Analysis of Polymeryl Chain Transfer Between Group 10 Metals and Main Group Alkyls during Ethylene Polymerization

Abstract

The ability of various group 10 α-diimine and salicylaldimine polymerization catalysts to undergo chain transfer with main group metal alkyls during ethylene polymerization has been investigated in depth. The catalyst systems with the most efficient chain transfer were found to be cationic (α-diimine)Ni catalysts paired with dialkyl zinc chaintransfer reagents, in which all growing polymeryl chains were transferred to Zn on the basis of 13 C NMR analysis. In these systems, chain transfer was found to be dependent on the sterics of both the catalyst and the chain-transfer reagent (CTR). When less sterically encumbered catalysts or CTRs were utilized, the relative rate of bimetallic chain transfer to chain propagation was increased; however, in cases where chain termination via β-H elimination was extremely rapid, chain transfer to Zn was kinetically not viable. Importantly, chain transfer from (α-diimine)Ni catalysts to Zn alkyls is also very sensitive to the strength of the Zn−C bond: ZnMe 2 (186 kJ/mol) is a significantly poorer chain-transfer reagent than ZnEt 2 (157 kJ/mol), despite being less sterically encumbered. Finally, the nature of the catalyst counteranion (MAO or B(ArF) 4 − ArF = 3,5-(CF 3 ) 2 C 6 H 3 ) does not have a significant impact on the rate of chain transfer to ZnR 2 relative to propagation, indicating that the same factors that determine propagation rates also determine bimetallic chain-transfer rates.

Structural analysis of linear/branched ethylene block copolymers

“…As shown by Hue et al the ratio of transfer to propagation rate constants for the diimine catalysts, with butanedione backbone, is in the order of 0.01 . This is significantly lower than the values usually used in modeling of the original CSP reaction .…”

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

“…Vinyl chain ends (at 111 and 136 ppm) would be expected from chain termination on the Ni due to β-H elimination, however these peaks are not present in this sample. 20,28 This data proves successful chain transfer from Ni to Zn and disproves competing side reactions involving the catalyst and chain transfer reagent that could alter the resulting polymer. Analysis of the polymer microstructure is also important because a change in the polymer microstructure could be indicative of a change in the nature of the catalyst species, which would make kinetic comparison impossible.…”

Zn‐assisted cooperative effect for copolymers made by heterodinuclear Fe−Ni catalyst

“…According to this, Tonks and co-workers disclosed that changing of iso-propyl groups on side aryl rings of α-diimine Ni catalyst (1) into methyl substituents (2) could increase the chain transfer to propagation rate. [17] While, in the case of hydrogen substituents (3), chain termination through the β-H elimination was dominant. The effect of substituents also could be observed in the work of Xiao and co-workers where using 1 and 2 afforded branched-hyperbranched PE block copolymers in the presence of DEZ.…”