Miniemulsion polymerization initiated by L‐ascorbic acid and sulfonate/sulfate surfactants

Abstract

AbstractStyrene miniemulsions that were stabilized by common anionic surfactants (sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, and disulfonated alkyl diphenyl oxide sodium salt) polymerized at 25 °C in the presence of L‐ascorbic acid without the addition of a free‐radical initiator. The polymerizations exhibited high rates and molecular weights, with conversions greater than 70% achieved in less than 1 h and weight‐average molecular weights greater than 1 × 106 g/mol. Polymers did not form in the absence of L‐ascorbic acid. Although the final conversion was only slightly independent on the L‐ascorbic acid concentration, it was dependent on the surfactant concentration. The rate and final conversion were also strongly dependent on the surfactant type. Moreover, it was possible to initiate polymerizations with a monomer‐soluble derivative of L‐ascorbic acid (L‐ascorbic acid 6‐palmitate), although the rates were dramatically reduced compared with those when water‐soluble L‐ascorbic acid was used. High yields and high‐molecular‐weight polymers were also produced with butyl acrylate and methyl methacrylate with L‐ascorbic acid in the presence of sodium dodecyl benzene sulfonate. The initiation was attributed to an interaction between the surfactant and L‐ascorbic acid, which formed a redox initiation system that generated radicals capable of adding monomer. These results are of particular significance for redox‐initiated emulsion/miniemulsion polymerizations with L‐ascorbic acid as the reducing agent and with sulfate or sulfonate surfactants. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 69–80, 2007