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Olefin Metathesis Polymerization: Overview01:13

Olefin Metathesis Polymerization: Overview

2.2K
Recently, the development of olefin metathesis polymerization advanced the field of polymer synthesis. Simply put, the reorganization of substituents on their double bonds between two olefins in the presence of a catalyst is known as the olefin metathesis reaction. The use of metathesis reaction for polymer synthesis is called olefin metathesis polymerization.
Ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists...
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Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)00:53

Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)

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Acyclic diene metathesis polymerization or ADMET polymerization involves cross-metathesis of terminal dienes, such as 1,8-nonadiene, to give linear unsaturated polymer and ethylene. As ADMET is a reversible process, the formed ethylene gas must be removed from the reaction mixture to complete the polymerization process.
Similar to cross-metathesis, ADMET also involves the formation of metallacyclobutane intermediate by [2+2] cycloaddition of one of the double bonds of a terminal diene with...
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Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)01:16

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)

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Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...
2.7K
Ziegler–Natta Chain-Growth Polymerization: Overview01:17

Ziegler–Natta Chain-Growth Polymerization: Overview

3.4K
Ziegler–Natta polymerization is another form of addition or chain‐growth polymerization used for synthesizing linear polymers over branched polymers. The catalyst used for polymerization is the Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, who developed it in 1953. This catalyst is an organometallic complex of titanium tetrachloride and triethyl aluminum, with the active form of the catalyst being an alkyl titanium compound. Using the Ziegler–Natta...
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Free-Radical Chain Reaction and Polymerization of Alkenes02:35

Free-Radical Chain Reaction and Polymerization of Alkenes

8.1K
The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a repeating unit, while the terminal groups are considered insignificant. The average degree of polymerization represents the number of repeating units in the polymer molecule and is denoted by the subscript n.
8.1K
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

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Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
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Updated: Sep 10, 2025

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry
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Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

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Late Metal Sandwich Catalysts for Olefin Polymerization.

Joseph T Medina1, Quan H Tran1, Girish G Ramachandru1

  • 1Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States.

Accounts of Chemical Research
|August 19, 2025
PubMed
Summary

New palladium and nickel catalysts enable the synthesis of ultrahigh molecular weight polyethylenes with controlled branching. These advanced olefin polymerization catalysts offer living polymerization characteristics and tunable properties for novel polymer structures.

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Area of Science:

  • Polymer Chemistry
  • Organometallic Chemistry
  • Materials Science

Background:

  • Polyolefins are crucial industrial polymers, typically made with early transition metal catalysts.
  • Early metal catalysts lack functional group tolerance and produce linear polyethylene, requiring comonomers for branching.
  • Developing new catalysts for controlled polyolefin synthesis is essential for advanced materials.

Purpose of the Study:

  • To design and implement novel palladium(II) and nickel(II) olefin polymerization catalysts.
  • To understand the mechanism of chain growth for improved polymer synthesis.
  • To create new polymer architectures with tailored properties.

Main Methods:

  • Synthesis of hindered nickel- and palladium-aryl-substituted diimine complexes.
  • Mechanistic investigations of chain growth and chain transfer processes.
  • Molecular modeling to design novel 'sandwich' catalyst structures with enhanced axial shielding.

Main Results:

  • Developed Pd(II) and Ni(II) catalysts with ortho-disubstituted aryl groups and 'sandwich' structures.
  • Achieved living polymerization of ethylene, producing ultrahigh molecular weight polyethylenes (Mw > 10^7 Da) with narrow molecular weight distributions.
  • Controlled polymer branching (9-100 per 1000 carbons) and thermal properties (Tm 17-132 °C) by varying reaction conditions.
  • Synthesized diblock and multiblock copolymers with controlled molecular weights and segment lengths.

Conclusions:

  • Late metal catalysts, particularly Ni(II) and Pd(II) diimine complexes, offer significant advantages over early metal catalysts.
  • Novel 'sandwich' catalysts provide exceptional control over molecular weight, branching, and polymer architecture.
  • These advancements enable the synthesis of advanced polyolefins with tunable mechanical properties and potential applications as compatibilizers.