Effect of temperature on the rates of aqueous polymerization of vinyl acetate initiated by SO<img src='http://www.niscair.res.in/jinfo/Subscript4.gif' border=0> free radIcals produced from potassIum persulphate and the redox reaction of ferrous ammonium sulphate and potassium persulphate

Abstract

The aqueous polymerization of vinyl acetate (VA) initiated by the redox system, ferrous ammonium sulphate (FAS) and potassium persulphate (KPS) has been studied over a wide range of temperature, 5 , to 65°C. It is noted that the separating polymer phase is a stable colloid, milky white at or below 10°C, but yellow at temperatures above 20°C. It is deep yellow above 50°C, but very faint yellow between 10 to 20°C. The colloidal stability (CS) of the latex solutions first decreases slightly and remains approximately constant between 20 to 40°C, and follows an increasing trend again above 40°C. The rates of polymerizations have been found to be maximum at (25 ± 2)°C<i>, </i> above or below which the rates decrease. The purified polymer, polyvinyl acetate (PVA),is found to contain iron and it is found to be insoluble in common solvents of PYA. Arrhenius plot for the activation energy <i>(E</i>_a<i>) </i> of the aqueous polymerization of VA in the system, FAS-VA-KPS, over the temperature range 5 to 65°C, is a curved line. <i>(E_a)</i> is about (+) 10.0 kJ/mol between 5 to 20°C, and about (-) 45.97 kJ/mol between 40 to 65°C. In the KPS-VA system, the initial rates of polymerization are found to increase with temperature (50 to 65°C), but the (CS) decreases with temperature. The latex solutions are always white and do not change colour with temperature.PVA is soluble in common solvents. <i>E_a</i> for the formation of PVA in the KPS-VA system is (+) 108.18 kJ/mol.