Amphiphatic Copolymer as Surfactant for Emulsion Polymerization of Styrene

The emulsion polymerization of styrene (St) using sodium persulfate (Na2S2O8) as an initiator has been kinetically investigated in the presence of amphiphatic copolymer as surfactant. Amphiphatic copolymer of three different composition types from vinyl acetate, monomer, and methoxy polyoxyethylene (PVAc-b-MPOE) (35:65, 27:73, 19:81 wt%:wt%) were prepared in the presence of benzoyl peroxide using a macroradical initiator technique. Fourier Transform Infrared Spectroscopy (FTIR) and 1H NMR were carried out to confirm the structure of the obtained copolymer. The rate of emulsion polymerization of styrene was found to be proportional to the 0.33rd, 0.375rd and, 0.385rd power of the (amphiphatic) surfactant concentration [E] and to the 0.67th, 0.71th, and 0.8th power of the initiator concentrations [I]. The apparent activation energy was found to be 91.7, 81.9, and 71.6 kJ/mol for 65, 73, and 81 wt% POE, respectively. It is seen that the number of the average particle diameter (Dn) decreases with increasing surfactant [E], while it increases with [I]. The number of polymer particles (Nt) increased with surfactant concentration but decreased with initiator concentration. The reaction order of Nt with respect to [E], was determined. Polydispersity index (Dw/Dn) (particle size distribution)of the prepared latices was found in the range from 1.05—1.20 with changing POE wt% and from 0.8 to 1.23 with varying initiator concentration.