Synthesis of Chain Shuttling Organometallic Compounds Capable of Producing Triblock Polyolefins

Abstract

Organometallic oligomeric compounds with dual-headed structure R’-(M-R-) n M-R’ were developed enabling the synthesis of triblock polyolefins. The compounds comprise divalent linkers (R) derived from trivinylcyclohexane between two main group metals and norbornyl capping groups (R’). Due to the difference in steric hindrance, the chain transfer reaction in polymerization selectively involves the less hindered M–R bond, resulting in growth of polymer chains only from the R linker group with metals on both ends. The metal-terminated polymer can be further functionalized to form telechelic polymers or used in coordinative chain transfer polymerization to produce various triblock polyolefins. This paper presents the synthetic strategy and demonstrates the production of triblock polymers using the compounds in a scalable continuous solution polymerization process.

Design of selective divalent chain transfer agents for coordinative chain transfer polymerization of ethylene and its copolymerization with butadiene

“…In this approach, the preparation of the CTA involves a multistep procedure based on the use of several catalysts and requires the purification of the CTA. 28…”

“…In this approach, the preparation of the CTA involves a multistep procedure based on the use of several catalysts and requires the purification of the CTA. 28 In this context, it is of interest to develop simple and straightforward syntheses of divalent chain transfer agents that enable controlling polymer chain growth exclusively on the bis-metalated moiety. The design of such a class of transfer agents would pave the way for the preparation of triblock copolymers in a selective manner.…”

Dual-Chain Polymerization at an Early Transition-Metal Single-Site Catalyst

“…Previous reports indicate that both methyls can undergo insertion of a diene to form a cycloalkyl hafnium complex. 13 However, no compelling evidence for growth of two polymer chains at a metal center has been reported. Additionally, knowing the concentration of actively propagating sites for polymer growth is key to the development of kinetic models with high fidelity and predictive accuracy.…”

Phenyl-Terminated Polyolefins via Living Coordinative Chain Transfer Polymerization with ZnPh2 as a Chain Transfer Agent

“…For the broader scope of controlled and nonliving coordinative chain transfer polymerization (CCTP), which includes Dow’s “chain-shuttling” process, − a few examples of main group metal CTAs that incorporate a functional group have been documented in the scientific literature for providing access to α-monofunctional and α,ω-difunctional polyolefin products . However, these CCTP systems and functionalized CTAs: (1) are constrained by a limited range of olefin monomers that can be employed (e.g., exclusive to ethene only or co-polymerizations with ethene), (2) require multistep syntheses of the functionalized CTA, (3) have not been validated for near-quantitative utilization of all functional group components of the CTA, and (4) are based on strategies for the in situ generation and utilization of functionalized CTAs that are of ill-defined structure.…”

“…On the one hand, perhaps the absence of any prior scientific evidence for the ability of ZnPh 2 to serve as a highly efficient chain transfer agent in either LCCTP or CCTP should not be surprising if one’s expectations are based on the widely proposed mechanism for how group transfer in these processes is thought to proceed. More to the point, Scheme presents the traditional view of bimetallic polymeryl group exchange that is believed to occur through a four-membered ring intermediate A . − However, while there is plenty of spectroscopic and structural evidence for alkyl group exchange occurring through dinuclear μ-alkyl bridging interactions, to the best of our knowledge, the literature is devoid of any similar study or evidence of aryl group exchange occurring between a transition-metal complex and a main-group organometallic through the formation of a bimetallic μ-aryl bridging interaction of the type displayed in intermediate B and that leads to the formation of the transition-metal-aryl bonded exchange product C . Indeed, the closest experimental support for the latter type of bimetallic μ-aryl bridging interaction can be found in the crystallographic analysis of ZnPh 2 in which the dimeric structure, [PhZn­(μ-Ph)] 2 , is observed in the solid state .…”