Permanganate-oxalic acid as a redox initiator in aqueous media. Part I. The initiating radical and general features

Abstract

Polymerization of aqueous methyl methacrylate solution by oxalic acid (4.0×10^-2 to 0.0625×10^-2 mole/l.) and permanganate (0.633×10^-5 to 63.3×10^-5 mole/l.) system as redox initiator has been studied. Oxalic acid by itself can not initiate polymerization in the dark but does so strongly even in diffuse light or weak illumination. Permanganate can initiate polymerization provided the solution is sufficiently acidic to dissolve the separated colloidal MnO₂ which tends to inhibit polymerization. The MnO₄^--oxalic acid system is a powerful redox initiator provided the acid strength (either of added H₂SO₄ or of oxalic acid itself) is sufficient to dissolve MnO₂. The polymer always separates as a coarse coagulum (suspension). The polymers have been examined for endgroups by the dye test as developed in this laboratory. Oxalic acid-initiated (in sunlight) as also oxalic acid-ferrous ion-initiated and KMnO₄-H₂C₂O₄-initiated polymers contain carboxyl endgroups. MnO₂-H₂SO₄ acid-initiated polymers, have been found to contain sulfate endgroups. On increasing the ratio of oxalic acid to permanganate, the carboxyl endgroups tend to decrease, and ultimately very faint test for carboxyl is obtained. This is in agreement with the suggestion made by previous workers that under such conditions carboxyl radical-producing reactions are suppressed.