High Refractive Index Photopolymers by Thiol-Yne "Click" Polymerization

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Synthesis

Background:

• High refractive index polymers are crucial for advanced optical applications.
• Existing photopolymerization methods often face limitations in achieving high refractive indices and optical clarity simultaneously.
• Thiol-yne click chemistry offers a versatile platform for polymer synthesis.

Purpose of the Study:

• To develop a scalable synthesis of high refractive index, optically transparent photopolymers.
• To explore the use of low-viscosity multifunctional thiol and alkyne monomers.
• To investigate the efficiency and characteristics of thiol-yne photopolymerization for creating novel polymer networks.

Main Methods:

• Synthesis of novel multifunctional thiol and alkyne monomers incorporating high refractive index cores (aryl, sulfide groups).
• Formulation of low-viscosity thiol-yne resins with a phosphine oxide photoinitiator.
• Photopolymerization of resins using 405 nm light at 30 mW/cm².
• Characterization of photopolymer properties, including refractive index and optical quality.

Main Results:

• Efficient thiol-yne polymerizations were achieved, yielding cross-linked photopolymers with refractive indices exceeding 1.68.
• The thiol-yne reaction introduced a high density of sulfide linkages, enhancing optical quality compared to thiol-ene systems.
• A significant polymerization-induced change in refractive index (up to 0.08) was observed with specific monomer combinations.
• Demonstrated application in two-stage photopolymeric holographic materials with low haze (<1.5%) and a dynamic range of ~0.02.

Conclusions:

• Scalable synthesis of high refractive index, optically transparent photopolymers is achievable via thiol-yne click chemistry.
• The developed monomers and polymerization method offer a promising route to high-performance optical materials.
• The resulting photopolymers are suitable for advanced applications such as holographic materials.