ON THE FREE-RADICAL MICROEMULSION POLYMERIZATION OF ALKYL METHACRYLATES

The o/w microemulsion polymerizations of alkyl methacrylates [methyl, MMA, ethyl (EMA), butyl (BMA) and 2-ethylhexyl (EHMA) initiated by a w ater-soluble initiator (ammonium peroxodisulfate, APS)] were investiga ted. The dependence of the rate vs conversion is described by a curve with a maximum at low conversion. The maximum rate of polymerization o f MMA, EMA, BMA and EHMA is found to be proportional to the 0.5th powe r of the initiator concentration and ca to the 2nd power of the monome r concentration. The dependence of the final molecular weight vs the i nitiator concentration favors the first radical loss process. The stro ng rate dependence on the monomer concentration is assumed to result f rom the different location of the reaction loci (in the interface or i n the core of monomer swollen micelles or particles) and the different contribution of the gel effect. The average number of radicals per pa rticle, the number of particles and the coemulsifier efficiency of mon omer increase with increasing alkyl chain length of monomer. (C) 1998 Elsevier Science Ltd. All rights reserved.