Some observations in the aqueous polymerizations of methyl methacrylate (MMA) initiated by the redox systems Fe²⁺ -S₂O<img src='http://www.niscair.res.in/jinfo/twobyeight.gif' border=0> and Fe²⁺ -H₂O₂

Abstract

It has been observed in the aqueous polymerizations of methyl methacrylate (MMA) initiated by the redox system, ferrous ammonium sulphate (FAS)-potassium persulphate (KPS), that at 10°C or below, the separating polymer phase is always a milky white precipitate remained suspended in the aqueous phase, while above 20°C, the polymer phase is a stable colloid and is yellow in colour (light or deep, depending on the concentration of the reactants, 10^-5 to 10^-3 mol/dm³)<i>. </i>The colloid stability of the latex solutions increases with the rise in temperature in the range 20 to 50°C. Between 10 to 20°C, the separating polymer phase is partly colloidal and partly coarse precipitate. If the polymerization is initiated by the Fenton's reagent (Fe²⁺-H₂O₂), under identical experimental conditions,. the polymer phase is always a precipitate in the temperature range 4 to 50°C. At or below 10°C, the latex particles are milky white, but above 10°C the particles are yellowish. It is suggested that the complex ions [Fe(H₂O)₅OH]²⁺, [Fe(H₂O)₄(OH)₂]⁺and [Fe(H₂O)₄(OH)₂(H₂O)₄Fe]⁴⁺, produced in the systems during the reactions (depending on temperature and <i>p</i>Hof the solution), are strongly adsorbed by the polymer molecules (PMMA)/latex particles, having sulphate (- 0 - SO<img src='/image/spc_char/3_bar.gif' border=0>) end groups (polymer from the KPS-MMA-FAS system),through the electrostatic interactions, and act as peptisers to the lyophobic polymer colloids. In the Fe²⁺-MMA-H₂O₂ system, the polymers having neutral OH end groups, do not adsorb strongly the positively charged ferric ion complexes. The purified polymers (PMMA) are found to contain iron.