Permanganate-oxalic acid as a redox initiator in aqueous media. Part II. Kinetics and degree of polymerization

Abstract

The rate of polymerization of aqueous methyl methacrylate under nitrogen at 32°C is proportional to the first power of catalyst (MnO₄^-) concentration (0.633 to 15.83×10^-5 mole/l.) at fixed concentrations of the activator (0.8×10^-2 mole/l.) and monomer (6.204×10^-2 mole/l.), independent of activator concentration over a wide range (0.50 to 0.0625×10^-2 mole/l.), and proportional to the first power of monomer concentration within the range (0.94 to 7.52×10^-2 mole/l.) at fixed concentrations of the catalyst (3.16×10^-6 mole/l.) and the activator (0.8×10^-2 mole/l.). The initial rate of polymerization attains a maximum value at 45°C., but falls with further rise in temperature. The rate of polymerisation is depressed by agitation after initiation, salts and organic solvents, and is accelerated by MnSO₄ and complexing agent like NaF (only at low monomer concentration), and in presence of peptizers like sodium cetyl sulfate or cetyltrimethylammonium bromide. The separating phase in the absence of peptizers is a course coagulum, and possibly a steady state with respect to radicals is not attained at high catalyst concentration. Injection of catalyst late in a run increases both the rate of polymerization and yield in unpeptized systems and does the reverse in peptized systems. The molecular weight of the polymers increases in the course of a run and is also affected by change of catalyst concentration but not by activator concentration in the range where the rate of polymerization is independent of activator concentration.