Using Novel Surfactants In Ultrasonically Irradiated Emulsion Polymerization To Prepare Polystyrene Nanoparticles

It is difficult to prepare polymer nanoparticles with narrow particle size distribution by emulsion polymerization. In this paper, two kinds of novel surfactants, the polymeric surfactant (CMC-A9) and the polymerizable surfactant (AREO7), and ultrasonic irradiation technology were used in emulsion polymerization in order to prepare functional polymer nanoparticles.Polymeric surfactant CMC-A9, which has high molecular weight and excellent surface activity, was used together with SDS in ultrasonically irradiated emulsion polymerization of styrene. The emulsion polymerization kinetics and the polymer properties were studied by FTIR, GC-MS, GPC, viscosimetry, TEM, etc. The results show that: (1) Using polymeric surfactants, high molecular weights (>106) polystyrene nanoparticles with narrow size distribution were obtained by ultrasonically irradiated emulsion polymerization. The single latex particle contains a few polymer chains with the average chain number of 2-19, which is called a pauci-chain polymer latex. The latex particle sizes, size distributions and polymer chains per particle can be controlled by changing the content of styrene, the concentration of CMC-A9 and the concentration of SDS. (2) Using of CMC-A9 together with SDS improves the polymerization rate and the monomer conversion dramatically. CMC-A9 added into the ultrasonically irradiated emulsion polymerization increases the monomer conversion in shorter time at lower ultrasonic power output. (3) The kinetics study indicates that the dominant nucleation is monomer droplet nucleation (a continuous nucleation withoutSimth-Ewart interval II), which is different from that of conventional emulsion polymerization and is more like that of microemulsion polymerization. That is why polymer nanoparticles are produced by ultrasonically irradiated emulsion polymerization.The nonionic surfmer AREO7 was first used in the ultrasonically irradiated emulsion polymerization of styrene. Through FTIR, GC-MS, DSC studies, it is found that the polymer produced is the copolymer of styrene and AREO7. The copolymer latexes polymerized in proper conditions display not only nanoparticles, bur also narrow size distribution. And the latexes have a structured morphology that the AREO7 units are mainly on the surface of particles. When AREO7 concentration increases, the size of copolymer latex decreases. However, there are more nanostructured copolymer gels, in which AREO7 molecules form an amphiphilic network, whereas polystyrene is located in hydrophobic droplet. The effect of AREO7 concentration on the polymerization was studied. -The results show that styrene conversion is higher under lower AREO7 concentration. AREO7 added into the polymerization raises the emulsion solid content and the composition of AREO7 in copolymer. The Tg of copolymers decreases with the increase of AREO7 composition in copolymers. Freeze-thaw test shows that the freeze-thaw stability of the copolymer emulsion is improved greatly due to the increasing composition of AREO7 in copolymers.