The initial rate of persulphate ( I ) decomposition at 50°C in the presence of nitrogen and methacrylonitrile (MAN) in an unbuffered aqueous solution (pH 4-7) may be written as:
-d(SzOg-)/dt cc (MAN)1.29'0.05 x (I) 1.20-tO.04 in the concentration ranges of persulphate ( I ) (0.25-2.50) X lo-' ( m/dm3) and of (MAN) 0.18-0.36 ( m/dm3). During the reaction, a white substance (polymethacrylonitrile) separates out in the colloidal state or in the precipitate form from the medium depending on the ionic strength of the medium. The pH of the medium was found to decrease rapidly and continuously with time in the absence of methacrylonitrile, but it decreased slowly and continuously with time in the presence of the monomer, MAN. If an additional quantity of MAN is injected late in a run, the rate of persulphate decomposition is further accelerated in a given run. However, the rate of persulphate decomposition is found to decrease continuously in the presence of MAN with time, i.e., as the monomer is converted to polymer. It is suggested that MAN accelerates the decomposition of persulphate ions, due to the following reactions in the aqueous phase: and where (MJ) is a-water soluble oligomeric or polymeric (j = 1-10) free radical. The estimated values of kS and klo are 1.05 X lop5 and 1.14 X lo3 (in dm3/m/s), respectively.