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Related Concept Videos

Radical Chain-Growth Polymerization: Chain Branching01:17

Radical Chain-Growth Polymerization: Chain Branching

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The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...
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Polymer Classification: Architecture01:14

Polymer Classification: Architecture

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Polymers are classified as linear or branched on the basis of their chain architecture. The polymer chains in linear polymers have a long chain-like structure with minimal to no branching at all. Even if a polymer features large substituent groups on the monomer, which appear as branches to the skeleton, it is not considered a branched polymer. A branched polymer contains secondary polymer chains that arise from the main polymer chain. The branching occurs when the polymer growth shifts from...
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Free-Radical Chain Reaction and Polymerization of Alkenes02:35

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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.
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Radical Chain-Growth Polymerization: Mechanism01:09

Radical Chain-Growth Polymerization: Mechanism

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The radical chain-growth polymerization mechanism consists of three steps: initiation, propagation, and termination of polymerization. The polymerization initiates when a free radical generated from the radical initiator adds to the unsaturated bond in the monomer. The unpaired electron of the free radical and one π electron in the unsaturated bond creates a σ bond between the free radical and the monomer. As a result, the other π electron in the unsaturated bond converts this...
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Step-Growth Polymerization: Overview01:03

Step-Growth Polymerization: Overview

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Step-growth or condensation polymerization is a stepwise reaction of bi or multifunctional monomers to form long-chain polymers. As all the monomers are reactive, most of the monomers are consumed at the early stages of the reaction to form small chains of reactive oligomers, which then combine to form long polymer chains in the late stages. Hence, the reaction has to proceed for a long time to achieve high molecular weight polymers.
Many natural and synthetic polymers are produced by...
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Radical Chain-Growth Polymerization: Overview01:10

Radical Chain-Growth Polymerization: Overview

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Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
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Updated: Jul 1, 2025

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization
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Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

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A commercially viable solution process to control long-chain branching in polyethylene.

Robert D Froese1, Daniel J Arriola1, Jaap den Doelder2

  • 1The Dow Chemical Company, Midland, MI 48647, USA.

Science (New York, N.Y.)
|March 14, 2024
PubMed
Summary

A novel ladder-like polyethylene architecture was created using solution polymerization and a dual-chain catalyst. This method offers an industrially viable alternative for producing long-chain branched polyethylene with tunable properties.

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Area of Science:

  • Polymer Chemistry
  • Materials Science

Background:

  • Traditional methods for introducing long-chain branching in polyolefins, like producing low-density polyethylene (LDPE), are energy-intensive and require high pressure.
  • Achieving controlled long-chain branching is crucial for tailoring polymer properties, but existing methods have limitations.

Purpose of the Study:

  • To develop a novel, industrially viable solution polymerization process for creating polyethylene with a ladder-like architecture.
  • To demonstrate a new mechanism for introducing long-chain branching using dual-chain catalysts and α,ω-dienes.

Main Methods:

  • Solution polymerization of ethylene with small amounts (<1 mole %) of α,ω-dienes.
  • Utilizing a dual-chain catalyst system with two growing polymer chains on the same metal center.
  • Characterization using molecular weight distribution analysis, Mark-Houwink analysis, nuclear magnetic resonance (NMR), and rheology (shear and extensional).

Main Results:

  • Successfully synthesized polyethylene with a ladder-like architecture, distinct from traditional LDPE.
  • The ladder-branching mechanism proceeded without requiring a steady-state concentration of pendant vinyl groups.
  • Characterization confirmed highly branched structures with rheological properties comparable to LDPE and its blends with linear low-density polyethylene (LLDPE).

Conclusions:

  • The developed solution polymerization process offers an efficient and controllable method for producing long-chain branched polyethylene.
  • This approach provides an industrially viable alternative to high-pressure methods for creating branched polyolefins.
  • The ladder-like architecture yields desirable rheological properties for various applications.