Neodymium catalysts

Figure 2. Insensitivity of cis content to polymerization temperature for uranium and neodymium catalysts.

The narrow molecular weight distributions accomplished by the supported catalysts were attributed to the absence of any organoaluminium co-catalyst dissocia-tion/reassociation processes at the heterogenized active neodymium centers. Furthermore, the order of the grafting sequence seemed to have minor implications for the catalyst performance. Control experiments have been conducted to explain the lower activity [0.9 (47) and 1.1 kg-PBD molNd h (48)] of the supported neodymium catalyst. Accordingly, an increase of the catalyst concentration (48) and use of a nonporous silica support (49) suggested that monomer diffusion and accessibility of the Nd centers are limited by the relatively small mesopores [dp = 2.4 (47) and 2.5 nm (48), after grafting]. 

Andreussi P, Lauretti E, Miani B (1994) Europrene Neods Improved cis- 1,4-Polybutadiene by Neodymium Catalysts, Stepol, Milano, Italy, Jun 6-10... 

A 250-ml reaction vessel was used as the polymerization reactor. Each polymerization reaction was carried out either under static conditions in a freezer, where the container was placed in a bath of glycol, or dynamically, by subjecting the container to agitation in a tank of glycol. Isoprene monomer having a purity of 99.2% was used. All polymerizations were conducted in 10-g containers and cyclohexane at 15°C with a solvent/monomer mass ratio of 9. In a typical polymerization the neodymium catalyst/diethyl aluminium chloride base varied from 150 to 500 pmol per 100 g of isoprene. 

Entry Quantity of Neodymium Catalyst (pmol) Reaction Time (h) Conversion Rate (%) Inherent Viscosity (dl/g) Mooney Viscosity cij-1, 4-Content Using MIR (%)... 

The tertiary amine can be aliphatic, cycloalkyl, or heterocyclic (including pyridine). The reaction of NaOH with an amine containing two distal alkene units, followed by addition of a neodymium catalyst leads to a bicyclic amine. " ... 

The f-transition metal catalysts were first described by von Dohlen [98] in 1963, Tse-chuan [99] in 1964 and later by Throckmorton [100]. In the 1980s Bayer [14] and Enichem [101] developed manufacturing processes based on neodymium catalysts. The catalyst system consists of three components [102] a carboxylate of a rare earth metal, an alkylaluminum and a Lewis acid containing a halide. A typical catalyst system is of the form neodymium(III) neodecanoate/diisobutylaluminum hydride/butyl chloride [103]. Neodymium(III) neodecanoate has the advantage of very high solubility in the nonpolar solvents used for polymerization. The molar ratio Al/Nd/Cl = 20 1 3. Per 100 g of butadiene, 0.13 mmol neodymium(III) neodecanoate is used. With respect to the monomer concentration, the kinetics are those of a first-order reaction. 

Later the growth model developed for a neodymium catalyst system was applied for the butadiene polymerization in gas phase. The ideas concerning the initial polymerization stages are in agreement with a core—shell model .The subsequent polymerization stages correspond to the polymeric flow model . 

It is generally accepted that, in the polymerisation of dienes on lanthanide catalysts, the growing chain is attached to the transition metal by an 7t-allyl bond and that the chain growth occurs by incorporation of the monomer via the metal-carbon o-bond. In the case of neodymium catalysts, the delocalised 7t-allyl type structure of the terminal unit has been observed by spectroscopic methods [8, 26, 28, 58-60]. The results reported in these papers show that the relative contents of cis-l,A- and tri2ns-1,4-units in polydienes depend on the type of solvent used, the polymerisation temperature, structure of diene monomer, and the composition of lanthanide-based catalysts. These data can be interpreted in terms of the concept of isomerisation equilibrium between anti- and syn-forms of n-allyl terminal unit. One of the arguments in favour of the existence of this isomerisation... 

Use of complex lanthanide catalysts allows a very high c/s-1,4 placement of isoprene monomer and preparation of polymers that are very close to natural rubber [212]. Thus, complex neodymium catalysts can yield polymers that are greater than 98% c/s-1,4 polyisoprenes. The preparation of such catalyst, however is difficult. Evans et al. reported, however, that simple Tmla, Ndia, and Dyl2 will initiate polymerization of isoprene without any additives and can also yield high c/s-1,4 placement [213] ... 

Neodymium catalysts show a different behavior. In this catalytic complex the neodymium is probably in the trivalent state and at least one Nd-Cl bond is present [369]. The AlEt3-Ti(OR)4 system is also a catalyst in which some alkoxy groups remain bonded to the titanium. Both catalysts give cis-, A isotactic polypentadiene. The anionic ligands bonded to the neodymium or the titanium atom of the catalytic species force the new monomer to reaet to the isotactic structure. 

POLYMERS FROM HYDROGENATED POLYDIENES PREPARED WITH NEODYMIUM CATALYSTS... 

Polybutadiene obtained by rare earth metal compounds has very high cis-1,4 content, and the polymerization is quasi-living. Therefore, we investigated in detail the modification of polybutadiene by neodymium catalyst with tin compound. 

A procedure was suggested for intensifying die complexation of neodymium ehloride with isopropyl alcohol in preparation of the neodymium catalyst for polyisoprene S5mthesis by using a small-size tubular turbulent difihiser-eonfiiser apparatus in the step of the reaction mixture formation. 

Intensification of the complexation of neodymium chloride with isopropyl alcohol by preliminary mixing of the reaction mixture in a tubular turbulent difiuser-confuser apparatus was studied. The procedure ensures acceleration of the process, incorporation of a larger amount of isopropyl alcohol in the complex, and high activity of the neodymium catalyst in the polyisoprene S5mthesis. 

Recently, Cai et al. (1984) declared that propylene can be polymerized with supported neodymium catalysts NdClj L/MgCl2 and NdCl3 L/MgCl2/AlCl3. ... 

Polymerization of propylene has not been successful with rare earth coordination catalysts under mild conditions for quite a long time. Cai et al. (1984) reported that propylene can be polymerized by a supported neodymium catalyst NdClj L/MgCl2 at 60°C and 9 atm with catalytic activity of 1077 g PP/gNd. Cogrinding NdClj L/MgClj with AlClj raised the catalytic activity, but the isotacticity of the polymer is only about 30%. 

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