Photopolymerization Using Metal Oxide Semiconducting Nanoparticles for Epoxy-Based Coatings and Patterned Films

Photopolymerization is fundamental to many applications such as printed circuit board manufacturing, dentistry, coating, and stereolithography 3D-printing. However, the current organic cationic initiators are toxic, expensive, and difficult to tune with respect to the wavelength of light required for the initiation of the photopolymerization. Different applications require different wavelengths of light to initiate photopolymerization. Thus, the ability to tune initiators is sought. Here, we show that metal oxide semiconducting nanoparticles photopolymerize epoxy via an oxidation reaction that we monitor using Fourier transform infrared spectroscopy, NMR, and titration techniques. Careful selection of metal oxide semiconducting materials with the desired band gap energy controls the wavelength of light to which this class of epoxy photoinitiators respondS. Additionally, those semiconducting nanoparticles are less expensive and less toxic relative to their commercial counterparts. Finally, semiconducting nanoparticles are standard materials with well-known syntheses offering a wide-range of readily available options. Our findings introduce a new class of epoxy photoinitiators that could impact industrial applications that rely on photopolymerization, as well as nanocomposites for which photoinduced reactions during use are undesirable.