Blend polyolefin elastomers based on a stereoblock elastomeric PP

The principles of the creation of new blend polyolefin elastomers with a controlled complex of properties based on a stereoblock elastomeric PP synthesized in the presence of asymmetric ansa-metallocenes are proposed. Original blend polymer materials with reduced hardness that are based on elastomeric PPs with different characteristics and a 50–70 wt % oil-extended ternary ethylene-propylene-diene elastomer were prepared through the method of dynamic vulcanization. The molecular-mass characteristics of PP have a considerable effect on the rheological properties of polyolefin elastomers. For successful processing of the resulting blends, the pristine component, the elastomeric PP, must have a weight-average molecular mass of M _w = (8?14) × 10⁴ and a low crystallinity.     

The influence of thermoplastic elastomers on structure and crystallisation behaviour of polyolefin blends

The influence of a styrene-ethylene/butylene-styrene triblock copolymer (SEBS) on an isotactic polypropylene / polyethylene blend was investigated. For comparison binary blends with polypropylene and SEBS alone were also prepared. The blends obtained by solution mixing were characterised by small-angle x-ray scattering, light microscopy and dynamic mechanical analysis. The role of SEBS as matrix reinforcer or interfacial agent is composition dependent. Experimental data also reveal a different influence of SEBS on the binary blends than on the ternary blends containing polyethylene.     

由富烯配体合成茂金属化合物的研究

报道了一系列富烯包括烷基取代富烯、6-氨基富烯和具有稠环结构的6-氨基苯并富烯经由去氢或加成反应合成取代二茂金属络合物;(1-二甲氨基)乙烯基环戊二烯基锂与过渡金属的络合反应在一定条件下可以发生分子内碳碳偶联及二甲基胺的消除反应,得到丙烯桥联茂金属化合物,从推导的反应历程提出该反应的反应机理;尚合成了两个新的外消旋手性化合物。     

Chemical and electrochemical oxidation of metallocenes,reactions of metallocenes with mercury salts

The products of chemical and electrochemical oxidation of metallocenes, (C₅H₅)₂M (M  Fe, Ru, Os), were investigated. (C₅H₅)₂Fe on Pt and Hg anodes was oxidized to the ferricenium cation while the electrolysis of osmocene on Pt electrode led to the previously unknown (C₅H₅)₂Os^oBF₄^? salt and oxidation of ruthenocene yielded the unstable (C₅H₅)₂Ru²⁺ cation. On a mercury electrode Ru and Os metallocenes gave the adducts [(C₅H₅)₂M]₂Hg(BF₄)₂. The stability constants of mercury-containing complexes were calculated using the polarographic data. The chemical interaction of metallocenes with HgX₂ also gave mercury-containing adducts. Chemical oxidation of ruthenocene resulted in salts with the metal in the +4 formal oxidation state.     

Polyethylene waxes by metallocenes

The syntheses of low‐molecular‐weight polyethylene (PE), in the presence of catalysts based on five different metallocene frameworks, have been compared. High yields and low molecular masses, typical of industrially relevant PE waxes, can be easily achieved by using overpressure of hydrogen. Particularly suitable for the production of PE waxes are catalytic systems based on the C₂ symmetric rac‐dimethyl‐silyl‐bis‐(2‐methyl‐4‐phenyl‐1‐indenyl)‐zirconium dichloride ( 1 ) and the C_2v symmetric bis‐cyclopentadienyl‐zirconium dichloride ( 5 ). The wax yields can be substantially increased by increasing the MAO/Zr molar ratio. The control of the PE molecular weight allows an easy control of physical properties. In fact, as M_n increases in the range 10³–10⁴ g/mol, the degree of crystallinity decreases from nearly 85 to 60% while the melting temperature increases from 125°C up to 135°C. Copyright © 2010 John Wiley & Sons, Ltd.     

Electronic effects in metallocenes

A comparative study of the PMR spectra of isoelectronic ferrocene and cobalticinium salt homologues has been undertaken. With cobalticinium salts the introduction of a positive charge leads to a decrease in the ring proton shielding, while the introduction of alkyl groups has a similar effect on the electronic structure of both the cobalticinium cation and ferrocene. It was found that the introduction of primary and secondary alkyl groups caused proton signal shifts not only in those rings which were directly substituted but also in unsubstituted metallocene rings. However, within the experimental accuracy of the method it was found that the tertiary butyl group has no influence on the proton chemical shifts in the free cyclopentadienyl ring. These results, as well as other chemical data, are explained by assuming that the heteroannular action of aliphatic substituents upon a metallocene system is generally controlled by resonance effects introduced by these groups.     

Metathesis route to bridged metallocenes

A variety of bridged metallocenes of Fe(II), Ru(II), Zr(IV), or Hf(IV) were prepared in good yield by the interannular ring-closing metathesis reaction of 1,1'-diallylmetallocenes using the Ru-carbene catalyst, and the present method was extended to diastereoselective reaction to give dl- or meso-bridged metallocenes with excellent stereoselectivity.     

New reactive additives for interface modification in multicomponent polyolefin systems

New reactive additives were synthesised and used as interface modifiers in different multicomponent polyolefine systems. The synthesis was carried out in computer‐controlled reactor by means of Diels‐Alder reaction and condensation. These additives are capable of combining the benefits of dispersing and coupling agents. A part of the synthesised reactive surfactants have also synergistic effect in flame retardant systems. Their surface‐active character facilitates the reactive compounding. The undesirable transport processes of stabilisers and components of flame‐retardants in polyolefine systems could be effectively controlled by interface modification.     

Muon implantation of metallocenes: ferrocene

Muon Spin Relaxation and Avoided Level Crossing (ALC) measurements of ferrocene are reported. The main features observed are five high field resonances in the ALC spectrum at about 3.26, 2.44, 2.04, 1.19 and 1.17 T, for the low-temperature phase at 18 K. The high-temperature phase at 295 K shows that only the last feature shifted down to about 0.49 T and a muon spin relaxation peak at about 0.106 T which approaches zero field when reaching the phase transition temperature of 164 K. A model involving three muoniated radicals, two with muonium addition to the cyclopentadienyl ring and the other to the metal atom, is postulated to rationalise these observations. A theoretical treatment involving spin-orbit coupling is found to be required to understand the Fe-Mu adduct, where an interesting interplay between the ferrocene ring dynamics and the spin-orbit coupling of the unpaired electron is shown to be important. The limiting temperature above which the full effect of spin-orbit interaction is observable in the muSR spectra of ferrocene was estimated to be 584 K. Correlation time for the ring rotation dynamics of the Fe-Mu radical at this temperature is 3.2 ps. Estimated electron g values and the changes in zero-field splittings for this temperature range are also reported.     

Polyurethane elastomers from tdi and castor oil

Polyurethane elastomers were prepared by reacting castor oil with toluene diisocyanate (TDI) in pure (80:20) and crude (TDI R) grades. Different elastomers were prepared by using several stoichiometric imbalances, always in defect of NCO groups. Their characterization involved the determination of the glass transition temperature (TMA), the sol fraction (extraction with toluene) and the concentration of elastically active network chains (swelling in benzene). Experimental results were compared with theoretical predictions resulting from a statistical model of the network formation.     

An all-atom force field for metallocenes

A new all-atom force field, for the molecular modeling of metallocenes was constructed. Quantum chemical calculations were performed to obtain several force field terms not yet defined in the literature. The remainder were transferred from the OPLS-AA/AMBER framework. The parametrization work included the obtention of geometrical parameters, torsion energy profiles, and distributions of atomic charges that blend smoothly with the OPLS-AA specification for a variety of organic molecular fragments. Validation was carried out by comparing simulated and experimental data for five different ferrocene derivatives in the crystalline phase. The present model can be regarded as a step toward a general force field for metallocenes, built in a systematic way, easily integrated with OPLS-AA, and transferable between different metal-ligand combinations.     

Group 4 metallocenes in bioorganometallic chemistry

Group 4 metallocene complexes can form adducts or condensation products with a variety of typical biogenic molecules. In this account, examples are presented and discussed for the reactions of zirconocene or titanocene complexes with suitably protected/deprotected carbohydrate derivatives. Some methodological developments are shown for the attachment of aminoacid or peptide derived functional groups at the Cp-rings of the Group 4 bent metallocenes. Eventually, the reactions of methylzirconocene- and methyltitanocene cations with a series of short oligopeptides are discussed that lead to the formation of primary κO-adducts followed by O,N,O-chelate complex formation with methane evolution. The dynamic features of some such systems are discussed.     

Synthesis of fullerenol-derived elastomers and conductive elastomers

Utilization of polyhydroxylated C₆₀ in a condensation reaction with diisocyanated oligo(tetramethylene oxide) led to the successful fabrication of elastomeric poly(urethane-ether) networks. These polymer networks exhibit interesting thermal behavior at low temperatures, improved tensile strength and elongation at ambient temperatures, and enhanced thermal mechanical stability at high temperatures. Design of conducting elastomers was made by carrying out an in situ polymerization of conductive polymer precursors in an interpenetrating fashion at the near-surface of polyhydroxylated C₆₀-hypercrosslinked elastomers. Results demonstrated that elastomers with an appreciable conductivity while retaining desirable elastic properties of the network can be achieved. The room-temperature conductivity of polyaniline interpenetrated (IPN) conducting elastomer was found to be 2.0 Scm⁻¹. The tensile strength and elongation at break of one conductive IPN elastomer was found to be 20 MPa and 480%, respectively. Interestingly, the strain dependent conductivity of these conducting elastomers was found to increase progressively above 200% of elongation. These results demonstrated, for the first instance, conductivity measurements of organic conducting elastomers at an elongation length of higher than 300%, showing a r.t. conductivity of >4.0 Scm⁻¹.     

Syntheses and models for stereospecific metallocenes

Stereospecific, bridged [LL']M(R)⁺ catalysts (L, L' = substituted-cp, ind, or flu; R = hydrocarbyl) have been prepared by three new synthetic procedures. Propylene polymerizations with our new catalyst synthetic reagents, tris(pentafluorophenyl)boron (F15), magnesium dichloride, and trityl tetrakis(pentafluorophenyl)borate (trityl-F20) are compared with results obtained with the N, N-dimethyl-anilinium-F20 salt and with methylaluminoxane (MAO). Trimethylaluminium (TMA) or triethylaluminium(TEAL) scavenged poisons in the MAO free polymerizations. The site-control mechanism is discussed.     

In situ polyolefin alloys

through sequential copolymerization of appropriate ethylene-propene mixtures into a preformed polypropene, or sligthly modified polypropene matrix (PP), it was possible to achieve and optimize some important property balances of the resulting multiphase copolymers, by finely tuning both the nature of the various phases and their volume and viscosity ratios. Thus, optimum stiffness/impact strength was achieved acting on the stereoregularity and molar mass distribution (MMD) of the polypropene matrix; transparency/impact strength by adjusting heterophase to matrix viscosity or density ratios and, finally, softness/transparency by generating large concentrations of highly amorphous ethylene-propene bipolymers (EPM).     

Uniform polyolefin and polymethacrylate

Preparations and properties of synthetic uniform polyolefins and polymethacrylates are described with emphasizing the necessity of their utilization for understanding the fundamental problems in polymer chemistry. Uniform polymer is a polymer composed of molecules uniform with respect to molecular weight and constitution. While classical organic chemistry provides means of constructing uniform polymers such as poly(methylene)s in stepwise manners, recent advances in separation technology such as supercritical fluid chromatography (SFC) have made it possible to isolate synthetic uniform polymers from its homologous mixture. Combinations of stereospecific polymerizations and the SFC technique have enabled us to prepare uniform polystyrenes and poly(methyl methacrylate)s with high stereoregularities, which are very useful for systematic studies on the nature of polymers. The thermal properties of these uniform polymers are discussed in some detail.     

Axial chiral metallocenes by two-fold ring-closing metathesis

Novel doubly bridged metallocenes have been prepared by remarkably selective two-fold alkene ring-closing metathesis. The solid state structures of 3 and 5 reveal 1,2',3,4'-connectivity and screw-shaped geometry of the molecules.     

Microemulsion elastomers

ABA-triblock copolymers bearing polymerizable methacrylate end-groups are covalently crosslinked in the droplet phase of W/O- and O/W-microemulsions. The resulting microemulsion elastomers combine the structure and the phase behavior of microemulsions with solid state properties such as elasticity or stability of shape. These new materials are characterized with the help of conductivity, dynamic-mechanical and dynamic light-scattering investigations. The influence of the chemical crosslinking process on the phase behavior and the dynamics of the underlying microemulsion is discussed.Dedicated to Prof. Dr. Hans-Friedrich Eicke on the occassion of his 65th birthday     

Developments of chiral metallocenes as polymerization catalysts

This review article describes developments in chiral metallocenes as polymerization catalysts focusing on C2 symmetric ansa-zirconocene complexes. Selective synthesis of rac-isomers of ansa-zirconocenes are surveyed. Isospecific polymerizations of propylene catalyzed by chiral zirconocenes are summarized. Advanced series of polymerizations by chiral metallocenes such as asymmetric polymerization and polymerization of polar monomers are also introduced.