The present work aims at the design of photoactive inorganic fillers by covalently attaching photoiniating groups onto silica nanoparticles. A series of tri(alkoxy)silyl functionalized acylphosphine oxides and other Norrish type I photoinitiators have been synthesized and coupled to nanosilica. The immobilization of the photoactive groups was evidenced by spectroscopic measurements, thermal gravimetric analysis, elemental analysis and other techniques. The modified particles were then incorporated into acrylate resins and thiol-ene resins to study the photoinitiation efficiency of the covalently bound initiators. The photopolymerization kinetics were monitored by FT-IR spectroscopy and photo-DSC under exposure to UV light, and compared to the results achieved with free (i.e., non-bound) photoinitiators. Rapid curing and high conversion yields were found both for acrylate and thiol-ene resins. The concept of using immobilized photoinitiators follows a general strategy towards low-migration photoinitiators as required, e.g., for UV curable printing inks. In this context, photocured samples were extracted and the amount of extractable photoinitiator was assessed. Moreover, negative-toned patterns were inscribed in thin thiol-ene films by photolithographic processes and characterized by microscopic techniques demonstrating the versatile applicability of the photoactive nanoparticles.  Another approach is related to the immobilization of azidophenyl units onto the surface of inorganic particles. Using this approach, these particles (e.g., silica) can be attached to the surface of chemically inert polymer films and fibres such as polyethylene and poly(ethylene terephthalate) by a photoinduced clic reaction. This paves the way towards inorganic protective layers on polymer surfaces.<br/>

Initiation of radical photopolymerization with photoactive silica particles

2019 Spring National Meeting

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