Aqueous polymerization of methacrylamide initiated by acidified bromate/thiourea redox system

Abstract

Abstract The polymerization of methacrylamide initiated by acidified bromate/thiourea has been studied at 35 ± 0,2°C in a nitrogen atmosphere. The rǒle of the acid (HCl) is to convert thiourea to isothiourea with a faster rate in contrast to a neutral or alkaline medium, and thus producing free radicals by oxidation of the latter. The rate of polymerization is independent of the activator (thiourea) concentration within the range of 0,4–1,0 · 10 −2 mol/dm 3 or very low (0,4 · 10 −2 mol/dm 3 ) concentrations of the activator. The rate varies linearly at low monomer concentration (up to 17,64 · 10 −2 mol/dm 3 ). The catalyst exponent comes out to be unit (1,1) in the studied range of the catalyst (KBrO 3 ) concentration. This might be due to the collision of an active centre with a chain breaking agent. The addition of a strong acid (HCl) within the pH range of 1,75–1,9 results in no change of the initial rate; the maximum conversion decreases, however, with the activator alone, an optimum being observed at pH 1,9. The initial rate and the limiting conversion increase with the increase in polymerization temperature up to 35 ± 0,2°C. The overall activation energy has been found to be 18,9 Kcal/mol within the temperature range of 25–45°C. Organic solvents (only water miscible) and small amounts of neutral salts (KCl and Na 2 SO 4 ) depress the initial rate and the maximum conversion. The addition of Na 2 F 2 does not show any variation in the polymerization rate in contrast to Cu‐ and Fe‐Salts.