Role of back‐biting in the stereoselectivity of Ni(II)‐catalyzed butadiene polymerization

Highly active and stereospecific polymerizations of 1,3-butadiene by using bis(benzimidazolyl)amine ligands derived Co(II) complexes in combination with ethylaluminum sesquichloride

“…Recently Costabile et al, showed experimentally the backbiting coordination of the double bond of the penultimate monomer in the polymer chain which in turn stabilizes anti-allyl group. This makes anti-syn isomerization which involves the rearrangement of conformation of last inserted unit an energetically demanding process, but not a forbidden one [35]. The present BD polymerization system, devoid of any bulky ancillary ligand, had a significant temperature effect on the microstructure of the polymers as illustrated by Fig.…”

Ethylene/1,3-butadiene cyclocopolymerization catalyzed by zirconocene systems

“…As widely clarified, the cyclopolymerization of 1,3-butadiene occurs with a mechanism involving an intramolecular insertion of the double bond added to the polymeryl chain after an unusual primary vinyl insertion of 1,3-butadiene (see Scheme 1). The primary insertion of 1,3-butadiene unusual in the generally well accepted diene homopolymerization mechanism [26][27][28][29][30][31][32], which involves the secondary coordination and insertion of a monomer unit, can be ascribed to the butadiene insertion on a metal -polymeryl r bond [33,34], associated to the bulkiness of the substituent in positions 3 and 3 0 of the catalytic precursor [12][13][14][15]. In particular, it was found that the steric hindrance of ligand substituents is responsible for the formation of cyclopropane rings.…”

New (Anilidomethyl)pyridine Titanium(IV) and Zirconium(IV) Catalyst Precursors for the Highly Chemo- and Stereoselective cis-1,4-Polymerization of 1,3-Butadiene

“…A large research interest about polymerization of 1,3-butadiene has been concentrated on the search of new catalytic systems able to simultaneously control both polymer microstructure, especially a cis -1,4-structure, and molecular weight distribution ( M w / M n , MWD), which will improve mechanical and thermal properties such as toughness, impact strength, clarity, and haze of the resulting polymers. − In this framework, it is worth remarking that just a slight increase in the cis -1,4 regularity of the polymers can lead to a great improvement in the elastic properties. In the latest decades, catalysts based on titanium, cobalt, and nickel complexes were successfully utilized for this purpose. ,− For example, the catalytic systems Ni(acac) 2 /MAO (acac = acetylacetonate) and CpTiCl 3 /MAO (Cp = η 5 - cyclopentadienyl) were able to produce polybutadiene with a content of cis-1,4 units higher than 80%. − Uranium allyl compounds have been used for the production of polybutadienes with a high content of cis-1,4 units yielding a product with improved physical properties . Recently, homogeneous lanthanide based systems were shown to produce polybutadienes with more than 95% cis-1,4-structure and a relative narrow MWD (<2.0). − Moreover, it was also reported that titanium based half-metallocenes with various types of alkyl substituents on the cyclopentadienyl ring, activated by methylalumoxane (MAO), are able to promote living polymerization of 1,3-butadiene to afford polymers presenting a narrow MWD …”

“…1,[9][10][11][12][13][14][15][16] For example, the catalytic systems Ni-(acac) 2 /MAO (acac = acetylacetonate) and CpTiCl 3 /MAO (Cp = η 5 -cyclopentadienyl) were able to produce polybutadiene with a content of cis-1,4 units higher than 80%. [17][18][19] Uranium allyl compounds have been used for the production of polybutadienes with a high content of cis-1,4 units yielding a product with improved physical properties. 20 Recently, homogeneous lanthanide based systems were shown to produce polybutadienes with more than 95% cis-1,4-structure and a relative narrow MWD (<2.0).…”