Miniemulsion Polymerization Of Styrene And Acrylic Monomers

Miniemulsion polymerizations of styrene and butyl acrylate in the presence of sodium dodecyl sulfate (SDS) as the surfactant and stearyl methacrylate (SMA) as reactive co-stabilizer were carried out. Various factors were investigated, including effects of SDS and SMA concentration, various ratio of SDS to SMA, different amounts of SDS added before and after sonification, different type of co-stabilizers and two type of initiators on polymer particle size. The results show that the surfactant is necessary to retard droplet coalescence caused by Brownian motion and settling and the costabilizer prevents Ostwald Ripening. By comparison with the size of monomer droplets and polymer particle, the probability of monomer droplet nucleation can be illustrated. The kinetics of conventional emulsion polymerization and kinetics of miniemulsion polymerization with water phase scavenger also perform as an assistant evidence to illustrate the nucleation mechanism. It shows that both homogeneous nucleation and monomer droplets nucleation coexist in the presence of a water-soluble initiator. Meanwhile, using oil-soluble initiator, the possibility of homogeneous nucleation is depressed effectively. As a result, monomer droplets are definitely the main loci of particle nucleation.Miniemulsion polymerizations containing MAA were carried out by using KPS as a water-soluble initiator. The mechanism of nucleation was investigated. The results show that the probability of monomer droplet nucleation is enhanced in the presence of MAA. Compared with kinetics of miniemulsion polymerization without functional monomers, the polymerization with MAA is retarded, possibly because the critical chain length for MAA containing oligomeric radicals to precipitate out of the aqueous phase should be longer as compared with that obtained from the polymerization in the absence of MAA. As a result, the homogenous nucleation is retarded to some extent. When using an oil-soluble initiator, the probability of monomer droplet nucleation is enhanced sharply comparing with the same recipe and methods of preparation except using a water-soluble initiator. In addition, adding the water-soluble initiator at the later stage of polymerization is proved to be the most efficient way to enhanced the final conversion of monomers. Miniemulsion polymerizations containing AA were also carried out by using KPS as a water-soluble initiator and AIBN as an oil-soluble initiator, respectively. Because AA is more hydrophilic than MAA, the system containing AA is less stable than that containing MAA. When [AA]=5%, scraps present heavily. However, [AA]<5%,the mechanism of nucleation and kinetics of polymerization are much the same as the system containing MAA.