Diene polymerization, lanthanides

Keywords Aluminum Diene polymerization Lanthanides Organometallics ... 

Figure 9. Catalyst activity of lanthanides in diene polymerization. Data from Ref. 22.

From the early 1960s onwards, the use of lanthanide (Ln) based catalysts for the polymerization of conjugated dienes came to be the focus of fundamental studies [31]. The first patent on the use of lanthanides for diene polymerization originates from 1964 and was submitted by Union Carbide Corporation (UCC) [32,33]. In this patent the use of binary lanthanum and cerium catalysts is claimed. Soon after this discovery by UCC, Throckmorton (Goodyear) revealed the superiority of ternary lanthanide catalyst systems over binary catalyst systems. The ternary systems introduced by Throckmorton comprise a lanthanide compound, an aluminum alkyl cocatalyst and a halide donor [34], Out of the whole series of lanthanides Throckmorton... 

Fig. 2 Activity profile of lanthanide metals in diene polymerization catalysis [92], reprinted with permission of John Wiley Sons, Inc.

Bruzzone M, Gordini S (1991) Lanthanide catalysts for diene polymerization Some peculiarities and unresolved questions. Meeting of the ACS Rubber Division, Detroit, MI, USA, Oct 8-11... 

Although heterobimetallic complexes with alkylated rare-earth metal centers were proposed to promote 1,3-diene polymerization via an allyl insertion mechanism, details of the polymerization mechanism and of the structure of the catalytically active center(s) are rare [58,83,118-125]. Moreover, until now, the interaction of the cationizing chloride-donating reagent with alkylated rare-earth metal centers is not well-understood. Lanthanide carboxylate complexes, which are used in the industrial-scale polymerization of butadiene and isoprene, are generally derived from octanoic, versatic, and... 

Chart 1 Carboxylate ligands employed in industrial scale lanthanide-based diene polymerization catalysts... 

Chart 3 Alkoxide and aryloxide ligands used in lanthanide diene polymerization catalysts and model compounds... 

Diene polymerization via lanthanide propanolate-based catalytic systems was first reported by U. Pedretti et al. [162], Several types of binary and ternary initiator systems have been developed since the late 1970s (see Table 7), including zz- and zsopropanolalc ligands [162], homo- and heteroleptic lanthanide species [163-165], and different types of organoaluminum cocatalysts [162,166-168]. Despite such extensive studies, structural evidence of the formation of alkylated rare-earth metal centers remained scarce. 

Table 8 Binary and ternary diene polymerization catalysts based on lanthanide butanolates, pentanolates, and decanolates...

Heterogeneous diene polymerization catalysts based on modified and unmodified silica-supported lanthanide complexes are known as efficient gas-phase polymerization catalysts for a variety of support materials and activation procedures (see Sect. 9). Metal siloxide complexes M(()SiR3 )x are routinely employed as molecular model systems of such silica-immobilized/ grafted metal centers [196-199]. Structurally authenticated alkylated rare-earth metal siloxide derivatives are scarce, which is surprising given that structural data on a considerable number of alkylated lanthanide alkoxide and aryloxide complexes with a variety of substitution patterns is meanwhile available. 

Lanthanide hydride derivatives are commonly synthesized by hydrogenol-ysis of lanthanide alkyl complexes [212], In order to further exploit the thermodynamic stability of the Al-N bond dizsobutylaluminum hydride (DIBAH), a common cocatalyst in diene polymerization mixtures and well-established reducing agent in organic synthesis, was used in the hydrogenol-... 

Table 15 Anionic, cationic, and neutral lanthanide allyl complexes reported in diene polymerization ...

Preformation of homoleptic lanthanide tris(tetramethylaluminate) complexes Ln(AlMe4)3 (Ln = Y, La, Ce, Pr, Nd, Sm, Gd) and Et2AlCl generated extremely active and highly cis-1,4-slcrcosclective binary diene polymerization initiators (Fischbach et al., 2006, personal communication) [150]. Optimal performance in isoprene polymerization was observed for most of the lanthanide metal centers for (Cl) (Ln) ratios of 2 1 (Table 16). Only the samarium... 

Scheme 70 Polymer-bonded lanthanide-based diene polymerization catalysts. PS = DVB-cross-linked polystyrene (2% divinylbenzene), PE = polyethylene (adopted from [293])...

Evans, W.J., Giarikos, D.G, and Ziller, J.W. (2001) Lanthanide carboxylate precursors for diene polymerization catalysis syntheses, structures, and reactivity withEt2Aia. Orgarwmetallics, 20, 5751-5758. 

Table 19 Polymerization of conjugated dienes by lanthanide precatalyst and different activator...

Recently, several lanthanide complexes, based on Nd, Ln, Sm, or Yb, have been smdied for controlling stereoregularity and activity of diene polymerizations and copolymerizations. Specifically, Nd-based catalysts have shown very good stereoregularity control over the production of high CM-polybutadiene rubber [36]. 

C-H Bond activation, with lanthanides Ethylene polymerization, with lanthanides Zeigler-Natta catalyst, lanthanide Diene polymerization, with lanthanides Olefin polymerization, with lanthanides Butadiene polymerization, with lanthanides Isoprene polymerization, with lanthanides Anionic propagation, at lanthanides Living polymers, at lanthanides Pseudo-living polymers, at lanthanides Reaction orders, diene polymerization Active sites, diene polymerization... 

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