Rare earths/main group metal alkyls catalytic systems for the 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene

Abstract

A series of lanthanum and neodymium complexes comprising the half-lanthanidocenes Cp*La(BH 4 ) 2 (THF) 2 (Cp* ¼ C 5 Me 5 ) (1) and Cp*Nd(BH 4 ) 2 (THF) 2 (2), the trisborohydrides La(BH 4 ) 3 (THF) 3 (3) and Nd(BH 4 ) 3 (THF) 3 (4), the trichlorides LaCl 3 (THF) 3 (5) and NdCl 3 (THF) 3 (6), the triisopropoxides La(O i Pr) 3 (7) and Nd(O i Pr) 3 (8), and the triaryloxide Nd(OC 6 H 3 -t Bu 2 -2,6) 3 (9) has been assessed for the chain transfer polymerization of isoprene. A transmetalation process is occurring efficiently with the borohydride complexes in the presence of magnesium dialkyl. A gradual decrease of the 1,4-trans stereoselectivity of the reaction is observed at the benefit of 3,4-selectivity with increasing quantities of magnesium dialkyl. This can be at least partially attributed to the growth of 3,4 polyisoprene units onto the magnesium atom. By combining dialkylmagnesium and trialkylaluminum, a 1,4-trans stereospecific reversible coordinative chain transfer polymerization of isoprene is reached using the half-lanthanocene Cp*La(BH 4 ) 2 (THF) 2 . V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: [4640][4641][4642][4643][4644][4645][4646][4647] 2010

Synthesis and characterization of soft-hard stereoblock polybutadiene with Fe(2-EHA)3 /Al(i -Bu)3 /DEP catalyst system

“…When the [Al]/[Fe] ratio was lower than 10, the resultant polymers were amorphous and consisted of nearly equal amount of 1,2‐ and cis −1,4 structure, and the rrrr contents were in a range of 38–47%. Meanwhile, the 1,2‐content of the polymer increased, and the M n decreased gradually with increasing [Al]/[Fe] ratio from 2 to 8, indicating a typical character of chain growth transfer polymerization . When the [Al]/[Fe] ratio further increased to 10 and above, s‐1,2‐PBDs with high 1,2‐contents (84.8–93.0%) and syndiotacticity (81.5–83.6%) were obtained.…”

Highly trans-1,4-stereoselective coordination chain transfer polymerization of 1,3-butadiene and copolymerization with cyclic esters by a neodymium-based catalyst system

“…46 decrease of stereoregularity was observed by raising the CTA stoichiometry. 17,18,46 Mg(n-Bu) 2 acted as both cocatalyst and CTA in this system. 17,18,46 Mg(n-Bu) 2 acted as both cocatalyst and CTA in this system.…”

“…S2), the peaks located at 32.85 and 130.14 ppm are attributed to the methylene and methyne carbons of the trans-1,4 unit, and the weak signal at 27.5 ppm is diagnostic of the cis-1,4-unit. 18,20 Interestingly, as the [Mg]/[Nd] ratio increased from 3.0 to 6.0, the M n of the polymer decreased almost half from 22500 g/mol to 10300 g/mol and the molecular weight distribution (MWD) remained quite narrow (M w /M n = 1.6-1.7), which is a typical character of chain growth transfer polymerization. 18,20 Interestingly, as the [Mg]/[Nd] ratio increased from 3.0 to 6.0, the M n of the polymer decreased almost half from 22500 g/mol to 10300 g/mol and the molecular weight distribution (MWD) remained quite narrow (M w /M n = 1.6-1.7), which is a typical character of chain growth transfer polymerization.…”

“…The past decades have witnessed remarkable advances in a variety of living/controlled polymerization (CLP) techniques such as anionic, cationic, and radical polymerizations that allow the precise control of molecular weight and polydispersity as well as composition of (co)polymers. [13][14][15][16][17][18] In contrast, much less research has been directed at CCTP of 1,3-butadiene (BD), especially for the case of trans-1,4 CCTP. In addition to the common features of CLP techniques, CCTP is of particular interest in terms of catalyst economy, the control and design of polymer microstructure, [1][2][3][4][5] and thus offering the opportunity to prepare a broad range of new classes of precision polymers.…”

Construction of an inducible cell‐communication system that amplifies Salmonella gene expression in tumor tissue

“…We reported the use of lanthanide‐based catalysts combined with metal alkyls for the coordinative chain polymerization (CCTP) and copolymerization of various monomers 11–17. Such a polymerization depicted in Scheme involving the use of a single catalyst and a chain transfer agent (CTA) has gained much interest these last years,18–23 notably due to its potentiality for catalyst economy and molecular weight control, polymer functionalization, and the control of statistical copolymers composition.…”