DISPERSION COPOLYMERIZATION OF POLYOXYETHYLENE MACROMONOMER AND STYRENE .2. EFFECT OF INITIATOR TYPE AND CONCENTRATION ON THE POLYMERIZATION PROCESS

The dispersion copolymerization of methacryloyl-terminated polyoxyethylene (PEG-MA) macromonomer and styrene initiated by a water/ethanol-soluble (2, 2'-azobis(N,N-dimethyleneisobutyramide, VA) and oil-soluble (dibenzoyl peroxide, DBP) initiators was investigated at 60 degrees C. The rate of polymerization and the number of particles were found to increase with increasing concentration of initiator. The initial rate of polymerization was found to be proportional to the 0.6 and 0.8th power of IVA] and [DBP], respectively. The rate per particle was observed to be proportional to the 0.17th and 23rd power of [VA] and [DBP], respectively. In the VA systems the polymerizations were faster and the molecular weights of graft copolymers larger. The dependence of the particle number was described by a curve with a minimum at ca 15 or 20% conversion. The partition of DBP molecules between the continuous phase and the polymer particles causes the formation of radicals in both phases. The DBP molecules or DBP radical fragments located in polymer particles take part in both initiation and termination events. The latter is suggested to be responsible for the low rates and molecular weights of graft copolymers.