Controlled radical polymerization of styrene by reverse iodine transfer polymerization (RITP) in miniemulsion: Use of hydrogen peroxide as oxidant

The use of molecular iodine I-2 in controlled radical polymerization, called reverse iodine transfer polymerization, represents a new, straightforward way to prepare controlled macromolecular architectures. Herein, miniemulsion polymerization of styrene in the presence of molecular iodine has been successfully performed. The polymerization of styrene was initiated by bis(4-tert-butylcyclohexyl) peroxydicarbonate at T = 60 degrees C with dodecyl sulfate sodium salt as surfactant and hexadecane as hydrophobe, yielding a stable and uncolored latex. A certain amount of iodine reacted with water to form hydroiodic acid, leading to an upward deviation of the experimental molecular weight from the theoretical value. However, when the iodine lost by hydrolysis was regenerated by continuous addition of hydrogen peroxide in acidic conditions, it led to the expected molecular weight (e.g., M-n,M-SEC = 7900 g mol(-1), M-w/M-n = 1.46, styrene conversion = 78%, M-n,M-theoretical = 7900 g mol(-1)). Hence, the molecular weight of the polymer chains could be accurately controlled by changing the concentration of iodine. Last, a chain extension was successfully performed in seeded emulsion polymerization, proving the living character of the polymerization.