bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermotropic copolyesters of 4‐hydroxybenzoic acid
Authors: Kricheldorf Hans R. , Conradi Arnd , Pakull Ralf , Schwarz Gert
Published: March 2011

Copolyesters of 4‐hydroxybenzoic acid were prepared by thermal polycondensation of 4‐acetoxybenzoic acid with various acetylated comonomers, such as 4‐mercaptobenzoic acid, 3‐hydroxybenzoic acid, N‐(4‐carboxyphenyl)4‐hydroxyphthalimide or hydroquinone in combination with 1,12‐dodecane bistrimellitimide. The copolyesters were characterized by elemental analyses, inherent viscosities, 1H‐ or 13C NMR spectroscopy, DSC‐measurements, WAXS‐measurements at temperatures between 25 and 425°C, microscopic observation, thermomechanical and thermogravimetrical analyses. Copolyesters containing 4‐mercaptobenzoic acid or N‐(4‐carboxyphenyl)4‐hydroxyphthalimide possess a reversible first order phase transition which represent a change of modifications and not a melting process. Both classes of copolyesters adopt the same kind of high temperature modification as poly(4‐hydroxybenzoate), namely a pseudo‐hexagonal chain packing. In contrast, copolyesters of 3‐hydroxybenzoic acid or copoly(ester imide)s with aliphatic spacer containing more than 50% 4‐hydroxybenzoic acid form a nematic phase over a broad temperature range. However, in the case of copolyesters derived from 3‐ and 4‐hydroxybenzoic acid the homogeneous nematic melt is thermodynamically unstable and gradually turns into a heterogeneous more or less crystalline material with blocks of 4‐hydroxybenzoate units.
Suspension polymerization of vinyl chloride and the processibility of poly(vinyl chloride)
Authors: Lukáš Rudolf
Published: March 2011

The most important technological procedure in the production of PVC is the suspension polymerization of vinyl chloride, as processibility of the polymer may be influenced to a considerable extent by the choice of polymerization conditions. Structure heterogeneities in PVC powders manifest themselves in plasticized PVC by the occurrence of “fish eye” particles. This review concerns the formation and properties of these particles and discusses the causes of their difficult processibility. Also, the relation between polymerization process and PVC dehydrochlorination is discussed and a new mechanism of its initiation based on the reactivity of cisoid enone structures is proposed. These structures catalyze elimination of hydrogen chloride from regular units of PVC by an interchain enzyme‐like mechanism giving rise to chloroallyl structures.
Structural parameters of the network formed first in in‐situ sequential interpenetrating polymer networks
Authors: Tabka M. T. , Widmaier J. M. , Meyer G. C.
Published: March 2011

As part of a study concerning poly(propylene glycol)‐based polyurethane / poly(methyl methacrylate) interpenetrating polymer networks, polyurethane networks were synthesized at various dilutions of the reaction medium and at different values of the [NCO]/[OH] ratio. The network defects arising in such materials were evaluated by three independent experimental approaches: solvent extraction, swelling behaviour, and compression measurements. It was found that the networks with the least defects are formed at high precursor concentration, with a [NCO] over [OH] excess of about 7%.
On the uniaxial stress‐strain dependence of highly swollen chemically crosslinked networks
Authors: Zrinyi M. , Kilian H.‐G. , Horkay F.
Published: March 2011

Many experiments show that the second Mooney‐Rivlin coefficient disappears for highly swollen chemically cross‐linked gels. Hence we are led to a paradox: Highly swollen gels seem to behave phenomenologically like phantom networks. Due to the finite extensibility of network chains, entanglements and excluded volume effects, one should ‐on the contrary‐ expect non‐Gaussian behaviour. On the basis of the phenomenological van der Waals equation of state, we have concluded that the virtual ideality of highly swollen gels is the consequence of a compensation between global interactions and excluded volume effects.
Pressure‐volume‐temperature measurements on polymers and polymer mixtures
Authors: Walsh David J. , Dee Gregory T. , Ougizawa Toshiaki
Published: March 2011

We have measured the PVT properties (density as a function of pressure and temperature) for polymers and polymer mixtures and analyzed these in terms of equations‐of‐state. The Cell Model equation (CM) gives a better description of the PVT properties of the pure polymers than the equation of Flory, Orwoll and Vrij (FOV). For the pure polymers we obtain the hard core pressure and hard core temperature. The hard core pressure depends on the cohesive energy, whereas the hard core temperature depends on the energy divided by the entropy. When we use the pure component parameters to describe mixture phase diagrams the CM equation is more consistent with experimental data. For the mixtures the energy depends on those of the pure components modified by an interaction parameter. The interaction parameter can thus be determined from the hard core pressures and temperatures. For high polymer mixtures the resulting parameter determined from the hard core pressure is unphysically large and negative whereas that from the hard core temperature is unphysically large and positive. Neither value coincides with those required to explain the phase diagrams or those obtained from methods such as heats of mixing of oligomers. We suggest possible reasons for this discrepancy.
Analysis of fracture behaviour of fibre reinforced polypropylene using R‐curve concept
Authors: Grellmann Wolfgang , Seidler Sabine , Nezbedova Eva
Published: March 2011

Experimental results for investigation of dynamical crack resistance curves in the instrumented Charpy impact test on polypropylene (PP)/glass fibre composites are presented. For this purpose the multiple specimen R‐curve method, stop‐block technique is used. With the aid of J‐integral versus stable crack growth (δa) curves the influence of a special coupler system on crack toughness as resistance against stable crack growth is discussed. It is shown that it is possible to quantify different energy dissipative processes with the new fracture mechanical material value J × T7 (T7 ‐ tearing modulus). The problems of determining physical crack initiation values for short fibre composites are discussed. The physical material background for using the ‘plastic hinge’ model to describe the deformation behaviour of PP/glass fibre composites is shown, using the example of selected crack opening displacement (σ) versus δa curves.
The effect of crosslinking of polyolefins on the crack growth rate during three‐point bending
Authors: Chodék Ivan
Published: March 2011

The effect of crosslinking on the stress ‐ strain curves and on the crack growth rate was investigated in three point experiments for notched samples of polyethylene, polypropylene, blends of PE and polypropylene, and PE filled with silica. The crosslinking was found to affect positively the tear resistance of multiphase materials. The stress ‐ strain curves as recorded during experiments for uncrosslinked samples show maxima which are entirely a result of the notch growth. The dependence is almost linear if the curves are recalculated with respect to the change of the sample cross‐section during the experiment. The same curve for crosslinked materials indicates a significant portion of plastic deformation. The rate of the crack growth of crosslinked samples is approx. by one order of magnitude lower than that of uncrosslinked materials.
Coupling of the phase and relaxation transitions in polymer mixtures
Authors: Shibanov Y U. D. , Godovsky Y U. K.
Published: March 2011

The coupling and the competition of two phase transitions (demixing and crystallization) and the coupling of both demixing and vitrification are investigated during phase transformations under far‐from‐equilibrium conditions. The coupling leads to formation of the different non‐equilibrium morphologies and to kinetic pecularities of phase transformations.
Regularities of adhesive failure in particulate filled polymers
Authors: Berlin A. A. , Zhuk A. V. , Knunjantz N. N. , Oshmjan V. G. , Topolkaraev V. A.
Published: March 2011

The effect of adhesion between matrix and filler on mechanical properties of composites is analyzed. It is shown, that the loss of adhesion (extension of exfoliated surface) leads to a marked reduction of uniaxial tension modulus. Regularities of interphase crack growth were found and dependences of initial (critical) and final angles of exfoliation upon mechanical and scale factors were obtained.
Development of ceramic‐matrix composites — A challenge to chemistry
Authors: Ziegler G.
Published: March 2011

In this contribution the state‐of‐the‐art of ceramic‐matrix composites is briefly summarized. A critical review of the different types of ceramic composites is given, particularly emphasizing the challenge to chemistry. As example two important problem areas, which may only be solved by contributions from chemistry, are discussed: some low‐ temperature processing techniques for ceramic composites which avoid damage of fibres by thermal or mechanical loading and/or by chemical reactions as well as the optimization and control of interfaces.
Lattice model theory of chain stiffening and relaxation properties of macromolecules in the nematic LC state
Authors: Gotlib Yuliy , Medvedev Grigoriy , Fridrikh Sergey
Published: March 2011

The relaxation properties of polymer chains In the nematic LC‐state or in the external quadrupole field may depend both on the variation of the conformation in the ordered state and on the activation barrier of the molecular (or external) field. This barrier should be surmounted during reorientation of chain elements. The lattice model theory of chain stiffening of macromolecules in the LC‐state is proposed. The calculation and comparison of the longitudinal and transversal relaxation spectra for the continuous and discrete rotameric mechanism of the mobility are performed. For the simplest model of a heterogeneous polymer chain the possibility of the more complex relaxational behavior i.e. the existence of two longitudinal and two transversal relaxation spectra was shown.
Degradation behaviour of polyurethane studied by linear temperature programmed pyrolysis FTIR spectroscopy
Authors: Herzog Klaus
Published: March 2011

FTIR spectrometers with two measurement beams offer the possibility to record and process spectra from 4000 to 400 cm−1 taken every 30 seconds in situ from a polyurethane film which is subjected to a programmed linear rise of temperature from ambient to 400°C and to take quasi simultaneously the spectra of the gaseous pyrolysis products. As an example, polyurethane (PUR) prepared from diphenylmethane diisocyanate (MDI) with polyesteralcohol from adipic acid was thermally degraded to isocyanate and polyester alcohol. Carbodiimid was found in the pyrolysis products and carbon dioxide was detected in the pyrolysis gas. The isocyanate evaporation and the thermal degradation of polyester alcohol were studied.
Polyolefin blends
Authors: Kresge E. N. , Lohse D. J. , Datta S.
Published: March 2011

Polyolefin blends of proper morphology exhibit physical properties from high‐extension, low‐modulus elastomers to high‐modulus tough resins. The morphology is controlled by rheology of the polymers, blending conditions and the use of graft polymer compatibilizers. The graft polymers were synthesized by polymerizing isotactic polypropylene with unsaturation in an ethylene‐propylene‐diene terpolymer. Graft copolymers result in smaller phase sizes and a more stable morphology for the blends. The development of polyolefin blends is reviewed with emphasis on materials with high concentration of elastomer phase.
Anionic synthesis of polystyrene and polybutadiene heteroarm star polymers
Authors: Quirk Roderic P. , Lee Bumjae
Published: March 2011

The use of living linking reactions of poly(styryl)lithium with 1,3‐bis(1‐phenylvinyl)benzene followed by crossover reactions with styrene or butadiene monomers has been used to prepare four‐armed heteroarm, star‐branched polymers. Bimodal molecular weight distributions have been observed for crossover reactions with both styrene and butadiene. Addition of THF ([THF]/[Li]=14–32) for crossover to styrene and lithium sec‐butoxide for crossover to butadiene produces monomodal molecular weight distributions. Symmetrical, four‐armed star polystyrenes have been synthesized; properties have been compared with a corresponding polymer prepared via a silicon tetrachloride linking reaction. Heteroarm, star‐branched polymers with two polystyrene arms and two polybutadiene arms with high 1,4‐microstructure have been prepared.
Effect of composition and structure on rheological properties of styrene‐butadiene block copolymers
Authors: Horák Zdenêk , Kruliš Zdenêk , Večerka František , Kováf Josef
Published: March 2011

Styrene‐butadiene copolymers of the S‐B‐S and S‐B‐S‐B‐S types, both unmodified and extended with paraffinic‐naphthenic oil, were studied by dynamic mechanical spectroscopy and capillary rheometry. In the triblocks at low deformation rates, an increase in 1‐vinylethylene unit content leads to an increase in complex dynamic viscosity |η*|. This may be explained by their different supermolecular structure with a higher proportion of long relaxation times. The pentablocks show a considerable effect of molecular parameters on their flow behaviour at low deformation rates. In all the systems, steady viscosity η shows no significant differences at higher shear rates. Obviously the supermolecular structure is disintegrated in these conditions and the effect of chemical structure is negligible. An expected decrease in viscosity in the whole range of deformation rates was observed with the oil‐extended copolymer. The dependences of complex dynamic viscosity on angular frequency were compared with those of steady viscosity on shear rate but no unequivocal conclusion as regards the validity of the Cox‐Merz rule could be reached.
Recovery of photodegraded polymers by surface treatment
Authors: Decker Christian
Published: March 2011

A two‐step process has been developed in order to renovate highly photodegraded polymers. It was applied to clear and pigmented commercial PVC plates, which were exposed to accelerated weathering. The brown highly degraded top layer was first removed by sandpapering, which makes the color disappear and restores the original impact resistance of PVC. In a second step, a thin film of a UV‐curable acrylic resin was sprayed onto the PVC plate, which thus recovered its initial transparency. After a 1s UV exposure, the coated PVC was found to exhibit an excellent resistance to chemicals, weathering and scratching. One of the distinct advantages of this new low‐cost recycling process is that it is based on existing technologies and can be carried out directly on the plastic structures to be renovated.
Effect of chain aggregation and ionic interactions on the proton dissociation equilibria of weak polyacids
Authors: Cesàro Attilio , Sagui Maria Celeste
Published: March 2011

A theoretical interpretation of the dissociation behavior of weak polyacids is given. Incorporation of conformational variability in the free energy of a polyelectrolyte system extends the validity of the counterion condensation theory to cases in which cooperative transitions and/or aggregation phenomena take place. Comparison of the theoretical predictions with experimental data on ionic polysaccharides, either natural or derivatives, is presented.
Biomimetic oxidation of thiol and application to odor‐removing fiber
Authors: Shirai Hirofusa , Hanabusa Kenji , Koyama Toshiki , Tsuiki Hisanaga , Masuda Etsuko
Published: March 2011

The oxidation of HO‐CH2‐CH2‐SH (RSH) by molecular oxygen and Fe(III)‐ as well as Co(II)‐multicarboxyphthalocyanine and the mechanism in homogeneous aqueous system were investigated. As application to enzyme‐like heterogeneous catalysts, Fe(III)‐as well as Co(II)‐octacarboxyphthalocyanine were supported on amorphous enriched rayon staple fiber and their enzyme‐like activities were estimated. These fibers were applicated to new odor‐removers acting as artificial enzyme systems.
Polymer networks containing polyether, polyamine or polysulfide chains
Authors: Goethals Eric J.
Published: March 2011

An overview of newer or less‐known synthetic methods for the synthesis of polymer networks containing ether, amine or sulfide functions or a combination of these functional groups with other functional groups, is presented. Emphasis is given on new methods starting from well ‐ defined telechelic prepolymers. A number of these prepolymers are obtained by living cationic systems, more particularly cationic ring‐opening and cationic vinyl ether polymerizations.
Preparation and photoluminescence characteristics of polysiloxane pendant tris(2,2′‐bipyridine)ruthenium (II) complex
Authors: Nagai Keiji , Nemoto Nobukatsu , Ueno Yukihiko , Ikeda Koji , Takamiya Nobuo , Kaneko Masao
Published: March 2011

Polysiloxanes containing pendant tris(2,2′‐bipyridine)ruthenium(II) complex (Ru(bpy)32+) were prepared by reaction of polysiloxane‐pendant 2,2′‐bipyridine (PSiO‐bpy) with cis‐Ru(bpy)2Cl2. In methanol solution, the polymer pendant Ru(bpy)32+ showed absorption maximum at 456nm and emission maximum at around 609nm, both of which are shifted to longer wavelength than the monomeric Ru(bpy)32+. The lifetime τ0 of the excited polymer complex with low Ru(bpy)32+ content was almost the same as that of the monomeric one in methanol (830ns), but τ0 of the polymer with higher complex content was shorter because of a concentration quenching. In a solid state, τ0 was much shorter (306–503ns) than that in a methanol solution contrary to the conventional polymeric system. Higher complex content in the polymer film caused higher glass transition temperature (Tg), but shorter τ0. These results indicate concentration quenching in the polymer film. The excited polymer pendant Ru(bpy)32+ was quenched by oxygen, and the relative emission intensity followed the Stern‐Volmer equation. In a methanol solution the quenching rate constant (kq) was the same order of magnitude as the monomeric complex, and independent of the complex content in the polymer. In a film, kq was higher for the polymer with higher complex content.
Cationoid living polymerisations
Authors: Plesch Peter H.
Published: March 2011

The cationoid living polymerisations have many of the characteristics of pseudo‐cationic (φ‐cat) polymerisations and none of those of cationic polymerisations. In contrast to the φ‐cat polymerisations by protonic acids, which are transfer‐dominated, those giving living polymerisations are propagated by esters which are part of a donor‐acceptor complex involving a “third reagent”. There are three types: The first is exemplified by an ester which is activated by a metal halide, e.g. HMI (from monomer M + HI) + ZnBr2, or oligoisobutyl acetate + BCl3. The second type is exemplified by a polymer triflate complexed by a dialkyl sulphide. The reagents which change the reactivity of the ester are termed “modifiers”. The acceptors, e.g. ZnBr2, which co‐ordinate to a donor group on the polymer, are positive modifiers (or activators). The donors, such as R2S, which coordinate onto an acceptor group at the end of the polymer, e.g. the acidic β‐H, are negative modifiers (or moderators).

The propagation by both types of modified ester probably involves a 6‐centred cyclic transition state. The same applies to a third type of φ‐cat propagation, in which a polymeric ester reacts with a D‐A complex formed from M + I2.

The formation of unwanted non‐living polymers of high DP and/or broad DPD, together with those resulting from living polymerisations, happens because the metal halides used in these reactions not only form the φ‐cat propagating centres, but also react with ionogenic impurities to initiate concurrent, short‐lived cationic polymerisations. These parasitic reactions can be suppressed by an excess of base, e.g. an ester or halide ions, which scavenge protons and carbenium ions. This phenomenon indicates that, whatever else is propagating the living polymerisations, it is unlikely to be carbenium ions.

The kinetic equations for the living polymerisations, developed here, make it possible to calculate propagation rate‐constants from rate and DP data; such calculations are shown for a variety of published results.
Cationic polymerization of cyclocarbonates
Authors: Kricheldorf Hans R. , Weegen‐Schulz Bettina , Jenssen Jörg
Published: March 2011

Trimethylenecarbonate (TMC) and neopentane diol carbonate (NPC) were polymerized with two groups of initiators, proton and carbenium ion donors or Lewis acids. Initiation with methyltriflate, triflic acid or triethyloxonium tetrafluoroborate in solution gave satisfactory yields (up to 90%) but only low molecular weights (Mn < 5000), due to rapid back‐biting degradation. IR‐ and NMR‐spectroscopy demonstrate that the propagation steps involve alkylation of the carbonyl oxygen and cleavage of the alkyl‐0 bond by analogy with lactones. Whereas borontribromide and trichloride form solid complexes with NPC or TMC, but do not initiate a polymerization, boron trifluoride is a good initiator. High yields (up to 99,5%) and high molecular weights (Mw > 105) were obtained. However, in analogy to triflic acid initiated polymerizations all polycarbonates contain ether groups. The molar fraction of the ether groups increases with the reaction temperature. High molecular‐weight polycarbonates containing ether groups were also obtained with other strong Lewis acids such as SnCl4, SnBr4 and TiCl4. In contrast, weak Lewis acids such as Bu2SnBr2 Bu3SnOMe and Sn(II)2‐ethylhexanoate yield polycarbonates free of ether groups. This finding and the NMR‐spectroscopically identified endgroups suggest that these weak Lewis acids initiate an insertion mechanism.
New aspects on the photoinitiated free radical promoted cationic polymerization
Authors: Yagci Yusuf , Schnabel Wolfram
Published: March 2011

General aspects of the photoinitiated free radical promoted cationic polymerization are discussed. The applicability of pyridinium salts, a new class of photoinitiators, of appropriate redox potential Ered1/2 in oxidizing carbon‐centered free radicals to carbocations capable of initiating the polymerization of various compounds is demonstrated. Moreover, the use of polysilanes as source for readily oxidizable free radicals is described. Furthermore, possibilities for preparing block copolymers by free radical promoted cationic polymerization are pointed out.
Stereochemistry of oligomers in stereospecific and conformational specific ionic polymerizations
Authors: Vogl Otto , Garner Charles , Simonsick William J. , Kratky Christoph , Ute Koichi , Hatada Koichi
Published: March 2011

Low molecular weight oligomers of methyl methacrylate (MMA) and perhaloacetaldehyde were studied as to their composition, end groups and stereochemistry. The oligomerization of methyl methacrylate can be directed toward almost pure isotactic or toward almost syndiotactic oligomers depending upon the intitiating system used. Perhaloacetaldehydes showed a stereospecificity which depended upon the size and bulkiness of the side group in the polymer chain. There is no dependence of the sterospecificity based on the initiating system and only isotactic polymers could be obtained which are not only stereospecific but also conformationally specific giving conformational specific isotactic 4/1 helices.
The role of association/complexation equilibria in the anionic polymerization of (meth)acrylates
Authors: Kunkel Dietmar , Müller Axel H. E. , Janata Miroslav , Lochmann Lubomír
Published: March 2011

The kinetics of the anionic polymerization of methacrylates and acrylates in THF as well as the MWD of the polymers formed depend on the concentration of active centres and of additives, such as lithium halides and lithium alkoxides. These results are discussed on basis of multiple equilibria between non‐associated, associated, and complexed ion pairs which are supported by viscosity measurements. The position of these equilibria determines the rate of polymerization, whereas the dynamics of interconversion determine the polydispersity. In the absence of additives the rate of monomer addition to non‐associated ion pairs competes with the rate of association. Addition of lithium chloride mainly affects the rate of interconversion between dormant and active species, whereas lithium tert‐butoxide forms adducts which stabilize the active centre.
Recent development in stereochemical control of heterogeneous Ziegler‐Natta catalysts
Authors: Soga Kazuo , Uozumi Toshiya , Park Joon Ryeo , Shiono Takeshi
Published: March 2011

A completely aspecific catalyst was prepared by supporting TiCl3 on MgCl2. The catalyst isospecificity could be drastically converted from aspecific into isospecific either by adding ethyl benzoate or by changing the cocatalyst from Al(C2H5)3 to Cp2Ti(CH3)2. On the other hand, the catalyst system composed of SiO2‐supported CpTiCl3 and methylaluminoxane (MAO) gave atactic polypropylene as well as a random copolymer of ethylene and propylene with frequent chemical inversion of propylene units. It was also found that the CpTiCl3/SiO2‐MAO catalyst system can afford poly(ethylene‐co‐1‐hexadecene) containing a large amount of 1‐hexadecene. The mechanisms of stereochemical control(isospecificity and regiospecificity) are discussed from these results.
Polyolefin based gas separation membranes
Authors: Lin Shangan , Lin Shaokun , Chen Xuexin
Published: March 2011

Three kinds of membrane material were prepared by means of modification or functionalization of polyolefin. They are terpolymer of ehtylene, propene and butene‐1 (EPB), poly (butadiene‐ block‐ dimethylsiloxane) copolymer (PB‐ b‐ PDMS), and sulfonated EPDM metallic salt ionomer (S‐ EPDM‐ Me). These materials are used as oxygen enrichment membranes. Some interesting results were obtained from the separation of oxygen and nitrogen, e. g. the permeation coefficients of oxygen (P) for EPB, PB‐b‐PDMS and S‐EPDM‐Me are 23.5 × 10−10, 59.7 × 10−10 and 12.1 × 10−10 cm3(STP) · cm/cm2 · s · cmHg, and the separation factors (P/P) are 3. 8, 4. 5 and 4. 5, respectively.
Monte Carlo modelling of the polymer glass transition
Authors: Paul W. , Binder K. , Batoulis J. , Pittel B. , Sommer K. H.
Published: March 2011

We are proposing a lattice model with chemical input for the computer modelling of the polymer glass transition. The chemical input information is obtained by a coarse graining procedure applied to a microscopic model with full chemical detail. We use this information on Bisphenol‐A‐Polycarbonate to predict it's Vogel‐Fulcher temperature out of a dynamic Monte Carlo Simulation. The microscopic structure of the lattice model is that of a genuine amorphous material, and the structural relaxation obeys the time temperature superposition.
A QSPR for the Tg of polymers: The Koehler‐Hopfinger approach using the tripos 5.2 force field
Authors: Vaz Roy J.
Published: March 2011

The Koehler Hopfinger model1,2 has been modified. The modification has worked fairly well with the Tripos 5.2 Force Field together with charges calculated using the Gasteiger Marsili method. This modification has been checked using the same monomers as those used in the original reference. The table, with monomers from a few chemical functionalities such as acrylates, ethers etc. was subjected to a Hierarchical Cluster Analysis which provided justification for creating “designer” equations for each class of chemical functionality. The “designer” equations for acrylates and olefins are described. The scheme utilized the Partial Least Squares (PLS) method as available within Sybyl 5.41 in order to draw the correlations.
Donor‐ and acceptor‐modified metallocene‐based homogeneous Ziegler‐Natta catalysts
Authors: Fischer David , Jüngling Stephan , Mülhaupt Rolf
Published: March 2011

The polymerization kinetics of propene polymerization using metallocene/methylaluminoxane (MAO) homogeneous catalysts have been investigated to explore the role of donor/acceptor interactions and to enhance the catalyst productivities. In the case of the non‐stereospecific Cp2ZrCl2/MAO model system it has been demonstrated that, in addition to the well known irreversible deactivation, reversible deactivations, which are second order relative to the zirconium active site concentration, account for the decay of the polymerization rate. While MAO injection during polymerization enhances the polymerization rate, zirconocene addition deactivates the catalyst which can be reactivated by injecting additional MAO. A sequence of dynamic equilibria involving the formation of active cationic metallocene intermediates as well as inactive zirconocene species, e.g., zirconocene dimers, is proposed. Lewis base and Lewis acid additives have been added as probes to examine the role of such equilibria in the case of metallocene‐based catalyst systems such as MAO‐activated Cp2ZrCl2, racemic ethylenebisindenyl zirconium dichloride (EBIZrCl2), and racemic ethylenebis (4,5,6,7‐tetrahydroindenyl) zirconium dichloride (EBTHIZrCl2). While the conventional donors such as 2,6‐ditert.butyl‐4‐methylphenol (BHT) and 2,2,6,6‐tetramethylpiperidine (TMP) reduce catalyst productivities, even at very low donor/Al molar ratios, increasing propene concentration and addition of trimethylboroxine (TMB) substantially enhance catalyst productivities and affect molecular weights of the polypropylene produced with metallocene/MAO catalysts.
Synthesis and properties of stereoregular fluoro‐polymers via ring‐opening metathesis polymerization of fluorinated norbornenes and norbornadienes. An overview and progress report
Authors: Davies Geoffrey R. , James Feast W. , Gibson Vernon C. , Hubbard Hugh V. ST. A. , Ivin Kenneth J. , Kenwright Alan M. , Khosravi Ezat , Marshall Edward L. , Mitchell Jonathan P. , Ward Ian M. , Wilson Brian
Published: March 2011

Since the first report of the ring‐opening metathesis polymerization of fluorinated monomers in 1979 considerable advances in precision and control of such syntheses have been achieved through the introduction of well defined initiators. It is now possible to carry out well controlled living and stereoregular polymerizations. The products of such syntheses can display unusually high relaxed dielectric constants, an observation which is crucial to the assignment of their tacticities and probably significant with regard to possible applications of this type of material.
Alkylidenic polymerization of alkynes from w‐based initiators: Kinetics and mechanism of activation by lewis acids
Authors: Lucas Christine , Soum Alain , Fontanille Michel
Published: March 2011

The polymerization of alkynes initiated by metathesis catalysts proceeds via a mechanism similar to that of the ring‐opening metathesis polymerization of cycloalkenes. Various polymerizing systems have been claimed by several authors as bringing about living character; they point out the strong influence of the substituents carried by the monomer which have been shown to hinder transfer and termination processes. Whatever the initiator used, the activity of the polymerizing system is low; this paper deals with the activation of Rudler type initiator by Lewis acids. The effect of AlR3, AlR2Cl, AlRCl2, BR3 and B(OR)3 is presented and discussed.
General principles of polymer processing modeling
Authors: Agassant J.F. , Vergnes B. , Vincent M.
Published: March 2011

Specific rheological and thermal properties of molten polymers and their consequences on the numerical simulation of forming processes are first reviewed. The strong coupling between flow kinematics and material temperature is pointed out. According to geometrical specificities, to the type of deformation the material is submitted to and to thermal conditions, continuum mechanics and energy balance equations can be simplified and more or less sophisticated rheological equations can be used. Finally, these considerations are applied to the modeling of steady extrusion and fiber spinning and of unsteady molding processes.
Reactive blending of polymers by interfacial free‐radical grafting
Authors: Lambla Morand , Seadan Manus
Published: March 2011

In blends of immiscible polymers, amphiphilic species are needed for both morphological stabilization and improvement of the mechanical properties throughout successive processing steps. In order to obtain the required concentration of amphiphilic copolymer at the interface, it seemed of interest to test the possibility of creating these species by in situ reactivity at the interface, for instance by condensation reactions occurring between functionalized polymers. There is another possibility based on the fact that most of the polymers are hydrocarbon compounds, so they are subjected to free‐radical reactivity by hydrogen abstraction on the different hydrocarbon sites. The created free‐radical polymeric species may react together leading to the well known reactions of crosslinking, grafting and/or chain degradation. Therefore, this work deals with reciprocal free‐radical reactivity of two kinds of semi‐crystalline polymers, namely one polyolefin (LDPE, HDPE, PP or EPR) associated with a polyamide (PA‐11 or PA‐6). The reaction has to occur mainly at the interface, where the resulting grafted copolymers have to be anchored for final stabilization of the biphasic system. The level of interfacial grafting and the resulting properties of the reacted blends were characterized carefully, confirming the efficiency of the interpolymeric grafting.
NMR characterization of biodegradable polyesters
Authors: Chûjô Riichirô
Published: March 2011

Biodegradable polyesters obtained by fermentation of Alcaligenes eutrophus are characterized with the aid of H, D, C NMR spectroscopy. Copolymers of 3‐hydroxybutyrate and 3‐hydroxyvalerate are Bernoullian or mixture of two Bernoullian copolymers depending on fermentation conditions. The reverse reaction was found in the reaction catalyzed by beta‐ketothiolase during biosynthetic pathway. The fractional population of gauche and trans conformers around the skeletal CH‐CH2 bond is 0.6:0.4 for both poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) in chloroform. This result suggests the possibility of formation of isomorphic crystals between copolymers with different composition ratios.
Chain segment ordering in uniaxially strained networks: A deuterium NMR investigation
Authors: Deloche Bertrand
Published: March 2011

The deuterium NMR (2H‐NMR) is used for probing the chain segment orientation in polymer networks under uniaxial stress. The method is based on the observation of an incomplete time averaging of quadrupolar interactions affixed to deuterated segments. The samples are end‐linked polydimethylsiloxane networks. The 2H‐NMR experiments are performed either on labelled network chains or an labelled probe polymer chains dissolved in the network. The basic results are the following:

— The induced uniaxial order is related to a uniaxial dynamics of chain segments around the direction of the applied constraint.

— A permanent orientation is observed on free polymer chains dissolved in the deformed networks.

— The mean degrees of orientational order induced along short and long chains in bimodal networks are the same.

These experimental facts appear as evidences for cooperative orientational couplings between chain segments in the deformed networks.
ESR studies on polymers with particular electronic and magnetic properties
Authors: Roth Hans‐Klaus , Krinichnyi Viktor I.
Published: March 2011

Measurements on insulating and conducting polymers from the polyaniline (PANI) family and investigations on semiconducting poly(tetrathiafulvalenes) (PTTF) have been used for illustration and discussion of some methodical questions of electron spin resonance (ESR). This concerns especially the new possibilities of the recently developed high‐resolution ESR in the 2 mm wave band. It was applied for the study of the nature and dynamics of paramagnetic centres (PC) and charge carriers in PANI and PTTF. The rate of the quasi‐one‐dimensional (1D) intrachain electron motion and of the three‐dimensional (3D) interchain electron hopping has been estimated separately. In iodine ‐ doped PTTF the maximum electrical conductivity is 10−4 S ·cm−1. It is almost identical with the 3D‐conductivity estimated by ESR and shows the typical temperature dependence of a semiconductor. The quasi‐1D‐conductivity is several orders of magnitude higher and shows in its dependence on temperature similarities with a metal. The PANI samples show in the highly doped form a maximum conductivity of about 10 S ·cm−1 and relativly small differences between the 1D‐ and 3D‐conductivity, supporting the model of metallic islands.
Synthesis of polysiloxanes with electron‐donating groups by anionic ring‐opening polymerization
Authors: Chojnowski Julian , Rózga Krystyna , Fortuniak Witold , Kowalewska Anna
Published: March 2011

Anionic kinetically controlled ring opening polymerization of cyclotrisiloxane is explored as a method of synthesis of copolymers having the chain composed of dimethylsiloxane units and siloxane units bearing an uncharged nucleophilic (electron‐donating, ED) group. Model monomers for these studies are derived from hexamethylcyclotrisiloxane (D3) in which one methyl group is replaced by the organophosphorus group of general formula ‐ (CH2) nP(X)Ph2 where X is lone pair, O or S. This method is shown to give significant advantages over the thermodynamically controlled homopolymerization and copolymerization of nucleophile‐substituted cyclosiloxanes which have so far been used for synthesis of ED substituted siloxane copolymers. The yield of the copolymers is much higher and the molecular weight distribution is narrow. The arrangement of the ED substituents along the chain, although not purely uniform, is much more regular as compared with the statistical distribution. The content of cyclic oligomers was higher than in the polymerization of unsubstituted D3, which is rationalized on the basis of intramolecular interaction of the counter‐ion with the ED groups.
Possibilities offered by plasma modification and polymerization to enhance the bio‐ and hemocompatibility of polyester membranes
Authors: Schué F. , Clarotti G. , Sledz J. , Mas A. , Geckeler K.E. , Göpel W. , Orsetti A.
Published: March 2011

The deposition of films from an argon plasma containing a mixture of ethylene oxide or hydrogen and perfluorohexane was tried to obtain very hydrophobic, less hydrophobic and intermediate coatings. This paper studies more extensively the deposition of a thin coating from a perfluorohexane and hydrogen plasma on polysulfone and polyhydroxybutyrate membranes to optimize their surface properties without affecting their filtering properties. The plasma deposition of smooth and very hydrophobic fluorocarbon coatings seems to increase the bio‐ and hemocompatibility of poorly biocompatible membranes. The treated substrates were characterized by measuring the mass variations, surface profilometry and contact angle measurements, as well as scanning electron microscopy and electron spectroscopy for chemical analysis.
Particle morphology effects on the performance of PMMA filled with aluminium hydroxide in a variety of fire tests
Authors: Hughes P. , V. Jackson G. , N. Rothon R.
Published: March 2011

The effect of aluminium hydroxide particle size and shape has been investigated on the performance of (polymethyl methacrylate) composites in a number of flammability tests. As a subsidiary exercise correlation between the tests has been investigated. The work has shown the expected effect of particle size on performance, with surface area giving the best measure of particle size if non‐spherical particles are involved. While the smallest particles always give the best results, the effect varies markedly according to the test and is most pronounced in the ISO ignitability test. Some possible explanations for these effects are proposed but more experiments are needed to choose between them. Correlation between the various tests is generally poor and reliance on any one of them for product development would be unwise.
Pyrolysis of flame retardants and fire protected polymers
Authors: Kettrup A. , Matuschek G. , Cyrys J. , Ohrbach K. H.
Published: March 2011

The simultaneously working combination of thermal analysis and mass spectrometry (TA/MS) is a very useful method for studying the degradation process of polymeric materials during thermal treatment [1–7]. Beside the thermal effects, as recorded from thermogravimetry (TG) or differential thermal analysis (DTA) the evolved degradation products can be determined and identified by the on ‐ line coupled mass spectrometer. Additional their temperature depending abundance can be registrated.

Combustion of polymers in horizontal (BIS) or vertical (VCI) furnaces and subsequent off line high resolution GC/MS analysis of pyrolysis products is suitable for the simulation of burning processes
Characterization of fire retardant polymer blends by temperature resolved in‐source pyrolysis mass spectrometry
Authors: Luijk R. , Pureveen J. , Commandeur J. M. , Boon J. J.
Published: March 2011

The characterization of fire retardant polymer blends by temperature resolved in‐source pyrolysis mass spectrometry (PYMS) is demonstrated with a few examples. Electron impact (EI) and electron capture negative ionization (ECNI) were used to identify the thermal degradation products of polymer blends containing brominated fire retardants.

PYMS (EI mode) offers an analytical instrument for a fast analysis of unknown mixtures of polymers and for the presence of fire retardant additives. Under electron impact conditions, in vacuo, low‐molecular weight additives like fire retardants mainly evaporate from the polymer matrix. PYMS (EI mode) has been used for the characterization of addition polymers like polystyrene and acrylonitrile‐butadiene‐styrene copolymer, and for condensation polymers like the polyester poly(butylene terephthalate).

Applying electron capture negative ionization, at low argon pressure in the ionization chamber, a more realistic pyrolysis situation is created because the premature loss of volatile additives is suppressed. The selectivity of ECNI for electron accepting groups like bromine makes it possible to study the influence of brominated compounds on the degradation processes in the melt. This is demonstrated by our studies on polystyrene and acrylonitrile‐butadiene‐styrene copolymer. High‐molecular weight pyrolysis products in the m/z range of 1000 ‐ 2000 are detected for p‐bromopolystyrene and for a blend of high impact polystyrene with the fire retardant system decabromodiphenyl ether/antimony(III) oxide. In addition to the formation of antimony bromides shown in earlier studies, the emission of the synergist antimony(III) oxide as a dimeric cluster (Sb4O6) or as a reduced Sb4 cluster is observed under PYMS conditions.
Chemical and physical properties of foamed cokes and their effect on inflammability
Authors: V. Gnedin E. , Novikov S. N. , A. Khalturinskij N.
Published: March 2011

By means of IR and Raman spectroscopy chemical and physical properties of foamed cokes, formed during combustion and pyrolysis of PP based compositions, containing intumescent fire retardants (IFR) were investigated. It was established that thermal conductivity coefficients of coke material lie in the range of 0.12–0.32 W/m/K and are weakly dependent on the initial composition of IFR. It was shown that the effectiveness of IFR is mainly determined by the internal microstructure of the foamed cokes and the kinetic parameters of their formation.
Chances and limitations of high‐performance polymers
Authors: Wartusch Johann
Published: March 2011

High Performance Polymers, especially when inherently flame retardant, are of potential interest for electrotechnical and electronic applications and are systematically investigated. In the course of R&D work on these materials ‐ in spite of a number of properties of high interest ‐ some deficiencies were found as, for example, predominantly poor metal adhesion. Further, in individual cases they possess poor stress cracking resistance, limited thermal stability and/or only medium hydrolytic stability. Moreover the industrial application of HPP is hindered by higher prices and nonavailability in larger quantities. In case of no success in current efforts (tailor made blends, surface modification) these deficiencies might contribute to a certain decline of HP polymers as already observed in a few cases.
Using pressure to improve polymer performance
Authors: Kleintjens L. A.
Published: March 2011

Pressure has been rediscovered as an additional parameter that can be used in optimizing the performance of traditional polymers. Some interesting advanced applications are under development. This paper reviews some promising research trends in areas such as process optimization, enhanced processing, the formation of polymer particles, polymer gels and plastics recycling.
Exchange and free radical grafting reactions in reactive extrusion
Authors: Hu Guo‐Hua , Flat Jean‐Jacques , Lambla Morand
Published: March 2011

The potential of two types of reactions for reactive extrusion was evaluated in our laboratory: exchange reactions of copolyesters and free radical grafting of monomers onto polyolefins. Specifically, the alcoholysis of ethylene and vinyl acetate copolymers, the transesterification of ethylene and alkyl acrylate copolymers (EAA) and the aminolysis of alkyl acrylate copolymers were investigated as the exchange reactions while the grafting of maleic anhydride (MA) onto polypropylene (PP) as the free radical reactions. The exchange reactions are very slow without catalysts. Tin derivatives, such as dibutyl tin dilaurate (DBTDL) and dibutyl tin oxide (DBTO), are good catalysts for the alcoholysis and the transesterification, but not for the aminolysis. For the latter, tautomeric compounds, such as 2‐pyridone and 2‐mercaptopyridone, are efficient. Comparative kinetic studies showed that, for all the three exchange reactions, the reacting medium (solution or the homogeneous melt) does not affect their reaction mechanisms nor their intrinsic rate constants. Additionally, mechanical mixing does not contribute to the overall reactions. As for the free radical grafting of MA, the presence of electron‐donating monomers and styrene (ST) in particular was shown to be very effective in improving the grafting yield while minimising the degradation of PP. This was proven to be due to the formation of a charge transfer complex between MA and such a monomer.
Poly(arylether oxazole)s and poly(arylether thiazole)s with pendent trifluoromethyl groups
Authors: Maier Gerhard , Nuyken Oskar , Hecht Reinhold
Published: March 2011

Bis(oxazolyl)benzenes and bis(thiazolyl)benzenes containing fluorine atoms and trifluoromethyl groups in the heteroaromatic moieties have been synthesized. These compounds can be used as monomers for the preparation of poly(arylether oxazole)s and poly(arylether thiazole)s with pendent trifluoromethyl groups. The high reactivity of the new oxazole monomers is demonstrated by the synthesis of the corresponding poly(arylene ethers) under extremely mild reaction conditions. The polymers have been characterized by spectroscopical methods, DSC, and dynamic thermogravimetry.
Reaction between polyesters and phosphorus compounds in the molten state
Authors: Jacques B. , Legras R. , Devaux J. , Nield E.
Published: March 2011

The reactions occurring between polyesters and phosphorus compounds in the molten state are investigated. A large molecular weight increase is observed in blends of Poly(ethylene terephtalate) and Poly(butylene terephtalate) after triphenyl phosphite addition. The formation of links containing phosphorus atoms between the polyester chain ends has been established. The weakness of this bond makes the observations difficult. An effect of phosphite on promoting the direct esterification between chain ends is suggested but not definitely proved yet.