Riboflavin-induced metal-free ATRP of (meth)acrylates

Abstract

Metal-free ATRP approach was improved by eliminating undesirable organic photocatalyst from the reaction medium by an application of a fully-biocompatible riboflavin (vitamin B2)-based molecule playing two crucial roles in photoinduced polymerization – as an ATRP initiator and photoinitiator simultaneously. The brominated ribitol tail constituted an ATRP initiator, while the unmodified isoalloxazine ring was excited to a highly reactive triplet excited state under blue light irradiation, and thus induced the photopolymerization of (meth)acrylates from the ribitol tail. The double initiation functionality of riboflavin provides brush-like polymers with side chains composed of poly(ethylene glycol) methyl ether methacrylate (OEGMA500) with narrow molecular weight distribution (Mw/Mn = 1.36) and preserved chain-end functionality proved by successfully conducted chain extension experiment with the final product characterized by low dispersity (Mw/Mn = 1.35). The riboflavin-induced polymerization of OEGMA500 was temporally controlled by switching on–off blue light irradiation without the loss of chain-end functionality after restarting the synthesis, resulting in well-defined polymer materials (Mw/Mn = 1.37). The results indicate precisely established reversible redox cycle of the riboflavin photosensitizer during polymerization, providing equilibrium between the active and dormant species, and thus controlled polymer products. The double-functional riboflavin molecule makes metal-free ATRP approach an efficient and green chemistry solution for the preparation of functional polymer materials. The prepared riboflavin-based brush-like polymers were visualized by atomic force microscopy (AFM).