Free radical polymerization initiated and controlled by visible light photocatalysis at ambient temperature

Abstract

A new method of free radical polymerization is developed on the basis of visible light photocatalysis using Ru(bpy)(3)Cl-2 that initiates and controls the polymerization at ambient temperature. The alpha-haloester and benzylic halide act as radical initiators that can be activated through the Ru(bpy)(3)(+) photoredox cycle under visible light irradiation. Successful free radical polymerizations of various methacrylates were realized using a Xe arc lamp as well as a household fluorescent lamp as light source. The polymerization is initiated with light on and immediately terminated upon turning the light off. In addition, the molecular weight of polymer can be varied by changing the ratio of monomer and initiator. The present photocatalytic method has merits of the mild reaction conditions with weak light irradiation, ambient temperature, and lower catalyst loading, which could be an alternative to the traditional thermal or photo-based free radical initiation methods. It is also advantageous over other photopolymerization methods in that the radical initiator is separated from the photosensitizer.