in annealed injected‐moulded poly(ethylene terephthalate) (PET). Both spectroscopic techniques appear to be suitable to detect structural changes that occur in PET submitted to different annealing temperatures. We suggest that these variations are directly related to conformational rather than crystallinity changes. The main drawbacks of PA‐FTIR are the lengthy adquisition time of spectra and the photoacoustic saturation that can appear in regions with quite high optical absorption coefficient. Conversely, FT‐Raman technique does not suffer from neither of these problems. However, the sensitivity to structural changes of certain infrared bands seems to be higher than that of analogous Raman bands and small structural details such as the regularity of chain folding, can only be detected in the infrared spectra.
Analysis of orientational relaxation in binary blends of long and short polystyrene chains by fourier transform infrared dichroism and small‐angle neutron scattering
Authors: Hayes Carmel , Mendes Eduardo , Bokobza Liliane , Boué François , Monnerie Lucien
Published: March 2011

Measurements of the local orientational order and average chain anisotropy in non‐uniform polystyrene are reported. Fourier‐transform infrared dichroism spectroscopy has been used to determine the effects of short deuterated chains (Mw = 500 to 188 000) on the orientational relaxation of long entangled chains (Mw = 2 000 000) in bidisperse melts uniaxially deformed above the glass transition temperature. While the long‐chain relaxation is found to be dependent on the short‐chain concentration, the local orientational order of the latter is molecular weight dependent consistent with the classical relaxation theories. The FTIR experiments are also combined with small‐angle neutron scattering measurements which probe the deuterated‐chain anisotropy in the defomed melts. There is evidence, from the combination of the two techniques, that although the short chains possess a negligible local orientational order, there exists an important anisotopy in the short chain distribution in space.
Application of ftir spectroscopy to the study of curing of glass reinforced polyester composites
Authors: Carmen Matías M. , Larena Alicia , De La Ulagares Orden M. , Urreaga Joaquín Martinez
Published: March 2011

The effect of glass fiber reinforcements on the curing behavior of unsaturated polyester commercial resins was investigated by Fourier transform infrared spectroscopy. Two different E‐glass fibers and two commercial resins were employed. The results indicate that both the glass fiber content and the fiber size have a pronounced effect on the ultimate values of the styrene conversion. Some complications found in the infrared analysis of commercial resins are also presented.
Utilization of complex initiators for the controlled polymerization of acrylic and methacrylic esters
Authors: Vlček Petr , Dvořánek Ladislav , Otoupalová Jaroslava , Janata Miroslav
Published: March 2011

The article presents a short overview of the controlled polymerization of (meth)acrylates assisted with Li tert.butoxide as the stabilizer of active centres. The “living” homopolymerizations of 2‐ethylhexyl acrylate, butyl acrylate and allyl methacrylate, and the synthesis of fully‐acrylate block copolymers are given as examples. The reaction conditions always need to be tuned up with respect to the monomer. The stabilizing effect of lithium 3‐methylpentoxide‐3, which seems to be a highly efficient type of the tert.alkoxide stabilizing additive, is briefly shown.
Synthesis of linear and star‐shaped phosphorus‐containing telechelic polymers via living cationic ring‐opening polymerization using a halobenzene/nickel(II) bromide catalyst
Authors: Kadokawa Jun‐ichi , Kobayashi Shiro
Published: March 2011

This paper reports a living cationic ring‐opening polymerization of 2‐phenyl‐1,3,2‐dioxaphosphorinane (a six membered cyclic phosphonite, 1) initiated by a new catalyst system of a halobenzene with NiBr2. The polymerization proceeded in a living nature to produce a poly(phosphinate) 2. The polymerizations of seven‐and five‐membered cyclic phosphonites with this catalyst system are also described. The kinetic analysis of the polymerization of 1, initiated with this catalyst system, has successfully been carried out. The difference of the nature in the polymerizations of five‐, six‐, and seven‐membered monomers is discussed. Syntheses of linear and star‐shaped telechelic polymers using di‐, tri‐, tetra‐, and hexahalobenzenes as a catalyst component are disclosed.
In‐situ polymer blends via chain transfer living polymerization (CTLP)
Authors: Yoon Hae Seong , Kim Kwang Ung , Lee Jonghwi , Lee Youngjun , Hwang Sung Sang , Park Tae Seok , Cho Jaecheol , Kim Jungahn , Inahn Byeong , Char Kookheon , Quirk Roderic P.
Published: March 2011

In‐situ polymer blends of polystyrene (PS)/poly(methyl methacrylate) (PMMA) with controlled and variable different compositions and molecular weights were found to be successfully synthesized by “chain transfer living polymerization (CTLP)” methodology by a combination of size‐exclusion chromatographic analysis, differential scanning calorimetry (DSC), UV/Vis and H NMR spectroscopy, and optical microscopic analysis. The PMMAs prepared in tetrahydrofuran (THF) in the presence of polystyrene exhibit highly syndiotactic stereoregularity (over 70 mol‐%) and a glass transition temperature over 120°C. A dispersed morphology was found even for blends with over 31 vol.‐% of the weight fraction of one component due to the discrepancy in the molecular weights of two components in the PS/PMMA blends. A ternary polymer blend system having PS/PMMA/PS ‐block‐ PMMA can be generated by control of the concentration of fluorene as the chain transfer agent in the CTLP.
Recent advances in the observation of disclinations of main‐chain nematic polymers
Authors: Qian Renyuan , Chen Shouxi , Song Wenhui
Published: March 2011

Experimental observation of disclinations of main‐chain nematic polymers is reviewed. The geometry of disclination structure is discussed both from observations of schlieren texture and the theory of curvature elasticity for a two‐dimensional case with equal splay and bend moduli. The effects of non‐equal elastic moduli, the nature of the disclination core and the observation of inversion wails are briefly mentioned. Examples of experimental observation of disclinations of high topological strengths up to S=4 are given. The main experimental methods to map the director field around disclinations are 1) lamellar decoration, 2) band‐texture decoration and 3) surface microcrack decoration. The methods are discussed and compared, and examples illustrated by electron micrographs or photomicrographs are presented.
Polymer modified and stabilized cholesteric liquid crystal materials for flat panel application
Authors: William Doane J. , Yang Deng‐Ke , Pfeiffer Matthias
Published: March 2011

Polymer dispersions, even in very low concentrations, can improve the performance of cholesteric liquid crystal materials necessary for their application in flat panel displays. Normal scattering mode, reverse scattering mode and reflective mode cholesteric liquid crystal materials are described. The roll of the polymer in each of these display modes is reviewed as are the unique electro‐optic characteristics of the dispersions.
Electroclinic properties of chiral smectic a liquid crystalline polymers and block copolymers
Authors: Chiellini Emo , Galli Giancarlo , Lagerwall Sven T. , Komitov Lachezar
Published: March 2011

The scope for the synthesis and investigation of chiral smectic A liquid crystalline (LC) polymers and block copolymers is discussed. LC block copolymers can combine the molecular order of liquid crystals and the supramolecular order typical of block copolymers, thus allowing to attain information on mesomorphic responses in restricted geometries. We present a general overview on several aspects of the syntheses and properties of LC block copolymers, specifically those obtained by starting from azomacroinitiators. These materials can exhibit an electroclinic effect, that is an electrically induced molecular tilt, which is characterized by a linear dependence on the applied field and a very fast response time in the paraelectric smectic A phase. The current progress in their potential application in electrooptics is outlined.
Wholly aromatic polyesters derived from 6‐hydroxy‐5‐phenyl‐2‐naphthoic acid and 4'‐hydroxy‐3′ ‐phenylbiphenyl‐4‐carboxylic acid
Authors: Jin Jung‐Il , Huh Seung‐Moo
Published: March 2011

Two series of new wholly aromatic copolyesters were prepared from 6‐hydroxy‐5‐phenyl‐2‐naphthoic acid (HPNA) and 4‐hydroxybenzoic acid (HBA), and 4'‐hydroxy‐3'‐phenylbiphenyl‐4‐carboxylic acid (HPBA) and 4‐hydroxybenzoic acid in varying mole ratio. The polyesters were synthesized in melts using the acetylated monomers. They were characterized for their crystallinity, liquid crystallinity, thermal transitions and thermal stability by wide‐angle X‐ray diffractometry, differential scanning calorimetry, thermogravimetry and on a polarizing microscope. In general, the HPNA copolyesters revealed higher degree of crystal‐Unities and greater melting temperatures than the HPBA copolyesters. This difference is explained by the planar geometry of naphthalene moiety in the HPNA structure. In contrast, the two phenylene rings of the HPBA unit along the backbone may not be coplanar. All of the polyesters appear to be thermotropic.
Orientational phenomena in comb‐shaped liquid crystal polymers induced by laser beam irradiation
Authors: Shibaev Valéry , Kostromin Sergey , Ivanov Sergey , Läsker Lutz , Fisher Thomas , Stumpe Joachim
Published: March 2011

Action of the laser illumination on optical properties of liquid crystalline (LC) comb‐shaped acrylic and methacrylic copolymers containing cyanobiphenyl mesogenic groups and azo dye fragments has been studied. Under an illumination the cis‐trans configurational changes of dye fragments take place and reorientation of the side groups towards a direction perpendicular to the electric vector of the actinic light occurs. As a result the photoinduced optical birefringence (δn = 0.05‐0.11) appears. The detailed study of dichrotic and optical properties of polymeric films, kinetics and relaxation of δn, as well as mechanism of orientational transformations during a laser illumination are discussed. The induced optical anisotropy of the films can be changed reversibly by rotating the electric vector of the laser beam in respect to the film that may be used in reversible optical data storage.
Characterization of the chain stiffness for a mesogen‐jacketed liquid crystal polymer: Poly{2,5‐BIS [(4‐Methoxybenzoyl)Oxy] Styrene}
Authors: Wan Xinhua , Zhang Fei , Wu Peiqiang , Zhang Dong , Feng Xinde , Zhou Qi‐Feng
Published: March 2011

Narrow‐distribution fractions of poly{2,5‐bis[(4‐methoxybenzoyl)oxy] styrene} ranging in weight‐average molecular weight Mw from 1.1 × 105 to 1.96 × 106 were studied by static light scattering and viscometry in THF at 25 ° C. From Mw and the intrinsic viscosity [ η ] Mark‐Houwink‐Sakurada equation was formulated with K=7.54×10−4 and ≈=0.82. The relation between [ η ] and Mw was analyzed according to Bohdanecky for the Kratky‐Porod wormlike chain, the ranges of the mass per unit length ML and the persistence length q were estimated as 35 nm−1 M<L42 nm<−1 and 11.5 nm <13.5 nm, respectively. The values of ≈ and q indicate that the polymer, though a liquid crystal polymer of the side‐chain type, has wormlike chain in dilute solution as most main chain liquid crystal polymers.
Some reactions of alumoxanes
Authors: Pasynkiewicz Stanislaw
Published: March 2011

The reactions of tetraalkyldialumoxanes (R2Al‐O‐AlR2)n or alkylalumoxane (AlOR)n with acetylacetone, some electron donors (ethers, amines, nitriles) and alcohols were discussed. The structures of alumoxanes were also considered. Despite a lot of studies the structure is not always clear and changes with a change of many parameters such as kind of ligands, synthetic conditions (solvents, reaction temperature, molar ratio of reactants), methods of isolation etc.
Proposals for structure and effect of methylalumoxane based on mass balances and phase separation experiments
Authors: Sinn Hansjörg
Published: March 2011

Methylaluminoxane prepared from trimethylaluminium on a surface of ice mainly can be described as [Al4O3(CH3)6]4. This is shown through analysis, phase separation experiments with diethyl ether and molecular weight determinations in benzene, 1, 4‐dioxane, tetrahydrofuran and trimethylaluminium. It is discussed that the reason for forming this ball‐like structure is the saturation of four coordinated Al4O3(CH3)6. This molecule has a cavern which contains a solvent molecule or a molecule of trimethylaluminium. The consequences for the formation of the catalytically active structure together with metallocene are discussed.
Alumoxanes in Russia: Synthesis, properties and application
Authors: Belov Gennadii P. , Korneev Nikolai N.
Published: March 2011

A short review of the fundamental investigations in the fields of synthesis, properties and application of alumoxanes for the last thirties years is given.
How to reduce the ratio mao/metallocene
Authors: Kaminsky W.
Published: March 2011

The optimal ratio of Al/Zr in Metallocene/Methylalumoxane catalysts lies between 5000 to 10000. Bimetallic deactivation reactions and equilibria are responsible for this high excess. Substitution at the cyclopentadienyl or indenyl ligands can decrease the possibility for a hydrogen transfer and deactivation resulting in higher activity, higher molecular weights of the polymers and less excess of MAO. The MAO/metallocene ratio can also be reduced by supporting the metallocene on silica.
Development of a method for the determination of the “free” trimethylaluminum content in methylalumoxane
Authors: Thorn‐Csányi Emma , Dehmel Jörg , Dahlke Barbara
Published: March 2011

Ultraviolet/visible (UV/VIS) spectroscopic investigation of the reaction between tungsten oxytetrachloride and methylalumoxane (MAO) respectively trimethylaluminum (TMA) resulted in a method for the determination of the amount of “free” TMA in MAO samples. The development of the method of investigation is described.
Metallocenes/methylalumoxanes: A 13C NMR study of the reaction equilibria and polymerization
Authors: Tritto Incoronata , Sacchi Maria Carmela , Locatelli Paolo , Li San Xi
Published: March 2011

A study of the reactions of Cp2Ti13CH3CI and Cp2Ti(CH3)2 with AIMe3 (TMA) and/or methylaluminoxane (MAO) and of the 13C 90% enriched ethylene polymerization in situ in the presence of the same catalytic systems has been made by 13C NMR spectroscopy. The NMR data have been compared with the catalytic activity. Active cation‐like species such as Cp2TiMe+CI·[AIMeO]n− and Cp2TiMe+Me·[AIMeO]n− and side products have been identified. The role of “free” and “associated” AIMe3, contained in MAO solutions, has been elucidated.
Metallocene/mao polymerization catalysts supported on cyclodextrin
Authors: Lee Dong‐Ho , Yoon Keun‐Byoung , Huh Wan‐Su
Published: March 2011

By treating cyclodextrin(CD) with methylaluminoxane (MAO such as PMAO or MMAO) or trimethylaluminium (TMA) followed by Cp2ZrCl2, CD/PMAO/Cp2ZrCl2, CD/MMAO/Cp2ZrCl2 and CD/TMA/Cp2ZrCl2 catalysts were prepared. The catalysts were analyzed by 13C‐CP/MAS NMR spectrometer and ICP to examine the structure of catalyst and content of Zr and Al. Ethylene polymerization was conducted with MAO or TMA as cocatalyst. Styrene polymerization was also carried out with α‐CD/MMAO/Cp*TiCl3 and α‐CD/TMA/Cp*TiCl3 catalysts. While the ordinary trialkylaluminium such as TMA as well as MAO can be used as cocatalyst for ethylene polymerization, only MAO could initiate the styrene polymerization with α‐CD supported catalysts.
The role of dormant sites in propene polymerization using methylalumoxane activated metallocene catalysts
Authors: Jüngling Stephan , Mülhaupt Rolf , Stehling Udo , Brintzinger Hans‐Herbert , Fischer David , Langhauser Franz
Published: March 2011

Propene polymerization of methylalumoxane (MAO) activated rac‐Me2Si(Benz[e]Indenyl)2ZrCl2 (BI) and rac‐Me2Si(2‐Me‐Benz[e]Indenyl)2ZrCl2 (MBI) was studied to investigate the influence of the ligand substitution pattern and the role of dormant sites. Poly(propene) end group composition as well as regio‐ and stereoirregularities were examined by means of 1H‐ and 13C‐NMR spectroscopy. Dormant sites, resulting from 2, 1‐propene insertion, were reactivated either by β‐hydrogen transfer to propene, yielding 2‐butenyl end groups, or by 1, 2‐insertion of propene, yielding regioirregularities. Propene polymerization in the presence of hydrogen gave n‐butyl end groups and less regioirregularities as expected for hydrogenolysis of such dormant sites. Methyl substitution in 2‐position of the benz[e]indenyl ligand suppressed β‐hydrogen transfer to propene, and increased molecular weight with increasing propene concentration. Also, activation energy increased from 30 kJ/mol (BI/MAO) to 59 kJ/mol (MBI/MAO). For both catalysts activity depended on propene concentration. The order of reaction relative to propene was 1.7.
The interaction of metallocenes with selected activators a contribution to determine the formation of ion pairs
Authors: Gürtzgen Stefan , Rieger Rainer , Uzick Wolfram
Published: March 2011

Electric conductivity measurements and 1H‐NMR spectroscopy were performed to get evidence for the formation of ion pairs as key intermediates in the metallocene activation by methylaluminoxane 3 or tris[pentafluorophenyl]boron 2.
Spontaneous copolymerizations in the reactions of electronrich dienes with electrophilic olefins
Authors: Hall H. K. , Padias Anne Buyle
Published: March 2011

The spontaneous thermal reactions of electron‐rich dienes with electrophilic olefins lead to both [4+2] cycloadducts and copolymers. The mechanism proposed for the initiation of the copolymerization involves the formation of a 2‐hexene‐1, 6‐diradical. Structure‐reactivity relationships are discussed.
A few comments on early polymer studies
Authors: Morawetz Herbert
Published: March 2011

This brief review deals with early studies of addition polymerization, polycondensation and investigations of starch, cellulose and rubber. It describes early attempts to measure molecular weights and the manner in which the influence of the “colloid school” impeded the development for polymer science.
Herman Mark: Life and accomplishments
Authors: Morawetz Herbert
Published: March 2011

This short outline of Herman Mark's career covers his youth in Vienna, his activity in the army during World War I, his years at the Kaiser Wilhelm Institute in Berlin‐Dahlem where he was mostly concerned with X‐ray crystallography, his career as the director of a research laboratory of high molecular compounds of the IG Farben in Ludwigshafen, his years at the University of Vienna where he designed the first academic curriculum of polymer chemistry and his final years at the Polytechnic Institute of Brooklyn (now Polytechnic University) where he created the first American doctoral program in polymer science. His activity was crucial to the recognition of polymer chemistry as an important scientific discipline and to its international organization. He was equally at home in the academic environment, and as an industrial and government consultant. His crucial scientific contributions included the first crystal structure of a macromolecule, the first derivation of the mechanical property of a fiber from molecular parameters and the statistical theory of rubber elasticity.
From the pioneers till tomorrow
Authors: Bikales Norbert M.
Published: March 2011

The evolution of polymer science has been astounding. Since the early days when Staudinger, Mark and others pioneered the then‐new field, it has grown enormously thanks to a breathtaking collection of talent. A series of major discoveries has taken place since the 1950s, and the number of practitioners has grown impressively. Polymer science is now deeper and broader, and well poised to advance science and benefit society.
Svedberg — Discoverer of the protein macromolecules
Authors: Rånby Bengt
Published: March 2011

The(odor) Svedberg* (1884‐1971), Uppsala University, was the first professor of physical chemistry in Sweden. He started his research in 1904 as a colloid chemist. He prepared inorganic dispersions by electrical discharge through organic liquids, measured particle size and size distribution of colloids by diffusion and sedimentation rates and invented the ultracentrifuge for convection‐free sedimentation of colloidal particles. In 1924 Svedberg applied the ultracentrifuge for studies of haemoglobin in aqueous solution. Unexpectedly he found that the protein was not a gel of associated small molecules. It sedimented as macromolecules of uniform mass (68 000 dalton), i.e. is monodisperse.

In subsequent work Svedberg found that other proteins like ovalbumin (from egg white) and haemocyanins from snails and other invertebrates also are monodisperse or contain a few uniform macromolecular components. After extensive studies of soluble protein molecules from a large number of animals and plants, Svedberg classified the species and could trace the relations for the species from the molecular mass of their protein macromolecules.

Studies of soluble polysaccharides from bulbs also showed well defined macromolecules of masses that could be related to the various botanical species. Other native substances like cellulose, other wood polysaccharides and starch were found to be of high molecular mass but polydisperse.

Svedberg's research in the 1920's and 1930's gave strong experimental support for Staudinger's macromolecular concept although Svedberg, at the time of his own important discoveries, was not influenced by Staudinger. Svedberg's discovery of the protein macromolecules and their uniform molecular mass initiated the macromolecular research in biochemistry.
Research and development activities on polymer for the 21st century in korea
Authors: Kim Un Young , Kim Kwang Ung
Published: March 2011

The polymer industries have been expanded steadily from the beginning of 1970's. Accordingly, the production capacity of commodity plastics reached 5.37 million tons in 1993, which ranked fourth in the world. The market for the engineering plastics is not fully matured yet, but the recent annual increasing rate was higher than 20% for demand and 40% for production. A state of the art for research and development activities on polymer for 21st century in Korea will be briefly reviewed in terms of technology evolution, polymers for electronic industry, for environment, and for energy saving.
Polymer research in industry: Between commodities and new frontiers
Authors: Rosenkranz Hans Jürgen
Published: March 2011

The situation of polymer chemistry has changed dramatically in the last few years. However, many challenges remain for polymer research. Some representative examples are given.
Control of living anionic polymerization of (meth)acrylates: Active complex species, macromolecular engineering and possible scaling‐up
Authors: Teyssie Philippe , Bayard Philippe , Jerome Robert , Varshney Sunil K. , Wang Jin‐Shan , Heim Philippe , Vuillemin Bruno
Published: March 2011

Tailored polymerization of acrylic and methacrylic esters, particularly methyl methacrylate (MMA), has been the topic of a frantic research effort during the last decade. It is the purpose of this paper to present one of the main lines of that quest, and to evaluate its potential versus other new approaches.
Transition metal catalyzed alternating copolymerizations of olefins and co
Authors: Rix F. , Barborak J. , Wagner M. , Tahliani S. , Desimone J. , Brookhart M. , Elder D.
Published: March 2011

Well defined Pd(II) catalysts of the type (N′N)Pd(CH3)(Solv.)+ B(Arf)4‐ (Arf = −3, 5‐(CF3)2C6H3) have been prepared for living alternating copolymerizations of olefins with CO. This talk will focus on the mechanistic details of chain growth as elucidated by 1H and 13C NMR spectroscopy, model studies of key migratory insertion steps and synthesis and properties of various copolymers and block copolymers based on styrenes, CH2=CHC6H4X [X = p‐C(CH3)3, p‐OC(O)CH3, p‐OC(O)C‐t‐Bu), p‐NHC(O)(C‐t‐Bu)]. Use of the catalysts based on the C2 symmetric, homochiral ligand 2, 2'‐bis[2‐[4(S)‐(Alkyl)‐1, 3‐oxazolinyl]]propane [Alkyl = CH3, CH(CH3)2] produces a copolymer, 1, with a highly isotactic microstructure and high optical activity in contrast to achiral ligands such as 1,10‐phenanthroline which produce copolymers with predominantly syndiotactic microstructure.
Synthesis and characterization of new aromatic liquid crystalline polyesters having phenyl substituents
Authors: Choi Tae‐Gyu , Chung Sung‐Jae , Huh Seung‐Moo , Yun Yong‐Kuk , Jin Jung‐Il
Published: March 2011

Two different series of new aromatic liquid crystalline (LC) polyesters were prepared from 3‐phenyl‐4, 4'‐biphenyldicarboxylic acid (PBDA) and 1‐phenyl‐2, 6‐naphthalenedicarboxylic acid (PNDA). PBDA and PNDA were polymerized with various aromatic diols such as hydroquinone, substituted hydroquinones, isomeric naphthalenediols and 4, 4'‐biphenol, and the resulting polyesters were characterized by DSC, WAXD, and on a cross‐polarizing microscope for the study of their thermal transition and crystallization properties, and mesophases formed therefrom.
Stereospecific polymerization and chiral initiation, chiral crystallization and chiral nucleation
Authors: Qin Meifang , Bartus Jan , Vogl Otto
Published: March 2011

Helical macromolecules which are configurationally and conformationally specific can now be synthesized. Monomer structures must be selected that demand spacial restriction for monomer addition. High specificity of monomer addition during polymerization has parallels in crystallization of some inorganic salts from aqueous solution. Initiation of highly specific polymerizations with chiral initiators give helical polymers with substantial one‐handedness. Nucleation of certain inorganic salts with chiral nucleating agents, the enantiomers of the salts produce enantiomerically pure chiral salts.
Supramolecular chemistry of cascade polymers: Construction, molecular inclusion, and inorganic connectivity
Authors: Newkome George R. , Güther Ralf , Cardullo Francesca
Published: March 2011

The construction of cascade polymers with novel properties is discussed. A flexible amide‐based cascade architecture facilitates changes of the molecular hydrodynamic radius as a function of environmental pH, provided that the periphery is coated with ionizable functional groups (e.g., carboxylic acids or amines). Thus, it is possible to expand or contract the internal void domains within these cascades. By extension of the heteroatom connectivity, we have prepared a novel multifunctional molecule possessing a predetermined spherical morphology, that utilizes a ruthenium(II) metal center coordinated to two different orthogonal 2,2':6',2″‐terpyridine moieties to build the arm(s) of the cascade polymer. This technology permits the placement of multiple metal complexes at predetermined internal sites within the hydrophilic‐surfaced MicellaneTM framework. The combination of these two strategies to build cascade polymers allows the creation of an unsymmetrical bolaamphiphile constructed from two separate and distinct macromolecules. We are able to build cascade molecules either with a terpyridine unit inside or outside the polyamide sphere. The use of a connecting ruthenium(II) center allows the specific formation of a stable complex between the discrete cascade polymers.
Chirality and dendrimers; the issue of chiral recognition at the nanoscopic level
Authors: Kremers John A. , Meijer E. W.
Published: March 2011

The synthesis and characterization of two chiral dendrimers, 1 and 2, in their racemic form is presented. The chirality is based on the construction of four constitutionally different, but chemically resembling, branches to an achiral core. A multi‐substituted pentaerythritol derivative is used as core and Fréchet's aromatic‐ether dendritic wedges of different generation are used as branches. The synthetic approach makes use of the consecutive attachment of the four branches by selective deprotection of the core. Both chiral dendrimers of different size have been synthesized from the same precursor. 1H‐NMR Spectroscopy indicates an overall chiral shape for 1, while for both 1 and 2 stratified structures are observed. Several attempts to resolve both dendrimers have not been successful so far, giving rise to a discussion on the degree of chirality in these dendrimers of nanometer dimensions.
Microbial synthesis, physical properties, and biodegradability of polyhydroxyalkanoates
Authors: Doi Yoshiharu
Published: March 2011

Poly((R)‐3‐hydroxybutyrate), P(3HB), is produced by Alcaligenes eutrophus from fructose or butyric acid. The kinetics and mechanism of P(3HB) biosynthesis are presented. Four types of copolymers, poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), poly (3‐hydroxybutyrate‐co‐3‐hydroxypropionate), poly (3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), and poly (3‐hydroxybutyrate‐co‐4‐hydroxybutyrate), are produced by several bacterial strains from various carbon substrates. These microbial polyesters are biodegradable thermoplastics whose physical properties can be regulated by varying the molecular structure and composition of copolymers.
Recent advances in the field of lactic acid/glycolic acid polymer‐based therapeutic systems
Authors: Vert Michel , Li Suming , Garreau Henri
Published: March 2011

The mechanism of degradation of bioresorbable lactic acid‐ and glycolic acid‐based aliphatic polyesters (PLA/GA) is still far from being totally understood although a majority of authors agree to consider in vivo degradation as essentially hydrolytic. In the past years, we have shown that hydrolysis of large size devices is heterogeneous, i.e. faster inside than at the surface because of reaction‐diffusion phenomena involving acid‐catalyzed ester cleavage reactions and water‐soluble macromolecular fragments. The proposed mechanism is recalled together with some direct or indirect consequences, namely induced crystallization at body temperature, size‐ and formulation‐dependence of the degradation rates. From these features, one can conclude that it is now possible to increase or decrease the degradation rate and to turn on or off heterogeneous degradation by using accelerating or braking factors, however, accurate piloting of the hydrolytic degradation of PLA/GA is still not feasible.
Hydrophilic‐hydrophobic interpenetrating polymer networks and dicyanate‐based semi‐ipn materials
Authors: Kim Young Duk , Lee Bong Keun , Jeon Eun Jin , Shin Yong Cheol , Kim Sung Chul
Published: March 2011

Hydrophilic‐hydrophobic IPN materials of poly(acrylic acid)‐poly(styrene‐co‐acrylonitrile) were synthesized and the pervaporation characteristics of the IPN membranes were evaluated for the separation of ethanol/water mixture. Hydrophilic‐hydrophobic IPN materials of polyurethane‐polystyrene were synthesized and the blood compatibility of the IPN's were measured for the biomedical application. Dicyanate‐engineering plastics semi‐IPN's were prepared and the morphology and mechanical properties were evaluated for the high temperature composite matrix materials.
Mechanical and morphological investigations of reactive polysulfone toughened epoxy networks
Authors: Yoon Tae Ho , Priddy Duane B. , Lyle Gregory D. , McGrath James E.
Published: March 2011

The diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin was toughened by aminophenyl functional reactive polyethersulfones (R‐PES) or by t‐butyl terminated non‐reactive polyethersulfones (T‐PES). The molecular weights of PES were controlled to afford 5,000 to 20,000 g/mole and loadings were also varied from 5 to 30 wt.%. Epoxy networks cured with 4, 4'‐diaminodiphenylsulfone (DDS) were subjected to Tg determinations, plane strain fracture toughness (K1C) measurements, chemical resistance tests and morphological studies by SEM. Very significantly improved K1Cfracture toughness was obtained with reactive PES toughening without loss of chemical resistance, while non‐reactive PES blended epoxy resins exhibited only slightly improved fracture toughness but poor chemical resistance. It was possible to load up to 30 wt.% of PES without utilizing solvent and the maximum K1Cfracture toughness with R‐PES was around 2.2 MPa‐m 0.5, which was equivalent to the neat thermoplastic resin. Ductile fracture of the PES phase is suggested as a major toughening mechanism and this is highly dependent of the excellent adhesion developed between the PES and epoxy phases due to the chemical bonds. The systems demonstrated that chemical resistance of thermosets can be combined with the tough characteristics of thermoplastics.
Recent developments in the radiation chemistry of elastomers
Authors: Bremner T. , Hill D. J. T. , O'Donnell J. H. , Perera M. C. S. , Pomery P. J. , Whittaker A. K.
Published: March 2011

The radiation chemistry of several elastomers has been reviewed, including that of polybutadiene, polyisoprene, polyisobutylene, halogenated rubbers, ethylene‐alkene copolymers and a range of polyurethanes. The properties investigated include the yields of volatile products and radicals and the new chemical structures formed on radiolysis. The roles of double bonds and hetero‐atoms, such as chlorine, in the radiation chemistry of the elastomers has also been discussed.
Networks of rigid molecules
Authors: Müller‐Nedebock Kristian K. , Aharoni Shaul M. , Edwards Sam F.
Published: March 2011

Networks of rigid molecules do not fit into the paradigm of classical theories of rubber elasticity. Some experimental properties of rigid polyamide networks are summarised, and the basis for a theoretical understanding of such systems is discussed and elaborated in terms of the properties such as the existence of several conformational states and twist of such network elements.