Upconversion‐Nanoparticle‐Assisted Radical Polymerization at λ=974 nm and the Generation of Acidic Cations

Abstract

Upconversion nanoparticles (UCNPs) sensitised photolytic cleavage of the blue/UV photoinitiator bis(4‐methoxybenzoyl) diethyl germanium (1). 1 initiated radical photopolymerisation in combination with NaYF4:TmYb@NaYF4 UCNPs. A λ=974 nm near‐infrared (NIR) laser served as the excitation source to generate blue and UV light. In addition, a metal‐free photo‐ATRP system (ATRP=atom transfer radical polymerisation), composed of iso‐propyl thioxanthone (ITX), N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) and α‐bromo(iso‐butyl) ethylester (α‐BrBuEt) was used instead of 1. This resulted in a significant smaller polydispersity compared to the UCNP/1 system. Control of polymerization was successfully demonstrated by means of a chain extension experiment showing control of chain termination. For the first time, we demonstrated photolytic formation of acidic cations in such NIR UCNP systems composed of an ITX/iodonium photoinitiator for the sensitized generation of acidic cations. In addition, 1 also resulted in crosslinking of 1,6‐hexanediol diacrylate (HDDA) in combination with UCNPs and NIR laser excitation. UV filter materials such as TiO2 do not significantly interfere with crosslinking.

Carbon Dots as a Promising Green Photocatalyst for Free Radical and ATRP‐Based Radical Photopolymerization with Blue LEDs

“…Chain termination may explain the higher dispersities obtained . Previous investigations carried out with up‐conversion nanoparticles also resulted in higher dispersities, and the heterogeneous nature of the photocatalyst was discussed as one possible reason . Nevertheless, this topic remains the subject of future experiments, which should give more detailed insight about the function of CDs as photocatalyst.…”

“…[22] Previous investigations carried out with up-conversion nanoparticles also resulted in higher dispersities,a nd the heterogeneous nature of the photocatalyst was discussed as one possible reason. [23] Nevertheless,t his topic remains the subject of future experiments, which should give more detailed insight about the function of CDs as photocatalyst. Despite the fascinating properties of CDs,t here are still many unanswered questions regarding their detailed structure and functionality.…”

Near‐Infrared Photoinduced Copper‐Catalyzed Azide‐Alkyne Click Chemistry with a Cyanine Comprising a Barbiturate Group

“…Nevertheless, these techniques do not facilitate the transfer of such systems to applications comprising inner filter materials absorbing in the UV−A part . This can be TiO 2 or yellow pigments in coating related applications –. These filler materials exhibit an open absorption window around 800 nm while the absorption in the UV range is typically high where they uptake the function of a filter material…”

High-resolution 3D photopolymerization assisted by upconversion nanoparticles for rapid prototyping applications

“…The idea of planar upconversion lithography has been demonstrated 18 . UCNP based photoinitiator systems and radical polymerization driven by NIR-light were shown 7 , 19 . NIR light converted to the green luminescence of NaYF 4 :Yb 3+ , Er 3+ nanoparticles, has been successfully used to induce straightforward thin polymer shell formation on UCNP surface for its hydrophilization 20 and drug loading 21 .…”