Syndiospecific polymerization of styrene catalyzed by half-titanocene catalysts

Those effective catalyst precursors for syndiotactic styrene polymerization, Cp*Ti(OCH₂-CHCH₂)₃ (I), Cp*Ti(OCH₂-CHCHC₆H₄)₃ (II), Cp*Ti(OCH₂C₆H₅)₃ (III), Cp*Ti(OCH₂C₆H₄OCH₃)₃ (IV) were synthesized, and the influence of catalyst ligands on the catalytic activity and properties of polymer were investigated. The polymer thus obtained coupled with higher molecular weight and higher syndiotacticity determined by GPC and ¹³C NMR as well as solvent extraction manners, respectively. Those catalysts promoted by methyaluminoxane (MAO) as cocatalyst exhibited higher catalytic activity. Of all catalysts mentioned foregoing, Cp*Ti(OCH₂-CHCHC₆H₄)₃ (II), Cp*Ti(OCH₂C₆H₅)₃/MAO (III) and Cp*Ti(OCH₂C₆H₄OCH₃)₃ (IV) catalysts showed higher activity and stability even at fairly low Al/Ti ratio of 600, and possessed excellent control of the stereoregular insertion of monomer, exhibited a significant increase of the ratio of the propagation rates to chain transfer termination. The kinetic and titration results also indicated that those metallocene catalysts (II), (III), and (IV) showed higher catalytic activity and produced polymer with higher molecular weight, because of a great number of active species, and lower ratio of Kβtr/Kp, higher ratio of Kβtr/Ktrs which indicate that β-H elimination was predominant.     

Novel monotitanocene and methylaluminoxane catalyst for syndiospecific polymerization of styrene

Syndiotactic polystyrene (sPS) was synthesized with a novel monotitanocene complex of η⁵‐pentamethylcyclopentadienyltri‐4‐methoxyphenoxy titanium [Cp*Ti(OC₆H₄OCH₃)₃] activated by methylaluminoxane (MAO) in different polymerization media, including heptane, toluene, chlorobenzene, and neat styrene. In all cases bulk polymerization produced sPS with the highest activity and molecular weight. Solution polymerization produced much better activity in heptane than in the other solvents. Using a solvent with a higher dipole moment, such as chlorobenzene resulted in lower activity and syndiotacticity because of the stronger coordination of solvent with the Ti(III) active species, which controlled syndiospecific polymerization of styrene. With bulk polymerization at a higher polymerization temperature the Cp*Ti(OC₆H₄OCH₃)₃–MAO catalyst produced sPS with high catalytic activity and molecular weight. The external addition of triisobutylaluminum (TIBA) to the Cp*Ti(OC₆H₄OCH₃)₃–MAO system catalyzing styrene polymerization led to significant improvement of activity at a lower Al:Ti molar ratio, while the syndiotacticity and molecular weight of the yields were little affected. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1243–1248, 2001     

Bimetallic Au-Cu/CeO2 catalyst: Synthesis,structure, and catalytic properties in the CO preferential oxidation

The preparation of bimetallic Au-Cu catalysts via the decomposition of the double complex salt [Au(en)₂]₂[Cu(C₂O₄)₂]₃ · 8H₂O is considered. It is found that this method of preparation allows us to selectively obtain Au_0.4Cu_0.6 solid solution nanoparticles on the surface of a support. The composition of the particles corresponds to the stoichiometry of the double complex salt. The properties of bimetallic Au-Cu/CeO₂ catalyst and monometallic Au/CeO₂ and Cu/CeO₂ catalysts were studied during the preferential oxidation of CO in a mixture containing CO₂ and H₂O. The experiments were performed in a catalytic flow system within a temperature range of 50–250°C with a mixture of the following composition, vol %: CO, 1; O₂, 0.6; H₂O, 10; CO₂, 20; H₂, 60; and the balance, He. The weight hourly space velocity (WHSV) was 276000 cm³/(g h). The bimetallic catalyst made it possible to oxidize a considerably larger amount of CO with higher selectivity with CO₂ and H₂O in the mixture, relative to the monometallic catalysts. The preferential oxidation of carbon monoxide in the presence of hydrogen is a promising method for the deep purification of hydrogen-containing gas mixtures in order to remove carbon monoxide. The purified hydrogen-containing gas can be used to feed portable power units based on low-temperature proton-exchange membrane fuel cells, for the synthesis of ammonia, and for hydrogenation in fine organic synthesis.     

Influence of montmorillonite on syndiotactic polymerization behavior of styrene

The influence of montmorillonite (MMT) on the syndiotactic polymerization behavior of styrene was studied. To avoid the hydrophilic surface of the MMT coming into contact with the catalyst, which could poison it, SAN was introduced between the MMT and Cp*Ti (OCH₃)₃. MMT was introduced into the catalytic system as a supporter for the Ti catalyst (supported catalytic system) or just dispersed in the polymerization solvent directly (in situ polymerization system). The polymerization results showed that surface modification of MMT dramatically affected the catalytic activity as well as the syndiotacticity of the polymers. This is mainly explained by the insulator SAN preventing the formation of the inactive/little active species Si? O? Ti and other atactic active species resulting from the reaction of the ? OH on the MMT layer surface with Cp*Ti(OCH₃)₃. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Comparative Study on CO2 Hydrogenation to Higher Hydrocarbons over Fe-Based Bimetallic Catalysts

This paper reports on notable promotion of C₂ ⁺ hydrocarbons formation from CO₂ hydrogenation induced by combining Fe and a small amount of selected transition metals. Al₂O₃-supported bimetallic Fe–M (M = Co, Ni, Cu, Pd) catalysts as well as the corresponding monometallic catalysts were prepared, and examined for CO₂ hydrogenation at 573 K and 1.1 MPa. Among the monometallic catalysts, C₂ ⁺ hydrocarbons were obtained only with Fe catalyst, while Co and Ni catalysts yielded higher CH₄ selectively than other catalysts. The combination of Fe and Cu or Pd led to significant bimetallic promotion of C₂ ⁺ hydrocarbons formation from CO₂ hydrogenation, in addition to Fe–Co formulation discovered in our previous work. CO₂ conversion on Ni catalyst nearly reached equilibrium for CO₂ methanation which makes this catalyst suitable for making synthetic natural gas. Fe–Ni bimetallic catalyst was also capable of catalyzing CO₂ hydrogenation to C₂ ⁺ hydrocarbons, but with much lower Ni/(Ni+Fe) atomic ratio compared to other bimetallic catalysts. The addition of a small amount of K to these bimetallic catalysts further enhanced CO₂ hydrogenation activity to C₂ ⁺ hydrocarbons. K-promoted Fe–Co and Fe–Cu catalysts showed better performance for synthesizing C₂ ⁺ hydrocarbons than Fe/K/Al₂O₃ catalyst which has been known as a promising catalyst so far.     

CO2 conversion through combined steam and CO2 reforming of methane reactions over Ni and Co catalysts

Ni‐Co bimetallic and Ni or Co monometallic catalysts prepared for CO₂ reforming of methane were tested with the stimulated biogas containing steam, CO₂, CH₄, H₂, and CO. A mix of the prepared CO₂ reforming catalyst and a commercial steam reforming catalyst was used in hopes of maximizing the CO₂ conversion. Both CO₂ reforming and steam reforming of CH₄ occurred over the prepared Ni‐Co bimetallic and Ni or Co monometallic catalysts when the feed contained steam. However, CO₂ reforming did not occur on the commercial steam reforming catalyst. There was a critical steam content limit above which the catalyst facilitated no more CO₂ conversion but net CO₂ production for steam reforming and water‐gas shift became the dominant reactions in the system. The Ni‐Co bimetallic catalyst can convert more than 70% of CO₂ in a biogas feed that contains ~33 mol% of CH₄, 21.5 mol% of CO₂, 12 mol% of H₂O, 3.5 mol% of H₂, and 30 mol% of N₂. The H₂/CO ratio of the produced syngas was in the range of 1.8‐2. X‐ray absorption spectroscopy of the spent catalysts revealed that the metallic sites of Ni‐Co bimetallic, Ni and Co monometallic catalysts after the steam reforming of methane reaction with equimolar feed (CH₄:H₂O:N₂ = 1:1:1) experienced severe oxidation, which led to the catalytic deactivation.     

Catalytic hydrogenolysis of CFC-12 (CC1<Subscript>2</Subscript>F<Subscript>2</Subscript>) over bimetallic palladium catalysts supported on activated carbon

Experiments were conducted for the hydrogenolysis of CFC-12 (CCl₂F₂) to CH₂F₂ over bimetallic palladium catalysts (Pd-Bi, Pd-Ru) supported on activated carbon. The characteristics of the bimetallic palladium catalysts were examined with ICP, XRD, TPD, TEM, and N₂ physisorption/H₂ chemisorption and the Pd-F formation was identified by XPS analysis. The catalytic activity of the bimetallic palladium catalyst (Pd-Bi/C, or Pd-Ru/C) was superior to that of the monometallic palladium catalyst. The bimetallic palladium catalysts showed much higher conversion rates (more than 99% of it was converted) than did the monometallic palladium catalyst (< 92%) and were deactivated to a lesser extent, even at high temperatures (>320 ‡C). The bimetallic components maintained the good dispersion of the Pd on the activated carbon support.     

Decane reforming reaction over Pt,Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on Y-zeolite

Pt, Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on NaY- and HY-zeolite were examined as a catalyst for producing gasoline from n-decane via simultaneous reforming and cracking. The catalysts were prepared by calcining and reducing metal-ion-exchanged Y-zeolite with O₂ and H₂ at 300°C., respectively. Thus prepared catalysts were characterized by hydrogen chemisorption and temperature programmed desorption of ammonia. Pt-Ni/NaY and Pt-Ir/NaY bimetallic catalysts offered the improved activity maintenance compared to Pt/NaY monometallic catalyst. The catalysts supported on HY-zeolite showed higher selectivity toward C₅–C₇ and skeletal isomers of C₅–C₇- and C₈–C₁₀ than those of the catalysts supported on NaY-zeolite, which is a desired characteristic for increasing octane value of gasoline these days. However, deactivation with reaction time was much more pronounced on HY-zeolite-supported catalyst. When the catalyst was prcsulfided with H,S, the stability with time on stream was enhanced and the selectivity was quite different from that of the catalyst before presulfiding. The acidity of Y-zeolite and presulfiding of catalyst greatly influenced the activny, selectivity and stability of Pt, Ir, Pt-Ir and Pt-Ni bimetallic catalysts supported on Y-zeolite in n-decane reforming reaction.     

Structure-Sensitivity of Propylene Hydrogenation over Cluster-Derived Bimetallic Pt-Au Catalysts

A series of Pt and Pt-Au catalysts supported on TiO₂ has been studied using C₃H₆ hydrogenation as a probe reaction to determine the composition of the active catalytic surface. The catalysts were characterized by H₂ chemisorption and TEM analysis to determine concentrations of surface Pt sites for TOF calculations and metal particle size distributions, respectively. Similar TOF values for C₃H₈ formation (approximately 30 sec⁻¹) were observed for a monometallic Pt/TiO₂ and a bimetallic Pt–Au/TiO₂ sample prepared by impregnation from individual salt precursors. In contrast, the TOF for C₃H₈ formation over a Pt₂Au₄/TiO₂ sample prepared from an organometallic Pt₂Au₄ cluster precursor was decreased to 0.07 sec⁻¹, suggesting strong structure sensitivity for the hydrogenation reaction over this catalyst. Characterization results indicate that Pt on the surface of the Pt₂Au₄/TiO₂ catalyst is heavily diluted by Au atoms. In combination with the kinetic results, this suggests that the highly diluted surface ensembles of Pt are too small to effectively catalyze C₃H₆ hydrogenation, although electronic effects induced by the presence of Au adjacent to Pt sites can not be excluded.     

Synthesis and characterization of soluble polyphosphazenes having pendent Cp* Fe(dppe) groups

Summary The reaction of HOC₆H₄CH₂CN , N₃P₃(O₂C₁₂H₈)₂(OC₆H₄CH₂CN)₂ and – [{NP(O₂C₁₂H₈)}_0.8 {NP (OC₆H₄CH₂CN)₂}_0.18 ]_n with Cp*Fe(dppe)I in dichloromethane solution and in the presence of TIPF₆ affords the new compounds [Cp*Fe(dppe)NCCH₂C₆H₄OH][PF₆]1 Cp* = C₅(CH₃)₅ [{N₃P₃ (O₂C₁₂H₈)₂(OC₆H₄CH₂CN•Cp*Fe(dppe))₂] [PF₆]₂ 2 and the copolymer [{NP{(O₂C₁₂H₈}_0.8 {NP(OC₆H₄CH₂CN•[Cp*Fe(dppe)][PF₆])₂}_O.8]_n 3 respectively. The σ coordination of the Cp*Fe(dppe) fragment toward the nitrile group is indicated by spectroscopic data. The copolymer 3 is soluble in several organic solvents with no significant cross-linking and has a Mw on the order of 1.260.000. Thermal effects of the incorporation of the organometallic fragment to the copolymer were investigated using differential scanning calorimetry (DSC) and therrnogravimetric analysis (TGA). Received: 7 May 2002/Revised version: 21 March 2003/ Accepted: 27 March 2003 Correspondence to C. Diaz     

Umsetzungen des Pentamethylcyclopentadienyl‐Halbsandwichkomplexes Cp*Ta(CO)4 mit Chlor,Brom und Iod

The reaction of Cp*Ta(CO)₄ ( 1 ) (Cp* = η⁵‐pentamethylcyclopentadienyl, η⁵‐C₅Me₅) with chlorine leads to Cp*TaCl₄ ( 2a ), whereas the corresponding reactions with bromine or iodine give the oxo‐bridged complexes [Cp*TaX₃]₂(μ‐O) (X = Br ( 3b ), I ( 3c )). The oxygen atom apparently stems from a carbonyl ligand. In the presence of air, the binuclear complexes 3a , b are converted into mononuclear Cp*Ta(O)X₂ ( 4b , c ). The X‐ray structural determination of [Cp*TaBr₃]₂(μ‐O) ( 3b ) confirms a linear Ta–O–Ta bridge with a Ta–O distance of 190,4(1) pm.     

Chemisorption Complexes on Alloy Surfaces

Abstract

Three factors have greatly promoted the recent revival of interest in catalysis by alloys.

The first was the finding that in industrial catalysis certain bimetallic systems are superior to monometallic catalysts. Sinfelt [1–5] had a particularly important share in the pioneering work supporting this finding. He showed that the selectivity for catalyzing nondestructive hydrocarbon reactions is often significantly tighter for a bimetallic catalyst than for its most active monometallic constituent. Even more important was the finding that bimetallic catalysts are frequently less susceptible to poisoning by, e.g., carbonaceous residues [1–6], As a consequence, their steady-state activity will be superior to that of monometallic catalysts even if the initial activity was lower.     

Ethylene/1‐octadecene copolymerization using [η5:η1‐C5Me4‐4‐R1‐6‐R‐C6H2O]TiCl2 catalysts

Copolymerization of ethylene with 1‐octadecene was studied using [η⁵:η¹‐C₅Me₄‐4‐R₁‐6‐R‐C₆H₂O]TiCl₂ [R₁ = ^tBu (1), H (2, 3, 4); R = ^tBu (1, 2), Me (3), Ph (4)] as catalysts in the presence of Al(i‐Bu)₃ and [Ph₃C][B(C₆F₅)₄]. The effect of the concentration of comonomer in the feed and Al/Ti molar ratio on the catalytic activity and molecular weight of the resultant copolymer were investigated. The substituents on the phenyl ring of the ligand affect considerably both the catalytic activity and comonomer incorporation. The 1 /Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄] catalyst system exhibits the highest catalytic activity and produces copolymers with the highest molecular weight, while the 2 /Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄] catalyst system gives copolymers with the highest comonomer incorporation under similar conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Organometallic Derivatives of Cyclotriphosphazene as Precursors of Nanostructured Metallic Materials: A New Solid State Method

The cyclic phosphazene trimers [N₃P₃(OC₆H₅)₅OC₅H₄N·Ti(Cp)₂Cl][PF₆] (3), [N₃P₃(OC₆H₄CH₂CN·Ti(Cp)₂Cl)₆][PF₆]₆ (4), [N₃P₃(OC₆H₄-Bu^t)₅(OC₆H₄CH₂CN·Ti(Cp)₂Cl)][PF₆] (5), [N₃P₃(OC₆H₅)₅C₆H₄CH₂CN·Ru(Cp)(PPh₃)₂][PF₆] (6), [N₃P₃(OC₆H₅)₅C₆H₄CH₂CN·Fe(Cp)(dppe)][PF₆] (7) and N₃P₃(OC₆H₅)₅OC₅H₄N·W(CO)₅ (8) were prepared and characterized. As a model, the simple compounds [HOC₅H₅N·Ti(Cp)₂Cl]PF₆ (1) and [HOC₆H₄CH₂CN·Ti(Cp)₂Cl]PF₆ (2) were also prepared and characterized. Pyrolysis of the organometallic cyclic trimers in air yields metallic nanostructured materials, which according to transmission and scanning electron microscopy (TEM/SEM), energy-dispersive X-ray microanalysis (EDX), and IR data, can be formulated as either a metal oxide, metal pyrophosphate or a mixture in some cases, depending on the nature and quantity of the metal, characteristics of the organic spacer and the auxiliary substituent attached to the phosphorus cycle. Atomic force microscopy (AFM) data indicate the formation of small island and striate nanostructures. A plausible formation mechanism which involves the formation of a cyclomatrix is proposed, and the pyrolysis of the organometallic cyclic phosphazene polymer as a new and general method for obtaining metallic nanostructured materials is discussed.     

Preparation and Characterization of Bifunctional Pt-Sn/H[Al]ZSM5 Catalysts

Bifunctional monometallic Pt/H[Al]ZSM5, Sn/H[Al]ZSM5 and bimetallic Pt-Sn/H[Al]ZSM5 (tin atomic fraction, X _Sn, of 0.46) catalysts were prepared and characterized by means of XPS, EPR, TEM and toluene hydrogenation. The species on their surface as well as the presence of an effect of the electronic and/or geometric type between Pt and Sn in the bimetallic catalyst, which would result in the existence of reduced tin species (Sn⁰ and/or Sn-Pt), were determined. These species were determined through XPS and would explain the decrease in the hydrogenating activity in the toluene hydrogenation reaction.     

Unusually High Selectivity to C2+ Alcohols on Bimetallic CoFe Catalysts During CO Hydrogenation

Silica-supported cobalt and iron catalysts (10% Co and 5% or 1% Fe) were prepared and tested in a flow reactor in the hydrogenation of CO, using H₂/CO = 2:1 (molar) ratio in the feed, an overall pressure of 20 bar, and temperatures of 493, 513 and 533 K. Activity and product distribution were found to depend strongly on the composition of the catalysts. Thus, the Fe-free catalyst was selective toward C₅₊ formation (67% selectivity to C₅₊) and a low methanation rate, while the Co-free counterpart was less selective toward C₅₊, with a simultaneous increase in the formation of lighter fractions and alcohols. The behavior of the bimetallic CoFe catalysts was different. In the bimetallic CoFe10/5-c catalyst, selectivity to alcohols increased with respect to the monometallic Co10-c, and this was moderately high (15% to C₃₊ OH alcohols). In the bimetallic CoFe10/1-c sample, selectivity to alcohols was fairly high (29%), and ethanol reached the highest proportion (17%) among the alcohols. Surface and structural information concerning the activated catalysts, derived from X-ray diffraction, temperature-programmed reduction, Mössbauer, and photoelectron spectroscopy, revealed the appearance of a CoFe phase under the conditions employed during the catalyst activation. In the bimetallic cobalt–iron catalysts, this CoFe phase is suggested to be responsible for the rather high selectivity toward alcohol formation.     

Oxygen-enhanced water gas shift on ceria-supported Pd–Cu and Pt–Cu bimetallic catalysts

Aiming at enhancing H₂ production in water gas shift (WGS) for fuel cell application, a small amount of oxygen was added to WGS reaction toward oxygen-enhanced water gas shift (OWGS) on ceria-supported bimetallic Pd–Cu and Pt–Cu catalysts. Both CO conversion and H₂ yield were found to increase by the oxygen addition. The remarkable enhancement of H₂ production by O₂ addition in short contact time was attributed to the enhanced shift reaction, rather than the oxidation of CO on catalyst surface. The strong dependence of H₂ production rate on CO concentration in OWGS kinetic study suggested O₂ lowers the CO surface coverage. It was proposed that O₂ breaks down the domain structure of chemisorbed CO into smaller domains to increase the chance for coreactant (H₂O) to participate in the reaction and the heat of exothermic surface reaction helping to enhance WGS kinetics. Pt–Cu and Pd–Cu bimetallic catalysts were found to be superior to monometallic catalysts for both CO conversion and H₂ production for OWGS at 300 °C or lower, while the superiority of bimetallic catalysts was not as pronounced in WGS. These catalytic properties were correlated with the structure of the bimetallic catalysts. EXAFS spectra indicated that Cu forms alloys with Pt and with Pd. TPR demonstrated the strong interaction between the two metals causing the reduction temperature of Cu to decrease upon Pd or Pt addition. The transient pulse desorption rate of CO₂ from Pd–Cu supported on CeO₂ is faster than that of Pd, suggesting the presence of Cu in Pd–Cu facilitate CO₂ desorption from Pd catalyst. The oxygen storage capacity (OSC) of CeO₂ in the bimetallic catalysts indicates that Cu is much less pyrophoric in the bimetallic catalysts due to lower O₂ uptake compared to monometallic Cu. These significant changes in structure and electronic properties of the bimetallic catalysts are the result of highly dispersed Pt or Pd in the Cu nanoparticles.     

Fischer–Tropsch synthesis on mono- and bimetallic Co and Fe catalysts supported on carbon nanotubes

An extensive study of Fischer–Tropsch synthesis (FTS) on carbon nanotubes (CNTs)-supported bimetallic cobalt/iron catalysts is reported. Up to 4 wt.% of iron is added to the 10 wt.% Co/CNT catalyst by co-impregnation. The physico-chemical properties, FTS activity and selectivity of the bimetallic catalysts were analyzed and compared with those of 10 wt.% monometallic cobalt and iron catalysts at similar operating conditions (H₂/CO = 2:1 molar ratio, P = 2 MPa and T = 220 °C). The metal particles were distributed inside the tubes and the rest on the outer surface of the CNTs. For iron loadings higher than 2 wt.%, Co–Fe alloy was revealed by X-ray diffraction (XRD) techniques. 0.5 wt.% of Fe enhanced the reducibility and dispersion of the cobalt catalyst by 19 and 32.8%, respectively. Among the catalysts studied, cobalt catalyst with 0.5% Fe showed the highest FTS reaction rate and percentage CO conversion. The monometallic iron catalyst showed the minimum FTS and maximum water–gas shift (WGS) rates. The monometallic cobalt catalyst exhibited high selectivity (85.1%) toward C₅+ liquid hydrocarbons, while addition of small amounts of iron did not significantly change the product selectivity. Monometallic iron catalyst showed the lowest selectivity for 46.7% to C₅+ hydrocarbons. The olefin to paraffin ratio in the FTS products increased with the addition of iron, and monometallic iron catalyst exhibited maximum olefin to paraffin ratio of 1.95. The bimetallic Co–Fe/CNT catalysts proved to be attractive in terms of alcohol formation. The introduction of 4 wt.% iron in the cobalt catalyst increased the alcohol selectivity from 2.3 to 26.3%. The Co–Fe alloys appear to be responsible for the high selectivity toward alcohol formation.     

Polyphosphazenes as Solid Templates for the Formation of Monometallic and Bimetallic Nanostructures

A simple synthetic route to monometallic and bimetallic nanostructured materials is presented. Pyrolysis of the organometallic iron co-polyphosphazenes, [{[N = P(R₁)₂]_0.8[N = P(OC₆H₄CH₂CN[Fe])₂]_0.15}{PF₆}_0.32]_n (1) and [{[N = P(R₁)₂]₀₅₅[N = P(OC₆H₄CH₂CN[Fe])₂]_0.2}{PF₆}_0.32]_n (2) with R₁ = OC₁₂H₈ [Fe] = CpFe(dppe)⁺ Cp = η−C₅H₅, dppe = PPh₂(CH₂)₂PPh₂ in air affords nanoparticles of the iron pyrophosphate Fe₂Fe₅(P₂O₇)₄, while the pyrolysis of both copolymers in air and in the presence of TlPF₆ yield bimetallic Tl, Fe nanostructures. The polyphosphazene acts as a hybrid organic–inorganic template. By carbonization, the organic part of the polymer provides holes where the metallic centers grow while the inorganic P = N acts as precursor for the formation of phosphorus oxides, which form the metal pyrophosphates or the stabilizing matrix. Pyrolysis of organometallic polyphosphazene polymers containing two organometallic fragments is discussed as a new and general method for obtaining bimetallic nanostructured materials.     

Polymerization of vinyl chloride with butyllithiums and metallocene catalysts

Polymerizations of vinyl chloride (VC) with butyllithium (BuLi) and metallocene catalysts were investigated. In the polymerization of VC with BuLi, the activity for polymerization decreased in the following order; t‐BuLi > n‐BuLi > s‐BuLi. A polymer controlled structurally in the main chain was found to be synthesized from the polymerization of VC with BuLi. The molecular weights of polymers obtained in bulk polymerization were higher than those of polymers obtained in solution. A linear relationship of the M_n of the polymer and the polymer yields was observed. The M_w/M_n of the polymer did not change significantly during polymerization, although the M_w/M_n was around 2. Thermal stability of the polymer obtained with BuLi was higher than that of polymer obtained with radical initiators, as determined by TGA measurements. In the polymerization of VC with Cp*TiX₃/MAO (X: Cl and OCH₃) catalysts, polymers were obtained with both catalysts, although the rate of polymerization was slow. The Cp*Ti(OCH₃)₃//MAO catalyst in CH₂Cl₂ gave higher‐molecular‐weight polymers in a better yield than in toluene. From elemental analysis and the NMR spectra of the polymers, the Cp*Ti(OCH₃)₃/MAO catalyst gave polymers consisting of repeating regular head‐to‐tail units, in contrast to the Cp*TiCl₃/MAO catalyst, which gave polymers having anomalous units.