Control over Branching Topology by Introducing a Dual Catalytic System in Coordinative Chain Transfer Polymerization of Olefins

Abstract

Coordinative polymerization brings opportunities for producing well-defined long-chain branched polyolefins specifically by using homogeneous single-site catalysts. Herein, we report a new dual catalytic system for the controlled formation of long-chain branches in a coordinative chain transfer polymerization. The growing polymers on the main aryl-substituted αdiimine nickel catalyst are frequently transferred via a chain transfer agent to the vinyl-producing catalyst, (Bipy) 2 FeEt 2 , where they are released as macromers through β-H elimination. The released macromers are incorporated into the growing polymer structure thanks to the high comonomer affinity of the main catalyst. By recurrence of this reaction cycle, a branch-on-branch structure is produced, which cannot be obtained using previous single or dual catalytic systems. The efficiency of the reaction is studied by performing ethylene and 1-hexene polymerizations at different reaction conditions. By increasing the amount of vinyl-producing catalyst, dramatic effects on the rheological properties are observed including increased dynamic moduli, prolongation of the G′−G″ crossover, and significant thermorheological complexity, all demonstrating formation of long branches. The microstructural analysis using 13 C NMR indicates that short-chain branches are vastly found in all samples due to the chain walking reaction. The spectroscopy and thermal analyses suggest that these short branches decrease by the addition of the vinyl-producing catalyst. This is presumably attributed to the high steric hindrance of the macromers, which forces the catalyst centers to preferentially attach to the primary carbons.

Extending Alkenes’ Value Chain to Functionalized Polyolefins

“…• Strategies to control the topology of polyolefins, such as chain walking polymerization. Using late transition metal catalysts, a wide range of engineered polyolefins of complex chain architectures can be designed through the control of ligands' steric and electronic parameters [73][74][75].…”

Resolving long-chain branch formation in tandem catalytic coordinative chain transfer polymerization of ethylene via thermal analysis

“…The low degree of control on the extent and length of long-chain branches in the single catalyst systems hampers the application of the former, while the separation and purification of unreacted macromers and, consequently, the high production cost of the two-catalyst systems suppress the industrial development of the latter [16]. In that sense, the new developments based on the CCTP reaction become more promising [17,18].…”

“…Subsequently, Cariou et al further improved this method by using a compatible polymerization and displacement catalyst which can not only form macromers in-situ but significantly reduces the reaction cost by regenerating the valuable CTA [20]. We have recently benefited from this reaction for the formation of a branch-on-branch microstructure by employing a highly comonomer-selective post-metallocene α-diimine nickel catalyst along with a compatible displacement catalyst [18]. Due to the inevitable chain-walking reaction [21], the final product contains various types of short-chain branches, on top of the long-chain branches, which resulted in a rubbery material.…”

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

“…[5] In addition to catalyst structure, polymerization parameters such as CSA type and concentration, ratio of the catalysts, polymerization time, temperature and monomer pressure have striking effects on the chain transfer efficiency (CTE), length of the olefinic blocks and polymer properties. [2,15,17,21,[37][38][39][40] On the other side, multinuclear catalysts have shown remarkable behaviour such as cooperative effects. [41,42] This metal•••metal interactions may change the polymerization mechanism and cause an increasing of catalytic features and polymer properties such as catalyst activity, selectivity of chain branching, Mw, tacticity and so on.…”

“…Even in the case of Fe catalysts, iso‐ propyl substituents on side aryl rings ( 4 ) demonstrated good response in this manner, while the efficiency decreased for methyl groups ( 5 and 6 ) [5] . In addition to catalyst structure, polymerization parameters such as CSA type and concentration, ratio of the catalysts, polymerization time, temperature and monomer pressure have striking effects on the chain transfer efficiency (CTE), length of the olefinic blocks and polymer properties [2,15,17,21,37–40] …”