Some observations in the aqueous polymerizations of vinyl acetate initiated by potassium persulphate and ferrous ammonium sulphate at 30°C in nitrogen atmosphere

Abstract

The heterogeneous aqueous polymerization of vinyl acetate (VA) has been detected by the instantaneous appearance of a bluish haze when. freshly prepared ferrous ammonium sulphate (FAS) solution (saturated with pure N₂ gas) is injected into the reactor containing aqueous solution of monomer (M) and potassium persulphate (KPS) in N₂ atmosphere at 30°C. The colloidal latex solution gradually becomes yellowish above 10°C, but it is milky white at or below 10°C. The reactions are found to be very fast, the conversion of monomer to polymer being about 66.0% in 5 minutes at 30°C when VA is 0.1625 mol dm^-3, [FAS] = [KPS] = 10^-3 mol dm^-3. The time average rate of polymerization, (<i>V</i><img src='http://www.niscair.res.in/jinfo/equation45.gif' border=0>)<i>, </i> i.e. <i>V</i><img src='http://www.niscair.res.in/jinfo/equation45.gif' border=0> = % conversion in time <i>t/time t, </i> may be written as:<br>

V<img src='http://www.niscair.res.in/jinfo/equation45.gif' border=0> <img src='http://www.niscair.res.in/jinfo/infinity.gif' border=0>

[VA]^x[FAS]^y[KPS]^z<br>

where x = 1.5. The order plots of FAS and of KPS have been found to be curved lines, <i>y= </i> 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 C 10^{- 5} mol dm ^{- 3}. The values of y and z are found to vary with molar ratio(r) of [KPS]/[FAS]. When (1/r)=0.05 to 0.10 y=0.50 and y=( - ) 0.15. when (1/r)= 1.0 to 5.0, z=0.40 when r=0.1 to 1.0, and z= 1.5 to 2.0, when r=0.05. Reaction (2), viz.<br> Fe²⁺ + SO<img src='http://www.niscair.res.in/jinfo/equation46.gif' border=0>^- -> Fe³⁺ -> SO<img src='http://www.niscair.res.in/jinfo/four1.gif' border=0>,<br> which decreases polymerization rates at higher [FAS], is possibly responsible partly for these abnormal reaction orders of the initiators. <i>V</i><img src='http://www.niscair.res.in/jinfo/equation45.gif' border=0> is found to decrease with increase in ionic strength (<img src='http://www.niscair.res.in/jinfo/equation45.gif' border=0>) of the medium. NaF, when added at the outset of polymerization, makes the latex solution colouriess, decreases the colloidal stability (CS), and marginally increases the polymerization rates (<i>V</i>)<img src='http://www.niscair.res.in/jinfo/equation45.gif' border=0>. H₂SO₄ acid (1.0 to 2.0 N) enhances <i>V</i><img src='http://www.niscair.res.in/jinfo/equation45.gif' border=0> and also the final % conversion. Polyvinyl acetate (PVA) does not dissolve in common solvents. It seems that at 30°C, the polymerization of VA under the experimental conditions in the KPS-VA- FAS system is a case of 'dead-end polymerization'.