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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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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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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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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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The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
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Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
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Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst
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Temporal Regulation of PET-RAFT Controlled Radical Depolymerization.

Valentina Bellotti1,2, Hyun Suk Wang1, Nghia P Truong1

  • 1Laboratory of Polymeric Materials, Department of Materials, ETH Zurich, Vladimir-Prelog-Weg-5, Zurich, 8093, Switzerland.

Angewandte Chemie (International Ed. in English)
|October 10, 2023
PubMed
Summary
This summary is machine-generated.

This study introduces a photocatalytic method for controlled polymer degradation using visible light. This technique allows for precise temporal control over depolymerization, enabling efficient recycling of polymers synthesized via RAFT polymerization.

Keywords:
DepolymerizationPET-RAFTPhotocatalysisReverse RDRPTemporal Control

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Area of Science:

  • Polymer Chemistry
  • Photocatalysis
  • Chemical Recycling

Background:

  • Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization is a versatile technique for synthesizing polymers with controlled architectures.
  • Chemical recycling of polymers is crucial for sustainability, but often lacks precise control over degradation processes.
  • Temporal control in polymer degradation is challenging, especially under mild conditions like visible light irradiation.

Purpose of the Study:

  • To develop a photocatalytic method for temporal control of radical depolymerization.
  • To enable precise on/off switching of polymer degradation under visible light.
  • To investigate the mechanistic insights into light-controlled polymer degradation for chemical recycling.

Main Methods:

  • Utilizing a photocatalytic approach combined with RAFT-controlled radical depolymerization.
  • Regulating the deactivation of depropagating polymer chains.
  • Suppressing thermal initiation during the process.
  • Employing visible light irradiation for controlled depolymerization cycles.

Main Results:

  • Achieved excellent temporal control over polymer depolymerization with multiple on/off cycles.
  • Demonstrated minimal depolymerization during dark periods (off-cycles).
  • Showcased efficient re-activation of polymer chain ends upon light re-exposure.
  • Observed a stepwise decrease in molecular weight, indicating controlled polymer chain unzipping.

Conclusions:

  • The developed photocatalytic RAFT-controlled depolymerization method offers precise temporal control.
  • This approach facilitates controlled chemical recycling of RAFT-synthesized polymers.
  • The methodology provides valuable mechanistic understanding of light-modulated polymer degradation.