Visible-Light Photoinitiation of (Meth)acrylate Polymerization with Autonomous Post-conversion

Area of Science:

• Polymer Chemistry
• Photochemistry
• Materials Science

Background:

• Radical photopolymerizations (RPPs) rapidly plateau after irradiation stops due to radical termination.
• This limitation restricts RPP use in applications with uneven light access, such as those with light-attenuating resins or irregular surfaces.
• Existing dark-curing photoinitiators (DCPIs) offer a solution by enabling polymerization post-irradiation.

Purpose of the Study:

• To develop a novel DCPI with absorption extending into the visible light spectrum.
• To enable efficient radical generation and dark-curing in RPPs under visible light.
• To overcome limitations of conventional RPPs in applications with poor light penetration.

Main Methods:

• Computational investigations (quantum chemical computations) to design and predict molecular properties.
• Synthesis and optical characterization (UV-vis spectroscopy) of the designed DCPI.
• Demonstration of photo- and dark-curing efficiencies using a visible light LED and a one-part system.

Main Results:

• A new DCPI, 5,7-dimethoxy-6-bromo-3-aroylcoumarin-DMPT/BPh4, was designed, synthesized, and characterized.
• The DCPI exhibits strong visible light absorption and facilitates dark-curing with >35% additional conversion post-irradiation.
• High initiator efficiency (2.82) and photo-reductant generation quantum yield (77%) were achieved.

Conclusions:

• The developed visible light DCPI significantly enhances polymerization beyond light cessation.
• This technology is suitable for RPPs involving light-attenuating resins and irregular surfaces.
• The improved photo- and dark-curing efficiencies are expected to expand RPP applications and production line efficiencies.