Visible Light Induced Living/Controlled Radical Polymerization of Acrylates Catalyzed by Cobalt Porphyrins

Visible light induced living radical polymerization of a wide scope of acrylates mediated by organocobalt porphyrins was developed. The photocleavage of the Co–C bond of organocobalt porphyrin produced carbon centered radicals, which initiated polymerization, and porphyrin cobalt(II), a persistent metal-centered radical. The organocobalt porphyrins were highly sensitive to external visible light irradiation so that photostimulus was used to control the initiation steps and regulate chain growth by reversibly activating the Co–C bond. Polymerization occurred spontaneously under irradiation and stopped promptly once shutting down light source. The scope of monomers was successfully extended from acrylamides to various hydrophobic and hydrophilic acrylates via the control of the light intensity. The structure of polyacrylate obtained was confirmed by 2D NMR, 13C NMR, GPC, and MALDI-TOF-MS. One of the unique features of this neat visible light induced polymerization process is that organocobalt porphyrins played dual roles of photoinitiators and mediators without addition of any dyes, photosensitizers, or sacrificial reagents.