The use of electrostatic association for rapid RAFT synthesis of histamine polyelectrolyte in aqueous solutions at and below 25 °C

Aqueous synthesis of a well-defined polyion or polyelectrolyte via reversible degenerative radical polymerisation (RDRP) in dilute solution at or below room temperature is increasingly imperative for emerging biological applications, such as in situ grafting of polyelectrolytes onto heat-sensitive proteins and DNA/RNA. However, the polymerisation generally suffers from a time-consuming and less effective process because of electrostatic repulsion. This problem can be circumvented by media-adjustable electrostatic association. Herein we report the use of electrostatic association for rapid and quantitative aqueous RAFT of histamine-based ionic monomers in dilute solutions under visible light irradiation at and below 25 °C. We demonstrate that electrostatic interactions dictate polymerisation rates, including the initialization period and chain growth. The use of bulky counter-anions and the addition of methanol and sodium chloride can enhance electrostatic association, and thus promote the chain-growth rate. More importantly, abnormal chain-growth acceleration can be achieved in a cold solution at 8 °C, which proceeds faster than at 25 °C, because of ion-pairing association. These external regulations over aqueous RDRP show general implications for rapid and quantitative aqueous synthesis of well-defined polyelectrolytes in dilute solutions at and below room temperature.