Development of Group IV Molecular Catalysts for High Temperature Ethylene-α-Olefin Copolymerization Reactions

Abstract

This Account describes our research related to the development of molecular catalysts for solution phase olefin polymerization. Specifically, a series of constrained geometry and nonmetallocene (imino-amido-type) complexes were developed for high temperature olefin polymerization reactions. We have discovered many highly active catalysts that are capable of operating at temperatures above 120 °C and producing copolymers with a useful range of molecular weights (from medium to ultrahigh depending on precatalyst identity and polymerization conditions) and α-olefin incorporation capability. Constrained geometry catalysts (CGCs) exhibit very high activities and are capable of producing a variety of copolymers including ethylene-propylene and ethylene-1-octene copolymers at high reactor temperatures. Importantly, CGCs have much higher reactivity toward α-olefins than classical Ziegler-Natta catalysts, thus allowing for the production of copolymers with any desired level of comonomer. In search of catalysts with improved performance, we discovered 3-amino-substituted indenyl-based CGCs that exhibit the highest activity and produce copolymers with the highest molecular weight within this family of catalysts. Phenanthrenyl-based CGCs were found to be outstanding catalysts for the effective production of high styrene content ethylene-styrene copolymers under industrially relevant conditions. In contrast to CGC ligands, imino-amido-type ligands are bidentate and monoionic, leading to the use of trialkyl group IV precatalysts. The thermal instability of imino-amido complexes was addressed by the development of imino-enamido and amidoquinoline complexes, which are not only thermally very robust, but also produce copolymers with higher molecular weights, and exhibit improved α-olefin incorporation. Imido-amido and imino-enamido catalysts undergo facile chain transfer reactions with metal alkyls, as evidenced by a sharp decrease in polymer molecular weight when the polymerization reactions were conducted in the presence of diethylzinc, an essential requirement for use in the production of olefin block copolymers via chain shuttling polymerization. Overall, the excellent characteristics of imino-amido-type catalysts, including high catalytic activities and ultrahigh molecular weight capabilities, make them good candidates for high temperature syntheses of block and random ethylene-α-olefin copolymers. Additionally, trialkyl imino-enamido complexes react quickly with various protic and unsaturated organic fragments, leading to a library of dialkyl precatalysts that, in several instances, resulted in superior catalysts. In conjunction with the development of transition metal catalysts, we also synthesized and evaluated activators for olefin polymerization. We found, for example, that, when conducted in coordinating solvents, the reaction between aluminum alkyls and tris(pentafluorophenyl)borane leads to the exclusive formation of alumenium borates, which are excellent activators for CGC complexes. Additionally, we developed a ser...

A Precision Ethylene‐Styrene Copolymer with High Styrene Content from Ring‐Opening Metathesis Polymerization of 4‐Phenylcyclopentene

“…Although polyethylene and polystyrene are ubiquitous plastics, synthesis of ethylene‐styrene (ES) copolymers have been historically challenging due to the markedly different monomer reactivities and, for many years, were deemed non‐viable with the limitations of traditional Ziegler–Natta catalyst systems . The advent of well‐defined “single‐site” or molecular catalysts over the last few decades has brought new attention to the efficacy and utility of ES copolymers . A broad scope of material properties are realized when traversing from low to high styrene (S) content which translates to a variety of applications for compatibilizers, packaging, films, foams, automobiles, construction materials, and bitumen modifiers .…”

Constrained Geometry Organotitanium Catalysts Supported on Nanosized Silica for Ethylene (co)Polymerization

“…The reaction temperature is usually run at temperature ≥ 140 °C for copolymerization of ethylene and 1-octene with unsupported Ti[(C 5 Me 4 )SiMe 2 (N t Bu)]Me 2 catalyst (activated with B(C 6 F 5 ) 3 ) in solution process [1,21]. However, for the silica-supported Ti[(C 5 Me 4 )SiMe 2 (N t Bu)]Cl 2 catalyst (activated with MAO) studied here, the catalyst activity decreased when reaction temperature was above 100 °C.…”

“…Ethylene homo-polymers and copolymers (abbreviated as PE) are the most common polymers, accounting for about 38% of all the global plastics made today [1]. Their applications include bags, films, housewares, bottles, containers, pipe, tubing, wire and cable insulation, conduits and coatings [2].…”

“…Their applications include bags, films, housewares, bottles, containers, pipe, tubing, wire and cable insulation, conduits and coatings [2]. About three quarters of the PE is produced via reactions catalyzed by transition metal catalysts, including Ziegler-Natta catalysts, metallocene catalysts, constrained geometry catalysts and supported metal oxides (Philips process) [1,3]. Metallocene catalysts and constrained geometry catalysts are single site catalysts, which can produce many new PE forms with enhanced properties [4].…”

Metallocenes

“…Soon thereafter, patent applications from workers at Dow (61) and Exxon (62) claimed high activities for olefin polymerization using the Ti complex 17. Constrained geometry catalysts (63) are well-suited for use in high temperature solution process for the following features: (1) high activity and polymer molecular weight at high temperatures (>120 • C); (2) high comonomerincorporation ability, allowing access to very low density polyethylenes; and (3) ability to generate long-chain branches. Particularly important structural developments include 18, which provides higher activity and higher MW capability at higher polymerization temperature (64), and 19 for highly effective ethylenestyrene random copolymerizations (65).…”