Redox initiator systems for emulsion polymerization of acrylates

The performance of different redox initiator couples to initiate the emulsion polymerization of butyl acrylate at low temperature (40–50 °C) was investigated in both batch and seeded semibatch polymerizations. Polymerizations were carried out mimicking industrial conditions, that is, technical grade monomer and no N₂ purging was used during the polymerizations. The redox systems used contained as oxidants persulfates or hydroperoxides and as reducing agents ascorbic acid, formaldehyde sulfoxilate (SFS), tetramethyl ethylene diamine (TMEDA), Bruggolit 6 and 7 (FF6 and FF7), and sodium metabisulfites. Batch experiments showed that for systems using persulfates, the ammonium persulfate (APS)/TMEDA system provided the lower induction period and higher conversion, whereas for the systems with hydroperoxide oxidants, tert‐butyl hydroperoxide (TBHP)/FF7, TBHP/SFS, and H₂O₂/FF7 were the best alternatives. When these selected systems were used in seeded semibatch experiments of BA with allyl methacrylate, it was found that to obtain similar kinetics and microstructure (gel content and crosslinking density) than in case of using a thermal initiator at 80 °C, the polymerization could be run at 40 °C if the reactor was purged with N₂. Alternatively, in absence of N₂ polymerization, temperature should be increased to 50 °C and initiator concentration increased. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2917–2927, 2009