Kinetics of emulsion crosslinking polymerization and copolymerization of allyl methacrylate

Abstract

The emulsion polymerization and copolymerization of allyl methacrylate (AMA) initiated by potassium peroxodisulfate (KPS) using sodium dodecylsulfate (SDS) as an emulsifier were studied. Polymerization shows two distinct non-stationary rate regions with the maximum rate at ca. 50% conversion. The maximum rate of polymerization is found to be proportional to 0.68 and 0.25 power of KPS and SDS concentrations, while the number of particles is proportional to 0.54 and 0.67 power, respectively. The increased number of polymer particles as reactive crosslinked-polymer microspheres, the polymerization in the polymer particle surface area, the small monomer/polymer weight ratio, and the gel effect are assumed to be operative. The particle size decreased and the particle number increased with increasing the KPS and SDS concentrations. Moreover, the particle size continued to increase with conversion, up to a high conversion; this is due to the particle growth events by both agglomeration and propagation reactions, and the continued nucleation of particles to a high conversion region. The non-uniform particle morphology results from the agglomeration of microgels between themselves and with large stable particles. The polymerization accompanied by crosslinking mainly occurs in the surface area of the particles because of the restricted penetration of radicals into crosslinked particle cores. Where the T g of the resulting polymer is much higher than the polymerization temperature, the particles become glassy during the polymerization, as is the typical case of AMA/methyl methacrylate (MMA) copolymerization; at a late stage of polymerization, the preferential polymerization in the surface area of polymer particles leads to the enhanced formation of network structure, resulting in the microgel-like polymers consisting of poly(MMA)-rich core and poly(MMA-co-AMA)-network shell.