Visible-Light-Mediated Polymerization of 1,3-Benzoxazines with Titanium Metal–Organic Frameworks

Titanium-based metal–organic frameworks (MOFs) (MIL-125 based) were utilized as photocatalysts for the first time, in the successful visible-light-mediated polymerization of monofunctional 1,3-benzoxazines (Bzs). Gel permeation chromatography (GPC) analysis revealed that the resulting model polybenzoxazines (PBzs) exhibited relatively high number-average molecular weights (Mn). The photopolymerization process was traced by NMR spectroscopy, evidencing complete monomer conversion with MIL-125 (Ti). Control experiments using UV light or diphenyliodonium hexafluorophosphate demonstrated negligible or no Bz polymerization under the same experimental conditions. To enhance the photocatalytic performance, MIL-125 (Ti) was modified through amine functionalization and silver (Ag) doping, which improved visible-light absorption, as confirmed by UV–vis spectroscopy. Moreover, a mechanism for the photocatalytic polymerization of Bzs was also proposed for which the unique contribution of MIL-125 (Ti) to commence the charge-transfer reaction was highlighted as well.