Organolanthanide complexes, initiation

Table 4. Polymerization of alkyl acrylates initiated by organolanthanide complexes... 

Divalent organolanthanide complexes can also initiate MMA polymerization. A divalent lanthanide complex, as a single-electron transfer reagent, can readily react with the monomer to generate a radical anion species, which subsequently couples into a bimetallic trivalent lanthanide enolate intermediate, which is the active center. Therefore, divalent organolanthanide complexes serve as bisinitiators for MMA polymerization [160]. 

Well-controlled block co-polymerization of 1-olefins with MMA or -caprolactone using the unique dual catalytic function of organolanthanide complexes which are active toward polymerization reactions of polar and non-polar monomers has been achieved with bridged [Me2Si(CsR4)2]LnFI (Ln = Y, Sm) type complexes. These initiators are highly active in co-polymerization processes without the presence of any co-catalyst (Scheme 271).985... 

SmH(C5Me5)2]2 system increased with increasing conversion, but MJMn remained constant, irrespective of the conversion. For p-propiolactone, the use of YOR(C5Me5)2 was more favorable. On the other hand, divalent organolanthanide complexes can initiate the polymerization of lactones, but the resulting polymers had rather broad molecular weight distributions. 

In 1992 Yasuda et al. [236, 237] reported that organolanthanide complexes of the type Cp 2Sm-R (where Cp is pentamethyl cyclopentadienyl, and R is either an alkyl, alkylaluminum or a hydride) initiate highly syndiotactic, living polymerizations of methacrylates. It was also reported that lanthanide complexes such as Cp 2Yb(THF)i 3, Cp 2Sm(THF)2, and (indenyl)2Yb(THF)2 can also initiate polymerizations of methylmethacrylate [238]. Although very low initiator efficiencies were... 

Nodono, M. Tokimitsu, T. Tone, S. Makino, T. Yanagase, A. Chain transfer polymerization of methyl methacrylate initiated by organolanthanide complexes. Macromol. Chem. Phys. 2000, 201, 2282-2288. 

Polymerization of methyl methacrylate ( = MMA) has been effected with the organolanthanide precatalysts [(C5Me5)2Sm( -H)]2 and (C5Me5)2LnMe(THF). Both complexes have been found to initiate the living, highly syndiospecific polymerization of methyl methacrylate, Eq. (12) [62],... 

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