KINETICS AND MECHANISM OF POTASSIUM PERSULFATE-INITIATED AQUEOUS POLYMERIZATION OF METHACRYLONITRILE AT 50-DEGREES-C IN AN INERT ATMOSPHERE OF NITROGEN GAS

The mechanism of persulphate-initiated aqueous polymerization of methacrylonitrile (MAN) has been investigated kinetically at 50-degrees-C in an inert atmosphere of nitrogen gas by the conventional gravimetric method within the solubility range of the monomer. It has been found that the rate of polymerization (R(p)) of MAN is proportional to the square root of the initiator concentration [I] and the 1.6 power of the monomer concentration [M], i.e. R(p) infinity [I]0.50 +/- 0.05[M]1.6 +/- 0.05 It has been suggested that both the monomer and the water-soluble monomeric/oligomeric free radicals react with the persulphate ions in aqueous solutions (pH 4 to 7), viz. reactions C and D, which would then compete with the well established reactions A and B: S2O8(2-) --> 2SO4.- (A) S2O8(2-) + H2O --> 2HSO4- + 1/2O2 at pH 5 to 7 (B) S2O8(2-) + M --> .M-O-SO3- + SO4.- (C) S2O8(2-) + (M(j).)w --> M(j)-O-SO3- + SO4.- j = 1 to 10 (D) where (M(j).)w is a water-soluble monomeric/oligomeric free radical. The separating polymer phase was in the aqueous solution as a stable colloid. The distribution coefficient of MAN between the polymer and the aqueous phase was found to be 1.8 +/- 0.2 at 50-degrees-C in the presence and absence of electrolytes ([K2SO4] = 7.5 x 10(-3) mol dm-3). The termination rate constants in the aqueous phase (k(tw)) and the polymer phase (k(tp)) have been estimated as k(tw) = 1.29 x 10(5) dm3 mol-1 s-1 and k(tp) = 1.90 X 10(2) dm3 mol-1 s-1, based on the literature value of k(p) of MAN as 26 dm3 mol-1 s-1 at 50-degrees-C. The locus of polymerization is partly in the aqueous phase and partly in the polymer phase.