ATRP with ppb Concentrations of Photocatalysts

Area of Science:

• Polymer Chemistry
• Photocatalysis
• Organic Synthesis

Background:

• Atom Transfer Radical Polymerization (ATRP) relies on a copper catalyst system for controlled polymerization.
• Low catalyst concentrations in ATRP are limited by irreversible oxidation of the activator, necessitating regeneration.
• Photoinduced ATRP (PhotoATRP) offers an efficient method for activator regeneration using light.

Purpose of the Study:

• To investigate the use of commercially available xanthene dyes as photocatalysts (PCs) for activator regeneration in PhotoATRP.
• To demonstrate controlled polymerization at very low copper catalyst concentrations using these xanthene dye PCs.

Main Methods:

• Utilized rose bengal (RB), rhodamine B (RD), and rhodamine 6G (RD-6G) as photocatalysts in ATRP.
• Employed green LED irradiation for polymerization initiation and activator regeneration.
• Investigated polymerization kinetics, molecular weight distributions, and chain-end fidelity.
• Conducted UV-vis, fluorescence, and laser flash photolysis studies to elucidate the reaction mechanism.

Main Results:

• Successfully controlled PhotoATRP using ppm levels of copper catalyst and ppb levels of xanthene dye photocatalysts.
• Achieved well-defined polymers with preserved livingness, narrow molecular weight distributions, and high initiation efficiencies.
• Demonstrated efficient polymerization even at wavelengths longer than the dyes' absorption maxima, albeit requiring higher loadings.
• Rose bengal and rhodamine 6G were effective at sub-ppm concentrations (≥ 10 ppb), while rhodamine B required 5 ppm.

Conclusions:

• Xanthene dyes are effective and versatile photocatalysts for copper-catalyzed PhotoATRP, enabling polymerization under mild conditions.
• The developed dual-catalytic system (copper complexes and xanthene dyes) allows for significant reduction in catalyst loading.
• This approach provides a pathway for greener and more economical synthesis of well-defined polymers.