Formation of particles in the preparation of carboxylated polystyrene latexes

Carboxylated polystyrene latexes have been prepared by copolymerizing acrylic acid at the appropriate degree of neutralization in the absence or presence of sodium dodecyl sulfate (SDS), and the particle formation process was investigated from the number and uniformity of particles. In the absence of SDS or in a concentration range of SDS lower than 6.41 mmole/l., the formation of particles can predominantly be attributed to the precipitation of growing radicals formed in the aqueous phase; whereas in a concentration range of SDS higher than 6.41 mmole/l., the formation of particles can predominantly be attributed to the initiation of polymerization in the interior of SDS micelles containing solubilized styrene by the collision of growing radicals formed in the aqueous phase. In the former range, the number of particles increases linearly with increasing concentration of SDS below the critical concentration of 1.60 mmole/l., which is sufficient to stabilize particles formed by the precipitation of growing radicals, and remains constant above the critical concentration. The effect of initiator concentration as well as amount of styrene on the formation of particles also supports the particle formation process described above.