ON THE IONIC SPECIES FORMED IN REACTIONS OF SULFUR-DIOXIDE WITH CYCLIC ETHERS AND PROPYLENE SULFIDE

The reactions of SO2 with various oxiranes, propylene sulfide, and oxe tane have been studied. It was found that SO2 activates these monomers toward ring opening polymerization. The spontaneous reactions lead to the formation of cationic active centers, on which the heterocyclic m onomer homopropagation and various cyclization processes mainly procee d. Anionic alternating copolymerization of SO2 with ethylene oxide or propylene oxide was observed after the spontaneous termination of cati onic active species. Zwitterions with active anionic sites are formed in the presence of pyridine. They can initiate the alternating copolym erization of SO2 and oxiranes. The relative reactivity of the oxiranes in the addition to anionic species increases in the following order: epichlorohydrin < glycidyl acetate < propylene oxide butyl glycidyl et her < ethylene oxide < 1,2-cyclohexene oxide. Styrene oxide, oxetane, and propylene sulfide undergo spontaneous reactions also in the presen ce of pyridine. In systems with the former two monomers the alternatin g copolymerization proceeds simultaneously with the processes initiate d by cationic centers; propylene sulfide, however, does not form copol ymers with SO2. Monomers of low ring strain like THF or trioxane do no t undergo ring opening in the presence of SO2 and pyridine.