SOME OBSERVATIONS IN THE AQUEOUS POLYMERIZATIONS OF VINYL-ACETATE INITIATED BY POTASSIUM PERSULFATE AND FERROUS AMMONIUM-SULFATE AT 30-DEGREES-C IN NITROGEN ATMOSPHERE

The heterogeneous aqueous polymerization of vinyl acetate (VA) has bee n detected by the instantaneous appearance of a bluish haze when fresh ly prepared ferrous ammonium sulphate (FAS) solution (saturated with p ure N-2 gas) is injected into the reactor containing aqueous solution of monomer (M) and potassium persulphate (KPS) in N-2 atmosphere at 30 degrees C. The colloidal latex solution gradually becomes yellowish a bove 10 degrees C, but it is milky white at or below 10 degrees C. The reactions are found to be very fast, the conversion of monomer to pol ymer being about 66.0% in 5 minutes at 30 degrees C when VA is 0.1625 mol dm(-3), [FAS] = [KPS] = 10(-3) mol dm(-3). The time average rate o f polymerization, (V-p'), i.e. V-p' = % conversion in time t/ time t, may be written as: V-p'proportional to[VA](x)[FAS](y)[KPS](z) where x = 1.5. The order plots of FAS and of KPS have been found to be curved lines, y = 0.50 to (-) 0.15, and z = 2.0 to 0.40, in the concentration ranges of VA from 0.0975 to 0.195 mol dm(-3), and of initiators [KPS] = [FAS] = 10(-3) to 5 X 10(-5) mol dm(-3). The values of y and z are found to vary with molar ration(r) of [KPS]/[FAS]. When (1/r) = 0.05 t o 0.10 y = 0.50 and y = (-) 0.15, when (1/r) = 1.0 to 5.0, z = 0.40 wh en r = 0.1 to 1.0, and z = 1.5 to 2.0, when r = 0.05. Reaction (2), vi z. Fe2+ + SO4.- --> Fe3+ + SO42-, which decreases polymerization rates at higher [FAS]; is possibly responsible partly for these abnormal re action orders of the initiators. V-p' is found to decrease with increa se in ionic strength (mu) of the medium. NaF, when added at the outset of polymerization, makes the latex solution colourless, decreases the colloidal stability (CS), and marginally increases the polymerization rates (V-p'). H2SO4 acid (1.0 to 2.0 N) enhances V-p' and also the fi nal % conversion. Polyvinyl acetate (PVA) does not dissolve in common solvents. It seems that at 30 degrees C, the polymerization of VA unde r the experimental conditions in the KPS-VA-FAS system is a case of 'd ead-end polymerization'.