Coordination−Insertion Copolymerization of Fundamental Polar Monomers

Concerted steric and electronic effects on α-diimine nickel- and palladium-catalyzed ethylene polymerization and copolymerization

For transition metal-based olefin polymerization catalysts, ligand steric and electronic effects can strongly influence important catalytic properties. However, the simultaneous tuning of both steric and electronic effects has not been explored in most of the previous studies. In this contribution, a strategy to tune the ligand electronic and steric effects in a concerted fashion is reported. In such a system, both dibenzhydryl groups and multiple methoxy/fluoro groups were installed in α-diimine ligands. In addition to strongly influencing ligand electronics, the methoxy/fluoro groups can interact with the dibenzhydryl groups and efficiently increase ligand sterics. In ethylene polymerization, this concurrent tuning of electronic and steric effects can lead to simultaneous enhancement of several parameters (activity, stability, polymer molecular weight, melting point, branching density) for both the nickel and palladium catalysts. The effectiveness of this strategy is highly attractive for future studies in other catalytic systems.

Remote Perfluoroalkyl Substituents are Key to Living Aqueous Ethylene Polymerization

In various nickel(II) salicylaldiminato ethylene polymerization catalysts, which are a versatile mechanistic probe for substituent effects, longer perfluoroalkyl groups exert a strong effect on catalytic activities and polymer microstructures compared to the trifluoromethyl group. This effect is accounted for by a reduced electron density on the active sites, and is also supported by electrochemical studies. Thus, β‐hydride elimination, the key step of chain transfer and branching pathways, is disfavored while chain‐growth rates are enhanced. This enhancement occurs to an extent that enables living polymerizations in aqueous systems to afford ultra‐high‐molecular‐weight polyethylene for various chelating salicylaldimine motifs. These findings are mechanistically instructive as well as practically useful for illustrating the potential of perfluoroalkyl groups in catalyst design.

Influence of initiating groups on phosphino-phenolate nickel catalyzed ethylene (co)polymerization

The influence of initiating groups on late transition metal catalyzed ethylene (co)polymerization was comprehensively studied for the first time.

Indole-bridged bisphosphine-monoxide palladium catalysts for ethylene polymerization and copolymerization with polar monomers

Novel indole-based C–N-bridged bisphosphine-monoxide palladium catalysts enable ethylene polymerization with completely different activities and molecular weights and copolymerization with polar comonomers.

Camphor-based phosphine-carbonyl ligands for Ni catalyzed ethylene oligomerization

Ni and Pd complexes of camphor-based phosphine-carbonyl ligands containing biaryl moiety are designed and synthesized. The Ni complexes can catalyze ethylene oligomerization and generate waxy higher olefins as well as oily lower olefins.

Synthesis of fluorinated polyethylene of different topologies via insertion polymerization with semifluorinated acrylates

Fluorinated polyethylene with different topologies can be generated via insertion polymerization with various late-transition-metal catalysts.

Bis(N-acylated imidazolin-2-imine) nickel catalyzed norbornene copolymerization with methyl acrylate

We herein report the synthesis of novel bis(N-acylated imidazolin-2-imine) nickel complexes for norbornene polymerization and copolymerization with polar monomers.

8-Arylnaphthyl substituent retarding chain transfer in insertion polymerization with unsymmetrical α-diimine systems

The 8-arylnaphthyl substituent is highly effective for retarding the chain transfer process during ethylene (co)polymerization due to the appropriate aryl orientation.

A N-bridged strategy enables hemilabile phosphine–carbonyl palladium and nickel catalysts to mediate ethylene polymerization and copolymerization with polar vinyl monomers

N-Bridged phosphine–carbonyl Pd(ii) and Ni(ii) catalysts enable the enhancement of molecular weights in ethylene polymerization and copolymerization with polar comonomers.

Light-mediated olefin coordination polymerization and photoswitches

This review outlines photoswitchable, transition metal-based olefin coordination polymerization catalysts ranging from homogeneous to heterogeneous, and monometallic to bimetallic regimes.

A computational study of the reactivity of rare-earth/phosphorus Lewis pairs toward polymerization of conjugated polar alkenes

The polymerization mechanism of methyl methacrylate (MMA) catalyzed by rare-earth/phosphorus (RE/P) Lewis pairs has been systematically studied through density functional theory (DFT) calculations.

Chemo- and Regioselective Functionalization of Isotactic Polypropylene: A Mechanistic and Structure-Property Study

Polyolefins represent a high-volume class of polymers prized for their attractive thermomechanical properties, but the lack of chemical functionality on polyolefins makes them inadequate for many high-performance engineering applications. We report a metal-free postpolymerization modification approach to impart functionality onto branched polyolefins without the deleterious chain-coupling or chain-scission side reactions inherent to previous methods. The identification of conditions for thermally initiated polyolefin C-H functionalization combined with the development of new reagents enabled the addition of xanthates, trithiocarbonates, and dithiocarbamates to a variety of commercially available branched polyolefins. Systematic experimental and kinetic studies led to a mechanistic hypothesis that facilitated the rational design of reagents and reaction conditions for the thermally initiated C-H xanthylation of isotactic polypropylene (iPP) within a twin-screw extruder. A structure-property study showed that the functionalized iPP adheres to polar surfaces twice as strongly as commercial iPP while demonstrating similar tensile properties. The fundamental understanding of the elementary steps in amidyl radical-mediated polyolefin functionalization provided herein reveals key structure-reactivity relationships for the design of improved reagents, while the demonstration of chemoselective and scalable iPP functionalization to realize a material with improved adhesion properties indicates the translational potential of this method.

Synthesis of Brominated Polyethylene by Copolymerization of Ethylene with ω–bromoalkene Catalyzed by a Metallocene and Methylaluminoxane System

The metallocene-catalyzed copolymerization of ethylene and 11–bromo–1–undecene was carried out to synthesize brominated polyethylene (PE). A modified methylaluminoxane (MMAO) solution was used as a cocatalyst and rac–Et(H4Ind)2ZrCl2 as a catalyst. The copolymerization showed a high activity and afforded the copolymer with a 11-bromo-1-undecene incorporation ranging from 1.0 to 4.3 mol%. When using a dried methylaluminoxane (dMAO) as a cocatalyst, the incorporation ratio of 11-bromo-1-undecene increased remarkably to 25.2 mol%. It was demonstrated that the type of MAO used as a cocatalyst affects the composition of the ethylene/11-bromo-1-undecene copolymer without changing the structure of the catalytic complex.