Upconversion particle-assisted NIR polymerization enables microdomain gradient photopolymerization at...

Area of Science:

• Polymer Chemistry
• Materials Science
• Photopolymerization

Background:

• Achieving high crosslinking and low shrinkage stress simultaneously in photopolymers is challenging.
• Conventional UV polymerization techniques often result in significant internal stress.
• Performance-enhancing photopolymer materials require careful control over curing processes.

Purpose of the Study:

• To introduce and investigate a novel photopolymerization method using upconversion particles-assisted NIR polymerization (UCAP).
• To demonstrate UCAP's ability to reduce shrinkage stress while enhancing mechanical properties of cured materials.
• To elucidate the unique mechanism by which UCAP achieves these improvements.

Main Methods:

• Utilizing upconversion particles that emit UV-vis light upon NIR excitation.
• Implementing a domain-limited gradient photopolymerization process centered on upconversion particles.
• Monitoring the curing system's state (fluid, gelation) and functional group conversion.
• Comparing mechanical properties and shrinkage stress with conventional UV polymerization.

Main Results:

• UCAP induces gradient photopolymerization within particle-centered domains.
• The curing system remains fluid until high functional group conversion, releasing stress before gelation.
• UCAP-cured materials exhibit high gel point conversion and significantly lower shrinkage stress.
• Materials cured via UCAP demonstrate superior mechanical properties compared to conventionally UV-cured counterparts.

Conclusions:

• Upconversion particles-assisted NIR polymerization (UCAP) offers a unique mechanism to overcome the trade-off between crosslinking and shrinkage stress.
• UCAP facilitates the preparation of high-performance photopolymer materials with enhanced mechanical strength and reduced internal stress.
• This approach presents a promising advancement for developing advanced photopolymer applications.