Studies On Styrene Emulsion Polymerization In The Presence Of Cyclodextrins And A Small Amount Of Surfactant

Due to their special structure with a hydrophobic cavity and a hydrophilic surface, cyclodextrins were able to enclose hydrophobic monomers of which the size was fit to cyclodextrin cavity. These monomers could polymerize directly in the aqueous phase and this gave a green way to the synthesis of polymer. In this article, emulsion polymerization of styrene (St) was carried out in the presence of P-cyclodextrin (β-CD) using a small amount of sodium dodecyl sulfate (SDS) as surfactant and potassium persulfate (KPS) as initiator. A new sequential feeding way was adopted in polymerization. The main contents and conclusions were as follows:(1) Complexation of SDS with P-CD was studied by cyclic voltammetry using polypyridyl metal complexes as electroactive probes. The complexation of SDS with β-CD eliminated the interaction between the metal complex and SDS. So it was concluded that P-CD was able to include SDS molecule. The inclusion complex of St with β-CD was synthesized by solvent method and characterized by UV, TG, XRD and1HNMR spectmm. It was proved that P-CD was able to include St molecule.(2) Taking emulsion polymerization of styrene as an example, the influence of the concentrations of initiator, surfactant and (3-CD, polymerization temperature, feeding way and including conditions on emulsion properties was investigated. Those emulsion properties included gel content, conversion, the particle size and its distribution, stability, etc. The mechanism of β-CD in polymerization process was studied as well. Furthermore, the particle size, its distribution and morphology of the latex particles were characterized by dynamic laser particle size analyzer and transmission electron microscopy (TEM). Results showed that: Stable latexes were obtained when the concentration of surfactant was under CMC and the amount of P-CD (based on the amount of St) was1%. The solid content of the latexes reached30%. The latexes were unstable in the presence of small amount of SDS but absence of P-CD. However, appropriate amount of β-CD could improve the emulsion stability due to steric hinerance and improve the monomer conversion due to the increase of the solubility of styrene in water. Therefore, the addition of appropriate amount of β-CD in emulsion polymerization could significantly decrease the amount of SDS, and reduced the drawbacks in conventional emulsion polymerization. It showed β-CD had practical value of the synthesis of polymer. But it must be paid attention to control the amount of β-CD because excessive amount of β-CD reduced the emulsion properties due to the complexation with SDS. In addition, the PS particles were spherical and the particle size distribution was very narrow and uniform.(3) In this paper, the kinetics of emulsion polymerization of St in the presence β-CD was also discussed using the method of the linear simulation. A kinetic equation could be denoted by Rp=k[KPS]0.5277[SDS]0.5631[St]0.543[p-CD]0.9987, and the activation energy (Ea) of emulsion polymerization was72.55kJ/mol.