Photopolymerization Using Thiol-Epoxy 'Click' Reaction: Anionic Curing through Photolatent Superbases

Area of Science:

• Polymer Chemistry
• Materials Science
• Photochemistry

Background:

• Thiol-epoxy "click" reactions provide advantages over traditional photochemical cross-linking, including air/moisture insensitivity and low volume shrinkage.
• Photolatent catalysts generate strong organic bases under light, enabling controlled polymerization.
• This approach is suitable for bulk polymerization, lithography, hydrogel formation, and creating photoactive materials.

Purpose of the Study:

• To review the emerging field of photoinduced anionic curing of epoxides by thiols.
• To highlight the development and application of photolatent catalysts for thiol-epoxy photopolymerization.
• To discuss the versatility of thiol-epoxy chemistry in creating advanced materials with tunable properties.

Main Methods:

• Utilizing photolatent catalysts to generate superbases upon irradiation (UV to near-infrared).
• Employing base-catalyzed ring-opening of epoxides by thiols for cross-linking.
• Exploring post-cross-linking modifications like sulfur alkylation and transesterification.

Main Results:

• Demonstrated advantages of thiol-epoxy photopolymerization: air/moisture insensitivity, low shrinkage, good adhesion, and reduced need for post-baking.
• Fabrication of micro- and nanosized patterns via lithography.
• Development of functional materials with antibiofouling (zwitterionic) and antibacterial (cationic) properties.
• Introduction of vitrimer properties for reshaping, shape memory effects, and 3D printing.

Conclusions:

• Photoinduced anionic curing of epoxides by thiols is a versatile and advantageous photopolymerization technique.
• Photolatent catalysts enable precise control over material properties and fabrication.
• Thiol-epoxy chemistry offers a pathway to advanced functional polymers, including hydrogels, photoactive materials, and recyclable thermosets.