Synergic Effect between Nucleophilic Monomers and Cu(II) Metal-Organic Framework for Visible-Light-Triggered Controlled Photopolymerization

A Cu(II) metal-organic framework (MOF), Cu2(bdc)2(dabco), was found to be an efficient heterogeneous catalyst for controlled photopolymerization under visible light. The MOF, composed of photostimulable metal sites, was used to catalyze both photoinitiation as well as radical chain control and required no external photoinitiator, dye sensitizer, or ligand. A simple light trigger allowed the photoreduction of Cu(II) to the active Cu(I) state, enabling controlled atom transfer radical polymerization (ATRP). Compared to conventional ATRP with homogeneous catalysts, the ionic-bonded framework imparts high stability and robustness to the catalytic Cu(II) species. Therefore, the polymerization of vinylpyridines (2-vinylpyridine, 2VP; and 4-vinylpyridine, 4VP), usually challenging by traditional polymerization strategies, was controlled up to high conversion (>85%) in 90 min, forming polymers with Ä < 1.3. Methacrylates such as 2-(dimethylamino)ethyl methacrylate (DMAEMA) and methyl methacrylate were polymerized by the Cu(II) MOF with good control as well. Moreover, as a heterogeneous catalyst, the MOF was easily separated, recovered, and repeatedly used for several photopolymerizations of 2VP and DMAEMA.