Coordinative Chain Transfer and Chain Shuttling Polymerization

Coordinative chain transfer polymerization, CCTP, is a degenerative chain transfer polymerization process that has a wide range of applications. It allows a highly controlled synthesis of polyolefins, stereoregular polydienes, and stereoregular polystyrene, including (stereo)block as well as statistical copolymers thereof. It also shows a green character by allowing catalyst economy during the synthesis of such polymers. CCTP notably allows the end functionalization of both the commodity and stereoregular specialty polymers aforementionned, control of the composition of statistical copolymers without adjusting the feed, and quantitative formation of 1-alkenes from ethene. A one-pot one-step synthesis of the original multiblock microstructures and architectures by chain shuttling polymerization (CSP) is also an asset of CCTP. This methodology takes advantage of the simultaneous presence of two catalysts of different selectivity toward comonomers that produce blocks of different composition/microstructure, while still allowing the chain transfer. This affords the production of highly performant functional polymers, such as thermoplastic elastomers and adhesives, among others. This approach has been extended to cyclic esters' and ethers' ring-opening polymerization, providing new types of multiblock microstructure. The present Review provides the state of the art in the field with a focus on the last 10 years.

Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst

We synthesized a series of Me2Si-bridged ansa-zirconocene complexes coordinated by thiophene-fused cyclopentadienyl and fluorenyl ligands (Me2Si(2-R1-3-R2-4,5-Me2C7S)(2,7-R32C13H6))ZrMe2 (R1 = Me or H, R2 = H or Me, R3 = H, tBu, or Cl) for the subsequent preparation of supported catalysts. We determined that the fluorenyl ligand adopts an η3-binding mode in 9 (R1 = Me, R2 = H, R3 = H) by X-ray crystallography. Further, we synthesized a derivative 15 by substituting the fluorenyl ligand in 9 with a 2-methyl-4-(4-tert-butylphenyl)indenyl ligand, derivatives 20 and 23 by substituting the Me2Si bridge in 12 (R1 = Me, R2 = H, R3 = tBu) and 15 with a tBuO(CH2)6(Me)Si bridge, and the dinuclear congener 26 by connecting two complexes with a –(Me)Si(CH2)6Si(Me)– spacer. The silica-supported catalysts prepared using 12, 20, and 26 demonstrated up to two times higher productivity in ethylene/1-hexene copolymerization than that prepared with conventional (THI)ZrCl2 (21–26 vs. 12 kg-PE/g-(supported catalyst)), producing polymers with comparable molecular weight (Mw, 330–370 vs. 300 kDa), at a higher 1-hexene content (1.3 vs. 1.0 mol%) but a lower bulk density of polymer particles (0.35 vs. 0.42 g/mL).

Investigations on the Ethylene Polymerization with Bisarylimine Pyridine Iron (BIP) Catalysts

The kinetics and terminations of ethylene polymerization, mediated by five bisarylimine pyridine (BIP) iron dichloride precatalysts, and activated by large amounts of methyl aluminoxane (MAO) was studied. Narrow distributed paraffins from initially formed aluminum polymeryls and broader distributed 1-polyolefins and (bimodal) mixtures, thereof, were obtained after acidic workup. The main pathway of olefin formation is beta-hydrogen transfer to ethylene. The rate of polymerization in the initial phase is inversely proportional to the co-catalyst concentration for all pre-catalysts; a first-order dependence was found on ethylene and catalyst concentrations. The inhibition by aluminum alkyls is released to some extent in a second phase, which arises after the original methyl groups are transformed into n-alkyl entities and the aluminum polymeryls partly precipitate in the toluene medium. The catalysis is interpretable in a mechanism, wherein, the relative rate of chain shuttling, beta-hydrogen transfer and insertion of ethylene are determining the outcome. Beta-hydrogen transfer enables catalyst mobility, which leads to a (degenerate) chain growth of already precipitated aluminum alkyls. Stronger Lewis acidic centers of the single site catalysts, and those with smaller ligands, are more prone to yield 1-olefins and to undergo a faster reversible alkyl exchange between aluminum and iron.

Evidence of coordinative chain transfer polymerization of isoprene using iron iminopyridine/ZnEt2 catalytic systems

Herein, the first example of a reversible iron-mediated chain transfer polymerisation of isoprene with ZnEt2 as the chain transfer agent is reported.