Polymerization catalysts neodymium

Neodymium phosphate-based catalysts were used as early as in 1978 for the polymerization of IP by Monakov et al. [249,250]. At a later stage neodymium phosphate-based catalyst systems were claimed by Asahi in a patent issued in the mid 1980s [251,252]. A neodymium-phosphate which is predominantly mentioned in the context of diene polymerization is neodymium bis(2-ethylhexyl)phosphate (NdP). In Chinese scientific literature NdP (Scheme 5) is often abbreviated by its commercial name Nd(P204)3-... 

The solubility of neodymium carboxylates in organic solvents is also improved by the addition of electron donors such as acetylacetone, tetrahy-drofuran, N,N -dimethylformamide, thiophene, diphenylether, triethylamine, pyridine, organic phosphorus compounds etc. Also the storage stability of neodymium carboxylates in organic solutions (reduction of sediment formation) is increased by these additives. Mixtures of the Nd-precursor and the respective additives are reacted in the temperature range 0-80 °C. The sequential addition of Al-compound and halide donor yield the active polymerization catalysts [409,410]. 

Table 7 Binary and ternary diene polymerization catalysts based on neodymium pro-panolates ...

Binary neodymium alk(aryl)oxide/dialkylmagnesium diene polymerization catalysts were reported by J.-F. Carpentier and coworkers [181,192], The homopolymerization of butadiene, and copolymerization with styrene and... 

Scheme 71 Preparation of heterogeneous neodymium-based diene polymerization catalysts on modified silica (adopted from [306])...

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. 

A common feature of catalysts based on 4 and 5f block elements is that of being able to polymerize both butadiene and isoprene to highly cistactic polymers, independently of the ligands involved. Butadiene, in particular, can reach a cistacticity as high as 99% with uranium based catalysts (3) and cistacticity of > 98% with neodymium based catalysts (4). This high tacticity does not change with the ligand nature (Fig. 1) in contrast to conventional catalysts based on 3-d block elements. A second feature of f-block catalysts is that the cis content of polymer is scarcely... 

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

This gives rise to dual valency state (+3 and +4) (23). As to the activity of lanthanide based catalysts we confirm a singular behavior that has been already reported by Chinese scientists (22) and that is summarized in Fig. 9. The activity of lanthanides in promoting the polymerization of butadiene and isoprene shows a large maximum centered on neodymium, the only exception being represented by samarium and europium that are not active, reasonably because they are reduced to bivalent state by aluminum alkyls, as pointed out by Tse-chuan and associates (22). 

We found that completely soluble compounds can be obtained in two ways. The first method, which is widely applicable, is to react a rare earth carboxylate with a small amount of an aluminum alkyl (11). Neodymium octoate can be converted into a product which is completely soluble in cyclohexane by reacting one mole of it with 1 to 5 moles of triethylaluminum. We also found that the rare earth salts of certain tertiary carboxylic acids are very readily soluble in non-polar solvents (12). In conjunction with a Lewis acid and aluminum alkyls, these compounds form highly active catalysts for the polymerization of butadiene. The neodymium Lewis acid aluminum alkyl molar ratio is within the range 1 (0.4-2.0) (10-40). 

A similar study with materials [Ln N(SiMe3)2 3] AS-380. (T = 250, 500, 700°C) revealed the implications of thermal pretreatment of the support for ethylene polymerization [117]. Materials featuring predominantly monopodal neodymium silylamido surface species produced the most achve catalysts [12b (100% monopodal) > 13b (40%)> 14b (25%), Table 12.6 cf, Nd[N(SiMe3)2]3 0.03 kg-PE molm h bar ]. Apparently, extensive replacement of silylamido by (surface) siloxo ligands, that is, an increase of podality of the supported species at... 

Si02-supported neodymium-based catalyst mixtures Nd(naph)3/Al2Et3Cl3/ A1( Bu)3 (54) and Al( Bu)2H (DIBAH), instead of Al( Bu)3, were also tested as initiators for the gas-phase polymerization of 1,3-butadiene by varying the polymerization temperature, nature and feed of co-catalyst and polymerization time (Table 12.8). High ds-1,4-contents (97.8-98.9%) and activities between 400 and 2300 kg-PBD molNd h bar were observed, but the polymers displayed broad molecular weight distributions of 2 < M /M < 8 [158-160]. 

Friebe, L., Nuyken, O. and Obrecht, W. Neodymium Based Ziegler/Natta Catalysts and their Application in Diene Polymerization. Vol. 204, pp. 1-154. 

In addition to these two studies the polymerization kinetics of three different Nd-compounds which were activated by DIBAH and EASC were comparatively studied. In this investigation a Nd alcoholate [NdA = neodymium(III) neopentanolate], a Nd phosphate [NdP = neodymium(III) 2-ethyl-hexyl-phosphate] and a Nd carboxylate (NdV) were compared with a special focus on the variation of the molar ratios of zzdibah/hncI and ci/ Nd [272]. For each of these ternary catalyst systems the polymerization activities depend... 

For the ternary neodymium phosphate-based catalyst systems (NdP/ DIBAH/EASC) a totally different dependence of polymerization rates on Ai/ Nd-rahos was reported [264-269,272]. According to these studies the catalyst system is highly active even at low Ai/MNd-ratios < 5 and polymerization rates decrease with increasing Ai/ Nd-ratios within the Ai/ Nd-range = 5-50 (Sect. 2.1.1.10) [272]. 

Tris-allyl-neodymium Nd(//3-C3I Ishdioxane which performs as a single site catalyst in solution polymerization was heterogenized on various silica supports which differed in specific surface area and pore volume. The catalyst was activated by MAO. In the solution polymerization the best of the supported catalysts was 100 times more active (determined by the rate constant) than the respective unsupported catalyst [408]. 

In addition to the studies in which supported catalysts are exclusively used for gas-phase polymerizations one study is available in which the supported catalyst is optimized in a solution process prior to its application in the gas phase. Tris-allyl-neodymium [Nd(/ 3- C3H5)-dioxane] which is a known catalyst in solution BD polymerization is heterogenized on various silica supports differing in specific surface area and pore volume. The catalyst is activated by MAO. In solution polymerization the best of the supported catalysts is 100 times more active (determined by the rate constant) than the respective unsupported catalyst [408]. In addition to the polymerization in solution, the supported allyl Nd catalyst is applied for the gas-phase polymerization of BD [578,579] the performance of which is characterized by macroscopic consumption of gaseous BD and in-situ-analysis of BD insertion [580]. 

Scheme 29 Polymerization of butadiene by 1,2- and 1,4-insertion with neodymium-based Ziegler/Natta-catalysts (charge and ligands of neodymium are omitted for clarity)...

Another feature of Nd-catalyzed BD polymerization which is reported by various authors is the reduction of cis- 1,4-content by the addition of donor compounds. The respective increase of trans- 1,4-moieties and decrease of cis- 1,4-moieties is also observed when the amount of the alkyl aluminum cocatalyst is increased. This feature does not depend on the nature of the Nd component and has for example been comparatively studied for three different catalyst systems (1) NdV/DIBAH/EASC, (2) neodymium neopen-... 

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