Effects of 2-hydroxyalkyl methacrylates on the styrene miniemulsion polymerizations stabilized by SDS and alkyl methacrylates

The effects of 2-hydroxyalkyl methacrylates (HEMA and HPMA) on the styrene miniemulsion polymerizations stabilized by SDS/lauryl methacrylate (LMA) or SDS/stearyl methacrylate (SMA) were investigated. A mixed mode of particle nucleation (monomer droplet nucleation and homogeneous nucleation) is operative during polymerization. Homogeneous nucleation plays a crucial role in the polymerizations stabilized by SDS/LMA, whereas monomer droplet nucleation becomes more important in the polymerizations stabilized by SDS/SMA. The polymerization kinetics is insensitive to the type of 2-hydroxyalkyl methacrylates, but the difference in the relative importance of monomer droplet nucleation and homogeneous nucleation is detected. Incorporation of 1-pentanol (C5OH) into the reaction mixture also shows a significant influence on the polymerizations stabilized by SDS/LMA or SDS/SMA. This is attributed to the formation of a close-packed structure of SDS and C5OH on the droplet surface, which acts as a barrier to the incoming oligomeric radicals.