Chlorophyll derivatives as catalysts and comonomers for atom transfer radical polymerizations

Abstract

Copper trisodium chlorophyllin is obtained from natural chlorophyll, and is widely used as a major green food colorant in cosmetics and in medical devices. Copper chlorophyllin also proves to be an efficient catalyst and comonomer for atom transfer radical polymerizations (ATRP). Aqueous ATRP of poly(ethylene glycol) acrylate (PEGA) results in PEGA-chlorophyllin copolymers with narrow molecular weight distributions and a controlled content of chlorophyllin. The reactions proceed with first order kinetics, and the polymer's molecular weight increases with conversion. The resulting copolymers could find application in drug delivery and in biomedical materials, or as solar energy harvesting materials. In order to suppress the incorporation of the catalyst into the growing polymer chains, the vinyl bond of chlorin e6, one of the major porphyrin components of chlorophyllin, is deactivated by hydrobromination and hydration. Complexation of copper by the porphyrin leads to a bio-derived catalyst which mediates the polymerization of PEGA, yielding homopolymers with molecular weights ranging from 4000–5000 g mol⁻¹ and dispersities ≤ 1.11. UV-Vis spectroscopy indicates that chlorophyllin is stable during the polymerization. Copper chlorophyllin is a plant-derived compound from a renewable feedstock that can be used for a more environmentally friendly route to ATRP.