Reversible breakage of the C–S bond: function of dl-methionine in PET-RDRP catalyzed by zinc protoporphyrin

Abstract

Traditional control agents such as dithiocarbonates and trithiocarbonates tend to have drawbacks such as difficult synthesis, high cost, and toxicity to living organisms, which hinder the wide-scale application of reversible-deactivation radical polymerization (RDRP). To overcome the limitations attributed to these control agents, DL-methionine is chosen as a novel control agent for the photoinduced electron/energy transfer-RDRP (PET-RDRP) of a series of monomers. The results indicate that either in DMSO or aqueous solution, DL-methionine is capable of initiating PET-RDRP. With the addition of a zinc protoporphyrin (ZnPTP) photo-catalyst under green light irradiation, polymers are afforded with good predictable molecular weights and narrow dispersity (Đ) compared to the absence of DL-methionine. First-order kinetics demonstrates that the polymerization system is consistent with controlled/living polymerization properties, and EPR analysis indicates the radical species and proposes the mechanism of polymerization. MALDI-TOF MS and chain extension confirm high end-group fidelity for polymers with the DL-methionine control agent. PET-RDRP using ZnPTP mediated by DL-methionine is developed, opening up the potential of purely biologically controlled radical polymerization systems.