Partitioned polymerization, 2. Simultaneous transfer of monomer and of initiator

Abstract The kinetics of the 2,2′‐azoisobutyronitrile (AIBN)‐initiated emulsion polymerization of methyl methacrylate and butyl methacrylate was studied in the presence or in the absence of 4‐stearoyloxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl radical (STMPO) situated in the oil (monomer) phase. The polymerization was initiated and oligomeric radicals were formed in the aqueous phase to which methyl methacrylate (butyl methacrylate) and AIBN were transferred. Polymerization does not take place in the oil phase because of the inhibitor present. Relatively short inhibition periods of polymerization observed in systems containing STMPO confirm that a small part of STMPO was transferred from the oil to the water phase. The length of the inhibition period in the emulsion polymerization is determined by a competition between the addition reaction of primary radicals with monomer and the termination reaction of primary radicals with STMPO as well as by the rate of STMPO scavenging by oligomer‐monomer and polymer‐monomer particles. The polymerization system studied belongs to a group of partitioned polymerization systems characterized by simultaneous transfer of monomer and initiator from the oil to the water phase, where the initiation of polymerization takes place.