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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

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Published on: November 29, 2018

Photoswitchable NHC-promoted ring-opening polymerizations.

Bethany M Neilson¹, Christopher W Bielawski

¹Department of Chemistry and Biochemistry, The University of Texas, Austin, Texas 78712, USA.

Chemical Communications (Cambridge, England)

|May 14, 2013

Summary

This study demonstrates photoswitchable ring-opening polymerizations using a novel N-heterocyclic carbene precatalyst. UV light stops polymerization, while visible light restarts it, offering precise control over polymer synthesis.

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Area of Science:

Polymer Chemistry
Organic Synthesis
Photochemistry

Background:

N-heterocyclic carbenes (NHCs) are versatile precatalysts.
Photoswitchable catalysts offer external control over reactions.
Ring-opening polymerization (ROP) is crucial for synthesizing polyesters.

Purpose of the Study:

To develop a photoswitchable NHC precatalyst for ROP.
To investigate the effect of UV and visible light on polymerization kinetics.
To demonstrate the reversible nature of the photoswitching mechanism.

Main Methods:

Synthesis of a dithienylethene-annulated NHC precatalyst.
Photochemical irradiation (UV and visible light) studies.
Kinetic analysis of ROP for ε-caprolactone and δ-valerolactone.

Main Results:

UV-induced photocyclization of the NHC precatalyst effectively inhibited ROP.
Polymerization rates were significantly attenuated under UV irradiation (k(amb)/k(UV) = 59).
Visible light exposure reversed the photocyclization, restoring catalytic activity and polymerization.

Conclusions:

The developed NHC precatalyst enables photoswitchable ROP.
This system provides a novel method for light-controlled polymer synthesis.
The reversible photoswitching mechanism offers precise control over polyester production.