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Related Concept Videos

Free-Radical Chain Reaction and Polymerization of Alkenes02:35

Free-Radical Chain Reaction and Polymerization of Alkenes

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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: Overview01:10

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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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Radical Chain-Growth Polymerization: Chain Branching01:17

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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

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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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Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)00:53

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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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Radical Chain-Growth Polymerization: Mechanism01:09

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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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Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers
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Fully Recyclable and Remarkably Robust Cross-Linked Polyethylene Networks via Direct Free-Radical Copolymerization

Logan M Fenimore, Mathew J Suazo, Sarah Mitchell1

  • 1Braskem America, 550 Technology Drive, Pittsburgh, Pennsylvania 15219, United States.

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Researchers developed recyclable polyethylene covalent adaptable networks (PE CANs) using a novel copolymerization method. These materials offer comparable properties to traditional cross-linked polyethylene (XLPE) and fully recover performance after recycling, presenting a sustainable alternative.

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Area of Science:

  • Polymer Chemistry
  • Materials Science
  • Sustainable Polymers

Background:

  • Cross-linked polyethylene (XLPE) is widely used but not recyclable due to permanent cross-links.
  • Developing recyclable thermosets is crucial for environmental sustainability in the polyolefin industry.

Purpose of the Study:

  • To synthesize dynamic covalently cross-linked polyethylene (PE CANs) via in-reactor copolymerization.
  • To evaluate the properties and recyclability of the novel PE CANs.
  • To offer a sustainable alternative to conventional XLPE.

Main Methods:

  • Free-radical copolymerization of ethylene with bis(2,2,6,6-tetramethyl-4-piperidyl methacrylate) disulfide (BTMA).
  • Characterization of PE CANs' crystallinity, dimensional stability, and thermomechanical properties.
  • Assessment of performance recovery after recycling through stress relaxation studies.

Main Results:

  • Successful in-reactor synthesis of PE CANs with high crystallinity and robust properties comparable to XLPE.
  • Demonstrated full recovery of cross-link density and thermomechanical performance after recycling.
  • Identified viscoelastic behavior driven by dynamic disulfide bond exchange and polymer chain dynamics.

Conclusions:

  • PE CANs represent a novel, recyclable alternative to non-recyclable XLPE.
  • The scalable free-radical copolymerization method enables sustainable production of high-performance polyolefins.
  • This advancement addresses the critical need for circularity in the plastics industry.