Visible-Light Photocatalytic Oxidation of DMSO for RAFT Polymerization

Area of Science:

• Photochemistry
• Polymer Science
• Organic Chemistry

Background:

• Dimethyl sulfoxide (DMSO) is commonly used in photochemical polymerizations to enhance solubility.
• The reactivity of DMSO as a solvent in these reactions is often overlooked in proposed initiation mechanisms.

Purpose of the Study:

• To investigate the role of DMSO oxidation by excited-state quinones in initiating polymerization.
• To explore the formation of initiating radicals and control over polymer properties.

Main Methods:

• Synthesis of a visible light-absorbing substituted anthraquinone photocatalyst.
• Nanosecond transient absorption spectroscopy to monitor reaction intermediates.
• Photoproduct analysis to identify radical species.
• Controlled polymerization of methacrylate monomers.

Main Results:

• Excited-state anthraquinone oxidizes DMSO, generating methyl radicals that initiate polymerization.
• Polymerization yields polymers with narrow molecular weight distribution.
• The solvent (DMSO) competes effectively with chain transfer agents for the excited photocatalyst.
• Polymerization proceeds efficiently even in the presence of oxygen.

Conclusions:

• The oxidation of DMSO by excited photocatalysts is a significant pathway for initiating polymerization.
• Solvent reactivity, particularly with strong excited-state oxidants like quinones, must be considered in photoinduced polymerizations in DMSO.
• This understanding has broad implications for designing and controlling photochemical polymerizations in DMSO.