MICROEMULSION POLYMERIZATION OF BUTYL ACRYLATE .1. EFFECT OF INITIATOR TYPE AND CONCENTRATION

The oil-in-water-type (o/w) microemulsion polymerizations of butyl acrylate initiated by a water- (ammonium peroxodisulfate, AP) - and oil-soluble (dibenzoyl peroxide, DBP, and 2,2'-azoisobutyronitrile, AIBN) radical initiators were investigated. Polymerizations with AP were faster than those with DBP or AIBN. The rate of polymerization shows initiation and termination intervals, but no constant interval. The rate of polymerization is found to be proportional to the 0.46th, 0.53rd and 0.24th power of the AP, AIBN and DBP concentration. The rate per particle is found to be proportional to the 0.29th, 0.32nd and 0.37th power of the AP, AIBN and DBP concentration. The number of radicals per particle was found to increase with increasing the initiator concentration. The most pronounced increase in the number of particles with increasing the initiator concentration was observed with AP, much less with AIBN and the slight decrease with DBP The molecular weights of polymers were found to vary only slightly with increasing the initiator concentration. The formation of radicals proceeds in the aqueous phase (Af and a water-soluble fraction of AIBN or DBP) and the monomer-swollen micelles (AIBN or DBP) as well. The polymer particles grow by recruiting monomer and emulsifier from the free monomer-swollen emulsifier micelles.